A squishy octopus-shaped machine less than an inch (two centimeters) tall is described this week in the journal Nature as the first self-contained robot made exclusively of soft, flexible parts.
Interest in soft robots has taken off in recent years, as engineers look beyond rigid Terminator-type machines to designs that can squeeze into tight spaces, mold to their surroundings or handle delicate objects safely.
Scientists and engineers in the field have long worked on hard-bodied robots, often inspired by humans and other animals with hard skeletons. These machines have the virtue of moving in mathematically predictable ways, with rigid limbs that can bend and straighten only around fixed joints. But they also require meticulous programming and extensive feedback to avoid bumping into things; even then, their motions often become erratic or even dangerous when dealing with humans, new objects, bumpy terrain or other unpredictable situations.
Robots inspired by flexible creatures such as octopuses, caterpillars or fish offer a solution. Instead of requiring intensive (and often imperfect) computations, soft robots built of mostly pliable or elastic materials can just mold themselves to their surroundings. Although some of these machines use wires or springs to mimic muscles and tendons, as a group, soft robots have ditched the skeletons that defined previous robot generations. With nothing resembling bones or joints, these machines can stretch, twist, scrunch and squish in completely new ways. They can transform in shape or size, wrap around objects and even touch people more safely than ever before.
Building these machines involves developing new technologies to animate floppy materials with purposeful movement, and methods for monitoring and predicting their actions. But if this succeeds, such robots might be used as rescue workers that can squeeze into tight spaces or slink across shifting debris; as home health aides that can interact closely with humans; and as industrial machines that can grasp new objects without previous programming.
However, engineering soft versions of key parts has challenged researchers. The octobot is made of silicone rubber. Its ‘brain’ is a flexible microfluidic circuit that directs the flow of liquid fuel through channels using pressure-activated valves and switches. “It’s an analogy of what would be an electrical circuit normally,” says engineer Robert Wood at Harvard University in Cambridge, Massachusetts, one of the study’s leaders. “Instead of passing electrons around, we're passing liquids and gases.”
Valves and switches in the robot’s brain are positioned to extend the arms in two alternating groups. The process starts when researchers inject fuel into two reservoirs, each dedicated to one group of four arms. These reservoirs expand like balloons and push fuel through the microfluidic circuit. As fuel travels through the circuit, changes in pressure close off some control points and open others, restricting flow to only one half of the system at a time. As that side consumes fuel, its internal pressure decreases, allowing fuel to enter the other side — which then pinches off the first side, and so on.
The robot's brain talks to its limbs through 3D-printed channels embedded in the body. To create the body, researchers poured silicone polymers into an octopus-shaped mould. Then, using a 3D printer, they injected special inks that maintained their form and position in the surrounding polymer. The scientists heated the octobot to cure its structure, which also caused the ink to evaporate — leaving behind a hollow network that infiltrates the octobot's limbs and links to its brain.
Many soft robots are tethered to compressed air tanks that provide power, but this can restrict their range of motion. Wood and his colleagues take a different approach, using a chemical reaction to power the octobot.
Their fuel is a 50 percent hydrogen peroxide solution. When this is exposed to platinum infused into two segments of the robot's internal network, it rapidly decomposes into a greater volume of water and oxygen. The resulting burst of pressurized gas in each segment inflates and extends one set of arms, eventually exiting through exhaust vents. The octobot currently runs for up to eight minutes on one milliliter of fuel.
It is not designed to perform any particular task, and doesn’t mimic the motions of a real octopus. Instead, it demonstrates the technology, says Wood. In the future, more sophisticated microfluidic circuits might improve endurance, and allow more complex movements when paired with the appropriate limb designs, the authors suggest.
“Now what needs to be worked out is how to reprogram the robots to perform different actions, to respond to the environment, and not just perform a pre-programmed sequence,” says materials engineer Robert Shepherd at Cornell University in Ithaca, New York. Shepherd is especially keen to see whether souped-up microfluidic circuits can be combined with flexible sensors to make smarter soft robots that are better able to adapt to changing conditions.
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.