Displacement improvement from variable pre-stretch diaphragm type Dielectric Elastomer Actuator

Dielectric Elastomer Actuator (DEA) is a promising technology for artificial muscle applications based on its large voltage-induced displacement and the ability to generate a large variety of motion. This paper presents a DEA based on a modified diaphragm configuration that improves electrically-induced displacement. Existing diaphragm DEAs are equal-biaxially pre-stretched before being constrained by rigid inner and outer rings. In this paper, we first apply equal-biaxial pre-stretch, and then relax its radial pre-stretch before securing it on the outer ring. By doing this, we allow the actuation space in a radial direction to be increased. Both analysis and experiment show significant improvement in actuation as compared to an equal-biaxially-secured one. Our analysis predicted a 53% more electrically-induced displacement as compared to that of equal-biaxially pre-stretched DEAs. Our experiments further showed that when actuated near electrical breakdown, a variable pre-stretched DEA can actuate more than 50% in its out-of-plane displacement with dead load. At large displacement, the output force of our modified DEA is also higher, thus increasing the stored mechanical energy. We hope to expand the applications of diaphragm DEAs with a variable pre-stretched diaphragm in robotic applications.