Virtual prototyping and digital twin

This study deals with a mixed static and dynamic optimization of four-parameter functionally graded material (FGM) doubly curved shells and panels. The two constituent functionally graded shell consists of ceramic and metal, and the volume fraction profile of each lamina varies through the thickness of the shell according to a generalized power-law distribution. The Generalized Differential Quadrature (GDQ) method is applied to determine the static and dynamic responses for various FGM shell and panel structures. The mechanical model is based on the so-called First-order Shear Deformation Theory (FSDT). Three different optimization schemes and methodologies are implemented. The Particle Swarm Optimization, Monte Carlo and Genetic Algorithm approaches have been applied to define the optimum volume fraction profile for optimizing the first natural frequency and the maximum static deflection of the considered shell structure. The optimization aim is in fact to reach the frequency and the static deflection targets defined by the designer of the structure: the complete four-dimensional search space is considered for the optimization process. The optimized material profile obtained with the three methodologies is presented as a result of the optimization problem solved for each shell or panel structure. © 2013 Francesco Tornabene and Alessandro Ceruti.

Unmanned Aerial Vehicles (UAVs) provide the ability to perform a variety of experimental tests of systems and unproven research technologies, including new autopilot systems and obstacle avoidance capabilities, without risking the lives of human pilots. This paper describes the activities of design, optimization, and flight operations of a UAV conceived at Clarkson University (USA) and equipped to perform wind speed measurements to support wind farmsite planning. The UAV design has been assisted and validated by the use of an automatic virtual environment for the assisted design of civil UAVs. This tool can be used as a "computing machine" for civil UAVs. The operator inputs the mission profile and other generic parameters and data about performance, aerodynamics, and weight breakdown are extracted. A mathematical model of the UAV for flight simulation and its dynamic computations, along with automatic drawing is also produced. Also an optimizer based on genetic algorithms has been added to the tools, so that the UAV design can be iteratively improved in order to most effectively perform the mission selected. A detailed design of the UAV was carried out using traditional methodologies, and results compared with new tools like X-PLANE simulator. The static stability computations described are deemed to be effective since the evaluation of the UAV pilot on flying qualities correlates with predictions. Copyright © 2013 SAE International.

This paper deals with the simulation of material texture by means of electro-tactile stimuli, which directly derive from real material properties. The research presents a novel tactile display by its hardware and software system architecture and the elaboration procedure to generate the stimulating signals, and validates the adopted simulation strategy by experimental testing. The tactile system elaborates data from scans of real material samples and generates electrical stimuli to reproduce roughness and texture coarseness sensations. It also adds a coherent sound feedback to improve the realism of the simulation. The research defines also an experimental protocol based on the theory of Psychophysics to carry out system calibration and tests with users. The scope is to validate the proposed tactile system as a new tool for material simulation, which can be adopted for material virtual prototyping in several fields (product design, textile and clothing, gaming and entertainment, virtual museum, rehabilitation, etc.). Experimentations have been carried out to measure the users' response to our different material classes (wood, paper, rubber and textile fabric). Experimental results concern how good the adopted simulation approach is and the analysis of the human tactile perception simulated by the system. Main findings relate to the system performance and the users' response in terms of signal recognition and material class discrimination. © 2013 Springer-Verlag London.

Keywords: Haptics , Material simulation , Material texture , Tactile system

The bioactivity of sol-gel synthesized poly(ε-caprolactone) (PCL)/TiO2 or poly(ε-caprolactone)/ZrO2 particles was already known. In designing innovative 2D composite substrates for hard-tissue engineering, the possibility to embed PCL/TiO2 or PCL/ZrO2 hybrid fillers into a PCL matrix was previously proposed. In the present study, the potential of 3D fiber-deposition technique to design morphologically controlled scaffolds consisting of PCL reinforced with PCL/TiO2 or PCL/ZrO2 hybrid fillers was demonstrated. Finite element analysis was initially carried out on 2D substrates to find a correlation between the previously obtained results from the small punch test and the Young's modulus of the materials, whilst mechanical and biological tests were suitably performed on rapid prototyped scaffolds to assess the effects of the inclusion of the hybrid fillers on the performances of the 3D porous structures. The role of the inclusion of the hybrid fillers in improving the compressive modulus (about 90 MPa) and the cell viability/proliferation was demonstrated. © 2013 Society of Plastics Engineers.

