Electromechanical coupling in cylindrical dielectric elastomer actuators

Dielectric elastomer actuators in a cylindrical configuration, called "spring roll", have been used by the Empa team for the first arm wrestling match between a human and a robotic arm driven by electroactive polymers (EAP) on the EAPAD conference 2005 in San Diego. In this work, electromechanical coupling in EAP is investigated at the example of spring rolls. The commonly used equation derived by Pelrine et al. (Sensors and Actuators A, 64, 1998) is analyzed and the influence of the uncoated ("passive") parts is evaluated. Longer passive parts cause a force reduction in axial direction which affects the performance of the actuator. Results have shown that (i) the equation of Pelrine represents a simplified description of electromechanical coupling; (ii) the equation can be used for modeling electromechanical coupling in spring rolls and (iii) the relative force reduction agrees to a great extent with the ratio between the uncoated area of a spring roll and the total (coated and uncoated) area. These results are relevant for design and optimization of spring rolls.