A Novel Index to Compare the Representation Quality of Objects Approximated with Spheres

Practical collision detection problems require very fast algorithms. The quality of the object representation plays a key role in the efficiency of these algorithms. In this paper a new index is presented which makes it possible to compare in terms of quality of representation different algorithms that approximate an object by means of spheres. Comparative results with other indexes are provided

Nuovo codice di calcolo per lo studio del contatto tra elementi elastici ed elementi rigidi

This paper presents a new tool to find the spatial configuration of a mechanical system which comprises elastic fibres interacting both with each other and/or with rigid bodies. The configuration is determined by means of the principle of the minimum elastic potential energy of the system. Coulomb friction is neglected at the contacts. The paper gives an overview on the optimal representation of the rigid body shapes in the collison detection problem. In particular, the paper presents an elastic fiber model and describes the rigid body representation adopted. Both have been implemented in the tool. Finally an application of the tool to the biomechanical field is presented which makes it possible to find the spatial configuration of the human ligaments at the ankle joint complex

Sulla qualità di rappresentazione di oggetti approssimati mediante primitive sferiche

Nell’ambito della verifica di collisione fra corpi l’efficienza degli algoritmi gioca un ruolo fondamentale congiuntamente alla precisione nella valutazione dei contatti. Molte delle tecniche adottate in letteratura per risolvere tale problematica si basano sull’approssimazione degli oggetti in studio mediante l’uso di primitive elementari quali, ad esempio, sfere. Efficienza e precisione degli algoritmi sono aspetti strettamente correlati alla qualità di rappresentazione degli oggetti. In questo lavoro viene presentato un nuovo indice che confronta, in termini di qualità di rappresentazione, i differenti algoritmi che approssimano un oggetto mediante primitive sferiche. La validazione dei risultati viene ottenuta attraverso l’analisi ed il confronto con altri indici presenti in letteratura. La validità dell’indice proposto viene infine messa in luce da un’applicazione ad un corpo a geometria complessa quale è la tibiotarsica umana. Both algorithm efficiency and contact evaluation accuracy play a key role when dealing with the problem of Collision Detection. Several techniques from the literature used to solve this problem are based on the object representation by means of spheres. Efficiency and precision of the algorithms are closely connected to the quality of the representation of the objects. In this report, a new index which evaluates the approximation quality of the representation of the object with spheres is presented. Comparing the proposed index with other indexes from previous researches proves its correctness. Finally, as an example of application to a complex geometry bone, from the human ankle highlights the efficiency of the index

Synthesis of Prosthesis Architectures and Design of Prosthetic Devices for Upper Limb Amputees

This chapter presents a procedure for the Determination of the Optimal Prosthesis Architecture for upper limb amputees (DOPA). The presented approach can consistently manage both the clinical aspects and the technical issues involved in the design of electromechanically actuated prostheses. The procedure is composed on one hand of algorithms useful for analyzing the patients\u2019 requirements and on the other hand of algorithms that perform kinematic and kinetostatic simulations of several architectures of artificial arms attempting to fulfil important activities of daily living. The systematic evaluation of the prosthesis models\u2019 performance can methodically guide designers in the synthesis of the optimal prosthesis that best suits the patients\u2019 requirements

State-of-the-Art of Hand Exoskeleton Systems

This paper deals with the analysis of the state-of-the-art of robotic hand exoskeletons (updated at May 2011), which is intended as the first step of a designing activity. A large number of hand exoskeletons (both products and prototypes) that feature some common characteristics and many special peculiarities are reported in the literature. Indeed, in spite of very similar functionalities, different hand exoskeletons can be extremely different for the characteristics of their mechanism architectures, control systems and working principles. The aim of this paper is to provide the reader with a complete and schematic picture of the state-of-the-art of hand exoskeletons. The focus is placed on the description of the main aspects that are involved in the exoskeleton design such as the system kinematics, the actuator systems, the transmission parts and the control schemes. Additionally, the critical issues provided by the literature analysis are discussed in order to enlighten the differences and the common features of different practical solutions. This paper may help to understand both the reasons why certain solutions are proposed for the different applications and the advantages and drawbacks of the different designs proposed in the literature. The motivation of this study is the need to design a new hand exoskeleton for rehabilitation purposes

Compliant Actuation Based on Dielectric Elastomers for a Force-Feedback Device: Modeling and Experimental Evaluation

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 visco-hyperelastic 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

Kinematic models of lower limb joints for musculo-skeletal modelling and optimization in gait analysis

Kinematic models of lower limb joints have several potential applications in musculoskeletal modelling of the locomotion apparatus, including the reproduction of the natural joint motion. These models have recently revealed their value also for in vivo motion analysis experiments, where the soft-tissue artefact is a critical known problem. This arises at the interface between the skin markers and the underlying bone, and can be reduced by defining multibody kinematic models of the lower limb and by running optimization processes aimed at obtaining estimates of position and orientation of relevant bones. With respect to standard methods based on the separate optimization of each single body segment, this technique makes it also possible to respect joint kinematic constraints. Whereas the hip joint is traditionally assumed as a 3 degrees of freedom ball and socket articulation, many previous studies have proposed a number of different kinematic models for the knee and ankle joints. Some of these are rigid, while others have compliant elements. Some models have clear anatomical correspondences and include real joint constraints; other models are more kinematically oriented, these being mainly aimed at reproducing joint kinematics. This paper provides a critical review of the kinematic models reported in literature for the major lower limb joints and used for the reduction of soft-tissue artefact. Advantages and disadvantages of these models are discussed, considering their anatomical significance, accuracy of predictions, computational costs, feasibility of personalization, and other features. Their use in the optimization process is also addressed, both in normal and pathological subjects