23-06-2010, 01:27 PM
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Touch Screen Technology
Introduction
A touch screen is a display which can detect the presence and location of a touch within the display area. The term generally refers to touch or contact to the display of the device by a finger or hand. Touch screens can also sense other passive objects, such as a stylus. However, if the object sensed is active, as with a light pen, the term touch screen is generally not applicable. The thumb rule is: if you can interact with the display using your finger, it is likely a touch screen - even if you are using a stylus or some other object.
Up until recently, most touch screens could only sense one point of contact at a time, and few have had the capability to sense how hard one is touching. This is starting to change with the emergence of multi-touch technology - a technology that was first seen in the early 1980s, but which is now appearing in commercially available systems.
The touch screen has two main attributes. First, it enables you to interact with what is displayed directly on the screen, where it is displayed, rather than indirectly with a mouse (computing) or touchpad. Secondly, it lets one do so without requiring any intermediate device, again, such as a stylus that needs to be held in the hand. Such displays can be attached to computers or, as terminals, to networks. They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDA), satellite navigation devices and mobile phone.
Applications
Touch screens emerged from academic and corporate research labs in the second half of the 1960s. One of the first places where they gained some visibility was in the terminal of a computer-assisted learning terminal that came out in 1972 as part of the PLATO project. They have subsequently become familiar in kiosk systems, such as in retail and tourist settings, on point of sale systems, on ATMs and on PDAs where a stylus is sometimes used to manipulate the GUI and to enter data. The popularity of smart phones, PDAs, portable game consoles and many types of information appliances is driving the demand for, and the acceptance of, touch screens.
The HP-150 from 1983 was probably the world's earliest commercial touch screen computer. It actually does not have a touch screen in the strict sense, but a 9" Sony CRT surrounded by infrared transmitters and receivers which detect the position of any non-transparent object on the screen.
Touch screens are popular in heavy industry and in other situations, such as museum displays or room automation, where keyboards and mouse do not allow a satisfactory, intuitive, rapid, or accurate interaction by the user with the display's content.
Historically, the touch screen sensor and its accompanying controller-based firmware have been made available by a wide array of after-market system and not by display, chip or motherboard manufacturers. With time, however, display manufacturers and System On Chip (SOC) manufacturers worldwide have acknowledged the trend toward acceptance of touch screens as a highly desirable user interface component and have begun to integrate touch screen functionality into the fundamental design of their products.
Technologies
There are a number of types of touch screen technology:-
Resistive
A resistive touch screen panel is composed of several layers. The most important are two thin metallic electrically conductive and resistive layers separated by thin space. When some object touches this kind of touch panel, the layers are connected at certain point; the panel then electrically acts similar to two voltage dividers with connected outputs. This causes a change in the electrical current which is registered as a touch event and sent to the controller for processing. When measuring press force, it is useful to add resistor dependent on force in this model -- between the dividers.
A resistive touch panel output can consist of between four and eight wires. The positions of the conductive contacts in resistive layers differ depending on how many wires are used. When four wires are used, the contacts are placed on the left, right, top, and bottom sides. When five wires are used, the contacts are placed in the corners and on one plate.
4 wire resistive panels can estimate the area (and hence the pressure) of a touch based on calculations from the resistances.
Resistive touch screen panels are generally more affordable but offer only 75% clarity [citation needed] (premium films and glass finishes allow transitivity to approach 85% [citation needed]) and the layer can be damaged by sharp objects. Resistive touch screen panels are not affected by outside elements such as dust or water and are the type most commonly used today. The Nintendo DS is an example of a product that uses resistive touch screen technology.
Surface acoustic wave
Surface acoustic wave (SAW) technology uses ultrasonic waves that pass over the touch screen 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 touch screen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touch screen.
Capacitive
A capacitive touch screen panel is coated with a material, typically indium tin oxide that conducts a continuous electrical current across the sensor. The sensor therefore exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes - it achieves capacitance. The human body is also an electrical device which has stored electrons and therefore also exhibits capacitance.
When the sensor's 'normal' capacitance field (its reference state) is altered by another capacitance field, i.e., someone's finger, electronic circuits located at each corner of the panel measure the resultant 'distortion' in the sine wave characteristics of the reference field and sends the information about the event to the controller for mathematical processing. Capacitive sensors can either be touched with a bare finger or with a conductive device being held by a bare hand. Capacitive touch screens are not affected by outside elements and have high clarity. The Apple iPhone is an example of a product that uses capacitance touch screen technology: the iPhone is further capable of multi-touch sensing.
