Feedback control of electrode offset voltage during functional electrical stimulation

Abstract

Control of the electrode offset voltage is an important issue related to the processes of functional electricalstimulation because excess charge accumulation over time damages both the tissue and the electrodes.This paper proposes a new feedback control scheme to regulate the electrode offset voltage to a predeter-mined reference value. The electrode offset voltage was continuously monitored using a sample-and-hold(S/H) circuit during stimulation and non-stimulation periods. The stimulation current was subsequentlyadjusted using a proportional–integral (PI) controller to minimise the error between the reference valueand the electrode offset voltage. During the stimulation period, the electrode offset voltage was main-tained through the S/H circuit, and the PI controller did not affect the amplitude of the stimulation current.In contrast, during the non-stimulation period, the electrode offset voltage was sampled through theS/H circuit and rapidly regulated through the PI controller. The experimental results obtained using anerve cuff electrode showed that the electrode offset voltage was successfully controlled in terms ofthe performance specifications, such as the steady- and transient-state responses and the constraint ofthe controller output. Therefore, the proposed control scheme can potentially be used in various nervestimulation devices and applications requiring control of the electrode offset voltage.