Active Mass-Offloading with Cable-Driven SEA for Tailored Support to Lower Limb Rehabilitation

Walk training with body weight support (BWS) can motivate mild and moderate patients after neural injury to actively control their gait and balance, and thus leads to intensive participation and promises effective recovery of the patients. We are building an active BWS system that allows patients to move in the three dimensional Cartesian space and provides well-controlled supportive force against gravity. Nevertheless, the dynamic load can still be challenging for the patients. In this work, a mass-offloading method has been designed with respect to the cable-driven series elastic actuator ( SEA) in the BWS system to virtually remove partial body mass. The acceleration signal of the subject is measured and fed back into the mass-offloading controller, which determines the required dynamic force from the actuator. Then, a nonlinear sliding mode controller regulates the force output of the cable-driven series elastic actuator. Thus, tailored body weight support and mass-offloading are provided to assist the subject with voluntary walking and balance control. Simulation experiments have validated the feasibility and efficacy of the mass-offloading method for the BWS system.