Abstract: Robotic cells are complex mechatronic systems whose final performance is determined by the interaction of the control logics with the mechanical behavior of the process. In this context it is fundamental to develop engineering methods and tools for the virtual prototyping of the cells that emulate both contributions. With such mechatronic digital models, it would be possible to replicate the real behavior of the systems and to optimize the cell productivity, up to building complete digital twins. This paper proposes an engineering method to develop realistic Virtual Prototypes of robotic cells including their geometry, operating logic, performance, and physical behavior. A case study on a robotic cell composed of two anthropomorphic robots for the flexible process of automatic assembly of industrial parts is presented to demonstrate the approach.

Keywords: Digital twin | Physics-based simulation | Robotic assembly | Virtual prototyping

Abstract: This article focuses on enhancing the range of motion (ROM) of the Tetra II joint, a spherical compliant joint consisting of three internally interconnected tetrahedron-shaped elements that achieve motion through elastic deformation. Despite its excellent precision, this specific design is constrained in terms of ROM due to internal contacts among the tetrahedral elements. To overcome this limitation, this study utilizes a computer-aided engineering (CAE) framework to optimize the configuration of the Tetra II joint and enhance its ROM. The resultant optimized joint, referred to as Tetra III, is subsequently compared to Tetra II in terms of both ROM and center shift. Finite element models (FEM) are employed to validate the optimization results and examine how various tetrahedron-shaped geometries impact the joint’s performance. The newly optimized joint exhibits a significantly higher ROM compared to the previous version, while maintaining excellent precision and overall smaller dimensions. Finally, to demonstrate its manufacturability, the Tetra III joint is produced using selective laser sintering (SLS) technology, with Duraform PA serving as the construction material. The successful fabrication serves as a demonstrative example of the improved design of the Tetra III joint.

Keywords: CAE | Compliant mechanisms | Flexure | PRBM | SLS | Spherical joint | Tetrahedron

Abstract: Nowadays, robots hold crucial roles in an increasing number of different fields, highlighting an ongoing transition to ever-closer collaboration between humans and machines. In this context, this new technological era has brought out safety issues and, consequently, robots need to be monitored with an appropriate control architecture and human–machine interaction forces should be correctly estimated. For this purpose, friction, inertia, external perturbation, and the intrinsic dynamic of the robots should be monitored. This specific work starts from the need to monitor human–robot interaction forces to ensure safety for users. A successful case study concerning the integration of additional sensors on a wrist robot that directly interacts with humans is shown. Its limits have been the inability to directly measure forces applied by users and the impossibility to know accurately the end-effector position. Firstly, introducing a force/torque sensor, the detection of the forces applied by the user to the robot has been enabled. The user’s force data have been used to measure force dissipation and, together with the smoothness of operation, to compare three different embeddable mechanisms. Moreover, the integration of a linear encoder allowed measuring the instantaneous end-effector position on a non-actuated linear guideway, consequently knowing the motor torque value and the force applied by the robot to the user. This has been compared to the interaction force estimated from the motor torques without the linear sensor. The error assessed between the force measured with the encoder and estimated without it is about 12.9%. These results demonstrate the importance of this new embedded system to detect human–machine interaction forces in an accurate way and prevent safety issues.

Keywords: CAD design | Human–robot interaction | Interaction forces | Mechanical design | Virtual prototyping

Abstract: Compliant mechanisms (CMs), along with soft robotics devices formed therewith, may be defined as engineering systems achieving force and motion transmission via the deflection of flexible members. CMs have increasingly gained a strong foothold in the scientific arena owing to their hinge-less nature, shock resistance, potential single-piece manufacturability, safety in human–machine interaction, minimal maintenance requirements, and adaptability to work in unstructured environments. In parallel, current advances in the production of inherently compliant sensory-motor apparatus, as well as progresses in the development of robust control methods, are paving the way to practical CM adoption in a large variety of engineering fields, here including healthcare, manufacturing, inspection/maintenance, and agrifood.

Keywords: Flexible manufacturing systems | Human computer interaction | Manufacturing processes | Mechatronics | Soft robotics | Special issues and sections

Abstract: This work describes the advancement in developing a cable-driven gear transmission joint designed as a basic element for a long-reach hyper-redundant robot. Hyper-redundancy allows the robot to perform auxiliary tasks such as obstacle avoidance and joint limits satisfaction. This feature makes hyper-redundant robots particularly useful for performing tasks in confined and hazardous environments and areas that are not reachable by a human operator. The long-reach feature of the robot requires a detailed study of the overall structure and its components. The joint must be capable of transmitting forces and movements over a long distance without losing the precision and accuracy of the end-effector, so it is designed to optimise the robot’s performance in terms of stiffness, structural resistance, and functional characteristics. In light of the above considerations, the main focus of this work is to improve the structural performance of the entire robotic system. Consequently, since the most critical component of the robot in terms of torsional deformation is the gear transmission joint, this paper aims to design a torsional stiffener element to reduce its deformation and, thus, an increase of torsional stiffness of the overall robotic system. Tube-shaped and rectangular-shaped stiffener elements, which can fit the joint design satisfying its geometrical constraints, are proposed. A computer-aided engineering approach is implemented to improve the precision of positioning of the end-effector by adding stiffener elements in the joint. Two sensitivity analyses, varying the geometry of the proposed stiffener elements, are performed to evaluate their performance in terms of added mass and displacement reduction.

Keywords: Cable-driven mechanism | Robotics | Torsional stiffening

Abstract: Manual handling tasks, both in daily activities and at work, require high dexterity and the ability to move objects of different shapes and sizes. However, musculoskeletal disorders that can arise due to aging, disabilities, overloading, or strenuous work can impact the natural capabilities of the hand with serious repercussions both in working and daily activities. To address this, researchers have been developing and proving the benefits of wrist exoskeletons. This paper, which is Part II of a study on wrist exoskeletons, presents and summarizes wearable wrist exoskeleton devices intended for use in rehabilitation, assistance, and occupational fields. Exoskeletons considered within the study are those available either in a prototyping phase or on the market. These devices can support the human wrist by relieving pain or mitigating fatigue while allowing for at least one movement. Most of them have been designed to be active (80%) for higher force/torque transmission, and soft for better kinematic compliance, ergonomics, and safety (13 devices out of 24, more than 50%). Electric motors and cable transmission (respectively 11 and 9 devices, out of 24, i.e., almost 50% and 40%) are the most common due to their simplicity, controllability, safety, power-to-weight ratio, and the possibility of remote actuation. As sensing technologies, position and force sensors are widely used in all devices (almost 90%). The control strategy depends mainly on the application domain: for rehabilitation, CPM (control passive motion) is preferred (35% of devices), while for assistance and occupational purposes, AAN (assistance-as-needed) is more suitable (38% of the devices). What emerges from this analysis is that, while rehabilitation and training are fields in which exoskeletons have grown more easily and gained some user acceptance (almost 18 devices, of which 4 are available on the market), relatively few devices have been designed for occupational purposes (5, with only 2 available on the market) due to difficulties in meeting the acceptance and needs of users. In this perspective, as a result of the state-of-the-art analysis, the authors propose a conceptual idea for a portable soft wrist exoskeleton for occupational assistance.

Keywords: industrialization issues | occupational sector | rehabilitation field | wearable devices | wrist exoskeletons

Abstract: This article presents a new design for a two-degrees-of-freedom compliant robotic wrist for upper limb prostheses that matches the maximum range of motion of a human wrist by utilizing cross axis flexural pivot (CAFP) as compliant joints. The wrist design is manufactured using additive manufacturing technology as a single, monolithic component. An optimization routine that utilizes the bi-beam constraint model technique to synthesize compliant joints in the wrist design is presented and verified using finite element analysis (FEA). This optimization routine includes the computation of passive contact profiles through the centroid approach to prevent buckling in the CAFP compliant beams caused by external forces. Furthermore, an accurate analysis of various tendon routing paths for the actuation of the wrist is conducted, providing a flexible and reliable solution to avoid unnecessary power consumption. The proposed wrist is lightweight, cost-effective, easy to maintain, and thanks to the utilization of CAFP joints, it is frictionless and immune to backlash. Experimental tests are conducted to verify the FEA results and confirm the range of motion achieved by the joint (i.e., $\pm 80^{\circ }$ of flexion/extension, $\pm 40^{\circ }$ of ulnar/radial deviation). Overall, this article demonstrates the development of a novel compliant robotic wrist that offers several advantages over traditional prostheses, including a wider range of motion, increased flexibility, and reduced maintenance costs.

Keywords: 2-DOF | Additive manufacturing | compliant mechanisms (CMs) | cross axis flexural pivot (CAFP) | monolithic design | Motion control | Optimization | prosthetic wrist | Prosthetics | Read only memory | Robots | Wrist

Abstract: Industrial Robots (IRs) are increasingly adopted for material subtraction or deposition functions owing to their advantages over machine tools, like cost-effectiveness and versatility. Unfortunately, the development of efficient robot manufacturing processes still faces unsolved issues related to the IRs poor positioning accuracy and to the tool path generation process. Novel engineering methods and tools are needed for CAD based programming of accurate paths and continuous robot motions to obtain the required manufacturing quality and tolerances. Within this context, to achieve smoothness along the tool path formed by linear G-code segments, the IR controllers’ approximation strategies, summarily reported in the manufacturer’s manuals, must be considered. The aim of this paper is to present the preliminary work carried out to identify the approximation algorithms of a Kuka IR when executing linear moves. An experimental study is conducted by varying the controller settings and the maximum translational velocity. The robot behavior has been acquired thanks to the controller tracing function and then processed to yield relations readily employable for the interpretation of G-Code commands and the subsequent generation of proper robot motion instructions. The obtained formulas allow to accurately predict the robot geometric path and kinematics within the corner transition between two linear segments.

Keywords: Corner smoothing | G-code translation | Manufacturing robots | Path approximation | Robot programming

Abstract: Nowadays, energy efficiency of industrial plants is an issue of primary concern. This research aims at minimizing the Energy Consumption (EC) of Industrial Manipulators (IMs) leveraging on Eco-programming strategies. In particular, building upon well-known methods for robot trajectory planning, a novel time-scaling approach is proposed, which employs a non-linear scaling function to better optimize EC. In this scenario, a Graphic User Interface (GUI) has been realized to ease the implementation of the presented algorithm, offering a fast and user-friendly tool to be used by robotic cell designers. Different manipulators models can be uploaded in the GUI to then automatically run the non-linear optimization process and retrieve a minimum-energy trajectory. As an instance, a 6 Degrees of Freedom IM has been considered; the obtained results have been compared with other methods known from the literature and validated through a commercial tool. The proposed method is verified to be more effective for energy-intensive trajectories, possibly reaching EC savings of more than 10 %.

Keywords: Eco-programming | Energy efficiency | Graphic User Interface | Industrial robotics | Smart manufacturing | Trajectory scaling

Abstract: The constant growth in global energy demand, and corresponding prices rise, is soaring new engineering methods for reducing energy consumption in manufacturing processes. For decades, industrial robotics have been enabling quality enhancement of end-products by using flexible manufacturing processes, without much concern to energy cost, but now a makeover is happening. Calls for sustainable and green manufacturing processes are being promoted across the globe with the aim to produce more goods and with less consumption. In this paper, a new method is presented focusing on the optimization of energy intake by industrial robots, without the need to change their hardware set and just modifying the trajectory planning of the end-effector. A test case scenario consisting of a robotic cell with 4 pick-and-place manipulators has been set to validate the method. Starting from a pre-scheduled trajectory, robots are moved at the highest speed and acceleration and, by performing the sequenced operations, the optimal trajectories are defined. The goal is to find a trajectory that minimizes the time cycle and the total energy consumption, while avoiding collisions between the robots’ links: comparing the results thereof to those of the pre-scheduled trajectory, noticeable energy saving has been obtained along with possible decrease of the cycle time.

Keywords: Computer-aided engineering tools | Energy efficiency | Robot scheduling | Trajectory planning | Virtual prototyping

Abstract: One of the main objectives of Industry 4.0 is to build up Smart Factories with improved performance as for productivity, together with lowered maintenance times and costs. In this perspective, Prognostic and Health Management (PHM) is a proactive method to industrial services enhancing maintenance according to the health of the system. PHM entails diagnostic and prognostic engineering tools to recognize the health of the system, and then to choose the prime maintenance actions. The diagnostic tool has to be capable to handle a sizeable volume of data and determine, by means of processing algorithms, the proper set needed for the analysis. The software named MADe can be used as a helpful utility to engineers; it is a model-based toolkit for Reliability, Availability, Maintainability and Safety (RAMS) analysis, capable of optimizing maintenance activities based on the information given by the software, relating to sensor choice and to maintenance strategies. In the PHM framework, the detection of incipient failures is central task of the monitoring the health status of systems that include components sensitive to fatigue or aging. In fact, timely diagnosis allows to schedule maintenance reducing the impact on production outcomes. Based on these considerations, the present paper explains a technique for detecting incipient failures in fatigue sensitive parts, by means of an Equivalent Damage Index (EDI), that can be calculated from the measured signals on the real plant. This procedure is validated, as well as other cutting-edge techniques, to prove its accuracy in detecting incipient breakdowns.

Keywords: Anomaly detection | CBM | Incipient failure | Industry 4.0 | MADe | PHM | Residual Life Estimation | Smart factory

Abstract: Robotic surgery is a set of techniques and technologies used to plan, move, and perform surgery, exploiting the capabilities of robots to overcome human limitations in minimally invasive operations. The use of robots guided by augmented reality has allowed surgeons to improve vision and precision during surgery. Despite the results achieved over the years, there is still a high clinical demand for improvements, which can only be reached using intelligent physical or virtual tools. The present work aims to develop a virtual prototype of robotized bone milling operations, when there is the need to virtually predict operative performance. The proposed model leverages the active connection between Simulink, the well-known numerical tool, and RecurDyn, a commercial CAE solver. In particular, the model parametrization and the simulation process are managed from Matlab, whereas the mechanical system is solved in RecurDyn. After a proper validation of the simulation framework with data taken from the literature, a set of parametric studies has been carried out to investigate the influence of the input parameters on the cutting process.

Keywords: Passively compliant spindle | Robotic milling optimization | Robotic surgery | Virtual prototyping

Abstract: Design For Assembly (DFA) aims at improving product design facilitating assembly phases via the application of evaluation metrics and design guidelines. However, DFA analyses are usually performed manually and the adoption of supporting tool is poor. This paper investigates the application of algorithms allowing to extract from CAD assembly models the required data to perform automated DFA analyses, thus providing a tool to support designers’ everyday works. In particular, attributes from geometric feature recognition algorithms, solids properties and assembly parts’ semantics are leveraged and mapped to the parameters required to accomplish DFA evaluations. The proposed approach is illustrated on a 3D printer for home use. At first, a manual DFA analysis has been performed on the product identifying product BOM, components properties, assembly cycle and times according to models in the literature. Then, the CAD model of the printer has been processed with some geometric algorithms to verify the possibility to extract the required data to be used as input to the DFA analysis. The test case has demonstrated the feasibility of the approach, even if some design considerations and improvement directions still need the critical evaluation of the designer.

Keywords: Assembly semantics | Design For Assembly | Feature recognition | Part recognition

Abstract: In the context of Industry 4.0, condition-based maintenance (CBM) for complex systems is essential in order to identify failures and mitigate them. After the identification of a sensor set that guarantees the system monitoring, three main problems must be addressed for effective CBM: (i) collection of the right data; (ii) choice of the optimal technique to identify the specific dataset; (iii) correct classification of the results. The solutions currently used are typically data driven and, therefore, the results are variable, as it is sometimes challenging to identify a pattern for all specific failures. This paper presents a solution that combines a data driven approach with an in-depth knowledge of the mechanical system’s behaviour. The choice of the right sensor set is calculated with the aid of the software MADe (Maintenance Aware Design environment), whereas the optimal dataset identification technique is pursued with a second tool called Syndrome Diagnostics. After an overview of such methodology, this work also presents RSGWPT (redundant second-generation wavelet packaged transform) analysis to show different possible outcomes depending on the available sensor data and to tailor a detection technique to a given dataset. Supervised and unsupervised learning techniques are tested to obtain either an anomaly detection or a failure identification depending on the chosen sensor set. By using the described method, it is possible to identify potential failures in the system so to awarely implement the optimal maintenance actions.

Keywords: Condition-based maintenance | Failure identification | RSGWPT | Supervised learning | Unsupervised learning

Abstract: The paper discusses the analytical expressions of a motion profile characterized by elliptic jerk. This motion profile is obtained through a kinematic approach, defining the jerk profile and then obtaining acceleration, velocity, and displacement laws by successive integrations. A dimensionless formulation is adopted for the sake of generality. The main characteristics of the profile are analyzed, outlining the relationships between the profile parameters. A kinematic comparison with other motion laws is carried out: trapezoidal velocity, trapezoidal acceleration, cycloidal, sinusoidal jerk, and modified sinusoidal jerk. Then, the features of these motion profiles are evaluated in a dynamic case study, assessing the vibrations induced to a second-order linear system with different levels of damping. The results show that the proposed motion law provides a good compromise between different performance indexes (settling time, maximum absolute values of velocity and acceleration).

Keywords: elliptic jerk | motion control | motion profiles | vibrations

Abstract: Despite an increase in the use of exoskeletons, particularly for medical and occupational applications, few studies have focused on the wrist, even though it is the fourth most common site of musculoskeletal pain in the upper limb. The first part of this paper will present the key challenges to be addressed to implement wrist exoskeletons as wearable devices for novel rehabilitation practices and tools in the occupational/industrial sector. Since the wrist is one of the most complex joints in the body, an understanding of the bio-mechanics and musculo-skeletal disorders of the wrist is essential to extracting design requirements. Depending on the application, each wrist exoskeleton has certain specific design requirements. These requirements have been categorized into six sections: purpose, kinematics, dynamics, rigidity, ergonomics, and safety. These form the driving factors behind the choice of a design depending on the objectives. Different design architectures are explored, forming the basis for the various technical challenges that relate to: actuation type, power source, power transmission, sensing, and control architecture. This paper summarizes, in a systematic approach, all the current technologies adopted, analyzes their benefits and limitations, and finally proposes future perspectives.

