Variable admittance control for climbing stairs in human-powered exoskeleton systems

Abstract

Online gait control in human-powered exoskeleton systems is still rich research field and represents a step towards fully autonomous, safe and intelligent navigation. Admittance Controller performs well on flat terrain walking in human-powered exoskeleton systems for acceleration and slowdown. We are the first who proposed Variable Admittance Controller (VAC) for smooth stair climbing control in Human-Powered Exoskeleton Systems. Trajectory correction technique transforms the interaction forces exerted on the exoskeleton from the pilot to appropriate intended joint flexion angles through dynamic viscoelastic models. We demonstrate the proposed control strategy on one degree-of-freedom (1-DOF) platform first, and then extend to the Human power Augmentation Lower Exoskeleton (HUALEX). The experimental results show that the proposed gait transition control strategy can minimize the interaction dynamics with less interaction force between the pilot and the exoskeleton compared to the traditional admittance controller. Compared to Ordinary Admittance Controller, the proposed VAC significantly improve the normalized Mean Squared Error (nMSE) of trajectory tracking from 2.751° to1.105°.