Multi-Joint Control and Functional Restoration System of Paralyzed Extremity Using Functional Electrical Stimulation

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Functional electrical stimulation (FES) is an electrical stimulation applied to peripheral or intramuscular nerve of paraplegic, hemioplegic and quadriplegic patients caused by spinal cord injury or brain damage and has been studied to reconstruct the paralyzed limb functions. Gait, standing and the other limb functions have been in part regained using open-loop FES system, but limited by some inaccurate controlled conditions. An accurate control of joint angle and muscle contractile force is required especially for the stable limb functions without support system. To satisfying this requirement feedback control FES system was developed in this study. The FES system with digital PID control was first constructed for bidirectional movement of flexion and extension on ankle and knee joints. In order to reduce undesirable oscillatory limb movement related to the nonlinear characteristic of muscle contraction, a command filter (LPF) and coactive muscle control of the agonist and antagonist were appended in the system. Further modification of the system using adaptive control, Model Reference Adaptive Control System, was also developed to attain smooth bidirectional movement of ankle and knee joints. In addition, a real time method estimating muscle tension from the EMG signal was developed by means of the auto regressive moving average model. Finally, FES system of standing posture control was developed and applied to paraplegic patients.