With the continuous development of touch display technology, it brings people a convenient way of operation, good visual effect, but ignores the touch operation to give users a tactile feedback.
Touch screen is a positioning device, the user can directly use the finger like a computer to enter the coordinates of the information, with the mouse, keyboard, is also an input device. Touchscreens have many advantages such as ruggedness, fast response time, space saving, and ease of communication.
The use of this technology, as long as the finger gently touch the computer display on the symbols or text can be realized on the host operation, so that human-computer interaction is more direct, this technology greatly facilitates those who do not understand the computer operation of the user. It is now widely used in industrial, medical, and communication fields for control, information query, and other aspects.
Types of Touch Screens
1. Resistive Touch Screens
Analog Resistive Screen
Analog Resistive Touch Screens are commonly known as "resistive screens", which utilize pressure sensing to control a touch screen. It is a kind of touch screen that utilizes pressure sensing for control.
It uses two layers of ITO plastic film coated with a conductive function, two pieces of ITO with a particle pivot point, so that the screen is not pressed when the two layers of ITO have a certain gap between the two layers of ITO, in the non-conductive state.
When the operator presses the screen with a fingertip or pen tip, the pressure will make the membrane concave, and the deformation will make the ITO layer contact conductive, and then by detecting the X-axis, Y-axis voltage changes converted to the corresponding pressure point, completing the entire screen touch processing mechanism.
Currently, analog resistive touchscreens are available in 4-wire, 5-wire, 6-wire, and 8-wire variations. The higher the number of wires, the greater the precision of the detection, but the higher the cost.
In addition, resistive screens do not support multi-touch, consume a lot of power, have a shorter lifespan, and require calibration because of the drift of the detection point when used over a long period of time. But resistive screen structure is simple, low cost, in capacitive touch screen before the maturity, once occupied most of the touch screen market.
Digital resistive screen
The basic principle of digital resistive screen is similar to the analog one, and the analog resistive screen is different from the glass substrate uniformly coated with ITO layer, the digital resistive screen is only the use of substrate with ITO stripes. Among them, the ITO stripes of the upper and lower substrates are perpendicular to each other.
A digital resistive screen is more similar to a simple switch, so it is often used as a membrane switch. Digital resistive screens allow for multi-touch.
2. Capacitive Touch Screens
Surface Capacitive
Surface Capacitive Touch Screens are designed to sense touch behavior on the surface of the screen by means of electric field sensing. Its panel is a piece of uniformly coated ITO layer, the four corners of the panel each has a line out to connect with the controller, the work of the touch screen surface to generate a uniform electric field.
The surface capacitive touch screen is characterized by a long service life, high light transmission, but low resolution, does not support multi-touch.
At present, it is mainly used in large-size outdoor touch screen, such as public **** information platform, public **** service platform 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 techniques can be categorized into two types: self-capacitive and interactive capacitive .
Self-capacitance, also known as absolute capacitance, uses the object being sensed as the other pole plate of the capacitor, which induces a charge between the sensing electrode and the electrode being sensed, and determines the position by detecting a change in that coupled capacitance. However, if there is a single point of touch, there is only one set of coordinates determined in the direction of the X-axis and Y-axis by the change in capacitance, and the coordinates combined are also 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 coordinates projected in the X and Y directions, then the combination of four coordinates. Obviously, only two coordinates are real, the other two are commonly known as "ghost points". Therefore, self-capacitive screens can't achieve true multi-touch.
Interactive capacitance, also called spanning capacitance, is the capacitance generated by the coupling of neighboring electrodes, and the change in interactive capacitance is sensed when the sensed object is close to the electric field lines from one electrode to the other. When the electrodes in the transverse direction send out excitation signals in turn, all the electrodes in the longitudinal direction receive the signals at the same time, so that the magnitude of the capacitance value of the intersection of all the transverse and longitudinal electrodes can be obtained, i.e., the magnitude of the capacitance of the entire two-dimensional plane of the touch screen. When the human finger is close, it will lead to a localized reduction in capacitance, and according to the touch screen 2D capacitance change data, 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 both of these types of projected capacitive sensors, the sensing capacitance can be designed in a certain way so that a finger touch can be detected at any given time, and that touch is not limited to one finger, but can be multiple fingers.
