Computer operation is easy and fast to achieve the purpose of operation by screen touch. This is one of the general trends in the widespread use of computers in the world. As long as there is a menu operation concept, it can be used immediately. Now there are several kinds of this technology. The principle and its application are reviewed.
The touch screen technology is mainly used to quickly and accurately process the coordinates of random touch points. Once this first problem is solved immediately, the remaining problems are the same as the mouse action.
At present, there are four kinds of mature touch screen technologies, namely infrared type, five-line resistance type, surface acoustic wave type and capacitive type, and the principle is as follows.
1 infrared touch screen
In the left side of the screen front frame (y-axis) and the lower side (x-axis) are respectively equipped with infrared emission tubes, and the opposite sides are respectively equipped with corresponding receiving tubes (as shown in Fig. 1), and the arrangement density of the tubes is related to its resolution. When the infrared matrix is ​​crossed in front of the screen, the user's finger touch point will block the infrared rays in both the horizontal and vertical directions passing through the point. Through the receiving tube, the computer calculates the position of the touch point by this parameter, and then performs the operation on the computer. purpose.
The matrix circuit and microprocessor control circuit of the infrared touch screen are installed in the frame in front of the screen, and communicate directly with the host through the keyboard interface, without independent power supply. The price is low, the installation is simple, but due to the limited arrangement of the transmitting and receiving tubes, The resolution is not high, and it is afraid of external infrared light interference and non-waterproof and dustproof, frame fragile and other shortcomings, mainly used in indoor stations and other simple operations.
2 five-wire resistive touch screen
It is a new patented technology created on the basis of four-wire resistive touch screen, which overcomes the shortcomings of short life and low definition.
The four-wire resistance technology is a thin layer of transparent indium oxide InO coated on the outer surface of the glass with the display screen. As a resistive layer, a horizontal working voltage of 5V to 0V is applied in the horizontal direction to form a uniform continuous voltage distribution. The conductive layer is further covered with a protective layer whose outer surface is scratch-hardened and whose inner surface is also coated with the same oxidized metal layer, and a vertical direct distribution voltage of 5V to 0V is also applied in the vertical direction. Separated by a number of transparent insulating isolation points of about one-thousandth of an inch (Figure 2). When the screen is touched, the two resistor layers are turned on at the contact position, passing the analog voltage modulus (Afi D). Conversion, the controller can calculate the x, y coordinate value of the contact. Because the external resistance coating of the four-wire resistive touch screen is frequently pressed, it is easy to cause cracking and change the uneven distribution of the coating voltage, resulting in inaccurate contact position calculation. The shortcomings of scrapping have created five-wire resistance technology.
The new feature of the five-wire resistive touch screen is that the outer resistive layer is only used as a conductor layer, and as one of the five wires, even if there is a crack, as long as it does not break, the detection calculation is not affected, which undoubtedly greatly enhances the use. Lifetime. In the inner resistance coating, the vertical and horizontal voltage distribution field technology of the four-wire resistance technology is creatively applied in the same coating, and its structure is shown in Fig. 3. In the thin strip of metal oxide A positive voltage difference is formed on the shaft, and a reverse voltage difference is formed through the median point to form the same four-wire mode. The inner and outer coatings are still separated by an insulating transparent isolation point. When pressed, there is a contact between the inner and outer coatings. , causing a partial pressure of a different resistance value at the upper end of the left downward voltage, according to which the controller calculates the horizontal coordinate value of the contact. Each contact on the inner coating has a different corresponding x-axis coordinate The coordinate of the contact y-axis direction is determined by the controller measuring the current value from the inner coating through the contact into the outer coating (one of the five wires). The five-wire resistive touch screen has a service life that greatly exceeds the four wires. 35 times, up to 35 million times, its light transmittance and clarity
3 surface acoustic wave technology touch screen
This technology is American technology, which uses the dynamic propagation of the mechanical ultrasonic wavefront to position the contacts on the display.
