A touch screen is a positioning device that allows users to input coordinate information directly to the computer with their fingers, just like a mouse or keyboard. Touch screen has many advantages such as robustness, fast response time, space saving, and easy communication.

The use of this technology, as long as the finger gently touch the computer display graphics or text to achieve the host operation, thus making human-computer interaction more direct, this technology is greatly convenient for those who do not know how to operate the computer users. Now has been widely used in industrial, medical, communication field control, information query and other aspects.

Touch screen types
1. resistive touch screen
Analog resistive screen
Analog resistive touch screen is what we usually call "resistive screen", is the use of pressure induction control of a touch screen.

It uses two layers of ITO (Indium Tin Oxide) plastic film coated with a conductive function, two pieces of ITO with particulate pivot points, so that the screen is not pressed when there is a certain gap between the two layers of ITO, in the state of non-conductive. When the operator presses the screen with a fingertip or pen tip, the pressure will make the film concave, the ITO layer contact conductive due to deformation, and then through the detection of X-axis, Y-axis voltage changes to convert the corresponding pressure point, the completion of the entire screen touch processing mechanism.

The current analog resistive touch screen has 4 lines, 5 lines, 6 lines and 8 lines and other types, as shown in Figure 1, the more lines, representing the higher precision can be detected, but the cost will also be relatively higher. Resistive screens do not support multi-touch, high power consumption, short life, while long-term use will bring detection point drift, requiring calibration. But the resistive screen structure is simple, lower cost, before the maturity of capacitive touch screen, once occupied most of the touch screen market.

Digital resistive screen
The basic principle of digital resistive screen is similar to the analog type, unlike the analog resistive screen in which the ITO layer is uniformly coated on the glass substrate, the digital resistive screen only uses the substrate with ITO stripes. The ITO stripes on the top and bottom 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 can achieve multi-touch.

2. Capacitive touch screen
Surface capacitive
Surface capacitive touch screen is to sense the touch behavior of the screen surface by means of electric field induction. Its panel is a uniformly coated ITO layer, the four corners of the panel have a line out to connect with the controller, the work of the touch screen surface to produce a uniform electric field. When a grounded object touches the surface of the screen, the electrode senses the change in charge on the surface of the screen and determines the coordinates of the touch point.

Surface capacitive touch screen has long service life, high light transmission rate, but low resolution, does not support multi-touch, currently mainly used in large size outdoor touch screen, such as public information platform (POI) and public service (sales) platform (POS) and other products.

Projected capacitive screen
Projected capacitive touch screens use electrostatic field lines emitted from the touch screen electrodes for sensing. Projected capacitive sensing technology can be divided into two types: self-capacitance and interactive capacitance.

Self-capacitance, also known as absolute capacitance, uses the object being sensed as the other pole of the capacitor, which induces a charge between the sensing electrode and the electrode being sensed, and determines the position by detecting the change in that coupling capacitance. However, if there is a single-point touch, the coordinates determined by the change in capacitance in the X-axis and Y-axis directions are only one set, and the combined coordinates are unique. If there are two touch points on the touch screen and these two points are not in the same X-direction or the same Y-direction, there are two coordinate projections in the X and Y-directions, respectively, then four coordinates are combined. Obviously, only two coordinates are real, and the other two are commonly known as "ghost points". Therefore, the self-capacitive screen can not achieve true multi-touch.

Interaction capacitance, also called cross capacitance, is the capacitance generated by the coupling of adjacent electrodes, and the change in interaction capacitance is felt when the sensed object approaches the electric field line from one electrode to another. When the horizontal electrodes send out the excitation signal in turn, all the longitudinal electrodes receive the signal at the same time, so that the size of the capacitance value at the intersection of all the horizontal and longitudinal electrodes can be obtained, that is, the size of the capacitance of the entire two-dimensional plane of the touch screen. When the human finger is close, it will cause the local electric capacity to decrease, and according to the data of the two-dimensional capacitance change of the touch screen, the coordinates of each touch point can be calculated, so even if there are multiple touch points on the screen, the real coordinates of each touch point can be calculated.

