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touch screen technology
Aug 17, 2018

The touch screen is a kind of positioning device. The user can directly input the coordinate information by pointing to the computer. Like the mouse and the keyboard, it is also an input device. The touch screen has many advantages such as ruggedness, fast response, space saving, and easy communication. With this technology, you can operate the host computer by gently touching the icon or text on the computer display with your finger, thus making human-computer interaction more direct. This technology is very convenient for those who do not understand computer operation. User. It has been widely used in industrial, medical, communications control, information inquiry and other aspects.


1, resistive touch screen


Analog resistive screen


The analog resistive touch screen is what we usually call a "resistance screen", which is a touch screen that is controlled by pressure sensing. It uses two layers of ITO (indium tin oxide) plastic film coated with conductive function. The two ITOs are provided with particle fulcrums, so that the screen has a certain gap between the two layers of ITO when it is not pressed, and it is in an unconducting state. When the operator presses the screen with the fingertip or the tip of the pen, the pressure will make the film concave, the ITO layer will be in contact with the conductive due to the deformation, and then the corresponding pressure point will be converted by detecting the X-axis and Y-axis voltage changes to complete the entire screen. Touch handling mechanism. At present, the analog resistive touch screen has various types such as 4-wire, 5-wire, 6-wire and 8-wire. As shown in Fig. 1, the more the number of lines, the higher the precision of the detectable, but the cost is relatively increased. The resistive screen does not support multi-touch, high power consumption, short life, and long-term use will bring detection point drift, which requires calibration. However, the structure of the resistive screen is simple and the cost is low. Before the maturity of the capacitive touch screen, it once occupied most of the touch screen market.


Digital resistance screen


The basic principle of the digital resistive screen is similar to that of the analog type. Unlike the analog resistive screen which uniformly coats the ITO layer on the glass substrate, the digital resistive screen uses only the substrate with the ITO stripe. The ITO stripes of the upper and lower substrates are perpendicular to each other. Digital resistive screens are more similar to a simple switch and are therefore often used as a membrane switch. Digital resistive screens enable multi-touch.


2, capacitive touch screen


Surface capacitive


The surface capacitive touch screen senses the touch behavior of the screen surface by electric field induction. Its panel is a uniform coated ITO layer, and each of the four corners of the panel has an outgoing line connected to the controller. When working, the surface of the touch screen produces a uniform electric field.


When a grounded object touches the surface of the screen, the electrode senses the change in the surface charge of the screen and determines the coordinates of the touch point. The surface capacitive touch screen has long service life and high light transmittance, but has low resolution and does not support multi-touch. Currently, it is mainly applied to large-size outdoor touch screens, such as public information platform (POI) and public service (sales) platform (POS). ) and other products.


Projected capacitive screen


The projected capacitive touch screen utilizes the electrostatic field lines emitted by the touch screen electrodes for sensing. Projected capacitive sensing technology can be divided into two types: self-capacitance and cross-capacitance. The self-capacitance, also known as the absolute capacitance, acts as the other plate of the capacitor, which senses the charge between the sensing electrode and the sensed electrode, and determines the position by detecting the change in the coupling capacitance. However, if it is a single touch, the coordinates determined in the X-axis and Y-axis directions are only one set by the capacitance change, and the combined coordinates are also unique; if there are two touches on the touch screen and the two points are not in the same X direction Or in the same Y direction, there are two coordinate projections in the X and Y directions, respectively, and four coordinates are combined. Obviously, only two coordinates are true, and the other two are commonly known as "ghost points." Therefore, the self-capacitive screen cannot achieve true multi-touch; the cross-capacitance is also called the cross-capacitance, which is the capacitance generated by the coupling of adjacent electrodes, and interacts when the perceived object approaches the electric field line from one electrode to the other. The change of the capacitance will be felt. When the lateral electrodes sequentially emit the excitation signal, all the electrodes in the longitudinal direction receive the signals at the same time, so that the capacitance values of all the intersections of the lateral and longitudinal electrodes can be obtained, that is, the two-dimensional plane of the entire touch screen. The size of the capacitor. When the human finger approaches, the local capacitance decreases. According to the two-dimensional capacitance change data of the touch screen, the coordinates of each touch point can be calculated, so even if there are multiple touch points on the screen, each touch point can be calculated. The true coordinates. In the above two types of projected capacitive sensors, the sensing capacitor can be designed according to a certain method so that the touch of the finger can be detected at any given time, and the touch is not limited to one finger, and may be Multiple fingers. Since 2007, Apple's iphone and iPad series products have achieved great success. The projected capacitive screen has begun to develop the well-type, and quickly replaced the resistive touch screen, becoming the mainstream touch technology in the market.


