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Touch screen display technology analysis and development trend

2018-01-02 14:35:00 Editor:MICRON 1

Touch screens originated in the 1970s, and were mostly installed in industrial or commercial equipment such as industrial control computers and POS terminals. The launch of the iPhone in 2007 has become a milestone in the development of the touch industry. Apple designed a mobile phone that requires at least 20 buttons to be done with only three or four buttons, and all the remaining operations are done by the touch screen. In addition to giving users a more direct and convenient operating experience, it also makes the appearance of the mobile phone more fashionable and thinner, increasing the intimacy of direct human-machine interaction, triggering enthusiastic pursuit of consumers, and opening the touch screen to the mainstream The journey of the control interface.


   Touch screen technology is a new type of human-computer interaction input method. Compared with traditional keyboard and mouse input methods, touch screen input is more intuitive. With recognition software, the touch screen can also realize handwriting input. The touch screen is composed of detection components and a touch screen controller installed in front of the display screen. When a finger or other object touches the touch screen installed on the front of the display, the touched position is detected by the touch screen controller and sent to the host through an interface (such as RS-232 serial port, USB, etc.). At present, the touch screen has developed from a single-point touch screen to a multi-point touch screen.


   With the increasing of multimedia information inquiry, people talk about touch screens more and more, because touch screens are not only suitable for the national conditions of China's multimedia information inquiry, but also touch screens have many advantages such as ruggedness, fast response speed, space saving, and easy communication. Using this technology, our users can operate the host as long as they lightly touch the icons or text on the computer screen with their fingers, thus making the human-computer interaction more straightforward. This technology greatly facilitates those who do not understand computer operations. User.


   As a newest computer input device, touch screen is a simple, convenient and natural way of human-computer interaction. It gives multimedia a new look and is a very attractive new multimedia interactive device. The application range of touch screens in our country is very broad, mainly for public information query; such as business query of the telecommunications bureau, tax bureau, bank, electric power and other departments; information query on the city streets; in addition, it is used in leadership office, industrial control, military command, etc. Electronic games, ordering songs and dishes, multimedia teaching, real estate pre-sales, etc. In the future, touch screens will enter the home.


  The advantages and applications of touch screen technology


  According to the working principle of the touch screen and the medium for transmitting information, we divide the touch screen into resistive type, acoustic pulse recognition (APR) type, surface acoustic wave (SAW) type, surface acoustic wave (SAW) type, capacitive type and infrared/optical type. Each type of touch screen has its own advantages and disadvantages. To understand which type of touch screen is suitable for that occasion, the key is to understand the working principles and characteristics of each type of touch screen technology.


   Resistive: From the current promotion and application, the resistive touch screen is the dominant touch technology. It consists of a glass panel, an iridium tin oxide (ITO) resistive coating, and a protective plate with a conductive coating, with silver bus bars along the edges. The two layers are separated by small insulation points. When the screen is touched, the guard plate bends and contacts the coating film on the glass. The controller can choose to drive the glass layer and the +5 V guard plate, and read the voltage generated by the guard plate and the glass layer, and determine the X and Y coordinates according to the pressure drop in the measured layer. This technology requires four wires, the aforementioned bus bar, which is called 4-wire resistive touch screen technology. Due to the constant bending of the guard plate, there are tiny cracks in the ITO coating film. The linearity and accuracy of the 4-wire resistive touch screen technology will deteriorate, and environmental changes will also cause accuracy drift. Continuously improved 5, 6, 7 and 8-wire resistive touch screens have been used to eliminate these effects.


   Acoustic Pulse Recognition (APR) type: APR is composed of a glass display coating or other hard substrate, and 4 piezoelectric sensors are installed on the back. The sensor is installed on two opposite corners of the visible area and connected to the control card through a bent cable. When the user touches the screen, the finger or the drag between the stylus and the glass collides or rubs, so sound waves are generated. The wave radiation leaves the contact point and travels to the sensor, generating an electrical signal in proportion to the sound wave. These signals are amplified in the control card and then converted into digital data streams. Compare the data with the previously stored sound list to determine the location of the touch. APR is designed to eliminate environmental influences and external sounds because these factors do not match the stored sound list.


  Surface Acoustic Wave (SAW) type: SAW touch screen is composed of a glass coating with piezoelectric sensors for sending and receiving for the X and Y axis. The controller sends an electrical signal to the transmitter sensor and converts the signal into ultrasonic waves in the surface of the glass. Through the reflector array, these waves cover the entire touch screen. The reflector on the opposite side collects and controls these waves to the receiving sensor and converts them into electrical signals. Repeat this process for each axis. Part of the propagating wave is absorbed when the user touches it. The received signals corresponding to the X and Y coordinates are compared with the stored digital distribution map to identify changes and calculate the coordinates.


