Analysis of working principle and characteristics of four touch screen technologies

The infrared touch screen uses an infrared matrix densely packed in the X and Y directions to detect and locate the user's touch. The infrared touch screen is provided with a circuit board outer frame on the front side of the display, and the circuit board arranges an infrared transmitting tube and an infrared receiving tube on four sides of the screen, and one-to-one correspondingly forms an infrared matrix which is horizontally and vertically crossed. When the user touches the screen, the finger blocks the two infrared rays passing through the position, so that the position of the touch point on the screen can be judged. Any touch object can change the infrared light on the contact to achieve touch screen operation. In the early concept, infrared touch screens had technical limitations such as low resolution, limited touch mode, and susceptibility to environmental interference, which once faded out of the market. Since then, the second-generation infrared screen has partially solved the problem of anti-light interference. The third and fourth generations have also improved their resolution and stability, but they have not made a qualitative leap in key indicators or comprehensive performance. However, those who know the touch screen technology know that the infrared touch screen is not affected by current, voltage and static electricity, and is suitable for harsh environmental conditions. Infrared technology is the final development trend of touch screen products. Touch screens using acoustics and other materials science techniques have insurmountable barriers, such as damage and aging of a single sensor, and the touch interface is subject to contamination, destructive use, and maintenance. As long as the infrared touch screen truly achieves high stability and high resolution, it will become the mainstream of the touch screen market instead of other technology products. The resolution of the past infrared touch screen is determined by the number of infrared pairs in the frame, so the resolution is low. The main domestic products on the market are 32x32 and 40X32. In addition, the infrared screen is sensitive to the lighting environment, and the illumination changes. When you are big, you will misjudge or even crash. These are the weaknesses of the infrared screens sold by domestic agents of non-infrared touch screens abroad. The resolution of the latest technology fifth-generation infrared screen depends on the number of infrared pairs, the scanning frequency and the difference algorithm. The resolution has reached 1000X720. As for the infrared screen, it is unstable under illumination conditions, from the second generation infrared touch screen. At the beginning, it has already better overcome the weakness of anti-light interference. The fifth-generation infrared touch screen is a new generation of intelligent technology products, which realizes 1000*720 high-resolution, multi-level self-adjusting and self-recovering hardware adaptability and highly intelligent discriminative identification, which can be used in various harsh environments for a long time. Any use. And can be customized for user extensions, such as network control, sound sensing, human proximity sensing, user software encryption protection, infrared data transmission and so on. Another major drawback of the original infrared touch screen promoted by the media is that it is poor in violent resistance. In fact, the infrared screen can completely select any riot glass that the customer considers satisfactory without increasing the cost and affecting the performance. This is something that other touch screens cannot follow.

4, surface acoustic wave touch screen

4.1, surface acoustic wave

Surface acoustic wave, a type of ultrasonic wave, a mechanical energy wave propagating in a shallow layer on the surface of a medium such as a rigid material such as glass or metal. Through the wedge-shaped triangular base (strictly designed according to the wavelength of the surface wave), the surface acoustic wave energy emission of the orientation and small angle can be achieved. The surface acoustic wave performance is stable, easy to analyze, and has very sharp frequency characteristics in the process of shear wave transmission. In recent years, the application in the direction of non-destructive testing, angiography and de-waveper has developed rapidly. Theoretical research on surface acoustic wave, semiconductor materials, sound The materials such as conductive materials and detection technologies are quite mature. The touch screen portion of the surface acoustic wave touch screen can be a flat, spherical or cylindrical glass plate mounted in front of a CRT, LED, LCD or plasma display screen. Vertical and horizontal ultrasonic transducers are fixed in the upper left and lower right corners of the glass screen, and two corresponding ultrasonic receiving transducers are fixed in the upper right corner. The four perimeters of the glass screen are engraved with a 45° angle from the sparse to densely spaced reflective stripes.

