Impedance control of ankle rehabilitation robot

Interaction control is an important aspect in rehabilitation robots to ensure system safety and allow effective rehabilitation. Due to the significant variability of human limb and joint characteristics, adaptability in the interaction controller is vital for enabling the adjustment of robot behavior to better suit the patient´s requirements. A parallel manipulator has been developed for ankle rehabilitation. Computer models for both the robot and human ankle have also been constructed for evaluation of controller performance. Using these models, computer simulations were carried out to investigate the potential advantage of using a variable impedance controller to perform ankle rehabilitation exercises. The impedance parameters of this controller are selected by referring to the ankle compliance as determined by the ankle model at corresponding foot configurations. Simulation results have shown that selecting the manipulator impedance in proportion to the environmental compliance has the effect of limiting force application in stiff directions such as those encountered when approaching limits of joint motion.