Geometric modeling and processing

In this work a modified beam approach to model the compressive behavior of additively manufactured BCC and reinforced BCC lattice structures is proposed. Three-dimensional beam models are of interest because of their reduced computational time, with respect to numerical models that involves solid mesh elements, but they are not able to capture the behavior of lattice structures in proximity of the unit cell nodes, that presents higher stiffness due to the struts intersection and consequent material overlapping. In order to overcome this drawback when using beam finite elements, a modified beam approach is used in this work considering each lattice cell strut subdivided in a central flexible portion and two rigid extremities. A numerical procedure is implemented to tune the rigid extremities length of the strut by means of numerical simulations that aims to reproduce accurately the compressive behavior of the lattice cell solid model. The experimental campaign conducted on different powder bed fusion manufactured lattice structures is presented and experimental results are provided along with a numerical-experimental correlation that proves the accuracy of the method.

Keywords: BCC lattice cells , Lattice beam model , Lattice structures , SLM

In this paper, the mechanical properties of a modified Body-Centred Cubic lattice cell with waved struts have been determined using FEM simulations with solid element mesh. The strut waviness introduces orthotropic properties in the cell and the correlation between geometrical cell parameters and resulting mechanical attitudes is calculated. For a complete determination of all the mechanical constants, uniaxial compression and in-plane shear have been simulated along different loading directions. Attention has been particularly paid to the definition of appropriate boundary constraints able to mimic the periodic condition that applies to a repetitive unit cell. At first, the numerical model has been validated with existing analytical and experimental results available in the literature, then parametric strut waviness has been introduced to this model. A systematic numerical study has been conducted on lattice cells with different density and different wave amplitude. Results have evidenced for the waved struts a considerable increase in the longitudinal uniaxial modulus and a negligible effect on the transverse moduli, while a slight reduction of the shear moduli is generally obtained in all the sliding planes. Poisson's ratios are highly affected both by density and waviness. The obtained results can be useful for the optimized definition of a lattice cell, tailored to the specific mechanical requirements of an advanced component.

Keywords: 3D lattice , BCC , FEM , Orthotropy , Waviness

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

Lattice structures for engineering applications are patterns of unit cells designed to make a larger functional structure. Research on lattice structures ranges in many fields, from mechanical characterization and cell and pattern designs in respect of their applications, to the manufacturing process and its final shape control. From the manufacturing point of view, some kinds of lattice structures can be infeasible when approached with traditional manufacturing methods. It may offer an inevitable limitation of their adoption. However, advancements in Additive Manufacturing (AM) have solved this manufacturing issue to a great extent, allowing to obtain major complexity of the cells that can be achieved. The topology, shape of the unit cell, and the characteristics of its replication pattern allow us to obtain many kinds of structures in respect of the different engineering requirements and manufacturing constraints. Nevertheless, the necessity of new or dedicated CAD-CAE approaches arises to manage the domains of multiscale modeling. These are some of the advantages and disadvantages that may arise while approaching the design of a component using lattice structures. The aim of this paper is to provide an overview that integrates the most recent applications of lattice structures with their related design and manufacturing issues so that, from a practical design point of view, any state-of-the-art improvements may be established in respect of the related field of applications. In this article, engineers and researchers may find a practical summary of the capabilities and processes of lattice structures that are currently available from a design and development point of view.

Keywords: additive manufacturing , cellular structures , design methodologies , functionally graded materials , lattice structures , TPMS

The rapid development of production methods and the introduction of additive manufacturing (AM) technologies have increased the design freedom and availability of unlabeled data. Typically, manufacturing process selection requires a large amount of labeled data which is expensive and difficult to reach. This is more critical with the continuous improvement of AM systems, which can be increasingly used to substitute traditional manufacturing technologies. Implementing unsupervised learning into manufacturing process selection and classification is beneficial since unsupervised learning uses unlabeled data. Hence, this paper aims to differentiate parts to be fabricated favorably by means of additive or traditional manufacturing technologies using image processing and unsupervised learning. The input image dataset is constructed from freely accessible web databases in which forty CAD (computer-aided design) models are available. The corresponding images of CAD models are extracted using the SOLIDWORKS 2022 software, where 42.50% are AM-ed, and the remaining are chosen from traditionally manufactured parts. The hierarchical clustering algorithm reported 87.50% accuracy, showing promising potential for manufacturing process classification and image processing applications.

