Disturbance Observer-Based Terminal Sliding Mode Control of a 5-DOF Upper-Limb Exoskeleton Robot

Peng Yang,Yan Zhang,Gaowei Zhang,Jie Wang,Lingling Chen,Xiao Ma

doi:10.1109/access.2019.2911348

Abstract

In this paper, a finite-time control strategy composed of disturbance observer and sliding mode controller is investigated for five-degree of freedom (5-DOF) upper-limb exoskeleton subject to system uncertainties and external disturbances. First, a new finite-time disturbance observer (FTDO) is constructed to handle unknown disturbances and modeling uncertainties. Second, a nonsingular fast terminal sliding mode (TSM) approach is presented to follow the desired joint angles. By combining the novel FTDO and the nonsingular fast TSM technology, the exoskeleton angle tracking errors can be forced to zero within a finite time. Furthermore, the stability of the exoskeleton system is illustrated via Lyapunov. Finally, the tracking performance of the proposed control scheme is verified by simulations.

Highlights

Exoskeleton robots have been explored for decreasing labor intensity or medical rehabilitation in recent years
In [14], sliding mode controller is employed to cope with nonlinear nature and reject uncertainties and disturbances of an exoskeleton robot
Yang et al.: Disturbance Observer-Based terminal sliding mode (TSM) Control of a 5 degrees of freedom (5-DOF) Upper-Limb Exoskeleton Robot to realize the exoskeleton to move according to human motion intention in the presence of uncertainties

Summary

INTRODUCTION

Exoskeleton robots have been explored for decreasing labor intensity or medical rehabilitation in recent years. In [14], sliding mode controller is employed to cope with nonlinear nature and reject uncertainties and disturbances of an exoskeleton robot. P. Yang et al.: Disturbance Observer-Based TSM Control of a 5-DOF Upper-Limb Exoskeleton Robot to realize the exoskeleton to move according to human motion intention in the presence of uncertainties. The information of system uncertainties and external disturbances can be estimated and compensate controller of exoskeleton robot to improve system robustness. Owing to the feedforward compensation, the proposed TSM combining the FTDO without opting large feedback gains can alleviate the chattering problem and guarantee fast and accurate tracking performance; (ii) On the basis of accurate disturbance estimation, the nonsingular fast TSM is applied to realize finite time stability of the whole exoskeleton robot. DESIGN PROCESS OF CONTROLLER This part constructs a nonsingular fast TSM controller for exoskeleton system combined with FTDO technique

FTDO DESIGN

NONSINGULAR FAST TSM CONTROLLER DESIGN

SIMULATION

CONCLUSIONS