Capacitive sensors work based on proximity, and do not have to be directly touched to be triggered. In most cases, direct contact to a conductive metal surface does not occur and the conductive sensor is separated from the user's body by an insulating glass or plastic layer. Devices with capacitive buttons intended to be touched by a finger can often be triggered by quickly waving the palm of the hand close to the surface without touching.
Infrared
An infrared (IR) touch screen panel employs one of two very different methods. One method uses thermal induced changes of the surface resistance. This method is sometimes slow and requires warm hands. Another method is an array of vertical and horizontal IR sensors that detect the interruption of a modulated light beam near the surface of the screen. IR touch screens have the most durable surfaces and are used in many military applications that require a touch panel display.
Optical imaging
A relatively-modern development in touch screen technology, two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared backlights are placed in the camera's field of view on the other sides of the screen. A touch shows up as a shadow and each pair of cameras can then be triangulated to locate the touch. This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.
Dispersive signal technology
Introduced in 2002, this system uses sensors to detect the mechanical energy in the glass that occur 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
This system uses more than two piezoelectric transducers located at some positions of the screen to turn the mechanical energy of a touch (vibration) into an electronic signal. This signal is then converted into an audio file, and then compared to preexisting audio profile for every position on the screen. This system works without a grid of wires running through the screen; the touch screen itself is actually pure glass, giving it the optics and durability of the glass out of which it is made. It works with scratches and dust on the screen, and accuracy is very good. It does not need a conductive object to activate it. It is a major advantage for larger displays. As with the Dispersive Signal Technology system, after the initial touch this system cannot detect a motionless finger.
Frustrated total internal reflection
This optical system works by using the principle of total internal reflection to fill a refractive medium with light. When a finger or other soft object is pressed against the surface, the internal reflection light path is interrupted, making the light reflect outside of the medium and thus visible to a camera behind the medium.
Touch Screen Technology Comparison Chart
Resistive Infrared Surface Acoustic Wave Capacitive
Touch resolution High High Average High
Clarity Average Good Good Good
Operation Finger or stylus Finger or stylus Finger or soft-tipped stylus Finger only
Durability Can be damaged by sharp objects Highly durable Susceptible to dirt and moisture Highly durable
Development
Virtually all of the significant touch screen technology patents were filed during the 1970s and 1980s and have expired. Touch screen component manufacturing and product design are no longer encumbered by royalties or legalities with regard to patents and the manufacturing of touch screen-enabled displays on all kinds of devices is widespread.
The development of multipoint touch screens 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 touch screen simultaneously.
With the growing acceptance of many kinds of products with an integral touch screen interface the marginal cost of touch screen technology is routinely absorbed into the products that incorporate it and is effectively eliminated. As typically occurs with any technology, touch screen hardware and software has sufficiently matured and been perfected over more than three decades to the point where its reliability is unassailable. As such, touch screen displays are found today in airplanes, automobiles, gaming consoles, machine control systems, appliances and handheld display devices of every kind. With the influence of the multitouch-enabled iPhone, the touch screen market for mobile devices is projected to produce US$5 billion in 2009.
The ability to accurately point on the screen itself is taking yet another step with the emerging graphics tablet/screen hybrids.
Ergonomics and usage
Finger stress
An ergonomic problem of touch screens is their stress on human fingers when used for more than a few minutes at a time, since significant pressure can be required and the screen is non-flexible. This can be alleviated with the use of a pen or other device to add leverage, but the introduction of such items can sometimes be problematic depending on the desired use case (for example, public kiosks such as ATMs). Also, fine motor control is better achieved with a stylus, a finger being a rather broad and ambiguous point of contact with the screen.
Fingernail as stylus
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 top of the forward edge of a fingernail can be used instead. (The thumb is optionally used to provide support for the finger or for a long fingernail, from underneath.)
The fingernail's hard, curved surface contacts the touch screen at a single 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 touch screen). Alternately, 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. Oddly, with capacitive touch screens, the reverse problem applies in that individuals with long nails have reported problems getting adequate skin contact with the screen to register keystrokes (note that ordinary styli do not work on capacitive touch screens nor do gloved fingers).
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.
Fingerprints
Touch screens also 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.
