Human-Robot Cooperative Adaptive Reinforcement Constraint Control for a Lower Limb Rehabilitation Exoskeleton Based on User’s Movement Intention

Exoskeletons used for rehabilitation must operate together with the patient to adapt to the biomechanical-inspired movements of the regular human gait cycle rather than operate by following a predefined trajectory without considering the human-robot interaction effects. This work presents the assessment of a lower limb exoskeleton whose motion is performed according to a collaborative approach given the movements of the human user and the relative force concerning the exoskeleton structure. The Opensim™ software serves to define the force and position reference trajectories to follow during the gait cycle, which serves as a reference for the hybrid control. These forces and movements are compared to the results of a virtual model that considers the interaction between the user and the exoskeleton in two possible scenarios. The first scenario contemplates the implementation of a position controller to generate interaction-independent movement of the exoskeleton. The second scenario considers the force exerted by the exoskeleton on the patient to trigger a force-based controller after trespassing a predefined value. This leads to a hybrid control scheme, which considers the position restrictions in the closed-loop feedback control strategy. Using this approach, the exoskeleton can collaborate actively with the user and provide motion as required, responding to position-controlled motion if the user is not opposed to the exoskeleton motion. This novel strategy permits the evaluation of a hybrid position-force controller for wearing the active orthosis. Numeric simulations show the performance of the proposed system. These outcomes confirm the supposed advantages of the proposed controller.

I. Introduction

Lower limb exoskeletons are active anthropomorphic wearable robotic orthoses supporting and providing regulated motion to the inferior section of the body. Depending on the rehabilitation task, the exoskeleton must enforce the controlled motion of articulations or align with the user’s motion [1]. According to their functionality and contribution to human activity, these devices can be categorized within the following main groups [2]: •

Human performance augmentation exoskeletons are intended for healthy users and do not replace any ability nor help the user recover the lost capacities [3].

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Assistance exoskeletons are mainly used by patients who permanently lose the ability to walk using these devices for daily activities [4].

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Rehabilitation exoskeletons aimed to help patients regain mobility through repetitive training strategies [5].