Touch Screens

Touch screens are devices that allow a user to provide input to a computer or electronic system by making physical contact or near-contact with the system's display. Most often seen in Automated Teller Machines (ATMs), information kiosks, and other public computers, touch screens are also widely used in computer graphics and animation. They also play a role in assistive technology for users with special needs.

Applications

Public computer systems are often designed around a touch screen, which is often the only visible component. Automated Teller Machines (ATMs) are the most common application, but falling prices for touch screen technology are making it available for other applications such as museum exhibits, ticket sales in airports and movie theaters, and public information kiosks. Touch screens are ideal for these applications because they provide input and output capabilities. They are often the only part of the system contacted by the user and are sturdier than many other input devices because they have no moving parts. These qualities make touch screen-based systems easy and inexpensive to maintain and repair.

Touch screens are used, like mice, as pointing devices. Instead of moving a mouse to activate and relocate the cursor, the user touches the screen to position the cursor. For specifying precise location, a touch screen often works with a stylus—a device like a pencil that has a rubber or plastic point. The user modifies what is seen on the screen by touching it, rather than by manipulating a cursor or other on-screen component with a mouse, keyboard, or joystick. Touch screens are invaluable to artists who have been trained to use pencils, brushes, and other implements that effect change wherever they touch the canvas.

Touch screens have revolutionized personal digital assistants (PDAs) . Older PDAs required the user to enter data using an extremely small keyboard. Modern PDAs consist almost entirely of a touch screen, which makes them substantially smaller and easier to use because the user can "write" information directly into the device.

In the late twentieth century, companies began to integrate touch screen technology with dry-erase boards (wall-mounted surfaces that allow the user to write with markers and erase the markings with a cloth). With these devices, whatever a user writes on the board can be simultaneously recorded and saved in a computer file.

Development

The touch screen was derived from the digitizing tablet, which is still in use as a computer peripheral . The digitizing tablet, developed by Dr. G. Sam Hurst in 1971 at the University of Kentucky, was designed to allow scientists to record data from graphs by placing the graph on the tablet and pressing the paper against the tablet with a stylus. In 1977 Elographics (now EloTouch Systems), the first commercial producer of digitizing tablets, paired with Siemens Corporation to develop a transparent version of the tablet on curved glass so that it could fit over a CRT (cathode ray tube) screen, which was then the predominant display technology. The first touch screens were built by hand, but advances soon allowed all of the layers to be produced by machine.

Touch Screen Technologies

Touch screens consist of a display component, typically a liquid crystal display (LCD) or CRT covered or surrounded with a transparent sensor device that allows the screen to detect the contact or proximity of an object. There is a wide variety of sensor devices. Some devices are not entirely transparent or create glare that makes the screen behind the device hard to see. The amount of pressure or types of contact needed to detect a touch varies from device to device. Devices also vary widely in accuracy (determining exactly where the touch occurred), durability (reliability with repeated use or in inclement circumstances), expected lifetime (time before failure of the device or parts of it), and response time (how long it takes the screen to detect a touch).

A 4-wire resistive (pressure sensitive) screen is made of two thin sheets separated by a grid of plastic dots. Each sheet, though clear, conducts electricity. When the user touches the screen, the sheets contact each other only at the spot where the user touched it. The screen measures the amount of electricity flowing between the two sheets to determine where the user touched. The term "4-wire" comes from the four wires used to provide and measure the currents on the screen. These are the cheapest and most common touch screens. A 5-wire screen increases durability by adding a sheet so that the surface touched by the user is not one carrying the currents. An 8-wire screen is the same as 4-wire screens except that it uses an extra set of wires to measure the currents and has increased durability.

Capacitive screens use a single thin sheet. The screen is connected to electric oscillators . A signal of a specific frequency is broadcast through the sheet creating an oscillating electric field around it. When the user comes near the screen with a conductive object, such as a finger, the electric field is changed, which changes the signal in the sheet. The screen can determine the location of the conductive object by measuring the signal in the sheet. Although these screens are much clearer and transparent than those covered with resistive sheets, they lose accuracy over time and do not detect the presence of non-conductive objects, such as gloved fingers.

Wave interruption screens send a wave of some kind over the surface of the screen. When the user puts a finger into the wave, the screen can detect where the interference occurred. An infrared screen has a row of infrared lights along two adjacent sides. The opposite sides have infrared detectors. When the light wave is interrupted by a finger, the screen can determine where the interruption is by measuring which detectors went into the shadows. With surface acoustic wave (SAW) screens, an inaudible sound wave is "played" over the surface of the screen. A finger near the screen will absorb some of the sound wave, even if it is gloved, and the screen can determine the location by the change in frequency and strength of the sound wave. With near-field imaging, an object changes the frequency and strength of an electric (radio) wave. As with capacitive screens, the object interfering with the wave must be capacitive. Unlike with capacitive screens, the object can be covered with thin non-conductive covering, like a glove.

For applications that require more accuracy in terms of screen sensitivity, there are touch screens that respond to a stylus. The stylus triggers the sensors in the same manner as a finger does, but allows the user to specify a more precise location for software action.

see also Animation; Information Retrieval; Personal Digital Assistants.

Salvatore Domenick Desiano