Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have made a soft robot that can crawl like a snake without having any rigid parts.

Kirigami, an ancient Japanese papercraft that relies on cuts to change the properties of a material, as compared to the folds of origami, have been used to make the soft robotic scales.

When the robot stretches, the flat kirigami surface will be transformed into a 3D-textured surface and it will grip the ground just like snakeskin. Snakes are actually capable of slithering up to 14 miles per hour They can also squeeze into a tight space, climb trees and swim. This is all possible because of the scales they have.

When a snake moves, its scales will grip the ground and propel the body forward. This is similar to how crampons will help hikers establish footholds in slippery ice. This is called locomotion and is helped by friction. It is possible due to the shape and positioning of the snake scales.

“There has been a lot of research in recent years into how to fabricate these kinds of morphable, stretchable structures,” Ahmad Rafsanjani, the first author of the paper, said. “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,” said Rafsanjani, who is also a postdoctoral fellow at SEAS.

Experiment with various cuts

The researchers have started making the robot skin with a simple flat plastic sheet. They have placed in a line of centimeter-scale cuts, using a laser cutter. The researchers then wrapped the sheet around an elastomer actuator which was like a tube once the cuts were made.

The actuator expands and contracts with air like a balloon. The kirigami cuts pop-out when the actuator expands. This forms a rough surface which grips the ground. When the actuator lets the air out, the cuts fold flat and push the crawler forward.

Opens door for new soft robots

The researchers have built a fully independent robot. It has integrated onboard control, sensing, actuation and power supply in a small tail. The robot has been tested crawling throughout Harvard’s campus. The team experimented with various-shaped cuts, which included triangular, circular and trapezoidal. They found out that trapezoidal cuts gave the robot a longer stride because they most closely resemble the shape of snake scales.

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

“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.” Bertoldi, who is also a William and Ami Kuan Danoff Professor of Applied Mechanics, said.

Source: Interesting Engineering, Harvard SEAS