2022-09-09 15:49:16 1159
A touch screen is a coordinate positioning system used in conjunction with a display, and has been used more and more widely as a simple and convenient input device. With the rapid development of flat panel display, the touch screen used in combination with LCD is widely used, among which the demand for personal digital assistant (IPDA), advanced copier, vehicle navigation, especially the PDA with pen input is promising.
1 Common touch screen
1.1 Resistive touch screen The main part of the resistive touch screen is a four-layer transparent composite film that is closely attached to the surface of the display. The structure is shown in Figure 1. The same position corresponds to different output voltages. The controller receives the voltage data converted by the ADC and calculates the position of the touch point (x, Y). After the structure of the resistive touch screen in Figure 1, the cursor is positioned at the touch position. This is the basic principle of the resistive technology touch screen. The key to resistive touch screens lies in material technology. Commonly used transparent conductive coating materials include ITO and nickel-gold coatings.
1.1.1 Four-wire resistance screen
When the two transparent IT0 conductive layers of the four-wire resistive touch screen work, each layer adds a constant voltage of 5v: one vertical direction, one horizontal direction, and a total of four cables are required. The features are low price, flexible touch and not affected by dirt, dust, water or light, and the four-wire resistive screen has high positioning stability and no drift. The four-wire resistive screen is widely used, and it is a touch screen with a dedicated driver chip ADS7843 among the four touch screens. Therefore, the low power consumption of the four-wire resistive screen is an important factor for its wide application in PDA, mobile phones and other portable devices.
1.1.2 Limitations of Resistive Screens
The outer layer of the composite film of the resistive touch screen is made of plastic material. Excessive force or touching with a sharp object may scratch the touch screen and cause it to be scrapped. Even a small scratch is fatal to a four-wire resistive touch screen, while for a five-wire resistive touch screen, as long as the outer conductive layer of the touch screen is not divided into independent small pieces and the inner layer is not damaged, it can still work normally.
1.1.3 Five-wire resistance screen
The base layer of the five-wire resistance technology touch screen applies voltage to the conductive working surface of the glass, and the outer conductive layer is only used as a pure conductor. When the user touches the screen, the system measures the position of the touch point by time-divisionally detecting the X-axis and Y-axis voltage values of the contact point of the inner layer ITO. It is characterized by high resolution and fast response speed. The surface hardness is high, and the durability is greatly enhanced compared with the four-wire resistance screen, and it can still be used for 30 million times of contact at the same point. The nickel-gold conductive layer on the surface has strong damage resistance, and scratches can also be used normally. At the same time, the transmittance of the five-wire resistive touch screen is also better than that of the four-wire resistive screen, but the five-wire resistive touch screen is more expensive.
1.2 Capacitive touch screen
The capacitive touch screen uses vacuum coating technology to coat the inner surface and interlayer of the glass screen with a layer of IT0, the outer layer is a glass protective layer, and the interlayer IT0 coating is used as the working surface. When the user touches the metal layer, a coupling capacitance is formed between the user and the surface of the touch screen due to the electric field of the human body. The finger draws a very small current from the point of contact. This current is divided from the electrodes on the four corners of the touch screen, and the current is proportional to the distance from the finger to the four corners. The controller calculates the proportion of the four currents to obtain the position of the touch point. Capacitive touch screen can be completely adhered to the display, and it is not easy to be damaged and broken: capacitive touch can use the bonding method of bonding pad, which has waterproof function, and this kind of touch screen has high resolution, sensitive response, good tactile feeling, waterproof and waterproof Dust, sunscreen and other characteristics, very suitable for harsh environments. The working principle of the capacitive screen determines that the touch object must be a conductor, and there is no response when a gloved hand or a non-conductive object is touched.
1.3 Surface Acoustic Wave Touch Screen
When the user touches the screen, the originally separated two conductive layers are connected at the touch point. 1.3.1 Surface Acoustic Wave Touch Screen Structure The four peripheries of the glass plate of the surface acoustic wave touch screen are engraved with 450 angles from sparse to dense. Sophisticated reflective stripes. The upper left and lower right corners 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 to receive the ultrasonic signals reflected twice by the reflection stripes. 1.3.2 Features of surface acoustic wave touch screen The surface acoustic wave touch screen is very stable, not affected by environmental factors such as temperature and humidity, has a long life (50 million touches), high light transmittance and clarity, no color distortion and drift, No need for calibration after installation, it has excellent scratch resistance and can withstand various rough touches. Since the surface acoustic wave touch screen directly adopts the rectangular coordinate system, the data conversion has no distortion, and the accuracy is extremely high, up to 4096 × 4096 pixels f4l . However, the surface acoustic wave screen needs frequent cleaning and maintenance, because dust, oil and even rain on the peripheral stripes of the screen will block the normal reflection of the touch screen sound wave, or make the waveform change and the receiver cannot recognize it normally; large water droplets on the touch screen, Oil stains, etc. will be mistaken by the touch screen as a touch point and cause a malfunction.
1.4 Infrared touch screen
1.4.1 The working principle of infrared touch screen The infrared touch screen is to install a circuit board frame with infrared emission tube and infrared reception tube on the surface of the display. When the user touches the screen, the finger will block the infrared rays passing through the position, and the change of the light signal causes the photoelectric detection circuit to output a changed electrical signal, and the position of the touch point on the screen can be located by processing the electrical signal. Any touch object that is opaque to infrared light can cause infrared transmission to achieve touch positioning.
1.4.2 The development trend of infrared touch screen The advantage of infrared touch screen is that it is completely transparent, does not affect the clarity of the display, and is not subject to current, voltage and static interference, and is suitable for harsh electromagnetic working environments. However, the way infrared touchscreens work also leads to some inevitable application pitfalls. At present, the development of infrared touch screen technology mainly revolves around two directions, one is to use new sensors to realize the function of touch screen (iv), and the other is to improve the defects of existing touch screen technology and enhance the application function. The development of infrared touch screen is mainly carried out with the improvement of resolution and anti-light interference performance. At the same time, the expansion of application functions, such as multi-touch, brings more abundant functions to the touch screen.
With the development of the information society, people need to obtain a variety of information. The information transmission system with the touch screen as the interactive window adopts advanced computer technology and uses various forms such as text, images, music, commentary, animation, video, etc. to intuitively and vividly transmit various information to people. Great convenience. The development of touch screen has shown the trend of multi-function, diversification and large screen. It is foreseeable that with the rapid development of touch screen technology, the application fields of touch screens will become wider and wider, and the performance will become better and better.