Comparison of advantages and disadvantages of various current touch technologies

    At present, the touch technologies applied to products mainly include infrared, resistive, capacitive, surface acoustic wave, optical imaging, image recognition, panel induction, electromagnetic, light spot, and ultrasonic. The following is an analysis of the advantages and disadvantages of various touch technologies.
1. Infrared type: The infrared matrix is ​​used to form the scanning lines of horizontal and vertical columns. When there is an object blocking the light source, the position can be determined.
    This is commonly known as a photo-interrupting switch. This technology is often seen in movies and is used for security detection. It is widely used, such as the positioning of the print head of a printer and the scroll wheel of a mouse, all using photo-interruption. Judgment, its disadvantage is that the real resolution is not high, it is easily affected by light, and the response speed is slow, but it can sense any object that can block the light.
The way to determine it is that there must be pairs of transmitters and receivers around.
    At present, infrared rays are also developed in a way that is not intercepted, but a mode in which objects are reflected after launch, which is similar to radar speed measurement. This method can also simulate multiple points, but there is still a shielding problem, and the cost of transmitting and receiving components Increase, if you want to deploy densely (increasing resolution), the associated cost will be higher.
   2. Resistive type: The two conductive layers are brought into contact through pressure, and the position of the object is calculated through the difference in impedance values.
In the early days, this technology was mostly used on small handwriting pads or touchpads, as well as membrane keyboards/waterproof keyboards, etc., as well as the early analog joysticks, which were calculated by using the potential difference generated by resistance. Now this technology is It is widely used on mobile phones or small-sized touch screens. The advantage is that it can be operated with objects that are enough to exert pressure, such as a hand and a pen, and the accuracy will be affected by temperature and humidity. The impedance value changes and changes.
The way to determine it is that there must be pressure when touching, so there will be a fairly elastic feeling, and the surface will be a soft material.
Due to the different process, it is divided into four-wire type, five-wire type, eight-wire type and so on.
    3. Capacitive: The position of the object is calculated by 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 were touched but did not need to be pressed, such as elevator buttons, were mostly made of metal in the early development, but now many non-conductive materials can be used. Most of the touchpads of notebook computers now use this technology, and the famous iPod also uses this technology, but its disadvantage is that it must be sensed by objects that can affect the electric field, and the response speed is also slow, and it may also be affected by nearby electromagnetic fields. resulting in accuracy errors.
    The judgment method can generally be tested by hand-held non-conductive materials (conductors such as hands must be at a certain distance from the contact surface)
There are two common technologies: surface capacitance (3M's MicroTouch) or projected capacitance (Apple uses projected capacitance). The advantage of projected capacitance is that it uses non-contact sensing, that is, it can be sensed through glass or suspended in the air. The advantage of the above is that the surface will not be worn out due to long-term use, and the current projected capacitor can not only have multiple points (currently required to be equipped with software) but also can achieve a large size (currently 100 inches) through a special process. Japan's Mitsubishi is more Use the human body to transmit different signals to achieve multi-point touch (that is, you can distinguish which person is touching).
     4. Surface acoustic wave: transmit high-frequency sound waves on the surface of the medium. When the sound waves are absorbed by soft materials, the position can be calculated.
This technology is gradually used on the touch screen, and its accuracy and response speed are better than those of resistance or capacitance, and it can also achieve larger size, but because it must be placed around the conductive carrier reflective antenna , so the size changes must be customized. At present, many game machines such as games have also begun to use this technology.
Its judgment method can be tested with hard conductive materials, generally it will not induce hard materials.
A new extension of this technology is the use of surface shock waves (patented by 3M), which are tiny vibrations generated when an object touches the touch surface to calculate the position.
    5. Optical image The position is calculated by observing the shadow of the object from the side through more than two sets of CIR (CMOS/CCD).
This technology has become more and more widely used with the maturity of CMOS/CCD technology. Now micro-CIR can output more than 100 pictures per second, so it is currently the fastest response technology. Of course, as the CIR resolution is getting higher and higher, the processing speed is getting faster and the photosensitive ability is getting better and better, and the size of the shadow can be judged, so more and more variable applications can be made, but the disadvantage is that it is easier affected by light.
    The judgment method is to observe the four corners, there must be more than two sets of CIRs, and there must be reflective or luminous substances (invisible light such as infrared ultraviolet, etc.) around them, or there must be luminescent substances on one side (invisible light such as infrared ultraviolet rays, etc.). Wait).
     At present, there are two common technologies, one uses infrared light to produce the shadow of an object, the other uses ultraviolet light to see the absorption of light by the object, and the more special one uses laser to see the reflection of the object.
      6. Image recognition: Use the Camera (CMOS/CCD) to observe the light and shadow changes of the contact surface from the front or back to calculate the position.