Ultrasonic transducers with vertical downward emission and horizontal left emission are fixed in the upper left and lower right corners of the display respectively (Fig. 4). The screen edges and opposite sides of the same direction are engraved with 45° for reflection. The wave-guided reflection fringes are closely spaced from each other (the parameters are related to the wavelength). The end of the transmitted wave along the opposite side--the upper right corner of the display screen is respectively mounted with the ultrasonic x-axis y-axis receiving and changing When working, the high-frequency electric signal generated by the surface acoustic wave screen controller is sent to the transducing transmitter to emit mutually perpendicular ultrasonic waves to form a dynamic ultrasonic matrix wave surface. When there is a contact on this working surface, The sound energy passing through the point will be absorbed. After receiving the change, the transducer notifies the controller to determine the coordinate value of the contact [2]. At present, the unique characteristic of the surface acoustic wave touch screen is that it can sense the third Axis (z-axis) coordinates. Due to its high resolution, accuracy and stability, the signal attenuation due to the pressure of the finger contacts is clearly resolved, so data can be easily obtained. This degree of freedom can be used for special control. , such as medical three
The surface acoustic wave screen has very good definition because it has no oxidized metal coating; its reinforced glass screen has high scratch-resistance, but it is afraid of other frequencies close to and multiplying ultrasonic, strong sound and vibration, and also afraid of the screen. Pollution, so it is suitable for indoor offices, research rooms, etc.
4 capacitive technology touch screen
Its structure is the simplest. It is coated with a transparent layer of oxidized and metal conductors in the double-layered glass in front of the display screen. The four corners lead out the four electrodes controlled by the controller. Through the leads, there is a high-frequency current in the sandwich conductor. Flow (Figure 5). Due to the presence of the human electric field, the touch point finger and the screen coating form a tiny coupling capacitance, and the high frequency current is easy to pass through the small capacitance. Thus, the high frequency on the symmetrical four electrodes The current is shunted through the contact small capacitor. This symmetrical change is detected by the controller. Since the current flowing into the four electrodes is inversely proportional to the distance from the finger contact to the four corners, the contact coordinate value can be calculated.
The capacitive technology touch screen is extremely sensitive and can sense a slight and fast touch (the response time is up to 3ms), so it is not afraid of pollution and gloved touch, but it is afraid of strong external electric field interference.
The performance of the above various types of touch screen is compared as Table 1.
Although the appearance of touch screen technology in China is not long, its popularization and application speed is much higher than that of developed countries in the world. It is very popular and has great development prospects. This is in line with China’s past economically underdeveloped English and slow computer popularization. The current urgent need for China's rapid economic growth is inseparable. Such a large market, accounting for more than 1/4 of the world's population, especially in cities, no matter the crowds of hotels, shopping malls, trading halls, airports, terminals and subways District, or science and technology education, personnel organization, business management, corporate accounting, party and government management, administrative business, etc. have a lot of demand.
Microcomputer touch screen technology uses a wide range of age coverage, for example, to promote the next generation of high-quality starting point, develop early childhood education, stimulate and induce children and young people to learn scientific knowledge; popularize the establishment of senior universities, and the older generation of in-service leaders Modern management methods have a certain meaning.
In terms of regional coverage, rural and remote mountainous areas, backward areas and frontier islands, where there are economic growth points, are gradually adopting the management model of microcomputer touch technology to support communication and development.
The touch screen is a new multimedia interactive device that is created by the stimulation of market growth and the renewal of thinking. It conforms to stable, accurate and high-speed efficiency. Its application greatly simplifies the computer input mode, and can operate the computer and query data with the touch of a finger. Analyze data, optimize solutions, choose decisions, and predict the future.
The touch screen gives the multimedia system a new look and is very attractive. Multimedia technology emerges in an endless stream, both of which provide better convenience for modern people.
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