Contractile Hydrostatically Coupled Dielectric Elastomer Actuators

The so-called hydrostatically coupled dielectric elastomer actuators (HC-DEAs) have recently been described as a means to improve versatility and safety of electroactive polymer actuators made of DEs. HC-DEAs use an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load. In this paper, we present the ongoing development of linear contractile HC-DEAs. The actuator is made of two rigid disks (circular frames) that support an active membrane, consisting of a DE film coated with compliant electrodes. The frames and the membrane delimit a closed chamber, filled with the fluid. The pressure of the fluid is used to provide the actuator with a barrel-like shape, while keeping the length of the structure limited by a counteracting element (such as an internal spring or the external load itself); combining this element with the internal pressure allows the structure to be axially precompressed. As a result of an electrical activation of the membrane, outward radial buckling and related axial contraction of the device are achieved. This paper presents preliminary assessment of static electromechanical performance of prototypes made of silicone and water, studying combined effects of precompression, voltage, and stress relaxation.