Feedback Control of an Exoskeleton for Paraplegics: Toward Robustly Stable Hands-free Dynamic Walking

This manuscript presents control of a high-DOF fully actuated lower-limb exoskeleton for paraplegic individuals. The key novelty is the ability for the user to walk without the use of crutches or other external means of stabilization. We harness the power of modern optimization techniques and supervised machine learning to develop a smooth feedback control policy that provides robust velocity regulation and perturbation rejection. Preliminary evaluation of the stability and robustness of the proposed approach is demonstrated through the Gazebo simulation environment. In addition, preliminary experimental results with (complete) paraplegic individuals are included for the previous version of the controller.Comment: Submitted to IEEE Control System Magazine. This version addresses reviewers' concerns about the robustness of the algorithm and the motivation for using such exoskeleton

Development of a hybrid PIC code for the simulation of plasma spacecraft interactions

Electric propulsion is gaining popularity in space industry. This type of propulsion is replacing chemical propulsion for different maneuvers. But it deeply modifies the ambient plasma that surrounds the satellites and can affect the operation of satellites. Modelling the interactions arising from electric propulsion is then critical. In the frame of SPIS, a simulation software designed to simulate plasma-spacecraft interactions, European Space Agency (ESA) started the AISEPS project which aimed at modelling these interactions. Here, we report the development of new features for SPIS during the last phase of the AISEPS project, how they operate and were tested. Using these developments, a complete spacecraft is modelled and the variation of its floating potential resulting from its solar array rotation is reproduced

Estimation of multiple flexibilities of an articulated system using inertial measurements

International audienceFor many articulated systems (i.e. systems com- posed of several mechanically connected objects), the assumption of full rigidity is only a mere approximation. The various flexibilities of the structure, if not accounted for, all hinder the positioning ability of the device, by generating biases in the estimations determined from rigid models. In this paper, we propose a sensor-based methodology for estimating the flexibilities of an open kinematic chain. To estimate the real position and orientation of the elements of the system, we reconcile data from Inertial Measurement Units (IMU) with the kinematics of the rigid system. We show that, under a model of punctual, spring-like deformations, this methodology allows one to observe all the deformations, if one IMU is installed downstream of each deformation in the chain. We design and test such an observer in simulation and on an exoskeleton, where it proved a suitable way of estimating the position of the flying foot. Experimental results, validated against a motion capture device, demonstrate the ability of this observer to fully capture the dynamics induced by these flexibilities

Towards Restoring Locomotion for Paraplegics: Realizing Dynamically Stable Walking on Exoskeletons

This paper presents the first experimental results of crutch-less dynamic walking with paraplegics on a lower-body exoskeleton: ATALANTE, designed by the French start-up company Wandercraft. The methodology used to achieve these results is based on the partial hybrid zero dynamics (PHZD) framework for formally generating stable walking gaits. A direct collocation optimization formulation is used to provide fast and efficient generation of gaits tailored to each patient. These gaits are then implemented on the exoskeleton for three paraplegics. The end result is dynamically stable walking in an exoskeleton without the need for crutches. After a short period of tuning by the engineers and practice by the subjects, each subject was able to dynamically walk across a room of about 10 m up to a speed of 0.15 m/s (0.5 km/h) without the need for crutches or any other kind of assistance

Towards Restoring Locomotion for Paraplegics: Realizing Dynamically Stable Walking on Exoskeletons

This paper presents the first experimental results of crutch-less dynamic walking with paraplegics on a lower-body exoskeleton: ATALANTE, designed by the French start-up company Wandercraft. The methodology used to achieve these results is based on the partial hybrid zero dynamics (PHZD) framework for formally generating stable walking gaits. A direct collocation optimization formulation is used to provide fast and efficient generation of gaits tailored to each patient. These gaits are then implemented on the exoskeleton for three paraplegics. The end result is dynamically stable walking in an exoskeleton without the need for crutches. After a short period of tuning by the engineers and practice by the subjects, each subject was able to dynamically walk across a room of about 10 m up to a speed of 0.15 m/s (0.5 km/h) without the need for crutches or any other kind of assistance