Design method of DEMES rotary joint

The dielectric elastomer minimum energy structure (DEMES) joint is a kind of soft rotary actuator that consists of a pre-stretched dielectric elastomer (DE) film and a flexible primary frame. The elastic energy stored in the DE film performs work on the frame, which makes the frame bend to a given angle. Applying a voltage on the DE film causes the DE film to relax and the frame can unfold. Removing the voltage causes the frame to bend again. From the perspective of energy conversion, it is proposed that the torque of the DE film on the frame is proportional to the volume of the DE film. This hypothesis was proved through theoretical derivation and was also verified by experiments in two popular types of DEMES rotary joint. Based on the hypothesis, we present a design method for DEMES joints and provide an application example. The proposed hypothesis provides a quantitative relationship between the torque of the DE film and its volume. This is of great significance for the application of DEMES joints in soft robots. (paper)