A Better, Cheaper Multitouch Interface

A new pressure-sensitive pad could improve large and small touch screens.

Over the past few years, the world has fallen in love with multitouch displays. But today's consumer interfaces have some drawbacks: touch screens such as those on the iPhone and Plastic Logic's upcoming e-reader only work with a finger, not a stylus or even a gloved hand. Other displays, such as Microsoft's Surface and Perceptive Pixel's wall-sized screens, are rigid, relatively expensive, and currently fairly bulky.

Pressure pad: New York University researchers have developed an inexpensive pressure-sensitive pad that creates images of objects that are in contact with it, such as a hand (top) and fingertips (below). The researchers built a prototype pad that connects to a computer to display a 3-D pressure image of a user’s hand (bottom). Credit: Ilya Rosenberg, Alexander Grau, Charles Hendee, Nadim Awad, Ken Perlin

Multimedia   Watch a video of the researchers' prototype pad.

New research from New York University, however, promises to make multitouch interfaces that are cheap and flexible and can be used by fingers and objects alike. The technology, called Inexpensive Multi-Touch Pressure Acquisition Devices (IMPAD), can be made paper thin, can easily scale down to fit on small portable devices, or can scale up to cover an entire table or wall. The researchers will present IMPAD next week at the Computer Human Interaction conference in Boston.

The iPhone captures information about touch by measuring a change in capacitance when a finger or other conducting object comes in contact with the display. Surface screens use cameras to see the position of objects on the tabletop. Perceptive Pixel's displays also use cameras, but in a different way. Those cameras are used to track infrared light as it scatters in the presence of a finger or stylus. While Perceptive Pixel's touch screens collect pressure information, it's still impractical to use cameras for smaller or touch interfaces. IMPAD takes a different approach by measuring a change in electrical resistance when a person or object applies different pressure to a specially designed pad, consisting of only a few layers of materials.

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"One of the problems that's been endemic to multitouch sensors is . . . you're either touching it or not touching it," explains Ken Perlin, a professor of media research at NYU. "A significant amount of potentially useful information is thrown away because the sensor isn't capturing the subtleties." But with a pressure-sensitive touch pad, a device can see how hard a person presses, opening up another dimension of the user interface. The researchers have shown that their pressure-sensitive touch pad can be used for virtual sculpting and painting applications and for a simulated mouse with left clicks, right clicks, and drags, as well as for musical instruments like a piano keyboard. (See video.)

The hardware that composes the demonstrated prototype is relatively straightforward, explains Ilya Rosenberg, a graduate researcher and lead author on the IMPAD paper. It consists of two plastic sheets, about 8 inches by 10 inches, each with parallel lines of electrodes, spaced a quarter inch apart. The sheets are arranged so that the electrodes cross, creating a grid; each intersection is essentially a pressure sensor. Crucially, both sheets are covered with a layer of force sensitive resistor (FSR) ink, a type of ink that has microscopic bumps on its surface. When something coated in the ink is pressed, the bumps move together and touch, conducting electricity. "The harder you press, the more it conducts," says Rosenberg.