Soft robots can easily crawl through loops and curves

The soft robot is made up of multiple parts that can fold into a flat disk and extend into a cylinder. Image credit: Princeton University

Engineers at Princeton University and North Carolina State University have combined ancient origami techniques with modern materials science to create a soft robot that can easily navigate a maze. In an article published in the latest issue of the journal Proceedings of the National Academy of Sciences, the researchers describe their process of creating a robot with modular cylindrical parts.

Steering soft robots has always been challenging because traditional steering devices increase the rigidity of the robot and reduce its flexibility. This new design overcomes these problems by building the steering system directly into the robot body. The concept of modular soft robots also gives people a further understanding of future robots that can grow, repair and develop new functions.

The newly created robot has the ability to assemble and disassemble on the move, which enables it to work both as a single robot and as a group. Each part is an independent unit that can communicate with each other and assemble on command, and can also be easily separated and connected again using magnets.

The researchers built the robot using cylindrical sections of an origami form known as a Kreslin pattern. The pattern allows each segment to twist into a flat disk and expand back into a cylinder. This twisting and stretching motion is the basis for the robot's ability to crawl and change direction. By folding a portion of the cylinder, the robot can also change direction as it moves forward.

The most challenging part of this work is to develop a mechanism to drive and manipulate the bending and folding motion of the robot. The researchers used two materials that react differently when heated: liquid crystal elastomer (contracts when heated) and polyimide (expands when heated), and combined them into thin strips along the creases of the Kresslin pattern. A stretchable heater made of silver nanowires is installed at each fold. The current on the nanowire heater heats the control strip, causing the two materials to deform due to different thermal expansion coefficients, thereby inducing folding. By adjusting the current and control strips, the researchers can precisely control folding and bending, driving the robot to move and turn precisely.