Microscale position control of an electroactive polymer using an anti-windup scheme

TLDR

Smart materials have been widely used for control actuation, and EAP microgrippers based on this control scheme will have significant applications such as picking‑and‑placing micro‑sized objects or as medical instruments. This paper presents a microscale position control system using a novel electroactive polymer (EAP). The authors built a third‑order ARMAX model of the EAP actuator using a chirp signal from 0.01 Hz to 1 Hz, and designed a digital PID controller with an integrator anti‑windup scheme based on that model. Test results show that the controller reduces overshoot from 79.7 % to 37.1 %, decreases control effort by 16.3 %, shortens settling time from 1.79 s to 1.61 s, and improves macro (0.8 mm) and micro (50 µm) step responses and position‑tracking performance, effectively mitigating degradation due to actuator saturation.

Abstract

Smart materials have been widely used for control actuation. In this paper, we present a microscale position control system using a novel electroactive polymer (EAP). We built a third-order model based on the system identification of the EAP actuator with an autoregressive moving average with exogenous input (ARMAX) method using a chirp signal input from 0.01 Hz to 1 Hz with the magnitude limited to ± 7 V. With the derived plant model, we designed a digital PID (proportional–integral–derivative) controller with an integrator anti-windup scheme. We provide test results on macro (0.8 mm) and micro (50 µm) step responses of the EAP actuator, and its position tracking capability is demonstrated. The overshoot decreased from 79.7% to 37.1% and the control effort decreased by 16.3%. The settling time decreased from 1.79 s to 1.61 s. The controller with the anti-windup scheme effectively reduced the degradation in the system performance due to actuator saturation. EAP microgrippers based on the control scheme presented in this paper will have significant applications including picking-and-placing micro-sized objects or as medical instruments.