Braille display demo refreshes with miniature fireballs

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Enlarge / The device can provide haptic information by expanding bubbles (left) or pushing pins (right).

Heisser, et. Al.

There have been a lot of advances in accessibility recently, with voice control, screen readers and more improving access to computers for many people. But something that was missing is a haptic device, which provides tactile information, think of a dynamic braille display. For many people, especially those with limited vision and hearing, this would be the most efficient way to interact with electronics. And a simple, inexpensive haptic device can have many applications beyond accessibility.

One of the reasons these have not become widely available is that they are difficult to manufacture. Physical actuators that can create a detectable pattern by touch take up a bit of bulk and are difficult to pack close to each other. They also tend to be expensive. Thus, a team of American-Israeli researchers studied alternatives to the physical material. And the researchers came up with an unexpected alternative: triggering a miniature fireball inside a flexible piece of polymer that can inflate like a balloon.

Replacement of material by combustion

In theory, making an updatable Braille display is relatively easy. All we need is a set of mechanical devices that can switch between high and low states. The reason these do not exist is that the commercially available mechanical devices are too large to be placed in close proximity. For example, researchers considered the possibility of using microfluidics to inflate a polymer bubble. But the valves needed for a grid of 2 × 3 devices would take up 18 times the area of ​​the device itself and cost around $ 250.

An actual row of these devices with sufficient resolution to reproduce a line of Braille text would be prohibitively expensive and would require a complicated three-dimensional arrangement of valves and tubes.

It might be possible to design a custom set of mechanical devices that could adapt to the required condition. But the team behind the new job decided to ignore the mechanical hardware altogether. Instead, the researchers decided to try combustion.

The basis of their material is a small, deformable polymer with tiny raised areas capable of repeatedly inflating like balloons and deflating later. Underneath, the researchers had a system of channels that fed a mixture of methane and oxygen to each of these polymer bubbles. And, at the base of the bubble, they had two wires that could carry enough current to allow a spark between them. These were made of liquid gallium, which allowed the device to be flexible and also allowed a certain degree of self-repair.

The spark ignites the gas mixture, causing a sudden increase in pressure – researchers have not determined whether there was a real detonation, but the combustion is powerful enough to create an audible noise. The pressure it generates expands the bubble above, creating a change in surface that can be felt when touched. And, as it expands, the polymer causes the pressure of the recently burnt gases to drop, which will cause their temperature to drop. Essentially, the device itself serves as a cooling system for the combustion, preventing it from building up heat.

A few small worries

The problem with the combustion turned out to be at the other end of the device, where fuel is introduced into it. Here, the researchers observed that the combustion spread through the supply lines and eventually burned down throughout the device. The team knew that this is usually avoided by placing a filter with small pores in the supply line. But the flames here moved so quickly that it didn’t work at first, forcing researchers to switch to larger filters until the flashback stopped.

The other problem is that, if you continuously perform a series of small explosions in order to keep the device inflated, you counteract the heat dissipation provided by the inflation itself. So although the wires can sparks at a very high frequency, you don’t actually want to use it to keep the device in its active state.

To work around this problem, the researchers included a magnetic locking pin in the device. Once the polymer expanded due to combustion, the pin would spring upward and lock into place. To reset the device, it would have to be physically pressed again. They demonstrated a working 3 × 3 prototype that can display a variety of simplified characters.

The need to physically reset the device is probably not as limited as it seems. You can imagine a device where the user has the ability to feel the haptic information and then tap on the elevated devices in order to reset them. Once reset, this can act as a trigger for displaying the next character.

The biggest problem is probably the use of fuel. Researchers are right that we live with fuel all around us. “We recognize that some may find the idea of ​​being so close to combustible chemicals disturbing,” they write, “but we note that billions of liquid butane lighters have remained in people’s front pockets since the 1800s. . ” Rather, the question is whether it is practical to expect people to insert a canister of fuel into their display every few weeks.

Beyond the practicality, however, it’s nice to see some work in this area, as there are many other contexts where haptic feedback can be valuable, including various augmented and artificial reality settings.

PNAS, 2021. DOI: 10.1073 / pnas.2106553118 (About DOIs).


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