|
Electroelastomers (electroactive elastomers, a.k.a. dielectric elastomers) such as those based on acrylic elastomer films with compliant electrodes, when highly prestrained, exhibited up to 380% electromechanical strain in area expansion at 5 to 6 kV. By rolling highly prestrained acrylic films around a compression spring, multifunctional electroelastomer rolls (MERs, or spring rolls) were obtained that combined load bearing, actuation, and sensing functions. The design was extended to two-degree-of-freedom (2-DOF) and 3-DOF spring rolls by patterning the electrodes along the circumferential spans of the rolls. Multiple-DOF spring rolls retained the linear actuation of 1-DOF spring rolls with additional bending actuation. New electroelastomers were developed that preserved the high strain and energy capability of the acrylic films but could respond one order of magnitude faster. One-DOF spring rolls using this new material exhibited response speeds up to 100 Hz, and power densities as high as 400 W/kg of actuator mass and 2000 W/kg of electroelastomer mass based on maximum force, stroke, and frequency. Further, new electroelastomers were prepared that exhibited 200% strain without the need for prestrain. These materials may enable new actuators containing no prestrain-supporting structures that are even lighter, more compact, and compliant. The new actuators would have a higher percentage of active mass and higher energy and power densities than those based on the prestrained acrylic films matching the characteristics of animals. A roll actuator containing no supporting structure was fabricated to output 33% strain. Preliminary lifetime measurements confirmed the potentially long lifetime of the electroelastomers. Improvements in MER design and materials have enabled a new generation of small walking robots, MERbot, with a multi-DOF spring roll as each of its six legs, as well as a new type of robot that can be quickly fabricated from a single flat multifunctional actuator structure. Such small flat robots can hop or jump two to three times their height and have been able to quickly clear obstacles equal to the robots' height.
|
