Robust torque control based on H∞ criterion of an active knee orthosis

The authors present in this paper a robust torque control of an active orthosis designed to assist the knee joint flexion/extension during physical therapy. The orthosis is driven by a rotary Series Elastic Actuator presented in authors´ previous paper. The adopted control strategy is based on H_∞ criterion in order to ensure good system performance even when it is subjected to parametric uncertainties and external disturbances. The controller performance is evaluated through the frequency response function analysis. Experimental results involving the interaction between a subject and the active knee orthosis are also presented to show the performance of the developed prototype.