Design of multiple degree-of-freedom sliding mode FES controller for concurrent stimulation of multiple mono and biarticulate muscles

This article presents a theoretical design of an FES controller to be used for stimulation of multiple mono and biarticulate muscles to restore multiple degree-of-freedom (DOF) motion in paralyzed individuals. The overall control strategy is based on multiple DOF musculo-skeletal model, nonlinear sliding mode control design, constrained optimization techniques to determine the needed muscle activations, and an additional inversion of the neuro-muscular stimulation relationship in order to obtain the needed controller output (electrical current amplitude/pulse-width). The combination of these methods leads to a controller that guarantees asymptotically stable tracking of reference position trajectories while assuring minimal (optimal) muscle activation and fatigue.