A little bit, slippery and slippery! Every day our low-headed people are on the mechanical screen WeChat, it seems that the touch has really changed the way of life of human beings. However, you are not curious as to why you are moving your finger on the glass. The machine knows what you are going to do? Well, let me reveal the touch technology for you.
Since the evolution of mobile phone functions, IT products have entered an intelligent era. Chips, screens, cameras, etc. have become the main force driving the intelligentization of IT products. But many people have not noticed that the constant updating of touch technology is the main reason why our products can be lighter, thinner and more intelligent.
Human-computer interaction was first carried out by physical devices such as buttons and mice, and then entered the era of touch we are in. The physical buttons are continuously reduced, and even products with virtual buttons are implemented. Nowadays, the continuous improvement of touch technology allows users to realize functions that can be realized by complicated operations through various gestures, strengths, and multi-touch.
The touch panel is also called Touch Panel, or Touch Screen, or Touch Pad, etc.. All electronic devices use the screen. If you don't want your screen to be occupied by a boring keyboard, you must use the touch screen. As the medium of human-machine dialogue, touch screen is the latest computer input device. It is the simplest, convenient and natural human-computer interaction method.
The history of touch screen technology
The background technology of the touch screen dates back to the 1940s, but there is a lot of evidence that the touch screen is practical until at least 1965.
1960s: the first touch screen
Historically, the first finger touch screen was thought to have been invented by EA Johnson in 1965 at the Royal Radar Institute in Malvern, England. Johnson first described his work in a paper entitled "Touch Display - A New Computer Input/Output Device" in Electronic Express. A diagram in the paper describes a touchscreen mechanism used by many of our smartphones today—known as capacitive touchscreens.
1970s: Invention of resistive touch screen
Although capacitive touch screens were first invented, they were surpassed by resistive touch screens in the early days of touch screens. The American inventor Dr. G. Samuel Hurst accidentally invented a resistive touch screen.
As a type of technology, the production cost of a resistive touch screen is usually very affordable. This type of touch technology is used mostly in restaurants, factories and hospitals because it is durable enough in these environments. Smartphone manufacturers used to use this resistive touch screen in the past, but in today's mobile phone field it only exists in low-end mobile phones.
1980s: Ten years of touch technology
In 1982, Nimish Mehta of the University of Toronto developed the first operational multi-touch device. Enter the research team and design a frosted glass board with a camera on the back that recognizes the different black spots displayed on the screen, which in turn can detect the action.
Soon after, an American computer expert, Myron Krueger designed the gesture interaction technology, he developed an optical system to track the movement of the record hand. The video place designed by Kruger was later called the video desk.
The research work was more than a decade earlier than the time when the touch technology appeared, and it had a huge impact. In the later stages of his career, Kruger became a pioneer in the art of virtual reality and interoperability.
Touch screens were commercialized in large numbers in the early 1980s. In September 1983, HP began its commercialization with its HP-150. The computer uses the MS-DOS operating system and comes with a 9-inch Sony CRT display that is recognized by the infrared illuminator and detector that the user's finger moves down on the screen, such as a poke to the screen, which blocks the corresponding Infrared rays, so that the computer determines the position of the finger.
1990s: Popular touch screen
In 1993, IBM and BellSouth jointly developed the Simon communication device, probably the world's first smartphone, although it was not the case at the time. It can turn pages, send and receive e-mails, with calendars, appointment plans, phone books, calculators, and pen-based artboards. It also has a resistive touch screen, so use the stylus to manipulate the menu bar and enter data.
That year Apple also started its personal digital assistant (PDA), the Newton PDA. The MessagePad 100 comes with handwriting recognition software that operates with a stylus.
The first decade of the 21st century and its transcendence
Due to the accumulation of previous technologies, the first decade of the 21st century has become a period of true prosperity for touch screen technology, and touch screen technology has become more and more accepted and loved by the public.
As the new millennium approaches, companies are injecting more resources to integrate touchscreen technology into their daily processing. In 2001, PortfolioWall debuted. The product is built by GM and Alias|Wavefront, and users can manipulate images, animations, and 3D models with just gestures.
In 2002, Sony introduced an input system called SmartSkin that recognizes multiple hand positions and multiple contacts simultaneously. This technology uses a capacitive sensor and a mesh antenna to calculate the distance between the hand and the surface, even in dim light conditions, without failure.
The real detonation of touch-screen phones is Apple’s launch of the first iPhone with high-resolution, multi-touch capabilities in 2007. The standard for touch screens has really been established. Today, capacitive touch screens have become standard equipment for smartphones.
Types of touch screen technology
The essence of the touch screen is the sensor. At present, according to the type of the sensor, the touch screen is roughly classified into four types: an infrared type, a resistive type, a surface acoustic wave type, and a capacitive touch screen.
