Nested saturation based control of an actuated knee joint orthosis

Wearable robots have opened a new horizon for assistance and rehabilitation of dependent/elderly persons. The present study deals with the control of an actuated lower limb orthosis at the knee joint level. The dynamics of the shank-foot-orthosis system are expressed through a nonlinear second order model taking into account viscous, inertial and gravitational properties. Shank-foot-orthosis system parameters are identified experimentally. Since the underlying dynamic model is nonlinear, a robust control strategy is needed to guarantee an accurate and precise movement generation. The proposed control strategy ensures, at the same time, the stability of the closed-loop system. A bounded control torque is applied to guarantee the asymptotic stability of the shank-foot-orthosis. The generated control respects the physical constraints imposed by the system. The effectiveness of the proposed control strategy is shown in real-time in terms of stability, position tracking performances and robustness with respect to identification errors and external disturbances. (C) 2013 Elsevier Ltd. All rights reserved.