Force, impedance and trajectory learning for contact tooling and haptic identification

Humans can skilfully use tools and interact with the environment by adapting their movement trajectory, contact force, and impedance. Motivated by the human versatility, we develop here a robot controller that concurrently adapts feedforward force, impedance, and reference trajectory when interacting with an unknown environment. In particular, the robot's reference trajectory is adapted to limit the interaction force and maintain it at a desired level, while feedforward force and impedance adaptation compensates for the interaction with the environment. An analysis of the interaction dynamics using Lyapunov theory yields the conditions for convergence of the closed-loop interaction mediated by this controller. Simulations exhibit adaptive properties similar to human motor adaptation. The implementation of this controller for typical interaction tasks including drilling, cutting, and haptic exploration shows that this controller can outperform conventional controllers in contact tooling

Impairment and Compensation in Dexterous Upper-Limb Function After Stroke. From the Direct Consequences of Pyramidal Tract Lesions to Behavioral Involvement of Both Upper-Limbs in Daily Activities

Impairments in dexterous upper limb function are a significant cause of disability following stroke. While the physiological basis of movement deficits consequent to a lesion in the pyramidal tract is well demonstrated, specific mechanisms contributing to optimal recovery are less apparent. Various upper limb interventions (motor learning methods, neurostimulation techniques, robotics, virtual reality, and serious games) are associated with improvements in motor performance, but many patients continue to experience significant limitations with object handling in everyday activities. Exactly how we go about consolidating adaptive motor behaviors through the rehabilitation process thus remains a considerable challenge. An important part of this problem is the ability to successfully distinguish the extent to which a given gesture is determined by the neuromotor impairment and that which is determined by a compensatory mechanism. This question is particularly complicated in tasks involving manual dexterity where prehensile movements are contingent upon the task (individual digit movement, grasping, and manipulation…) and its objective (placing, two step actions…), as well as personal factors (motivation, acquired skills, and life habits…) and contextual cues related to the environment (presence of tools or assistive devices…). Presently, there remains a lack of integrative studies which differentiate processes related to structural changes associated with the neurological lesion and those related to behavioral change in response to situational constraints. In this text, we shall question the link between impairments, motor strategies and individual performance in object handling tasks. This scoping review will be based on clinical studies, and discussed in relation to more general findings about hand and upper limb function (manipulation of objects, tool use in daily life activity). We shall discuss how further quantitative studies on human manipulation in ecological contexts may provide greater insight into compensatory motor behavior in patients with a neurological impairment of dexterous upper-limb function

Design and acceptability assessment of a new reversible orthosis

International audience— We present a new device aimed at being used for upper limb rehabilitation. Our main focus was to design a robot capable of working in both the passive mode (i.e. the robot shall be strong enough to generate human-like movements while guiding the weak arm of a patient) and the active mode (i.e. the robot shall be able of following the arm without disturbing human natural motion). This greatly challenges the design, since the system shall be reversible and lightweight while providing human compatible strength, workspace and speed. The solution takes the form of an orthotic structure, which allows control of human arm redundancy contrarily to clinically available upper limb rehabilitation robots. It is equipped with an innovative transmission technology, which provides both high gear ratio and fine reversibility. In order to evaluate the device and its therapeutic efficacy, we compared several series of pointing movements in healthy subjects wearing and not wearing the orthotic device. In this way, we could assess any disturbing effect on normal movements. Results show that the main movement characteristics (direction, duration, bell shape profile) are preserved

Movement-Based Control for Upper-Limb Prosthetics: Is the Regression Technique the Key to a Robust and Accurate Control?

Due to the limitations of myoelectric control (such as dependence on muscular fatigue and on electrodes shift, difficulty in decoding complex patterns or in dealing with simultaneous movements), there is a renewal of interest in the movement-based control approaches for prosthetics. The latter use residual limb movements rather than muscular activity as command inputs, in order to develop more natural and intuitive control techniques. Among those, several research works rely on the interjoint coordinations that naturally exist in human upper limb movements. These relationships are modeled to control the distal joints (e.g., elbow) based on the motions of proximal ones (e.g., shoulder). The regression techniques, used to model the coordinations, are various [Artificial Neural Networks, Principal Components Analysis (PCA), etc.] and yet, analysis of their performance and impact on the prosthesis control is missing in the literature. Is there one technique really more efficient than the others to model interjoint coordinations? To answer this question, we conducted an experimental campaign to compare the performance of three common regression techniques in the control of the elbow joint on a transhumeral prosthesis. Ten non-disabled subjects performed a reaching task, while wearing an elbow prosthesis which was driven by several interjoint coordination models obtained through different regression techniques. The models of the shoulder-elbow kinematic relationship were built from the recordings of fifteen different non-disabled subjects that performed a similar reaching task with their healthy arm. Among Radial Basis Function Networks (RBFN), Locally Weighted Regression (LWR), and PCA, RBFN was found to be the most robust, based on the analysis of several criteria including the quality of generated movements but also the compensatory strategies exhibited by users. Yet, RBFN does not significantly outperform LWR and PCA. The regression technique seems not to be the most significant factor for improvement of interjoint coordinations-based control. By characterizing the impact of the modeling techniques through closed-loop experiments with human users instead of purely offline simulations, this work could also help in improving movement-based control approaches and in bringing them closer to a real use by patients

