Mitigating IPMC Back Relaxation Through Feedforward and Feedback Control of Patterned Electrodes
AuthorFleming, Maxwell Jonathan
AdvisorLeang, Kam K
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The goal of this thesis is to minimize the back relaxation behavior in ionic polymer-metal composite (IPMC) actuators. With low driving voltage (<5V) and the ability to be operated in aqueous environments, IPMCs have gained great attention in recent years for use in many applications including soft bio-inspired actuators and sensors. There are, however, drawbacks to IPMC actuators, including the "back relaxation" effect. Specifically, when subjected to an excessively slow dynamic input, the IPMC actuator will slowly relax back toward its original position. As this effect can causeexcessive positioning error, it is important to compensate for the behavior to enhance applications in robotics and other bio-inspired systems. Methods do already exist to compensate for back relaxation, however they mostly involve undesirable fabricationprocesses or control methods with high voltage demands. By circumventing back relaxation using alternative means, any number of IPMC applications could be improved. For instance, IPMC-guided surgical tools could be controlled more precisely, gripping strength could be increased for an IPMC-powered hand prosthesis, and IPMC-based underwater autonomous systems could have enhanced maneuvering. The contribution of this work is the use of sectored IPMCs to mitigate back relaxation. This class of IPMC typically uses patterned electrodes to produce complex motion or even self-sensing capabilities. In this work, however, a new controltechnique is proposed, allowing the IPMC sectors to be actuated in opposite directions such that the back relaxation components counteract each other. A feedforward control method is designed around this concept and shown to effectively mitigate the back relaxation effect. Performance is further improved by integrating feedback control. Experimental results using a very slow reference and the integrated feedforward and feedback control method show a nearly 97% reduction in tracking error as compared to the uncompensated case. Furthermore, the IPMC's position can bemaintained for a period of 1200 seconds with minimal evidence of back relaxation. Furthermore, the control inputs in this case are bounded and significantly reduced, as compared to other control methods using unsectored IPMCs.