Keywords: design architectures | exoskeletons requirements | wearable devices | wrist exoskeletons

Abstract: This article presents the development of a prototype robotic eye-motion system for a novel simulator of ocular and craniofacial trauma that was developed for practical skills training of eye surgeons and first responders. The simulator fills a gap in the ophthalmological training domain, specifically between virtual reality-based systems for cataract and retinal repair and part-task trainers without quantitative measurement capabilities. Combining physical anatomical modules, instrument tracking and embedded sensors with a data acquisition/feedback system in a portable bench-top structure, it offers an alternative to animal- and cadaver-based training. The prototype robotic eye system described includes multiple human eye globe motion features: eye pitch and yaw motion, proptosis, and sensing of applied force to detect pressure/load applied to the globe.

Keywords: Computer-aided design | Medical robotics | Simulation-based-training | Virtual and physical prototyping

Abstract: In this article, we describe the design, fabrication, and validation of a push-latch gripper produced via additive manufacturing, which is capable of performing planar grasps of objects with two opposite parallel surfaces. In particular, the gripper modes of operation are presented, along with an efficient virtual prototype of the system based on a pseudo-rigid body approximation. Such model is proven to be considerably more computationally efficient as compared to the corresponding finite element simulation, while still accurately capturing the fundamental behaviors of the mechanism. Finally, quantitative performance assessments are reported to practically show how fused filament fabrication of Nylon components can be an excellent approach for creating monolithic robotic mechanisms with embodied intelligence that can be effectively employed for pick and place operations. Furthermore, this work represents one further example of an alternative approach to mechanisms development that combines part minimization, faster design iterations, and high repeatability.

Keywords: Additive manufacturing (AM) | compliant mechanisms | design methods | grasping | industry applications | manipulation

Abstract: The paper discusses the energetic efficiency of a SCARA-like manipulator with elastic balancing of the gravity force. The mechanical architecture and the main kinematics aspects of the robot are briefly recalled. Multibody simulations are performed to assess the improvement of energy efficiency which can be obtained by means of the elastic balancing. Then further tests are carried out comparing the energy efficiency of two different Cartesian position control schemes: a classical integer-order KD controller and a fractional-order KDHD controller. Simulation results show that the differences are minimal.

Keywords: Energy efficiency | SCARA robot | SDG9 | Static Balancing

Abstract: This article reports a study evaluating the effect of continuous assistance via an active exoskeleton during orientation tasks of the human wrist in a serious game. The proposed platform features a complete system that may be used for robot-assisted rehabilitation in clinics, offering support for both the therapist and the patient. It gives the possibility to customize the rehabilitation session by regulating the assigned task difficulty, the assistance level offered by the exoskeleton, and the wrist Degrees of Freedoms (DoFs) to be supported, providing a versatile, easy-to-use, rehabilitation station. The setup consists of a 3-DoFs wrist exoskeleton activated by three electric motors, connected to a wheeled station containing the control unit and the host PC to actuate the exoskeleton. The exoskeleton allows to monitor the positions of the human wrist joints and the force applied to the device by the user while performing a movement. Advanced software has been implemented to create a stimulating environment during therapy through virtual reality. The Flight Simulator serious game has been used to investigate the user's wrist Range of Motion (RoM) covered while reaching twenty targets. Thirteen healthy subjects tested the system under two different conditions, considering the device assistance on/off. Results show a significantly higher performance under assistance, rather than without it, on the exploitation of the wrist RoM and on the intuitiveness of movements during the orientation task. A reduction of around 30% of the overall muscle stress has been measured, highlighting the assistance efficacy of the system.

Keywords: Human-Robot Interaction | Mechanism Design | Medical and Rehabilitation Robots | Motor Control | Wearable Device | Wrist Exoskeleton

Abstract: The manufacturing and assembly of small parallel mechanisms are often complex because of the required tolerances and high part count. The present work focuses on the use of additively manufactured compliant mechanisms to overcome some of these difficulties. As a reference, this work considers a recent work on a two degrees of freedom parallel orientational mechanism. Several aspects related to the design and manufacturing of this type of small-scale system are addressed by considering two implementations of the mechanism, one developed following a “traditional” approach with linkages and pin joints, and the other developed following a “flexible” approach using additively manufactured flexures. The two versions of the mechanism are finally compared to provide qualitative and quantitative indications of their motion precision and capacity to withstand loads.

Keywords: Additive manufacturing | Compliant mechanisms | Flexure hinges | Parallel kinematics

Abstract: This paper presents the development of an underactuated prosthetic hand that offers a cost-effective, functional, and human-like alternative for individuals with upper limb amputations. The design and virtual prototyping of the hand focus on achieving a size, weight, and appearance that closely resemble a human hand, aiming to enhance user acceptance. The prosthetic hand consists of ten degrees of freedom (DoF), with four of them being actuated. Among these, three degrees of actuation (DoA) are controlled by electric motors and a tendon transmission system, while the remaining DoA is manually actuated by the user through a spring plunger. The underactuated design incorporates compliant hinges based on springs and a mechanism that decouples the motors from the fingers, enabling more natural movements and greater adaptability to different objects. By incorporating a tendon transmission system and manual thumb actuation, users can easily accomplish basic grasping tasks without relying on complex control systems. To evaluate the gripping abilities and maximum gripping force of the hand, a virtual prototype has been created and tested in different grasping scenarios. This assessment allows for performance evaluation and refinement of the design. To improve affordability and accessibility for a wider range of users, the prosthetic hand has been designed with a focus on cost-effective components and widespread utilization of additively manufactured parts.

Abstract: This study presents the design and validation of a compliant Delta robot created through additive manufacturing (AM) with a monolithic structure. The use of AM expedites the development cycle of robots, enabling faster prototype development and deployment, as well as facilitating experimentation with new robot kinematics. The use of compliant joints poses a challenge in achieving substantial workspaces for robots. However, parallel architectures are well-suited for implementing flexible joints because they require lower ranges of motion for individual joints than serial architectures. Thus the Delta configuration was chosen for this study. A Design for Additive Manufacturing (DfAM) strategy was adopted to minimize the need for support structures and maximize mechanical strength. The overall performance of the Delta was evaluated quantitatively in terms of stiffness and precision. The stiffness test aimed to measure the device's capability to withstand applied loads, while the repeatability test assessed the robot's precision and accuracy Moreover, FEM verification was adopted. Structural simulations are a powerful tool for verifying the experimental results of a robotic system. The approach presented in this work offers an interesting avenue for robot design with significant potential for future advancements and practical applications and sheds light on the trade-offs that designers should consider when adopting this methodology.

Abstract: This paper presents the design and virtual prototyping of a constant force gripper for food handling and harvesting, aimed at reducing the production costs associated with manual labor performed by human workers. The gripper has been designed using advanced Computer-Aided Design (CAD) software to be easily fabricated using additive manufacturing techniques. The solution involved the use of a lumped compliant element to obtain the desired constant force output, resulting in a gripper that is easily maintainable and cost-effective. The use of a constant force mechanism eliminates the need for dedicated sensors and complex control algorithms to avoid object damage, as completely closing the grasp is sufficient for every operation. The optimization of the compliant element shape has been crucial for achieving the desired constant force output and has required a Matlab software optimization framework using the pseudo-rigid body model equations and an fmincon algorithm. The virtual prototyping approach, using a flexible multi-body dynamics software, has enabled fast and easy testing of the CAD design, leading to an optimized final design with high performance and precision. The study results have demonstrated the potential of virtual prototyping for the design and optimization of advanced robotic systems in cost-sensitive industries, particularly in the food harvesting sector.

Keywords: Compliant Element | Computer Aided Engineering | Constant Force Device | Food Harvesting | Virtual Prototyping

Abstract: This article presents a nonlinear model of an inversion-based generalized cross-spring pivot (IG-CSP) using the beam constraint model (BCM), which can be employed for the geometric error analysis and the characteristic analysis of an inversion-based symmetric cross-spring pivot (IS-CSP). The load-dependent effects are classified into two ways, including the structure load-dependent effects and beam load-dependent effects, where the loading positions, geometric parameters of elastic flexures, and axial forces are the main contributing factors. The closed-form load–rotation relationships of an IS-CSP and a non-inversion-based symmetric cross-spring pivot (NIS-CSP) are derived with consideration of the three contributing factors for analyzing the load-dependent effects. The load-dependent effects of IS-CSP and NIS-CSP are compared when the loading position is fixed. The rotational stiffness of the IS-CSP or NIS-CSP can be designed to increase, decrease, or remain constant with axial forces, by regulating the balance between the loading positions and the geometric parameters. The closed-form solution of the center shift of an IS-CSP is derived. The effects of axial forces on the IS-CSP center shift are analyzed and compared with those of a NIS-CSP. Finally, based on the nonlinear analysis results of IS-CSP and NIS-CSP, two new compound symmetric cross-spring pivots are presented and analyzed via analytical and finite element analysis models.

Keywords: Center shift | Compliant cross-spring pivot | Compliant mechanisms | Load-dependent effects | Loading positions | Nonlinear analysis

Abstract: This article reports the analysis and preliminary design of a passive, wearable, upper limb exoskeleton to support workers in industrial environments in a vast range of repetitive tasks, offering an effective strategy to reduce the risk of injuries in production lines. The system primary purpose is to compensate for gravity loads acting on the human upper limb. The proposed exoskeleton is based on 6 Degrees-of-Freedom (DoFs) kinematics with 5-DoFs for the shoulder joint (two displacements plus three rotations) and 1-DoF for the elbow. Gravity compensation is implemented with passive elastic elements to minimize weight and reduce cost. A detailed analytical tool is developed to support the designer in the preliminary design stage, investigating the exoskeleton kinetic-static behaviour and deriving optimal design parameters for the springs over the human arm workspace. By defining specific functional requirements (i.e., the user’s features and simulated movements), computationally efficient optimization studies may be carried out to determine the optimal coefficients and positions of the springs, thus, maximizing the accuracy of the gravity balancing. Two different solutions for the arrangement of the elastic elements are investigated, and obtained results are validated with a commercial multi-body tool for some relevant movements of the user’s arm.

Keywords: Arms | Design Optimization | Exoskeletons | Gravity | Gravity balancing | Kinematics | Shoulder | Springs | Task analysis | Upper Limb Exoskeleton | Virtual Prototyping | Wearable Devices

Abstract: This paper describes the design and development of a new mechanical layout for the integration of additional sensors on robots that directly interact with humans. This specific work starts from the need to control human-robot interaction forces in order to ensure safety for users. The activity consisted on the conceptualization and design of a new mechanism, with the aim of including two sensors: a force/torque sensor to measure interaction forces and a linear encoder that let to know the real configuration of the device. The solution has been tested on a specific device named WristBot, whose limits are the inability to directly measure forces applied to it by humans and the impossibility to know precisely the end-effector position, with the consequences of relevant errors in calculating the interaction forces. The results obtained validate the designed mechanism comparing it with the old one mounted on the robot and prove the benefits of integrating additional sensors into the system.

Keywords: CAD design | Human-robot interaction | Industrial robotics | Interaction forces | Mechanical optimization

Abstract: The fourth industrial revolution is characterized by flexible production systems that can respond to the demand for high variability and customization of the product. To maintain the efficiency of the production process, automated and flexible solutions are mandatory. This paper describes an approach to design Virtual Prototypes of robotic cells and support designer in the definition and simulation of the manufacturing system. The identified model is capable of replicating the performance of the cell under different aspects in a holistic manner: geometry, operating logic, performance, and physical behavior. The design approach is demonstrated on a robotic cell composed of two anthropomorphic robots for the flexible process of automatic assembly of mechanical parts. The resulting model proves to be straightforward, accurate and complete.

Keywords: Digital Twin | Physics-based simulation | Robotic assembly | Virtual Prototype

Abstract: The paper presents the development of the scaled prototype of an oscillating-arm Wave Energy Converter (WEC), for onshore installation, suitable to be placed above breakwaters. The mechanical architecture is based on a four-bar linkage moved by a floating buoy with alternate heave motion. The mechanical energy is transferred to the electrical rotary generator with the interposition of a mechanical rectifier, to obtain unidirectional motion at higher speed. Since the power take-off system is fully electromechanical, without pneumatic or hydraulic components, the proposed WEC is characterized by high efficiency and reliability. The functional design of the proposed WEC and its control layout are summarized. Finally, the methodology for designing the 1:15 scale model, destined for the preliminary experimental validation, is discussed, and the embodiment design of the model is outlined.

Keywords: Oscillating arm | Scaled prototype | SDG7 | Wave energy converter

Abstract: Nowadays, Industrial Robots (IRs) have become widespread in many manufacturing industries. Medium and high payload IRs cover a significant percentage of the overall factory Energy Consumption (EC). This article focuses on the IRs eco-programming to minimize the EC of a robot, being energy efficiency one of the fundamental aims of sustainable manufacturing. By leveraging well-known trajectory scaling methods, this research develops a novel, versatile, fast, and efficient process to define the IR optimal velocity/acceleration profile in time, keeping the geometry of the trajectory fixed. A complete IR system model that founds application in various types of 6 degrees of freedom articulated manipulators has been developed by considering electrical motors, actuator drive systems, and controller cabinet losses. A new optimization technique based on Dynamic Time Scaling of trajectories is presented, and the obtained results are compared with other methods used in the scientific literature. When performing critical path analysis, the EC of the robot system is estimated to be cut down, being the robot motion time fixed, by about 13% through this novel approach. The model has been validated through commercial software, and the proposed optimization algorithm has been implemented in a user-friendly interface tool.

Keywords: Eco-programming | Energy efficiency | Industrial robotics | Industry 4.0 | Sustainability | Trajectory scaling

Abstract: The original article contained a mistake. Figure 10 in the original article is not the correct one but a duplicate of Fig. 11. The correct Figure is as follows:(Figure Preseneted.).

Abstract: New technological advances are changing the way robotics are designed for safe and dependable physical human–robot interaction and human-like prosthesis. Outstanding examples are the adoption of soft covers, compliant transmission elements, and motion control laws that allow compliant behavior in the event of collisions while preserving accuracy and performance during motion in free space. In this scenario, there is growing interest in variable stiffness actuators (VSAs). Herein, we present a new design of an anthropomorphic elbow VSA based on an architecture we developed previously. A robust dynamic feedback linearization algorithm is used to achieve simultaneous control of the output link position and stiffness. This actuation system makes use of two compliant transmission elements, characterized by a nonlinear relation between deflection and applied torque. Static feedback control algorithms have been proposed in literature considering purely elastic transmission; however, viscoelasticity is often observed in practice. This phenomenon may harm the performance of static feedback linearization algorithms, particularly in the case of trajectory tracking. To overcome this limitation, we propose a dynamic feedback linearization algorithm that explicitly considers the viscoelasticity of the transmission elements, and validate it through simulations and experimental studies. The results are compared with the static feedback case to showcase the improvement in trajectory tracking, even in the case of parameter uncertainty.

Keywords: Dynamic feedback linearization | Physical prototyping | Static feedback linearization | Upper-limb prosthesis | Variable stiffness

Abstract: In the last decades, compliant mechanisms have been widely studied but their application has not been widespread due to their susceptibility to fatigue and the lack of systematic design methodologies. In this paper, the authors propose a new approach to be used in the automated machinery mechanism design (the mechanisms are usually subjected to predominant inertial loads) that exploits the capability of the compliant joints to store and release elastic energy in order to reduce the motor torque requirements. Thanks to the carbon-fiber reinforced 3D printing technologies, the compliant joint stiffness can be properly designed to obtain, for the considered mechanism, a resonant condition during its nominal functioning. Moreover, topology optimization can be successfully employed to reduce the mechanism component inertia (keeping the same overall mechanism stiffness) and thus, further diminish the torque requirements. In order to assess the quality of the proposed approach, a pusher mechanism used in a real automated machine has been considered. A prototype has been manufactured to evaluate the effect of the compliant joint introduction and the topology optimization on the motor torque reduction. To validate the results, an experimental campaign has been conducted. Comparison between the standard design approach and the new one emphasizes the superior contribution of compliant joint introduction on the motor torque reduction: a 97% and 96% reduction on the RMS and peak motor torque, respectively, is achieved resorting to the new design approach. Although a high repeatability is achieved, a slight deviation of the trajectory with respect to the ideal one is however registered.

Keywords: Additive manufacturing | Continuous fibre reinforced thermoplastics | Size optimization | Topology optimization

Abstract: Researchers involved in the development of dexterous robotic hands agree that a mechatronics approach to hand design is the only way to generate new levels of functional capabilities. As reported by several authors, the problems relative to the single component or subsystem design must be solved within a general frame of compatibility and integrability. In this paper the virtual and physical prototyping of a three-fingered gripper designed to be mounted on an autonomous underwater vehicle (AUV) for underwater manipulation as well as sampling specimens is reported. In particular, an overall description of the gripper design is discussed, with special attention to the required actuation and tendon transmission system, its integration within the mechanical structure and the required control architecture. Different solutions for the joint configuration and the structure of the tendon network adopted for the transmission system are presented. The integrated design of the finger is reported and the motivations leading to this particular implementation are thoroughly addressed, taking into account both the mechanical constraints and the control requirements. The overall finger design is modular, so that other design solutions comprising multiple fingers (e.g. for in-hand manipulation purposes or realization of cage gripper) are easily achievable by adding further modules without increase the overall dimensions of the device. Virtual prototype results are finally provided and discussed to prove the gripper behaviour and capabilities.

Keywords: Autonomous underwater vehicles | Tendons

Abstract: This paper introduces a novel upper limb robotic exoskeleton designed to assist industrial operators in a wide range of manual repetitive tasks, such as tool handling and lifting/moving of heavy items. Due to its reduced size and high maneuverability, the proposed portable device may also be employed for rehabilitation purposes (e.g. as an aid for people with permanent neuromuscular diseases or post-stroke patients). Its primary function is to compensate the gravity loads acting on the human shoulder by means of a hybrid system consisting of four electric motors and three passive springs. The paper focuses on the exoskeleton mechanical design and virtual prototyping. After a preliminary review of the existent architectures and procedures aimed at defining the exoskeleton functional requirements, a detailed behavioral analysis is conducted using analytical and numerical approaches. The developed interactive model allows to simulate both kinematics and statics of the exoskeleton for every possible movement within the design workspace. To validate the model, the results have been compared with the ones achieved with a commercial multibody software for three different operator’s movements.

