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Resistive

By George Mcdonald,2014-06-24 15:39
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触控萤幕;又称为触控面板、轻触式萤幕!英文?Touch panelTouchscreensTouch pad等,;是個可接收觸

    頭!無論是手指或膠筆尖等,等輸入訊號的感應式液晶顯示裝置;當接觸了螢幕上的圖形按鈕時;螢幕上的觸覺

    反饋系統可根據預先編程的程式驅動各種連結裝置;可用以取代機械式的按鈕面板;並藉由液晶顯示畫面製造出

    生動的影音效果。

    而簡單說是指種可觸控式的螢幕;通常是在半反射式液晶面板上覆蓋一層壓力板;其對壓力有高敏感度;當物體

    施壓於其上時會有電流訊號產生以定出壓力源位置;並可動態追蹤。

此为最大尺寸。

    按传感器工作原理;觸控螢幕大致上可分為,

    ; 電容式

    ; 電阻式

    ; 紅外線式

    ; 聲波式。

    Resistive

    A resistive touchscreen panel comprises several layers, the most important of which are two thin, transparent electrically-resistive layers separated by a thin space. These layers face each other, with a thin gap between. One resistive layer is a coating on the underside of the top surface of the screen. Just beneath it is a similar resistive layer on top of its substrate. One layer has conductive connections along its sides, the other along top and bottom.

    When an object, such as a fingertip or stylus tip, presses down on the outer surface, the two layers touch to become connected at that point: The panel then behaves as a pair of voltage dividers, one axis at a time. For a short time, the associated electronics (device controller) applies a voltage to the opposite sides of one layer, while the other layer senses the proportion (think percentage) of voltage at the contact point. That provides the horizontal [x] position. Then, the controller applies a voltage to the top and bottom edges of the other layer (the one that just sensed the amount of voltage); the first layer now senses height [y]. The controller rapidly alternates between these two modes. As well, it sends position data to the CPU in the device, where it's interpreted according to what the user is doing.

    Resistive touch is used in restaurants, factories and hospitals due to its high resistance to liquids and contaminants. A major benefit of resistive touch technology is its low cost. Disadvantages include the need to press down, and a risk of damage by sharp objects. Resistive touchscreens also suffer from poorer contrast, due to having additional reflections from the extra layer of material placed over the screen.

Surface acoustic wave

    Surface acoustic wave (SAW) technology uses ultrasonic waves that pass over the touchscreen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. Surface wave touchscreen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touchscreen.

    Capacitive

    Capacitive touchscreen of a mobile phone

    Main article: Capacitive sensing

    A capacitive touchscreen panel consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide (ITO). As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance. Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing. Unlike a resistive touchscreen, one cannot use a capacitive touchscreen through most types of electrically insulating material, such as gloves; one requires a special capacitive stylus, or a special-application glove with an embroidered patch of conductive thread passing through it and contacting the user's fingertip. This disadvantage especially affects usability in consumer electronics, such as touch tablet PCs and capacitive smartphones in cold weather.

    Surface capacitance

    In this basic technology, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel. As it has no moving parts, it is moderately durable but has limited resolution, is prone to false signals from parasitic capacitive coupling, and needs calibration during manufacture. It is therefore most often used in simple applications such as industrial controls and kiosks.

    Projected capacitance

    Back site of Multitouch Globe create on base of Projected Capacitive Touch (PCT) technology. For more information please look: multitouch

    Projected Capacitive Touch (PCT) technology is a capacitive technology which permits more accurate and flexible operation. An X-Y grid is formed either by etching a single conductive layer to form a grid pattern of

    electrodes, or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form the grid (comparable to the pixel grid found in many LCD displays) that the conducting layers can be coated with further protective insulating layers, and operate even under screen protectors, or behind weather- and vandal-proof glass. Due to the top layer of a PCT being glass, it is a more robust solution than resistive touch technology. Depending on the implementation, an active or passive stylus can be used instead of or in addition to a finger. This is common with point of sale devices that require signature capture. Gloved fingers may or may not be sensed, depending on the implementation and gain settings. Conductive smudges and similar interference on the panel surface can interfere with the performance. Such conductive smudges come mostly from sticky or sweaty finger tips, especially in high humidity environments. Collected dust, which adheres to the screen due to the moisture from fingertips can also be a problem. There are two types of PCT: Self Capacitance and Mutual Capacitance. A PCT screen consists of an insulator such as glass or foil, coated with a transparent conductor sensing (Copper, ATO, Nanocarbon or ITO). As the human finger (is also a conductor) touching the surface of the screen results in a distortion of the local electrostatic field, measurable as a change in capacitance.Now PCT used mutual capacitance, which is the more common projected capacitive approach and makes use of the fact that most conductive objects are able to hold a charge if they are very close together. If another conductive object, in this case a finger, bridges the gap, the charge field is interrupted and detected by the controller. All PCT touch screens are made up of an electrode - a matrix of rows and columns. The capacitance can be changed at every individual point on the grid (intersection). It can be measured to accurately determine the exactly touch location. All projected capacitive touch (PCT) solutions have three key features in common: • Sensor as matrix of rows and columns. • Sensor lies behind the touch surface. • Sensor does not use any moving parts.

