Development and iterative learning-enhanced sliding mode control of a bioinspired knee exoskeleton

Abstract

This paper introduces a novel knee exoskeleton designed to provide assistive torque to the knee joint and facilitate postoperative rehabilitation. Drawing inspiration from the anatomy of the human knee joint, the exoskeleton incorporates a biomimetic structure that integrates the “optimal axis of rotation” with the trajectory of the instantaneous center of rotation. This design effectively mitigates the issue of kinematic misalignment in the human-machine joint, offering a more comfortable wearing experience for users. Furthermore, a highly integrated quasi-direct drive system is incorporated into the knee exoskeleton. The drive system can deliver a continuous torque of 18 N·m and a peak torque of 45 N·m to sufficiently meet the daily walking needs of patients. From a control perspective, a unified sliding mode control strategy based on iterative learning control is proposed to maintain high tracking accuracy. This strategy enables the system to achieve accurate tracking of the knee motion trajectory by continuously updating the control inputs through successive gait cycles. Experimental results demonstrate that the designed biomimetic joint mechanism effectively resolves the issue of misalignment in the human-machine joint. Furthermore, the synergistic control strategy demonstrates excellent steady-state precision and transient robustness in terms of trajectory tracking during human-exoskeleton cooperative walking.

Keywords

Human-machine misalignment / Knee exoskeleton / Sliding mode control / Iterative learning control

References

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The Authors. Published by Zhejiang University Press Co., Ltd.