Robust Assistive Force Control of Leg Rehabilitation Robot

In this paper, a wire-driven tension control algorithm using a rotary type series elastic actuator is proposed, which is developed for assistive force control of the rehabilitation robots to help the Straight Leg Raise (SLR) exercise. A robot developed to assist SLR exercise is introduced, which adopts Series Elastic Actuator (SEA) as the actuator system and wires as transmission. SEA, which has drawn attentions for its high controllability of force, can also control the tension in the proposed SLR robot. Nonlinearity such as time varying dynamics caused by wire compression, however, deteriorates the torque control performance of SEA. This paper attacks this issue by analyzing the performance of a robust control algorithm using disturbance observer (DOB). The nonlinearity of wire compression and tension is considered model variation, and design methodology for DOB is discussed taking into consideration the model variation.