Reversible Underwater Adhesion for Soft Robotic Feet by Leveraging Electrochemically Tunable Liquid Metal Interfaces

Abstract

Soft crawling robots have potential applications for surveillance, rescue, and detection in complex environments. Despite this, most existing soft crawling robots either use nonadjustable feet to passively induce asymmetry in friction to actuate or are only capable of moving on surfaces with specific designs. Thus, robots often lack the ability to move along arbitrary directions in a two-dimensional (2D) plane or in unpredictable environments such as wet surfaces. Here, leveraging the electrochemically tunable interfaces of liquid metal, we report the development of liquid metal smart feet (LMSF) that enable electrical control of friction for achieving versatile actuation of prismatic crawling robots on wet slippery surfaces. The functionality of the LMSF is examined on crawling robots with soft or rigid actuators. Parameters that affect the performance of the LMSF are investigated. The robots with the LMSF prove capable of actuating across different surfaces in various solutions. Demonstration of 2D locomotion of crawling robots along arbitrary directions validates the versatility and reliability of the LMSF, suggesting broad utility in the development of advanced soft robotic systems.

Soft electrochemical bubble actuator with liquid metal electrode using an embodied hydrogel pneumatic source

“…The dark grey-colored residue is observed previously in systems that use sodium chloride solution. 30 The oxide buildup can increase the resistance of the device. To avoid the oxide residue, we used carbon felt as an anode.…”

A Data‐Driven Review of Soft Robotics

“…[ 563 ] Another noteworthy liquid‐metal‐based design led to demonstration of adhesion control for soft robots in slippery and underwater environments. [ 564 ]…”

“…[563] Another noteworthy liquid-metal-based design led to demonstration of adhesion control for soft robots in slippery and underwater environments. [564] Often derived from electricity through Joule heating in soft robotics, [500] the thermal medium was selected for a robotic component regardless of the origin of the change in temperature, as long as the researchers characterized the performance of their robotic component relative to temperature. In another example beyond Joule heating, heat from sunlight could be described as an optical medium, [500] but we classified this work as a thermal medium based on the original researchers' characterization of absorption to generate heat.…”

A tripodal wheeled mobile robot driven by a liquid metal motor

“…2 Gallium-based liquid metal (LM) is a kind of liquid alloy material that is similar to mercury but has extremely low toxicity. Via adjustment of the applied external physical field, this controllable liquid metal droplet (LMD) provides new solutions and opportunities for many disciplines and research directions, [3][4][5] especially in the fields of flexible electronics, [6][7][8] microfluidics, [9][10][11][12] soft sensors, 13-15 actuators, [16][17][18][19] micro-robotics, [20][21][22][23][24] and biomaterials. [25][26][27][28] Among them, the liquid metal motor (LMM) is a novel driving concept that presents obvious flexible advantages compared to traditional small motors, such as infinitely variable speed without a transmission chain, noiseless operation, a simple structure, and easy maintenance.…”