Add analog and pneumatic to the list of control system options for soft robots.
In a study published online this week, robotics researchers, engineers and materials scientists from Rice University and Harvard University show that it is possible to make non-programmable electronic circuits that control the actions of soft robots by processing information encoded in bursts of compressed air.
Colter Decker, an undergraduate student at Rice, lead author of the study, said: Proceedings of the National Academy of Sciences. Electronic control systems, he said, have been refined and refined for decades, and recreating computer circuits “with analogues for pressure and flow rate rather than voltage and current” made it easier to integrate pneumatic computation.
Decker, a senior specialist in mechanical engineering, built his soft robotic control system primarily from everyday materials such as plastic drinking straws and rubber bands. Despite its simplicity, experiments have shown that air-driven system logic gates can be configured to perform operations called logic functions that are meat-and-potatoes in modern computing.
“The goal was never to completely replace electronic computers,” Coulter said. There are many cases where soft robots or wearables need to be programmed for just a few simple movements, he said, and it is possible that the technology described in the paper could be “much cheaper, safer to use and more durable” than traditional electronic controls.
As a freshman, Decker began working in the lab of Daniel Preston, an associate professor of mechanical engineering at Rice. Decker studied fluid control systems and became interested in creating one when he won a competitive summer research fellowship that would allow him to spend a few months working at Harvard University’s chemistry lab and materials scientist George Whitesides.
The project turned into a month-long collaboration between the two research groups, and Decker had nine study co-authors, including corresponding authors Preston and Whitesides.
Decker and his colleagues created two components, a piston-like actuator that translates air pressure into mechanical force and a valve that can be switched between two states – off and on. The components were made from parts that included plastic drinking straws, flexible plastic tubing, rubber bands, parchment paper, and thermoplastic polyurethane sheets that could be attached to a desktop heat press or a hot iron.
The research team showed that the two components can be combined into one device, a bistable valve that acts as a switch and uses air pressure as input and output. A certain amount of air pressure is needed to flip the switch between off and on states. The valves are closed by rubber bands, and are programmed by adding or subtracting rubber bands, which changes the amount of pressure required to activate. In tests, Decker has shown that circuits can be used to control a soft robot shaped like a hand, an airbag, and a shoebox-sized robot that can walk a preprogrammed number of steps, retrieve an object and return to its starting position.
“The biggest achievement of this work is the integration of both digital and analog control into the same system architecture,” Preston said. Having both means that pneumatic control circuits can be programmed digitally, he said, using “the ones and zeros you think of in a traditional computer. But we can also bring in analog capabilities, the continuous stuff.” “This allows us to simplify the overall system architecture and realize new capabilities that were not accessible in previous work.”
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Colter J. Decker et al, Programmable soft valves for digital and analog control, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2205922119
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