Touch Screen Technology
Introduction
A touch screen is a display which can detect the presence and location of a touch within the display area. The term generally refers to touch or contact to the display of the device by a finger or hand. Touch screens can also sense other passive objects, such as a stylus. However, if the object sensed is active, as with a light pen, the term touch screen is generally not applicable. The thumb rule is: if you can interact with the display using your finger, it is likely a touch screen - even if you are using a stylus or some other object.
Up until recently, most touch screens could only sense one point of contact at a time, and few have had the capability to sense how hard one is touching. This is starting to change with the emergence of multi-touch technology - a technology that was first seen in the early 1980s, but which is now appearing in commercially available systems.
The touch screen has two main attributes. First, it enables you to interact with what is displayed directly on the screen, where it is displayed, rather than indirectly with a mouse (computing) or touchpad. Secondly, it lets one do so without requiring any intermediate device, again, such as a stylus that needs to be held in the hand. Such displays can be attached to computers or, as terminals, to networks. They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDA), satellite navigation devices and mobile phone.
Applications
Touch screens emerged from academic and corporate research labs in the second half of the 1960s. One of the first places where they gained some visibility was in the terminal of a computer-assisted learning terminal that came out in 1972 as part of the PLATO project. They have subsequently become familiar in kiosk systems, such as in retail and tourist settings, on point of sale systems, on ATMs and on PDAs where a stylus is sometimes used to manipulate the GUI and to enter data. The popularity of smart phones, PDAs, portable game consoles and many types of information appliances is driving the demand for, and the acceptance of, touch screens.
The HP-150 from 1983 was probably the world's earliest commercial touch screen computer. It actually does not have a touch screen in the strict sense, but a 9" Sony CRT surrounded by infrared transmitters and receivers which detect the position of any non-transparent object on the screen.
Touch screens are popular in heavy industry and in other situations, such as museum displays or room automation, where keyboards and mouse do not allow a satisfactory, intuitive, rapid, or accurate interaction by the user with the display's content.
Historically, the touch screen sensor and its accompanying controller-based firmware have been made available by a wide array of after-market system and not by display, chip or motherboard manufacturers. With time, however, display manufacturers and System On Chip (SOC) manufacturers worldwide have acknowledged the trend toward acceptance of touch screens as a highly desirable user interface component and have begun to integrate touch screen functionality into the fundamental design of their products.
Technologies
There are a number of types of touch screen technology:-
Resistive
A resistive touch screen panel is composed of several layers. The most important are two thin metallic electrically conductive and resistive layers separated by thin space. When some object touches this kind of touch panel, the layers are connected at certain point; the panel then electrically acts similar to two voltage dividers with connected outputs. This causes a change in the electrical current which is registered as a touch event and sent to the controller for processing. When measuring press force, it is useful to add resistor dependent on force in this model -- between the dividers.
A resistive touch panel output can consist of between four and eight wires. The positions of the conductive contacts in resistive layers differ depending on how many wires are used. When four wires are used, the contacts are placed on the left, right, top, and bottom sides. When five wires are used, the contacts are placed in the corners and on one plate.
4 wire resistive panels can estimate the area (and hence the pressure) of a touch based on calculations from the resistances.
Resistive touch screen panels are generally more affordable but offer only 75% clarity [citation needed] (premium films and glass finishes allow transitivity to approach 85% [citation needed]) and the layer can be damaged by sharp objects. Resistive touch screen panels are not affected by outside elements such as dust or water and are the type most commonly used today. The Nintendo DS is an example of a product that uses resistive touch screen technology.
Surface acoustic wave
Surface acoustic wave (SAW) technology uses ultrasonic waves that pass over the touch screen 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 touch screen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touch screen.
Capacitive
A capacitive touch screen panel is coated with a material, typically indium tin oxide that conducts a continuous electrical current across the sensor. The sensor therefore exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes - it achieves capacitance. The human body is also an electrical device which has stored electrons and therefore also exhibits capacitance.
When the sensor's 'normal' capacitance field (its reference state) is altered by another capacitance field, i.e., someone's finger, electronic circuits located at each corner of the panel measure the resultant 'distortion' in the sine wave characteristics of the reference field and sends the information about the event to the controller for mathematical processing. Capacitive sensors can either be touched with a bare finger or with a conductive device being held by a bare hand. Capacitive touch screens are not affected by outside elements and have high clarity. The Apple iPhone is an example of a product that uses capacitance touch screen technology: the iPhone is further capable of multi-touch sensing.
