Variable-Gains Bi-Power Reaching Law of SMC with Terminal Model-Based Switching Surfaces for a 7-DoF Exoskeleton Robot

This paper deals with the problem of robust trajectory tracking of a robot interacting with a human and subject to uncertainties and the problem of chattering in sliding mode. Indeed, a new controller for robotic manipulator systems using terminal model-based sliding manifolds is proposed. Moreover, a bi-power reaching law with variable-gains is designed to reduce the phenomenon of chattering and to ensure fixed-time stability of the exoskeleton robot trajectories into the sliding manifolds. The chattering is not reduced thanks to the new reaching law only but also thanks to the designed model-based sliding manifolds that allow a decoupled control inputs. The proposed controller is experimentally implemented on an upper-limb rehabilitation exoskeleton robot with seven rotary joints. A Comparison study with super-twisting second-order sliding mode is also presented to show the effectiveness of the developed technique.