A Rigid-Flexible Integrated Ankle Dorsiflexion Exoskeleton for Gait Assistance: Design, Control, and Characterization

Abstract

The ankle joint is the core hub of human walking and bears the gait load. Its flexibility and stability are crucial to balance walking efficiency, and damage prevention. Insufficient dorsiflexion torque can significantly reduce walking efficiency and stability. Therefore, this paper designs an ankle exoskeleton to assist dorsiflexion motion. Firstly, the system adopts a rigid-flexible integrated structural design, meeting the wearer’s rigid support while reducing the quality of the exoskeleton system and increasing the flexibility to the wearer. Meanwhile, a cable-driven and load alignment transmission structure was designed to improve interaction comfort and data acquisition accuracy. Secondly, a multi-sensor feature-level perception system fused with hidden markov models (HMM) is proposed to accurately identify different gait types. Finally, an impedance control strategy based on force-position feedback is constructed to provide suitable assistive moments for users to walk at different velocities. Four subjects participated in surface electromyography (sEMG) and metabolic cost experiments. Experimental results show that exoskeleton equipment achieves precise assisting ranges, and the Rate of Change with average dorsiflexion sEMG signal and metabolic cost reduction with exoskeleton assistance is 18.52% and 11.49% respectively compared with unwearing conditions.