Decoupled PID control with gain adaptation for a cycling dynamic knee rig

This paper presents the deployment and validation of a control structure for a dynamic knee rig used to gain insight into the kinematics and kinetics of the human knee joint. The dynamic knee rig is able to implement a bicycle motion onto the knee joint using five different actuators. Two actuators control the position of the ankle, one actuator mimics the quadriceps force and two more actuators impose the hamstring forces. Identification of the subsystems of the rig is performed using the ARX method. The obtained mathematical models are used to tune the controller parameters of the proportional-integral-derivative (PID) controllers which control each subsystem. Apart from PID controllers, the control structure also contains feedforward action, decouplers and gain adaptation mechanism. The controllers are tested using a mechanical hinge as knee joint The results indicate a good trajectory tracking performance of the controllers.