This Robot Leaves Behind a Paper Trail

As a general rule of thumb, robots can be made with rigid components and controlled with great precision, or they can be made of softer, more flexible materials, but with much less precision in their control systems. Unfortunately, many use cases require that a robot be both flexible and controlled with precision. Such robots could be used in delicate medical procedures, where the ability to navigate through narrow passages and avoid causing damage is essential. They could also find applications in space exploration, manufacturing, and beyond.

Existing materials and techniques are not getting the job done, so a team of engineers at Princeton and North Carolina State University came up with a completely different approach to the problem of controlling a soft robot. The team blended modern technology with the ancient art of origami to develop a worm-like modular soft robot that can crawl forward, backward, and make turns without rigid components. And given the modular approach that was taken, robots of this sort can work together in a swarm, or join into a larger structure to complete more complex tasks.

The robot is formed from cylindrical segments, each of which is folded into a Kresling pattern. This pattern is a common origami fold that causes a cylinder to snap into a flat disk-like shape when force is applied to it in the proper way. This bistable nature of the folds, which makes them tend to want to be in one state or the other, was leveraged by the control system.

By applying a small amount of force in the right location, the cylinder can be made to partially fold or unfold, which makes it wiggle around in a controlled way that can be harnessed. This was accomplished by utilizing a pair of temperature-sensitive materials, a liquid crystal elastomer and polyimide, that shrink or expand at different rates when heated. These soft, stretchable materials were attached to the origami folds, then a silver nanowire was installed on them. When electrical current is channeled through this wire, it quickly heats up, causing the temperature-sensitive materials to deform, which in turn partially folds the origami structure.

Through a careful orchestration of the timing of bends at different points along the length of the robot, it can be coaxed into moving. This could be a turn or forward movement, depending on how the operator applies current to the nanowire heaters. For segments to attach to one another, they only need to get close enough that a set of magnets can pull them together.

While these robots are certainly not the right tool for every use case that requires a soft robot, their ability to grow, heal, and adapt to new situations makes them very intriguing. It was also noted that the method of actuation that was introduced in this work could be applied to other types of origami folds in theory, which could further expand the possible uses of this novel platform. But first, there are a few kinks to work out — the robot’s movements are quite slow at this time. But the team hopes to speed it up with some additional work in the near future.