Dynamics of Electrohydraulic Soft Actuators

We have discovered two timescales that govern the dynamic behavior of electrohydraulic actuators: a viscous timescale and an inertial timescale, which depend on geometry and materials system of the actuator, and applied mechanical load and voltage. Depending on the ratio of these timescales, the actuators operate either in a viscous regime in which viscous resistance limits the actuation speed or in an inertial regime in which high speed actuation is possible.

Using the Peano-HASEL actuator as a model system, we investigated the actuation speed of electrohydraulic actuators theoretically and experimentally. A scaling analysis revealed the existence of the two timescales. To confirm the scaling analysis, we measured the time in which Peano-HASEL actuators contract and elongate when subject to weights and excited with square wave voltage signals. We varied geometry, materials system, voltages, and weights such that the actuation speed of the actuators varied by multiple orders of magnitude and observed very good agreement with the scaling analysis. Additionally, we derived a dynamic model for Peano-HASEL actuators. Even though our analysis was limited to the Peano-HASEL actuator, its results can be applied to other types of electrohydraulic actuators.

The paper has been published in PNAS and can be found here: https://doi.org/10.1073/pnas.2006596117