Adaptive Force and Position Control Based on Quasi-Time Delay Estimation of Exoskeleton Robot for Rehabilitation

Rehabilitation robots have become an influential tool in physical therapy treatment since they are able to provide an intensive rehabilitation treatment for a long period of time. However, this technology still suffers from various problems such as dynamics uncertainties, external disturbances, and human-robot interaction. In this paper, we present a new integral second-order terminal sliding mode control incorporating quasi-time delay estimation (Q-TDE) applied to an exoskeleton robot with dynamics uncertainties and unknown bounded disturbances. Unlike the conventional TDE approach, the proposed Q-TDE uses delayed one step only of the control input of the system to approximate the uncertain dynamics while avoiding the delays on all states of the system. The proposed controller aims to perform passive and active rehabilitation protocols without the need for velocity and acceleration measurements of the robot system. A finite time of both selected sliding surface and estimation error simultaneous is achieved using an appropriate Lyapunov function. Experimental results with healthy subjects found using a virtual reality environment confirm the effectiveness of the proposed control.