    Mutual capacitance

    In mutual capacitive sensors, there is a capacitor at every intersection of each row and each column. A 16-by-14 array, for example, would have 224 independent capacitors. A voltage is applied to the rows or columns. Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field which reduces the mutual capacitance. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location by measuring the voltage in the other axis. Mutual capacitance allows multi-touch operation where multiple fingers, palms or styli can be accurately tracked at the same time.

    Self-capacitance

    Self-capacitance sensors can have the same X-Y grid as mutual capacitance sensors, but the columns and rows operate independently. With self-capacitance, the capacitive load of a finger is measured on each column or row electrode by a current meter. This method produces a stronger signal than mutual capacitance, but it is unable to resolve accurately more than one finger, which results in "ghosting", or misplaced location sensing. Infrared

    Infrared sensors mounted around the display watch for a user's touchscreen input on this PLATO V terminal in 1981. The monochromatic plasma display's characteristic orange glow is illustrated.

    An infrared touchscreen uses an array of X-Y infrared LED and photodetector pairs around the edges of the screen to detect a disruption in the pattern of LED beams. These LED beams cross each other in vertical and horizontal patterns. This helps the sensors pick up the exact location of the touch. A major benefit of such a system is that it can detect essentially any input including a finger, gloved finger, stylus or pen. It is generally used in outdoor applications and point of sale systems which can't rely on a conductor (such as a bare finger) to activate the touchscreen. Unlike capacitive touchscreens, infrared touchscreens do not require any patterning on the glass which increases durability and optical clarity of the overall system.

    Optical imaging

    This is a relatively modern development in touchscreen technology, in which two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared back lights are placed in the camera's field of view on the other side of the screen. A touch shows up as a shadow and each pair of cameras can then be pinpointed to locate the touch or even measure the size of the touching object (see visual hull). This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units. Dispersive signal technology

    Introduced in 2002 by 3M, this system uses sensors to detect the Piezoelectricity in the glass that occurs due to a touch. Complex algorithms then interpret this information and provide the actual location of the touch. The technology claims to be unaffected by dust and other outside elements, including scratches. Since there is no need for additional elements on screen, it also claims to provide excellent optical clarity. Also, since mechanical vibrations are used to detect a touch event, any object can be used to generate these events, including fingers and stylus. A downside is that after the initial touch the system cannot detect a motionless finger. Acoustic pulse recognition

    In this system, introduced by Tyco International's Elo division in 2006, the key to the invention is that a touch at each position on the glass generates a unique sound. Four tiny transducers attached to the edges of the touchscreen glass pick up the sound of the touch. The sound is then digitized by the controller and compared to a list of prerecorded sounds for every position on the glass. The cursor position is instantly updated to the touch

    location. APR is designed to ignore extraneous and ambient sounds, as they do not match a stored sound profile. APR differs from other attempts to recognize the position of touch with transducers or microphones, as it uses a simple table lookup method rather than requiring powerful and expensive signal processing hardware to attempt to calculate the touch location without any references. The touchscreen itself is made of ordinary glass, giving it good durability and optical clarity. It is usually able to function with scratches and dust on the screen with good accuracy. The technology is also well suited to displays that are physically larger. As with the Dispersive Signal Technology system, after the initial touch, a motionless finger cannot be detected. However, for the same reason, the touch recognition is not disrupted by any resting objects.

    Construction

    There are several principal ways to build a touchscreen. The key goals are to recognize one or more fingers touching a display, to interpret the command that this represents, and to communicate the command to the appropriate application.

    In the most popular techniques, the capacitive or resistive approach, there are typically four layers:

    1. Top polyester coated with a transparent metallic conductive coating on the bottom

    2. Adhesive spacer

    3. Glass layer coated with a transparent metallic conductive coating on the top

    4. Adhesive layer on the backside of the glass for mounting.

    When a user touches the surface, the system records the change in the electrical current that flows through the display.

