But each year, soft robots gain new abilities. They’ve learned to jump, squirm, and grip. And they can handle tomatoes without bruising the fruit, emerge unscathed after being run over by a car, and journey through radiation, disaster zones, and outer space, all without the challenges facing their harder peers. For people and animals, they have a “cooperative function”: a soft touch.
Recently, researchers in the lab of George M. Whitesides, the Woodford L. and Ann A. Flowers University Professor, have invented soft replacements for the last hard parts required to build a robot. Instead of electricity and wires, pressurized air expands and contracts rubber inflatables to create movement, soft valves take over for the hard, and soft digital logic replicates the same capabilities of an electronic computer.
Now, postdoctoral scholar Daniel J. Preston’s latest innovations give these robots new, complex movements. As first author on a study published late last month in Science Robotics, he introduces the first soft ring oscillator, which gives these machines the ability to roll, undulate, sort, measure liquids, and swallow.
“It’s another tool in the toolkit to make these smart, soft robots without any electronics, and without any hard valves,” Preston says.
Until now, ring oscillators were made with electronic transistors or microfluidics. Electronics always require hard components. Most microfluidics do, too. Many use glass for their pressurized water or air systems. Preston’s macroscale pneumatic ring oscillator relies on inverters and air. They manipulate the air pressure in his robot’s rubber tubes: If the input is high pressure, the output will be low pressure, and vice versa. When three or other odd numbers of gates are connected in a ring, one gate’s shift triggers the next, which triggers the next, and on and on.
“The cool response that you get when you combine an odd number of these inverters in a loop is an instability that travels around the loop,” Preston says. He likens it to a Slinky that collapses in order to spring down a flight of stairs, creating a constant pace without the need for another push.
To test what the soft ring oscillator could do, Preston and his team created five prototypes. Each uses a single, constant source of air pressure to run three pneumatic actuators (the inverters).