  Capacitive: The capacitive touch screen technology can be further subdivided into surface capacitive and projected capacitive. Surface capacitive technology is to coat the same conductor on the glass panel. The electrodes around the edge of the panel distribute the low voltage evenly across the conductive layer, creating a uniform electric field. When you touch it, you get current from every corner. The controller measures the current ratio obtained from each corner to calculate the touch position.


   Projected capacitive touch screen consists of fine lines of sensor grid between two protective glass layers. Parts can be placed behind user-installed materials, including vandal-proof glass up to 18 mm thick. When touched, a capacitance is formed between the finger and the sensor. The touch position can be calculated from the electrical characteristics of the changed sensor grid.


   Infrared/Optical: High-resolution infrared (IR) technology uses a small frame around the display, with surface mounted LEDs on it, a photoreceptor on the opposite side, and an infrared transparent frame hidden behind it. The controller continuously sends LEDs to construct an infrared light scanning grid. One or more infrared light on each axis will be blocked when touched, so that the corresponding X and Y coordinates can be determined.


   The prominent advantages and typical applications of the above-mentioned main touch screen technologies are summarized in Table 1.

  


Analysis of the three mainstream touch screens


  As far as electronic products, especially consumer products are concerned, how to transform the user's complex control actions into an intuitive, convenient and productive experience is the ultimate challenge for user interface design. On the one hand, the user interface design should take into consideration the five sensory needs of the user's vision, hearing, taste, smell and touch, and on the other hand, the impact of user needs on the device or system. Although most of the products launched on the market are effective, they mainly deal with the user's vision and touch separately. From simple buttons or keys on computer keyboards, mobile phone keyboards, MP3 players, household appliances and even TV remote controls, to more advanced click and scroll features such as volume adjustment sliders, scroll wheels, and track pads [LU1], output The position (that is, the result of the user's input or manipulation action [LU2]) is completely different from the user's input position. It would be great if the input and output, that is, the sense of vision and touch, can be completely consistent! And this consistency of vision and touch is the basic advantage of touch screens. Making vision and touch fully consistent is simple to say, but it is a far-reaching technological breakthrough that will completely change the way users interact with electronic products, so some people call this a revolution in user interface.


  The transparent nature of the touch screen allows users to directly "touch" different content on the display. People are lamented by such a user interface design. Because users no longer need to find this or that button around the electronic device, such as a computer mouse or keyboard or even a dial button on a mobile phone, but directly interact with the application solidified in the device's "brain" (that is, its operating system). This is a revolutionary change. This control method allows users to directly control the powerful operating system and applications, all at the user's fingertips. Of course, we can use the mouse and the tracking [LU3] board to access the application on the computer screen, but this kind of manipulation is not directly touching the display, and it cannot allow the user to integrate with the screen and embedded applications. In fact, we can use the touch screen through all kinds of actions or gestures we can imagine, so that the display screen becomes vivid and vivid. As long as the eyes see it, we can interact simply by touching it. At present, touch screens are mainly divided into three categories: single-point touch; multi-point touch to identify finger direction; multi-point touch to identify finger position.


  The development of touch screen functions is from simple to complex. The original product only supports the simplest operation [LU4] control, which is to touch a point on the screen to realize the control. For example, we operate every day at the POS terminal in the attached supermarket or the check-in terminal at the airport. In the past, we could only control it through the mechanical buttons around the screen. On this basis, the single-point touch screen achieved a great improvement in the user interface. Of course, mechanical and new capacitive touch-sensitive buttons are ubiquitous in our homes, offices and other places: mobile phones, fixed phones, remote controls, TVs, computers and their various peripherals, game consoles, refrigerators, microwave ovens, ovens, and In-vehicle electronic control equipment such as radio and air conditioning, etc. Now, the single-point touch screen directly integrates the user control interface on the display, so traditional mechanical buttons are no longer needed.


This screen brings two major benefits to the user interface. One is that the design space of the device is optimized, which is particularly beneficial to small devices, because it can "install" the screen and buttons in the same area at the same time; the other is that the buttons can be bound to the operation Any application in the system, so the number of "buttons" used by the device can be unlimited. The above functions are mainly based on resistive touch screen technology and have been widely promoted in various applications such as consumer electronics, airport newsstands, grocery store POS terminals and car GPS systems.


