Snakes Inspire New Class of Crawler Bots

Kirigami cutting has produced skin that a robot can use to propel itself along. (Image by Ahmad Rafsanjani/Harvard SEAS) Posted for media use

By Sunny Lewis

CAMBRIDGE, Massachusetts, February 22, 2018 ( News) – Harvard researchers have developed a robot modeled on snakeskin with soft robotic scales made using kirigami – an ancient Japanese paper craft that relies on cuts to change the properties of a material.

As the robot stretches, the flat kirigami surface is transformed into a 3D-textured surface, which grips like snakeskin and crawls along.

“These all-terrain soft robots could one day travel across difficult environments for exploration, inspection, monitoring and search and rescue missions or perform complex, laparoscopic medical procedures,” envisions the paper’s senior author, Dr. Katia Bertoldi, a professor of applied mechanics at Harvard University.

Bertoldi, who is a new associate faculty member of the Wyss Institute for Biologically Inspired Engineering at Harvard, says this form of snake-inspired locomotion is something brand new. The ancient art of kirigami is inspiring a new class of materials.

“We believe that our kirigami-based strategy opens avenues for the design of a new class of soft crawlers,” Bertoldi said.

“It turns out that figuring out how structures can deform, fold, interact with light, and absorb energy has applications in a variety of fields, and it’s been exciting to see our lab’s work contribute to such a diverse array of advances,” she said.

The key to this new class of crawlers is in the shape and function of the scales of a snake’s skin.

As a snake moves, its scales grip the ground, propelling its body forward. Called friction-assisted locomotion, this type of movement is possible because of the shape and positioning of snake scales.

Now, a team of researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has developed a soft robot that uses the same principles of locomotion as a snake to crawl without any rigid components.

“There has been a lot of research in recent years into how to fabricate these kinds of morphable, stretchable structures,” says Ahmad Rafsanjani, a postdoctoral fellow at SEAS and first author of the paper, published Wednesday in the journal “Science Robotics.”

“We have shown that kirigami principles can be integrated into soft robots to achieve locomotion in a way that is simpler, faster and cheaper than most previous techniques,” Rafsanjani said.

Kirigami, from the Japanese word kiri, meaning “cut,” and kami, meaning “paper,” is a variation of origami, the Japanese art of paper folding.

The researchers started with a simple, flat plastic sheet. Using a laser cutter, they embedded an array of centimeter-scale cuts, of different shapes and sizes.

The team experimented with various-shaped cuts, including triangular, circular and trapezoidal. They found that trapezoidal cuts, which most closely resemble the shape of snake scales, give the robot a longer stride.

Once cut, the researchers wrapped the sheet around a tube-like elastomer actuator, which expands and contracts with air like a balloon.

When the actuator expands, the kirigami cuts pop out, forming a rough surface that grips the ground. When the actuator deflates, the cuts fold flat, propelling the crawler forward.

The researchers built a fully untethered robot with these capabilities. It has integrated on-board control, sensing, actuation and power supply packed into a tiny tail.

They tested the soft robot by letting it crawl on the Harvard’s campus. See a video of the robot’s test crawl at Harvard.

“We show that the locomotive properties of these kirigami-skins can be harnessed by properly balancing the cut geometry and the actuation protocol,” said Rafsanjani. “Moving forward, these components can be further optimized to improve the response of the system.”

This research was supported by the U.S. National Science Foundation.

Citation: “Kirigami skins make a simple soft actuator crawl,” By Ahmad Rafsanjani, Yuerou Zhang, Bangyuan Liu, Shmuel M. Rubinstein and Katia Bertoldi. Science Robotics 21 Feb 2018: Vol. 3, Issue 15, eaar7555

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