Open-loop control of IPMC actuators under varying temperatures

Because of size and complexity concerns, implementing feedback control for ionic polymer-metal composite (IPMC) actuators is often difficult or costly in many of their envisioned biomedical and robotic applications. It is thus of interest to develop open-loop control strategies for these actuators. Such strategies, however, are susceptible to change of IPMC dynamics under varying environmental conditions, a predominant example being the temperature. In this paper we present a novel approach to open-loop control of IPMC actuators in the presence of ambient temperature changes. First, a method is proposed for modeling the temperature-dependent actuation dynamics. The empirical frequency response of an IPMC actuator, submerged in a water bath with controlled temperature, is obtained for a set of temperatures. For each temperature, a transfer function of a given structure is found to fit the measured data. A temperature-dependent transfer function model is then derived by curve-fitting each zero or pole as a simple polynomial function of the temperature. Open-loop control is then realized by inverting the model at a given temperature based on the auxiliary temperature measurement. However, the obtained model for IPMC actuators is of non-minimum phase and cannot be inverted directly. A stable but non-causal algorithm is adopted to implement the inversion. Furthermore, a finite-preview algorithm is proposed to enable near real-time tracking of desired outputs. Experimental results show that the proposed approach is effective in improving the tracking performance of IPMC actuators under varying temperatures.