Closed-Loop Cadence and Instantaneous Power Control on a Motorized Functional Electrical Stimulation Cycle

Motorized functional electrical stimulation (FES) cycling is a rehabilitation therapy in which electrical stimulation is used to activate lower body muscles to pedal a cycle in conjunction with motorized assistance. FES cycling has been demonstrated to improve cardiovascular parameters, muscle mass, and motor control of people with neurological conditions (NCs). A common FES cycling objective is simultaneous cadence and power (torque) tracking; however, it is unclear how to best coordinate the FES and motor contributions and if power should be tracked instantaneously or averaged over a period of time. This article develops a new FES cycling controller using a switched Lyapunov-like dwell-time analysis for the nonlinear, uncertain cycling system to conclude global exponential cadence tracking and uniformly ultimately bounded power tracking. To evaluate the performance of the developed controller, comparisons are made with two previously developed FES cycling controllers through experiments on seven able-bodied participants and six participants with NCs. For a desired cadence of 50 RPM and a desired power of 10 W, the developed controller demonstrated the smallest tracking errors with an average cadence and power error of 0.01 +/- 1.03 RPM and 0.00 +/- 0.94 W, respectively, in the able-bodied population and an average cadence and power error of 0.02 +/- 1.87 RPM and 0.00 +/- 2.46 W, respectively, in the population of people with NCs. Results suggest that the electric motor should be used to track cadence and the FES induced muscle torques should be used to track instantaneous power.