Low voltage electrohydraulic actuators for untethered robotics

Rigid robots can be precise but struggle in environments where compliance, robustness to disturbances, or energy efficiency are crucial. This has led researchers to develop biomimetic robots incorporating soft artificial muscles. Electrohydraulic actuators are promising artificial muscles that perform comparably to mammalian muscles in speed and power density. However, their operation requires several thousand volts. The high voltage leads to bulky and inefficient driving electronics. Here, we present hydraulically amplified low-voltage electrostatic (HALVE) actuators that match mammalian skeletal muscles in average power density (50.5 W kg−1) and peak strain rate (971 % s−1) at a 4.9 times lower driving voltage (1100 V) compared to the state-of-the-art. HALVE actuators are safe to touch, waterproof, and exhibit self-clearing properties. We characterize, model, and validate key performance metrics of our actuator. Finally, we demonstrate the utility of HALVE actuators on a robotic gripper and a soft robotic swimmer.

Methods
Polarization loop measurements of PVDF-HFP and P(VDF-TrFE-CTFE) were conducted using a Radiant Precision Premier II, equipped with a Radiant Precision 10kV HVI-SC and a high-voltage amplifier Trek Model 609E-6. Measurements were done at ambient temperature (20C).

Sample preparation: The P(VDF-TrFE-CTFE) samples had a surface of 5 mm × 5 mm and a thickness of 5 μm. For sample preparation, the bottom electrode pattern was first etched onto a PET film. Subsequently, P(VDF-TrFE-CTFE) was blade-casted onto this PET film and electrode. The top aluminum electrode was then sputter-coated onto the P(VDF-TrFE-CTFE) using a Safematic CCU-010. The PVDF-HFP samples had a surface of 5 mm × 5 mm and a thickness of 10 μm. Aluminum electrodes were sputter-coated onto both sides of a PVDF-HFP film using a Safematic CCU-010.

Several bipolar PE loops were recorded while incrementally increasing the applied field amplitude from 10 V/μm up to 300 V/μm.