Comparison of Advantages and Disadvantages of Current Various Touch Technologies

   At present, the touch technologies applied to products mainly include infrared, resistive, capacitive, surface acoustic wave, optical image, 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 horizontal and vertical scanning lines. When an object blocks the light source, the position can be determined.

    This is commonly known as the photo-interruption switch. This technology is often seen in movies and is used for security detection. It is widely used, such as the positioning of the printing head of the printer, and the scroll wheel of the mouse. 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, the development of infrared rays is not an interception method, but a mode in which objects are reflected after emission, which is a bit similar to radar speed measurement. This method can also simulate multiple points, but there are still shielding problems, and the cost of transmitting and receiving components Increase, if you want to build densely (increase resolution), the related costs will be higher.

   2. Resistive type: The two conductive layers are brought into contact through pressure, and then the position of the object is calculated based on the difference in impedance value.

This technology was mostly used in small handwriting pads or touch pads in the early days, as well as membrane keyboards/waterproof keyboards, etc., as well as early analog joysticks, which were calculated 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 sufficient to exert pressure, such as hands and pens. The accuracy will be affected by changes in impedance value caused by temperature and humidity.

The judgment method is that there must be pressure when touching, so it will feel quite elastic, and the surface will be made of soft material and its technology.

Due to different manufacturing processes, there are four-wire, five-wire, eight-wire and so on.

    3. Capacitive: Calculate the position of the object through the change of the electric field affected by the conductive substance

This technology has been used in TV channel 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. Nowadays, many non-conductive materials can be used. Nowadays, most notebook computer touchpads use this technology, and the famous iPod also uses this technology. However, its disadvantage is that it must be sensed through an object that affects the electric field, and the response speed is also slow. In addition, it may also be affected by nearby electromagnetic fields. The influence causes accuracy error.

    The judgment method can generally be tested with a non-conductive material held in hand (conductors such as hands must have 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 is that the surface will not wear out due to long-term use, and the current projected capacitor can not only have more points (currently requires software) but also a large size (currently 100 inches) through a special process. Japan's Mitsubishi is even more Use the human body to transmit different signals to achieve multi-person touch (that is, it can be distinguished which person is touching).

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     4. Surface acoustic wave: High-frequency sound waves are transmitted on the surface of the medium. When the sound waves encounter soft materials and are absorbed, the position can be calculated.

This technology is gradually being used on touch screens. Its accuracy and response speed are better than resistive or capacitive ones. It can also be larger in size, but it requires reflection antennas to be placed around the conductive carrier. , so the size changes must be customized. At present, many game machines such as games have begun to adopt this technology.

The judgment method can be tested with hard conductive materials, generally it will not be sensitive to hard materials.

A new extension of this technology uses surface shock waves (patented by 3M), which are tiny vibrations generated when an object contacts the touch surface to calculate the position.

    5. Optical image Through more than two sets of CIR (CMOS/CCD), the position is calculated by observing the shadow of the object from the side.

This technology is becoming more and more widely used as CMOS/CCD technology matures. Now micro-CIR can output more than a hundred images per second, so it is currently the fastest response technology. Of course, as the CIR resolution becomes higher and higher, the processing speed becomes faster and faster, the photosensitivity becomes better and better, and the size of the shadow can be judged, so more and more varied applications can be made. 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 CIR, and there must be reflective or luminous materials (invisible light such as infrared ultraviolet rays, etc.) or one side of which has luminescent materials (invisible light such as infrared ultraviolet rays). wait).

     There are currently two common technologies. One uses infrared light to produce the shadow of an object, the other uses ultraviolet light to see the object's absorption of light, and the more special one uses laser to see the object's reflection.

      6. Image recognition: use the camera (CMOS/CCD) to calculate the position by observing the light and shadow changes on the contact surface from the front or back.

     This is something that many people who study interactive games or multi-touch will definitely come into contact with. The most famous method in terms of technology is the method proposed by Jeff Han. The most popular Microsoft Surface also uses similar technology, and its technical advantage is that it can be distinguished The shape of the object is exposed, and more applications can be made. However, the disadvantage is that the camera is used to observe from the front or back, so a certain space and distance are required, and infrared is used as the image light source, which is susceptible to interference, and cannot be used with a flat-panel display, and most of them need to be used with a projection method.