Keywords: Computer aided design | Gravity balancing | Robotic arm | Upper limb exoskeleton | Virtual prototyping

Abstract: In this paper, the concept of isotropic compliance is extended to the field of compliant mechanisms. Starting from the design of a rigid-body mechanism, a planar compliant system is determined by applying the rigid-body replacement method. The static behaviour of the isotropic compliant mechanism is validated by finite element simulations and experimental tests. The extension of the proposed method to the Euclidean Space E(3) is discussed.

Keywords: Compliant mechanism | Isotropic compliance | Pseudo-rigid body model | Rigid body replacement

Abstract: The Cross-Axis Flexural Pivot (CAFP) is a well-established compliant rotational joint characterized by a highly configurable behavior. Its classic form, consisting of two uniform beams that cross at an arbitrary angle, has been thoroughly examined via either theoretical approaches or Finite Element Analysis (FEA). Conversely, the effects of utilizing variable section beams have had minor consideration, possibly due to the more complex modeling phase. The present paper addresses the analysis of CAFPs incorporating beams whose width and thickness are assumed to vary along the axis with either linear or parabolic functions. The CAFP planar behavior is studied resorting to the Beam-Constraint Model (BCM) for different load cases, namely with an ideal rotation applied to one rigid link or a more practicable cable-driven actuation. To extend the use of BCM to large deflections, each CAFP's beam is modeled as a chain of two BCM elements, named Bi-BCM. A preliminary study has been carried out to establish empirical equations that provide the BCM characteristic coefficients for every considered beam shape. Next, these have been used to perform the pivot behavioral analysis and to generate, as an output of the sensitivity studies, the performance maps of stiffness, maximum stress and center shift. These results have been verified with FEA, which confirmed the Bi-BCM accuracy for any tested configuration. Finally, direct comparisons between predicted behaviors of the CAFP actuated via the flexible cable and experimental data obtained with 3D printed specimens further validated the proposed Bi-BCM model.

Keywords: Cable-Driven actuation | Chained-Beam constraint model | Compliant mechanisms | Cross-Axis flexural pivot | Finite element analysis | Variable section beams

Abstract: Beam-based Compliant Mechanisms (CMs) are increasingly studied and implemented in precision engineering. Straight beams with uniform cross section are the basic modules in several design concepts, which can be deemed as standard CMs. Their behavioral analysis can be addressed with a large variety of techniques, including the Euler–Bernoulli beam theory, the Pseudo-Rigid Body (PRB) method, the beam constraint model and the discretization-based methods. This variety is unquestionably reduced when considering nonstandard CMs, namely design problems involving special geometries, such as curve/spline beams, variable section beams, nontrivial shapes and contact pairs. The 3D Finite Element Analysis (FEA) provides accurate results but its high computational cost makes it inappropriate for optimization purposes. This work compares the potentialities of computationally efficient modeling techniques (1D FEA, PRB method and chained-beam constraint model), focusing on their applicability in nonstandard planar problems. The cross-axis flexural pivot is used as a benchmark in this research due to its high configurable behavior and wide range of applications. In parallel, as an attempt to provide an easy-to-use environment for CM analysis and design, a multi-purpose tool comprising Matlab and a set of modern Computer-Aided Design/Engineering packages is presented. The framework can implement different solvers depending on the adopted behavioral models. Summary tables are reported to guide the designers in the selection of the most appropriate technique and software framework. Lastly, efficient design procedures that allow to configure nonstandard beam-based CMs with prescribed behavior are examined with two design examples.

Keywords: CAD/CAE software framework | Compliant Mechanisms | Cross-axis flexural pivot | Design methods | Shape optimization | Virtual Prototyping

Abstract: The optimization of the energy consumption of Industrial Robots (IRs) has been widely investigated. Unfortunately, on the field, the prediction and optimization strategies of IRs energy consumption still lack robustness and accuracy, due to the elevated number of parameters involved and their sensitivity to environmental working conditions. The purpose of this paper is to present, and share with the research community, an extensive experimental campaign that can be useful to validate virtual prototypes computing the energy consumption of robotic cells. The test cell, comprising a high payload IR equipped with multiple sensors and different payloads, is firstly described. The testing procedures are then presented. Experimental results are analyzed providing novel qualitative and quantitative evaluations on the contribution and relevance of different power losses and system operating conditions, clearly depicting the nonlinear relation between the energy consumption and various freely programmable parameters, thus paving the way to optimization strategies. Finally, all the experimental tests data are provided in the form of an open research dataset, along with custom Matlab scripts for plotting graphs and maps presented in this paper. These tests, which are verifiable via the shared dataset, consider the overall measured IR energy consumption (as drawn from the electric network) and highlight that, in some industrially interesting case scenarios, optimization potentials for energy savings of more than 50% are possible.

Keywords: Energy optimization | Experimental campaign | Industrial robotics | Industry 4.0 | Sustainable manufacturing

Abstract: This paper reports about the design of a bio-inspired compliant wrist, whose mobility (i.e. ulnar-radial deviation and flexion-extension) has been realized by employing two pairs of contact-aided Cross-Axis Flexural Pivots (CAFPs), actuated via remotely-placed servo-motors and tendon transmissions. The human wrist behaves differently when deflecting in clockwise or anticlockwise direction, both in terms of maximum angular deflection and passive stiffness. The device proposed hereafter aims at mimicking such natural asymmetry, while withstanding unexpected external loads. In order to fulfill these requirements, two contacts are included: (i) a pure rolling contact (named passive contact), achieved via a cam mechanism guiding the CAFP deflection and ensuring the wrist resistance to compressive loads; (ii) a purposely shaped contact pair (named active contact), acting on one beam of the CAFP so as to increase its stiffness. The design procedures and tools specifically developed for the wrist optimization are described. In the first step, a CAFP shape optimization is performed, followed by the synthesis of the active contact pair. In the second step, the centrodes are computed and then used to generate the passive contact profiles. At last, the third step focuses on the definition of the tendons routing. To prove the validity of the numerical models, a physical prototype of the wrist is produced and tested. Direct comparisons between simulations and experiments confirm the efficacy of the proposed design method.

Keywords: CAD/CAE multi-software framework | Compliant mechanism | Cross-axis flexural pivot | Robotic wrist | Shape optimization | Virtual prototyping

Abstract: This article reports the preliminary analysis and design of a novel 6 degrees of freedom, passive, upper limb exoskeleton for industrial applications. The aim is to conceive a wearable device to support workers in a vast range of repetitive tasks, offering an effective strategy to reduce the risk of injuries in production lines. The exoskeleton primary purpose is to compensate for the gravity loads acting on the human upper limb via the action of five springs. By reaching the static balancing through the use of passive elements only, several advantages in terms of reduced weight and cost can be provided. In this scenario, a detailed analytical approach has been developed to study the exoskeleton statics and synthesize the springs within the human upper limb workspace. In particular, a 3R balancer is designed for the exoskeleton shoulder joint and a set of computationally efficient optimization studies are carried out to determine the optimal coefficients and positions of the springs. The obtained results have been validated with a commercial multibody tool.

Keywords: Design Optimization | Gravity Balancing | Upper Limb Exoskeleton | Virtual Prototyping | Wearable Devices

Abstract: Servo-Actuated Mechanisms (SAM) are capable of improving the flexibility and reconfigurability of modern automatic machines. On one hand, as compared to fully mechanical drives, SAM may suffer from non-negligible positioning inaccuracies, whose effect can become unacceptable in case of undesired part deformations during high dynamic motions. On the other hand, it may be the case that parts of the system are purposely designed to provide an highly compliant behaviour, so as to potentially increase the device safety in case of interaction with humans. In both cases, practical strategies to reduce the SAM positioning errors are necessary. As a possible solution to such issue, in this paper, an integrated approach to improve the accuracy of a partially compliant SAM in position-controlled tasks is described. The method exploits a multi-software framework comprising Matlab and RecurDyn, namely a commercial Computer-Aided Engineering (CAE) tool that can be used to simulate the motion of systems comprising both rigid and flexible bodies. Starting from an initial, sub-optimal, motion law of the input link, a trajectory optimizer iteratively runs the CAE solver and automatically computes an optimal, compensated, position profile. The obtained results show that the method may represent a useful tool for analyzing/designing partially compliant SAM, whenever analytical models are either too complex or not readily available.

Abstract: This paper presents a nonlinear model of an inversion-based generalized cross-spring pivot (IG-CSP) using the beam constraint model (BCM), which can be employed for the geometric error analysis and the characteristic analysis of an inversion-based symmetric cross-spring pivot (IS-CSP). The load-dependent effects are classified in two ways, including structure load-dependent effects and beam load-dependent effects, where the loading positions, geometric parameters of elastic flexures, and axial forces are the main contributing factors. The closed-form load-rotation relations of an IS-CSP and a non-inversion-based symmetric cross-spring pivot (NIS-CSP) are derived with consideration of the three contributing factors for analyzing the load-dependent effects. The load-dependent effects of IS-CSP and NIS-CSP are compared when the loading position is fixed. The rotational stiffness of the IS-CSP or NIS-CSP can be designed to increase, decrease, or remain constant with axial forces, by regulating the balance between the loading positions and the geometric parameters. The closed-form solution of the center shift of an IS-CSP is derived. The effects of axial forces on the IS-CSP center shift are analyzed and compared with those of a NIS-CSP. Finally, based on the nonlinear analysis results of IS-CSP and NIS-CSP, two new compound symmetric cross-spring pivots are presented and analyzed via analytical and FEA models.

Keywords: Center shift | Compliant cross-spring pivot | Load-dependent effects | Loading positions | Nonlinear analysis

Abstract: In the last decade composite materials, previously almost exclusively used in aerospace and automotive industries, are becoming widespread thanks to the introduction of the fused filament fabrication (FFF) process in the additive manufacturing technology. With respect to the standard and more widely used material subtractive technologies, the FFF layer-by-layer construction process is capable of manufacturing parts featuring very complex geometry. Moreover, the deposition of reinforcing filaments provides components with highperformance mechanical characteristics. Since FFF is a relatively new technology, studies are still needed to fully understand the mechanical behavior of composite materials realized with FFF and how all the process parameters (e.g., layer thickness, filament deposition direction, type of matrix and reinforcement, the interaction between matrix and reinforcement) affect the final result. This paper deals with the preliminary experimental analysis of straight beams realized in carbon-fiber-reinforced Nylon White composite material with the MarkForged MarkTwo threedimensional printer. Envisaged application of the considered straight beams is as flexible elements in compliant mechanisms. In particular, tensile and bending tests are performed on nine different straight beam specimens in order to provide a first understanding on how the filament disposition within the sample affects its mechanical response. From the results it is found that the proper position of the reinforcement filaments provides a very effective means to tune the selective compliance of beam flexures.

Keywords: Additive Manufacturing | Compliant Mechanisms | Composites | Continuous Fiber-Reinforced Thermoplastics | Straight Beam Flexures

Abstract: In the last decade, additive manufacturing technologies (AMT) have spread widely in the industrial field, mostly for fast prototyping but also for the production of finished parts that need a high level of customization. With respect to the well-established material subtractive technologies (MST), some limitations due to component shape can be overcome with AMT. Topology optimization (TO) combined with AMT is a powerful tool capable of realizing components characterized by similar stiffness but smaller inertia concerning those realized with MST. This tool can be very useful in automatic machinery design in order to reduce the required motor torque. In fact, in this realm, the mechanisms are usually subjected to predominant inertial loads. Moreover, since the introduction of fuse filament deposition modeling (FDM) of continuous fiber-reinforced thermoplastics (CFRT), mechanical characteristics comparable to highperformance metal materials can be reached. Thus, rigidity and precision can be achieved as well. In addition to TO, with FDM and size optimization (SO), the designer can easily realize components characterized by a proper stiffness to be included in mechanisms to tune their dynamic mechanical characteristics. In fact, due to their ability to passively store and release mechanical energy, elastic elements can be introduced in a mechanism in order to compensate for kinetic energy variations, which drastically reduce motor torque requirements. The required elasticity can be easily introduced in the mechanism by replacing standard kinematic pairs with Compliant Joints (CJ) in the form of flexible lamina, also assuring lightness, precision and ease of realization. This paper analyzes the potentiality of FDM in combination with TO and CJ design (CJD) for the realization of automated machinery mechanisms subjected to inertial loads. A pusher mechanism is considered: The pros and cons of adopting the procedure are shown with respect to the standard procedure.

Keywords: Additive Manufacturing | Continuous Fiber-Reinforced Thermoplastics | Size Optimization | Topology Optimization

Abstract: The concept of a statically balanced mechanism with a single rotational degree-of-freedom is presented. The proposed device achieves static balancing by combining positive stiffness elements and negative stiffness elements within an annular domain. Two designs are discussed. The first is composed of an Archimedean spiral and two pinned-pinned pre-buckled beams. The overall mechanism is modeled via an analytical approach and the element dimensions are optimized. The optimal configuration is then tested through finite element analysis (FEA). A second approach replaces the spiral beam with elastic custom-shaped spline beams. A FEA optimization is performed to determine the shape and size of such spline beams. The behavior of the negators is used as reference for the optimization so as to achieve a complete balancing. A physical prototype of each configuration is machined and tested. The comparison between predicted and acquired data confirmed the efficacy of the design methods.

Keywords: Compliant mechanisms | Conceptual design | Design optimization | Statically balanced mechanisms

Abstract: This paper reports about the virtual and physical prototyping of an antagonistic Variable Stiffness Actuator (VSA) to be used on robotic arms specifically realized for physical human-robot interaction. Such antagonistic actuation system, which comprises purposely conceived Compliant Transmission Elements (CTEs) characterized by a nonlinear relation between the deflection and the applied torque, allows to simultaneously control both the joint's position and stiffness. The CTE's beams geometry, namely slender spline beams, has been defined by means of an automatic routine leveraging on Matlab and ANSYS and allowing for the shape optimization of complex flexures. The synthesized springs are characterized by a predefined quadratic torque-deflection characteristic, which is shown to guarantee a precise stiffness modulation while avoiding the need for a joint's position sensor. After shape optimization, the CTE is fabricated via additive manufacturing and subsequently tested. The acquired data show a very good consistency with the numerical results, although highlighting a non-negligible hysteresis due to material damping. Therefore, in order to cope with such unavoidable effect along with other parameter uncertainties and unmodeled effects (e.g. static friction), a robust feedback controller is proposed, allowing for the simultaneous and decoupled regulation of joint position and stiffness. Finally, a VSA prototype is produced and tested. Experimental results confirm that the VSA behaves as expected.

Keywords: Compliant mechanisms | Multi software framework | Shape optimization | Sliding mode controller | Variable stiffness actuators

Abstract: The use of integrated Computer Aided Design/Engineering (CAD/CAE) software capable of analyzing mechanical devices in a single parametric environment is becoming an industrial standard. Potential advantages over traditional enduring multi-software design routines can be outlined into time/cost reduction and easier modeling procedures. To meet industrial requirements, the engineering education is constantly revising the courses programs to include the training of modern advanced virtual prototyping technologies. Within this scenario, the present work describes the CAD/CAE project-based learning (PjBL) activity developed at the University of Genova as a part of course named Design of Automatic Machines, taught at the second level degree in mechanical engineering. The PjBL activity provides a detailed overview of an integrated design environment (i.e. PTC Creo). The students, divided into small work groups, interactively gain experience with the tool via the solution of an industrial design problem, provided by an engineer from industry. The considered case study consists of an automatic pushing device implemented in a commercial machine. Starting from a sub-optimal solution, the students, supervised by the lecturers, solve a series of sequential design steps involving both motion and structural analysis. The paper describes each design phase and summarizes the numerical outputs. At last, the results of the PjBL activity are presented and commented by considering the opinions of all the parties involved.

Keywords: Engineering education | Integrated CAD/CAE design | Interactive education | Project-based learning | Virtual modeling

Abstract: The paper discusses the application of Reinforcement Learning to the control of an onshore Wave Energy Converter (WEC). The proposed WEC features a simple and low-cost architecture. It is characterized by an oscillating floating rocker arm which moves a four bar linkage in the vertical plane. A mechanical rectifier, based on two one-way clutches and a multiplier gearbox, transforms the low speed oscillating motion of the four bar into a higher-speed unidirectional rotation of the electrical generator. The dynamic model of the WEC, based on multibody approach and Linear Wave Theory, is presented. Then a Reinforcement Learning (RL) algorithm, a Q-learning method, is applied to dynamically adjust the generator speed-torque ratio as a function of the sea state. Simulation results show the effectiveness of this model-free adaptive control in tuning the system in order to maximize the generated power. Starting from a simple monochromatic model of the sea, the presented approach is verified according to sea conditions of increasing complexity, and finally to long term time series, obtained from measurements of real sea states in the considered geographical region. The tuning of the hyper-parameters of RL algorithm with respect to the speed of convergence and optimality of generated power is also discussed.

Keywords: Linear Wave Theory | Oscillating arm | Q-learning | Reinforcement Learning | WEC

Abstract: Up to date, Dielectric Elastomer Actuators (DEA) have been mostly based on either silicone or acrylic elastomers, whereas the potential of DEAs based on inexpensive, wide-spread natural and synthetic rubbers has been scarcely investigated. In this paper, a DEA based on a styrene-based rubber is demonstrated for the first time. Using a Lozenge-Shaped DEA (LS-DEA) layout and following a design procedure previously proposed by the authors, we develop prototypes featuring nearly-zero mechanical stiffness, in spite of the large elastic modulus of styrenic rubber. Stiffness compensation is achieved by simply taking advantage of a biaxial pre-stretching of the rubber DE membrane, with no need for additional stiffness cancellation mechanical elements. In the paper, we present a characterization of the styrene rubber-based LS-DEA in different loading conditions (namely, isopotential, isometric, and isotonic), and we prove that actuation strokes of at least 18% the actuator side length can be achieved, thanks to the proposed stiffness-compensated design.

