FEA of dielectric elastomer minimum energy structures as a tool for biomimetic design

Ctenophores or "comb jellies" are small sea creatures that propel themselves with rows of ciliated bending actuators or 'paddles'. In some species the actuators are coordinated via mechano-sensitivity; the physical contact of one paddle triggers the motion of the next resulting in a wave of activation along the row. We seek to replicate this coordination with an array of capacitive self-sensing Dielectric Elastomer Minimum Energy Structure(s) (DEMES) bending actuators. For simplicity we focused on a conveyor application in air where four DEMES were used to roll cylindrical loads along some rails. Such a system can automatically adjust to changing load dynamics and requires very little computational overhead to achieve coordination. We used a finite element modelling approach for DEMES development. The model used a hybrid Arruda-Boyce strain energy function augmented with an electrostatic energy density term to describe the DEA behaviour. This allowed the use of computationally efficient membrane elements giving simulation times of approximately 15 minutes and thus rapid design development. Criteria addressing failure modes, the equilibrium state, and stroke of the actuators were developed. The model had difficulty in capturing torsional instability in the frame thus design for this was conducted experimentally. The array was built and successfully propelled teflon and brass rollers up an incline. Noise in the capacitive sensor limited the sensitivity of the actuators however with PCB circuit fabrication this problem should be solved.