Safety-enhanced control for a MuscleDrive waist-assistive exoskeleton

Abstract

This study introduces the MuscleDrive Powered Waist-Assistive Exoskeleton (PWE), which is specifically designed with comprehensive safety features in both its hardware and software components. The hardware of the MuscleDrive PWE incorporates fluidic muscle actuators (FMAs) to improve mechanical compliance, taking advantage of their lightweight and elastic properties. The software component features an innovative control system that utilizes the PSTC-RLESO controller. This controller ensures precise and reliable torque trajectory tracking during normal operation and facilitates smooth, safe recovery from significant torque errors during abnormal interactions. Using the Lyapunov stability theorem, this study demonstrates that the closed-loop states of the MuscleDrive PWE with PSTC-RLESO are globally uniformly ultimately bounded (UUB). Experimental comparisons between PSTC-RLESO and a PID controller show that PSTC-RLESO significantly enhances safety during MuscleDrive PWE operation while maintaining efficient tracking performance. In the experiments, safety performance is assessed through damping injection by PSTC-RLESO. Additionally, tests conducted on seven healthy subjects indicate that the MuscleDrive PWE provides adequate torque assistance and ensures user safety, as evidenced by surface electromyography (sEMG) da ta and questionnaire responses.