The presented work addresses the implementation of Functional Electrical Stimulation (FES) into a closed-loop control system as a means of rehabilitation for patients with spinal cord injury (SCI). FES is a neuroprothesis technique applied to reinnervate the motor function in affected muscles. In clinical settings, FES is applied via an open-loop system which is not an efficient approach. Therefore, this study focuses on experimentally applying two model-free feedback controllers: a Proportional-Integral (PI) controller and a Model Reference Adaptive Control (MRAC) algorithm. A comparative study evaluating these controllers is carried out in vitro mimicking the knee-joint tracking system. The experimental setup is composed of a muscle-mass-spring system where the muscle is stimulated while forces are measured and the muscle position is tracked. Thus, the muscle’s instantaneous position is used as feedback signal. Consequently, the effectiveness of both controllers is evaluated to develop improved strategies for the system’s tracking.

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