Capacitive sensors work based on proximity, and do not have to be directly touched to be triggered. In most cases, direct contact to a conductive metal surface does not occur and the conductive sensor is separated from the user's body by an insulating glass or plastic layer. Devices with capacitive buttons intended to be touched by a finger can often be triggered by quickly waving the palm of the hand close to the surface without touching.
Infrared
An infrared (IR) touch screen panel employs one of two very different methods. One method uses thermal induced changes of the surface resistance. This method is sometimes slow and requires warm hands. Another method is an array of vertical and horizontal IR sensors that detect the interruption of a modulated light beam near the surface of the screen. IR touch screens have the most durable surfaces and are used in many military applications that require a touch panel display.
Optical imaging
A relatively-modern development in touch screen technology, two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared backlights are placed in the camera's field of view on the other sides of the screen. A touch shows up as a shadow and each pair of cameras can then be triangulated to locate the touch. This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.
Dispersive signal technology
Introduced in 2002, this system uses sensors to detect the mechanical energy in the glass that occur 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
This system uses more than two piezoelectric transducers located at some positions of the screen to turn the mechanical energy of a touch (vibration) into an electronic signal. This signal is then converted into an audio file, and then compared to preexisting audio profile for every position on the screen. This system works without a grid of wires running through the screen; the touch screen itself is actually pure glass, giving it the optics and durability of the glass out of which it is made. It works with scratches and dust on the screen, and accuracy is very good. It does not need a conductive object to activate it. It is a major advantage for larger displays. As with the Dispersive Signal Technology system, after the initial touch this system cannot detect a motionless finger.
Frustrated total internal reflection
This optical system works by using the principle of total internal reflection to fill a refractive medium with light. When a finger or other soft object is pressed against the surface, the internal reflection light path is interrupted, making the light reflect outside of the medium and thus visible to a camera behind the medium.
Touch Screen Technology Comparison Chart
Resistive Infrared Surface Acoustic Wave Capacitive
Touch resolution High High Average High
Clarity Average Good Good Good
Operation Finger or stylus Finger or stylus Finger or soft-tipped stylus Finger only
Durability Can be damaged by sharp objects Highly durable Susceptible to dirt and moisture Highly durable
Development
Virtually all of the significant touch screen technology patents were filed during the 1970s and 1980s and have expired. Touch screen component manufacturing and product design are no longer encumbered by royalties or legalities with regard to patents and the manufacturing of touch screen-enabled displays on all kinds of devices is widespread.
The development of multipoint touch screens 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 touch screen simultaneously.
With the growing acceptance of many kinds of products with an integral touch screen interface the marginal cost of touch screen technology is routinely absorbed into the products that incorporate it and is effectively eliminated. As typically occurs with any technology, touch screen hardware and software has sufficiently matured and been perfected over more than three decades to the point where its reliability is unassailable. As such, touch screen displays are found today in airplanes, automobiles, gaming consoles, machine control systems, appliances and handheld display devices of every kind. With the influence of the multitouch-enabled iPhone, the touch screen market for mobile devices is projected to produce US$5 billion in 2009.
The ability to accurately point on the screen itself is taking yet another step with the emerging graphics tablet/screen hybrids.
Ergonomics and usage
Finger stress
An ergonomic problem of touch screens is their stress on human fingers when used for more than a few minutes at a time, since significant pressure can be required and the screen is non-flexible. This can be alleviated with the use of a pen or other device to add leverage, but the introduction of such items can sometimes be problematic depending on the desired use case (for example, public kiosks such as ATMs). Also, fine motor control is better achieved with a stylus, a finger being a rather broad and ambiguous point of contact with the screen.
Fingernail as stylus
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 top of the forward edge of a fingernail can be used instead. (The thumb is optionally used to provide support for the finger or for a long fingernail, from underneath.)
The fingernail's hard, curved surface contacts the touch screen at a single 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 touch screen). Alternately, 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. Oddly, with capacitive touch screens, the reverse problem applies in that individuals with long nails have reported problems getting adequate skin contact with the screen to register keystrokes (note that ordinary styli do not work on capacitive touch screens nor do gloved fingers).
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.
Fingerprints
Touch screens also 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.
