Intelligent Machines

A Touch Screen that Plays Sticky

“Programmable friction” provides a new kind of feedback.

An experimental touch screen that uses variable friction to make different areas feel sticky or rough could point the way to a new paradigm in interfaces.

Rough ride: The T-PaD display generates a tactile sensation as a user operates a virtual scroll bar.

The touch screen uses high-frequency vibrations to create a thin layer of air between the glass and the user’s finger. The finger slips easily over the layer of air but catches slightly on the glass when the vibrations are turned off. Varying the vibrations as the user’s finger moves can cause different parts of the screen to feel slick or sticky.

“It adds a feeling of realism,” says Vincent Lévesque, a computer scientist at the University of British Columbia in Vancouver. “It’s more physical. It feels like there are real buttons that actually exist.” Lévesque and colleagues demonstrated a prototype of the device at the ACM Conference on Human Factors in Computing Systems in Vancouver this week.

The screen is one of a number of new devices that offer complex tactile feedback. Some mobile phones on the market, for example, use vibrations to generate a click or some other tactile signal. But the new device, called a tactile pattern display (T-PaD), is meant to do more than just buzz or click, says Ed Colgate, a mechanical engineer at Northwestern University whose team developed the touch screen.

“We’re not just about giving signals,” he says. “We’re about giving physical sensations like the experience you have when you interact with the real world.”

The T-PaD uses piezoelectric discs positioned against a glass plate. When a current is run through the discs, they vibrate at 26 kilohertz and transmit the vibrations to the glass. Lasers track the motion of a user’s finger and vary the vibrations accordingly.

For instance, when a finger runs across a button, the vibrations will slow or stop, giving the impression that that part of the screen is sticky. If you drag a file into a folder, you’ll feel the screen get sticky as your finger hits the target. Turning a wheel or moving a scroll bar on the screen, you’ll feel your finger move over tactile “tick marks.” Turning the vibrations on and off very quickly—for instance, every time a finger moves a millimeter across the screen—can make part of the screen feel rough, as if it is covered with a grating.

In a paper presented at the ACM conference, Lévesque and colleagues showed that the tactile feedback allowed people to complete tasks slightly more quickly. The users also generally liked the touch screen, although some complained that their fingers became tired after using it for a while.

“It’s actually quite magic when you touch it. It’s really neat,” says Vincent Hayward, a mechanical engineer at Université Pierre et Marie Curie in Paris, who is familiar with the device. However, he warns that the approach has problems—the prototype is bulky and uses a lot of power. It also provides feedback only while a finger is moving. Tapping on the screen doesn’t produce any special sensation. He says that he expects the tactile displays to eventually make their way into consumer electronics. “There’s a lot of engineering to be done,” admits Colgate. “But it is by no means theoretically impossible.”

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