System Reconfiguration to Control Knee Extension with Time Delay Nonlinearity in Closed-Loop FES

Functional Electrical Stimulation (FES) assists individuals with neuromuscular impairments during rehabilitation exercises conducted in open-loop and closed-loop. Typically, during the design phase, the closed-loop FES system mainly consists of a feedback controller, a second-order model, or a knee extension model to represent the actual knee. Closed-loop FES or feedback controllers are generally better, but their performance drops in real-world scenarios due to nonlinear factors like fatigue, time delay, spasm, and spasticity. These lead to suboptimal performance of the feedback controllers and even failure, diminishing their effectiveness in assisting patients. In response to these challenges, this paper investigates four different techniques of system reconfiguration, which involves changing the closed-loop system structure to mitigate the adverse effects of time delay in real-world FES applications. To evaluate the effectiveness of the four techniques, a feedback PID controller, knee extension model or second-order critically damped system were developed and tested using MATLAB/Simulink software. The simulation results demonstrate that the first system reconfiguration technique improves system behaviour and enhances FES controller performance. This research marks a significant step towards improving the practicality and adaptability of FES technology for individuals with neuromuscular impairments.