Keywords: hierarchical clustering , image processing , machine learning , manufacturing process selection , unsupervised learning

This article introduces the Differential Entropy-based Compactness Index (DECI), a new metric for synthetically describing the spatial distribution of point clouds. DECI is founded on the differential entropy (DE) of point clouds, and if they depict a moving object distribution, the index enables real-time monitoring. Historical data analysis allows for the study of DECI trends and average values in defined intervals. Multiple practical applications are suggested, including risk assessment, congestion measurement, traffic control (including autonomous systems), infrastructure planning, crowd density, and health analysis. DECI's real-time and historical insights are valuable for decision-making and system optimization and hold potential as a feature in machine learning applications.

Keywords: 3D geometry distribution assessment , compactness index , differential entropy , point clouds , real-time , risk assessment

Hygienic design is an engineering approach focusing on the development of food processing systems and equipment in compliance with hygienic requirements such as food contact compatibility, easy cleaning, and special maintenance needs. Currently, hygienic design knowledge is fragmented and a method to list and collect this knowledge in a structured database is missing. The paper aims at providing a knowledge-based (KB) system to collect hygienic design rules and to exploit these rules in the development of food processing machines and equipment. The KB system is based on a specific ontology that has been used to collect 78 hygienic design rules from different sources. The rules repository can be considered a backbone for the subsequent development of a CAD-based tool for an automatic search and detection of non-compliant design features early in the development of food processing systems. The KB system is used to validate the compliance of fish stick production equipment, starting from the CAD model and the analysis of the geometrical features. Results highlight how the adoption of the KB system at an early stage of the design anticipates hygienic design issues, avoiding several design reviews when these products are defined. Future developments aim at widening the rules repository and creating an automatic tool to perform the feature analysis directly in the CAD environment.

Keywords: Design for manufacturing , Engineering design , Food equipment , Food industries , Hygienic design , Knowledge-based system

Total knee arthroplasty (TKA) is the surgical procedure of choice for end-stage osteoarthritis. Even if it is widely performed, there is still dissatisfaction with the surgical procedure in about 20-30% of patients. Factors such as malalignment of the implant and the size of the components have been reported as the most common reasons for post-operative complaints. Custom-made prostheses have been introduced to replicate each individual joint geometry and kinematics. In this study, a novel approach is proposed to automate custom-made knee implant design. The aim is to create a pipeline, where customized implants can be designed automatically for a large number of patients, reducing the time for design. Firstly, a manual procedure for designing the implant is defined. The lower part of the femur is extruded with a thickness that matches with the natural anatomy of the patient and cut planes are used to design the customized femoral implant. Then, an automatic procedure is developed. For the purpose, a statistical shape model of femur, based on 33 patients, is created and employed. The procedure is tested with 5 study cases showing the potential of the methodology. Results will be furtherly validated on a larger scale.

Keywords: 3D Modelling , Customization , Human Modelling , Personalized , Statistical Shape Model , Total Knee Arthroplasty

Hybrid sandwich structures are often used in the aviation industry thanks to their high strength-to-weight ratio and resistance to bending and buckling. Today, through Additive Manufacturing technologies, it is possible to use different materials to create topology-optimized structures with complex shapes using lattice structures. In this work, a numerical approach is proposed to study the behaviour of a hybrid sandwich structure which can be used as a reinforcement for a control surface of a lightweight aircraft. A comparative analysis is conducted between a conventional honeycomb lattice core and lattice truss core structures.

Keywords: Additive Manufacturing , Design for Manufacturing , Hybrid Structures , Lattice Structures

The standard method of design and manufacturing customised orthoses is still very time-consuming due to their often very complex shape. Different authors have tried to solve this problem but, unfortunately, the proposed approaches cannot be easily used in clinical practice because they require substantial interaction among medical staff and engineers or technicians. The aim of this work is to present the framework of a new design approach that could allow clinicians to easily model a customised orthosis, without a skilled technician develops the entire procedure. In particular, an automatic process based on Generative Design has been implemented. The obtained results have demonstrated that the implemented algorithm is simple to use and could allow also not-skilled users to design customised orthoses.