 

In the above two types of projected capacitive sensors, the sensing capacitance can be designed in a certain way so that the touch of a finger can be detected at any given time, the touch is not limited to a finger, but can also be multiple fingers. 2007 since the great success of Apple's iphone, iPad series products, projected capacitive screens began a spurt of development, the Rapidly replace the resistive touch screen, become the mainstream touch technology in the market now.

 

3. Infrared touch screen
Infrared touch screen is the use of X, Y direction on the dense infrared matrix to detect and locate the user's touch. Infrared touch screen in front of the display is installed in a circuit board frame, the circuit board on all sides of the screen lined up infrared transmitter and infrared receiver, one by one corresponds to the horizontal and vertical cross infrared matrix. When the user touches the screen, the finger will block the position through the horizontal and vertical two infrared, according to which you can determine the location of the touch point in the screen.

Infrared touch screen with high light transmission, not subject to current, voltage and static interference, touch stability and other advantages, but the infrared touch screen will be subject to changes in ambient light, will be affected by remote control, high-temperature objects, incandescent lamps and other sources of infrared, and reduce its accuracy. Early infrared touch screen appeared in 1992, the resolution is only 32 × 32, vulnerable to environmental interference and misoperation, and requires the use of a certain amount of shading environment.

After 20 years of development, the current advanced infrared touch screen in the normal working environment life of more than 7 years, in tracking finger movement trajectory, accuracy, smoothness and tracking speed can meet the requirements of the user's writing can be very smoothly converted to image trajectory, fully support handwriting recognition input. Infrared touch screen is mainly used in all kinds of public places without infrared and bright light interference, offices and requirements are not very precise industrial control places.

4. Acoustic wave touch screen
Surface acoustic wave touch screen
Surface acoustic wave touch screen is the touch technology through acoustic waves to position. In the four corners of the touch screen, were pasted in the X direction and Y direction of the emission and reception of acoustic wave sensors, surrounded by 45 ° reflective stripes. When the finger touches the screen, the finger absorbs part of the acoustic energy, and the controller detects the attenuation of the received signal at a certain moment, so that the location of the touch point can be calculated.

Surface acoustic wave technology is very stable and very high precision, in addition to the general touch screen can respond to the X and Y coordinates, but also respond to its unique third axis Z axis coordinates, that is, the pressure axis response. With this feature, each touch point is not just two digital switch states with and without touch, but becomes an analog switch capable of sensing force: the greater the amount of pressure, the wider and deeper the attenuation gap on the received signal waveform.

Among all types of touch screens, only surface acoustic wave touch screen has the performance of sensing touch pressure. Surface acoustic wave touch screen is not affected by temperature, humidity and other environmental factors, high clarity (extremely high resolution), good light transmission, highly durable, good scratch resistance, responsive, long life, can maintain a clear and translucent image quality, no drift, only need to install a correction, good resistance to violence, the most suitable for public information inquiries and offices, institutions and public places where the environment is relatively clean.

Bending acoustic wave type touch screen
Bending acoustic wave touch screen is based on the technology of sound pulse recognition. When the object touches the surface of the touch screen, the sensor will detect the frequency of the sound wave, by comparing the frequency with the standard frequency stored in the chip in advance, determine the location of the touch point. In this way, false recognition caused by environmental factors such as clothing, luggage, dust and insects can be eliminated.

Surface-type touch screens propagate sound waves along the surface of the substrate, while bending-type sound waves propagate inside the substrate, so bending-type has better resistance to environmental interference than surface-type. At present, the bending touch screen is generally used for more than 5 inch kiosk, financial equipment and vending machines.

5. Optical imaging touch screen
Optical imaging touch screen is a touch technology using light to locate the four corners of the screen are set up in the light source and light capture sensor, when the object touches the surface of the touch screen, the light changes, the touch IC module analyzes the changes in the light sensor to determine the location of the touch.

Optical imaging touch screen is highly durable, suitable for use in complex environments and supports multi-touch, but is susceptible to misidentification by ambient light, dust, insects and other influences. The technology is currently only used in more than 10 inches of desktop monitors, education / training, etc.

6 electromagnetic induction touch screen
Electromagnetic induction touch screen sensor set up after the display, the sensor in the display surface to produce an electromagnetic area, the electronic pen touches the display surface, the sensor can be calculated by the electromagnetic change to determine the location of the touch point.

