Engineers at UC Riverside have unveiled a pneumatic computer memory that can be used to control software robots. Innovation overcomes one of the biggest obstacles to the advancement of soft robotics: the fundamental mismatch between pneumatics and electronics. The work is published in the open access journal, PLOS A.

Pneumatic flexible robots use pressurized air to move soft, rubbery limbs and grippers and are superior to traditional rigid robots at performing delicate tasks. They are also safer for humans. Baymax, the caring companion robot from the 2014 Disney animated film, Big Hero 6, is a pneumatic robot for good reason.

But existing flexible pneumatic robot control systems still use electronic valves and computers to maintain the position of the robot’s moving parts. These electronic parts add considerable cost, size, and power demands to soft robots, limiting their feasibility.

To advance soft robotics into the future, a team led by bioengineering doctoral student Shane Hoang, his advisor, bioengineering professor William Grover, computer science professor Philip Brisk, and mechanical engineering professor Konstantinos Karydis, looked to the past.

“Pneumatic logic” predates electronic computers and once provided advanced levels of control in a variety of products, from thermostats and other components in air conditioning systems to mechanical pianos in the early 1900s. In pneumatic logic, air , not electricity, flows through circuits or channels and air pressure is used to represent all or nothing or true / false. In modern computers, these logical states are represented by 1 and 0 in the code to start or end electrical charges.

Flexible pneumatic robots need a way to remember and maintain the positions of their moving parts. The researchers realized that if they could create a pneumatic logic “memory” for a software robot, they could eliminate the electronic memory currently used for this purpose.

The researchers fabricated their pneumatic random access memory, or RAM, using microfluidic valves instead of electronic transistors. Microfluidic valves were originally designed to control the flow of liquids on microfluidic chips, but they can also control the flow of air. The valves remain sealed to a pressure differential even when disconnected from an air supply line, creating trapped pressure differentials that function like memories and maintain the states of a robot’s actuators. Dense arrays of these valves can perform advanced operations and reduce the expensive, cumbersome, and power-hungry electronic equipment typically used to control pneumatic robots.

After modifying the microfluidic valves to handle higher airflows, the team produced an 8-bit pneumatic RAM chip capable of controlling larger and faster flexible robots, and incorporated it into a pair of hands in 3d printed rubber. Pneumatic RAM uses air at atmospheric pressure to represent a “0” or FALSE value, and vacuum to represent a “1” or TRUE value. The flexible robotic fingers are extended when connected to atmospheric pressure and contracted when connected to vacuum.

By varying the combinations of atmospheric pressure and vacuum in the channels of the RAM chip, the researchers were able to make the robot play notes, chords and even an entire song – “Mary Had a Little Lamb” – on a piano. Click here to see a video of the robot playing the piano.

In theory, this system could be used to run other robots without any electronic hardware and only a battery-powered pump to create a vacuum. The researchers note that without positive pressure anywhere in the system – only normal atmospheric pressure – there is no risk of accidental overpressure and violent failure of the robot or its control system. Robots using this technology would be particularly safe for delicate use on or around humans, such as portable devices for infants with motor disabilities.

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The article “A pneumatic random access memory for the control of soft robots” is available here. The research was supported by the National Science Foundation.

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