Stimulation current control for load-aware electrotactile haptic rendering: Modeling and simulation

This paper presents our work on generalization of the first-order fingertip skin bio-impedance model that is presented to the instantaneous stimulation current. The generalized dynamic model is based on our experimental finding that one of the bio-impedance parameter, stratum corneum resistance R_p, is inversely related to the stimulation current. The model is necessitated by the type of our constant-voltage-driver (CVD)-based electrotactile haptic rendering system, which features closed-loop load-aware capability in contrast to constant-current-driver (CCD) systems. Relying on this model and on-line estimated bio-impedance parameters, by employing a direct model reference adaptive control (MRAC) method, the stimulation current output to the fingertip skin tracking a desired pulsed reference current is realized. The modeling and control results based on the generalized model are shown to be preliminarily valid from simulation when compared to experimental results. This work will be useful in developing a smart load - aware electrotactile haptic rendering system that is capable of adapting the stimulation current from changing electro-bioimpedance conditions of the fingertip skin.