Model predictive control-based knee actuator allocation during a standing-up motion with a powered exoskeleton and functional electrical stimulation

Abstract

In this paper a lower-limb powered exoskeleton is combined with functional electrical stimulation of the quadriceps muscle to achieve a standing-up motion. As two actuation mechanisms (FES and the motors) act on the knee joints, it is desirable to optimally coordinate them. A feedback controller that stabilizes the desired standing-up motion is derived. The knee torques, computed by the feedback controller, are further distributed to FES and the knee electric motors by using a ratio allocation that is solved via a model predictive control method. The optimization method relies on a fatigue dynamical model. Simulations and the experimental results of the ratio allocation approach are reported for the standing-up motion.