Design and Evaluation of a Bilateral Mobile Ankle Exoskeleton With High-Efficiency Actuation

Lower-limb exoskeletons can improve human mobility and endurance, especially for people with leg impairments. To minimize metabolic penalty and maximize assistance capacity, the design of the mobile exoskeleton needs to compromise between the system weight and actuation power. In the paper, we developed a lightweight high-torque mobile bilateral ankle exoskeleton with compliant end-effectors and a high-efficiency actuation. The system can provide 80 Nm assistive torques for both ankles with 3.4 kg entire exoskeleton weight by actuators' parallel connection and cooperative operation. Developed embedded hardware implemented a real-time torque controller comprising the damping-injected feedback control, model-based feedforward compensation, and iterative learning, achieving more than 10 Hz gain-limited closed-loop bandwidths and less than 2% torque tracking error. Preliminary physiological experiments demonstrated the exoskeleton's ability to reduce soleus muscle activities by over 50% at different walking speeds. Our work proved that the lightweight exoskeleton system can provide rather large torque assistance with fairly good bandwidth and tracking accuracy, promising to promote more exoskeleton applications in real life and rehabilitation.