Adaptive Super-Twisting Sliding Mode Control To Drive Knee Joint Actuated Orthosis

This paper presents the design of a robust control algorithm for precise positioning control of a knee joint orthosis system used for rehabilitation purposes. In order to guarantee operational safety and robustness in the presence of complex dynamical modelling errors and sinusoidal movement scenarios, a super twisting second-order sliding mode control (SOSMC) is formulated to suppress the chattering issue that arises in traditional sliding mode control by using a threshold parameter with respect to the Lyapunov function in the adaptive law, guaranteed to have finite-time stable trajectory performance. Stability analysis of the proposed approach is demonstrated in the closed loop using Lyapunov theory. Finally, numerical simulation results illustrate promising tracking performance in terms of tracking error, stability, and robustness of the system against the co-contraction test.