Soft robot takes inspiration from caterpillar to squeeze into tiny spaces

It works through an electric current.
Loukia Papadopoulos
A caterpillar inspired robot.jpg
A caterpillar inspired robot.

NC State University 

Researchers at North Carolina State University have engineered a soft robot that can move forward, backward, and dip under narrow spaces by functioning just like a caterpillar. Users can steer the robot in many directions simply by using heat.

“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 Yong Zhu, corresponding author of a paper on the work and the Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering at NC State, as stated by the press release.

“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.

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

“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.”

The novel robot has two layers of polymer, one which shrinks and one which expands when exposed to heat. Furthermore, silver nanowires are embedded in the expanding layer of the polymer to support an electric current. Thus the robot can be controlled through heat generated by the current.

More current, more movement

“We demonstrated that the caterpillar bot is capable of pulling itself forward and pushing itself backward,” said Shuang Wu, first author of the paper and a postdoctoral researcher at NC State. 

“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 robot provides such precise control as to allow the researchers to steer it under a very low gap. Researchers could also control the both forward and backward motion as well as how high the robot 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,” Zhu concluded in the press statement. 

“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 study was published in the open-access journal Science Advances.

Study abstract:

Many inspirations for soft robotics are from the natural world, such as octopuses, snakes, and caterpillars. Here, we report a caterpillar-inspired, energy-efficient crawling robot with multiple crawling modes, enabled by joule heating of a patterned soft heater consisting of silver nanowire networks in a liquid crystal elastomer (LCE)–based thermal bimorph actuator. With patterned and distributed heaters and programmable heating, different temperature and hence curvature distribution along the body of the robot are achieved, enabling bidirectional locomotion as a result of the friction competition between the front and rear end with the ground. The thermal bimorph behavior is studied to predict and optimize the local curvature of the robot under thermal stimuli. The bidirectional actuation modes with the crawling speeds are investigated. The capability of passing through obstacles with limited spacing are demonstrated. The strategy of distributed and programmable heating and actuation with thermal responsive materials offers unprecedented capabilities for smart and multifunctional soft robots.

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