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Development of Programmable, Non-Electronic Circuits Controlling Soft Robots’ Actions

Robotics scientists, materials scientists, and engineers from Rice University and Harvard University demonstrated that it is possible to build non-electronic, programmable circuits that regulate the soft robots’ actions by processing data programmed in bursts of compressed air.

Rice University student Colter Decker, a senior majoring in mechanical engineering, demonstrates a glove that was used to demonstrate the analog features of soft pneumatic control circuitry for soft robotics. (Photo by Brandon Martin/Rice University)

Part of the beauty of this system is that we're really able to reduce computation down to its base components.

Colter Decker, Study Lead Author and Undergraduate, Rice University

He stated that electronic control systems have been refined and honed for several years, and reconstructing computer circuitry “with analogs to pressure and flow rate instead of voltage and current” made it simpler to integrate pneumatic computation.

Decker, who is a senior majoring in mechanical engineering, built his soft robotic control system majorly from day-to-day materials such as rubber bands and plastic drinking straws.

Despite their ease, experiments showed the air-driven logic gates of the system could be configured to function operations known as Boolean functions, which are modern computing’s meat and potatoes.

The goal was never to entirely replace electronic computers,” Colter added. He says that there are several cases where wearables or soft robots need to be just configured for a few easy movements, and it is likely the technology established in the study “would be much cheaper and safer for use and much more durable” than conventional electronic controls.

Decker started working as a freshman in the lab of Daniel Preston, an Assistant Professor of Mechanical Engineering at Rice. Decker analyzed fluidic control systems and got fascinated with making one when he succeeded in a competitive summer research fellowship that will enable him to devote a few months to work in the lab of George Whitesides, a Harvard Chemist and Materials Scientist.

The project transformed into a one-month-long association between the two study teams. Nine co-authors were involved with Decker in this research, along with co-corresponding authors Preston and Whitesides.

Decker and co-workers formed two components. Firstly, a piston-like actuator that transforms air pressure into mechanical force and a valve that can be substituted between two states, on and off. The components were built from plastic drinking straws, rubber bands, flexible plastic tubing, parchment paper, and thermoplastic polyurethane sheets that can be bonded with a desktop hot iron or heat press.

The study group demonstrated that the two components could be integrated into one device, which is a bistable valve that functions like a switch and employs air pressure as input and output. To flip the switch between the states of on and off, a particular quantity of air pressure is required.

The valves are kept shut by rubber bands, and they are automated by including or removing rubber bands—changing the quantity of pressure needed for activation. Decker showed in tests that the circuits could be deployed to regulate a pneumatic cushion, a soft, hand-shaped robot, and a shoebox-sized robot that can walk a pre-programmed number of steps, retrieve an item, and go back to its initial location.

The biggest achievement in this work is the incorporation of both digital and analog control in the same system architecture,” stated Preston. With both implies the pneumatic control circuits can be configured digitally, with the “ones and zeroes that you think of in a traditional computer.”

“But we can also bring in analog capabilities, things that are continuous,” he stated. “That allows us to really simplify the overall system architecture and achieve new capabilities that weren't accessible in prior work.”

It is exceptional for an undergraduate to be the study’s lead author in an esteemed journal like the Proceedings of the National Academy of Sciences. Still, Preston stated that the success of Decker was not a chance occurrence.

The undergraduates at Rice are truly top-notch, and Colter, in his case, actually has risen to essentially what I would say is the level of a Ph.D. student in terms of some of his output as an undergraduate researcher.

Daniel Preston, Assistant Professor, Mechanical Engineering, Rice University

Haihui Joy Jiang, Samuel Root, Jonathan Alvarez, Jovanna Tracz and Lukas Wille of Harvard, Anoop Rajappan of Rice, and Markus Nemitz of Worcester Polytechnic Institute are the additional co-authors of the study.

The study was funded by the Department of Energy (DE-SC0000989), the National Science Foundation (2144809, 2011754, 2025158), the Rice University Academy of Fellows, and the Harvard University Center for Nanoscale Systems.

Soft robotics controlled by programmable soft valves for digital and analog control
Soft robotics controlled by programmable soft valves for digital and analog control. Image Credit: Rice University

Journal Reference:

Decker, C. J., et al. (2022) Programmable soft valves for digital and analog control. Proceedings of the National Academy of Sciences.

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