Keywords: Actuator | Dielectric elastomer | Negative spring design | Stiffness compensation

Abstract: In the last decade, the adoption of additive manufacturing technologies (AMT) (3D printing) has increased significantly in many fields of engineering, initially only for rapid prototyping and more recently also for the production of finished parts. With respect to the long-established material subtractive technologies (MST), AMT is capable to overcome several limitations related to the shape realization of high-performance mechanical components such as those conceived via topology optimization and generative design approaches. In the field of structures and mechanisms, a major advantage of AMT over MST is that, for the same loading and constraining conditions (including kinematic and overall encumbrance), it enables the realization of mechanical components with similar stiffness but smaller volume (thus smaller weight, density being equal). Recently, the potentialities of AMT have also been increased by the introduction of the fuse filament deposition modeling (FDM) of continuous fibre-reinforced thermoplastics (CFRT), which combines the ease of processing of plastic AMT with the strength and specific modulus of the printed components that are comparable to those attainable via metallic AMT. In this context, the present paper investigates the potentialities of FDM-CFRT for the realization of mechanisms subjected to predominant inertial loads such as those found in automated packaging machinery. As a case study a Stephenson six-bar linkage powered in direct drive by a permanent magnet synchronous motor is considered. Starting from an existing mechanism realized in aluminum alloy with traditional MST, a newer version to be realized with FDM-CFRT has been conceived by keeping the kinematics fixed and by redesigning the links via three-dimensional topology optimization. To provide a fair comparison with the more traditional design/manufacturing approach, size optimization of the original mechanism made in aluminum alloy has also been performed. Comparison of the two versions of the mechanism highlights the superior performances of the one manufactured via FDM-CFRT in terms of weight, motor torque requirements and motion precision.

Keywords: Additive manufacturing technology | Continuous fibre-reinforced thermoplastic | Size optimization | Topology optimization

Abstract: The paper describes a novel Clench-and-Release Device (CRD), which can be used to quickly replace the rear wheels of bikes equipped with disk brakes, while also being suitable for front wheels. Since a quick wheel replacement is a pressing demand during competitions, the CRD reduces time wasted in situations like flat tire replacement. At the same time, it can be useful also for amateur bikers, who desire a simple way to lock/release a wheel without the risk of getting dirty or being unable to properly align the brake’s disk and pads. In fact, thanks to the CRD, both brake and pinion packs are kept in place at all times and the chain remains engaged with the gears, even after wheel removal. Although similar devices can be found on the market, the proposed CRD provides an improved design since: (i) pinions and brake are placed on the same side with respect to the wheel symmetry plane perpendicular to the wheel axis of rotation; (ii) the front and the rear wheel share the same hub; (iii) manual operations are definitely easier; (iv) the wheels are compatible with different types of transmission; (v) the brake discs are more protected in case of crashing. A patent for the Italian region has been filed.

Keywords: Computer-aided design | Through axle shaft | User centered design | Wheel quick release | Wheels’ fast removal

Abstract: This paper reports the design of a monolithic long-stroke constant force compliant mechanism (CM). The device is suitable for applications requiring a predefined force magnitude at the contact interface, such as manipulation systems. Starting from a compliant slider-crank mechanism providing a constant force within a rather limited deflection range, the paper describes the shape optimization carried out with the aim of extending the CM available stroke. In the first design step, the pseudo-rigid body (PRB) method is used to synthesize a sub-optimal lumped compliance solution. Secondly, two improved beam-based alternatives are evaluated by means of an integrated software framework, comprising Matlab and ANSYS. These new embodiments make use of a variable thickness beam, whose shape and dimensions have been optimized so as to provide a constant reaction force in an extended range. In particular, straight and spline segments are respectively used for the first and second prototype. With reference to the lumped compliance configuration, the available stroke has been increased of amounts equalling to 467% in the straight segments version (namely, from 3 mm to 14 mm) and to 833% in the spline segments version (namely, from 3 mm to 25 mm). All the predicted behaviors have been validated via physical experiments on 3D printed specimens. The proposed multi-step design flow may also be applied to a large variety of CMs, starting from their PRB model.

Keywords: compliant mechanisms | constant force mechanisms | pseudo-rigid body method | shape optimization | software integration

Abstract: Human-centered design is based on the satisfaction of the user needs mainly related to performances, interaction, usability, accessibility, and visibility issues. However, the quality of the interaction process is hidden and usually difficult to detect. The paper proposes a multi-disciplinary assessment tool for the evaluation of the human-machine interaction, based on the collection of physiological data and anthropometrical performance data. Such a method can be used both within on-field tests and virtual simulations, supporting the spread of digital approaches in industry. The methodology allows objectifying how users interact with machine or interface items, thanks to the collection of the users’ performance during task execution, the digitalization of collected data, and the evaluation of users’ physical and mental workload. Such a system has been applied to an industrial case study focusing on agricultural machinery driving and control to support the system re-design in terms of interface features, commands’ location and grouping, and positioning of additional devices.

Keywords: Digital factory | Ergonomics | Human factors | Human-centered design | Human-machine interaction

Abstract: This paper reports the study of a planar Cross-Axis Flexural Pivot (CAFP) comprising an additional contact pair. The proposed device may be useful for applications requiring a revolute joint that behaves differently when deflecting clockwise/anti-clockwise. The presence of the contact pair reduces the free length of one flexures, resulting in a considerable increment of the overall joint stiffness. The pivot behaviour is investigated, for different load cases, via the Chained-Beam-Constraint Model (CBCM), namely an accurate method to be applied in large deflection problems. A framework comprising Matlab and ANSYS is developed for testing the CAFP performances in terms of rotational stiffness, parasitic shift and maximum stress, with different combinations of geometrical aspect ratios and contact extensions. Results achieved via CBCM for a pure rotation applied to the CAFP's output link are then verified through Finite Element Analysis. The resulting performance maps show good agreement between the numerical results. Furthermore, the CBCM shows an improved computational efficiency, which is a crucial aspect for preliminary design steps. At last, direct comparison between simulations and experiments, developed by means of two custom test rigs, confirms the efficacy of the proposed design method for the modeling of contacts in large deflection problems.

Keywords: Chained-beam-constraint model | Contact-aided compliant mechanism | Cross-Axis Flexural Pivot | Multi software framework

Abstract: Nowadays, more than in the past, marine industries are paying increasing attention to the environmental impact of ships and vessels. Several solutions have been studied and adopted with the final aim of reducing the exhaust gas emissions, mainly acting on the fuel consumption reduction. Within this scenario, the aim of this article is to investigate the energy performance and the fuel saving potential when employing a magnetic continuously variable transmission in a marine propulsion system. Such magnetic continuously variable transmission, considered among other possible continuously variable transmission designs since its torque capabilities are perfectly suitable for the application at hand, is employed in order to optimize the overall propulsion efficiency through an appropriate optimal variation of the reduction ratio as a function of the propeller loads. A secondary benefit, although not less important, is that the magnetic continuously variable transmission is an oil-free transmission that consequently offers a lower environmental impact as compared to traditional lubricated gearboxes. Owing to these considerations, in the article, the magnetic continuously variable transmission size is first selected on the basis of a simplified static model of the vessel. Subsequently, a dynamic mathematical model representing the overall drivetrain dynamic of the propulsion plant is developed, with the purpose of simulating the transmission behaviour during fast ship manoeuvres. Then, in order to test the effectiveness of the proposed design, a trawler is selected as a case study. This particular ship type has been chosen as it provides a variegated operative profile in terms of speed and required thrust, thus being a representative case of those ships in which a continuously variable transmission installation could effectively provide practical benefits. A quantitative analysis of the plant efficiency is finally provided and critically discussed.

Keywords: continuously variable transmission | fuel consumption | Marine propulsion plant | ship energy efficiency | time domain simulation

Abstract: At present, energy consumption strongly affects the financial payback period of industrial robots, as well as the related manufacturing process sustainability. Henceforth, during both design and manufacturing management stages, it becomes crucial to assess and optimize the overall energy efficiency of a robotic cell by means of digital manufacturing tools. In practice, robotic plant designers and managers should be able to provide accurate decisions also aimed at the energy optimization of the robotic processes. The strong scientific and industrial relevance of the topic has led to the development of many solutions but, unfortunately, state of the art industrial manipulators are equipped with closed controllers, which heavily limit the feasibility and performance of most of the proposed approaches. In light of the aforementioned considerations, the present paper presents a novel simulation tool, seamlessly interfaced with current robot offline programming tools used in industrial practices, which allows to automatically compute energy-optimal motion parameters, thus reducing the robot energy consumption, while also keeping the same productivity and manufacturing quality. The main advantage of this method, as compared to other optimization routines that are not conceived for direct integration with commercial industrial manipulators, is that the computed parameters are the same ones settable in the robot control codes, so that the results can automatically generate ready-to-use energy-optimal robot code. Experimental tests, performed on a KUKA Quantec KR210 R2700 prime industrial robot, have confirmed the effectiveness of the method and engineering tool.

Keywords: Automatic code generation | Energy optimization | Industrial robotics | Industry 4.0 | Robot offline programming | Sustainable manufacturing | Virtual prototyping

Abstract: Compliant Mechanisms (CMs) are currently employed in several engineering applications requiring high precision and reduced number of parts. For a given mechanism topology, CM analysis and synthesis may be developed resorting to the Pseudo–Rigid Body (PRB) method, in which the behavior of flexible members is approximated via a series of rigid links connected by spring-loaded kinematic pairs. From a CM analysis standpoint, the applicability of a generic PRB model requires the determination of the kinematic pairs’ location and the stiffness of a set of generalized springs. In parallel, from a design standpoint, a PRB model representing the kinetostatic behavior of a flexible system should allow to compute the flexures’ characteristics providing the desired compliance. In light of these considerations, this paper describes a Computer-Aided Design/Engineering (CAD/CAE) framework for the automatic derivation of accurate PRB model parameters, on one hand, and for the shape optimization of complex-shape flexures comprising out-of-plane displacements and distributed compliance. The method leverages on the modelling and simulation capabilities of a parametric CAD (i.e. PTC Creo) seamlessly connected to a CAE tool (i.e. RecurDyn), which provides built-in functions for modelling the motion of flexible members. The method is initially validated on an elementary case study taken from the literature. Then, an industrial case study, which consists of a spatial crank mechanism connected to a fully-compliant four-bar linkage is discussed. At first, an initial sub-optimal design is considered and its PRB representation is automatically determined. Secondly, on the basis of the PRB model, several improved design alternatives are simulated. Finally, the most promising design solution is selected and the dimensions of a flexure with non-trivial shape (i.e. hybrid flexure) is computed. This technique, which combines reliable numerical results to the visual insight of CAD/CAE tools, may be particularly useful for analyzing/designing spatial CMs composed of complex flexure topologies.

Keywords: CAD/CAE integration | Distributed compliance | Pseudo rigid body models | Shape optimization | Spatial compliant mechanisms

Abstract: In this paper the design of a linear long-stroke quasi-constant force compliant mechanism (CM) is presented and discussed. Starting from a flexure-based slider-crank mechanism, providing the required constant force within a rather limited deflection range, the paper reports about the shape optimization carried out with the specific aim of extending the available CM operative range. The proposed device is suitable in several precision manipulation systems, which require to maintain a constant-force at their contact interface with the manipulated object. Force regulation is generally achieved by means of complex control algorithms and related sensory apparatus, resulting in a flexible behavior but also in high costs. A valid alternative may be the use of a purposely designed CM, namely a purely mechanical system whose shape and dimensions are optimized so as to provide a force-deflection behavior characterized by zero stiffness. In the first design step, the Pseudo-Rigid Body (PRB) method is exploited to synthesize the sub-optimal compliant configuration, i.e. the one characterized by lumped compliance. Secondly, an improved design alternative is evaluated resorting to an integrated software framework, comprising Matlab and ANSYS APDL, and capable of performing non-linear structural optimizations. The new embodiment makes use of a variable thickness beam, whose shape and dimensions have been optimized so as to provide a constant reaction force in an extended range. Finally, a physical prototype of the beam-based configuration is produced and tested, experimentally validating the proposed design method.

Abstract: Position-controlled servo-systems mostly make use of electric rotary motors and gearboxes and, if necessary, a transmission mechanism to convert rotary into linear motion. Even so, especially in the field of automatic machines for packaging, it should be highlighted that most of the required movements are usually linear, so that Linear Electric Motors (LEM) should somehow represent a more convenient solution for designers. LEM can directly generate the required trajectory avoiding any intermediate mechanism, thus potentially minimizing the number of linkages/mechanical parts and, therefore, the undesired backlash and compliance that come along. On the other hand, particularly within small-medium enterprises, LEM may be rarely employed despite obvious advantages, mostly due to their high-cost as compared to rotary actuators and the lack of knowledge of the achievable performance. In light of these considerations, the present paper reports an industrial case study where an automatic machine for packaging, comprising distributed actuation and several tasks requiring a linear motion, has been completely redesigned employing different kind of LEM (i.e. iron-core and iron-less). Such machine architecture is compared to a “traditional” design where brushless gearmotors are coupled to linkage systems. The paper mainly focuses on the selection criteria for the LEM system and on the engineering tools employed during the different design stages. Qualitative and quantitative conclusions are finally drawn, which may provide useful hints for designers that are willing to actually employ LEM-based solutions in an industrial scenario.

Keywords: CAD/CAE | Engineering Design Methods and Tools for Industry 4.0 | High Precision Manufacturing | Modelling | Simulation

Abstract: Dielectric Elastomer Transducers (DETs) are a promising technology for the development of actuators, generators and sensors with high performance and low cost. Practical application and economic viability of DETs is strongly affected by their reliability and lifetime, which depend on the maximum strain and electrical loads that are cyclically applied on such devices. To date, only limited information is available on the fatigue life performances of dielectric elastomer materials and of the transducers made thereof. This paper reports on a first lifetime constant electric-stress test campaign conducted on 38 free-expanding frame-stretched circular DET specimens, made of the silicone elastomer film Elastosil 2030 250/150 by Wacker with blade-casted carbon-black silicone-elastomer electrodes, that have been subjected to nearly square wave electric field signals with 1 Hz frequency, 50% duty cycle and with amplitudes ranging from 65 MV/m to 80 MV/m.

Keywords: Dielectric Elastomer | Electrical Breakdown | Electrical Degradation | Fatigue Life | Reliability

Abstract: The paper presents an experimental setup suited to a starting introduction of high school and undergraduate students to basic topics in vibrations, data acquisition and signal processing. The setup is portable, based on low-cost gear motor, sensors and control electronics, with 3D printed custom parts, and it has been used in different education contexts. Its specification, realization, features and usage are discussed in the paper.

Keywords: Engineering Education | High School | Mechanical Vibrations | Mechatronic Systems | Undergraduate Students

Abstract: Elloboat is a tracked vehicle for launching and beaching of small boats and watercrafts, capable of operating in a wide range of operative conditions, here including rescue applications. This paper presents the vehicle architecture and discusses the main design issues. The effects of track dimensions on terrain compaction, bulldozing resistances and, consequently, on track sinkage are analyzed by means of the Bekker model. Obviously, track dimensions also influence the vehicle mass and size, leading to a complex engineering problem. Since vehicle speed and acceleration are limited, stability during locomotion can be assessed using a quasi-static approach, computing the longitudinal and lateral tipping angles for a given vehicle configuration and payload position, and imposing a proper limit to their minimum. Stability analysis can be exploited not only in the design phase, but also for the real-time evaluation of the actual margin of stability, so as to help the operator in the vehicle path/speed planning.

Keywords: Beaching | Bekker Theory | Launch | Small Boat | Tracked Vehicle | Watercraft

Abstract: This paper reports about project-based learning activities carried out within the course of Design of Automatic Machines at the University of Genova. This didactic experience, provided to the students enrolled in the second-level degree in Mechanical Engineering, aims at providing the knowledge of those methods and tools required to optimally design functional parts of automatic machines, here including the mechanical architecture and the actuation subsystem. Lecture hours are equally devoted to the introduction of theoretical concepts and to lab exercises, which leverage on the extensive and advanced use of dedicated CAD/CAE software tools (i.e. PTC Creo). In particular, the projects are related to the in-depth study of automated packaging systems, initial (sub-optimal) design solutions being provided by an industrial partner with years of practice in the sector. After a description of the educational goals, the presentation discusses the phases of the activity and the main methodological aspects. In addition, the adopted tools for the design and simulation of the developed systems are discussed in detail.

Keywords: CAD-based shape optimization | CAD/CAE tools | Design parametrization

Abstract: Robotic deburring (RD) still requires long and delicate physical tests to tune the process-parameters, thus drastically reducing the robotic cell productivity. Henceforth, engineering methods and tools are needed to optimise the RD application within a virtual environment, replicating the real behaviour of the robot tooling under different process conditions, namely unpredictable variety of burr size/shape and limited accuracy of the robot motions. To this purpose, the spindle compliance, which plays a fundamental role, is unfortunately not evaluated by state-of-the-art simulation tools. The present paper proposes a virtual prototype (VP) of a radially-compliant spindle, suitable to assess and optimise the deburring efficiency in different case scenarios. A multi-body model of the spindle, integrated with the process behavioural model, predicts process forces and optimal deburring parameters, delivering the contour maps of the envisaged deburring error as function of feed rate and tool compliance. An industrial case-study is provided.

Keywords: parameter design | passively compliant spindle | robotic deburring | virtual prototyping

Abstract: The paper presents the third version of the hybrid leg-wheel ground mobile robot Mantis, a small-scale platform designed for inspection and surveillance tasks. The locomotion system is based on the cooperating action of a couple of actuated front legs and wheels, along with a passive rear carriage. The system performs wheeled locomotion on even grounds and hybrid locomotion in case of terrain irregularities or obstacles. This architecture combines high speed, energy efficiency, maneuverability and stable camera vision on flat terrains with good motion capabilities in unstructured environments. In the embodiment design presented hereafter, referred to as Mantis 3.0, the rear carriage has been equipped with four passive wheels, instead of two as in the previous versions, in order to improve the stability during steep stair climbing maneuvers; moreover, the legs, the main body and the rear carriage have been significantly redesigned in order to be realized by additive manufacturing techniques, with the final aim of obtaining a low-cost device suitable for Open Source distribution.

Keywords: Additive manufacturing | Ground mobile robot | Hybrid leg-wheel locomotion | Low-cost robotics | Step climbing

Abstract: The paper presents, through an example, two different approaches to introduce mechanism kinematics to first-cycle mechanical engineering students. Analytical solution and traditional graphic methods are considered, both supported by state-of-the-art software tools. Advantages and disadvantages of both approaches from an educational point of view are outlined during example development. Finally a summarizing discussion is proposed.