Since Apple's iPhone and iPad series products have been a huge success since 2007, projected capacitive screens have begun to develop in spurts, rapidly replacing resistive touchscreens as the mainstream touch technology in the market today.
3. Infrared Touch Screens
Infrared touch screens utilize a dense matrix of infrared rays in the X and Y directions to detect and locate the user's touch.
Infrared touch screen in front of the monitor to install a circuit board frame, the circuit board in the screen on all sides of the infrared transmitter tube and infrared receiver tube, one by one into the horizontal and vertical cross infrared matrix. When the user touches the screen, the finger will block the location of the horizontal and vertical two infrared. Accordingly, 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 electrostatic interference, touch stability and high advantages. But infrared touch screen will be subject to changes in ambient light, will be subject to remote control, high temperature objects, incandescent lamps and other infrared sources of influence, and reduce its accuracy.
Early infrared touch screen appeared in 1992, the resolution is only 32 × 32, susceptible to environmental interference and misbehavior, and requires the use of a certain shade in the environment.
After 20 years of development, the current advanced infrared touch screen in the normal operating environment life expectancy of more than 7 years, in tracking the finger movement trajectory, accuracy, smoothness and tracking speed can meet the requirements of the user's writing can be converted into a very smooth image trajectory, fully support handwriting recognition input.
Infrared touch screen is mainly used in all kinds of public **** place without infrared and strong light interference, office and requirements are not very precise industrial control place.
4. Acoustic Touch Screens
Surface Acoustic Wave Touch Screens
Surface Acoustic Wave Touch Screens are a touch technology that uses acoustic waves to position itself.
In the four corners of the touch screen, the X and Y direction of the transmitting and receiving sound wave sensors are pasted, and the surrounding area is engraved with 45 ° reflective stripes. When a finger touches the screen, the finger absorbs some of the acoustic energy, and the controller detects the attenuation of the received signal at a certain point in time, from which the location of the touch point can be calculated.
Surface acoustic wave technology is very stable and highly accurate, and in addition to the X and Y coordinates to which touchscreens generally respond, it also responds to its unique third axis, the Z coordinate, which is the pressure axis response.
Of all the types of touchscreens, only surface acoustic wave touchscreens have the ability to sense touch pressure. Surface acoustic wave touch screen is not affected by temperature, humidity and other environmental factors, high clarity, good light transmission, high durability, good scratch resistance, responsive, long life, can maintain a clear and transparent image quality, no drift, only need to be installed once the calibration, good resistance to violence, the most suitable for the public **** information query and the office, the authorities and the environment is relatively cleaner the use of public **** place.
Bending acoustic touch screen
Bending acoustic touch screen is based on the technology of sound pulse recognition.
When an object touches the surface of the touchscreen, a sensor detects the frequency of the sound wave and determines the location of the touch point by comparing that frequency to a standard frequency pre-stored on a chip.
Surface-mounted touchscreens propagate sound waves along the surface of the substrate, while curved-mounted sound waves propagate inside the substrate, so curved-mounted is better than surface-mounted in terms of resistance to environmental interference. Currently, curved touchscreens are generally used in kiosks, financial devices, and vending machines that are more than 5 inches in size.
5. Optical imaging touch screen
Optical imaging touch screen is a touch technology that uses light to locate the light source and light capture sensor in the four corners of the screen were set up, when the object touches the surface of the touch screen, the light changes, and the touch IC module analyzes the changes in the light sensor to determine the location of the touch.
Optical imaging touch screens are highly durable, suitable for use in complex environments, and support multi-touch, but are susceptible to misrecognition by ambient light, dust, insects, and other influences.
6. Electromagnetic induction touch screen
Electromagnetic induction touch screen inductor set in the display after the inductor in the display surface to produce an electromagnetic area, the electronic pen touched the surface of the display, the inductor can be calculated by the electromagnetic change to determine the location of the touch point.
Compared to other touchscreen technologies, electromagnetic inductive touchscreens have the highest accuracy and resolution, consume less power, are thinner and lighter, and are particularly suited to war environments and built environments, and are currently used primarily by the U.S. military.
Other touchscreen technologies currently on the market in addition to the above touch technology, there are pressure-sensitive, digital acoustic wave-guided, oscillating pointer, and other types of touch technology, generally used for special purposes.