Actual industrial robotic systems offer performance to effectively cope with the requirements in manufacturing dealing with flexibility and quality. However, their known limits in accuracy do not allow to extend their field of application to high-accuracy machining, actually covered by state-of-the-art CNC machine tools. The European Project COMET has recently proposed an approach to develop a robotic reconfigurable workcell with enhanced accuracy for machining, through the full integration of different theoretical models, technological solutions and manufacturing strategies. The present paper presents and demonstrates the effectiveness of a demo reconfigurable machining workcell for one of its possible configurations, based on CAM off-line programming. In particular, an experimental campaign has been designed and realized in order to discuss the dimensional and geometrical quality obtained for an aluminium automotive part in comparison with quality and costs offered by a standard 5-axis CNC machine tool. © 2013 IEEE.

Contract furniture design is oriented to develop customized products for the creation of a finished commodity for hospitality, offices, retails, restaurants, stores. It is assuming a growing importance all over the Europe and represents a preferred channel for promoting Made in Italy offer. Numerous competences with different skill, abilities and background are necessary to fulfill market requirements. Stakeholders are arranged into complex inter and intra temporary networks where sometimes-conflicting interests and purposes need to converge into a single and integrated design solution. Contract furniture combines product design with interior and architectural design requests to provide coherent furniture by assembling custom high-quality items from different firms. As a consequence, the design process is complex and collaboration is imperative to achieve the expected goals. This paper explores contract furniture design and defines a technological platform to support team working. The proposed methodology is applied to an industrial case study in the hospitality and retail sectors. Method application brings to define the system platform architecture and its main software modules. © 2013 The Design Society.

Keywords: Collaborative and participatory design , Design process modeling and management , Teamwork in design

Machining using industrial robots is currently limited to applications with low geometrical accuracies and soft materials due to weaknesses of the robot structure, insufficient controller performance and the lack of suitable software tools. This paper proposes a modular approach to overcome these obstacles, applied both during program generation (offline) and execution (online). Offline predictive machining errors compensation is achieved by means of an innovative programming system, based on kinematic and dynamic robot models. Realtime adaptive machining error compensation is also provided by sensing the real robot positions with an innovative tracking system and corrective feedback to both the robot and an additional high dynamic compensation mechanism on piezo-actuator basis. Due to the modularity of the approach, an individual setup can be compiled for each actual use-case. Final experimental validation of the components is currently ongoing in multiple robot cells, covering several application areas as aerospace, automotive or mould construction. © Springer-Verlag Berlin Heidelberg 2013.

Keywords: 3D-piezo-actuator compensation mechanism , Engineering methods , Robotic machining

The development of computational fluid dynamic (CFD) models of air ingress into the vacuum vessel (VV) represents an important issue concerning the safety analysis of nuclear fusion devices, in particular in the field of dust mobilization. The present work deals with the large eddy simulations (LES) of fluid dynamic fields during a vessel filling at near vacuum conditions to support the safety study of Loss of Vacuum Accidents (LOVA) events triggered by air income. The model's results are compared to the experimental data provided by STARDUST facility at different pressurization rates (100 Pa/s, 300 Pa/s and 500 Pa/s). Simulation's results compare favorably with experimental data, demonstrating the possibility of implementing LES in large vacuum systems as tokamaks. © 2013 Elsevier B.V.

Keywords: Dust mobilization , Experiments , LES , Loss of Vacuum Accident , Nuclear fusion safety , Numerical simulation

An automatic manufacturing system design must be optimized with a simulation including all the interacting devices. The simulation should be controlled by the real control system with a hardware in the loop approach. So the techniques for modeling the mechanisms must be effective for the model to be run without violating the real-time protocol. This paper reports a method to model the motor load by means of a reduced moment of inertia, where all the part downstream from the motor output shaft is transformed in function of the only one mechanism degree of freedom. The resulting model behaves as the real nonlinear mechanism, but it is computationally efficient since it is not ruled by the multibody 3D CAD mathematics. © (2013) Trans Tech Pudlications, Switzerland.

Keywords: Co-simulation , Digital product design , Virtual prototyping

The reduction of energy consumption is today addressed with great effort in manufacturing industry. In this paper, we improve upon a previously presented method for robotic system scheduling. By applying dynamic programming to existing trajectories, we generate new energy optimal trajectories that follow the same path but in a different execution time frame. With this new method, it is possible to solve the optimization problem for a range of execution times for the individual operations, based on one simulation only. The minimum energy trajectories can then be used to derive a globally energy optimal schedule. A case study of a cell comprised of four six-link manipulators is presented, in which energy optimal dynamic time scaling is compared to linear time scaling. The results show that a significant decrease in energy consumption can be achieved for any given cycle time. © 2004-2012 IEEE.

