Combustion Makes Braille Mobile
A tiny grid of soft actuators may finally give blind people a portable read.
Now a group of researchers out of Cornell University have made the first steps toward creating a truly portable braille display.
And it’s powered by combustion.
“It turns out that the physical mechanisms that we love for making actuators at larger scales all act up and cause problems when you scale down that small,” said Ronald Heisser, a graduate researcher at Cornell University’s Sibley School of Mechanical and Aerospace Engineering, and lead author of the paper “Valveless microliter combustion for densely packed arrays of powerful soft actuators,” published in the Proceedings of the National Academy of Sciences this September.
Solenoids at that scale, for instance, would have wires with fewer wraps, and would need a higher current to make up for it. “But when you increase the current, you’re adding more heat to the system,” Heisser said. “When you are packing all these actuators together that are operating off electromagnetic fields, when you apply voltage to one, you’re affecting the ones around it.” Thermal actuators face a similar issue at braille scale: the heat that might dissipate between actuators in a larger system heats up all the actuators when they are packed so tightly.
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“This is a space that has been challenging for a long time,” Heisser said, “and really no one had tried combustion in any real way for a bunch of arrays spaced close together.” In his set up, a methane and oxygen mixture is ignited by sparks from liquid metal electrodes. The tiny explosions inflate soft silicone membrane “pistons”, making them rise six millimeters in under a millisecond. To prove its effectiveness with braille, Heisser sat magnetically latching pegs atop the silicone membranes. When the membranes inflate, they push the pegs up, and the magnets lock them in place.
The fuel is constantly flowing through the device so there is immediate expulsion of waste as the chambers become ready for the next actuation. The quantity of fuel the device uses will allow it to be portable, but not likely as small and sleek as a smartphone. A page of braille is 6,000 dots. If you repeatedly used and refreshed all those dots it would take upwards of a million pages to use the same amount of energy as one fifteen-gallon tank of gasoline. That’s roughly 600 readings of War and Peace. “It’s greenhouse gases, it’s combustion, but it’s not like everybody in the world that’s blind is going to be using this every day,” says Heisser. “I think we’re all right on that front.”
In creating the gas-powered braille display, Heisser stumbled on a convenient discovery that makes the system more streamlined and easier to produce. His advisor had asked him to put a strip of rubber over the inlet ports to act as a one-way check valve. “I just never did it,” Heisser said. But he went ahead and tested the display without the strip anyway. What he found was that there was no need for a valve.
“We make a spark in the combustion chamber—by the time the flame gets to the inlet port it stops itself, almost magically.” In combustion chambers of any size, the walls absorb some of the heat. If they absorb enough, combustion stops. That never happens in a car because there’s so much fuel and, in essence, so little wall. “But as you shrink down,” Heisser explained, “you have a smaller volume, so the flame sees more wall and will actually quench itself.”
Valves or no valves, soft combustion-powered actuators could have applications beyond braille. They could, perhaps, be used to power microrobots, or work as pumps with microfluidic devices, or tools in the operating room when a tiny powerful punch is needed.
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Michael Abrams is a science and technology writer based in Westfield, N.J.