Infrared touch screen
The infrared touch screen is provided with a circuit board outer frame on the front side of the display, and the circuit board arranges an infrared transmitting tube and an infrared receiving tube on four sides of the screen, and one-to-one correspondingly forms an infrared matrix which is horizontally and vertically crossed. When the user touches the screen, the finger blocks the two infrared rays passing through the position, so that the position of the touch point on the screen can be judged. Any touch object can change the infrared light on the contact to achieve touch screen operation. The infrared touch screen is immune to current, voltage and static interference and is suitable for certain harsh environmental conditions. Its main advantages are low cost, easy installation, no need for a card or any other controller, and can be applied to computers of all grades.
Resistive touch screen
The main part of the resistive touch screen is a resistive film screen that fits perfectly with the surface of the display. Two layers of OTI transparent oxidized metal conductive layer are applied to the tempered glass surface. Controlled by pressure sensing. When the finger touches the screen. The two conductive layers have contact at the touch point and the resistance changes. Signals are generated in both X and Y directions and then transmitted to the touch screen controller. The controller detects this contact and calculates the position of (X, Y), which then operates according to the way the mouse is simulated. The resistive touch screen is not afraid of dust, water and dirt, and can work in harsh environments. However, since the outer layer of the composite film is made of a plastic material, the explosion resistance is poor, and the service life is affected to some extent.
Surface acoustic wave touch screen
Surface acoustic waves are mechanical waves that propagate along the surface of a medium. An ultrasonic transducer is mounted on the corner of the touch screen. A high-frequency sound wave can be sent across the surface of the screen, and when the finger touches the screen, the sound waves on the contact are blocked, thereby determining the coordinate position. The surface acoustic wave touch screen is not affected by environmental factors such as temperature and humidity, and has extremely high resolution, excellent scratch resistance, long life, high light transmittance, and can maintain clear and translucent image quality, and is most suitable for use in public places. However, dust, water and dirt can seriously affect its performance, requiring frequent maintenance and keeping the screen clean.
Capacitive touch screen
The touch screen works by the current sensing of the human body, and a transparent special metal conductive material is attached to the surface of the glass. When a conductive object touches, the capacitance of the contact is changed, so that the position of the touch can be detected. . However, there is no reaction when wearing a gloved hand or holding a non-conducting object because of the addition of a more insulating medium. Capacitive touch screens are good for sensing light and fast touches, scratches, dust, water and dirt, making them suitable for use in harsh environments. However, since the capacitance varies with temperature, humidity or environmental electric field, its stability is poor, the resolution is low, and it is easy to drift.
Detailed explanation of the working principle of resistive and capacitive touch screens
Resistive touch screen works
The resistive touch panel is mainly composed of two film substrates coated with ITO (indium tin oxide) on one side, and the upper and lower plates need to be filled with transparent elastic spacers to separate them. It is shown that the lower plate must be a rigid thick glass to prevent deformation, while the upper plate needs to induce an external force to deform, so that it is necessary to explode glass or plastic.
During normal operation, the upper and lower plates are connected to the voltage and are in the off state. When the external force is pressed, the upper plate is deformed and the lower plate is in contact with the lower plate. At this time, a voltage change is generated, and the touch point coordinates can be accurately measured by the voltage change ( Because the upper and lower plates are touched by the upper and lower plates, the upper and lower plates are changed into a resistor divided into two, and the value of the resistance value is proportional to its distance from the edge to calculate the X and Y coordinates. Therefore, the accuracy of the resistive touch screen mainly depends on the conversion accuracy of this coordinate voltage, so it is very dependent on the accuracy of the A/D converter (voltage sensitivity of the magnitude).
Because the resistive screen is controlled by pressure, it does not have to be controlled by hand. The pen, credit card, etc. can be operated. Even if it is worn, it does not matter, and it is isolated from the outside world, so it has the advantage of dustproof and antifouling; If the "touch" is too light, the resistive screen will not respond, so you should use a light stamp. The resistive screen has low cost and low technical threshold. Moreover, it needs to be tapped when operating the resistive touch screen, so it is easy to be bad, and the sensitivity is not so good, and the drawing and writing are not smooth.
Capacitive touch screen works
However, what really brings the trend of smartphones is the capacitive touch screen, which consists of a glass substrate coated with a conductive film on both sides, and is covered with a thin layer of SiO2 dielectric on the upper plate. As shown in the figure, the upper electrode is used to form a plate capacitance sensing capacitance change with the human body (ground), and the lower plate is used to shield external signal interference.
When working, the upper transparent electrode needs to be connected to the voltage and draw four electrodes at the four corners. Therefore, when the finger touches the upper SiO2 layer, since the human body is electrically conductive, sufficient coupling capacitance is generated between the human body and the upper transparent electrode. And calculate the touch position coordinates according to the change of the capacitance value measured with the four corners (or the periphery) (the closer the touch position is, the larger the capacitance). However, this kind of surface capacitive touch (Surface Capacitive) can not meet the popular multi-touch. If you want to achieve multi-touch, you must use a new technology called Projected-Capacitive Touch, which mainly changes the surface of the sensing electrode. Laying in one or two layers and patterning (mainly diamond), one layer is responsible for the X direction and one layer is responsible for the Y direction. It is then positioned by a change in the electrode capacitance in the X and Y directions.
