Control of functional electrical stimulation in the presence of electromechanical and communication delays

In this paper, we show the feasibility of remotely controlling the elbow extension through functional electrical stimulation (FES) of the triceps muscle. Particularly, we present the experimental results obtained with the new automatic control method, designed to achieve position tracking between a user and the remote manipulator device. The major advantage of the controller is its ability to compensate for the electromechanical delay (EMD) during an FES and the communication delay (CD) due to a remote actuation. Another advantage of the developed FES controller is that only the error state and delay knowledge are required to elicit desired muscle contractions, i.e., the control implementation does not depend on model knowledge of highly nonlinear and time-varying muscle dynamics. The experimental results show its superior performance in comparison to the proportional integral derivative (PID) controller. The control performance of the PID controller and the new controller were tested for different values of a composite delay (EMD + CD).