Soft origami robot bends and twists in mazes

A soft robot that bends and twists through mazes has been developed by engineers at Princeton and North Carolina State University using origami and modern materials science.

The robot is made of segments that can fold into a flat disk and extend into a cylinder. Partial folds bend the robot and allow for motion and steering
The robot is made of segments that can fold into a flat disk and extend into a cylinder. Partial folds bend the robot and allow for motion and steering - Frank Wojciechowski/Princeton University

Soft robots can be challenging to guide because steering equipment often increases the robot’s rigidity. The new design builds the steering system directly into the robot’s body, said Tuo Zhao, a postdoctoral researcher at Princeton. The team’s research is detailed in PNAS.

The researchers created the robot out of modular, cylindrical segments that can operate independently or join to form a longer unit, all of which contribute to the robot’s ability to move and steer.

Zhao said the robot’s ability to assemble and split up on the move allows the system to work as a single robot or a swarm.

“Each segment can be an individual unit, and they can communicate with each other and assemble on command,” he said in a statement. “They can separate easily, and we use magnets to connect them.”

Zhao works in Glaucio Paulino’s lab in the Department of Civil and Environmental Engineering and the Princeton Materials Institute. 

“We have created a bio-inspired plug-and-play soft modular origami robot enabled by electrothermal actuation with highly bendable and adaptable heaters,” said Paulino. “This is a very promising technology with potential translation to robots that can grow, heal, and adapt on demand.”

The researchers began by building their robot out of cylindrical segments featuring a Kresling pattern. The pattern allows each segment to twist into a flattened disk and expand back into a cylinder. This twisting, expanding motion is the basis for the robot’s ability to crawl and change direction. By partially folding a section of the cylinder, the researchers can introduce a lateral bend in a robot segment. By combining small bends, the robot changes direction as it moves forward.

Researchers at NC State developed a mechanism to control the bending and folding motions used to drive and steer the robot.

They used two materials that shrink or expand differently when heated (liquid crystal elastomer and polyimide) and combined them into thin strips along the creases of the Kresling pattern. The researchers also installed a thin stretchable heater made of silver nanowire network along each fold.

Electrical current on the nanowire heater heats the control strips, and the two materials’ different expansion introduces a fold in the strip. By calibrating the current, and the material used in the control strips, the researchers can precisely control the folding and bending to drive the robot’s movement and steering.

Shuang Wu, a postdoctoral researcher at NC State, said the lab’s previous work used the stretchable heater for continuously bending a bilayer structure. “In this work we achieved localised, sharp folding to actuate the origami pattern. This effective actuation method can be generally applied to origami structures [with creases] for soft robotics,” Wu said.

The researchers said that the current version of the robot has limited speed, and they are working to increase the locomotion in later generations. They also plan to experiment with different shapes, patterns, and instability to improve the speed and the steering.