Xiaobin Ji
This thesis contributes to the field of Dielectric Elastomer Actuators (DEAs). DEAs are electrostatically driven soft actuators that are fast, capable of generating large actuation strains, high forces, and present high power density. A wide range of applications have been developed based on DEAs including: soft tunable optical devices, soft robotics and wearable haptic devices. DEAs generally require several kilovolts to operate. This high voltage leads to bulky control electronics and can limit consumer acceptance.
In this thesis work, we have decreased the DEAs voltage to below 450V while maintaining high performance, and report novel applications for the low-voltage DEAs.
The approach that we use to decrease the DEAs driving voltage is decreasing the dielectric elastomer (DE) membranes thickness. When the DE membrane is made thin, the properties of electrodes used for thin DE membranes become more critical than the ones for thick DE membranes. The stretchable electrodes must be made thin and soft to achieve low stiffness to not limit the thin DE membrane actuation, and should have high electrical conductivity to enable the DEA fast charging and discharging.
We developed two types of electrodes in this thesis. The first was a thin, transparent and extremely soft ionogel electrode, which we patterned to serve as an optical grating. The ionogel served simultaneously as the transparent electrode for the DEA and as the optical grating elements. Under high electric fields, the ions in the ionogel migrated into the dielectric, limiting lifetime, especially for thin dielectrics.
We then developed ultrathin stretchable conductors based on Carbon Nanotubes, using Langmuir monolayer method for 2D assembly. The nanometer thick stretchable conductors enabled single layer DEAs with a 1.4 µm-thick silicone dielectric layer to generate 8% area strain below 100 V. To increase the DEAs output force, we increased the dielectric membrane thickness to 6 µm, and stacked the DEAs. The DEAs reached full actuation area strain of 25% at 450V, and operated at a frequency from DC to higher than 200 Hz. The sub 500 V operating voltage enabled sub-gram control electronics including battery, which allowed the integration of all the power and control elements with the DEA for compact untethered devices. The high speed enabled a broad range of applications. We developed an untethered 1 g, 4 cm long soft DEA-driven robot capable of carrying its own power supply, and autonomously navigating complex paths. We used 18 µm-thick DEAs as wearable haptic devices, capable to generate notification signals from 1 Hz to 500 Hz on the fingertip.
We decreased the DEA operating voltage by an order of magnitude, enabling wider use of DEAs in soft robotics and wearables.
EPFL2019
