The day's not too far off that a smartphone, instead of providing on-screen driving directions, could guide someone to her destination with a little nudge. Literally.
For about the past decade, Lynette Jones, a senior research scientist in MIT’s Department of Mechanical Engineering has been developing touch-based ( haptic ) communication systems that convey information via small vibrating motors worn against the skin. Think of rescue workers wearing a belt that buzzes to alert them of danger from the left, or a visually impaired person receiving buzz-based, turn-by-turn directions through a new city.
Now Jones and her team has measured exactly how these motors interact with skin and how people perceive the vibrations, which could help develop more effective haptic devices in the future.
Jones built an array of microaccelerometers that she placed on test subjects' arms, hands and thighs. The accelerometers measured the vibrations coming from a small "pancake motor," a flat vibrating motor used in cellphones. In fact, a person wearing a "tactile display" made with these motors would feel buzzes much like those of a cellphone on silent/vibrate mode.
The accelerometer experiment was designed to determine how skin actually vibrates. "Skin is a very pliant medium," Jones said, so the motor's vibrations traveled only an average of a third of an inch (8 millimeters) before dropping off.
Jones then fitted participants with a three-by-three array of motors and asked the participants to pinpoint which motor was buzzing at any given time. In this experiment, people seemed to have trouble singling out individual buzzers.
Jones said this implies that future tactile displays would need to have its motors placed almost an inch (24 mm) apart.
Jones has developed a few prototype tactile displays, one similar to a belt with motors distributed around the circumference, and a device resembling a corset, with 16 motors along the back. Figuring out how those could best be used to impart information comes next.
"We're looking at changing the raw waveform of the vibration, so some signals feel rougher and others smoother," Jones said.
The team is also experimenting with varying the speed of the vibrations.
"People are very good at picking up tempo changes," Jones said. "You can use that for urgency, or proximity, or [for warning someone] that something's going to happen soon."
A paper describing the new research in haptic displays will appear in a forthcoming issue of IEEE Transactions on Haptics.
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