Comparison of advantages and disadvantages of curr

Comparison of advantages and disadvantages of current touch technologies
At present, the touch technologies applied to products mainly include infrared, resistance, capacitance, surface acoustic wave, optical image, image recognition, panel induction, electromagnetic, light spot and ultrasonic. The advantages and disadvantages of various touch technologies are analyzed below.
1. Infrared type: use the infrared matrix to form horizontal and vertical scanning lines. When an object blocks the light source, the position can be determined.
This is commonly known as the light blocking switch. This technology is often seen in movies and is used for security detection. It is widely used. For example, the positioning of printer print head and the roller of mouse are determined by light blocking. Its disadvantage is that the real resolution is not high, it is easy to be affected by light and the reaction speed is slow, but it can sense any object that can block the light.
The judgment method is that there must be paired transmitters and receivers around.
At present, infrared ray has been further developed. It is not a blocking method, but a reflection mode encountered by objects after launch, which is a bit similar to radar velocity measurement. This method can also simulate multiple points, but there is still a shielding problem, and the cost of transmitting and receiving components increases. If it is to be densely deployed (improve resolution), the relevant cost will be higher.
2. Resistance type: make two conductive layers contact through pressure, and then calculate the object position through the difference of impedance value.
In the early days, this technology was mostly used on small handwriting boards or touch boards, as well as membrane keyboards / waterproof keyboards, and early analog rocker, which were calculated by the potential difference generated by resistance. Now this technology is widely used on mobile phones or small touch screens. Its advantage is that it can be operated by objects such as hands and pens that can exert pressure, The accuracy will be affected by temperature and humidity, resulting in the change of impedance value.
The judgment method is that there must be pressure when touching, so it will feel quite elastic, and the surface will be soft.
Due to different processes, there are four wire type, five wire type, eight wire type, etc.
3 .  Capacitive: calculate the position of the object through the change of the electric field affected by the conductive material
This technology has been used on TV station selectors 20 years ago. Later, many buttons that touch but do not need to be pressed down, such as elevator buttons, were mostly made of metal in the early development, but now many non-conductive materials can be used. Now most of the touch boards of notebook computers use this technology, and the famous iPod also uses this technology, However, its disadvantage is that it must be induced by objects that will affect the electric field. At the same time, the reaction speed is slow. In addition, it may be affected by the nearby electromagnetic field and produce accuracy error.
Generally, the judgment method can be tested with the hand-held non-conductive material (the conductor, such as the hand, must be a certain distance from the contact surface)
There are two common technologies: surface capacitor (microtouch of 3M) or projection capacitor (projection capacitor used by Apple). The advantage of projection capacitor is that it adopts non-contact induction, that is, it can be separated from glass or suspended induction. In application, the advantage is that the surface will not be worn out due to long-term use, and at present, projection capacitor can not only be multi-point through special process (at present, it needs to be equipped with software) and it can be very large (at present, it is 100 inches). Mitsubishi of Japan uses the human body to transmit different signals to achieve multi person and multi-point touch (that is, it can distinguish who is touching).
4. Surface acoustic wave: high frequency acoustic wave is transmitted on the surface of the medium. When the acoustic wave is absorbed by soft material, the position can be calculated.
This technology is gradually used on the touch screen. Its accuracy and response speed are better than those of resistance or capacitance. It can also achieve large size. However, because it must place reflective antennas around the conductive carrier, size changes must be customized. At present, many game consoles such as game consoles have also begun to adopt this technology.
The judgment method can be tested with hard conductive materials. Generally speaking, hard materials will not be induced.
A new extension of this technology is the use of surface shock wave (patented by 3M), which is the small vibration generated when an object contacts the touch surface to calculate the position.
5. The optical image passes through more than two groups of CIR (CMOS / CCD) to observe the shadow of the object from the side and calculate the position.
With the maturity of CMOS / CCD technology, this technology is more and more widely used. Now micro CIR can output more than 100 pictures per second, so it is the fastest technology at present. Of course, with the higher and higher resolution of CIR, the faster and faster processing speed, the better and better photosensitivity, and the size of shadow can be judged, Therefore, more and more changeable applications can be made, and its disadvantage is that it is more vulnerable to the influence of light.
   The judgment method is to observe four corners, there must be more than two groups of CIR, and there must be reflective or luminous substances around (invisible light such as infrared ultraviolet, etc.) or luminous substances on one side (invisible light such as infrared ultraviolet, etc.).
At present, there are two common technologies, one is to use infrared light to produce the shadow of the object, the other is to use ultraviolet light to see the light absorption of the object, and the more special is to use laser to see the reflection of the object.
6. Image recognition: the position is calculated by observing the light and shadow change of the contact surface on the front or back with camera (CMOS / CCD).
This is something that many researchers will come into contact with in interactive games or multi touch. The most famous technology is the method proposed by Jeff Han. Now the most popular Microsoft surface also uses similar technology. Its technical advantage is that it can distinguish the shape of the contact object and make more applications, but its disadvantage is that it uses camera to observe from the front or back, Therefore, it needs a certain space and distance, and the use of infrared as the image light source is easy to be disturbed, and it can not be used with flat panel display. Most of them need to be used with projection.
