Electrically-driven phase transition actuators to power soft robot designs

TL;DR

This paper presents a novel electrically-driven soft actuator utilizing liquid-gas phase transition with water, achieving high strain and pressurization rates, and demonstrates its integration into soft robotic systems.

Contribution

Introduction of a liquid-gas phase transition soft actuator with water, including a fluid selection method and nonlinear control for improved performance and integration into robots.

Findings

Achieved strain rates over 16%/s and pressurization rates of 100 kPa/s.

Blocked forces exceeding 50 N at 24 V.

Successful integration into soft robotic systems like a biomimetic hand and quadruped.

Abstract

In the quest for electrically-driven soft actuators, the focus has shifted away from liquid-gas phase transition, commonly associated with reduced strain rates and actuation delays, in favour of electrostatic and other electrothermal actuation methods. This prevented the technology from capitalizing on its unique characteristics, particularly: low voltage operation, controllability, scalability, and ease of integration into robots. Here, we introduce a liquid-gas phase transition electric soft actuator that uses water as the working fluid and is powered by a coil-type flexible heating element. It achieves strain rates of over 16%/s and pressurization rates of 100 kPa/s. Blocked forces exceeding 50 N were achieved while operating at voltages up to 24 V. We propose a method for selecting working fluids which allows for application-specific optimization, together with a nonlinear control approach that reduces both parasitic vibrations and control lag. We demonstrate the integration of this technology in soft robotic systems, including a cable-driven biomimetic hand and a quadruped robot powered by liquid-gas phase transition.