Enhancing Human Walking Economy Through a Biomimetic Cable-Driven Ankle Exoskeleton

Enhancing the walking economy is a primary goal in the application of exoskeletons for gait assistance. However, traditional exoskeletons often face challenges due to rigid designs and the additional distal mass they introduce, limiting their effectiveness. In this study, inspired by the muscle-tendon complex of the human calf, we present a cable-driven ankle exoskeleton designed to provide targeted assistance during plantarflexion movements at the ankle joint. The proposed exoskeleton integrates a compact, lightweight actuation unit with a flexible fabric shank sleeve, ensuring efficient torque transmission from the motor to the ankle joint. A feedback-based cascaded repetitive control system, combined with a multi-sensor fusion communication framework, was developed to achieve precise force control. The system's actuation performance was evaluated through benchtop experiments, demonstrating a bandwidth of approximately 13.5 Hz and a force tracking error of 5 % under position disturbances. Treadmill experiments further validated the effectiveness of the exoskeleton, showing a 7.53 % improvement in walking economy compared to no-assistance conditions. These findings highlight the potential of the proposed design to advance the development of cable-driven exoskeletons for improved gait assistance.