     The judgment method is that there must be a distance, such as the table to the ground, and the other is that it must be equipped with a projector.

There are several ways to generate light sources based on their technology. For example, Jeff Han conducts the light source in acrylic, so the light sources are placed around it, while Surface irradiates infrared light sources on the back (inside the table). Here Previously, Microsoft also proposed a method (TouchLight) that uses the superposition of the images of two cameras to determine. Some foreign graduate students use water bags to generate light source transmission. There are quite a lot of variability. Many floor or wall interactive advertisements on the market also use this method. In a similar way, there are many game consoles that use this method to design games. Japan has even developed a remote control that uses this technology to use your hand as a TV.

  7. Panel sensing: insert CIR (CMOS/CCD) on the panel (LED/LCD) to detect the amount of light change to calculate the position.

This is a relatively new technology, but it still needs a breakthrough in the manufacturing process, because it is not easy to have a light source and a light sensor between the panels at the same time, especially the LCD panel, because it uses a back light source, so many light elements (reflection or refraction) are required ) to complete, the famous Jeff Han used LED panels to achieve the technology.

The judging method is currently uncommon, so there is no obvious judging method, but observing Jeff Han's model, there must be visible gaps between light sources.

    This is a technology that is very likely to be mass-produced in the future, because the panel and touch control are integrated at the same time, and multi-point discrimination can be done without requiring a large space and long distance, and multi-point discrimination will not be required due to shading problems Added many algorithms to handle.

8. Electromagnetic type: use the magnetic field generated by the coil to change the current change generated by the receiving antenna to calculate the position.

    This is the technology used in the early digital boards or drawing boards. Later, most Tablet PCs also adopted this technology. Then there are touch screens for teaching and the screens on digital podiums. 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 cannot be used when placed on a table with a metal desktop. Now Then there won't be this problem.

The judgment 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 point: Observe the position of the luminous point through the Camera (CMOS/CCD).

     This technology was first integrated into rear projection TVs for interactive whiteboards, and later integrated into projectors for presentations. Currently, many interactive electronic whiteboards use this technology. The disadvantages are low accuracy and jitter. phenomenon (because of the distance), and must have a pen that emits a light point. Its advantage is that it can achieve remote control, which is very convenient for large-scale presentations. Currently, the most famous Wii game console uses this technology (Note: The release The long and expensive "receiver" under the TV is actually just two infrared LEDs inside, and the real camera is on the handle, so the value of the handle is far greater than the "receiver", although a It sells for more than 700, and one piece sells for more than 1,000. Selling that "receiver" is really profitable~ Haha, smart Nintendo).

    The judgment method is also very simple. There must be a small box in the distance with a camera hidden inside, just like image recognition, except that what he judges is a light spot (somewhat similar to Jeff Han using his hands to touch acrylic light guides to generate light point).

At present, this technology can also be divided into visible light or invisible light, single light spot/multiple light spots, 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 similar to the light gun, and the whiteboard uses light flashing to transmit button signals like a remote control, and uses red or green light to reflect whether it is pressed, etc.).

    Ultrasound: Use an ultrasonic transmitter to emit ultrasonic waves to two or more 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 receiving end and then reflected by the object to calculate the distance, while the ultrasonic wave is sent by 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, which is the same as that of the optical image, which uses triangulation to calculate the position. The difference is that the distance obtained by the ultrasonic wave is 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 for teaching purposes, because they still need a pen to match them. The disadvantage is that the accuracy is not high and it will shake (distance influence), There are also slow response times and so on.

    The way to judge it is to locate two long receivers that look like microphones, and the current products on the market will definitely hear the vibration of the wings of a fly due to the relationship between the frequency of the sound waves.

    This technology is made into many 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 at the same corner but with a certain distance, or at a certain distance. 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, it can be placed. In theory, the farther the distance, the more accurate the calculation, but in fact, the sound wave is easy to attenuate and be interfered, so the distance is too far At this time, interference and attenuation problems will increase.