Conventional robots are typically actuated by hard actuators, while biological entities consist mostly of soft muscles. Being soft imparts a functionality of compliance, thereby greatly enhancing the range of actuation and the degrees of freedom. Here, we demonstrate a soft electromechanically-active polymer capable of an electrically-induced linear strain beyond 500% that is continuously tunable by voltage. Previous experiments on the same material have demonstrated that by harnessing and bypassing electromechanical instability, soft electroactive polymers may bi-stably switch between an actuated state and an uncharged state of about 323% linear strain. In this paper, we use theory to inspire the possibility of suppressing electromechanical instability using pre-stretch by applying a non-isotropic pre-stretch onto the membrane, so as to achieve an ultra-large actuation strain that is continuously tunable by voltage. This geometry that enables such a large magnitude of actuation is simple and highly amenable to integration in robotic systems. With an electrically-induced strain of at least two orders of magnitude larger than conventional actuators, we expect our demonstration to expand the range of application for soft actuators.
Keywords: dielectric elastomer; theory and experiment; ultra-actuation.