Working Principle and characteristic analysis of four touch screen technologies

The infrared touch screen uses the dense infrared matrix in the X and Y directions to detect and locate the user's touch. The infrared touch screen installs an outer frame of the circuit board in front of the display, and the circuit board arranges infrared transmitting tubes and infrared receiving tubes on the four sides of the screen, forming a horizontal and vertical cross infrared matrix one by one. When the user touches the screen, the finger will block the two horizontal and vertical infrared rays passing through this position, thus the position of the touch point on the screen can be judged. Any touching object can change the infrared ray on the contact to realize the touch screen operation. In the early stage, the infrared touch screen had technical limitations such as low resolution, limited touch mode and misoperation due to environmental interference, which once faded out of the market. After that, the second generation of infrared screens partially solved the problem of anti-light interference. The third generation and the fourth generation also improved their resolution and stability performance, but they did not make a qualitative leap in key indicators or comprehensive performance. However, people who know touch screen technology all know that infrared touch screen is not interfered 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 material technology all have their insurmountable barriers, such as the damage and aging of a single sensor, the fear of contamination of the touch interface, destructive use, complicated maintenance and so on. As long as infrared touch screen truly achieves high stability and high resolution, it will certainly replace other technical products and become the mainstream of touch screen market. In the past, the resolution of infrared touch screen was determined by the number of infrared tubes in the frame, so the resolution was relatively low. The main domestic products in the market were 32x32, 40X32, in addition, it is also said that the infrared screen is sensitive to the factors of lighting environment, and will misjudge or even crash when the lighting changes greatly. These are the weaknesses of infrared screens sold and publicized by foreign non-infrared touch screens and domestic agents. However, the resolution of the fifth generation infrared screen of the latest technology depends on the number of infrared tubes, scanning frequency and the difference algorithm. The resolution has reached 1000X720. As for the infrared screen, it is unstable under the illumination condition, since the second generation of infrared touch screen, the weakness of anti-light interference has been better overcome. The fifth generation infrared touch screen is a brand new generation of intelligent technology products, which realizes 1000*720 high resolution, multi-level self-adjustment and self-recovery hardware adaptability and highly intelligent identification, it can be used arbitrarily in various harsh environments for a long time. And it can be customized and expanded for users, such as network control, sound sensing, human body proximity sensing, user software encryption protection, infrared data transmission, etc. Another major drawback of the infrared touch screen originally advertised by the media is the poor anti-violence property. In fact, the infrared screen can completely choose any anti-riot glass that customers think satisfied without increasing the cost and affecting the performance, this is something other touch screens cannot follow.
4. Surface acoustic wave touch screen
4.1. Surface acoustic wave
Surface acoustic wave, a kind of ultrasonic wave, is a mechanical energy wave spreading in the shallow layer of the surface of medium (such as rigid materials such as glass or metal. Through wedge-shaped triangular base (strictly designed according to the wavelength of surface wave), directional and small angle surface acoustic wave energy emission can be achieved. Surface acoustic wave performance is stable and easy to analyze, and it has very sharp frequency characteristics in the process of Heng Bo transmission. In recent years, it has developed rapidly in the direction of nondestructive testing, radiography and wave retractors, the theoretical research related to surface acoustic wave, semiconductor material, acoustic conduction material, detection technology and other technologies have been quite mature. The touch screen part of surface acoustic wave touch screen can be a flat, spherical or cylindrical glass plate installed in front of CRT, LED, LCD or plasma display screen. The upper left corner and the lower right corner of the glass screen are respectively fixed with vertical and horizontal ultrasonic transmitting transmitters, while the upper right corner is fixed with two corresponding ultrasonic receiving transmitters. The four peripherals of the glass screen are engraved with very precise reflective stripes with an angle of 45 ° from sparse to dense.
4.2. Working principle of surface acoustic wave touch screen
Take the X-axis transmitting transducer in the lower right corner as an example: the transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into acoustic wave energy and transmits it to the left surface, then a group of precise reflection stripes under the glass plate reflect the acoustic wave energy to an upward uniform surface for transmission, and the acoustic wave energy passes through the surface of the screen, then, the reflected stripes on the top gather into a line to the right and spread to the receiving transducer of the X-axis, and the receiving transducer turns the acoustic energy of the returned surface into an electrical signal. When the transmitting transducer emits a narrow pulse, the acoustic wave energy arrives at the receiving transducer through different ways, arriving at the rightmost earliest and arriving at the leftmost latest, these sound wave energies which arrive early and arrive late are superimposed into a wider waveform signal. It is not difficult to see that the received signals gather all the sound wave energies that have gone through different paths in the direction of X axis, the distance they traveled on the y-axis is the same, but on the x-axis, the farthest distance is twice as long as the nearest one. Therefore, the time axis of this waveform signal reflects the position before the superposition of each original waveform, which is the x-axis coordinate. When the waveform of the transmitted signal and the received signal is not touched, the waveform of the received signal is exactly the same as the reference waveform. When fingers or other objects that can absorb or block the energy of sound waves touch the screen, the energy of sound waves that the x axis moves upward through the fingers is partially absorbed, there is an attenuation gap in the received waveform, that is, at a certain moment. The signal of the receiving waveform corresponding to the blocking part of the finger decays a notch, and the touch coordinate controller can analyze the attenuation of the received signal by calculating the notch position and determine the X coordinate from the notch position. After that, the Y coordinate of the touch point is determined by the same process of Y 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 Z axis coordinates of the third axis, that is, it can sense the touch pressure of the user. The principle is calculated by the attenuation of the received signal. Once the three axes are determined, the controller will send them to the host.
