The infrared touch screen uses the infrared matrix densely distributed in the X and Y directions to detect and locate the user's touch. The infrared touch screen is equipped with a circuit board outer frame in front of the display. The circuit board arranges infrared emitting tubes and infrared receiving tubes on the four sides of the screen to form a horizontal and vertical cross infrared matrix in a one-to-one correspondence. When the user touches the screen, the finger will block the horizontal and vertical two infrared rays passing through the position, so the position of the touch point on the screen can be judged. Any touch object can change the infrared ray on the contact to realize the touch screen operation. In the early conception, infrared touch screens had technical limitations such as low resolution, limited touch methods, and susceptibility to environmental interference and misoperation, and thus 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 resolution and stability, but they have not made a qualitative leap in key indicators or overall performance. However, everyone who knows touch screen technology knows that infrared touch screens are not interfered by current, voltage and static electricity, and are suitable for harsh environmental conditions. Infrared technology is the ultimate development trend of touch screen products. Touch screens using acoustics and other material science technologies have their own insurmountable barriers, such as damage to a single sensor, aging, fear of contamination of the touch interface, destructive use, and complicated maintenance. As long as the infrared touch screen truly achieves high stability and high resolution, it will replace other technical products and become the mainstream of the touch screen market. In the past, the resolution of infrared touch screens was determined by the number of infrared pairs in the frame, so the resolution was low. The main domestic products on the market were 32x32 and 40X32. In addition, infrared screens are more sensitive to light environment factors, and the light changes more. Misjudgments or even crashes when they are old. These are the weaknesses of the infrared screens sold and promoted by domestic agents of foreign non-infrared touch screens. The resolution of the latest technology fifth-generation infrared screen depends on the number of infrared pairs of tubes, scanning frequency and difference algorithm. The resolution has reached 1000X720. As for the infrared screen is unstable under light conditions, from the second-generation infrared touch screen From the beginning, the weakness of anti-light interference has been better overcome. The fifth-generation infrared touch screen is a new generation of intelligent technology products. It realizes 1000720 high resolution, multi-level self-adjustment and self-recovery hardware adaptability and highly intelligent discrimination and recognition, which can be used in various harsh environments for a long time. Use it at will. And can be customized for user expansion functions, such as network control, sound sensing, human proximity sensing, user software encryption protection, infrared data transmission, etc. The other major shortcoming of the infrared touch screen promoted by the original media is its poor resistance to riots. In fact, the infrared screen can use any riot glass that customers find satisfactory without adding too much cost and affecting performance. This is something other touch screens cannot imitate.
(1) Écran tactile à ondes acoustiques de surface
1. Surface acoustic wave
Surface acoustic wave, a type of ultrasonic wave, is a wave of mechanical energy that propagates shallowly on the surface of a medium (such as rigid materials such as glass or metal). Through the wedge-shaped triangular base (strictly designed according to the wavelength of the surface wave), directional, small-angle surface acoustic wave energy emission can be achieved. Surface acoustic wave is stable, easy to analyze, and has very sharp frequency characteristics in the process of transverse wave transmission. In recent years, it has developed rapidly in the direction of non-destructive flaw detection, imaging and de-wave. The theoretical research of surface acoustic wave, semiconductor materials, acoustics Technologies such as guiding materials and testing technologies are already quite mature. The touch screen part of the surface acoustic wave touch screen can be a flat, spherical or cylindrical glass plate, which is installed in front of the 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 transducers, and the upper right corner is fixed with two corresponding ultrasonic receiving transducers. The four peripheries of the glass screen are engraved with very precise reflection stripes with a 45 degree angle ranging from sparse to dense.
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 sound wave energy and transmits it to the left surface, and then a set of precision reflection stripes under the glass plate The sound wave energy is reflected into an upward uniform surface for transmission. The sound wave energy passes through the surface of the screen, and then is gathered into a rightward line by the upper reflection fringe to propagate to the X-axis receiving transducer, and the surface acoustic wave that the transducer will return The energy becomes an electrical signal. When the transmitting transducer emits a narrow pulse, the sound wave energy arrives at the receiving transducer through different paths. The one on the far right is the earliest to arrive, and the one on the left is the last to arrive. The sonic energy that arrives early and arrives late is superimposed into one. With a wider waveform signal, it is not difficult to see that the received signal gathers all the acoustic energy returned by different paths in the X-axis direction. They travel the same distance on the Y-axis, but on the X-axis, the farthest ratio is The closest one has traveled twice the maximum distance on the X axis. Therefore, the time axis of this waveform signal reflects the position before the superposition of the original waveforms, which is the X-axis coordinate. Waveforms of the transmitted signal and the received signal 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 sound wave energy touches the screen, the sound wave energy going up on the X axis through the finger part is partially absorbed, reflecting that there is an attenuation gap in the waveform on the received waveform, that is, at a certain point in time. The received waveform attenuates a notch corresponding to the signal at the part blocked by the finger. The touch coordinate is obtained by calculating the position of the notch. The controller analyzes the attenuation of the received signal and determines the X coordinate by the position of the notch. After that, the same process on the Y axis determines the Y coordinate of the touch point. 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 coordinate, that is, it can sense the magnitude of the user's touch pressure. The 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 host.
