According to the working principle of information transmission and touch screen media, we put the touch screen is divided into four types, they were resistive, inductive and capacitive infrared type, surface acoustic wave, following a brief introduction to the various types of touch screen:
The resistive touch screen body part of the screen is a multilayer film and liquid crystal screen surface is very complex, which consists of a layer of glass or organic glass is used as the base, the surface coated with a layer of transparent conductive layer (OTI, indium oxide), which is covered with a layer of outer surface hardening, smooth scratch resistant plastic layer and its inner surface is also coated with a layer of OTI, there are many tiny between two layers of conductive layer (less than 1/1000 inches) of the transparent isolation points separated them insulation. When a finger touches the screen, the two conductive layer OTI a contact point, because the direction of one side of the conductive layer on the Y axis of the 5V uniform field voltage, the voltage detection layer changes from zero to zero, the switch on the controller to detect, A/D conversion, and then the voltage value compared with 5V. You can touch the Y axis point, in that position on the X axis, which is the most basic principle of resistive touch screen in common. Resistance screen according to the number of out of line, divided into four lines, five wire and other wire resistance touch screen. The A surface of the five wire resistance touch screen is a conductive glass instead of a conductive coating layer, and the process of the conductive glass greatly improves the service life of the conductive glass, and the transmittance can be improved.
OTI coating the resistive touch screen is thin and brittle fracture, the coating is too thick, will reduce the transparency and reduce the formation of internal reflection definition, OTI is more of a thin layer of plastic protective layer, but still easy to be damaged by sharp objects; and because often be touched, the use of OTI surface after a certain period of time there will be a small crack, even if one of the variants, the outer OTI damage and fracture, will lose as a conductor, touch screen is not a long life. But the resistive touch screen is not affected by dust, water and dirt.
The touch screen is controlled by pressure sensing. It is composed of two layers of transparent conductive layer touch screen, the distance between the two layers is only about 2.5 microns. When the finger is pressed on the touch screen, the two layers of conductive layers are contacted, the resistance changes, and signals are generated in the X and the Y in the two directions, and then the touch screen controller is sent. This kind of touch screen can work under the bad environment, but the handle and the light transmission is bad, and it is suitable for the occasion with the gloves and the hands. Resistive touch screen is the key material technology, commonly used transparent conductive coating material:
A, ITO, indium oxide, weak conductive characteristic is when the thickness down to 1800 angstroms (a = 10-10 m) will suddenly become transparent when the light transmittance is 80%, then the thin down light transmittance decreased to 300 when the thickness rose to 80%. ITO is the main material used in all touch screen and capacitive touch screen. In fact, the working surface of the touch screen is the ITO coating.
B, nickel and gold coating, five wire outer conductive layer of the resistive touch screen is using a malleable nickel gold coating material, the outer conductive layer due to the frequent use of touch, malleable nickel gold materials in order to extend the service life, but the process is more expensive. Although the nickel deposit conductive layer has good ductility, but only for transparent conductors, not suitable for working face as a resistive touch screen, because of its high conductivity, and the metal is very difficult to achieve uniform thickness, suitable for voltage distribution layer, layer can only be used as a probe.
The structure of the capacitive touch screen is mainly that a transparent film layer is plated on the glass screen, and a protective glass is additionally arranged on the conductor layer.
The capacitive touch screen is provided with a long and narrow electrode on the four sides of the touch screen. When the user touches the screen, because the body electric field, the fingers and the conductor layer can be formed between a coupling capacitor, a four electrode current will flow to the contact, and the current strength and the finger to the electrode is proportional to the distance, the proportion and intensity in the touch screen controller will calculate the current, accurately calculate the touch point position. Double glass capacitive touch screen can not only protect the conductor and the sensor, effectively prevent external environmental factors impact on the touch screen, the screen even if the piles of dirty dust or grease, capacitive touch screen that can accurately calculate the touch location.
Capacitive touch screen is a transparent glass on the surface of a special metal conductive material. When the finger is touched on the metal layer, the capacitance of the contact changes, so that the frequency of the oscillator connected is changed. Because of the variation of capacitance with temperature, humidity or grounding, the stability is poor, and the drift phenomenon often occurs. This kind of touch screen is suitable for the debugging phase of system development.
The touch screen is installed on the touch screen on the frame of the emission and receiving of infrared sensing devices on the surface of the screen, the formation of infrared detection network, any object can change the touch contact and the realization of infrared touch screen operation. Infrared touch screen is free from current, voltage and electrostatic interference, suitable for some harsh environmental conditions. The utility model has the advantages of low cost, convenient installation, no need of cards or any other controller, and can be used on various grades of computers. In addition, because there is no capacitor charging and discharging process, the response speed is faster than the capacitance type, but the resolution is low.
The principle of infrared touch screen is very simple, only on the display with the distance from the frame, no need to add a coating on the surface of the screen or feeder controller. An infrared transmitting tube and a receiving tube are arranged on the four sides of the light spot frame. The user with a finger touch screen of a point, it will be blocked after the location of horizontal and vertical two infrared computer can calculate the touch point position immediately. Because the infrared touch screen is not affected by the current, voltage and electrostatic interference, it is suitable for some harsh environmental conditions. The utility model has the advantages of low cost, convenient installation, no need of cards or any other controller, and can be used on various grades of computers. However, due to the addition of the frame in the ordinary screen, in the use of the frame around the infrared emission tube and receiving tube is easy to damage.
Surface acoustic wave is a mechanical wave propagating along the surface of the medium. The touch screen is composed of touch screen, acoustic generator, reflector and acoustic receiver, wherein the acoustic generator can send a high-frequency sound waves across the surface of the screen when the finger touch screen, the acoustic contact is prevented, thereby determine the coordinate position. Surface acoustic wave touch screen is not affected by temperature, humidity and other environmental factors, high resolution, has an excellent scratch resistant, long service life (50 million no fault); high transmittance (92%), the image quality can keep clear and transparent; do not drift, just installed a correction; third axis (i.e. in response, the pressure axis) suitable for use in public places. The touch screen part of the surface acoustic wave touch screen can be a flat surface, a spherical surface or a cylindrical glass plate, which is arranged in front of the CRT, LED, LCD or the plasma display screen. This glass plate is only a pure reinforced glass, unlike other touch screen technology is not any film and coating. The upper left corner and the lower right corner of the glass screen are respectively provided with a vertical and horizontal ultrasonic transmitting transducer, and two corresponding ultrasonic receiving transducers are fixed at the upper right corner. The four sides of the glass screen are engraved with a very precise reflection fringe of the 45 degree angle from sparse to dense.
In summary, according to the working principle of information transmission and touch screen media, it can be divided into four categories: resistive touch screen, capacitive touch screen, infrared touch screen, and surface acoustic wave touch screen.