Proxy-based sliding mode control of a robotic ankle-foot system for post-stroke rehabilitation

Robotic platform-based ankle–foot rehabilitation systems have been proved effective in treating joint spasticity and/or contracture of stroke survivors. However, simple force or velocity limiters are not adequate, since they cannot explicitly guarantee slow and overdamped motions without overshoot. In this paper, we propose a proxy-based sliding mode control (PSMC)-based approach, to avoid unsafe behaviors of a robotic ankle–foot rehabilitation system. The proposed method has three advantages: (1) without deteriorating tracking performance during normal operation, it guarantees overdamped, slow, and safe recoveries after abnormal events; (2) it provides a simple and accurate way to confine the output torque exerted on the subject’s ankle; (3) though effective, the control law avoids the necessity to identify the specific system model or build state observer, which is usually difficult for human–robot interaction system. A 71-year-old stroke patient and 10 able-bodied subjects were recruited for the experi...