Fast-terminal sliding mode control based on dynamic boundary layer for lower limb exoskeleton rehabilitation robot

Aiming at the chattering problem of sliding mode control in the trajectory tracking of lower limb exoskeleton rehabilitation robot (LLERR), this paper proposes a fast-terminal sliding mode control based on dynamic boundary layer (DFTSMC) for LLERR. First, based on the fast-terminal sliding mode surface and the double power reaching law, the compensation term of the control law is designed. Then, a dynamic boundary layer is designed to suppress the chattering of the system state. Finally, based on the virtual prototype of LLERR, a co-simulation is carried out with Matlab and Recurdyn multi-body dynamics software. The traditional PID control based on the computed torque method, the traditional fast-terminal sliding mode control (FTSMC) and the DFTSMC were compared. The control performance of fast terminal sliding mode control and the simulation results show that the DFTSMC improves the convergence speed of the system state, suppress the chattering of the sliding mode control and enhances the robust performance of LLERR.