Product design and engineering

A new method for tolerance/variation analysis of multi-station assemblies of compliant parts is presented. Based mainly on the 'unit displacement' and 'sensitivity matrix' method, it allows for the use of statistical variations in key points to predict the final shape variation of multi-station assemblies. 'Linear contacts' between parts are included to avoid part-to-part intersections. The evaluation of what happens at the end of the assembly process enables users to analyse different assembly configurations in the early design phase. Implemented in the Matlab environment, it requires two linear FEA runs for each assembly station. Two case studies are presented and discussed. Copyright © 2008 Inderscience Enterprises Ltd.

Keywords: Compliant parts/assemblies , Contact modelling , FEA , Finite element analysis , Linear static analysis , Multi-station assemblies , Statistical variations , Tolerance analysis

The design of solutions for robotic extenders of wheelchairs must take into account both objective and subjective metrics for everyday activities in human environments. Virtual Reality (VR) constitutes a useful tool to effectively test design ideas and to verify performance criteria. This paper presents the development of a simulation environment, where three different manipulators to be mounted on a commercially available wheelchair have been considered. Experimental results are discussed in a significant case study, based upon users' feedback. © The Eurographics Association 2008.

Keywords: Human robot interaction , Kinematics , Rehabilitation robotics , Virtual Reality

The present work deals with the re-designing of a locomotive, according to in force European standards, in the field of active and passive safety. The paper illustrates the use and the management of heterogeneous product information (2D drawings, technical documentation, photos), Virtual Reality tools and digital human models, for the re-designing of a locomotive, using a collaborative approach with a total absence of the reference digital models. The project development has been organised using a top-down approach in a collaborative environment. Finally, by means of the digital prototype of locomotive, a series of aesthetic, functional and ergonomic analyses, in virtual environment, has been performed. © Springer Verlag France 2007.

Keywords: Collaborative design , Ergonomics , Top-downapproach , Virtual reality

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.

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.

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

Fine porcelain products get their peculiar characteristics at the end of their thermal process. During the firing, the product is subjected to shrinkage and a considerable amount of the material mass becomes viscous, causing the product shape to be modified due to the own object weight. As the final object shape is a relevant characteristic for both usability and aesthetics of the commercial product, the activity purpose was to devise a methodology to automatically detect the raw product shape required to match a provided final geometry. Such a methodology has been implemented by means of commercial CAD/FEM tools and should be used in porcelain products design. The research consists of three parts. During the first one an extensive experimental campaign has been carried out in order to model the behavior of the heat treated material; by using the experimental data a numerical model of the material behavior has been built. In the second part the model reliability has been tested by means of a set of FE analysis. Such an analysis simulates the effects of stresses caused by the real industrial firing process. In the end, during the third part, inverse firing process FE simulations have been performed. These simulations will allow the designer to know the raw-product geometry, in order to obtain the expected finished product. Copyright © 2008 by ASME.

The problem of integrating topological optimization tools in product development process (PDP) is becoming more and more urgent since nowadays they are widely employed in several engineering fields (civil, aeronautics, aerospace, automotive). The interest for these tools is due to their capacity to better mechanical properties through a global optimization of the product in terms of weight, stiffness, resistance and cost. In particular, there is a lack of specific tools for automatic feature recognition on voxel models generated by the topological optimization tools. Our paper presents an innovative methodology that allows the integration of topological optimizers in the product development process by means of a wise and rational knowledge management and an efficient data exchange between different systems. The target has been reached through the implementation of CAD automation modules which decrease the working time and give the possibility to effectively schematize the designer's knowledge. Copyright © 2008 by ASME.

The efficacy of virtual reality (VR) as a design support technique is widely recognised by industries. However, the efficiency of the routine employment of VR into the product development process (PDP) still finds an obstacle in the poor integration of the tools employed. The use of VR still needs long and quite hard procedures to work effectively; the models have to be converted into a format that is compatible with VR systems and each task requires an effort to prepare the virtual environment or to post-process the results that depend on the complexity of the task. This work analyses some VR applications into the PDP and describes some ideas to effectively support the operator that prepares the virtual environment. These ideas have been tested by developing four software interfaces, able to create an easy data exchange link between VR and other design tools like CAD, CAE and computer aided control engineering (CACE). © 2007 Springer-Verlag London Limited.

