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Could “Force Illusions” Help Wearables Catch On?

Researchers have made haptic interfaces that create the sensation of being pushed or pulled by an invisible force.
July 21, 2014

What if the compass app in your phone didn’t just visually point north but actually seemed to pull your hand in that direction?

Two Japanese researchers will present tiny handheld devices that generate this kind of illusion at next month’s annual SIGGRAPH technology conference in Vancouver, British Columbia. The “force display” devices, called Traxion and Buru-Navi3, exploit the fact that a vibrating object is perceived as either pulling or pushing when held. The effect could be applied in navigation and gaming applications, and it suggests possibilities in mobile and wearable technology as well.

Tomohiro Amemiya, a cognitive scientist at NTT Communication Science Laboratories, began the Buru-Navi project in 2004, originally as a way to research how the brain handles sensory illusions. His initial prototype was roughly the size of a paperback novel and contained a crankshaft mechanism to generate vibration, similar to the motion of a locomotive wheel. Amemiya discovered that when the vibrations occurred asymmetrically at a frequency of 10 hertz—with the crankshaft accelerating sharply in one direction and then easing back more slowly—a distinctive pulling sensation emerged in the direction of the acceleration.

With his collaborator Hiroaki Gomi, Amemiya continued to modify and miniaturize the device into its current form, which is about the size of a wine cork and relies on a 40-hertz electromagnetic actuator similar to those found in smartphones. When pinched between the thumb and forefinger, Buru-Navi3 creates a continuous force illusion in one direction (toward or away from the user, depending on the device’s orientation).

The second device, called Traxion, was developed within the last year at the University of Tokyo by a team led by computer science researcher Jun Rekimoto. Traxion also generates a force illusion via an asymmetrically vibrating actuator held between the fingers. “We tested many users, and they said that it feels as if there’s some invisible string pulling or pushing the device,” Rekimoto says. “It’s a strong sensation of force.”

Both devices create a pulling force significant enough to guide a blindfolded user along a path or around corners. This way-finding application might be a perfect fit for the smart watches that Samsung, Google, and perhaps Apple are mobilizing to sell.

Haptics, which is the name for the technology behind tactile interfaces, has been explored for years in limited or niche applications. But Vincent Hayward, who researches haptics at the Pierre and Marie Curie University in Paris, says the technology is now “reaching a critical mass.” He adds, “Enough people are trying a sufficient number of ideas that the balance between novelty and utility starts shifting.”

Nonetheless, harnessing these kinesthetic effects for mainstream use is easier said than done. Amemiya admits that while his device generates strong force illusions while being pinched between a finger and thumb, the effect becomes much weaker if the device is merely placed in contact with the skin (as it would be in a watch).

The rise of even crude haptic wearable devices could accelerate this kind of scientific research, though. “A wearable system is always on, so it records data constantly,” Amemiya explains. “This can be very useful for understanding human perception.”

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