Feedback control of the bending response of ionic polymer-metal composite actuators

Many physical models of ionic polymer have been developed. However, these models are not suitable for use in the design of control systems for Ionic Polymer-Metal Composite(IPMC) actuators. In this paper an empirical model of IPMC is developed and used for closed-loop control. The empirical model is developed by measuring the step response of 20mm x 10mm IPMC actuator in a cantilever configuration . Using this empirical model, a compensator was designed using a linear observer-estimator in state space. Since the IPMC has a slow time constant, it cannot be used to actuate high frequency signals. The design objectives were to constrain the control voltage to less than 2 Volts and minimize the settling time by using feedback control. The controller was designed using Linear Quadratic Regulator(LQR) techniques which reduced the number of design parameters to one variable. This LQR parameter was varied and simulations were performed which showed settling time of 0.15 seconds for closed-loop as compared to a open-loop settling time of 7 seconds. The maximum control input varied from 1.1 Volts to 2.5 Volts for the simulations depending on the LQR parameter. The controller was later used in experimentation to check simulations. Results obtained were consistent to a high degree. Closed-loop settling time was observed to be 0.95 seconds and the maximum control input was less than 2.3 Volts. Experimentation also revealed a high overshoot and oscillations before settling which occurred due to the excitation of IPMC at its natural frequency. Thus, need to include the higher frequency dynamics was highlighted.