Abstract: This paper discusses the mechanical architecture of Elloboat, an unmanned Tracked Vehicle (TV) for launching and beaching of watercrafts and small boats (up to a length of 3.5 meters). The mechanical architecture of Elloboat comprises a central saddle connected to two lateral tracks by parallelogram linkages, which may be driven by linear or rotary actuators to lift/lower the payload. The TV is able to pick the boat form a support, to travel along the beach and to perform launching while almost completely submerged. On the contrary, during beaching, the boat is relieved from the water and then transported to storage. The Elloboat mechanical architecture is redundantly constrained and actuated. In the following, after a detailed description of the device, the TV kinematic and static behaviours according to different actuation schemes are discussed on the basis of a mobility analysis and then by multibody simulations, with rigid and flexible models of joints.

Keywords: beaching | launching | multibody simulation | small boat | tracked vehicle | watercraft

Abstract: This paper introduces the design of a fully-compliant Spherical Joint (SJ), obtained by the in-parallel connection of two identical open chains each composed of three equal circular flexible beams, having coincident centers of curvature and mutually orthogonal axes of minimum rotational stiffness. Thanks to its particular topology, the SJ provides a fully isotropic behavior, the two chains being placed in space so as to be symmetric with respect to the beams' center of curvature. At first, the overall system compliance matrix is derived by means of an analytical procedure, in order to obtain a parametric formulation of the SJ behavior within the small deflection range. Then, after finite element validation of the analytical model, an optimization study of the beam geometry is developed, with the aim of maximizing the ratio between the SJ primary to secondary compliance factors. At last, the potential advantages and drawbacks of the proposed design are discussed by numerically evaluating the joint performance in terms of parasitic motions within the large deflection range (namely, when large external loads are applied to the envisaged center of spherical motion).

Keywords: Circular flexible beams | Compliance matrix | Compliant mechanisms/actuators | Design graphs | Finite element analysis | Spherical joint

Abstract: In this paper, a novel design of a fully compliant locking device is presented, for possible application in robotic actuation systems. The synthesis method based on a rigid linkage mechanism is explained, a parametrization scheme is proposed, and an optimization procedure is conducted using kinetostatic flexible multi-body analysis in conjunction with global optimization techniques. The performance of the optimized locking device design is validated via numerical simulations.

Abstract: Industrial robots are commonly designed to be very fast and stiff in order to achieve extremely precise position control capabilities. Nonetheless, high speeds and power do not allow for a safe physical interaction between robots and humans. With the exception of the latest generation lightweight arms, purposely design for human-robot collaborative tasks, safety devices shall be employed when workers enter the robots workspace, in order to reduce the chances of injuries. In this context, Variable Stiffness Actuators (VSA) potentially represent an effective solution for increasing robot safety. In light of this consideration, the present paper describes the design optimization of a VSA architecture previously proposed by the authors. In this novel embodiment, the VSA can achieve stiffness modulation via the use of a pair of compliant mechanisms with distributed compliance, which act as nonlinear springs with proper torque-deflection characteristic. Such elastic elements are composed of slender beams whose neutral axis is described by a spline curve with non-trivial shape. The beam geometry is determined by leveraging on a CAD/CAE framework allowing for the shape optimization of complex flexures. The design method makes use of the modeling and simulation capabilities of a parametric CAD software seamlessly connected to a FEM tool (i.e. Ansys Workbench). For validation purposes, proof-concept 3D printed prototypes of both non-linear elastic element and overall VSA are finally produced and tested. Experimental results fully confirm that the compliant mechanism behaves as expected.

Abstract: A spherical flexure is a special kind of compliant hinge specifically conceived for spherical motion. It features an arc of a circle as centroidal axis and an annulus sector as cross-section, circle and annulus having a common center coinciding to that of the desired spherical motion. This paper investigates a compliant spherical 3R open chain that is obtained by the in-series connection of three identical spherical flexures having coincident centers and mutually orthogonal axes of maximum rotational compliance. The considered spherical chain is intended to be used as a complex flexure for the development of spatial parallel manipulators. The compliance matrix of the proposed chain is first determined via an analytical procedure. Then, the obtained equations are used in a parametric study to assess the influence of spherical flexure geometry on the overall stiffness performances of the considered 3R open chain.

Keywords: Compliance matrix | Spherical flexures | Spherical mechanisms

Abstract: In this paper, a novel 3D printed Rotational Joint (RJ) embedding an integrated elastic element is presented. The RJ, produced as a single piece by means of an FDM printer, comprises a traditional pin hinge coupled with a pair of spiral torsion springs, providing the desired compliance for the application at hand. Benefits of the proposed design include monolithic manufacturing and possibility to be successfully employed in robotic articulated devices requiring joint elasticity for their functioning. On the other hand, the sub-optimal RJ behavior, mainly caused by the unavoidable friction between 3D printed mating surfaces, must be accurately taken into account for design purposes. In this context, preliminary reliability tests have been performed showing promising results in terms of lifetime and negligible fatigue effects. Then, a mathematical model of the system is derived, which comprises the spring elasticity along with any frictional effects that may be due to either the pin hinge itself or the tendon transmission (frequently employed in underactuated robotic devices). The model parameters have been empirically evaluated by comparing simulated and experimental data. In addition, the last part of the paper describes how the proposed RJ can be effectively employed for the design of modular, underactuated fingers, providing three degrees of freedom and a single tendon transmission. To this end the model of the joint module proposed in this work will be the starting point for the geometry dimensioning of a finger with a desired free closure motion.

Abstract: Industrial process plants are increasingly becoming complex structures with high level of automation. Nonetheless, the final plant productivity and the overall equipment efficiency does not solely depend on an optimized engineering design/installation practice, but also on human operators supervision. In parallel, along with the classic demand to minimize costs and time-to-market during the design phases, issues concerning human safety and failure prevention play a crucial role, one of the highest target being the avoidance of dangerous process states. Within this context, Simulation-Based-Training (SBT) allows plant operators to learn how to command complex automated machineries within a secure virtual environment. Similar to its usage in medical, aerospace, naval and military fields, SBT for manufacturing systems can be employed in order to involve the user within a realistic scenario, thus providing an effective, lifelike, interactive training experience under the supervision of experienced personnel. In addition, also according to previous literature, industry-driven SBT may be effectively envisaged as a natural extension of the plant life-cycle simulation practice, comprising Design Simulation & Optimization, Virtual Commissioning, Operator Training, up to Plant Maintenance. In this context, since the overall system behavior depends both on manufacturing process dynamics and Control Logics, the main challenge for an effective SBT is related with the development of a real-time environment where control system responsiveness is fully reproduced. Owing to this consideration, this paper reports a successful industrial case study, concerning a novel SBT workbench used for steel plants operator training, discussing both the virtual prototyping phase and the development of a real-time simulation architecture. In particular, a hybrid process simulation is employed, where a virtual process model is coupled with physical PLC and Human–Machine Interface, thus achieving an accurate reproduction of the real plant/operator interaction.

Keywords: Hybrid virtual/physical simulation | Industrial case study | Simulation-based-training | Virtual commissioning | Virtual prototyping

Abstract: This paper presents a new method for optimizing the layout position of several Industrial Robots (IRs) placed within manufacturing work-cells, in order to execute a set of specified tasks with the minimum energy consumption. At first, a mechatronic model of an anthropomorphous IR is developed, by leveraging on the Modelica/Dymola built-in capabilities. The IR sub-system components (namely mechanical structure, actuators, power electronic and control logics) are modeled with the level of detail strictly necessary for an accurate prediction of the system power consumption, while assuring efficient computational efforts. Secondly, once each IR task is assigned, the optimal work-cell layout is computed by using proper optimization techniques, which numerically retrieve the IR base position corresponding to the minimum energy consumption. As an output to this second development stage, a set of color/contour maps is provided, that depicts both energy demand and time required for the task completion as function of the robot position in the cell to support the designer in the development of an energy-efficient layout. At last, two robotic manufacturing work-cells are set-up within the Delmia Robotics environment, in order to provide a benchmark case study for the evaluation of any energy saving potential. Numerical results confirm possible savings up to 20% with respect to state-of-the-art work-cell design practice.

Abstract: Virtual prototyping enables the validation and optimization of mechanical devices similar to physical testing, saving time and costs in the product development, especially in case of heavy machines with complex motions. However, virtual prototyping is usually deployed only at the end of the design process, when the product architecture has already been developed. The present paper discusses the introduction of virtual prototypes since the conceptual design stage as “Virtual Concepts”, in which coarse models of machinery design variants are simulated to interactively evaluate several solutions and support best design choices. Virtual concept modeling and interactive preliminary validation, along with its later integration into a virtual prototype, are expressly investigated using multi body dynamics software. A verification case study concerning a large vibrating screen is presented, in order to demonstrate that dynamic virtual concepts can enable an easier and effective interactive evaluation of the design variants, thus increasing the design process predictability. Finally, current challenges to be solved for the practical adoption of virtual concept simulations as an integral part of the industrial design process are critically discussed.

Keywords: CAD based simulation | Design process | Vibrating screen | Virtual concepts | Virtual prototyping

Abstract: Quick-Release Hooks (QRHs) are connection devices for chains or metal ropes, which can be unfastened under full-load conditions by using a limited opening force. Despite their widespread use, the scientific literature about the mechanical behaviour of QRHs is rather limited. This paper deals with the kinematic and quasi-static analysis of a class of QRHs, based on a spring-loaded four-bar mechanism operating in the proximity of a singularity configuration. The quasi-static analysis allows to estimate the opening force as a function of the mechanism geometry and of the safety spring's features. At last, a multibody model of the system is developed, in order to validate the analytical model and to evaluate the influence of friction in revolute joints.

Keywords: Multibody modelling | Quasi-static analysis | Quick-release hook

Abstract: This paper presents a novel robot simulation tool, fully interfaced with a common Robot Offline Programming software (i.e. Delmia Robotics), which allows to automatically compute energy-optimal motion parameters, for a given end-effector path, by tuning the joint speed/acceleration during point-to-point motions whenever allowed by the manufacturing constraints. The main advantage of this method, as compared to other optimization routines that are not conceived for a seamless integration with commercial industrial manipulators, is that the computed parameters are the same required by the robot controls, so that the results can generate ready-to-use energy-optimal robot code.

Keywords: Computer-Aided Robotic tools | Delmia Robotics | Energy Optimization | Industrial Robots | Sustainable Manufacturing

Abstract: The actual use of Industrial Robots (IR) for assembly systems requires the exertion of suitable strategies allowing to overcome shortcomings about IR poor precision and repeatability. In this paper, the practical issues that emerge during common “peg-in-hole” assembly procedures are discussed. In particular, the use of passive Remote Center of Compliance (RCC) devices, capable of compensating the IR non-optimal performance in terms of repeatability, is investigated. The focus of the paper is the design and simulation of a flexure-based RCC that allows the prevention of jamming, due to possible positioning inaccuracies during peg insertion. The proposed RCC architecture comprises a set of flexural hinges, whose behavior is simulated via a CAE tool that provides built-in functions for modelling the motion of compliant members. For given friction coefficients of the contact surfaces, these numerical simulations allow to determine the maximum lateral and angular misalignments effectively manageable by the RCC device.

Keywords: Compensation Strategies | Compliant Flexures | Peg-in-hole assembly | RCC Device | Robotic assembly | Virtual Prototyping

Abstract: Compliant Mechanisms (CMs) are employed in several applications requiring high precision and reduced number of parts. For a given topology, CM analysis and synthesis may be developed resorting to the Pseudo-Rigid Body (PRB) approximation, where flexible members are modelled via a series of spring-loaded revolute joints, thus reducing computational costs during CM simulation. Owing to these considerations, this paper reports about a practical method to determine accurate PRB models of CMs comprising out-of-plane displacements and distributed compliance. The method leverages on the optimization capabilities of modern CAE tools, which provide built-in functions for modelling the motion of flexible members. After the validation of the method on an elementary case study, an industrial CM consisting of a crank mechanism connected to a fully-compliant four-bar linkage is considered. The resulting PRB model, which comprises four spherical joints with generalized springs mounted in parallel, shows performance comparable with the deformable system.

Keywords: CAD/CAE Tools | Carachteristic Parameters | Compliant Mechanisms | Flexible Multi-Body Dynamics | Pseudo-Rigid Body Models

Abstract: The paper presents the design of an onshore Wave Energy Converter (WEC) named ALETTONE (At Least Energy Thanks To Neptune), which is characterized by a low cost mechanical architecture based on a four-bar linkage with mobility in a vertical plane. The lower link is a floating rocker arm moved by the hydrostatic and hydrodynamic forces exerted by the sea water, whereas the upper rocker arm is connected to a rotating electric generator via a transmission composed of either a single or a pair of one-way clutches coupled to a speed multiplier gearbox. Due to its simplicity, this WEC concept seems to be an interesting solution for energy generation in isolated locations. After a description of the overall design, the dynamic model of the system is presented, along with simulation results in case of monochromatic and panchromatic waves.

Keywords: Four-bar mechanism | Multibody simulation | Onshore generation | Wave energy converter

Abstract: According to recent researches, it is desirable to extend Industrial Robots (IR) applicability to strategic fields such as heavy and/or fine deburring of customized parts with complex geometry. In fact, from a conceptual point of view, anthropomorphic manipulators could effectively provide an excellent alternative to dedicated machine tools (lathes, milling machines, etc.), by being both flexible (due to their lay-out) and cost efficient (20-50% cost reduction as compared to traditional CNC machining). Nonetheless, in order to successfully enable highquality Robotic Deburring (RD), it is necessary to overcome the intrinsic robot limitations (e.g. reduced structural stiffness, backlash, time-consuming process planning/optimization) by means of suitable design strategies and additional engineering tools. Within this context, the purpose of this paper is to present recent advances in design methods and software platforms for RD effective exploitation. Focusing on offline methods for robot programming, two novel approaches are described. On one hand, practical design guidelines (devised via a DOE method) for optimal IR positioning within the robotic workcell are presented. Secondly, a virtual prototyping technique for simulating a class of passively compliant spindles is introduced, which allows for the offline tuning of the RD process parameters (e.g. feed rate and tool compliance). Both approaches are applied in the design of a robotic workcell for high-accuracy deburring of aerospace turbine blades.

Keywords: Engineering methods | Industrial robotics | Intelligent factory | Virtual prototyping

Abstract: Quick-Release Hooks (QRH) are particular accessories for connecting chains or metal ropes, that can be remotely unfastened under full-load conditions via application of an external force with limited magnitude. Despite their widespread use, and aside from a number of patents, the scientific literature related to QRH performance is rather limited. This paper reports about the modelling of a class of QRH, which relies on the use of a four-bar linkage mechanism operating in the proximity of a singularity configuration. Design graphs depicting the main functional parameters are reported. At last, a multibody model of the system is developed, which validates the analytical results while providing an insight of the frictional forces effect on the device modelling and performance.

Keywords: Kinematic analysis | Multibody modelling | Parameter design | Quick-release hook | Static analysis

Abstract: This paper introduces and investigates a compliant spherical 3R open chain that is obtained by the in-series connection of three identical circularly-curved beam flexures with coincident centers of curvature and mutually orthogonal axes of maximum rotational compliance. The considered open chain is intended to be used directly as a spherical mechanism in pointing devices or as a complex spherical flexure for the development of spatial parallel manipulators. The compliance matrix of the proposed chain is first determined via an analytical procedure. After finite element validation, the obtained equations are used in a parametric study to assess the influence of circularly-curved beam flexure geometric parameters on the overall stiffness performances of the considered compliant spherical 3R open chain. In addition, comparison with an equivalent compliant spherical chain employing straight beam flexures is reported to highlight the added benefits of using circularly-curved beam flexures in terms of reduced parasitic motions.

Keywords: Circularly-curved beam flexures | Compliance matrix | Finite element analysis | Parasitic motions

Abstract: Position-controlled Servo-Systems (SeSs) may be envisaged as a key technology to keep the manufacturing industry at the leading edge. Unfortunately, based on the current state-of-the-art, these mechatronic devices are well performing but intrinsically energy intensive, thus compromising the overall system sustainability. Therefore, traditional design and optimization paradigms, previously focused on productivity and quality improvement, should be critically reviewed so as to introduce energy efficiency as an optimality criterion alongside with the global production rate. In particular, focusing on mono-actuator systems with one degree-of-freedom, among the several design factors that can influence the SeS overall performance, the end-effector motion law can be easily modified without either hardware substitution or further investments. In this context, the purpose of the present paper is twofold. On one side, an effective method for the quick set-up of an energy-predictive CAD-based virtual prototype is discussed. In parallel, an energy comparison of some commonly employed Point-To-Point motions and optimization cost functions is provided. For what concerns the trajectory interpolation scheme, a standard optimization problem based on the aforementioned virtual model is solved by means of either algebraic or trigonometric splines. For what concerns the optimality criterion, either the system energy consumption or the root-means square value of the actuator torque are taken into account. In general, torque-based approaches, which may be preferred since they do not require a full knowledge of the SeS electrical parameters, can be effectively employed only when friction effects are negligible as compared to purely inertial loads. In parallel, cubic algebraic splines outperform other types of trajectories, although losing continuity of the resulting jerk profile.

Keywords: CAD/MBD tools | Eco-Design methods | Servo-Systems | Trajectory comparison | Virtual prototyping

Abstract: This paper introduces and investigates a novel Spherical Flexure (SF), specifically conceived for application on spherical compliant mechanisms. The flexure features an arc of a circle as a centroidal axis and an annulus sector as cross-section, circle and annulus having a common center coinciding to that of the desired spherical motion. In this context, each element of the SF spatial compliance matrix is analytically computed as a function of both flexure dimensions and employed material. The theoretical model is then validated by relating analytical data with the results obtained through three-dimensional Finite Element Analysis. Finally, SFs are compared to Circularly Curved-Beam Flexures (CCBFs) in terms of parasitic motions.

