Taming the viscoelastic creep of dielectric elastomer actuators

We present a simple open-loop method to suppress the viscoelastic drift of dielectric elastomer actuators (DEAs). Viscoelastic creep is one of the drawbacks of DEAs, especially when made with acrylic elastomer membranes (VHB). This leads to a time-dependent strain response to a voltage input, thus making the precise control of DEAs difficult. Closed-loop methods can be used to mitigate this issue, but they require additional sensors for the strain feedback, or a complex power supply if capacitive self-sensing is used. Our method is based on quasi-linear viscoelasticity and relies on two simple characterisation tests: 1) a slow voltage ramp to characterise the steady-state strain versus voltage behaviour, and 2) a strain versus time response to a voltage step input. The model then enables to calculate the voltage profile required to obtain a target strain output. A simple analytical expression can be used to generate strain step responses. The method enables to suppress the viscoelastic drift and to increase the response speed of DEAs. To obtain arbitrary strain profiles (sinusoid, square, etc.), the required voltage can be numerically calculated, thus making the method a simple and versatile tool to compensate the viscoelasticity, and generate precise strain profiles from DEAS, without the need for closed-loop operation.