Touch screen technology
1. Embedded touch screen structure
At present, the touch screen is basically the use of external structure, this structure of the display module and the touch module is a relatively independent of the device, and then through the back-end of the laminating process will be the two devices. The integration of the two devices is done through the back-end lamination process, but this relatively independent external structure will affect the thickness of the product, which is not in line with the trend of increasingly thin and light touch display products.
As a result, the concept of embedded touchscreens has arisen, where the embedded structure embeds the touch module into the display module so that the two modules become one and are no longer two relatively independent devices.
Compared to the traditional external structure, the advantages of the embedded structure are:
- Only 2 layers of ITO glass are needed, reducing material costs, improving light transmission, and being thinner and lighter
- No need for back-end lamination of the touchscreen module and TFT module, improving yields
- Simultaneous production of the touchscreen unit and the TFT module reduces the transportation costs for the module
- The touchscreen unit is produced at the same time as the TFT module.
Additionally, embedded touchscreens can be categorized into two types: In-cell technology and On-cell technology.
In-cell technology
The definitions of the two technologies are slightly different, but the principles are similar, both are embedded in the LCD module. In-cell technology integrates the touch screen below the color filter, and occupies a portion of the display area due to placing the touch sensor inside the LCD panel, so some of the display effect is sacrificed. In-cell technology integrates the touch sensor under the color filter, occupying a portion of the display area, so sacrificing some of the display effect, but also making the process complex, high yield is difficult to achieve.
On-cell technology
On-cell technology is the integration of the touch screen on the color filter, not embedded in the LCD panel inside the touch sensor, only in the color filter base plate and polarizer plate can form a simple transparent electrode can be, reducing the technical difficulties. the main challenges of On-cell are The main challenge for On-cell is the amount of noise coupled to the sensing layer of the display, and the touch screen components must utilize sophisticated algorithms to deal with this noise. On-cell technology provides all the benefits of integrating a touch screen into a display, such as making the touch panel thinner and lighter with significantly lower costs, but the overall system cost reduction is still far less than that of Incell technology.
The concept of in-cell was first proposed by TMD in 2003, and then Sharp, Samsung, AUO, LG, and other companies have proposed this concept and published some research results, but due to technical issues, they have not been able to achieve commercialization.
Embedded touch screen has been nearly 10 years of development time, the current commercialization from the realization of a certain distance, but embedded touch screen represents the future direction of development of the touch screen, and actively reserve embedded technology manufacturers will be in the future market competition in a relatively advantageous position.
2. Multi-touch technology
In 2007, Apple realized multi-touch functionality through projected capacitive technology, which provided an unprecedented user experience, reflecting the difference with other touch technologies at the time, making multi-touch technology a market trend.
Currently, multi-touch technology has evolved from two-finger zooming, three-finger scrolling, and four-finger panning to supporting more than five points of touch recognition and multiple input modes, with multi-touch technology moving towards more detailed screen object manipulation and a greater degree of freedom in the future.
3. Hybrid touch technology
Currently, although there are many types of touch technology, each has its own advantages and disadvantages, and no one technology is perfect. In recent years, some people have begun to put forward the concept of hybrid touch technology, that is, in a piece of touch surface using two or more than two kinds of touch recognition technology, to achieve a variety of touch technology to realize the advantages and disadvantages of the purpose of complementary.
Currently, capacitive and resistive based hybrid touch screen has been developed, the touch screen can be operated by stylus and finger, support multi-touch, etc., significantly improve the recognition efficiency of the touch screen. As the user's touch technology requirements continue to improve, 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 has brought people convenient operation and good visual effects, but neglected to give users a tactile feedback when touching operations.
Currently, there is not much research on haptic feedback technology. The U.S. company Immersion launched a haptic feedback technology called "Forcefeedback", which uses a mechanical motor to generate vibration or motion, which can simulate the tactile effects of jumping, falling objects, and damping movements, and is currently used more haptic feedback technology.
Senseg's "E-sense" technology uses the principle of bioelectric fields to generate a haptic feedback. The development of more realistic haptic feedback technology can bring users a new touch experience, so haptic feedback technology is also a future direction of touch technology development.