Contactless coupling of dielectric elastomer membranes with magnetic repulsion

Abstract

Dielectric elastomer (DE) actuators such as conventional double cone configurations have demonstrated that coupled DE membranes can be rigidly-coupled to execute antagonistic out-of-plane actuation. This paper presents experimental analysis of the compliant coupling in the emerging magnetically-coupled DE actuator (MCDEA) design, which exploits contactless magnetic repulsion to create a frictionless coupling between DE membranes. The compliance of this coupling enables the advantage of having two different actuation modes: antagonistic reciprocation and bi-directional expansion. However, since this compliance adds an additional degree-of-freedom, it increases the complexity of the actuator's dynamics because the coupling distance can exhibit oscillatory behavior that is distinct from each of the actuator's output oscillations in terms of phase difference and frequency. In this work, the relationship between DEA membrane stiffness and required magnetic force is experimentally analyzed before we present an investigation into the phase space of the compliant coupling and its relationship with the stroke amplitude. It is shown that the fundamental frequency of the MCDEA's output stroke (46.1 Hz) corresponds to a super-harmonic frequency of the magnetic coupling that is double that of the output. The fundamental frequency of the coupling (87.6 Hz) is found to correspond to a second resonant peak in the MCDEA's output with a much lower amplitude than at 46.1 Hz. This suggests that the dynamics can be exploited by controlling the excitation frequency for unidirectional push/pull or bidirectional expansion/contraction actuation, which creates potential for new compliant DE actuator and generator designs.