High-Performance Soft Electrostatic Actuators for Untethered Robotics

Compared to pneumatic actuators, electrically-driven soft actuators offers clear system-level advantages for a wide range of soft robotic applications, such as haptics and mobile robots. Removing the external low energy-efficiency compressor is a key step towards untethered and portable operation.<br/>Pneumatic actuation is however very appealing for soft robotics, as it enables compliant actuators with a very high force density. Electrothermally actuated devices can offer similar forces, but have energy efficiency that is too low for realistic untethered operation. In contrast, electrostatic actuation can offer both very high efficiency and high energy and force density, but requires voltages of several kilovolts, which can lead to bulky power supplies.<br/>I will present several approaches my lab has taken to realize high force density electrostatic actuators for soft machines. We followed two main routes: a) lower the drive voltage below 500 V, thus allowing the use of milligram scale electronics, and b) increasing electrostatic actuators performance to a point where HV supplies weighing a few grams are acceptable in untethered soft robots.<br/>We use µm-thick dielectrics, high permittivity and high electrical breakdown strength films, and low stiffness electrodes to both push up energy density and reduced drive voltage. We reduced the drive voltage of Dielectric Elastomer Actuators (DEAs) from several kV to 400 V, a level at which we can use SMD components for compact control electronics (mass 350 mg for 2 channels at 1 kHz). By combining electrostatic zipping with hydraulic coupling in elastomer shells, the above-mentioned materials choices have led to HAXEL actuators that can generate up to 200 W/kg, for diameters from 2 mm to 20 mm, used in mobile robots and in wearable haptics.<br/>Finally, I will discuss our progress in increasing efficiency and lifetime of stretchable electrohydrodynamic (EHD) soft pumps, that generate a flow using high electric fields. Such pumps will enable soft robots with the advantages of pneumatic actuation, but without requiring an external compressor. We show how soft grippers benefit from this pumping technology.