Keywords: Optimization methods , scheduling , trajectory

Computer-aided tools can help to realize custom-fit products characterized by a strict interaction with human body and definitely improve quality of life, in particular of people with disabilities. The paper refers to this context and to a specific custom-fit product, the lower limb prosthesis. It presents an innovative framework centred on virtual models of the patient's body, to design and configure lower limb prosthesis, both transfemoral and transtibial. The framework integrates virtual prototyping and knowledge-based tools to support the orthopaedic technician during all the steps of the lower limb prosthesis design, suggesting rules and procedures for each task. First, the considered product is introduced, and then, the new design framework is described as well as main steps and related tools, from socket modelling to standards component selection and final prosthesis assembly. Results of preliminary experimentation and final remarks conclude the paper. © 2012 Springer-Verlag.

Keywords: Custom-fit products , Knowledge-based systems , Lower limb prosthesis , Socket , Virtual prototyping

An algorithm for both human-like motion generation and joint torques computation for digital humans is addressed in this paper. This goal has been achieved using techniques derived from robotics. In particular, the so-called augmented Jacobian has been used to solve the inverse kinematics problem with a single closed loop inverse kinematics algorithm. Furthermore, a position control for the center of mass of the kinematic chain, and for its projection on the support plane (center of pressure), has been implemented to achieve easy posture control. Thus, the inverse kinematics can be solved taking into account the static balance of the digital human. Moreover, the proposed algorithm allows simulating quite complex tasks, which involve the motion of the whole body, by means of only few task-related control points arbitrary located on the whole kinematic chain. The resulting movements are quite natural even for complex tasks as can be seen on the simulation experiments reported which show the effectiveness of the proposed approach. Finally, the joint torques can be computed thanks to the kinetostatics duality: the results are in accordance with biomechanical analyses. © 2011 Springer-Verlag.

Keywords: Digital humans , Human-like motion generation , Kinetostatic duality , Low-back biomechanical analysis , Multiple-point kinematic control , Posture control

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.

Background: A fundamental pre-requisite for the clinical success in dental implant surgery is the fast and stable implant osseointegration. The press-fit phenomenon occurring at implant insertion induces biomechanical effects in the bone tissues, which ensure implant primary stability. In the field of dental surgery, the understanding of the key factors governing the osseointegration process still remains of utmost importance. A thorough analysis of the biomechanics of dental implantology requires a detailed knowledge of bone mechanical properties as well as an accurate definition of the jaw bone geometry.Methods: In this work, a CT image-based approach, combined with the Finite Element Method (FEM), has been used to investigate the effect of the drill size on the biomechanics of the dental implant technique. A very accurate model of the human mandible bone segment has been created by processing high resolution micro-CT image data. The press-fit phenomenon has been simulated by FE analyses for different common drill diameters (D A = 2.8 mm, D B = 3.3 mm, and D C = 3.8 mm) with depth L = 12 mm. A virtual implant model has been assumed with a cylindrical geometry having height L = 11 mm and diameter D = 4 mm.Results: The maximum stresses calculated for drill diameters D A, D B and D C have been 12.31 GPa, 7.74 GPa and 4.52 GPa, respectively. High strain values have been measured in the cortical area for the models of diameters D A and D B, while a uniform distribution has been observed for the model of diameter D C . The maximum logarithmic strains, calculated in nonlinear analyses, have been ε{lunate} = 2.46, 0.51 and 0.49 for the three models, respectively.Conclusions: This study introduces a very powerful, accurate and non-destructive methodology for investigating the effect of the drill size on the biomechanics of the dental implant technique.Further studies could aim at understanding how different drill shapes can determine the optimal press-fit condition with an equally distributed preload on both the cortical and trabecular structure around the implant. © 2012 Frisardi et al.; licensee BioMed Central Ltd.

Changeability accomplishes the engineering design of competitive sustainable manufacturing systems, considered as industrial products characterized by inherent life cycle. Main drivers for changeability are manufacturing system reconfigurability and hybridization. A Hybrid Reconfigurable System (H-RS) is characterized by the coexistence and cooperation of industrial robots and skilled human workers to perform complex tasks within a common reconfigurable production environment. H-RSs rise use-productivity along their total system life cycle, fostering the evaluation and implementation of feasible and innovative technologies, and increasing the utilization ratio and the multiple use-or re-use-of resources. The paper proposes an engineering method which aims at enhancing changeability in H-RSs through the application of a multi level reconfigurability approach within a digital environment. The method includes the advanced design and modeling of digital devices which embed mechanics, electronics, control logic and software code. Advanced models are exploited to analyze the system performance in the system domain of changes and to realize an effective human training. An industrial case study describes the application of the method to the design of a hybrid reconfigurable workcell for manufacturing and assembly of top class car chassis. © 2012 Springer-Verlag.