Keywords: Compliance matrix | Finite Element Analysis | Parasitic motions | Spherical Flexures

Abstract: Industrial robotics provides high flexibility and reconfigurability supported by a user-friendly programming, but still lacks in accuracy. An effective workcell calibration reduces errors in robot manufacturing and enables robot machining applications. A novel workcell calibration method is embedded in an integrated design framework for an in-depth exploitation of CAD-based simulations and offline programming. The method is composed of two steps: first calibration of the workpiece-independent equipment in the workcell layout and final automated online calibration of workpiece-dependent equipment. The method is finally applied to a changeable robotic workcell for finishing aluminium cast housings for aerospace gear transmissions characterised by complex shapes and by close dimensional and geometrical specifications. Experimental results prove the method effectiveness in enhancing accuracy in robot machining.

Keywords: Aerospace industry | Industrial robotics | Integrated design | Workcell calibration

Abstract: Monolithic Flexure-based Compliant Mechanisms (MFCM) can be used to conceive nonlinear springs with a desired load-displacement profile at one point of their structure. For a given MFCM topology, these particular springs can be conveniently dimensioned by resorting to the well-known Pseudo-Rigid-Body approximation, whose accuracy strongly depends on the modelling precision of the flexures’ principal compliance. For various types of flexures, closed-form solutions have been proposed, which express the compliance factors as functions of the flexure dimensions. Nonetheless, the accuracy of these relations is limited to slender, beam-like hinges undergoing rather small deflections. In order to overcome such limitations, this paper provides empirical equations, derived from finite element analysis, that can be used for the optimal dimensioning of circular, elliptical, and corner-filleted flexural hinges with general aspect ratios, on the basis of both principal compliance and maximum bearable stress. At first, an accuracy comparison with previously published results is provided. Then, as a case study, a nonlinear spring based on a double slider-crank MFCM and with a desired load-displacement profile is dimensioned and verified via finite element analysis. The corresponding MFCM prototype, produced by means of water jet cutting, is finally tested on a tensile stage. Both numerical and experimental results confirm that the aforementioned empirical equations outperform the closed-form solutions provided in the past literature when modelling thick cross-section hinges undergoing significant deflections.

Keywords: Compliant mechanisms | Design methods | Finite element analysis | Flexural hinges | Pseudo-rigid-body model

Abstract: In this paper, an engineering method for the power flow assessment of a position-controlled servo-mechanism is outlined. The considered system is composed of a permanent magnet synchronous motor coupled to a standard power converter, and directly connected to a slider crank mechanism. After the accurate description of a consistent power flow model, a sequential identification technique is discussed, which allows to determine the dynamic parameters of linkage, electric motor and electronic driver by means of non-invasive experimental measures. The proposed model allows to accurately predict the major sources of power loss within the system.

Keywords: Design of Experiments | Power flow assessment | Servo-actuated mechanism | Virtual prototyping

Abstract: Spiral Torsion Springs (STS) are generally manufactured employing medium/high-carbon steel alloys shaped as thin rods with rectangular cross section. Meanwhile, plastic materials (e.g. ABS or PLA), currently used in freeform manufacturing processes, may not be suited for several applications, owing to the low material yield strength and the rather poor fatigue life. Despite the above-mentioned limitations, the main advantages of a 3D printing process, as compared to more traditional manufacturing techniques, are the design flexibility and the possibility to directly integrate elastic components within a joint mechanism produced as a single (monolithic) part. In particular, provided that the external forces acting on the spring coils are maintained within a certain threshold and that the spring geometry is suitably optimized, a reliable 3D-printed STS alternative to traditional steel springs is actually feasible. Given these premises, the main purpose of the present paper is to propose a model-based optimization algorithm that allows to optimally size STS for user-specified torque-deflection characteristics. Optimal STS geometries are then realized in ABS via Fused Deposition Manufacturing, and subsequently tested with a purposely-designed experimental set-up. Furthermore, the behavior of each STS sample (in terms of stiffness and equivalent Von Mises stress) is evaluated by means of non-linear finite elements analysis, in order to check the correspondence with the expected behavior. Finally, numerical and experimental results are provided, which demonstrate the prediction capabilities of the proposed modeling/optimization techniques, and confirm that well-behaved STS can be conceived and produced. Envisaged applications concern the development of smart structures for robot design, such as multi-articulated compliant robotic chains that can be used as low-cost manipulators (i.e. arm) or as mini-manipulators (i.e. fingers). The proposed approach effectively simplifies the production and the assembly of the mechanism, also allowing for an easier integration of embedded sensory-actuation systems.

Abstract: At the current state-of-the-art, Robotic Deburring (RD) has been successfully adopted in many industrial applications, but it still needs improvements in terms offinal quality. In fact, the effectiveness of a RD process is highly influenced by the limited accuracyof the robot motions and by the unpredictable variety of burr size/shape. Tool compliance partially solves the problem, although dedicated engineering design tools are strictly needed, in order to identify those optimized parameters and RD strategies that allow achieving the best quality and cost-effectiveness. In this context, the present paper proposes a CAD-based Virtual Prototype (VP) of a pneumatic compliant spindle, suitable to assess the process efficiency in different case scenarios. The proposed VP is created by integrating a 3D multi-body model of the spindle mechanical structure with the behavioural model of the process forces, as adapted from previous literature. Numerical simulations are provided, concerning the prediction of both cutting forces and surface finishing accuracy.

Keywords: CAD-based tools | Compliant spindle | Robotic deburring | Virtual Prototyping

Abstract: Industrial Robotics (IR) may be envisaged as the key technology to keep the manufacturing industry at the leading edge. Unfortunately, at the current state-of-the-art, IR is intrinsically energy intensive, thus compromising factories sustainability in terms of ecological footprint and economic costs. Within this scenario, this paper presents a new framework called AREUS, focusing on eco-design, eco-programming and Life Cycle Assessment (LCA) of robotized factories. The objective is to overcome current IR energetic limitations by providing a set of integrated technologies and engineering platforms. In particular, novel energy-saving hardware is firstly introduced, which aim at exchanging/storing/recovering energy at factory level. In parallel, innovative engineering methods and software tools for energy-focused simulation are developed, as well as energy-optimal scheduling of multi-robot stations. At last, LCA methods are briefly described, which are capable to assess both environmental and economic costs, linked to the flows of Material, Energy and Waste (MEW). A selected list of industrially-driven demonstration case studies is finally presented, along with future directions of improvement.

Keywords: Computer-Aided-Robotics | DC-grid | Energy-Efficient Industrial Robotics | LCA | Optimal Sequences

Abstract: This paper quantitatively reports about a practical method to improve both position accuracy and energy efficiency of Servo-Actuated Mechanisms (SAMs) for automated machinery. The method, which is readily applicable on existing systems, is based on the 'smart programming' of the actuator trajectory, which is optimized in order to lower the electric energy consumption, whenever possible, and to improve position accuracy along those portions of the motion law which are process relevant. Both energy demand and tracking precision are computed by means of a virtual prototype of the system. The optimization problem is tackled via a traditional Sequential-Quadratic-Programming algorithm, that varies the position of a series of virtual points subsequently interpolated by means of cubic splines. The optimal trajectory is then implemented on a physical prototype for validation purposes. Experimental data confirm the practical viability of the proposed methodology.

Keywords: Energy Efficiency | Position Accuracy | Trajectory Optimization | Virtual Prototyping

Abstract: Programmable servo-actuated mechanisms can enhance the flexibility and the reconfigurability of modern manufacturing systems. Differently from fully mechanical design solutions (such as mechanical cams) and especially in the case of high-dynamic motions, servomechanism performance depends on several interacting factors, namely electric motor and linkage dynamics, controller efficacy, and requested motion law. In particular, point-to-point (PTP) trajectories are usually designed in order to comply with technological constraints, imposed by the required interaction with the handled product, and to maximize some optimality criterion such as, for instance, energy efficiency or limited actuation torques. In this context, the present paper proposes a novel method for designing energy and peak-power optimal PTP motions. A standard optimization problem is solved by means of either cubic or quintic splines. Nonetheless, differently from previous approaches, the optimization cost functions are based on a virtual prototype of the system, which comprises behavioral models of power converter, controller, and electric motor coupled with the mechanical system. Results are then compared with experimental data obtained on a physical prototype. The comparison quantitatively shows that better-behaved PTP trajectories can be designed by including the dynamic contribution of each subsystem component.

Keywords: Electronic cams | high-speed machinery | intelligent manufacturing | mechatronic design methods | trajectory generation | virtual prototyping

Abstract: The selection of conceptual design alternatives is crucial in product development. This is due both to the fact that an iterative process is required to solve the problem and that communication among design team members should be optimized. In addition, several design constraints need to be respected. Although the literature offers several alternative selection methods, to date, only very few are currently being used in industry. A comparison of the various approaches would improve the knowledge transfer between design research and practice, helping practitioners to approach these decision support tools more effectively. This paper proposes a structured comparison of two decision support methods, namely the Fuzzy-Analytic Hierarchy Process and Pugh’s Controlled Convergence. From the literature debate regarding selection methods, four relevant criteria are identified: computational effort, suitability for the early design stages, suitability for group decision making, and ease of application. Finally a sensitivity analysis is proposed to test the robustness of each method. An industrial case study is described regarding an innovative and low-cost solution to increase the duration of heel tips in women’s shoes. The selection of conceptual design alternatives of the heel tip presents complex challenges because of the extremely difficult geometric constraints and demanding design criteria.

Keywords: Concept selection | Engineering design methods | Fuzzy-analytic hierarchy process | Pugh’s controlled convergence

Abstract: A novel design for a dielectric elastomer (DE) actuator is presented. The actuator is obtained by coupling a cylindrical DE film with a series of slender beams axially loaded beyond their buckling limit. Similar to previous published solutions, where different actuator geometries were coupled with compliant mechanisms of various topologies, the elastic beams are designed so as to provide a suitable compensating force that allows obtaining a quasi-constant available thrust along the entire actuator stroke. Whilst the elastic beam are sized on the basis of an analytical procedure, the overall system performance is evaluated by means of multiphysics finite element (FE) analysis, accounting for the large deflection of the buckled-beam springs (BBSs) and for the DE material hyperelasticity. Numerical and experimental results are finally provided, which demonstrate the prediction capabilities of the proposed modeling method and confirm that well-behaved cylindrical actuators can be conceived and produced.

Abstract: In the field of pharmaceutical processing, last generation automatic machines autonomously modify their behavior in order to achieve the best manufacturing quality and productivity despite ever changing process requirements. Mechatronics, as a synergistic integration of electro-mechanical equipment and software control logics, enables such adaptive self-optimizing behaviors. Unfortunately, due to the complex interactions between the different technologies, the final performance of these systems can be effectively validated and optimized only on a physical prototype, with limited possibilities to introduce possible design changes. Therefore, in order to enable validation/optimization of high performance machinery during engineering design stage, a mechatronic Virtual Prototyping (VP) technology is strongly needed. Within this context, the present work discusses a mechatronic VP method based on a Hardware-in-the-Loop, hybrid-process simulation approach, where interactive real-time simulations can effectively assess the real final performance under changing process scenarios. In particular, a case study concerning a high-speed automatic machines for pharmaceutical capsules filling is thoroughly discussed.

Keywords: Hardware-in-the-Loop | Intelligent Manufacturing | Mechatronic Design | Virtual Prototyping

Abstract: Simulation-Based-Training (SBT) allows to train the operators of complex machinery within a safe virtual environment by means of effective lifelike learning experiences. SBT has been efficiently used in medical, aerospace and military fields and it may provide a competitive advantage also for the training of operators in mechatronic plants. In fact, at the current state of the art, human-machine interaction still heavily impacts on the final performances of automated plants. Since the fast-evolving process dynamics of the machinery is controlled and supervised by complex software logics, the main challenge for effective and valid SBT concerns the development of a real-time simulation, where the control system responsiveness is fully reproduced. This paper deals with a novel SBT workbench used for steel plants operator training, discussing the real-time simulation architecture developed for the purpose. Following a hybrid process simulation approach, real-time control Hardware-In-the-Loop technology assures seamless and accurate reproduction of the real plant, also achieving the desired Man-in-the-Loop practice for the operator interaction. A conceptual architecture for a virtual interactive prototype is proposed, including controllers and interfaces for trainer and trainees. A case study on an electric arc furnace is implemented within a Virtual Commissioning tool, analyzing its capabilities and limitations.

Abstract: Multipurpose and programmable servo-actuated mechanisms may be envisaged as the key technology for increasing flexibility and re-configurability of modern automated machinery. Unfortunately, based on the current state-of-the-art, these mechatronic devices are extremely flexible but generally energy intensive, thus compromising the overall system sustainability. Nonetheless, the system power consumption can be partially reduced if energy optimality is introduced as a design goal along with the global productivity. Naturally, as a first step towards the practical implementation of any energy-optimality criterion, the end user should be capable of predicting the system power flow, including the major sources of energy loss. In this context, this paper firstly presents a reliable model of a servo-actuated mechanism accounting for linkage, electric motor and power converter behavior. Then, a novel identification method is discussed, which allows the separate determination of the models parameters by means of non-invasive experimental measures. The method is finally validated by comparing predicted and actual power flows in a simple mechatronic system, which is composed of a slider-crank mechanism directly coupled with a position-controlled permanent magnet synchronous motor.

Abstract: In this chapter, the closed-form compliance equations for Circularly Curved-Beam Flexures are derived. Following a general modeling procedure previously described in the literature, each element of the spatial compliance matrix is analytically computed as a function of both hinge dimensions and employed material. The theoretical model is then validated by comparing analytical data with the results obtained through Finite Element Analysis. Finally, a case study is presented concerning the potential application of these types of flexures in the optimal design of compliant robotic fingers. © Springer Science+Business Media Dordrecht 2014.

Keywords: Circularly curved-beam flexures | Compliance matrix | Finite element analysis | Robotic fingers

Abstract: In this paper, the closed-form compliance equations for spherical flexures are derived. Each element of the spatial compliance matrix is analytically computed as a function of both hinge dimensions and employed material. The theoretical model is then validated by relating analytical data with the results obtained through Finite Element Analysis. Finally, for a generic loading condition, spherical flexures are compared to circularly curved-beam hinges in terms of secondary compliance factors and maximum stress.

Keywords: Compliance matrix | Finite element analysis | Parasitic motions | Spherical flexures

Abstract: Dielectric Elastomers (DEs) are deformable dielectrics, which are currently used as active materials in mechatronic transducers, such as actuators, sensors and generators. Nonetheless, at the present state of the art, the industrial exploitation of DE-based devices is still hampered by the irregular electro-mechanical behavior of the employed materials, also due to the unpredictable effects of environmental changes in real world applications. In many cases, DE transducers are still developed via trial-and-error procedures rather than through a well-structured design practice, one reason being the lack of experimental data along with reliable constitutive parameters of many potential DE materials. Therefore, in order to provide the practicing engineer with some essential information, an open-access database for DE materials has been recently created and presented in [1]. Following the same direction, this paper addresses the temperature effect on the visco-hyperelastic behavior of two DE candidates, namely a natural rubber (ZRUNEK A1040) and a well-known acrylic elastomer (3M VHB 4905). Measurements are performed on pure shear specimens placed in a climactic chamber. Experimental stress-strain curves are then provided, which makes it possible to predict hyperelasticity, plasticity, viscosity, and Mullins effect as function of the environmental temperature. Properties of these commercial elastomeric membranes are finally entered in the database and made available to the research community.

Abstract: This paper quantitatively reports about potential energy savings on robotic assembly lines for the automotive industry. At first, a detailed system model is described, which improves previously published results by explicitly considering both manipulator and electrical drive dynamics. The model closely captures experimental data in terms of actuation torques and servodrive voltages, which are directly used to derive the plant input power. Two practical methods are then evaluated for reducing the overall energy consumption. The methods rely on: 1) implementation of energy-optimal trajectories obtained by means of time scaling, concerning the robots' motion from the last process point to the home positions and 2) reduction of energy consumption by releasing the actuator brakes earlier when the robots are kept stationary. Simulation results, based on the production timing characteristics measured at a real plant, clearly shows that the system energy consumption can be effectively reduced without negative effects on the production rate. © 2004-2012 IEEE.

Keywords: Energy efficient robotics | robotic manufacturing | trajectory planning | virtual prototyping

Abstract: Large displacement compliant joints can substitute traditional kinematic pairs in robotic articulated structures for increasing ease-of-assembly, robustness, and safety. Nonetheless, besides their limited motion capabilities, compliant joints might be subjected to undesired spatial deformations which can deteriorate the system stability and performance whenever a low number of control inputs is available. In all these cases, it is convenient to select/design joint morphologies which enable a selectively compliant behavior, i.e., a low stiffness along a single desired direction. Within this context, this paper outlines an engineering method for quantifying the joint's selective compliance by means of local and global performance indices. The approach is validated by comparing two beam-like flexures whose analytic solution is known from the literature. Finally, two joint morphologies, previously employed in the fabrication of robotic/prosthetic hands, are critically compared on the basis of the proposed criteria. © 1996-2012 IEEE.

Keywords: Design criteria | large displacement compliant joints | performance evaluation

Abstract: This paper summarizes recent activities carried out for the development of an innovative anthropomorphic robotic hand called the DEXMART Hand. The main goal of this research is to face the problems that affect current robotic hands by introducing suitable design solutions aimed at achieving simplification and cost reduction while possibly enhancing robustness and performance. While certain aspects of the DEXMART Hand development have been presented in previous papers, this paper is the first to give a comprehensive description of the final hand version and its use to replicate human-like grasping. In this paper, particular emphasis is placed on the kinematics of the fingers and of the thumb, the wrist architecture, the dimensioning of the actuation system, and the final implementation of the position, force and tactile sensors. The paper focuses also on how these solutions have been integrated into the mechanical structure of this innovative robotic hand to enable precise force and displacement control of the whole system.Another important aspect is the lack of suitable control tools that severely limits the development of robotic hand applications. To address this issue, a new method for the observation of human hand behavior during interaction with common day-to-day objects by means of a 3D computer vision system is presented in this work together with a strategy for mapping human hand postures to the robotic hand. A simple control strategy based on postural synergies has been used to reduce the complexity of the grasp planning problem. As a preliminary evaluation of the DEXMART Hand's capabilities, this approach has been adopted in this paper to simplify and speed up the transfer of human actions to the robotic hand, showing its effectiveness in reproducing human-like grasping. © The Author(s) 2014.

