Multisensor Input for CPG-Based Sensory—Motor Coordination

International audienceThis paper describes a method for providing in real time a reliable synchronization signal for cyclical motions such as steady-state walking. The approach consists in estimating online a phase variable on the basis of several implicit central pattern generator associated with a set of sensors. These sensors can be of any kind, provided their output strongly reflects the timedmotion of a link. They can be, for example, spatial position or orientation sensors, or foot sole pressure sensors. The principle of the method is to use their outputs as inputs to nonlinear observers of modified Van der Pol oscillators that provide us with several independent estimations of the overall phase of the system. These estimations are then combined within a dynamical filter constituted of a Hopf oscillator. The resulting phase is a reliable indexing of the cyclic behavior of the system, which can finally be used as input to low-level controllers of a robot. Some results illustrate the efficiency of the approach, which can be used to control robots

Online Generation of Cyclic Trajectories Synchronized with Sensor Input

On s'intéresse à la question suivante : comment synchroniser en ligne une commande cyclique avec un signal capteur lui aussi cyclique ? Nous modélisons notre mesure à l'aide d'un oscillateur non-lineaire, et en construisons un observateur. Ensuite, on vient "filtrer" les mesures capteur à l'aide de l'observateur. Ce dernier étant également un oscillateur, il est possible d'estimer sa phase, et de générer une commande paramètrée temporellement par cette phase. Nous évaluons la méthode et caractérisons sa robustesse aux erreurs d'estimation des paramètres, ainsi qu'aux changements de rythme du signal d'entrée. Finallement, une application de cette méthode à la réhabilitation fonctionnelle des patients hémiplégiques est présentée

Restauration fonctionnelle de la posture et de la marche : vers la coordination des membres valides et déficients

When controlling postural movements through artificial prosthetic limbs or Functional Electrical Stimulation, an important issue is the enhancement of the interaction of the patient with the artificial system through his valid limb motions. We address the problem of the coexistence of voluntary controlled with artificially controlled movements. We propose to observe the valid limbs through movement sensors in order to optimize the interaction at two levels: a strategic level, where we aim at identifying as soon as possible the postural task the patient intends to execute, and a tactic level, where we aim at monitoring the ongoing task in order to estimate some movement parameters. Particularly, to ensure legs coordination during walking, the CPG (Central Pattern Generator) concept is introduced, and we propose a robust phase estimation method based on the observer of a non-linear oscillator. This framework mixes discrete and continuous behaviors; this duality raises some integration issues and implies to setup a hybrid command architecture. Two additional constraints are the required number of sensors, as well as the complexity of the algorithms, that both have to be kept as low as possible. The proposed solutions are based on movement models, and have been validated through real time experiments.Ces travaux s'inscrivent dans le cadre de la restauration fonctionnelle du mouvement des membres inférieurs. Plus précisément, nous nous intéressons au problème de la cohabitation entre les mouvements volontaires et les mouvements contrôlés artificiellement par des techniques telles que l'électro-stimulation fonctionnelle. Nous proposons dans cette thèse d'observer le mouvement des membres valides à l'aide de micro-capteurs embarqués pour améliorer le contrôle des membres déficients chez les patients handicapés. Deux niveaux de coordination sont introduits : un niveau stratégique, où l'on cherche à identifier au plus tôt le mouvement que le patient souhaite effectuer, et un niveau tactique, où l'on cherche à estimer des paramètres du mouvement en cours de réalisation. Notamment, pour assurer la coordination des deux jambes durant la marche, le concept de CPG (Central Pattern Generator) est introduit, et nous proposons une méthode robuste de détection de phase basée sur l'observateur d'un oscillateur non-linéaire. Ce cadre de travail mélange des comportements discrets et continus, et implique la mise en place d'une architecture de commande hybride permettant l'intégration de ces deux aspects. Deux contraintes fortes sont la réduction du nombre de capteurs, et la faible complexité des algorithmes. Les solutions proposées font appel à des modèles des mouvements observés, et ont été validées par des expérimentations temps-réel

Online generation of cyclic leg trajectories synchronized with sensor measurement

International audienceThe generation of trajectories for a biped robot is a problem which has been largely studied for several years, and many satisfying offline solutions exist for steady-state walking in absence of disturbances. The question is a little more complex when the generation of the desired trajectories of joints or links has to be achieved or adapted online, i.e. in real time, for example when it is wished to strongly synchronize these trajectories with an external motion. This is precisely the problem addressed in this paper. Indeed, we consider the case where the "master" motion is measured by a position sensor embedded on a human leg. We propose a method to synchronize the motion of a robot or of other device with respect to the output signal of the sensor. The main goal is to estimate as accurately as possible the current phase along the gait cycle. We use for that purpose a model based on a nonlinear oscillator, which we associate an observer. Introducing the sensor output in the observer allows us to compute the oscillator phase and to generate a synchronized multilinks trajectory, at a very low computational cost. The paper also presents evaluation results in terms of robustness against parameter estimation errors and velocity changes in the input

A Magnetometer-Based Approach for Studying Human Movements

International audienceThis paper investigates the use of body-mounted magnetic field sensors for the analysis of certain human movements. We demonstrate that, in several usual dynamic situations, magnetometers allow to estimate accurately a body inclination while being insensitive to its acceleration. Doing this, it is then possible to combine this information together with the one provided by an accelerometer to separate in a very accurate way the gravitational and kinematical components of acceleration. The proposed method is illustrated by the study of the sit-to-stand movement, estimating trunk inclination and absolute acceleration

Réhabilitation Fonctionnelle de la Posture et de la Marche : Vers une Coordination des Membres Valides et Déficients

National audienc

Rehabilitation of Functional Posture and Walking: Coordination of healthy and Impaired Limbs

International audienc

Dispositif et Procédé de Suivi du Mouvement d'un Etre Vivant

Extension : 22/05/08 EP2083684 (A1) JP2010509010 (A) US2009281462 (A1)Le système comprend un capteur (1) mesurant une position du mouvement, un contrôleur artificiel (3) convertissant les signaux du capteur en variables d'état du mouvement complet, corrélées à un modèle de référence, en faisant des ajustements incessants d'estimation de ces variables tirées directement des signaux du capteur au moyen de résultats tirés du modèle de référence. La commande qui est alors fournie pour compléter le mouvement a une bonne synchronisation avec la portion accomplie sans l'aide du système. Application notamment pour reproduire ou compléter la marche d'une personne invalide d'une jambe

Decentralized optimization of energy exchanges in an electricity microgrid

International audienceWe propose to control a local electricity grid, a " microgrid " , in a decentralized fashion to reduce energy costs by coordinating the generation and consumption decisions made by the individual Distributed Energy Resources (DERs) composing the system. Our control scheme relies on the so-called Alternative Direction Method of Multipliers or ADMM, the essentials of which we summarize in the first part of the paper. Then we describe our models for loads, batteries, solar panels and wires before investigating different scenarios in which our coordination scheme may be more beneficial than independent decision-making. The first scenario demonstrates how our coordinated control strategy may reduce total expenses under variable tariffs of energy. Since this first method does not, however, ensure a gain for each user of the microgrid individually, our second scenario explores a slightly different control strategy designed to ensure an individual benefit to each user, at the cost of decreasing the total benefit

Sensing Valid Limb Attitude to Improve Deficient Limb Artificial Control

(Abstracts Conférence International Society for Posture and Gait Research)International audienc