High-performance dielectric elastomer unimorph bending actuators without pre-stretch

Dielectric elastomer (DE) single films for bending actuators are normally used with pre-stretch to increase the performance of the actuation. However, pre-stretch requires a high effort in the production of the actuators. In this work, a simple DE bending actuator in a unimorph configuration with high actuation performance is presented. For the manufacturing of the actuator, a silicone film is coated with conductive carbon nanoparticles in a silicone matrix as electrodes on both sides and laminated with a non-stretchable, but highly bendable and light weight polymer film, which acts as a strain limiting layer. Stiffening bars on the strain limiting layer impede an uncontrolled actuator deformation. The bending angle and the displacement of the actuator tip were measured at variable field strength up to 80 kV/mm. In a single DE layer configuration with an electrode area of 50 mm x 30 mm, a bending angle of 15° and a tip displacement of 7 mm were reached. A mathematical model for the bending actuator was applied to compare experimental and theoretical results and to optimize the relevant parameters. By using thermoplastic polyurethane (TPU) as an alternative elastomer material, a bending angle of 40° and a tip displacement of 18 mm could be achieved with the same actuator dimensions and optimized parameters. The simple unimorph bending actuators are promising tools for sensitive grippers on soft robots.