Phantom-Mobility-Based Prosthesis Control in Transhumeral Amputees Without Surgical Reinnervation: A Preliminary Study

Transhumeral amputees face substantial difficulties in efficiently controlling their prosthetic limb, leading to a high rate of rejection of these devices. Actual myoelectric control approaches make their use slow, sequential and unnatural, especially for these patients with a high level of amputation who need a prosthesis with numerous active degrees of freedom (powered elbow, wrist, and hand). While surgical muscle-reinnervation is becoming a generic solution for amputees to increase their control capabilities over a prosthesis, research is still being conducted on the possibility of using the surface myoelectric patterns specifically associated to voluntary Phantom Limb Mobilization (PLM), appearing naturally in most upper-limb amputees without requiring specific surgery. The objective of this study was to evaluate the possibility for transhumeral amputees to use a PLM-based control approach to perform more realistic functional grasping tasks. Two transhumeral amputated participants were asked to repetitively grasp one out of three different objects with an unworn eight-active-DoF prosthetic arm and release it in a dedicated drawer. The prosthesis control was based on phantom limb mobilization and myoelectric pattern recognition techniques, using only two repetitions of each PLM to train the classification architecture. The results show that the task could be successfully achieved with rather optimal strategies and joint trajectories, even if the completion time was increased in comparison with the performances obtained by a control group using a simple GUI control, and the control strategies required numerous corrections. While numerous limitations related to robustness of pattern recognition techniques and to the perturbations generated by actual wearing of the prosthesis remain to be solved, these preliminary results encourage further exploration and deeper understanding of the phenomenon of natural residual myoelectric activity related to PLM, since it could possibly be a viable option in some transhumeral amputees to extend their control abilities of functional upper limb prosthetics with multiple active joints without undergoing muscular reinnervation surgery

Effects of Hand Configuration on the Grasping, Holding, and Placement of an Instrumented Object in Patients With Hemiparesis

Objective: Limitations with manual dexterity are an important problem for patients suffering from hemiparesis post stroke. Sensorimotor deficits, compensatory strategies and the use of alternative grasping configurations may influence the efficiency of prehensile motor behavior. The aim of the present study is to examine how different grasp configurations affect patient ability to regulate both grip forces and object orientation when lifting, holding and placing an object.Methods: Twelve stroke patients with mild to moderate hemiparesis were recruited. Each was required to lift, hold and replace an instrumented object. Four different grasp configurations were tested on both the hemiparetic and less affected arms. Load cells from each of the 6 faces of the instrumented object and an integrated inertial measurement unit were used to extract data regarding the timing of unloading/loading phases, regulation of grip forces, and object orientation throughout the task.Results: Grip forces were greatest when using a palmar-digital grasp and lowest when using a top grasp. The time delay between peak acceleration and maximum grip force was also greatest for palmar-digital grasp and lowest for the top grasp. Use of the hemiparetic arm was associated with increased duration of the unloading phase and greater difficulty with maintaining the vertical orientation of the object at the transitions to object lifting and object placement. The occurrence of touch and push errors at the onset of grasp varied according to both grasp configuration and use of the hemiparetic arm.Conclusion: Stroke patients exhibit impairments in the scale and temporal precision of grip force adjustments and reduced ability to maintain object orientation with various grasp configurations using the hemiparetic arm. Nonetheless, the timing and magnitude of grip force adjustments may be facilitated using a top grasp configuration. Conversely, whole hand prehension strategies compound difficulties with grip force scaling and inhibit the synchrony of grasp onset and object release

Contributions à l'exploitation d'exosquelettes actifs pour la rééducation neuromotrice

