Variable impedance control of a parallel robot for ankle rehabilitation

This paper proposes a novel variable impedance controller for a redundantly actuated parallel robot to allow execution of passive ankle rehabilitation exercises while taking into consideration of human biomechanics online. By using a biomechanical model of the human ankle which describes the kinematics and dynamics of the ankle foot structure, the kinematic parameters of the ankle can be estimated online to allow identification of the constrained direction of motion. Impedance adjustment heuristics were also formed by investigating the ankle stiffness over a range of joint displacements through the use of the ankle model developed. The variable impedance controller can prevent application of excessive actuator forces which could threaten the safety of the patient.