An Adaptive Sliding Mode Variable Admittance Control Method for Lower Limb Rehabilitation Exoskeleton Robot

Yao Tu,Huang Shen,Guangzhong Cao,Jiyuan Song,Xiaodong Zhang,Aibin Zhu,Zhitao Shen

doi:10.3390/app10072536

Abstract

As passive rehabilitation training with fixed trajectory ignores the active participation of patients, in order to increase the active participation of patients and improve the effect of rehabilitation training, this paper proposes an innovative adaptive sliding mode variable admittance (ASMVA) controller for the Lower Limb Rehabilitation Exoskeleton Robot. The ASMVA controller consists of an outer loop with variable admittance controller and an inner loop with an adaptive sliding mode controller. It estimates the wearer’s active muscle strength and movement intention by judging the deviation between the actual and standard interaction force of the wearer’s leg and the exoskeleton, thereby adaptively changing admittance controller parameters to alter training intensity. Three healthy volunteers engaged in further experimental studies, including trajectory tracking experiments with no admittance, fixed admittance, and variable admittance adjustment. The experimental results show that the proposed ASMVA control scheme has high control accuracy. Besides, the ASMVA can not only increase training intensity according to the active muscle strength of the patient during positive movement intention (so as to increase active participation of the patient), but also increase the amount of trajectory adjustment during negative movement intention to ensure the safety of the patient.

Highlights

With increase in the global aging population, the number of patients with lower limb dyskinesia caused by diseases such as locomotive syndrome and sarcopenia is on the rise
It can increase the training intensity according to the active muscle strength of the patient during the patient’s active movement intention to increase the patient’s active participation, and increase the trajectory adjustment amount during the patient’s negative movement intention to ensure patient’s safety
This paper presented a human-exoskeleton coordinated control strategy based on adaptive sliding mode variable admittance control method for a lower limb rehabilitation exoskeleton robot, which could estimate the patient’s active joint torque based on human-exoskeleton interaction force, adjust the control parameters of the admittance controller adaptively according to the patient’s movement intention, and increase the flexibility of interaction and active participation of the patients

Summary

Introduction

With increase in the global aging population, the number of patients with lower limb dyskinesia caused by diseases such as locomotive syndrome and sarcopenia is on the rise. According to research on medical theory and clinical experience, patients with locomotive syndrome and sarcopenia can prevent muscle atrophy and promote muscle functional recovery through high-intensity and repetitive exercise rehabilitation training [1]. The lower limb rehabilitation exoskeleton (LLRE) robot is a human mechatronic system that integrates the robot and the wearer [2]. By simulating normal human walking gait, it helps patients with lower limb motor dysfunction to exercise lower limb muscles and restore function [3,4]. In the study of LLRE, especially in control strategies and methods, researchers focus.

Methods

Results

Discussion

Conclusion