Keywords: CACE , CAD , CAD-VR integration , CAE , Virtual prototyping , Virtual reality

The aim of this work is to assess the fracture risk prediction of the cancellous bone in the body of a lumbar vertebra when the mechanical parameters of the bone, i.e. stiffness, porosity, and strength anisotropy, of elderly and osteoporotic subjects are considered. For this purpose, a non-linear three-dimensional continuum-based finite element model of the lumbar functional spinal unit L4-L5 was created and strength analyses of the spongy tissue of the vertebral body were carried out. A fabric-dependent strength criterion, which accounts for the micro-architecture of the cancellous bone, based on histomorphometric analyses was used. The strength analyses have shown that the cancellous bone of none of the subject types undergoes failure under loading applied during normal daily life like axial compression; however, bone failure occurs for the osteoporotic segment, subjected to a combination of the compression preloading and moments in the sagittal or in the frontal plane, which are conditions that may not be considered to occur 'daily'. In particular, critical stress conditions are met because of the high porosity values in the horizontal direction within the cancellous bone. The computational approach presented in the paper can potentially predict the material fracture risk of the cancellous bone in the vertebral body and it may be usefully employed to draw failure maps representing, for a given micro-architecture of the spongy tissue, the critical loading conditions (forces and moments) that may lead to such a risk. This approach could be further developed in order to assess the effectiveness of biomedical devices within an engineering approach to the clinical problem of the spinal diseases. © 2008 IMechE.

Keywords: finite element analysis , fracture criterion , lumbar spine , osteoporosis , soft biological tissues

Finite element (FE) simulations can be utilized to predict contact pressures at the bone/implant interface as well as to identify the position and shape of the contact region. However, the accuracy and reliability of FE models of the bone/implant interface reconstructed from tomographic images may be affected by a number of factors such as the presence of image artifacts, the magnitude of geometric errors made in the reconstruction process, the type of boundary and loading conditions hypothesized in the model, the nonlinear solver utilized for computing the contact pressure distribution, and the element type. This paper attempts to estimate the global effect of the aforementioned factors. For this purpose, a cylindrical contact problem - pin/muff - portraying a simplified model of the bone/implant interface is considered. The accuracy of numerical predictions is estimated by comparing contact pressures predicted by an FE model reconstructed from computed tomography (CT) scan images and by an "ideal", experimentally validated FE model. Two different couplings, i.e. chromium-cobalt alloy and titanium implants, are considered. In the former case, image artifacts complicate the reconstruction process of model geometry and lead to less accurate predictions on contact pressure distribution; conversely, the limited streaking effects occurring in the titanium pin case allow us to precisely reconstruct coupling geometry. Finally, a rather clear correlation between errors on contact pressure and geometric errors made in the reconstruction process is found only for the titanium pin. © 2008 World Scientific Publishing Company.

Keywords: Bone/implant interface , CT scans , Cylindrical contact , Finite element analysis , Image artifacts , Model reconstruction

Mandibular symphyseal distraction osteogenesis is a clinical procedure utilized in orthodontics for solving problems of dental overcrowding on the mandibular arch. A critical issue is to evaluate the optimal duration of the latency period between the osteotomy and the first aperture of distraction device. In fact, the latency period should change with the patient's age. To this end, a computational mechanobiological model has been developed in order to find optimal durations of latency period for young, adult, and elder patients. The model is implemented in a finite element framework simulating the process of tissue differentiation in the bone callus formed after osteotomy. The biophysical stimulus regulating the tissue differentiation process is hypothesized to be a function of the octahedral shear strain and interstitial fluid flow velocity. The resulting spatial distribution of stiffness properties in the callus region is analyzed in order to assess the risk of premature bone union of osteotomy edges. The three-dimensional (3D) finite element model (FEM) of human mandible is reconstructed from computed tomography (CT) scans and also includes a tooth-borne device. Under unilateral occlusion, the mandible is submitted to full mastication loading or to mastication forces reduced by 70%. The results show that optimal durations of the latency period for preventing premature bone union are about 5-6 days for the young patient, 7-8 days for the adult patient, and 9-10 days for the elder patient. These durations seem rather insensitive to the magnitude of mastication forces. Finally, distraction force values predicted by the present mechanobiological model are in good agreement with data reported in the literature. © 2008 World Scientific Publishing Company.

Keywords: Aging , Finite element analysis , Mandibular distraction osteogenesis

The aesthetic impact of a product is an important parameter that makes the difference among products technologically similar and with same functionalities. Product shape, which is strictly connected to the aesthetic impact, has different meanings if seen from the design and the engineering point of view. The conceptual design of shape of aesthetic products is usually performed by designers at the beginning of the product development cycle. Subsequent engineering design and studies, such as structural and fluid-dynamic analyses, lead to several design reviews where the original shape of the object is often modified. The design review process is time consuming, requires the collaboration and synchronization of activities performed by various experts having different competences and roles, and is performed using different tools and different product representations. Then, computer aided tools supporting conceptual design and analysis activities within the same environment are envisaged. The paper presents the conceptual description of an environment named PUODARSI that allows designers to modify the shape of a product and evaluate in real-time the impact of these changes on the results of the structural and fluid dynamic analyses in an Augmented Reality (AR) collaborative environment. Main problems in integrating tools developed for different purposes, such as, haptic interaction, FEM and CFD analyses, AR visualization concern the feasibility of the integration, the data exchange, and the choice of those algorithms that allow all that while guaranteeing low computational time. The paper describes the main issues related to the choice of hardware and software technologies, and the PUODARSI system implementation. © The Eurographics Association 2008.

