Supply an arm with air

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Everyone could use a third arm sometimes, but for some it would be especially useful.

Mechanical Engineers at Rice University George R. Brown School of Engineering built a handy extra limb capable of grabbing things and going, powered only by compressed air. This is one of many ideas they implemented with a textile-based energy harvesting system.

The proof-of-principle robotic devices designed and built by Daniel Prestonassistant professor of mechanical engineering, lead authors Rachel Shveda and Anoop Rajappan and their team are intended for people with disabilities and are durable enough for everyday use, they said.

How the project described in Scientists progress uses air differs from the now famous Preston Laboratory manipulation of dead spiders as catchers. These pneumatic devices draw their power from walking.

The prototype “arm” is a piece of fabric that hugs the body when not in use, but extends outward when activated and incorporates an elastomer liner on the surface to maintain grip on slippery objects. For the demonstrations, Rice’s former student Shveda, now a US Coast Guard officer, operated the arm with a switch. Preston said future versions may have sensors that anticipate the wearer’s intent and complement movement.

In addition to the curling arm that can grab a cup or other small objects when the hands are full, the Rice lab has built a shirt with a bellows-like actuator attached to the armpit that expands, allowing the wearer to pick up a 10 pound object. Testing the garment on a mannequin showed it could do this without the aid of human muscles.

“Census statistics indicate that there are approximately 25 million adults in the United States who struggle to lift 10 pounds with their arms,” says Rajappan, a postdoc supported by the Rice Academy of Fellows. “It’s something we commonly do in our daily lives, picking up household items or even a baby.”

The system requires two components: textile pumps built into the soles of walking shoes that harvest air pressure and pneumatic actuators that use this pressure when needed. The push-ups are filled with open-cell polyurethane foam that allows them to spring back into shape after every step.

Preston said the pump is small enough to be comfortable. “The stiffness of the foam is roughly equivalent to that of a typical shoe insert,” he says. “We wanted to make sure it looked like something you would actually want to have inside your shoe.”

Testing by the Rice Lab has shown the devices produce the equivalent of 3 watts of power with over 20% conversion efficiency, easily outperforming electromagnetic, piezoelectric, and triboelectric strategies for striking energy harvesting at the foot, one of which designed by students at Rice Oshman Engineering Design Kitchen.

Preston said all the components for a single device cost the lab about $20. The products were simple to assemble and robust enough to be cleaned in a washing machine without performance degradation.

“The manufacturing approach uses techniques that are already used in the apparel industry, things like cutting sheets of textile and sticking them together with heat and pressure,” he says. “We are ready to think about translating our work into products. »

Rajappan said that in addition to test units, the lab has also developed mathematical models to predict an assistive device’s performance based on the user’s weight and walking speed, among other parameters. “One way forward will be to use the model to optimize performance for specific user groups,” he says.

“We’re also thinking of devices like pneumatic actuators that apply therapeutic compression for things like deep vein thrombosis, blood clots in the legs,” says Rajappan. “Anything that requires air pressure can be powered by our system.”

“Now that we’re providing the power, we can tap into all the existing work on actuation,” adds Preston. “That would include things like gloves that help people close their hands, elbow and shoulder joint assistance, and other devices that still rely on typically stiff and bulky power supplies that are either uncomfortable , or needing to be attached to an external infrastructure.”

He noted that conversations with fashion consultants may take place in his future, to keep wearers from looking like the Michelin Man.

“We managed to get it to be fairly low profile, but yeah, that’s definitely something to think about, especially with actuators,” says Preston.

Co-authors are graduate students Te Faye Yap, Zhen Liu, Marquise Bell, and Barclay Jumet of Rice and Vanessa Sanchez of Harvard University.

The National Science Foundation (2144809, 1842494) supported the research.

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