  Functional electrical stimulation (FES) is used to activate the dysfunctional
lower limb muscles of individuals with neuromuscular disorders to produce
cycling as a means of exercise and rehabilitation. However, FES-cycling is
still metabolically inefficient and yields low power output at the cycle crank
compared to able-bodied cycling. Previous literature suggests that these
problems are symptomatic of poor muscle control and non-physiological muscle
fiber recruitment. The latter is a known problem with FES in general, and the
former motivates investigation of better control methods for FES-cycling.In
this paper, a stimulation pattern for quadriceps femoris-only FES-cycling is
derived based on the effectiveness of knee joint torque in producing forward
pedaling. In addition, a switched sliding-mode controller is designed for the
uncertain, nonlinear cycle-rider system with autonomous state-dependent
switching. The switched controller yields ultimately bounded tracking of a
desired trajectory in the presence of an unknown, time-varying, bounded
disturbance, provided a reverse dwell-time condition is satisfied by
appropriate choice of the control gains and a sufficient desired cadence.
Stability is derived through Lyapunov methods for switched systems, and
experimental results demonstrate the performance of the switched control system
under typical cycling conditions.
