Force control of ionic polymer-metal composite actuators with carbon-based electrodes

Abstract

To perform tasks such as hold an object with a constant force, the reliable control of an ionic electroactive polymer actuator is essential. The composite under research is an IPMC actuator with electrodes composed of nanoporous carbon and membrane made of ionic polymer. Compared to traditional platinum electrodes, these novel electrodes do not crack in clusters and have highly controllable properties which preserve even when the actuator is deformed. So far, there are no reports on the dynamic force response of this composite. We present the first attempts of testing the force dynamics of an IPMC with nanoporous carbon electrodes under open-and closed-loop controls. As many attempts have been focused on the sensorless force control of ionic electroactive polymers, we first investigate the uncompensated dynamics of the actuator, then use the direct inverse model to obtain the desired tracking performance. We also aim to identify the conditions, under which the actuator is suitable for sensorless control. Furthermore, we improve the tracking ability of the actuator using a feedback controller where the force sensor data is available and incorporate a feedforward controller into the feedback control system. Based on the experiments, the resulting effects on the tracking performance are observed.

Soft Actuators for Small‐Scale Robotics

“…When a step‐voltage is applied, the actuator displays a fast initial reaction followed by a slow relaxation, the direction of which is dependent on the polyelectrolyte used . Researchers have proposed many actuator models and considered closed‐loop control for handling this positional drift, but, as of yet, no appropriate internal sensing option has been found . Due to the time it takes water and hydrated ions to dissipate through the surface electrodes, operating the actuator at lower frequencies leads to higher displacements .…”

Fractional-order modeling and control of ionic polymer-metal composite actuator

“…From the perspective of applications, such behavior is rather considered as a material drawback that hinders the performance and has to be compensated by proper control. So far IPMC actuators with nanoporous carbon electrodes have been successfully controlled using system identification and model inversion [23,24], or model predictive control based scheme [25], however, in this work we focus on more advanced methods exploiting fractional-order (FO) calculus.…”

Challenges and Perspectives in Control of Ionic Polymer-Metal Composite (IPMC) Actuators: A Survey

“…As a result, the authors conclude that the sensor-less control of IPMC actuators is limited in applications where precise control is required. The similar approach for tracking the force of the IPMC actuator was employed in [36]. The results of both force and displacement tracking lead to similar conclusions regarding the applicability of the inversion-based sensor-less control.…”