4.3. Features of surface acoustic wave touch screen
High definition and good light transmittance. It is highly durable and has good scratch resistance (it has surface film relative to resistance, capacitance, etc ). Sensitive response. It is not affected by environmental factors such as temperature and humidity, and has high resolution and long service life (50 million times under good maintenance); high light transmittance (92%), which can maintain clear and transparent image quality; no drift, only one correction is required during installation; there is a third axis (I .e. pressure shaft) response, which is widely used in public places at present. The surface acoustic wave screen needs to be maintained frequently, because dust, oil stain and even liquid of beverage stain on the surface of the screen, which will block the guided wave slot on the surface of the touch screen and make the wave unable to be emitted normally, or make the waveform change and the controller cannot recognize it normally, thus affecting the normal use of the touch screen. Users should pay strict attention to environmental sanitation. The surface of the screen must be wiped frequently to keep the screen bright and clean, and the screen should be completely erased regularly.
Surface acoustic wave screen
The three corners of the sound wave screen are respectively pasted with the transducer that emits and receives sound waves in the X and Y directions (transducer: made of special ceramic materials, which is divided into transmitting transducer and receiving transducer. It is to convert the electrical signal sent by the controller through the touch screen cable into acoustic wave energy and the surface acoustic wave energy converged by the reflected stripes into electrical signal .), Four sides are engraved with reflective stripes of reflecting surface ultrasonic wave. When fingers or soft objects touch the screen, part of the acoustic energy is absorbed, so the received signal is changed, and the X and Y coordinates of the touch are obtained through the processing of the controller.
Four-wire resistive screen
The four-wire resistance screen is covered with two transparent conductive layers ITO (ITO: indium oxide, weak conductive body) between the surface protective coating and the base layer. The characteristic is that when the thickness drops to 1800 ANGS (ANGS = 10) it will suddenly become transparent when it is below, and the light transmittance will decrease when it is thinner, and will increase when it reaches the thickness of 300. It is the main material of all resistance screens and capacitive screens .), The two layers correspond to X and y axes respectively, and the doors are insulated by fine transparent insulating particles. The pressure generated when touching connects the two conductive layers, and the X touched by the change of resistance value is obtained, Y coordinate.
Five wire resistive screen
The base layer of the five-wire resistance screen is covered with the transparent conductive layer ITO which adds the voltage fields in both directions of X and Y to the same layer, and the outermost layer is the gold conductive layer (gold conductive layer: the outer conductive layer of the five-wire resistive touch screen is made of gold coating material with good ductility. Due to frequent touch of the outer conductive layer, the purpose of using gold material with good ductility is to prolong the service life .) It is only used as a pure conductor. When touching, the position of the touch point is measured by the method of time-sharing detection of the voltage values of the x-axis and y-axis of the contact point. Four lead wires are required for the inner ITO and one for the outer ITO, with a total of five lead wires.
Capacitive screen
The surface of the capacitive screen is coated with transparent conductive layer ITO, the voltage is connected to the four corners, and the tiny direct current is scattered on the surface of the screen, forming a uniform electric field. When touching the screen by hand, the human body acts as one pole of the coupling capacitor, the current collects from the four corners of the screen to form the other pole of the coupling capacitor, and the relative distance from the current to the touch position is calculated by the controller to obtain the touch coordinates.
Hong external screen
The infrared touch screen uses the dense infrared matrix in the X and Y directions to detect and locate the user's touch. The infrared touch screen installs an outer frame of the circuit board in front of the display, and the circuit board arranges infrared transmitting tubes and infrared receiving tubes on the four sides of the screen, forming a horizontal and vertical cross infrared matrix one by one. When the user touches the screen, the finger will block the two horizontal and vertical infrared rays passing through this position, thus the position of the touch point on the screen can be judged. Any touching object can change the infrared ray on the contact to realize the touch screen operation.