Working principle of surface acoustic wave touch screen
Taking the x-axis transmitting transducer at the following angle as an example, the transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into acoustic energy and transmits it to the left surface, and then a group of precision reflection stripes under the glass plate reflect the acoustic energy into an upward uniform surface for transmission, and the acoustic energy passes through the screen surface, Then, the reflected fringes on the upper side gather into sound waves propagating to the right and give them to the x-axis receiving transducer, which changes the returned surface acoustic wave energy into an electrical signal.
When the transmitting transducer emits a narrow pulse, the acoustic energy reaches the receiving transducer through different ways, the earliest on the right and the latest on the left. The early and late acoustic energy are superimposed into a wide waveform signal. It is not difficult to see that the received signal gathers all the acoustic energy returning through different long and short paths in the axis direction. They travel the same distance on the y-axis, but on the x-axis, the farthest one travels twice the maximum distance on the x-axis than the nearest one. Therefore, the time axis of this waveform signal reflects the position before the superposition of each original waveform, that is, the x-axis coordinate.
When there is no touch, the waveform of the received signal is exactly the same as the reference waveform. When a finger or other object that can absorb or block the acoustic energy touches the screen, the acoustic energy walking upward through the finger on the x-axis is partially absorbed and reflected on the received waveform, that is, there is an attenuation gap in the waveform at a certain time. The received waveform attenuates a notch corresponding to the signal of the finger blocking part. The controller analyzes the attenuation of the received signal and determines the X coordinate from the position of the notch. Then, the Y coordinate of the touch point is determined in the same process of the f axis. In addition to the X and Y coordinates that the general touch screen can respond to, the surface acoustic wave touch screen also responds to the third axis Z axis coordinates, that is, it can sense the user's touch pressure. Its principle is calculated from the attenuation at the attenuation of the received signal. Once the three axes are determined, the controller transmits them to the main engine.
The controller detects touch by comparing the received signal with the reference waveform in the non touch condition. This process allows the controller to ignore impurities such as dust and scratches. The controller continuously detects and eliminates impurities and pollution factors. When a "touch" remains unchanged for about 3 seconds, the controller will determine and eliminate impurity factors.In this case, a new reference waveform is required to effectively ignore impurities and restore the normal operation of the touch screen. If the impurities are removed, the controller will repeat the new reference waveform requirement procedure again.Technical principle of surface acoustic wave touch screen
It is designed by using the characteristics of. Taking the x-axis as an example, the control circuit generates a transmission signal (electrical signal), which is converted into ultrasonic vibration in the thickness direction by the x-axis transmission transducer on the glass screen, and the ultrasonic wave is refracted by the wedge seat under the transducer to generate components propagating along the glass surface. When the ultrasonic wave encounters the 45 degree inclined reflection ray on the way forward, it generates a component 90 degrees with the incident wave and parallel to the y-axis. The component is transmitted to the other side of the x-direction of the glass screen, and also encounters the 45 degree inclined reflection ray. After reflection, it is transmitted to the x-axis receiving transducer in the direction opposite to the emission direction. The x-axis receiving transducer converts the recovered sound wave into an electrical signal. The control circuit processes the electrical signal to obtain the waveform representing the acoustic energy distribution of the glass screen. When there is touch, the finger will absorb part of the acoustic energy, and the recovered signal will attenuate. The program can analyze the attenuation to determine the coordinates of the touch point in the X direction. Similarly, the coordinates in the y-axis direction can be determined. As soon as the coordinates in the X and Y directions are determined, the touch point will be uniquely determined.
The subtlety of the acoustic screen design is that only a pair of transducers in each direction can detect the whole touch surface, and the height is high; Unlike the infrared touch screen, at least dozens of transmitting / receiving tube pairs are required in each direction. With the increase of screen size or resolution, the number of transmitting / receiving tube pairs needs to be increased proportionally. The key to its implementation is the reflection array. The precise and accurate spacing distribution of the reflection array ensures the consistency of the recovered signal.Since the signal attenuation is directly related to the finger touch force, the acoustic screen can also respond to the z-axis coordinate, that is, the touch force, which becomes very useful and interesting in some cases.Surface acoustic wave touch screen features
(1) Surface acoustic wave touch screen is a high durability structure, anti scratch and anti violence. Because the working surface of the surface acoustic wave touch screen is a layer of invisible and unbreakable acoustic energy, the base glass of the touch screen does not have any interlayer and structural stress (the surface acoustic wave touch screen can be developed to be directly made on the CRT surface without any "screen"). Therefore, it is very anti violent and suitable for use in public places.(2) Clear and beautiful. Because the structure is few, there is only one layer of ordinary glass, and the transmittance and clarity are much better than those of capacitive and resistive touch screens.(3) Fast response. It is the fastest of all touch screens and feels very smooth when used.
(4) Stable performance. Because the principle of surface acoustic wave technology is stable, and the controller of surface acoustic wave touch screen calculates the touch position by measuring the position on the time axis at the attenuation time, the surface acoustic wave touch screen is very stable and the accuracy is very high. At present, the accuracy of surface acoustic wave technology touch screen is usually 4096x4096x256.
(5) The disadvantage of the surface acoustic wave touch screen is that the dust and water droplets on the surface of the touch screen also block the transmission of the surface acoustic wave. Although the smart control card can distinguish it, when the dust accumulates to a certain extent, the signal attenuates very badly. At this time, the surface acoustic wave touch screen becomes dull or even does not work. Therefore, on the one hand, the surface acoustic wave touch screen introduces the dust-proof touch screen, and on the other hand, it is recommended to clean the touch screen regularly every year.
(6) The touch screen can be activated with fingers, gloved fingers or soft substances that can absorb the energy of sound waves. If a beverage bottle is placed on the flat acoustic touch screen, the system does not take the bottle as a touch, but continues to recognize the touch signal activated by the finger. This is not possible for resistive and capacitive touch screens.(7) The surface acoustic wave touch screen can accurately know what dust and water droplets are, what fingers are and how many are touching. Because our fingers touch with the precision of 4096x4096x256, the touch data of 65 times per second cannot be the same, while the dust or water droplets remain the same at all. When the controller finds that a "touch" occurs, the silk remains unchanged for more than 3 seconds, and it is automatically recognized as an interference.
(8) The surface acoustic wave touch screen also has a third axis (Z axis), that is, the pressure axis response. This is because the greater the user's power to touch the screen, the wider and deeper the attenuation gap on the received signal waveform. At present, among all touch screens, only acoustic touch screen has the performance of sensing touch pressure. With this function, each touch point is not just two simple states with and without touch, but a switch of analog value that can sense power. This function is very useful. For example, in multimedia information query software, one button can control the playback speed, color brightness and volume of animation or images.
(comprehensive arrangement: Tonghao technology and Baidu know)
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