3. Features of surface acoustic wave touch screen
The clarity is high and the light transmittance is good. Highly durable, good scratch resistance (have a surface film relative to resistance, capacitance, etc.). Responsive. Not affected by environmental factors such as temperature and humidity, high resolution, long life (50 million times under good maintenance); high light transmittance (92 percent ), can maintain clear and bright image quality; no drift, just install it One-time calibration; there is a third axis (ie pressure axis) response, which is currently used more in public places. Surface acoustic wave screens need frequent maintenance, because dust, oil stains or even beverage liquid contaminates the surface of the screen, which will block the wave guide groove on the surface of the touch screen, causing the wave to not be emitted normally, or the waveform changes and the controller cannot recognize it normally, thus affecting For normal use of the touch screen, the user shall strictly pay attention to environmental hygiene. The surface of the screen must be wiped frequently to keep the screen smooth and clean, and a thorough erasure should be done regularly.
Surface acoustic wave screen
The three corners of the sonic screen are respectively pasted with transducers (transducers: made of special ceramic materials) that emit and receive sound waves in the X and Y directions. They are divided into transmitting transducers and receiving transducers. It is the control The electrical signal sent by the device through the touch screen cable is converted into acoustic wave energy and the surface acoustic wave energy converged by the reflection fringe into an electrical signal.), the four sides are engraved with the reflection fringes of the ultrasonic wave on the reflecting surface. When a finger or a soft object touches the screen, part of the sound wave 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 resistive screen is covered with two transparent conductive layers of ITO (ITO: indium oxide, weak electrical conductor) between the surface protective coating and the base layer. The characteristic is that when the thickness drops below 1800 angstroms (angstroms = 10-10 meters) It suddenly becomes transparent, and the light transmittance decreases when it becomes thinner. When the thickness reaches 300 angstroms, the light transmittance rises again. It is the main material of all resistive screens and capacitive screens.), the two layers correspond to the X and Y axes, respectively. It is insulated with fine transparent insulating particles. The pressure generated when touching makes the two conductive layers connect, and the X and Y coordinates of the touch are obtained due to the change in resistance value.
Five-wire resistive screen
The base layer of the five-wire resistive screen is covered with a transparent conductive layer ITO that applies the voltage fields in the X and Y directions to the same layer, and the outermost gold conductive layer (gold conductive layer: the outer conductive layer of the five-wire resistive touch screen is used It is a gold coating material with good ductility. The outer conductive layer is frequently touched. The purpose of using a good ductile gold material is to extend the service life.) Only used as a pure conductor. When touching, use time-sharing to detect the contact point The X-axis and Y-axis voltage values are used to measure the position of the touch point. Four leads are required for the inner layer of ITO and one for the outer layer, totaling 5 leads.
Capacitive screen
The surface of the capacitive screen is coated with a transparent conductive layer of ITO, and the voltage is connected to the four corners. The small DC dispersion is on the surface of the screen to form a uniform electric field. When the screen is touched by hand, the human body acts as one pole of the coupling capacitor. For one pole, the controller calculates the relative distance from the current to the touch position to obtain the touch coordinates.
Infrared screen
The infrared touch screen uses the infrared matrix densely distributed in the X and Y directions to detect and locate the user's touch. The infrared touch screen is equipped with a circuit board outer frame in front of the display. The circuit board arranges infrared emitting tubes and infrared receiving tubes on the four sides of the screen to form a horizontal and vertical cross infrared matrix in a one-to-one correspondence. When the user touches the screen, the finger will block the horizontal and vertical two infrared rays passing through the position, so the position of the touch point on the screen can be judged. Any touch object can change the infrared ray on the contact to realize the touch screen operation.
