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Touchscreens are display overlays which have the ability to display and
receive information on the same screen. The effect of such overlays allows a
display to be used as an input device, removing the keyboard and/or the mouse as
the primary input device for interacting with the display's content. Such
displays can be attached to computers or, as terminals, to networks.
Touchscreens also have assisted in recent changes in the design of personal
digital assistant (PDA), satellite navigation and mobile phone devices, making
these devices more usable.
Applications
Enlarge picture
Some games for the Nintendo DS use the touchscreen as a primary controlling
device, but other games use it as a secondary controlling device
Touchscreens have become commonplace since the invention of the electronic touch
interface in 1971 by Dr. Samuel C. Hurst. They have become familiar in retail
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, touchscreens.
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.
Touchscreens 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 touchscreen sensor and its accompanying controller-based
firmware have been made available by a wide array of after-market system
integrators 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 touchscreens as a highly
desirable user interface component and have begun to integrate touchscreen
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 (premium films and glass finishes allow transmissivity to approach 85%)
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.
Surface Acoustic Wave (SAW): Surface Acoustic Wave 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
touchscreen.
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 send 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, but their complex signal
processing electronics increase their cost.
Infrared
An infrared touch screen panel employs one of two very different methodologies.
One method used thermal induced changes of the surface resistance. This method
was sometimes slow and required warm hands. Another method is an array of
vertical and horizontal IR sensors that detected 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.
Strain Gauge
In a strain gauge configuration the screen is spring mounted on the four corners
and strain gauges are used to determine deflection when the screen is touched.
This technology can also measure the Z-axis. Typically used in exposed public
systems such as ticket machines due to their resistance to vandalism.
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 afford ability, 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 styli.
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.
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.[1]
Graphics tablet/screen hybrid technique: This new technique is definitionally
not really a touchscreen, but has the same properties, in addition to having
much more accuracy. It is a graphics tablet that incorporates an LCD into the
tablet itself, allowing the user to draw directly "on" the display surface. It
should not be mixed up with tablet pc hybrids.
Development
Virtually all of the significant touchscreen technology 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 manufacturing of touchscreen-enabled displays on all
kinds of devices is widespread.
The development of multipoint touchscreens facilitated the tracking of more than
one finger on the screen. Operations that are only possible with more than one
finger are possible. These devices also allow multiple users to interact with
the touchscreen simultaneously.
With the growing acceptance of many kinds of products with an integral
touchscreen interface the marginal cost of touchscreen technology is routinely
absorbed into the products that incorporate it and is effectively eliminated. As
typically occurs with any technology, touchscreen hardware and software has
sufficiently matured and been perfected over more than three decades to the
point where its reliability is unassailable. As such, touchscreen displays are
found today in airplanes, automobiles, gaming consoles, machine control systems,
appliances and handheld display devices of every kind.
The ability to accurately point on the screen itself is taking yet another step
with the emerging graphics tablet/screen hybrids.
Ergonomics and usage
An ergonomic problem of touchscreens 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.
Yet all of these ergonomic issues can be bypassed simply 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 touchscreen 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
touchscreen.) 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.
When a touchscreen monitor is mounted vertically a condition often called
"gorilla arm" can occur, because holding ones arm out horizontally for a
prolonged time causes the arm to feel quite heavy (like a gorilla's).
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