Multiple-degrees-of-freedom electroelastomer roll actuators

Abstract

Electroelastomers (electroactive elastomers) such as the 3M VHB 4910 acrylic adhesivefilms have exhibited up to 380% strain in area expansion at 5–6 kV when they are highlyprestrained. By rolling highly prestrained electroelastomer films around a compressionspring, we have demonstrated multifunctional electroelastomer rolls (MERs, orspring rolls) that combine load bearing, actuation, and sensing functions. Weextended the design to two-degree-of-freedom (2-DOF) and 3-DOF spring rolls bypatterning the electrodes to align radially on two and four circumferential spans of therolls, respectively. Multiple-DOF spring rolls retain the linear actuation of 1-DOFspring rolls with additional bending actuation. Mathematical equations are derivedto correlate the bending angle and lateral force of the rolls with the actuatedstroke in one of the electroded spans. Two-DOF spring rolls with a 1.4 cm outsidediameter, 6.8 cm axial length, and 11 g weight have been fabricated; these rolls have a90° maximum actuation bending angle, 0.7 N maximum lateral force, and up to 15 N blocked axial force.Three-DOF spring rolls with a 2.3 cm outside diameter, 9.0 cm axial length, and 29 g weight exhibita 35° maximum bending angle and 1.0 N maximum lateral force. These specifications can bemodified by variations in roll parameters according to the equations. Multi-DOF springrolls are easy to fabricate, compact, multifunctional, and mechanically robust.They represent a radically new actuation technology and may enable a number ofunique applications. We have demonstrated a small walking robot, MERbot,with one 2-DOF spring roll as each of its six legs. The robot’s speed is as high as13.6 cm s−1 or two-thirds of its length per second. ‘Sushi rolls’ have also been fabricated: theseconsist of six 2-DOF springs connected in series and monolithic in structure.The sushi rolls can be driven so as to generate wavelike or serpentine motion.