T FEATURE DISPLAYS & UIS TACTILE DISPLAY USING BEAT PHENOMENON
NLT Technologies explores the latest technology in its multi-touch tactile display, offering 240Hz electrostatic force generated by the beat phenomenon in a region where excited X electrodes cross-excited Y electrodes, generating tactile sensation
T
he success of multi-touch touchscreens has enabled intuitive
human-display interaction through touch surfaces. People have been interacting with displays not only via the visual sensory channel but the tactile sensory channel. This meets user demand for rich tactile feedback. There are three types of tactile displays with visual information: first, the touch surface vibrates with actuators such as piezoelectric devices, second an electrostatic tactile display in which the electrode is located under an insulator layer, and third an electro-tactile display that directly activates sensory nerves via an electrical current. Researchers from NLT Technologies,
(NLT) have created an LCD prototype, developing tactile touch technology. The technology gives new dimension in the sense of tactile texture to the users by using electric vibrations and reproduces skin sensations as if they are tracing actual objects on the display.
The researchers have proposed an electrostatic tactile display with regional stimulation, which is illustrated in Figure 1. This display panel consists of a glass substrate, multiple X and Y electrodes made of an indium tin oxide (ITO) on the substrate in a matrix arrangement, and anacrylic insulator layer that covers the electrodes. This display panel presents localised stimulus at the region where excited X electrodes cross excited Y electrodes. The stimulus is presented when a finger
K Figure 1
slides across the region. Users experience tactile texture of fine roughness in the region. By selecting electrodes to be excited, this display panel presents the stimulus at arbitrary positions around which the X electrode crosses the Y electrode. NLT's display has employed the beat phenomenon of voltage waveforms between electrodes to present the stimulus.
Figure 2
TECHNICAL FEATURES Figure 2 shows how this display presents tactile sensation to the finger. It is a cross- sectional view of the display in the region where excited X electrodes cross excited Y electrodes. The Y electrodes are excited by applying an AC voltage V1 with a frequency of f1 (ex. 1000Hz). The X electrodes are excited with an AC voltage V2 with a frequency of f2 (ex. 1240Hz). When a finger (represented as electrode P) comes into contact with the surface, multiple X
12 OCTOBER 2014 | ELECTRONICS Figure 1: In this case, the electrostatic force Fel
induced between electrodes P and Xa is obtained using the following formula known as the electrostatic force of the parallel plate capacitor. Where e is the dielectric constant of the insulator and S is the electrode area of
Electrostatic tactile display using beat phenomenon of voltage waveforms between electrodes
Figure 2:
Principle of tactile display using a beat phenomenon of voltage waveforms
the parallel plate capacitor. In the same way, the electrostatic force Fe2 is induced between electrodes P and Yb. The total electrostatic force of electrode P is Ftotal=2(Fel+Fe2) in the case of the figure. By substituting Acos2πf1t for V1 and substituting Acos2πf2t for V2, we obtain Ftotal: where A is the voltage amplitude and f1 and f2 are frequencies of V1 and V2 respectively. The envelope of Ftotal has a frequency of
and Y electrodes oppose electrode P. These electrodes form parallel plate capacitors of which the capacitance is C. The voltage of electrode P (Vp) can be estimated as VP (V1+V2)/2 when the resistance R is large.
The new tactile touch display enables multiple users to individually feel the texture of the image
240Hz, which is the beat frequency of f1 and f2. When the finger slides across the surface in this region, the sensation is presented by detecting horizontal deformation of the skin produced by dynamic friction variation transformed from electrostatic force variation of this beat frequency. The beat frequency of around 240Hz is susceptible by the tactile sensory system, especially the pacinian corpuscles, while that around 1000Hz applied to the X and Y electrodes is not. Thus, users perceive tactile sensation only in the region where excited X electrodes cross-excited Y electrodes. The important parameters to intensify the stimulus generated by the beat phenomena are electrode pitch and lateral space between the X and Y electrodes. In this prototype, the electrode pitch is set at around 1.7mm. The lateral space between the X and Y electrodes is minimised by adopting a diamond-shaped electrode.
MULTI-FINGER TACTILE DISPLAY A conventional tactile touch system (e.g., smartphones) presents the same sensation over the entire surface so that all fingers coming into contact with the surface experience the same sensation. In contrast, the new NLT tactile touch technology provides regional stimulation, which is provided by electrostatic force. The electrostatic force is generated by the beat phenomenon in a region where excited X electrodes cross excited Y electrodes, which presents tactile sensation to the users. The tactile touch technology applied to the panel provides multi-finger interaction. If multiple fingers touch the display at the same time, the digits on the area where the image is shown will feel the appropriate texture.
NLT Technologies
www.nlt-technologies.co.jp/en +1 408 816 7029
Enter 206 / ELECTRONICS
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