Improving the safety of ankle-foot rehabilitation system with hybrid control

The safety is an important issue in robot-assisted rehabilitation systems. In this paper, we present a therapist-joined hybrid control method to improve the safety of a robotic ankle-foot system for post stroke rehabilitation, combining therapist-joined zero torque control and proxy-based sliding mode control in the continuous passive motion based rehabilitation. The zero torque control is applied when measuring the range of motion of the subject to obtain its extreme joint angle and largest resistance torque. According to these data, a subject-suited position controller of proxy-based sliding mode control can be specified to implement passive stretching, with desired trajectory designed and torque output limited for the subject individually. Experiments were performed to demonstrate the feasibility of the proposed method on improving safety.