Contrôle de l'équilibre des humains virtuels

Ce chapitre aborde le problème de l'analyse de l'équilibre et de la synthèse par la ommande de la coordination des mouvements d'humains virtuels pour la simulation réaliste d'activités physiques quotidiennes ou professionnelles. nous discutons dans un premier temps les notions d'équilibre postural et de stabilité de cet équilibre dans le cadre particulier des mannequins numériques. Nous introduisons un modèle mécanique pour des mannequins en interaction physique avec l'environnement. À partir d'une formulation générale du problème de l'équilibre, nous examinons un certain nombre de moyens proposés pour caractériser et quantifier la stabilité de l'équilibre des systèmes mécaniques contraints. Nous introduisons la notion de perturbation admissible pour la dynamique posturale vis-à-vis des contraintes de persistance et de non-glissement des appuis. Enfin, nous proposons des techniques de synthèse par la commande de fonctions motrices pour une coordination de l'ensemble du système postural et de manipulation satisfaisant explicitement les contraintes d'équilibre des appuis

Assessment of physical exposure to musculoskeletal risks in collaborative robotics using dynamic simulation

Many industrial tasks cannot be executed by a robot alone. A way to help workers in order to decrease the risk of musculoskeletal disorders is to assist them with a collaborative robot. Yet assessing its usefulness to the worker remains costly because it usually requires a prototype. We propose a dynamic simulation framework to model the performing of a task jointly by a virtual manikin and a robot. It allows to measure physical quantities in order to perform an ergonomic assessment of the robot. Experiments are carried out on two different robots. The results show that the proposed simulation framework is helpful for designing collaborative robots. Further work includes enhancing the simulation realism and validation on a real robot

Activity-dependent regulation of T-type calcium channels by submembrane calcium ions

International audienceVoltage-gated Ca 2+ channels are involved in numerous physiological functions and various mechanisms finely tune their activity, including the Ca 2+ ion itself. This is well exemplified by the Ca 2+-dependent inactivation of L-type Ca 2+ channels, whose alteration contributes to the dramatic disease Timothy Syndrome. For T-type Ca 2+ channels, a long-held view is that they are not regulated by intracellular Ca 2+. Here we challenge this notion by using dedicated electrophysiological protocols on both native and expressed T-type Ca 2+ channels. We demonstrate that a rise in submembrane Ca 2+ induces a large decrease in T-type current amplitude due to a hyperpolarizing shift in the steady-state inactivation. Activation of most representative Ca 2+-permeable ionotropic receptors similarly regulate T-type current properties. Altogether, our data clearly establish that Ca 2+ entry exerts a feedback control on T-type channel activity, by modulating the channel availability, a mechanism that critically links cellular properties of T-type Ca 2+ channels to their physiological roles

Automatic selection of ergonomic indicators for the design of collaborative robots: a virtual-human in the loop approach

Conference of 2014 14th IEEE-RAS International Conference on Humanoid Robots, Humanoids 2014 ; Conference Date: 18 November 2014 Through 20 November 2014; Conference Code:112990International audienceThe growing number of musculoskeletal disorders in industry could be addressed by the use of collaborative robots, which allow the joint manipulation of objects by both a robot and a person. Designing these robots requires to assess the ergonomic benefit they offer. However there is a lack of adapted assessment methods in the literature. Many biomechanical quantities can represent the physical solicitations to which the worker is exposed, but their relevance strongly depends on the considered task. This paper presents a method to automatically select relevant ergonomic indicators for a given task to be performed with a collaborative robot. A virtual human simulation is used to estimate thirty indicators for varying human and robot features. A variance-based analysis is then conducted to extract the most discriminating indicators. The method is validated on several different tasks. The relevance of the proposed approach is confirmed by the obtained results

Voltage-gated calcium channels in genetic diseases

AbstractVoltage-gated calcium channels (VGCCs) mediate calcium entry into excitable cells in response to membrane depolarization. During the past decade, our understanding of the gating and functions of VGCCs has been illuminated by the analysis of mutations linked to a heterogeneous group of genetic diseases called “calcium channelopathies”. Calcium channelopathies include muscular, neurological, cardiac and vision syndromes. Recent data suggest that calcium channelopathies result not only from electrophysiological defects but also from altered α1/CaV subunit protein processing, including folding, posttranslational modifications, quality control and trafficking abnormalities. Overall, functional analyses of VGCC mutations provide a more comprehensive view of the corresponding human disorders and offer important new insights into VGCC function. Ultimately, the understanding of these pathogenic channel mutations should lead to improved treatments of such hereditary diseases in humans

Self-adjusting, Isostatic Exoskeleton for The Human Knee Joint

International audienceA knee-joint exoskeleton design that can apply programmable torques to the articulation and that self-adjusts to its physiological movements is described. Self-adjustment means that the articular torque is automatically produced around the rotational axis of the joint. The requirements are first discussed and the conditions under which the system tracks the spatial relative movements of the limbs are given. If these conditions are met, the torque applied to the joint takes into account the possible relative movements of the limbs without introducing constraints. A prototype was built to demonstrate the applicability of these principles and preliminary tests were carried out to validate the design

Motion safety and constraints compatibility for multibody robots

International audienceIn this paper we propose a methodology to ensure safe behaviors of multibody robots in reactive control frameworks. The permanent satisfaction of constraints being insufficient to ensure safety, this approach focuses on the constraints expression: the compatibility between these constraints is studied, and safe alternatives are ensured when compatibility cannot be established. Case studies involving obstacles, joint position, velocity and acceleration limits illustrates the approach. A particular method is developed to take full advantage of a smooth state of the art avoidance techniques (Faverjon and Tournassoud in Proceedings of the 1987 IEEE international conference on robotics and automation, pp. 1152-1159, 1987) while maintaining safety. Experiments involving a 6-DOF manipulator operating in a cluttered environment illustrate the reliability of the approach and validate the expected performances

Constraints Compliant Control: Constraints compatibility and the displaced configuration approach

International audienceMost of the literature reactive control laws have much difficulties to handle properly constraints such as joint limits, obstacles and saturations, including them as equalities in the Inverse Velocity Kinematics (IVK) problem. Actually, it seems relevant to handle them through inequalities, as the constraints are more numerous than the number of DOFs. However, the intuitive constraints expression can lead to incompatibilities between constraints, which necessarily induces constraints violations. This paper brings two distinct contributions. First, the usual constraints inequalities are modified to make them compatible permanently. Second, an intuitive and efficient constraint compliant control law is proposed