    Dispersive-signal technology which 3M created in 2002, measures the piezoelectric effect the voltage

    generated when mechanical force is applied to a material that occurs chemically when a strengthened glass

    substrate is touched.

    There are two infrared-based approaches. In one, an array of sensors detects a finger touching or almost touching the display, thereby interrupting light beams projected over the screen. In the other, bottom-mounted infrared cameras record screen touches.

    In each case, the system determines the intended command based on the controls showing on the screen at the time and the location of the touch.

    Development

    Most touchscreen patents were filed during the 1970s and 1980s and have expired. Touchscreen component manufacturing and product design are no longer encumbered by royalties or legalities with regard to patents and the use of touchscreen-enabled displays is widespread.

    The development of multipoint touchscreens facilitated the tracking of more than one finger on the screen; thus, operations that require more than one finger are possible. These devices also allow multiple users to interact with the touchscreen simultaneously.

    With the growing use of touchscreens, the marginal cost of touchscreen technology is routinely absorbed into the products that incorporate it and is nearly eliminated. Touchscreens now have proven reliability. Thus, touchscreen displays are found today in airplanes, automobiles, gaming consoles, machine control systems, appliances, and handheld display devices including the Nintendo DS and the later multi-touch enabled iPhones; the touchscreen market for mobile devices is projected to produce US$5 billion in 2009.

     The ability to accurately point on the screen itself is also advancing with the emerging graphics tablet/screen hybrids.

    October 2011: TapSense can distinguish between different parts of the hand, such as fingertip and fingernail, so it can be functioned as lower case and capital letter instruction.

    Ergonomics and usage

    Fingernail as stylus

    Pointed nail for easier typing. The concept of using a fingernail trimmed to form a point, to be specifically used as a stylus on a writing tablet for communication, appeared in the 1950 science fiction short story Scanners Live in Vain.

    These ergonomic issues of direct touch can be bypassed by using a different technique, provided that the user's fingernails are either short or sufficiently long. Rather than pressing with the soft skin of an outstretched fingertip, the finger is curled over, so that the tip of a fingernail can be used instead. This method does not work on capacitive touchscreens.

    The fingernail's hard, curved surface contacts the touchscreen at one very small point. Therefore, much less finger pressure is needed, much greater precision is possible (approaching that of a stylus, with a little experience), much less skin oil is smeared onto the screen, and the fingernail can be silently moved across the screen with very little resistance, allowing for selecting text, moving windows, or drawing lines. The human fingernail consists of keratin which has a hardness and smoothness similar to the tip of a stylus (and so will not typically scratch a touchscreen). Alternatively, very short stylus tips are available, which slip right onto the end of a finger; this increases visibility of the contact point with the screen.

    Fingerprints

    Touchscreens can suffer from the problem of fingerprints on the display. This can be mitigated by the use of materials with optical coatings designed to reduce the visible effects of fingerprint oils, or oleophobic coatings as used in the iPhone 3G S, which lessen the actual amount of oil residue, or by installing a matte-finish anti-glare screen protector, which creates a slightly roughened surface that does not easily retain smudges, or by reducing skin contact by using a fingernail or stylus.

    Combined with haptics

    Touchscreens are often used with haptic response systems. An example of this technology would be a system that caused the device to vibrate when a button on the touchscreen was tapped. The user experience with touchscreens lacking tactile feedback or haptics can be difficult due to latency or other factors. Research from

    the University of Glasgow Scotland [Brewster, Chohan, and Brown 2007 and more recently Hogan] demonstrates that sample users reduce input errors (20%), increase input speed (20%), and lower their cognitive load (40%) when touchscreens are combined with haptics or tactile feedback [vs. non-haptic touchscreens]. Gorilla arm

    The Jargon File dictionary of hacker slang defined "gorilla arm" as the failure to understand the ergonomics of

    vertically mounted touchscreens for prolonged use. The proposition is that the human arm held in an unsupported horizontal position rapidly becomes fatigued and painful, the so-called "gorilla arm". It is often cited as a prima facie example of what not to do in ergonomics. Vertical touchscreens still dominate in applications such as ATMs and data kiosks in which the usage is too brief to be an ergonomic problem.

     Discomfort might be caused by previous poor posture and atrophied muscular systems caused by limited physical exercise. Fine art painters are also often subject to neck and shoulder pains due to their posture and the repetitiveness of their movements while painting.

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