Keywords: grasping | mechatronic design | optoelectronic sensors | postural synergies | Robotic hands | tendon transmission | twisted string

Abstract: Servo-actuated mechanisms are increasingly sub-stituting fully mechanical drives in order to increase flexibility and reconfigurability of modern automatic machines. The overall servomechanism performance, especially in the case of high-dynamic motions, is the direct consequence of several interacting factors, namely electric motor and linkage dynamics, controller efficacy, and requested motion law. In particular, Point-To-Point (PTP) trajectories are usually designed in order to comply with technological constraints, imposed by the required interaction with the handled product, and to maximize some optimality criterion such as, for instance, energy efficiency or limited actuation torques. In this context, the present paper proposes a novel method for generating either energy-optimal or torque-optimal PTP motions described by piecewise fifth-order polynomials. The optimization cost functions are based on a virtual prototype of the system, which comprises behavioral models of power converter, controller and electric motor coupled with the mechanical system. Results are then compared with experimental data obtained on a physical prototype. The comparison quantitatively shows that better-behaved PTP trajectories can be designed by including the dynamic contribution of each sub-system component. © 2013 IEEE.

Keywords: Servo-Actuated Mechanism | Trajectory Generation | Virtual Prototyping

Abstract: In this paper, a quantitative comparison is made between straight beam and curved beam flexures for application on selectively compliant mechanisms. Following a general procedure previously described in the literature, the closed-form compliance equations for both flexural hinges are firstly derived. Then, the two morphologies are compared in terms of maximum achievable rotation and selective compliance (i.e. capability of providing low stiffness along a single desired direction). In particular, the performance of each design solution is quantified by means of purposely defined quality indexes, analytically computed on the basis of the hinges compliance matrix. Finally, the potentials of these types of flexures for the optimal design of compliant robotic fingers are critically discussed. © 2013 IEEE.

Keywords: Compliant mechanisms | performance evaluation | robotic fingers

Abstract: Fixture systems have a great importance in modern manufacturing and assembly because of the high number of scenarios in which they are used. Fixture design is a complex task since the system effectiveness depends both on position and type of locators. Several authors deal with the problem of determine the most suitable design for fixture systems but their investigation is commonly limited to the evaluation of the effects due to the locators' position. In the present work a design method is proposed to evaluate the fixture systems considering also the locators' type. Since it is possible to model the fixtures as multi-performance systems, the comparison is performed by introducing appropriate sensitivity indexes. The effectiveness of the design method is proved through the application to an automotive case study. © (2013) Trans Tech Publications, Switzerland.

Keywords: Automotive | Design for manufacturing | Fixture system | Tolerance analysis

Abstract: This paper proposes a fast and on-site method for the dynamic identification of industrial robots from low-sampled position and torque data. Owing to the basic architecture of the employed controller, only trapezoidal-velocity trajectories can be enforced for identification purposes. Differently from previous literature, where this kind of trajectories were performed with limited joint velocities and range of motions, the procedure proposed hereafter is characterized by fast movements performed on wide angular ranges. Furthermore, in order to identify the influence of friction without deriving complex friction models, a novel method is outlined that decouples frictional torques from gravitational, centrifugal and inertial ones. Finally, although multiple experiments of different kinds have been performed, inertial parameters are determined in one singular step, thus avoiding possible error increase due to sequential identification algorithms. © (2013) Trans Tech Publications, Switzerland.

Keywords: Friction decoupling | Industrial robots | Low frequency sampling | System identification

Abstract: The replication of the human hand's functionality and appearance is one of the main reasons for the development of robot hands. Despite 40 years of research in the field [1], the reproduction of human capabilities, in terms of dexterous manipulation, still seems unachievable by the state-of-the-art technologies. From a design perspective, even defining the optimal functionalities of a robotic end-effector is quite a challenging task since possible applications of these devices span industrial robotics, humanoid robotics, rehabilitation medicines, and prosthetics, to name a few. Therefore, it is reasonable to think that the design solutions, which are well suited to a single domain, might not be readily taken as general guidelines. For example, industrial manipulators are often equipped with basic grippers, which are conceived so as to increase the throughput and the reliability, and are assumed to operate in structured environments. In this case, the enhanced manipulation skills and the subsequent cost increases must be carefully motivated by the application requirements. © 2013 IEEE.

Abstract: Constant-force actuators based on dielectric elastomers can be obtained by coupling a dielectric elastomer film with particular compliant frames whose structural properties must be carefully designed. In any case, the practical achievement of a desired force profile can be quite a challenging task owing to the time-dependent phenomena, which affect the dielectric elastomer's electromechanical response. Within this scenario, a hyperviscoelastic model of a rectangular constant-force actuator is reported. The model, based on the bond graph formalism, can be used as an engineering tool when designing and/or controlling actuators that are expected to work under given nominal conditions. Simulations and experimental results are provided, which predict the system response to fast changes in activation voltage and actuator position as imposed by an external user. © The Author(s) 2012.

Keywords: bond graph modeling | Dielectric elastomer actuator | quasi-linear viscoelasticity

Abstract: This article presents a finite-deformation fully-coupled thermo-electro-elastic continuum model that is suited for the analysis, design, and control of solid-state transduction devices based on electrostrictive elastomers. In the model, electrostrictive elastomers are considered as isotropic modified-entropic hyperelastic dielectrics that deform in response to a simultaneous combination of electrical, thermal, and mechanical stimuli. The model is thermodynamically consistent and comprises general balance equations, which do not require the postulation of any force or stress tensor of electrical origin, together with phenomenological invariant-based constitutive relations, which necessitate the minimum number of material parameters to be determined via experimental tests only. Comparison with existing theories and experimental results are provided that validate the proposed thermo-electro-elastic model. © The Author(s) 2012.

Keywords: actuator | dielectric elastomers | Electroactive polymers | electrostrictive | thermo-electro-elasticity

Abstract: This paper reports about the design and modeling process of high performance servo-actuated mechanisms for automatic machines.Besides being a delicate and time consuming process, coupled simulations based on virtual prototyping finally offer the chance to integrate engineering methods proper of control system engineering and mechanical design. In particular, the main target of this work isto investigate how different virtual prototyping approaches, each havingincreasing level of detail, can contribute to the appropriate prediction of the expected machine performance.These results are then compared with experimental data obtained on a real servomechanism prototype. The comparison quantitatively demonstrate the improvement on torque prediction and position error reduction when detailed models of the controller and the electric motor dynamics are coupled with the mechanical system model. © (2013) Trans Tech Publications, Switzerland.

Keywords: Co-simulation | Digital product design | Integrated mechatronic design | Virtual prototyping

Abstract: Massive parallel arrays of discrete actuators are forceregulated robots that undergo continuous motions despite being commanded through a large but finite number of states only. Realtime control of such systems requires fast and efficient methods for solving their inverse static analysis, which is a challenging problem. Artificial intelligence methods are investigated here for the on-line computation of the inverse static analysis of a planar parallel array featuring eight three-state force actuators and possessing one degree of revolute motion.

Keywords: Dielectric Elastomer | Inverse Kinematic | Inverse Kinematic Algorithm | Recurrent Neural Network | Recurrent Neural Network Model

Abstract: A continuum model is described for the study of the electro-elastic finite deformations of dielectric elastomers. The model: i) derives directly from a global energy balance; ii) does not require the postulation of any force or stresstensor of electrical origin; iii) only requires the knowledge of permittivity and shear moduli of the considered material; and iv) is presented in Lagrangian form which is suited for the implementation in multi-physic finite element simulation environments.

Abstract: A novel design for a Dielectric Elastomer (DE) actuator is presented. The actuator is obtained by coupling a cylindrical DE film with a series of slender beams axially loaded beyond their buckling limit. Similarly to previous published solutions, where different actuator geometries were coupled with compliant mechanisms of various topologies, the elastic beams are designed so as to provide a suitable compensating force that allows obtaining a quasi-constant available thrust along the entire actuator stroke. The overall system performance are subsequently evaluated by means finite element analysis, accounting for the large deflection of the buckled-beam springs and for the DE material hyperelasticity. Final results confirm that compact and better behaved constant force cylindrical actuators can be obtained, which potentially outperform similar devices in terms of achievable stroke. Copyright © 2013 by ASME.

Abstract: Artificial Muscles based on Dielectric Elastomers (DE) can potentially enable the realization of bio-inspired actuation systems whose intrinsic compliance and damping can be varied according to the task requirements. Nonetheless, the control of DE-based Variable Impedance Actuators (VIA) is not trivial owing to the non-linear viscoelastic response which characterizes the acrylic dielectrics commonly employed in practical devices. In this context, the purpose of the present paper is to outline a novel strategy for the control of DE-based VIA. Although the proposed methodology is applicable to generic DE morphologies, the considered system is composed of a couple of conically-shaped DE films in agonistic-antagonistic configuration. Following previously published results, the system dynamic model is firstly recalled. Then, a DE viscoelasticity compensation technique is outlined together with a control law able to shape the DE actuator impedance as desired. The operative limits of the system are explicitly considered and managed in the controller by increasing the operating DE actuator stiffness if required. In addition, the problem of model uncertainties compensation is also addressed. Finally, as a preliminary step towards the realization of a practical DE-based VIA, the proposed control approach is validated by means of simulations. Copyright © 2013 by ASME.

Abstract: Industrial robotics provides high flexibility and reconfigurability, cost effectiveness and user friendly programming for many applications but still lacks in accuracy. An effective workcell calibration reduces the errors in robotic manufacturing and contributes to extend the use of industrial robots to perform high quality finishing of complex parts in the aerospace industry. A novel workcell calibration method is embedded in an integrated design framework for an in-depth exploitation of CAD-based simulation and offline programming. The method is composed of two steps: a first offline calibration of the workpiece-independent elements in the workcell layout and a final automated online calibration of workpiece-dependent elements. The method is finally applied to a robotic workcell for finishing aluminum housings of aerospace gear transmissions, characterized by complex and non-repetitive shapes, and by severe dimensional and geometrical accuracy demands. Experimental results demonstrate enhanced performances of the robotic workcell and improved final quality of the housings. © Springer-Verlag Berlin Heidelberg 2013.

Keywords: Aerospace industry | Industrial robotics | Integrated design | Workcell calibration

Abstract: Deburring of aerospace components is a complex task in case of large single pieces designed and optimized to deliver many mechanical functions. A constant high quality requires accurate 3D surface contouring operations with engineered tool compliance and cutting power. Moreover, aeronautic cast part production is characterized by small lot sizes with high variability of geometries and defects. Despite robots are conceived to provide the necessary flexibility, reconfigurability and efficiency, most robotic workcells are very limited by too long programming and setup times, especially at changeover. The paper reports a design method dealing with the integrated development of process and production system, and analyzes and compares a CAD-based and a digitizer-based offline programming strategy. The deburring of gear transmission housings for aerospace applications serves as a severe test field. The strategies are compared by the involved costs and times, learning easiness, production downtimes and machining accuracy. The results show how the reconfigurability of the system together with the exploitation of offline programming tools improves the robotic deburring process. © Springer-Verlag Berlin Heidelberg 2013.

Keywords: CAD-based tools | Digitizers | Industrial robotics | Integrated design | Offline programming

Abstract: The interest in novel methods and tools for opt imizing the energy consumption in robotic systems is cur- rently increasing. From an industrial point of view,it is desirable to develop energy saving strategies also applicable to established manufacturing systems with no need for either hardware substitu tion or further investme nts. Within this scenario,the present paper reports amethod for reducing the total energy con- sumption of pick-and-place manipulators for given TCP position profiles.Firstly,electromechanical mod- els of both serial and parallel manipulators are derive d.Then,the energy-optimal trajectories are calculated, by means of constant time scaling,starting from pre-scheduled trajectories comp atible with the actuation limits. In this manner,the robot work cycle can be energetically optimized also when the TCP position profiles have been already definedon the basis of technological constraints and/or design choices aimed at guarante eing manufacturing process efficacy/robustness.The effectiveness of the pro- posed procedure is finallyevaluated on two simulation case studies. Copyright © 2013 Published by Elsevier Ltd. All rights reserved.

Keywords: Electromechanical modeling | Energy efficiency | Robotic manufacturing | Virtual prototyping

Abstract: Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact force-feedback devices such as, for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the present paper addresses the development of a force feedback controller for an agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliant mechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the viscohyperelastic nature of the DE material. The model is then linearized and employed for the design of a force controller. The controller employs a position sensor, which determines the actuator configuration, and a force sensor, which measures the interaction force that the actuator exchanges with the environment. In addition, an optimum full-state observer is also implemented, which enables both accurate estimation of the time-dependent behavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminary experimental results are provided to validate the proposed actuator-controller architecture.

Keywords: Agonist-antagonist actuation | Dielectric elastomers | Force-feedback control | Haptic interfaces

Abstract: Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact Variable Stiffness Actuators (VSAs), thanks to their large power densities, low costs and shock-insensitivity. Nonetheless, the development of DE-based VSA is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the purpose of the present paper is to investigate the practical feasibility of DE-based VSA. As a case study, two conically-shaped actuators, in agonistic-antagonistic configuration, are modeled accounting for the visco-hyperelastic nature of the DE films. The model is then linearized and employed for the design of a stiffness controller. The control algorithm requires the knowledge of the actuator configuration (via a position sensor) and of the force exchanged with the environment (via a force sensor). An optimum full-state observer is then implemented, which enables both accurate estimation of the DE time-dependent behavior and adequate suppression of sensor measurement noise. At last, experimental results are provided together with the description of an effective electronic driver that allows an independent activation of the agonistic-antagonistic DE membranes. Copyright © 2012 by ASME.

Abstract: Monolithic Flexure-based Compliant Mechanisms (MFCM) can functionally act as nonlinear springs by providing a desired load-displacement profile at one point on their structure. Once the MFCM topology is chosen, these particular springs can be conveniently synthesized by resorting to the well-known Pseudo- Rigid-Body approximation, whose accuracy strongly depends on the modeling precision of the flexures' principal compliance. For various types of flexures, closed-form solutions have been pro- posed which express the compliance factors as functions of the flexure dimensions. Nonetheless, the reliability of these analyt- ical relations is limited to slender, beam-like, hinges undergo- ing small deflections. In order to overcome such limitations, this paper provides empirical equations, derived from finite element analysis, that can be used for the optimal design of circular, el- liptical, and corner-filleted flexural hinges with general aspect ratios on the basis of both principal compliance and maximum bearable stress. As a case study, a nonlinear spring conceived as a four-bar linkage MFCM is synthesized and simulated by means of finite element analysis. Numerical results confirm that the aforementioned empirical equations outperform their analyt- ical counterparts when modeling thick cross-section hinges un- dergoing large deflections. © 2012 by ASME.

Abstract: This paper quantitatively reports about potential energy savings on robotic assembly lines for the automotive industry. The key aspect of the proposed approach is that both cell production rate and robot hardware limitations are considered as strict constraints, so that no plant revision is needed. The methodology relies on: a) calculation of energy-optimal trajectories, by means of time scaling, concerning the robots' motion from the last process point to the home positions; b) reduction of the energy consumption via earlier release of the actuator brake when the robots are kept stationary. Simulation results are presented, which are based on the production timing characteristics measured on a real plant. © 2012 IEEE.

Keywords: Energy Efficiency | Industrial Robots | Production Planning | Trajectory Scaling

Abstract: With the aim of reproducing the grasping and manipulation capabilities of humans, many robotic devices have been developed all over the world in more than 50 years of research, starting from very simple grippers, normally used in industrial activities, to very complex anthropomorphic robotic hands. Unfortunately, the reduced functionality and/or reliability of the devices developed so far prevent, together with the cost, their usability in unstructured environments, and in particular in human everyday activities. The adoption of design solutions inherited from conventional mechanics and the lack of purposely developed sensors and actuators are among the main causes of the partial fail in achieving the final goal of reproducing human manipulation capabilities. Our research activity aims at developing innovative solutions concerning the mechanical design, the sensory equipment and the actuation system for the implementation of anthropomorphic robotic hands with improved reliability, functionality and reduced complexity and cost, considering also aspects related to safety during human-robot interaction, paving the way toward the next generation of robotic hands. © 2012 Springer-Verlag GmbH Berlin Heidelberg.

Abstract: The interest in novel engineering methods and tools for optimizing the energy consumption in robotic systems is currently increasing. In particular, from an industry point of view, it is desirable to develop energy saving strategies applicable also to established manufacturing systems, being liable of small possibilities for adjustments. Within this scenario, an engineering method is reported for reducing the total energy consumption of pick-and-place manipulators for given end-effector trajectory. Firstly, an electromechanical model of parallel/serial manipulators is derived. Then, an energy-optimal trajectory is calculated, by means of time scaling, starting from a pre-scheduled trajectory performed at maximum speed (i.e. compatible with actuators limitations). A simulation case study finally shows the effectiveness of the proposed procedure. © 2011 IEEE.

Keywords: energy efficiency | Pick-and-place manipulators

Abstract: After a brief reminder about advantages and problems related to the application of large displacement elastic joints in robotic structures, this paper outlines an approach for quantifying the joint's performance in terms of selective compliance (i.e. capability of providing low stiffness along a single desired direction). Local and global performance indexes are proposed which can be used to discern which joint best suits the application requirements. The approach is validated by comparing two beam-like flexures and two novel compliant joints with non trivial morphology. © 2011 IEEE.

Keywords: Large displacement compliant joints | Robotic fingers

Abstract: The development of safe, energy efficient mechatronic systems is currently changing standard paradigms in the design and control of industrial manipulators. In particular, most optimization strategies require the improvement or the substitution of different system components. On the other hand, from an industry point of view, it would be desirable to develop energy saving methods applicable also to established manufacturing systems being liable of small possibilities for adjustments. Within this scenario, an engineering method is reported for optimizing the energy consumption of serial manipulators for a given operation. An object-oriented modeling technique, based on bond graph, is used to derive the robot electromechanical dynamics. The system power flow is then highlighted and parameterized as a function of the total execution times. Finally, a case study is reported show- ing the possibility to reduce the operation energy consumption when allowed by scheduling or manufacturing constraints. Copyright © 2011 by ASME.

Abstract: Variable stiffness actuators can be used in order to achieve a suitable trade-off between performance and safety in robotic devices for physical human-robot interaction. With the aim of improving the compactness and the flexibility of existing mechanical solutions, a variable stiffness actuator based on the use of flexures is investigated. The proposed concept allows the implementation of a desired stiffness profile and range. In particular, this paper reports a procedure for the synthesis of a fully compliant mechanism used as a nonlinear transmission element, together with its experimental characterization. Finally, a preliminary prototype of the overall joint is depicted. © 2011 American Society of Mechanical Engineers.

