Precision Cascade Force Control of Multi-DOF Hydraulic Leg Exoskeleton

Hydraulic exoskeleton is a kind of the human robot interaction system, which can augment the human performance in the application of heavy load carrying. Due to the existence of complicated multijoint nonlinear dynamics and various uncertainties, traditional robust control of these systems is hard to be realized in most of the practical research. In this paper, an adaptive robust cascade force controller is proposed for 3-DOF hydraulic leg exoskeleton to achieve accurate tracking of human motion. Specifically, the control strategy includes two levels. The desired joint positions, which can be assumed as the human motion intent as well, are generated in the high-level by attenuating the integral of human-machine interaction force. And in the low-level, an observer-based MIMO motion controller is developed for 3-DOF dynamics to track the generated human motion intent accurately. Adaptive robust control algorithms are developed in both control levels to address the strongly coupled high-order dynamics under parametric uncertainties and uncertain disturbances. Comparative simulations show that the human-machine interaction force can be attenuated exactly and robust performance to various uncertainties can be guaranteed, validating the effectiveness of the proposed scheme.