A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus.
The touchscreen has two main attributes. First, it enables one to interact directly with what is displayed, rather than indirectly with a cursor controlled by a mouse or touchpad. Secondly, it lets one do so without requiring any intermediate device that would need to be held in the hand. Such displays can be attached to computers, or to networks as terminals. They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDA), satellite navigation devices, mobile phones, and video games.
History
(right), also developed by Stumpe at CERN in 1972.]]
In 1971, the first "Touch Sensor" was developed by Doctor Sam Hurst (founder of Elographics) while he was an instructor at the University of Kentucky. This sensor, called the "Elograph," was patented by The University of Kentucky Research Foundation. The "Elograph" was not transparent like modern touch screens; however, it was a significant milestone in touch screen technology. In 1974, the first true touch screen incorporating a transparent surface was developed by Sam Hurst and Elographics. In 1977, Elographics developed and patented five-wire resistive technology, the most popular touch screen technology in use today.
Touchscreens first gained some visibility with the invention of the computer-assisted learning terminal, which came out in 1975 as part of the
PLATO project. Touchscreens have subsequently become familiar in everyday life. Companies use touch screens for kiosk systems in retail and tourist settings,
point of sale systems,
ATMs, and 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 acceptance of, touchscreens.
From 1979–1985, the Fairlight CMI (and Fairlight CMI IIx) was a high-end musical sampling and re-synthesis workstation that utilized light pen technology, with which the user could allocate and manipulate sample and synthesis data, as well as access different menus within its OS by touching the screen with the light pen. The later Fairlight series III models used a graphics tablet in place of the light pen.
The HP-150 from 1983 was one of the world's earliest commercial touchscreen computer. It did not have a touchscreen in the strict sense; instead, it had a 9" Sony Cathode Ray Tube (CRT) surrounded by infrared transmitters and receivers, which detected the position of any non-transparent object on the screen.
Until recently, most consumer touchscreens 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 commercialization of multi-touch technology.
Touchscreens are popular in hospitality, and in heavy industry, as well as kiosks such as museum displays or room automation, where keyboard and mouse systems do not allow a suitably 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. Display manufacturers and chip 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 variety of touchscreen technologies.
Resistive
A resistive touchscreen panel is composed of several layers, the most important of which are two thin, electrically conductive layers separated by a narrow gap. When an object, such as a finger, presses down on a point on the panel's outer surface the two metallic layers become connected at that point: the panel then behaves as a pair of 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.
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 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 touchscreen panel is one which consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide (ITO). As the human body is also a 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.
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
Projected Capacitive Touch (PCT) technology is a capacitive technology which permits more accurate and flexible operation, by
etching the conductive layer. An
X-Y grid is formed either by etching a single 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).
The greater resolution of PCT allows operation without direct contact, such 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, PCT is a more robust solution versus 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.
Mutual Capacitance
In mutual capacitive sensors, there is a
capacitor at every intersection of each row and each column. A 12-by-16 array, for example, would have 192 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 stylus 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
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 triangulated 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
mechanical energy 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
This system, introduced by
Tyco International's Elo division in 2006, uses
piezoelectric transducers located at various positions around the screen to turn the mechanical energy of a touch (vibration) into an electronic signal. The screen hardware then uses an algorithm to determine the location of the touch based on the transducer signals. 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;
# Top polyester layer coated with a transparent metallic conductive coating on the bottom
# Adhesive spacer
# Glass layer coated with a transparent metallic conductive coating on the top
# 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 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 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 multi-touch enabled iPhone; 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.
Ergonomics and usage
Finger stress
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 for certain types of touchscreen. This can be alleviated for some users with the use of a pen or other device to add leverage and more accurate pointing. The introduction of such items can sometimes be problematic, depending on the desired use (e.g., public kiosks such as A.T.M.s). Also, fine motor control is better achieved with a stylus, because a finger is a rather broad and ambiguous point of contact with the screen itself.
Fingernail as 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. The thumb is optionally used to provide support for the finger or for a long fingernail, from underneath. This method does not work on capacitive touch screens.
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). 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.
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, such as the
oleophobic coating used in the
iPhone 3G S, or by reducing skin contact by using a fingernail or stylus.
Combined with haptics
The user experience with touchscreens without 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] 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 touch screens for prolonged use. The proposition is that 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.
Comparison of touchscreen technologies
The following information is supplied by Mass Multimedia Inc., a Colorado-based company selling touch screen technology.
{| class="wikitable"
|-
! Technology
! 4-Wire Resistive
! Surface Acoustic Wave
! 5-Wire Resistive
! Infrared
! Capacitive
|-
! Durability
| 3 year
| 5 Year
| 5 Year
| 5 Year
| 2 Year
|-
! Stability
| High
| Higher
| High
| High
| Ok
|-
! Transparency
| Bad
| Good
| Bad
| Good
| Ok
|-
! Installation
| Built-in/Onwall
| Built-in/Onwall
| Built-in/Onwall
| Onwall
| Built-in
|-
! Touch
| Anything
| Finger/Pen
| Anything
| Finger/Pen
| Conductive
|-
! Intense light-resistant
| Good
| Good
| Good
| Bad
| Bad
|-
! Response time
| <10ms
| 10ms
| <15ms
| <20ms
| <15ms
|-
! Following Speed
| Good
| Low
| Good
| Good
| Good
|-
! Excursion
| No
| Small
| Big
| Big
| Big
|-
! Monitor option
| CRT or LCD
| CRT or LCD
| CRT or LCD
| CRT or LCD
| CRT or LCD or LED
|-
! Waterproof
| Good
| Ok
| Good
| Ok
| Good
|}
Screen protectors
Some touchscreens, primarily those employed in
smart phones, use transparent plastic protectors to prevent any scratches that might be caused by day to day use from becoming permanent.
See also
Energy harvesting
Flexible keyboard
Gestural interface
Graphics tablet
Graphics tablet-screen hybrid
Tablet PC
Touchpad
Touchscreen remote control
Touch switch
Dual-touchscreen
Notes
References
External links
Howstuffworks - How do touchscreen monitors know where you're touching?
MERL - Mitsubishi Electric Research Lab (MERL)'s research on interaction with touch tables.
Jefferson Y. Han et al. Multi-Touch Interaction Research. Multi-Input Touchscreen using Frustrated Total Internal Reflection.
Dot-to-Dot Programming : Building Microcontrollers
EDN 11/9/95 - A great, but old, article that gets into some nice specifics.
Tablet PC
Category:Computer hardware
