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Rehabilitation of the Paralyzed Lower Limbs Using Functional Electrical Stimulation: Robust Closed Loop Control

Functional electrical stimulation (FES) is used to excite paralyzed muscles that would otherwise be uncontrollable by paraplegic patients. Consequently, the patient could recover partially some of its lower limb functions improving thus the cardiovascular system, increasing oxygen uptake and bettering the whole quality of life. The main challenge that we face when applying FES to the paralyzed lower limbs is to avoid hyperstimulation and to defer the muscular fatigue as much as possible. One of our goals is to compute the needed patterns stimulation (current and/or pulse width) necessary to perform a desired given motion of the knee joint. This later is actuated by two groups of antagonist muscles: quadriceps and hamstrings causing respectively extension and flexion of the knee. The muscle model used in this study is based on a physio-mathematical formulation of the macroscopic Hill and microscopic Huxley concepts. Parameters of the biomechanical model (muscles-knee) were identified based on experimental measures. Afterward, we apply two robust nonlinear control strategies: the High Order Sliding Mode (HOSM) controller and the Model Predictive Controller (MPC) also known as receding horizon controller. These controllers have been evaluated in simulation to hightlight i) their performance in terms of capability of tracking a pre-defined reference trajectory and ii) the robustness against force perturbation and model mismatch. The performances of these controllers have also been compared with a classical pole placement controller.