Higher-order sliding mode control of leg power in paraplegic FES-Cycling

In this paper, we propose a robust control methodology based on high order sliding mode (HOSM) for control of the leg power in FES-Cycling. A major obstacle to the development of control systems for functional electrical stimulation (FES) has been the highly non-linear, time-varying properties of neuromusculoskeletal systems. A useful and powerful control scheme to deal with the uncertainties, nonlinearities, and bounded external disturbances is the sliding mode control (SMC). The main drawback of the classical sliding mode is mostly related to the so-called chattering which is dangerous for FES applications. To avoid chattering, HOSM approaches were proposed. Keeping the main advantages of the original approach, at the same time they totally remove the chattering effect and provide for even higher accuracy in realization. The results of simulation studies and experiments on two paraplegic subjects show the superior performance of the leg power control during different conditions of operation using HOSM control scheme.