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Multi-touch Haptic Display Vibrates Desired Points on Screen

2014/07/01 00:58
Tetsuo Nozawa, Nikkei Electronics
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NLT Technologies Ltd (former NEC LCD Technologies Ltd) announced that it has developed a technology to realize a multi-touch haptic display in a lecture delivered at SID 2014, an international academic conference that took place in June 2014 in the US (lecture number: 43.3).

With tactile feedback, when the user touches a specific image such as a button displayed on a screen, the user is notified of it with a vibration. As a result, it becomes easy for the user to confirm that the finger touched the screen and the button is pressed, etc.

However, there have been some problems with the technology. Many existing haptic displays use a technology that physically vibrates a display surface with tiny motors and actuators when a fingertip touches a touch panel. With this method, the entire display vibrates when a finger touches one point on the display. Therefore, when multiple fingers or multiple users are touching a multi-touch haptic display, it does not function well.

This time, NLT Technologies realized a "very high resolution" muti-touch haptic display by combining (1) a method that gives a feeling of touching a display to a finger by using electrostatic force and (2) x- and y-axis transparent electrodes similar to those of a passive matrix display.

The method using electrostatic force was co-developed by Disney Research and Carnegie Mellon University in 2010 and named "TeslaTouch." When an alternating-current (AC) voltage with a low frequency of about 200Hz is applied to a display surface and a finger slightly moves on the display, the fingertip senses the voltage change and the user feels as if the display is vibrating even though it is not. This method is also called "electrovibration." However, a multi-touch haptic display cannot be realized only with this technology.

With the second method, NLT Technologies succeeded in generating a vibration with TeslaTouch only at a desired point on the display. Specifically, 1,240Hz and 1,000Hz AC voltages were applied to the x and y axes of a passive matrix type, respectively. Then, at the intersection point of the two axes, an "undulation" of the difference frequency (240Hz) of the 1,240Hz and 1,000Hz frequencies occurs. When the fingertip senses it, the user feels as if the point is vibrating.

Technically, it is possible not only to realize a multi-touch haptic display but also to actively change the locations of "vibrating" points as well as the frequency and waveform of the undulation for each point of the display while displaying an image. It is also possible to enable the user to feel the "movement" of a movie with vibrations.