From medicine to disaster response, robots have repeatedly proven their worth through their ability to squeeze into tight spaces. Reporting in Science Robotics, roboticists have unveiled prototypes for machines that can be deployed in interesting new ways through growing and unfolding, giving them useful access to all kinds of nooks and crannies.
Researchers at the University of California, Santa Barbara, and Stanford University have created a tube-like robot inspired by the way neurons, roots and vines can move through their environments by growing through them. The machine has a fairly simple construction: it consists of a hose-like polyethylene membrane wound in a reel in a base section and pumped with air so that it everts (that is, turns itself inside out) at its tip.
It can extend up to 72 meters, a 25,000 percent increase over its original size, and can “grow” in this manner quite quickly – up to 22 miles per hour, a rate comparable to locomotion in animals and other robots.
Go to the light
The machine can also sense its environment and navigate. A camera at its tip is continually moving outward, and can detect targets such as light sources or moving objects. To direct itself to a target, the left or right air chamber at the tip will inflate, increasing its size and forcing the tip to progress in the opposite direction. In a demonstration video, the tube navigates around wooden blocks as it moves toward a light bulb like a vine seeking sunlight.
“Vines can push through tiny cracks in a wall to get to where there is sunlight available, all the while keeping connected to their roots and sending nutrients back and forth,” says study co-author Laura Blumenschein of Stanford’s Department of Mechanical Engineering. “If we could make a system that imitates those behaviors, but at a much faster speed, there could be many useful tasks it could accomplish.”
Potential applications such as neurosurgery and search and rescue are seen in another demo video. The robot first slithers under a door, then approaches a steaming pipe, curls around and above it, and then forms its tip into a hook. The hook grabs hold of a valve and manages to pull it down, shutting off the steam. A miniature version of the robot is also seen moving in a scale model of a brain ventricle, where an ablation tool extends from its tip before it deflates and retracts. Other use cases include slithering under a 75-kg crate and then inflating to jack it up, putting out a fire with water and air inside the tube itself, and forming a helical antenna. The tube-bot is also robust – it can travel through sticky flypaper and glue and over nails without slowing – and can move on the surface of water or, by deploying adhesive pads, up smooth vertical walls.
“With designs like ours, growing robots can rival traditional mobile robots and navigate some environments that prove challenging to robots currently,” says Blumenschein. “All the robots are currently made by hand. Especially for applications where we want to control the direction of the robot, this isn’t really feasible, and we would have to develop automated manufacturing in order to produce the lengths of robot body desired.”
Another way of getting into tight spaces is by deploying in very compact form. Robots that unfold themselves to perform useful tasks have been created many times, but batteries and wires to power them can limit their effectiveness. Researchers at Harvard University, the Institute for Biologically Inspired Engineering, and Ajou University in South Korea have developed wireless, battery-free devices that rely on passive electronic components to fold and unfold like origami.
These tetrahedrons were made in large and smaller versions, with folding lines measuring 12 cm on the former and 1.7 cm on the latter. They can fold along three axes, forming a pyramid-like structure when all their sides are folded up. The devices can move thanks to structures built into their joints: Shape Memory Alloy (SMA) coils that regain their original shape when heated, and miniature circuits that become energized by resonance frequencies. When electrical current heats the SMAs, and matching the electromagnetic field to each circuit’s resonance frequency, the devices can fold their sides, either individually or simultaneously.
In demonstration videos, the researchers showed how the tetrahedron technology could be adapted to construct a miniature ship in a bottle that can raise its sail wirelessly. They also created a battery-free micro-origami robotic arm equipped with SMA actuators and a gripper. The arm can perform simple left-right, up-down motions and its gripper can pick up objects such as a sponge.
“I think this has tremendous potential for biomedical robots,” says study co-author Robert Wood, a professor of engineering and applied sciences at Harvard. “For example, robots that you could swallow and then use this strategy to control their motions for diagnostic procedures, biopsies, drug delivery, etc. We are planning to build representative prototypes for these applications using the techniques described in the paper.”