The judgment method is obviously to have a distance, such as from the table to the ground. In addition, it must be equipped with a projector at present.
According to its technology, there are several ways to generate light source. For example, Jeff Han conducts the light source in acrylic, so the light source is arranged around, The surface irradiates the infrared light source on the back (inside the table). Before that, Microsoft also proposed to use the image superposition of two cameras to determine (touchlight), there are also foreign graduate students who use water bags to generate light source conduction, which is quite changeable. Many floor or wall interactive advertisements on the market also use similar methods, and many game consoles use this method to design games. Japan has even developed a remote controller that can be used as a TV by hand at the remote end.
7. Panel sensing: install CIR (CMOS / CCD) in the panel (LED / LCD) to detect the change of light to calculate the position.
This is a relatively new technology, but it still needs to be broken through in the manufacturing process, because it is not easy to have a light source and light sense between the panels at the same time, especially the LCD panel. Because the back light source is used, many optical elements (reflection or refraction) are required to complete it, and the famous Jeff Han uses the LED panel to realize this technology.
At present, the judgment method is not common, so there is no obvious judgment method. However, observing Jeff Han's model, there must be a visible gap between the light sources.
This is a technology that is likely to be mass-produced in the future, because the panel and touch can be integrated at the same time, and multi-point discrimination can be done without large space and long distance, and multi-point discrimination will not need to add many algorithms to deal with the masking problem.
8. Electromagnetic type: use the magnetic field generated by the coil to change the current change generated through the receiving antenna to calculate the position.
This is the technology used in the early digital board or drawing board. Later, tablet PCs mostly use this technology. Next, the touch screen for teaching and the screen on the digital podium also use this technology, The only disadvantage is that a charged pen must be used (wacom has exclusive induction technology, which can generate electricity from the antenna end without battery). In the early days, the electromagnetic anti-interference ability was not strong, and many handwriting tablets could not be used when they were placed on the metal desktop. Now there will be no such problem.
The judgment method is very simple. There must be an exclusive pen, and there must be a coil in the middle of the pen to generate a magnetic field. At present, many interactive electronic whiteboards (non image scanning) also use this technology.
Light spot: observe the position of luminous spot through camera (CMOS / CCD).
This technology was integrated into the back projection TV as an interactive whiteboard in the early stage, and later integrated into the projector for briefing. At present, many interactive electronic whiteboards use this technology, which has the disadvantage of low accuracy, There will be jitter (because of the distance), and there must be a pen that can emit light spots. Its advantage is that it can achieve long-distance control, which is very convenient for large briefings. At present, the most famous Wii game console uses this technology (Note: the long expensive "receiver" under the TV is actually just two infrared LEDs. The real camera is on the handle, so the value of that handle is much greater than that "receiver". Although one sells more than 700 and the other sells more than 1000, it's really easy to make money selling that "receiver" ~ hehe, smart Nintendo).
The judgment method is also very simple. There must be a small box with camera in the distance, just like image recognition, but what he judges is a light spot (a little similar to Jeff Han's light spot generated by touching acrylic light guide with his hand).
At present, this technology can also be divided into visible light or invisible light, single light point / multi light point, red light / green light, flashing signal / no flashing signal, etc, Various combinations can also develop different application areas (Wii is used to judge the position of similar light gun, whiteboard uses light flash to transmit button signals like remote control, and red light or green light to reflect whether to press, etc.).
Ultrasonic: use the ultrasonic transmitter to send ultrasonic waves to more than two groups of receivers to calculate the position
Ultrasonic positioning is somewhat similar to radar. The difference is that the radar signal is transmitted by the receiving end and received after encountering the reflection of an object to calculate the distance, Ultrasound is a handheld device (pen) the ultrasonic wave is sent from the top to be received. There are two receivers. The main reason is that the position can be calculated through triangular positioning. The same as the optical image, the position is calculated through triangular positioning. The difference is that the ultrasonic wave obtains the distance from the transmitting end to the receiving end, while the optical image is calculated through the angle. At present, this kind of application is used in tablet, electronic whiteboard and so on Most of the touch screens used by people are mainly for teaching purposes, because they still need a pen to match. Their disadvantages are low accuracy, jitter (distance influence), slow response speed and so on.
The judgment method is that there must be two long receivers like microphones, and the products on the market will hear the sound like the vibration of fly wings due to their sound wave frequency.
Due to different applications, this technology is made into quite a number of different types of products. The technical principles are the same, but the receiver is separated on both sides of the sensing surface, or in the same corner but with a certain distance, or on one side. As long as the two receivers have a certain distance from the ultrasonic transmitting source, they can be placed, Theoretically, the farther the distance is, the more accurate the calculation is, but in fact, the sound wave is easy to attenuate and be disturbed. Therefore, when the distance is too far, the problem of interference and attenuation will increase.