Non-linear sliding mode control of the lower extremity exoskeleton based on human–robot cooperation

• Published in: International journal of advanced robotic systems Vol. 13; no. 5
• Main Authors: Zhu, Shiqiang, Jin, Xinglai, Yao, Bin, Chen, Qingcheng, Pei, Xiang, Pan, Zhongqiang
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 11.10.2016; Sage Publications Ltd; SAGE Publishing
• Subjects: Anthropomorphism; Computer simulation; Control stability; Control systems design; Controllers; Cooperation; Electromyography; Exoskeletons; Jacobi matrix method; Jacobian matrix; Kinematics; Least squares method; Methods; Neural networks; Nonlinear control; Radial basis function; Robots; Robust control; Sensors; Sliding mode control; Stability analysis; Surface stability; Tracking; China; lower extremity exoskeleton; Human–robot cooperation; RBF neural network; inverse Jacobian matrix; non-linear sliding mode control; saturation function
• ISSN: 1729-8806; 1729-8814
• DOI: 10.1177/1729881416662788

This article presents a human–robot cooperation controller towards the lower extremity exoskeleton which aims to improve the tracking performance of the exoskeleton and reduce the human–robot interaction force. Radial basis function neural network is introduced to model the human–machine interaction which can better approximate the non-linear relationship than the general impedance model. A new method to calculate the inverse Jacobian matrix is presented. Compared to traditional damped least squares method, the novel method is proved to be able to avoid the orientation change of the velocity of the human–robot interaction point by the simulation result. This feature is very important in human–robot system. Then, an improved non-linear robust sliding mode controller is designed to promote the tracking performance considering system uncertainties and model errors, where a new non-linear integral sliding surface is given. The stability analysis of the proposed controller is performed using Lyapunov stability theory. Finally, the novel methods are applied to the swing leg control of the lower extremity exoskeleton, its effectiveness is validated by simulation and comparative experiments.