Cadence control of stationary cycling induced by switched functional electrical stimulation control

Cycling induced by functional electrical stimulation (FES) is an effective means for exercise and rehabilitation of individuals suffering from neurological disorders such as stroke, spinal cord injury, and cerebral palsy. To achieve FES-cycling, potential fields are alternately applied across muscle groups in the lower extremities. Alternating stimulation of various muscle groups according to the crank position makes the FES-cycling system a switched system with autonomous state-dependent switching. This paper examines FES-cycling from a switched systems analysis perspective. Specifically, a switched sliding mode controller is developed to yield approximate tracking of a desired cadence despite an uncertain, nonlinear cycle-rider model. Cadence tracking is proven via a common Lyapunov-like function and experimental results are provided to demonstrate the performance of the switched controller.