Since the mainstream is multi-touch now, I will talk a little bit about his evolution. There are two main types of multi-touch Projected Capacitive: Self-Capacitive and Mutual. Capacitive).
Self-capacitance It scans the electrode capacitance of each X and Y directly, so when two touch points are used, two additional ghost points (Ghost Points) will be generated. As shown in the figure, the left side is a graphical representation of the two-layer electrode (multiple For diamonds, it requires only one layer of ITO to form X and Y electrodes by photolithography. On the right side is the schematic diagram. From the schematic diagram, when touching (X2, Y0) and (X1, Y3) at the same time, since the capacitance of the four electrodes is measured, two extra points (X1, Y0) and two extra points are added. (X2, Y3), this is Ghost Points, which can only be solved by software. Although the self-capacitance has the problem of Ghost-Points, the self-capacitance position has high precision and sensitivity. The biggest advantage is that it can be used as a Single layer ITO film. However, when the size is large (>15 inches), the number of pins increases, resulting in an increase in the number of pins. Very high, and after the number of points, the middle line will not go out, the ITO must be thinned, so the resistance will increase, and the number of scans will increase. It seems that there is no advantage, but now the Apple phone seems to be walking. Self-capacitance touch technology, these technologies should have broken through.
Mutual-Cpacitiveor Trans-Capacitive requires two layers of ITO film. The X and Y electrodes are separated at each node by a special structure, so that it scans the Intersection capacitor instead of The electrode is capacitord. Only the contact of the two layers of ITO at the intersection must be separated, and it is necessary to use MEMS technology to bridge it like an interchange.
Both self-capacitance and mutual capacitance rely on the introduction of capacitance from the body capacitance to the electrode, so these two technologies are called charge-transfer capacitive touch (Charge-Transfer).
The advantage of capacitive touch is that it is fast and can be used without slipping. However, it can only be manipulated with conductive objects. It has the disadvantage that if the touch area is large (palm), you may have an action before you touch it. Because the large coupling capacitance is large, the screen is triggered, so it It is sensitive to changes in the electric field caused by external electric field or temperature and humidity. However, it is a layer of glass plate structure, so the transmittance is up to 90% higher than the resistance type.
However, it is difficult to achieve a uniform electric field for both resistive and capacitive touch screens, so it can only be used for panel sizes up to 20 inches. If you want to make a large-screen touch, you must use wave-type touch technology (mainly surface acoustic wave or infrared wave). It mainly installs infrared or acoustic transmitter/receiver at the four corners or edges. When the touch blocks the sound wave or In the case of infrared rays, the corresponding receiver can not determine the coordinates when it does not receive the signal. This touch screen is afraid of dirty, afraid of oil, too delicate, and is easily affected by environmental fluctuations.
Circuit part of touch technology
Most of the time spent on the principle and structure of the sensing module of the touch panel, but there must be a circuit part in the sensing part, and the main part of the circuit part of the touch is: signal detection, coordinate positioning, and gesture recognition ( Slide/zoom in/click).
For the MCU circuit, which circuit units are mainly needed, the most important one is the ADC (this is necessary for all Sensors), followed by the Scan Control and DSP (signal processing), and the scanning circuit must require the clock signal, so the Timer is required. . Gesture recognition is implemented by a unit called Finger Tracking. Finally, the code of User configure needs to use EEPROM or Flash.
There are two main difficulties in design: 1) high resistance and increased capacitance, and 2) noise coupling (Noise Coupling). The former is mainly due to the increasing size of the screen, so that the ITO electrode is getting longer and longer, so the resistance is getting larger and larger, and the electrode is getting longer and longer, so that the capacitance area is getting larger and larger, so the capacitance is also larger. The final problem is RC-delay. Extend, and the solution is either to speed up the scan by increasing the voltage, or to change the metal wiring (Ag). The latter (mainly coupling) is mainly due to the larger and larger panels. It is easy to receive the interference of environmental noise mainly by shielding, and the other interference comes from the interference of the switching power supply. This can only be achieved by adding Noise Cancellation before the ADC. achieve.
Touch screen technology has become a computer input method that is most acceptable to ordinary people after keyboard, mouse, tablet, and voice input. Because of this technology, the user can directly touch the icon or text on the computer display screen with his finger to realize the operation of the host, thereby making the human-computer interaction more straightforward. This technology is very convenient for the user, very Suitable for multimedia information inquiry. It gives multimedia a new look and is an attractive new multimedia interactive device.
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