Although single-point touch screen and resistive touch screen technology are surprising and revolutionary, they still have two major shortcomings. One is that resistive technology relies on the physical movement of the touch screen [LU5], although the impact [LU6] is not significant, but After normal wear and aging, performance will decline; second, this technology only supports single-point touch, that is, only one finger can be used to perform a single action on a certain area of the screen at a time. Why is the user's interaction with the device limited to a single finger? Apple has made an incalculable contribution to the user interface revolution. Its iPhone uses an inductive capacitive touch screen. Even in miniaturized devices such as smart phones, to fully utilize the functions of applications and operating systems, multiple fingers are required to achieve optimal usability. Because of Apple, it is now difficult for users to imagine how they used to zoom in and out of photos and change the orientation of photo albums and web page views without supporting two-finger gestures.


Other technological innovators are continuing to use this multi-touch technology on a variety of device systems, including Google G-1 and Blackberry Storm smartphones, MacBook Pro and HP touchsmart desktop and laptop computers, portable media players, and many others Application etc. Now, users have new expectations, hoping to further improve the way users interact with their electronic products, and various electronic products are also vying to achieve this new requirement of users.


  Like the single-point touch screen, the multi-point touch screen that recognizes the direction of the finger also has a limitation, that is, the number of operating points that this technology can simultaneously recognize on the screen is limited. Why can only two operating points be recognized at a time? The user’s two hands have ten fingers. When the users interact with each other, they will appear on the screen.


   More fingers. This is the origin of the concept of multi-touch that recognizes the position of the finger, it can realize the manipulation of more than two fingers.


  Cypress calls this technology "multi-touch full-area input", which further improves the reliable usability of the touch screen and can meet the needs of a variety of feature-rich applications. Reliability refers to our ability to accurately capture the original data of all touch points on the screen with the highest granularity, and minimize the confusion caused by inaccurate positioning of the touch points on the screen. Usability refers to the ability of many powerful applications to benefit from screen manipulation with hands or more than two fingers on screens of different sizes. 3D interactive games, keyboard input and map operations are some of the main objects that use this touch screen function.


   Fundamentally speaking, multi-touch global input technology provides all touch data at their fingertips for device and system OEM manufacturers, helping them to be creative to develop the next generation of new and practical technologies. The TrueTouch touch screen solution launched by Cypress Semiconductor is an application example of multi-touch full-area input. TrueTouch uses Cypress's PSoC programmable system-on-chip architecture, which integrates an 8-bit microcontroller with programmable analog and digital blocks. Can achieve unparalleled flexibility and configurability. The inductive capacitive touch screen controller of the TrueTouch solution can be extended to support screens of various sizes, and can flexibly support single-point touch, multi-point touch that recognizes finger direction, and multi-point touch technology that recognizes finger position. TrueTouch can highly integrate external components, and is particularly suitable for working with various touch screen sensors or LCD displays. The flexible PSoC architecture allows designers to easily modify in the final stage of product design, which is not possible with other touch screen products.


  The future development trend of touch screen


   The current touch technology still has problems such as poor light transmission of the material source used in the screen, which affects the clarity of the display, or the coordinate drift after long-term use, which affects the accuracy of use. Moreover, the world’s major touch screen manufacturers are mostly concentrated in Japan, the United States, South Korea and other countries and Taiwan of China; the main technology, key components and raw materials are basically in the hands of Japanese and American manufacturers, and the touch screen/touch panel in mainland China The industry is basically in its infancy. But because of this, the whole touch industry has a very large room for growth in the future, and it is also expected to become an important field for the future innovation and development of Chinese electronics companies. At present, touch screens are mainly focused on small-size applications. The future development will be a world of touch and remote control. Therefore, the development of large-size touch screens is the current development trend of touch screens. Innotech Hengyuan is developing in the field of large-size touch screens. With advanced technology, especially in the application field of multi-touch, its multi-touch technology developed under WINDOWS7 has been widely used in the market, giving the public a refreshing feeling in the application of the market, and is deeply loved by the general public. Therefore, the future world is a touch world, a remote control world, and the development of large-size touch screens has broad space.


  According to iSuppli's forecast, under the stimulation of Apple's iPhone hot sales and its exquisite user interface, global shipments of touch screen display modules will more than double in 2008-2012. In view of this strong growth prospect, approximately 60 manufacturers demonstrated their touch screen sensors, modules or system technologies during the 2008 International Society for Information Display (SID) exhibition held in Los Angeles, USA last month. In 2008, the global market for touch screen module shipments will reach 341 million, and sales will reach US$3.4 billion. According to the latest forecast released by iSuppli this week, iSuppli predicts that the market will grow to 833 million by 2013, with a compound annual growth rate of 19.5% from 2008 to 2013. It is estimated that the global sales of touch screen modules in 2013 will rise from US$3.4 billion in 2008 to US$6.4 billion, with a compound annual growth rate of 13.7%. In the touch screen market, there are more than 100 suppliers, more than 300 OEM/integrators and many types of technologies. The market will usher in a broad prospect.