Robust Control of a 2-DOF Lower Limb Exoskeleton Rehabilitation Robot Using Nonsingular Terminal Sliding Mode

Abstract

In the training of patients assisted by lower limb exoskeleton rehabilitation robots (LLERRs), precise control is desired under a given trajectory to achieve a certain training effect. In this paper, a nonsingular terminal sliding mode (NTSM) control strategy is put forward for a 2-degree-of-freedom (DOF) LLERR. Initially, a Lagrange equation is used to establish the dynamic model of the 2-DOF LLERR. Then, the NTSM controller is designed for the LLERR, where the stability of the closed-loop control system is substantiated in the Lyapunov sense. For comparison, a conventional PID controller is also designed as the benchmark. Finally, MATLAB-OpenSim co-simulations are carried out to test the control performance with disturbance. The simulation results illustrate that the proposed NTSM control method possesses apparent advantages, which is reflected in higher tracking precision and tougher robustness compared with the benchmark controller.