Neuro-motor rehabilitation is one the the new application areas of physically interactive robots. In this domain, the aim is to design machines that are able of assisting an impaired patient's motions when he/she practices physical exercises. One of the key topics is to provide machines capable of finely mastering mechanical forces distributed along human members. This has motivated the development of robotic exoskeletons. However, most of the research so far has focused on kinematics of these devices, with little attention paid to the force transmission question. Rather, this thesis is mostly dedicated to this crucial aspect. The main contributions are in the domain of design and control of robotic exoskeletons, with a main objective defined by the quality of force control. In the domain of design, we have exploited literature results regarding the robot structure and actuation mechatronics. Indeed, a starting point of this research is an existing back-drivable exoskeleton called ABLE, designed by CEA-LIST for assisting human arm. Given this particular robot, which is representative of the state of the art in terms of mechanical properties, we have worked on the mechanical coupling between the robot and the human arm. This has yielded to a general method aimed at designing passive fixation mechanisms between exoskeletons and human members. These mechanisms allows to guarantee global isostaticity and to select transmitted forces in such a way that they are fully controllable. The method is successfully applied to ABLE, with experimental evidence of an increased quality of interaction. Regarding the control aspects, our work has focused on the so-called transparent mode, when the robot has to follow the patient's movement while minimizing the disturbances. We have deployed an original multi-contact force controller, which also uses as an input a prediction of the patient's movement. This mixed force/position controller is, again, successfully experimented on ABLE. A last result of this work concerns evaluation of the interaction quality during comanipulation tasks. Indeed, in order to be able of quantifying improvements brought by design and control developments, it has been necessary to setup a method aimed at reproducibly evaluate the quality of human-robot physical interaction. This is achieved through analyzing simultaneous records of forces and gesture kinematics.La rééducation neuromotrice est un des nouveaux champs d'application de la robotique en interaction physique. Dans ce domaine, on cherche à concevoir des machines pouvant assister les mouvements de patients atteints de troubles neuromoteurs dans la réalisation d'exercices physiques. Un des enjeux importants est de pouvoir proposer des machines capables de maîtriser des efforts mécaniques distribués le long des membres du patient durant les mouvements. Ceci a conduit la communauté à travailler au développement de structure exosquelettiques. L'essentiel des recherches en cours est focalisé sur les aspects cinématiques plus que sur le problème des transmissions d'efforts. C'est au contraire à ces aspects cruciaux qu'est consacrée la présente thèse. Pour améliorer la qualité du contrôle des efforts dans la mise en oeuvre des exosquelettes robotiques, les principales contributions se situent dans les domaines de la conception et de la commande. S'agissant de la conception, nous avons exploité des résultats existants dans la littérature pour la structure mécanique et la mécatronique d'actionnement, en utilisant l'exosquelette réversible ABLE conçu au CEA LIST. Partant de ce modèle, représentatif de l'existant, nous avons travaillé sur le problème du couplage mécanique entre le robot et le bras. Ce travail a permis de proposer une méthode générale pour synthétiser des mécanismes de fixation articulés passifs entre un exosquelette et un membre humain. Les fixations ainsi conçues garantissent l'isostaticité globale de l'ensemble. L'étude théorique générale est appliquée à ABLE, montrant une amélioration nette de la qualité de l'interaction. S'agissant de la commande, nous avons déployé une commande en efforts multi-contacts, ce qui constitue en soit une originalité, puis proposé de faciliter l'accompagnement des mouvements du sujet en exploitant une anticipation de trajectoire, grâce à un contrôleur mixte force/position. Là encore, l'apport expérimental évalué sur l'exosquelette ABLE est probant. Un dernier résultat important de la thèse concerne l'évaluation de la qualité de l'interaction homme-exosquelette dans des tâches de comanipulation. En effet, pour pouvoir quantifier l'apport des différentes propositions dans le domaine de la conception et de la commande, nous avons dû établir une méthode permettant d'étudier de manière reproductible l'interaction physique homme-robot, en analysant simultanément les efforts et la cinématique des gestes

Prothèses robotiques : vers un nouveau dualisme ?

L’objectif de cette étude est prioritairement d’apporter un point de vue technique sur les dispositifs technologiques de réparation du corps, aspect d’autant plus nécessaire pour conduire une réflexion réaliste et solide sur les relations entre l’homme, la société et la technologie, que se produit un décalage croissant entre la réalité technique et l’imaginaire technologique ; il conviendra donc aussi de s’attacher à en comprendre les causes, en espérant enrayer l’apparition d’un nouveau dual..