High-strain helical dielectric elastomer actuators

To advance the field of soft robotics, novel linear actuators that provide high strain, high strain rate, and high specific power are needed. This work deals with a novel, helically self-coiled dielectric elastomer actuator that exhibits such properties. We present the corresponding manufacturing process, the resulting prototypes, and an analytical modeling approach. The actuator was manufactured by bonding a strip of unidirectional non-crimp carbon fiber fabric to a pre-stretched silicone film. Due to the tension in the silicone, the strip rolls up and forms a helix when released. The unidirectional fabric was used as an electrode with the fibers running perpendicular to the strip. Therefore, the electrode is highly ductile lengthwise, but the cross-section of the strip remains undeformed despite inherent stress due to the pre-strain. A second electrode placed on the outside of the helix results in a contracting actuator when activated. Prototypes showed strains of up to 5.6 % at actuation frequencies of 2 Hz. To aid the design of the prototypes an analytical modeling approach was developed. Theoretical considerations showed that applying a second electrode on the inside of the helix instead of the outside leads to an expanding actuator. Combining these two approaches will further increase the deformation potential.