Admittance Control of Motorized Functional Electrical Stimulation Cycle

Motorized functional electrical stimulation (FES) cycling is a promising rehabilitation option for individuals with neurological conditions. Closed-loop motorized FES cycling requires multiple controllers to actuate the rider's muscles through FES and the cycle's electric motor, ultimately resulting in cooperative human-robot interaction. In this paper, the rider's muscle track cadence when kinematically efficient and the cycle's electric motor tracks admittance, guaranteeing stable, safe interaction. A Lyapunov-like switched systems analysis is utilized to conclude global exponential tracking of the cadence error system and passivity of the cycle's admittance controller with respect to the rider. Multiple experiments are conducted on one able-bodied participant to demonstrate the efficacy of the developed controller and investigate the effect of manipulating individual admittance parameters.