Keywords: CAD , Customised orthosis , Generative design , Reverse engineering

3D reconstructed models are becoming more diffused daily, especially in the Cultural Heritage field. These geometric models are typically obtained from elaborating a 3D point cloud. A significant limit in using these methods is the realignment of different point clouds acquired from different acquisitions, particularly for those whose dimensions are millions of points. Although several methodologies have tried to propose a solution for this necessity, none of these seems to solve definitively the problems related to the realignment of large point clouds. This paper presents a new and innovative procedure for the fine registration of large point clouds. The method performs an alignment by using planar approximations of roof features, taking the roof's extension into account. It looks particularly suitable for the alignment of large point clouds acquired in urban and archaeological environments. The proposed methodology is compared in terms of accuracy and time with a standard photogrammetric reconstruction based on Ground Control Points (GCPs) and other ones, aligned by the Iterative Closest Point method (ICP) and markers. The results evidence the excellent performance of the methodology, which could represent an alternative for aligning extensive photogrammetric reconstructions without the use of GCPs.

Keywords: multi-UAV scanning registration , particle swarm optimization , point cloud registration , shape features recognition

The traditional manual method of analysis of ceramic finds involves expert operators in long and routine activities whose results depend on their subjectivity, specialization, and professional experience. This implies that the analysis of sherds is carried out using few data affected by high uncertainty. These limitations are even more clear with fragments with small axially symmetric portions whose elements of the investigation are not axially symmetric, such as handles, spouts, decorations. In this way both the axis of symmetry of the original object and the reference planes and/or axes of the characteristic dimensions of the elements are identified with such approximations as to compromise subsequent analyses and comparisons. To overcome these limitations, in this paper a new computer-based procedure is proposed. As a case study, the analysis fragments of jugs/bowls with trilobed spouts found in the site of Amiternum, coming from 12th-13th century contexts are considered; their analysis is fundamental to analyze the site where they were found since there is no archival documentation about their use.

The sweep features of constant radius are particularly significant for the purposes of the historical-archaeological investigation and classification of ancient artifacts. The paper focuses on the automatic recognition of this specific class of features from triangulated 3D models experimentally acquired from cultural heritage objects. This is not a trivial problem. The ancient artifacts, although repeatable, are unique handmade pieces with a geometry commonly characterized by complex and non-analytical shapes. Their surfaces are also usually damaged and worn, so that the related geometric properties are altered or lost. The methodology proposed here is inspired by the one previously developed by the authors for the automatic segmentation of fillets, rounds and grooves from high-density triangulated models of mechanical components. The paper, in particular, focuses on the aspects of this methodology that must be tuned to allow the recognition of the sweep features of constant radius from archaeological finds. The methodology has been implemented and finally applied to an archaeological find acquired by a laser scanner.

Keywords: 3D archaeology , 3D digital models , Computer methods in archaeology , Feature recognition , Laser scanning

Total Knee Arthroplasty (TKA) is a widely performed surgical procedure, which is advised to treat knee osteoarthritis. However, the literature reported that 25% of the patients are unsatisfied by the functional outcomes after the intervention. The main causes seem to be the prosthesis malalignment and the anatomical mismatch between the prosthetic components and the different people anatomy. Even if there exist several commercial solutions, whose aim has always been to provide a reliable prosthesis with high survivorship, the most recent scientific literature is focusing its aim to improving the patients' clinical outcome, kinematics and satisfaction. For this reason, three approaches have been experimented and then discussed with an orthopedic surgeon. Open-source software applications for 3D modelling have been exploited, such as 3D Slicer and Meshmixer. Starting from medical images, through the segmentation process, the 3D model of the knee has been reconstructed. For the first approach, standard off-the-shelf prosthesis have been used for the virtual planning of the intervention. To overcome the limits of this method, two more customized approaches have been experimented. The first one is based on the patient-specific resurfacing prosthesis that fits the patient's anatomy, preserving the femur and maintaining the natural joint line. The third approach allows to create a customized prosthesis, that is a compromise between the two previous methods. Among the three previous procedures, the most suitable one can be chosen according to the patient's anatomy, knee size and articular cartilage damage.