The aesthetic impact of a product is an important parameter that makes the difference among products technologically similar and with same functionalities. The shape, which is strictly connected to the aesthetic impact, has different meanings if seen from the design and the engineering point of view. This paper describes an environment based on an integration of Mixed- Reality technologies, haptic tools and interactive simulation systems, named PUODARSI whose aim is to support designers and engineers during the phase of design review of aesthetic products. The environment allows the designer to modify the object shape, through the use of haptic devices, and the engineer to run the fluid-dynamics simulation on the product shape. The paper describes the main problems faced in integrating tools, originally developed for different purposes and in particular issues concerning data exchange, and the choice of those algorithms that guarantees low computational time as required by the application.

Keywords: Design review , Fluiddynamics analysis , Haptic interfaces , Mixed-Reality

Exploring how to enhance and assist the design process with the support of new Information and Communication Technologies is a growing field of research. The analysis of the design processes of aesthetic shapes highlights open issues that make the processes inefficient and generate some questions about how to improve the process performances. Examples of questions are: how to generate more and better ideas, how to become more creative and how to exploit at best people know-how. The research presented in this paper reasons about issues related to aesthetic shapes perception and proposes some solutions at the basis of future design tools based on new ways of working and new ways of interaction. Copyright © 2008 by ASME.

Virtual Reality (VR) systems provide new modes of human computer interaction that can support several industrial design applications improving time savings, reducing prototyping costs, and supporting the identification of design errors before production. Enhancing the interaction between humans and virtual prototypes by involving multiple sensorial modalities, VR can be adopted to perform ergonomic analysis. The main problems deal with the evaluation both of functional and cognitive sample users behavior as VR interfaces influence the perception of the ergonomic human factors. We state that ergonomic analysis performed in virtual environment can be successful only if supported with a structured protocol for the study both of functional and cognitive aspects and with the proper VR technologies combination that answers to the specific analysis tasks. An ergonomic analysis protocol is presented. It allows the assessment of the consumers/ response in term of behavioral and cognitive human factors, comprehending both operational and emotional agents. The protocol is also used to identify the best combination of visualization and haptic interfaces to perform the analysis. An experimental example, belonging to house appliances field is adopted to investigate the application of the protocol in the virtual set up. Copyright © 2008 by ASME.

This paper presents a haptic system the authors have developed for shape exploration in the field of industrial design. The system consists of a novel haptic-based digital technology, allowing designers to add the tactile experience to the visual one. The haptic interface developed allows designers to see and haptically feel through free hand motions an object surface during its creation and evolution. The system closes the loop of shape modification and its subsequent evaluation: It is possible to evaluate the "what f' related to a new product shape, applying the modfication and comparing the solutions more and more times, and generate and maintain djfferent versions. That improves the level of interaction of designers with the digital models, exploits their skills, and shortens the product development life cycle. Copyright © 2008 by ASME.

Keywords: Haptic interfaces , Haptically enhanced design tools , Haptics in design

Virtual Reality (VR) technologies provide novel modes of human computer interaction that can be used to support industrial design processes. The integration can be successful if supported by a method to qualify, select and design the VR technologies according to the company's requirements in order to improve collaboration in extended enterprises and timesaving. The aim of the present work is the definition of a method to translate the company's expectations into heuristic values that allow the benchmarking of VR systems. The method has been tested on a real test case. Copyright © 2007 by ASME.

Keywords: Benchmarking criteria , Design review , Virtual reality

The paper presents the results of a research project aiming at developing an innovative framework for conceptual design of products based on innovative haptic interfaces. The framework consists of a CAD (Computer Aided Design) system enhanced with intuitive interaction tools and modalities for modeling, modification and evaluation of shapes. The system aims at exploiting designers' skills in modeling products, improving the products design process by reducing the necessity to build several physical models for evaluating and testing the product designs. The system proposes an emotional engineering approach by supporting product designers in translating their sensibility into physical design factors, allowing easy and fast creation and evaluation of diverse shape solutions. The system requirements have been defined after observing designers during their daily work and translating the way they evaluate and modify shapes using hands and craft tools into specifications for the modeling system and the haptic tool. The system prototype has been tested by designers who have found it intuitive and effective to use. Copyright © 2007 by ASME.

In this study, a methodology based on co-simulation was developed for the multibody parametric modelling of a motorcycle with an anthropomorphic model of the rider. This co-simulation uses two different software programs, integrated to ensure a complete exchange of information between them in real time. The paper reports the effects induced by the movement of the rider's body on the dynamics and performance of a motorcycle. The legs of an anthropomorphic model were used as kinematics to control transverse movements of the motorcycle. The control system inputs are the geometric characteristics of the road (length, width and radius of curvature) and the speed of the vehicle along the track. For the dynamic behaviour of the motorcycle, the only channels currently operated by the control system are steering angle and engine torque, which are determined in accordance with the input parameters.

Keywords: Control , Dynamic , Motorcycle , Multibody , Rider