In recent years, an entirely new class of robot — inspired by natural forms and built using soft, flexible elastomers — has taken the field by storm, with designs capable of gripping objects, walking, and even jumping.
Yet despite those innovations, so-called “soft” robots still carried some “hard” parts.
In particular, said Philipp Rothemund, a doctoral student working in the lab of Woodford L. and Ann A. Flowers University Professor George Whitesides, the inflation and deflation of the robots was typically controlled by off-the-shelf pneumatic valves — until now.
Rothemund and postdoctoral fellow Daniel Preston have created a soft valve that could replace such hard components, and could lead to the creation of entirely soft robots. The valve’s structure can also be used to produce unique, oscillatory behavior and could even be used to build soft logic circuits. The valve is described in a recently published paper in Science Robotics.
In addition to Rothemund and Preston, the study is co-authored by Alar Ainla, Lee Belding, and Sarah Kurihara from the Department of Chemistry and Chemical Biology, Zhigang Suo from the Kavli Institute for Bionano Science & Technology, and Whitesides.
“People have built many different types of soft robots … and all of them in the end are controlled by hard valves,” Rothemund said. “Our idea was to build these control functions into the robot itself, so we wouldn’t need these hard, external parts anymore. This valve combines two simple ideas — first, the membrane is similar to ‘popper’ toys, and the second is that when you kink these tubes, it’s like when you kink a garden hose to block the water flow.”
The valve demonstrated by Preston and Rothemund is built into a cylinder that is separated by a silicone membrane, creating an upper and lower chamber.
Pressurizing the lower chamber forces the membrane to pop up, and releasing the pressure causes it to pop back down to its “resting” state. Each chamber also contains a tube that can be kinked when the membrane switches orientations, effectively turning the valve on or off.
“Whichever direction it’s in, it’s kinking a tube above or below,” Preston said. “So when it’s popped down, the bottom tube is kinked, and there’s no air flow through the bottom tube. When the membrane pops up, the top tube is kinked, the bottom tube will unkink, and air can flow through the bottom tube. We can switch back and forth between these two states … to switch the output.”