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Caterpillar-like soft robot can squeeze through narrow gaps

Professional Engineering

The caterpillar-bot's movement is driven by a pattern of silver nanowires that use heat to control the way it bends (Credit: Shuang Wu, NC State University)
The caterpillar-bot's movement is driven by a pattern of silver nanowires that use heat to control the way it bends (Credit: Shuang Wu, NC State University)

A caterpillar-like soft robot can move forwards, backwards, and squeeze through narrow spaces, its creators have said, opening up potential applications in search-and-rescue missions.

Developed by researchers at North Carolina State University, the robot’s movement is driven by a unique pattern of silver nanowires that use heat to control the way it bends, allowing users to steer the robot.

“A caterpillar’s movement is controlled by local curvature of its body – its body curves differently when it pulls itself forward than it does when it pushes itself backward,” said Professor Yong Zhu, corresponding author of a paper on the work.

“We’ve drawn inspiration from the caterpillar’s biomechanics to mimic that local curvature, and use nanowire heaters to control similar curvature and movement in the caterpillar-bot.”

The device consists of two layers of polymer, which respond differently when exposed to heat – the bottom layer shrinks, while the top layer expands.

The pattern of silver nanowires includes multiple ‘lead points’, where electric current can be applied. The researchers controlled which sections of the nanowire pattern heated up by applying an electric current to different lead points, and controlled the amount of heat by applying more or less current.

“Engineering soft robots that can move in two different directions is a significant challenge in soft robotics,” said Zhu. “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.”

First author Shuang Wu said: “We demonstrated that the caterpillar-bot is capable of pulling itself forward and pushing itself backward.

“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 robot could be steered under a very low gap, by controlling its backward and forward movements as well as how high it bent upwards.

“This approach to driving motion in a soft robot is highly energy efficient, and we’re interested in exploring ways that we could make this process even more efficient,” said Zhu. “Additional next steps include integrating this approach to soft robot locomotion with sensors, or other technologies for use in various applications – such as search-and-rescue devices.”

The paper was published in Science Advances.

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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.


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