Thermally Actuated Caterpillar-Inspired Soft Crawling Robot

Researchers have developed a caterpillar inspired soft-robot that can move in two different directions by controlling the heat being applied.

Engineering soft robots that can move in two different directions is a significant challenge in soft robotics. Enabling soft robots to move in almost any direction can be adapted not only for the purpose of crawling or walking but also for enabling muscle-like movement for performing a variety of tasks.

Researchers at North Carolina State University have demonstrated a caterpillar-like soft robot that can move forward, backward and dip under narrow spaces. The caterpillar-bot’s movement is driven by a novel pattern of silver nanowires that use heat to control the way the robot bends, allowing users to steer the robot in either direction.

“The embedded nanowire heaters allow us to control the movement of the robot in two ways. We can control which sections of the robot bend by controlling the pattern of heating in the soft robot. And we can control the extent to which those sections bend by controlling the amount of heat being applied,” says Yong Zhu, corresponding author of the paper.

The caterpillar-bot consists of two layers of polymer, which respond differently when exposed to heat. The bottom layer shrinks, or contracts, when exposed to heat. The top layer expands when exposed to heat. A pattern of silver nanowires is embedded in the expanding layer of polymer. The pattern includes multiple lead points where researchers can apply an electric current. The researchers can control which sections of the nanowire pattern heat up by applying an electric current to different lead points, and can control the amount of heat by applying more or less current.

The caterpillar-bot is capable of pulling itself forward and pushing itself backward. Shuang Wu, first author of the paper and a postdoctoral researcher at NC State said “In general, the more current we applied, the faster it would move in either direction. However, we found that there was an optimal cycle, which gave the polymer time to cool—effectively allowing the ‘muscle’ to relax before contracting again. If we tried to cycle the caterpillar-bot too quickly, the body did not have time to ‘relax’ before contracting again, which impaired its movement.”

The researchers also demonstrated that the caterpillar-bot’s movement could be controlled to the point where users were able steer it under a very low gap—similar to guiding the robot to slip under a door. In essence, the researchers could control both forward and backward motion as well as how high the robot bent upwards at any point in that process.

Reference :  Shuang Wu et al, Caterpillar-Inspired Soft Crawling Robot with Distributed Programmable Thermal Actuation, Science Advances (2023).

DOI: 10.1126/sciadv.adf8014. www.science.org/doi/10.1126/sciadv.adf8014

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