     This is something that many people who study interactive games or multi-touch will definitely come into contact with. In terms of technology, the most famous method is the method proposed by Jeff Han. Now the most popular Microsoft Surface also uses similar technology. Its technical advantage is that it can be distinguished. However, the disadvantage is that the camera is used to observe from the front or the back, so a certain space and distance are required, and the infrared light is used as the image light source, which is easy to be affected. interference, and cannot be used with flat-panel displays, most of them need to be used with projection.
     The way to determine it is to obviously have a distance, such as the table to the ground, and the other is that it must be matched with a projector at present.
According to its technology, there are several ways to generate light sources. For example, Jeff Han conducts the light source in the acrylic, so the light source is arranged around, while the Surface illuminates the infrared light source on the back (inside the table). Here Previously, Microsoft also proposed the method of using two cameras to superimpose the image (TouchLight), and foreign graduate students used water bags to generate light source conduction. The variability is quite large. Many floor or wall interactive advertisements on the market also use In a similar way, there are many game consoles that use this method to design games, and Japan has even developed a remote control that can be used as a TV at the far end using this technology.
  7. Panel induction: CIR (CMOS/CCD) is inserted in the panel (LED/LCD) to detect the change of light to calculate the position.
This is a relatively new technology, but there is still a breakthrough in the process, because it is not easy to have a light source and a light sensor between the panels at the same time, especially for LCD panels, because the back light source is used, many optical elements (reflection or refraction) are required. ) to complete, and the famous Jeff Han uses LED panels to implement the technology.
The method of determining it is currently uncommon, so there is no obvious method for determining it, but observing Jeff Han's model, there must be a visible gap between the luminous sources.
    This is a technology that is very likely to be mass-produced in the future, because the panel and touch are integrated at the same time, and multi-point discrimination can be done without requiring a large space and a long distance, and multi-point discrimination will not be required due to shading problems. Add many algorithms to handle.
8. Electromagnetic: use the coil to generate a magnetic field to change the current change generated by the receiving antenna to calculate the position.
    This is the technology used in the early digital tablet or drawing tablet. Later, Tablet PC also mostly adopts this technology, and then there are touch screens for teaching, and the screens on the digital platform also use this technology. The only disadvantage is that it has certain disadvantages. You need to use a charged pen (Wacom has an exclusive induction technology that can induce electricity from the antenna end, no battery is required), the early electromagnetic anti-interference ability is not strong, and many writing tablets can not be used when they are placed on a metal table top, now There will be no such problem.
The determination method is very simple, there must be a dedicated 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 the light-emitting point through the Camera (CMOS/CCD).
     In the early days, this technology was integrated on rear projection TVs for interactive whiteboards, and later integrated into projectors for presentations. At present, many interactive electronic whiteboards use this technology. The disadvantage is that the accuracy is low and there will be jitter. phenomenon (because of the distance), and there must be a pen that can emit light points. The long and 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 of the "receiver", although one It sells for more than 700, and one sells for more than 1,000. It is really profitable to sell that "receiver"~ Hehe, smart Nintendo).
    The determination method is also very simple. There must be a small box hiding a Camera in the distance, just like image recognition, but it is only a light spot (somewhat similar to Jeff Han using his hand to touch the acrylic light guide to generate light) point).
At present, this technology can also be divided into visible light or invisible light, single light spot/multiple light spot, red light/green light, flashing signal/no flashing signal, etc. Various combinations can also develop different application areas (Wii is used for position determination similar to a light gun, and the whiteboard uses light flashes like a remote control to transmit button signals, and red light or green light is used to reflect whether it is pressed, etc.).
    Ultrasonic: The ultrasonic transmitter is used to transmit ultrasonic waves to more than two sets of receivers to receive and calculate the position
    Ultrasonic positioning is a bit similar to radar, the difference is that the radar signal is transmitted by the receiver and then reflected by the object and then received to calculate the distance, while the ultrasonic wave is sent from the handheld device (pen) to receive it, and there must be two receivers. The main reason is that the position can be calculated through triangulation. The same as the optical image, the position is calculated by triangulation. The difference is that the ultrasonic wave obtains the distance from the transmitter to the receiver, while the optical image is calculated through the angle. Such applications include handwriting boards, electronic whiteboards, and some people use them as touch screens. Most of them are mainly used for teaching purposes, because they still need a pen to match. The disadvantage is that the accuracy is not high and it will shake (distance effect). There is also a slow response time and so on.
    The way to determine it is to have two long receivers that look like microphones, and the products currently on the market will definitely hear a sound like the vibration of the wings of a fly due to the frequency of the sound waves.
    This technology makes quite a few different types of products due to different applications. The technical principle is the same, but the receivers are separated on both sides of the sensing surface, or in the same corner but with a certain distance, or in a certain There is a certain distance on one side. As long as there is a certain distance between the two receivers and the ultrasonic emission source, they can be placed. In theory, the farther the distance is, the more accurate the calculation is, but in fact, the sound wave is easily attenuated and interfered, so the distance is too far. Then the interference and attenuation problems will increase.