Keywords: Automotive , Changeability , Digital environment , Hybrid Reconfigurable System

Engineering changeability-oriented and cost-driven approaches are needed by enterprises to design and optimize manufacturing and assembly systems for the demanding production requirements of the present industrial scenario. The integrated design of Reconfigurable Systems addresses tailored flexibility through modularity, integrability of resources, product and process customization, and system convertibility and diagnosability. The cooperation of robot and humans in hybrid environments offers a good trade-off between changeability, high quality and low costs, by exploiting the human dexterity and cognitive proactivity, together with robotic accuracy and performances. Virtual prototyping methods and digital manufacturing solutions are now mature and effective enough to play a strategic role within the hybrid reconfigurable system (H-RS) design and optimization process. The present research work proposes an engineering method to design and optimize H-RSs, by using virtual prototyping and digital manufacturing as a strategic support for the analysis and synthesis of the technical solutions, especially those related to human-robot cooperation. An industrial case study on a hybrid reconfigurable assembly system of a top class car aluminum chassis is finally presented. © 2011 Springer-Verlag.

Keywords: Automotive industry , Digital manufacturing , Hybrid reconfigurable system , Virtual prototyping

The paper describes the preliminary results of a research activity on the design of consumer-product interaction by means of interactive Virtual Prototypes (iVPs). Differently from Virtual Prototypes (VPs), which can be defined as an integration of geometries and functional multi-domain and multi-physics models, interactive Virtual Prototypes can be implemented as an integration of functional models for each sense - in this case vision, touch and hearing - which are parametric and independent from each other, so that they can be modified on request. Thanks to the use of iVPs the interaction design approach can be reversed. In fact, first the iVP can be used for the design and evaluation with final users of the consumer-product interaction, and then the resulting interaction parameters can be mapped back to the functional models of the VPs by following a sort of reverse engineering activity. So, the interaction specifications are not derived by questionnaires and focus groups with potential customers, but products are shown, tested, and customised directly with the potential buyers. This method presents several advantages for companies. It allows designers to more easily and directly capture the voice of the customers by gathering an immediate feedback about new interaction modalities, and also to design and validate at the same time the emotional response of their products. Besides, these studies and validations can be performed when the product design is in its infancy and technical decisions have not been taken, with the consequent advantage that design changes are not too expensive. The paper demonstrates the validity and potentiality of the methodology through some case studies. Copyright © 2012 by ASME.

The paper describes the development of a multimodal environment that can be used as a tool to train operators to perform maintenance tasks of industrial products during their lifecycle. The environment provides a visual and haptic representation of a product through the use of commercially-available hardware and software technologies. The new environment mixes interactive simulations of products, based on Virtual Reality technologies, and the information included in the traditional instruction manuals. The paper discusses about what can be effectively simulated with the available technology, and how the current technological limitations can be overcome by using the potentialities offered by a multimodal approach. Technology limitations can also be overcome by mixing two different strategies for coupling parts: the physics-based and the constraint-based approach. A case study provided by a company working in the field of household appliances has been used to prove the concept, to develop, test and finally refine the multimodal environment. The paper describes the development of the multimodal environment and presents the results of the user tests. Copyright © 2012 by ASME.

In finite element analysis of sheet metal forming the use of combined isotropic-kinematic hardening models is advisable to improve stamping simulation and springback prediction. This choice becomes compulsory to model recent materials such as high strength steels. Cyclic tests are strictly required to evaluate the parameters of these constitutive models. However, for sheet metal specimens, in case of simple axial tension-compression tests, buckling occurrence during compression represents a serious drawback. This is the reason why alternative set-ups have been devised. In this paper, two experimental arrangements (a cyclic laterally constrained tension-compression test and a three-point fully reversed bending test) are compared so as to point out the advantages and the disadvantages of their application in tuning the well-known Chaboche's hardening model. In particular, for tension-compression tests, a new clamping device was specifically designed to inhibit compressive instability. Four high strength steel grades were tested: two dual phases (DP), one transformation induced plasticity (TRIP) and one high strength low alloy material (HSLA). Then, the Chaboche's model was calibrated through inverse identification methods or by means of analytical expressions when possible. The proposed testing procedure proved to be successful in all investigated materials. The achieved constitutive parameters, obtained independently from the two experimental techniques, were found to be consistent. Their accuracy was also been assessed by applying the parameter set obtained from one test to simulate the other one, and vice versa. Clues on what method provides the better transferability are given. © 2012 American Society of Mechanical Engineers.

Keywords: Chaboche's model , cyclic plasticity , high strength steel , sheet metal forming , tension-compression test , three-point bend test