Human-in-the-Loop Cooperative Control of a Walking Exoskeleton for Following Time-Variable Human Intention.

Abstract

This article presents a human-in-the-loop cooperative control of a walking exoskeleton to provide assistance to the user and enhance human mobility. First, a dynamic mathematical model of the human-exoskeleton system is derived, and then, a human-in-the-loop cooperative control framework is proposed in two ways: separable cooperative control (SCC) and interactive cooperative control (ICC), respectively. The SCC introduces a space division of the human and the exoskeleton, while the ICC allows the robot to perceive the human intention and follows human motor, thereby improving the collaborative performance. The ICC formulates the impedance connection between the human and the exoskeleton in the divided orthogonal subspaces of walking, such that the robot is able to modify its position of center of mass (COM) when its motor trajectory deviates the one of the human. In addition, a novel adaptation control is proposed to deal with the unmodeled dynamics and trajectory tracking. Finally, to validate the effectiveness of our proposed controller, a series of experiments are conducted in three adults in gait at different speeds. It shows that the proposed controller can preserve the periodic walking gait and inherit the robustness of dealing with perturbations during walking.