A New Ankle Robotic System Enabling Whole-Stage Compliance Rehabilitation Training

Robot-assisted physical therapy can encourage a subject's voluntary participation to achieve rapid motor function recovery. To enhance the subject's cooperation, and training safety during training sessions, we develop a new ankle robotic system with three rehabilitation training strategies based on an admittance controller, namely, patient-passive compliance exercise, isotonic exercise, and patient-active exercise, which fully consider the patient's muscle strength level, and different stages of recovery. The developed parallel two-UPS/RRR ankle rehabilitation robot is actuated by two servo linear actuators, and one servo motor, and has three rotational degrees of freedom. The mechanism is simple, and ensures that the rotation center of the ankle joint complex from different patients coincides with the robot's rotation center. All three strategies are based on the admittance controller, and its derivatives, and the controller's output is obtained based on proportional, and time-shifting methods according to the continuous measured torque. In particular, the developed two-UPS/RRR ankle robotic system covers the whole-stage compliance rehabilitation training, ensuring the safety of full-cycle training sessions. Experiments of the three rehabilitation training strategies were carried out on five healthy subjects, with the results showing good compliance, and trajectory tracking performance.