A New Integral Second-Order Terminal Sliding Mode Control with Time Delay Estimation for an Exoskeleton Robot with Dynamics Uncertainties

This paper presents a new Integral Second-Order Terminal Sliding Mode Control incorporating Time Delay Estimation applied to passive rehabilitation protocols of an exoskeleton robot with dynamics uncertainties and unknown bounded disturbances. The use of second-order sliding mode is due to its attractive characteristics of accuracy, attenuation of chattering and fast convergence. However, its problem is that the unknown dynamic of the exoskeleton robot and external disturbances caused by its different wearers can be amplified by the second derivative of the sliding surface, which leads to instability of the exoskeleton system. Using Time Delay Estimation will estimate the uncertain dynamics while overcoming the main limitation of second-order sliding mode. The stability analysis is formulated and proved based on Lyapunov function. An experimental session with a healthy subject was set up to test the effectiveness of the proposed control.