Robust and Safe Control of a Knee Joint Orthosis

This paper concerns the control of a knee joint orthosis for rehabilitation and assistive purpose. The dynamics of shank-orthosis system can be represented as a second order nonlinear model which takes viscous, inertial and gravitational properties into consideration and the human effort is considered as an external torque. In this paper, an adaptive proxy-based sliding mode control (APSMC) is proposed to guarantee an accurate and robust tracking performance of shank-orthosis system. The main advantages of this control law are 1) on-line parameters regulation which ensures a better tracking performance and robustness with respect to parameter uncertainties and external disturbance. 2) the safety of the robot is guaranteed in the presence of a large tracking error which results from the abnormal operation. The effectiveness of the APSMC is verified by comparison with three control methods, PID control, adaptive PID control and traditional proxy-based sliding mode control, in the real-time experiments using knee orthosis with two healthy subjects. The experiment results show that APSMC improves tracking accuracy and robustness. Last but not least, the intrinsic safety is guaranteed by APSMC.