Singular Wire-Driven Series Elastic Actuation with Force Control for a Waist Assistive Exoskeleton, H-WEXv2

Abstract

This article presents a design of an electrically powered waist-assistive exoskeleton H-WEXv2 to reduce back-muscle fatigue and prevent back-injury of industrial workers. It utilizes a wire-driven mechanism based on a singular series elastic actuation to achieve system performances in aspect of cost, weight, operational time, and system endurance and maintainability for industrial feasibility. This proposed mechanism consisting of a ball screw drive and a series elastic actuator enables H-WEXv2 to accomplish better control maneuverability on powered flexion/extension while maintaining the advantage of allowing natural human walking with almost zero impedance. Also, to transfer torque determined by a high-level controller, a SEA force controller was implemented by measuring elastic displacements of installed spring elements at both hip joints. In order to evaluate the effectiveness of the developed robot installed with the proposed mechanism, electromyographic (EMG) signals of relevant muscles of ten subjects related to target waist motions were measured and compared for three cases: 1) wearing H-WEXv1, 2) wearing H-WEXv2, and 3) wearing nothing. Finally, the statistical analysis on acquired EMG signals verified the effectiveness of waist assistance provided by H-WEXv2.