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What if you could have an extra limb extending from your hip, to help lift and carry small objects needed for day-to-day tasks? That is exactly what a team of researchers from Rice University in Texas have created, powering it with nothing more than compressed air.
Geared towards people living with disabilities, the ‘third arm’ is one of several simple creations integrated with a ‘textile-based energy harvesting system’.
Designed and built by mechanical engineer Daniel Preston and colleagues including Rachel Shveda and Anoop Rajappan, the arm is a piece of fabric that hugs the body when not in use. When activated, it extends outwards and wraps around the targeted object. An elastomer lining on the surface helps maintain its grip, which is released when the arm is deactivated.
Unlike the Preston lab’s now-famous manipulation of dead spiders as grabbers, the air needed to power the pneumatic devices comes from walking. Textile pumps embedded in the soles of shoes harvest air pressure, and pneumatic actuators make use of that pressure where needed. The pumps are filled with open-cell polyurethane foam that allows them to recover their shape after every footfall.
The pump is small enough to be comfortable, said assistant professor Preston. “The stiffness of the foam is about on par with a typical shoe insert,” he said. “We wanted to make sure this felt like something you'd actually want to have inside of your shoe.”
In addition to the curling arm, which can grip a cup or other small objects while hands are full, the Rice lab also built a shirt with a bellows-like actuator attached at the armpit, which expands to enable the wearer to pick up a 4.5kg object.
“Census statistics say there are about 25m adults in the United States who find it difficult to lift 10 pounds (4.5kg) with their arms,” said Rajappan, a lead author of a paper on the work. “That’s something we commonly do in our daily lives, picking up household objects, or even a baby.”
Tests by the Rice lab showed the devices produce the equivalent of 3W of power with a conversion efficiency of more than 20%, easily outperforming electromagnetic, piezoelectric and triboelectric strategies for foot-strike energy harvesting.
All the components for a single device cost the lab about $20, Preston said. The products are reportedly simple to assemble and robust enough to be cleaned in a washing machine with no degradation.
The lab also developed mathematical models to predict how well an assistive device would perform based on a user’s weight and walking speed, among other parameters.
“One way to take this forward will be to use the model to optimise performance for specific user groups,” said Rajappan. “We’re also thinking about devices like pneumatic actuators that apply therapeutic compression for things like deep vein thrombosis, blood clots in the legs. Anything that requires air pressure can be powered by our system.”
Preston added: “Now that we’re providing the power, we can tap into all the existing work on actuation. This would include things like gloves that help people close their hands, assistance at both the elbow and shoulder joints and other devices that still rely on typically rigid and bulky power supplies that are either uncomfortable or require being tethered to external infrastructure.”
Future work could include discussions with fashion designers “to keep wearers from resembling the Michelin Man”, Preston said.
The work was published in Science Advances.
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