Keywords: 3D modelling , Customized knee prosthesis , Total knee arthroplasty planning

Emerging production technologies, in particular Additive Manufacturing (AM), nowadays are extremely suitable for creating highly complex products, tending towards the concept of ‘complexity for free', which is often associated with AM. However, there are no adequate guidelines to provide decision support for the correct selection of the most economically appropriate technology. Indeed, from literature it has been highlighted the need to develop a technology selection methodology based no longer on production volume but on product complexity. This paper investigates this need by presenting an approach to determine the geometrical (or shape) complexity index of a part, which, combined with the assembly complexity, represents the driver for helping to decide the best production technology (traditional or additive). The geometrical complexity index has been determined based on complexity judgments, provided by CAD modelling experts, for a sample of CAD models. In this way, it has been possible to define a preliminary complexity index model, strictly linked to the CAD model information. The results showed that the geometrical complexity metrics from the literature, if individually considered, are not comprehensive. However, a combination of them makes it possible to obtain an index that best reflects the subjective judgement of the experts. In addition, by combining the geometrical and assembly complexity with a cost analysis it is possible to obtain convenience zones for better selecting the production technology.

Keywords: CAD , Geometrical complexity , Survey , Technology selection

This work proposes a geometric approach to inverse kinematics of hyper-redundant manipulators used for remote maintenance of nuclear fusion reactors. The approach is particularly suited to be adopted in real-time human-in-the-loop control strategies involving high-frequency control feedback and requiring safe interaction between the manipulator and the in-vessel environment. The capability of the inverse kinematic method to find a solution for a set of different robot end-effector poses, inside a toroidal environment, was tested on the HyRMan kinematics, i.e. the Hyper Redundant Manipulator developed in the framework of the Divertor Tokamak Test (DTT) project. The simulation tests were aimed at assessing performance of the proposed method in terms of accuracy in the end-effector positioning, computational burden, distance from obstacle, distance from joint angles and torque limits and success rate of the task execution. The achieved results were compared to the ones obtained through an iterative method proposed in literature, i.e. the one based on the computation of the Jacobian pseudo-inverse, demonstrating overall higher performance of the proposed approach and comparable ability to safely avoid obstacles and joint limits.

Keywords: Hyper-Redundant Manipulators , Inverse Kinematics , Nuclear Fusion , Remote Maintenance

A Cayley map for the special Euclidean group SE(3) is introduced to relate, for a soft continuum robot, the Lie algebra of internal deformations with the Lie group of rigid–body motions. This Cayley map is used for approximated and exact kinematic shape reconstruction of soft continuum robots, under the hypothesis of constant deformations. This map could be used for deriving computationally efficient interpolation schemes for soft robots, since it does not involve transcendental functions as those introduced by the exponential parametrization of soft robot kinematics.

Keywords: Cayley transform , Differential geometry , Kinematics , Soft robotics

Today it is more and more mandatory for all commercial companies to comply with the principles and methodologies of Industry 4.0 and to achieve the related capabilities protecting their competitiveness and taking a leading-edge position on market as regards technologies. Specifically, the whole production and sale system must achieve the fundamental characteristics of Industry 4.0 approach, but specially the manufacturing companies must also change and update their management procedures, internal organization, resource training, assets and all production process to keep safe their current business capacities. This evolution process is even more critical for Small and Medium Enterprises (SME), that traditionally tend to be conservative and to protect their way of operation, usually characterized by a low level of automation. The work presented focuses on the design and integration of a semi-automatic welding cell of train bolster in a SME which is currently realizing a project aimed to the acquisition of Industry 4.0 capabilities, with special focus on manufacturing processes. Among them, one of the most important is the production of welded-steel critical structures, that the Company supplies to prime manufacturer of railway rolling stock systems. The experience gained during the activity, the criticalities due to the integration processes and the adopted design methodologies are here described. The work has been carried out consistently with the Systems Engineering principles, starting from the requirements elicitation and analysis to the systematic approach for the design and integration activities.

Keywords: CAD , Design methodologies , Industry 4.0 , Internet of things (IoT) , Systems engineering , Welding process

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