Switched motorized assistance during switched functional electrical stimulation of the biceps brachii to compensate for fatigue

Rehabilitation treatments for neurological conditions that result in movement disorders often include functional electrical stimulation (FES) to restore limb function and increase muscle strength. FES elicits muscle contractions to cause a specific movement, such as a biceps curl. Experimental evidence by the authors suggests that switching stimulation across multiple electrodes along the biceps brachii based on the resulting torque effectiveness results in more efficient movements. More repetitions are permitted before the muscle fatigues to a point that would terminate the therapy session. Rehabilitation robotics utilize motors to either assist or resist the user. In this paper, a robotic system is used for two objectives: To track the desired trajectory during biceps brachii extension and to provide assistance during flexion when the muscle fatigues. A switched controller is designed for the FES muscle input and for the motor input that accounts for muscle stimulation saturation. Both controllers are used to track a desired angular position trajectory of the forearm about the elbow. Global exponential tracking is proven using a common Lyapunov function. Experimental results demonstrate the tracking performance of the combined controllers.