Towards the position control of conducting polymer trilayer bending actuators with integrated feedback sensor

Conducting polymers have a wide range of reversibly controllable properties, leading to a number of potentially useful devices for robotic applications, including actuators, sensors and batteries. Conducting polymers have the advantages of low weight, low cost, flexibility, small activation potentials (<2V), biocompatibility and the ability to be manufactured using relatively straightforward techniques. Trilayer bending actuators which utilise the controllable change in volume of conducting polymers are potentially useful devices, but their speed and positioning ability must be improved. Significant research effort has been directed towards improving conducting polymer actuator performance through its chemistry, but the use of compensating control systems has had relatively little focus. This paper experimentally investigates three potential control systems for a trilayer bending actuator - feedforward gain control, feedforward inversion-based control and inversion-based PI control. It was found that the inversion-based PI control system provided the best performance, but the implementation utilised a large laser displacement sensor. To limit the requirement for such a large feedback sensor, a trilayer bending actuator with an integrated displacement sensor is proposed, exploiting the additional sensing capability of conducting polymers.