Compared to other touch screen technology, electromagnetic induction touch screen accuracy and resolution is the highest, low power consumption, more thin and light, especially suitable for use in the war environment and construction environment, the technology is currently mainly used in the U.S. military.

Other touch screen technology currently on the market in addition to the above touch technology, there are pressure-sensitive, digital acoustic guidance, oscillating pointer and many other touch technology, generally used for special purposes.

Touch screen technology
1. inline touch screen structure
The current touch screen is basically an external structure, this structure of the display module and touch module are two relatively independent devices, and then through the back-end lamination process to integrate the two devices, but this relatively independent external structure will affect the thickness of the product, does not meet the trend of touch display products increasingly thin and light. This gives rise to the concept of embedded touch screen, embedded structure of the touch module embedded in the display module, so that the two modules into one, and no longer two relatively independent devices.

Compared to the traditional external structure, the advantages of the embedded structure is: only 2 layers of ITO glass, lower material costs, increased translucency, thinner; no touch screen module and TFT module back-end lamination, improve yield; touch screen set and TFT module production at the same time, reducing the module's transportation costs. In-cell touch screen can be divided into two types: In-cell technology and On-cell technology.

In-cell technology
The definition of the two technologies are slightly different, but the principle is similar, both touch screen embedded in the LCD module. in-cell technology to integrate the touch screen in the color filter below, because the touch sensor is placed inside the LCD panel, occupying part of the display area, so the sacrifice of part of the display effect, but also make the process becomes complex, high yield is difficult to achieve.

On-cell technology
On-cell technology integrates the touch screen on the color filter, instead of embedding the touch sensor inside the LCD panel, a simple transparent electrode is formed between the color filter backplane and the polarizing plate, reducing the technical difficulty. on-cell's main challenge is the amount of noise coupled to the sensing layer of the display, and touch screen components must use sophisticated algorithms to handle this noise. on -cell technology provides all the benefits of integrating the touch screen into the display, such as making the touch panel thinner and lighter with significant cost reduction advantages, but the overall system cost reduction is still far less than Incell technology.

The concept of inline was first proposed by TMD in 2003, followed by Sharp, Samsung, AUO, LG and other companies have proposed this concept, and have published some research results, but due to technical problems, have not been able to achieve commercialization.

Embedded touch screen has nearly 10 years of development time, there is still some distance from the commercialization, but the embedded touch screen represents the future direction of the development of touch screen, the active reserve embedded technology manufacturers will be in a relatively advantageous position in the future market competition.

2 multi-touch technology
Apple in 2007 through the projected capacitive technology to achieve multi-touch functionality, the function provides an unprecedented user experience, reflecting the differences with other touch technologies at the time, making multi-touch technology has become the market trend.

At present, multi-touch technology has been from the beginning of only two fingers can achieve zoom, three fingers scrolling and four fingers paddle shift, to support more than 5 points of touch recognition and multiple input methods, etc., the future of multi-touch technology will be to achieve more detailed screen object manipulation with the direction of more freedom of development.

3. Hybrid touch technology
Although there are many types of touch technology, but each technology has its own advantages and disadvantages, no one technology is perfect. In recent years, some people have begun to propose the concept of hybrid touch technology, that is, the use of two or more touch recognition technology on a touch surface, to achieve the purpose of complementing the advantages and disadvantages of a variety of touch technologies.

Currently has been developed based on capacitive and resistive hybrid touch screen, the touch screen can be operated by the stylus and finger, support multi-touch, etc., significantly improve the efficiency of touch screen recognition. With the increasing user requirements for touch technology, a single touch technology certainly can not meet the needs of people, so the hybrid touch technology will certainly become one of the future development direction of touch technology.

4. Haptic feedback technology
The continuous development of touch display technology to bring people a convenient way of operation and good visual effects at the same time, but ignore the touch operation to give users a tactile feedback. At present, there is not much research on haptic feedback technology, the United States Immersion company launched a haptic feedback technology called "Forcefeedback", the technology is the use of mechanical motors to generate vibration or movement, it can simulate jumping, objects falling and damping movement and other haptic effects, but also is currently used more Haptic feedback technology.