4.2, the surface acoustic wave touch screen works

Take the X-axis transmit transducer in the lower right corner as an example: The transmit transducer converts the electrical signal sent by the controller through the touch screen cable into acoustic energy that is transmitted to the left surface, and then a set of precision reflective stripes on the underside of the glass plate. The sound energy is reflected into an upward uniform surface, and the sound energy passes through the surface of the screen, and then the upper reflective strips are gathered into a rightward line to the X-axis receiving transducer, and the receiving surface acoustic wave that the transducer will return. The energy becomes an electrical signal. When the transmitting transducer emits a narrow pulse, the acoustic energy reaches the receiving transducer through different routes, the earliest arrival on the far right, the latest arrival on the far left, and the arrival of these early arrival and late arrivals. For wide waveform signals, it is easy to see that the received signal gathers all the acoustic energy returned by different paths in the X-axis direction. The distance they travel on the Y-axis is the same, but on the X-axis, the farthest ratio Recently, I have gone twice as much as the X-axis maximum distance. Therefore, the time axis of this waveform signal reflects the position before the original waveform is superimposed, that is, the X-axis coordinate. Transmitted and Received Signal Waveforms When there is no touch, the received signal has exactly the same waveform as the reference waveform. When a finger or other object capable of absorbing or blocking the energy of the sound wave touches the screen, the sound energy of the X-axis passing the finger portion is partially absorbed, and the reaction has a decaying gap on the receiving waveform at a certain moment. The receiving waveform corresponding to the finger blocking part signal attenuates a gap, and the position of the notch is calculated by the touch coordinate controller to analyze the attenuation of the received signal and determine the X coordinate from the position of the notch. The same process of the Y axis then determines the Y coordinate of the touch point. In addition to the X, Y coordinates that the general touch screen can respond to, the surface acoustic wave touch screen also responds to the Z-axis coordinate of the third axis, that is, the value of the user's touch pressure can be sensed. The principle is calculated from the amount of attenuation at the attenuation of the received signal. Once the three axes are determined, the controller passes them to the host.

4.3, surface acoustic wave touch screen features

High definition and good light transmission. Highly durable, good scratch resistance (surface film with respect to resistance, capacitance, etc.). Responsive. Not affected by environmental factors such as temperature and humidity, high resolution, long life (50 million times in good maintenance); high light transmittance (92%), able to maintain clear and translucent image quality; no drift, just install One calibration; there is a third axis (ie pressure axis) response and is currently used more in public places. The surface acoustic wave screen needs frequent maintenance, because dust, oil stains and even liquid of the beverage are stained on the surface of the screen, which will block the waveguide groove on the surface of the touch screen, so that the wave cannot be normally emitted, or the waveform is changed and the controller cannot recognize it properly, thus affecting For the normal use of the touch screen, the user must pay strict attention to environmental sanitation. The surface of the screen must be wiped frequently to keep the screen clean and regularly wiped thoroughly.

Surface acoustic wave screen

The three corners of the sound wave screen are respectively affixed with transducers for transmitting and receiving sound waves in the X and Y directions (transducers: made of special ceramic materials, divided into transmitting transducers and receiving transducers. The electrical signal sent by the touch screen cable is converted into acoustic energy and the surface acoustic wave energy condensed by the reflective fringes becomes an electrical signal.) The four sides are engraved with reflective stripes of the reflected surface ultrasonic waves. When a finger or a soft object touches the screen, part of the sound wave energy is absorbed, and thus the received signal is changed, and the X, Y coordinates of the touch are obtained by the processing of the controller.

Four-wire resistive screen

The four-wire resistive screen is covered with two transparent conductive layers ITO between the surface protective coating and the substrate (ITO: indium oxide, weakly conductive, characterized by a thickness of less than 1800 angstroms (A = 10-10 meters)) It will suddenly become transparent, and then the light transmittance will decrease. When the thickness reaches 300 angstroms, the light transmittance will rise again. It is the main material of all resistive screens and capacitive screens.), the two layers correspond to the X and Y axes respectively. Insulated with fine transparent insulating particles, the pressure generated when the touch is made to turn on the two conductive layers, and the X, Y coordinates of the touch are obtained due to the change in the resistance value.

Five-wire resistive screen

The base layer of the five-wire resistive screen is covered with a transparent conductive layer ITO which adds the voltage fields in the X and Y directions to the same layer, and the outermost layer of gold conductive layer (gold conductive layer: the outer conductive layer of the five-wire resistive touch screen is used) It is a ductile gold coating material. The outer conductive layer is used for the purpose of prolonging the service life due to frequent touch. The purpose of the gold material is to use it as a pure conductor. When touched, the contact point is detected by time division. The method of the X-axis and Y-axis voltage values measures the position of the touch point. The inner layer of ITO requires four leads and one outer layer, for a total of five leads.

Capacitive screen

The surface of the capacitive screen is coated with a transparent conductive layer ITO, the voltage is connected to the four corners, and the small DC electric diffusing part is on the surface of the screen to form a uniform electric field. When the screen is touched by the hand, the human body acts as a coupling capacitor, and the current is collected from the four corners of the screen to form a coupling capacitor. At one pole, the coordinates of the touch are obtained by the controller calculating the relative distance of the current to the touch position.

Infrared screen

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