3, infrared touch screen


The infrared touch screen uses an infrared matrix densely packed in the X and Y directions to detect and locate the user's touch. The infrared touch screen is provided with a circuit board outer frame on the front side of the display, and the circuit board arranges the infrared emitting tube and the infrared receiving tube on the four sides of the screen, one by one corresponding to the infrared matrix of the horizontal and vertical intersecting. When the user touches the screen, the finger blocks the two infrared rays passing through the position, and accordingly, the position of the touch point on the screen can be determined. The infrared touch screen has the advantages of high light transmittance, no interference from current, voltage and static electricity, high touch stability, etc., but the infrared touch screen is subject to changes in ambient light and may be subjected to infrared sources such as remote controls, high temperature objects, incandescent lamps, and the like. Influence, while reducing its accuracy. The early infrared touch screen appeared in 1992, the resolution is only 32 × 32, it is easy to be disturbed by environmental interference, and it is required to be used in a certain shading environment.


After 20 years of development, the current advanced infrared touch screen has a life span of more than 7 years under normal working conditions. When tracking the movement path of the finger, the accuracy, smoothness and tracking speed can meet the requirements, and the user's writing can be smoothly converted. Image track, fully supports handwriting recognition input. Infrared touch screens are mainly used in various public places, offices, and industrial control places where infrared rays and strong light are not disturbed.


4, acoustic wave touch screen


Surface acoustic wave touch screen


The surface acoustic wave touch screen is a touch technology that is positioned by sound waves. At the four corners of the touch screen, sensors for transmitting and receiving sound waves in the X and Y directions are respectively attached, and 45° reflection stripes are engraved around the periphery. When the finger touches the screen, the finger absorbs a part of the sound energy, and the controller detects the attenuation of the received signal at a certain moment, thereby calculating the position of the touch point.


The surface acoustic wave technology is very stable and has very high precision. In addition to the X and Y coordinates that the general touch screen can respond to, it also responds to its unique third-axis Z-axis coordinate, which is the pressure axis response. With this function, each touch point is not just a two-switch state with touch and no touch, but an analog switch that can sense the force: the greater the pressure, the attenuation gap on the received signal waveform. The wider and deeper.


Of all types of touch screens, only surface acoustic wave touch screens have the ability to sense touch pressure. The surface acoustic wave touch screen is not affected by environmental factors such as temperature and humidity, high definition (high resolution), good light transmittance, high durability, good scratch resistance, responsiveness, long life and clear and transparent image. Quality, no drift, only one calibration at the time of installation, good anti-violence performance, most suitable for public information inquiry and use in offices, institutions and relatively clean public places.


Curved acoustic wave touch screen


The curved acoustic wave touch screen is based on sound pulse recognition technology. When an object touches the surface of the touch screen, the sensor will detect the frequency of the sound wave, and by comparing the frequency with a standard frequency pre-stored in the chip, the position of the touch point is determined, thereby eliminating clothing, luggage, dust and Misidentification caused by environmental factors such as insects. The acoustic wave of the surface touch screen propagates along the surface of the substrate, and the curved sound wave propagates inside the substrate, so the curved anti-interference performance is superior to the surface type. At present, curved touch screens are generally used for kiosks, financial equipment and vending machines of more than 5 inches.


5, optical imaging touch screen


The optical imaging touch screen is a touch technology that uses light to position the light source and the light trap sensor at the four corners of the screen. When the object touches the surface of the touch screen, the light changes, and the touch IC module analyzes the light sensor. The change determines the location of the touch. The optical imaging touch screen has high durability, is suitable for use in complex environments, and supports multi-touch, but is susceptible to misidentification by ambient light, dust, insects, and the like. Currently, the technology is only used in desktop monitors, education/training, etc. above 10 inches.


6, electromagnetic induction touch screen


The sensor of the electromagnetic inductive touch screen is disposed behind the display screen, and the sensor generates an electromagnetic area on the surface of the display. When the electronic pen touches the surface of the display, the sensor can determine the position of the touch point by calculating the electromagnetic change. Compared with other touch screen technologies, electromagnetic induction touch screens have the highest accuracy and resolution, low power consumption, and are lighter and thinner. They are especially suitable for use in war environments and built environments. Currently, the technology is mainly used in the US military.


In addition to the above-mentioned touch technologies, other touch screen technologies include pressure sensing, digital acoustic waveguide, and oscillating pointers, which are generally used for special purposes.


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