Further Results on Predictor-Based Control of Neuromuscular Electrical Stimulation

Abstract

Electromechanical delay (EMD) and uncertain nonlinear muscle dynamics can cause destabilizing effects and performance loss during closed-loop control of neuromuscular electrical stimulation (NMES). Linear control methods for NMES often perform poorly due to these technical challenges. A new predictor-based closed-loop controller called proportional integral derivative controller with delay compensation (PID-DC) is presented in this paper. The PID-DC controller was designed to compensate for EMDs during NMES. Further, the robust controller can be implemented despite uncertainties or in the absence of model knowledge of the nonlinear musculoskeletal dynamics. Lyapunov stability analysis was used to synthesize the new controller. The effectiveness of the new controller was validated and compared with two recently developed nonlinear NMES controllers, through a series of closed-loop control experiments on four able-bodied human subjects. Experimental results depict statistically significant improved performance with PID-DC. The new controller is shown to be robust to variations in an estimated EMD value.

Robust compensation of electromechanical delay during neuromuscular electrical stimulation of antagonistic muscles

“…Examples of linear control methods include proportional integral derivative (PD/PID), linear quadratic Gaussian control, pole placement method, gain scheduling control method [13][14][15]. Nonlinear control methods [4][5][6][7][8][9][16][17][18] have also been recently developed for NMES. These nonlinear methods have improved performance over linear control methods.…”

“…These nonlinear methods have improved performance over linear control methods. Robust nonlinear control of NMES is especially more relevant, and controllers have been developed to compensate for the nonlinear and uncertain muscles dynamics [5,7], time-varying phenomena such as muscle fatigue [19], and electromechanical delay [18,19].…”

“…Recently, a robust compensation control method was developed for an uncertain input delayed system with additive disturbances [21] and it suggests that a PD/PID controller can be augmented with a delay compensator that contains a finite integral of past control values to transform the delayed system into a delay-free system. Modified PD/PID controllers have been extended to compensate for EMD during NMES [18,19].…”

“…A proportional-derivative (PD)-type closed-loop controller with delay compensation (DC) to deal with the EMD was designed for stimulating antagonistic muscle pairs in a musculoskeletal system. Unlike previous controllers that produce joint flexion with the help of gravity [9,18,19] or controlled by correctional forces such as robot arms [22,24], the developed controller will flex and extend a limb joint by stimulating agonist and antagonist muscles. The controller is designed to transition smoothly between the stimulation of the antagonist muscles.…”

“…These nonlinear methods were proved to have enhanced performance over linear control methods in previous researches [4][5][6][7][8][9][16][17][18]. Among these nonlinear control techniques, robust nonlinear control of NMES in [5,7] is especially more relevant given the nonlinear and uncertain muscle dynamics, time-varying phenomena such as muscle fatigue [19], and electromechanical delay [18,19].…”