Abstract: Viscoelastic contact interfaces can be found in various robotic components that are covered with a compliant surface (pad) such as anthropomorphic hands, biomimetic haptic/tactile sensors, prostheses, and orthoses. In all these cases, it is desirable to obtain thin and resistant pads with predetermined compliance and damping properties (e.g., mimicking the human skin and pulpy tissues). In order to overcome the limits of homogeneous layers of a soft viscoelastic material, which is commonly used in the aforementioned devices, this paper suggests the adoption of soft pads that are composed of a continuous external layer (skin) coupled with an internal layer having fluid-filled voids. The process to design the pad starts with the selection of a hyperelastic medium with proper tribological features, whose constitutive parameters are determined by numerically fitting nonlinear stress-strain curves under pure homogenous deformations. The optimization of the internal layer morphology is then achieved through nonlinear finite element analysis (FEA) that provides an estimate of hardness and friction influence on the pad static compliance. Finally, the pad is filled with a viscous fluid that is chosen to modify time-dependent phenomena and to increase damping effects. The effectiveness of the procedure is proven by designing and modeling better-behaved artificial pads that mimic human-finger dynamic properties. © 2011 IEEE.

Keywords: Finite deformations | finite element analysis (FEA) | hyperelasticity | quasi-linear model | viscoelastic contact

Abstract: An analytical model and an operational procedure are presented, which make it possible to optimize conically shaped dielectricelastomer linear actuators for known materials and desired force/stroke requirements. The actuators are obtained by coupling a dielectric elastomer film with a compliant frame which is sized by means of a pseudorigid body model. Depending on the frame design, the actuators can work monodirectionally or bidirectionally. Simulation and experimental results are provided which demonstrate the efficacy of the proposed design procedure and show that well-behaved conically shaped actuators can be conceived and produced. © 2006 IEEE.

Keywords: Compliant mechanisms | dielectric elastomer actuators | optimal design

Abstract: Constant-Force actuators based on Dielectric Elastomers (DE) can be obtained by coupling a DE film with particular compliant frames whose structural properties must be carefully designed. In any case, the practical achievement of a desired force profile can be quite a challenging task owing to the time-dependent phenomena which affect the DE electromechanical response. Within this scenario, a hyper-viscoelastic model of a rectangular Constant-Force actuator is reported. The model, based on the Bond Graph formalism, can be used as an engineering tool when designing and/or controlling actuators which are expected to work under given nominal conditions. Numerical simulations are provided which predicts the system response to fast changes in activation voltage and actuator position as imposed by an external user. © 2011 by ASME.

Abstract: In order to overcome the limits due to the fact that homogeneous layers of soft material placed over robotic limbs behave differently with respect to biological models, this paper suggests the adoption of soft covers (pads) with differentiated structure. In particular, it is proposed to divide the allowable pad thickness into two layers: a continuous external layer (skin) and a discontinuous internal layer, so that the overall stiffness can be adjusted by properly shaping the discontinuous layer. The methodology adopted for designing the internal layer is composed of two steps. Firstly, the cover surface is conceptually split into finite elementary triangular sub-regions. Secondly, the internal layer of each triangular element is designed in order to replicate the shape of the non-linear compression law which is typical of endoskeletal structures covered by pulpy tissues. A series of symmetrically-disposed inclined micro-beams is used for the purpose. Once the compression law of each triangular element is known, the overall pad compliance can be modulated by correctly choosing the number and size of the elements composing the pad. Equipment and results of a combined experimental and numerical analysis (FEM) are presented. The results confirm that the proposed concept can be an effective solution when designing soft covers whose behavior need to match the compliance of the biological counterpart. As an example, artificial pads which mimic the human finger behavior are presented. © 2010 by ASME.

Abstract: The development of safe and dependable robots for physical human-robot interaction is actually changing the way robot are designed introducing several new technological issues. Outstanding examples are the adoption of soft covers and compliant transmissions or the definition of motion control laws that allow a compliant behavior in reaction to possible collisions, while preserving accuracy and performance during the motion in the free space. In this scenario, a growing interest is devoted to the study of variable stiffness joints. With the aim of improving the compactness and the flexibility of existing mechanical solutions, a variable stiffness joint based on the use of compliant flexures is investigated. The proposed concept allows the implementation of a desired stiffness profile and range along with the selection of the maximum joint deflection. In particular, this paper reports a systematic procedure for the synthesis of a fully-compliant mechanism used as a non-linear transmission, together with a preliminary design of the overall joint. © 2010 by ASME.

Abstract: The majority of soft pads for robotic limbs studied so far were made by visco-elastic polymeric solids whose behavior is significantly influenced by the rate of application of the external loads or displacements. In particular, contact interfaces which are intrinsically visco-elastic are found, for instance, in human fingers and feet or in various robotic devices covered by a compliant surface. An outstanding instance are anthropomorphic hands where time-dependent phenomena profoundly affects the stability and sustainability of the grasp. Alternatively to homogenous solid pads, this paper proposes the use of fluid filled soft structures with differentiated layer design [1] that is the adoption of a single solid material, dividing the overall thickness of the pad into a continuous skin layer coupled with an internal layer having communicating voids. The voids are then hermetically sealed and, in case, filled with fluid. Given the allowable pad thickness, the purpose is to tailor the pad properties to the specific application by 1) selecting a skin material characterized by proper tribological features, 2) designing an inner layer geometry so as to obtain a specific static compliance, 3) filling the pad with a viscous fluid chosen so as to modify time-dependent phenomena and increase damping effects. The proposed concept is validated by designing artificial pads whose viscoelastic properties are either similar or more pronounced when compared to those of the human fingertip. ©2010 IEEE.

Keywords: Experimental analysis | Human fingers | Robotic hands | Soft fingertip design

Abstract: A fully mechanical, infinitely variable transmission (IVT) based on the use of an oscillating inertia is described. The system includes a four-bar linkage mechanism, an epicyclic gear train, and a pair of one-way clutches. The IVT can be used in place of both gearbox and clutch in self-propelled vehicles. A mathematical model is presented. Numerical simulations compare the behavior of a car fitted with a manual gearbox and the same car fitted with the IVT.

Abstract: A novel mathematical procedure is presented, which makes it possible to optimize lozenge-shaped dielectric-elastomer-based linear actuators for known materials and desired force/stroke requirements. Simulation and experimental results are provided which both demonstrate the efficacy of the proposed optimization procedure with respect to traditional design approaches and show that simpler, cheaper, lighter, and better-behaved lozenge-shaped actuators can be conceived, which do not require any integration of compliant frame elements.

Keywords: Dielectric elastomers | Optimal design. | Smart actuators

Abstract: After a brief reminder about previous work, this paper addresses the dynamic characterization of fluid-filled soft pads for robotic hands. The adopted pad specimens are constituted by a single hyper-elastic material having hardness similar to that of the human thumb. The overall pad thickness is then divided into a continuous skin layer and an internal layer having communicating voids which are hermetically sealed and filled with a viscous fluid. Despite a more complicated design, it has been proven [1-3] that the pads present enhanced compliance and damping properties, a lower thickness and a higher surface hardness when compared to previously published solutions. In addition, a quasi-linear model, frequently used to describe the behavior of soft biological tissues can be applied in order to predict and control the pad interaction with the environment during grasping and manipulation tasks. In particular, the experimental tests necessary to evaluate the parameters which determine the pad dynamic response are described and discussed in detail.

Keywords: Quasi-linear model | Soft fingers | Viscoelasticity

Abstract: Actuators based on Dielectric Elastomers are a promising technology in robotic and mechatronic applications. The overall actuator performances are influenced by the non-linear and highly coupled electrical and mechanical behavior of the employed materials. To date, the practical electro-mechanical response and controllability of actuators based on Dielectric Elastomers are limited by the inadequacy of the employed driving circuits, which are based on voltage-regulated converters. In this paper, first a novel activation strategy is proposed for Dielectric Elastomer actuators, which is based on a custom electronic driver derived from the flyback transformer topology. Second, two closed-loop controllers employing the proposed electronic driver are presented and compared for the accurate and fast regulation of the position of Dielectric Elastomer actuators. Experimental results are reported which show that the proposed electronic driver outperforms the traditional driving circuits in terms of energy efficiency, fast open-loop actuator activation and good closed-loop actuator controllability. © 2009 Elsevier Ltd. All rights reserved.

Keywords: Dielectric Elastomers | Driving circuits | Position control | Smart actuators

Abstract: A conically shaped Dielectric Elastomer (DE) linear actuator is presented which is obtained by coupling a DE film with a compliant mechanism. The compliant mechanism is designed, by means of a pseudo-rigid-body model, to suitably modify the force generated by the elastomer film. The resulting actuator provides a nearly constant force along the entire actuator stroke when the DE film is activated and returns to an initial rest position when the DE film is deactivated. Experimental activity fully validates the proposed concept. Possible applications of this kind of actuator are Braille cells, light weight robots and haptic devices. © 2009 IEEE.

Keywords: Compliant mechanisms | Dielectric elastomer actuators

Abstract: In this paper, an overall description of the design of a robotic hand is discussed, with particular attention to the required sensory subsystem, its integration within the mechanical structure of the hand and the required control architecture. Different solutions for the joint configuration and the structure of the tendon network adopted for the transmission system are present together with three types of sensors applied on the finger and on the actuators. The integrated design of the hand finger and the sensors is reported and the motivations leading to this particular implementation are thoroughly addressed, taking into account both the mechanical constraints and the control requirements.

Keywords: Robot control | Robotic design | Robotic hands | Sensor systems | Sensors integration

Abstract: The interest in actuators based on dielectric elastomer films as a promising technology in robotic and mechatronic applications is increasing. The overall actuator performances are influenced by the design of both the active film and the film supporting frame. This paper presents a single-acting actuator which is capable of supplying a constant force over a given range of motion. The actuator is obtained by coupling a rectangular film of silicone dielectric elastomer with a monolithic frame designed to suitably modify the force generated by the dielectric elastomer film. The frame is a fully compliant mechanism whose main structural parameters are calculated using a pseudo-rigid-body model and then verified by finite element analysis. Simulations show promising performance of the proposed actuator. © 2008 by ASME.

Abstract: A fully mechanical infinitely variable transmission (1VT) based on the use of an oscillating inertia is described. The system includes a four-bar linkage mechanism, an epicyclic gear train and a pair of one-way clutches. The proposed IVT can be used in place of both gear-box and clutch in self-propelled vehicles. A basic model is used for a first attempt sizing of the transmission kinematic parameters. A more accurate model, achieved using Bond Graphs, is used to investigate the dynamic effect of inertias, one-way clutch compliance, and minor design changes in the kinematic parameters. Finally, simulations compare the behavior of a car fitted with a manual gear-box and the same car fitted with the proposed IVT. © 2008 by ASME.

Abstract: This paper describes the nonlinear Finite Elements Analysis (FEA) of soft fingertips for robotic hands in contact conditions.The purpose is to test the reliability of FEA when designing fingertips with differentiated layer design, that is the adoption of a single elastic material, dividing the overall thickness of the pad into layers with different structural design (e.g.a continuous skin layer coupled with an internal layer with voids).The pads are shaped around a rigid core and their behavior is investigated under compressive contact loads.The applicability of various nonlinear hyperelastic constitutive models for predicting the pad behavior is explored under the hypothesis of large deflections.Two materials have been tested whose mechanical properties are determined experimentally.One of these materials can be used in rapid prototyping printers and its properties are presented for the first time.Experimental activity fully validates the proposed FEA models concerning homogeneous pads.At last two different and innovative pad geometries are proposed showing that FEA confirms to be a powerful tool for predicting the compliance of soft fingertips if the right hypothesis and simplifying assumptions are made.

Keywords: Contact mechanics | FE analysis | Robotic hand | Soft fingertip

Abstract: Most of robotic soft pads studied so far were made with a thick layer of homogeneous material shaped around a rigid core; their behavior has been widely investigated in the literature, mainly under compressive contact load, showing typical non-linear relationship between contact deformation and applied load (the so called power law). This paper proposes differentiated layer design, that is the adoption of a single elastic material, dividing the overall thickness of the pad into layers with different structural design (e.g. a continuous skin layer coupled with an internal layer with voids). The purpose is to modify the actual pad compliance and the resulting power law; in particular, given the material and the allowable pad thickness, to increase the compliance with respect to a non structured pad. Some possible internal layer structures are described, compatible with rapid prototyping manufacturing. Their compressive behaviors are tested and comparatively evaluated showing that the concept can work and be exploited for useful application.© 2009 IEEE.

Keywords: Experimental analysis | Fingertip design | Robotic hands | Soft fingers

Abstract: A novel design for a Dielectric Elastomer (DE) actuator is presented. The actuator is obtained by coupling a conically shaped DE film with a compliant mechanism. The compliant mechanism is designed to suitably modify the force generated by the elastomer film. The resulting actuator provides a nearly constant force along the entire actuator stroke when the DE film is activated and quickly returns to an initial rest position when the DE film is deactivated. The electromechanical properties of the DE film are measured experimentally. The sizing of the compliant mechanism is obtained through a pseudo-rigid-body model and subsequently verified through finite element analysis. Simulations show that the designed actuator works as desired. Possible applications of this kind of actuator are MRI compatible devices, haptic devices and Braille cells. ©2009 IEEE.

Keywords: Compliant mechanisms | Dielectric elastomer actuators

Abstract: The interest in actuators based on dielectric elastomer films as a promising technology in robotic and mechatronic applications is increasing. The overall actuator performances are influenced by the design of both the active film and the film supporting frame. This paper presents a single-acting actuator, which is capable ofsupplying a constant force over a given range of motion. The actuator is obtained by coupling a rectangular film of silicone dielectric elastomer with a monolithic frame designed to suitably modify the force generated by the dielectric elastomer film. The frame is a fully compliant mechanism whose main structural parameters are calculated using a pseudo-rigid-body model and then verified by finite element analysis. Simulations show promising performance of the proposed actuator. © 2009 by ASME.

Abstract: In this paper, an overall description of the design of a robotic hand is discussed, with particular attention to the required sensory subsystem, its integration within the mechanical structure of the hand and the required control architecture. Different solutions for the joint configuration and the structure of the tendon network adopted for the transmission system are present together with three types of sensors applied on the finger and on the actuators. The integrated design of the hand finger and the sensors is reported and the motivations leading to this particular implementation are thoroughly addressed, taking into account both the mechanical constraints and the control requirements.

Keywords: Robot control | Robotic design | Robotic hands | Sensor systems | Sensors integration

Abstract: A novel mathematical procedure is proposed, which makes it possible to optimize lozenge-shaped dielectric-elastomer-based linear actuators for known materials and desired force/stroke requirements. Simulation results are provided which both demonstrate the efficacy of the novel procedure with respect to traditional design approaches and show that simpler, cheaper, lighter and better- behaved lozenge-shaped actuators can be conceived which do not require any integration of compliant frame elements. © 2009 Springer-Verlag Berlin Heidelberg.

Abstract: The in terest in actuators based on dielectric elastomer films as a promising technology in robotic and mechatronic applications is increasing. The overall actuator performances are influenced by the design of both the active film and the film supporting frame. This paper presents a single-acting actuator which is capable of supplying a constant force over a given range of motion. The actuator is obtained by coupling a rectangular film of silicone dielectric elastomer with a monolithic frame designed to suitably modify the force generated by the dielectric elastomer film. The frame is a fully compliant mechanism whose main structural parameters are calculated using a pseudo-rigid-body model and then verified by finite element analysis. Simulations show promising performance of the proposed actuator. Copyright © 2008 by ASME.

Abstract: A fully mechanical infinitely variable transmission (IVT) based on the use of an oscillating inertia is described. The system includes a four-bar linkage mechanism, an epicyclic gear train and a pair of one-way clutches. The proposed IVT can be used in place of both gear-box and clutch in self-propelled vehicles. A basic model is used for a first attempt sizing of the transmission kinematic parameters. A more accurate model, achieved using Bond Graphs, is used to investigate the dynamic effect of inertias, one-way clutch compliance, and minor design changes in the kinematic parameters. Finally, simulations compare the behavior of a car fitted with a manual gear-box and the same car fitted with the proposed IVT. Copyright © 2008 by ASME.

Abstract: Actuators based on Dielectric Elastomer films have been rising as a promising technology in robotic and mechatronic applications. Their overall behavior is highly influenced by the geometry and structural properties of the frame that is coupled with the active film. In this paper, a compound-structure compliant frame is proposed with the aim of obtaining an actuator capable of providing a quasi-constant force over a certain range of motion. A diamond shaped frame, designed to support the pre-stretched active film, is coupled with a delta shaped element, designed to modify the overall actuator stiffness and improve its performance. Both the diamond and the delta element are fully compliant mechanisms whose main structural parameters are calculated using pseudo-rigid-body models and then verified through finite element analysis. Simulations show promising performance of the proposed actuator. © 2008 Springer Science+Business Media B.V.

Keywords: compliant mechanisms | dielectric elastomer actuators | frame design

Abstract: Benign Paroxyrnal Positional Vertigo and variants, collectively called "vestibular lithiasis", designate a common disorder caused by a malfunction of the inner ear. These pathologies are connected with the presence of dense particles within the semicircular canals which interfere with the sensing capabilities of angular velocity in the patient, causing nystagmus and vertigo. Some of these conditions can be treated by repositioning maneuvers physically done by the doctor that moves the head of the patient along different poses in space. Despite the fact that the treatment shows a success rate up to 80-90%, the failure rate remains highly significant and it is proven that precision repeatability and unlimited 360° manoeuvrability can improve diagnostic and treatment potential for overcoming this kind of vertigo. In this paper the kinematic design of a serial robot that will execute repositioning maneuvers automatically is performed through a simplified task based kinematic design technique. The aim of the method is to find the minimum number of degrees of freedom to carry out a set of given tasks as well as the manipulator's topology and the Denavit-Hartenberg parameters. The proposed procedure firstly minimizes the number of degrees of freedom only and then a cost function connected to the total link length. © 2007 IEEE.

Keywords: BPPV | Data structure | Discrete optimization techniques | Genetic algorithm | Inverse kinematic | Task based design