Touchscreen
A touchscreen (or touch screen) is a type of display that can detect touch input from a user. It consists of both an input device (a touch panel) and an output device (a visual display). The touch panel is typically layered on the top of the electronic visual display of a device. Touchscreens are commonly found in smartphones, tablets, laptops, and other electronic devices.
The display is often an LCD, AMOLED or OLED display.
A user can give input or control the information processing system through simple or multi-touch gestures by touching the screen with a special stylus or one or more fingers.[1] Some touchscreens use ordinary or specially coated gloves to work, while others may only work using a special stylus or pen. The user can use the touchscreen to react to what is displayed and, if the software allows, to control how it is displayed; for example, zooming to increase the text size.
A touchscreen enables the user to interact directly with what is displayed, instead of using a mouse, touchpad, or other such devices (other than a stylus, which is optional for most modern touchscreens).[2]
Touchscreens are common in devices such as smartphones, handheld game consoles, and personal computers. They are common in point-of-sale (POS) systems, automated teller machines (ATMs), and electronic voting machines. They can also be attached to computers or, as terminals, to networks. They play a prominent role in the design of digital appliances such as personal digital assistants (PDAs) and some e-readers. Touchscreens are important in educational settings such as classrooms or on college campuses.[3]
The popularity of smartphones, tablets, and many types of information appliances has driven the demand and acceptance of common touchscreens for portable and functional electronics. Touchscreens are found in the medical field, heavy industry, automated teller machines (ATMs), and 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 have acknowledged the trend toward acceptance of touchscreens as a user interface component and have begun to integrate touchscreens into the fundamental design of their products.
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.
Multi-touch projected capacitance screens
A very simple, low cost way to make a multi-touch projected capacitance touchscreen, is to sandwich an x/y or diagonal matrix of fine, insulation coated copper or tungsten wires between two layers of clear polyester film. This creates an array of proximity sensing micro-capacitors. One of these micro-capacitors every 10 to 15 mm is probably sufficient spacing if fingers are relatively widely spaced apart, but very high discrimination multi-touch may need a micro-capacitor every 5 or 6 mm. A similar system can be used for ultra-high resolution sensing, such as fingerprint sensing. Fingerprint sensors require a micro-capacitor spacing of about 44 to 50 microns.[109]
The touchscreens can be manufactured at home, using readily available tools and materials, or it can be done industrially.
First, a "continuous-trace" wiring pattern is generated using a simple CAD system.
The wire is threaded through a plotter pen and plotted directly, as one continuous wire, onto a thin sheet of adhesive coated, clear polyester film (such as "window film"), using a standard, low cost x/y pen plotter.[53] After plotting, the single wire is gently cut into individual sections with a sharp scalpel, taking care not to damage the film.
A second identical polyester film is laminated over the first film. The resulting touchscreen film is then trimmed to shape, and a connector is retro-fitted.
The end product is extremely flexible, being about 75 microns thick (about the thickness of a human hair). It can even be creased without loss of functionality.
The film can be mounted on, or behind non-conducting (or slightly conducting) surfaces. Usually, it is mounted behind a sheet of glass up to 12 mm thick (or more), for sensing through the glass.
This method is suitable for a wide range of touchscreen sizes from very small to several meters wide - or even wider, if using a diagonally wired matrix.[73][66]
The end product is environmentally friendly as it uses recyclable polyester, and minute quantities of copper wire. The film could even have a second life as another product, such as drawing film, or wrapping film. Unlike some other touchscreen technologies, no complex processes or rare materials are used.
For non-touchscreen applications, other plastics (e.g. vinyl or ABS) may be used. The film can be blow molded or heat formed into complex three dimensional shapes, such as bottles, globes or car dashboards. Alternatively, the wires can be embedded in thick plastic such as fiber glass or carbon fiber body panels.
Single touch resistive touchscreens
In the resistive approach, which used to be the most popular technique, there are typically four layers:
When a user touches the surface, the system records the change in the electric current that flows through the display.
Dispersive signal
Dispersive signal technology 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.
Infrared
There are two infrared-based approaches. In one, an array of sensors detects a finger touching or almost touching the display, thereby interrupting infrared light beams projected over the screen. In the other, bottom-mounted infrared cameras record heat from 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[edit]
The development of multi-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 touchscreen simultaneously.
With the growing use of touchscreens, the cost of touchscreen technology is routinely absorbed into the products that incorporate it and is nearly eliminated. Touchscreen technology has demonstrated reliability and is found in airplanes, automobiles, gaming consoles, machine control systems, appliances, and handheld display devices including cellphones; the touchscreen market for mobile devices was projected to produce US$5 billion by 2009.[110]
The ability to accurately point on the screen itself is also advancing with the emerging graphics tablet-screen hybrids. Polyvinylidene fluoride (PVDF) plays a major role in this innovation due its high piezoelectric properties, which allow the tablet to sense pressure, making such things as digital painting behave more like paper and pencil.[111]
TapSense, announced in October 2011, allows touchscreens to distinguish what part of the hand was used for input, such as the fingertip, knuckle and fingernail. This could be used in a variety of ways, for example, to copy and paste, to capitalize letters, to activate different drawing modes, etc.[112][113]
Ergonomics and usage[edit]
Touchscreen enable[edit]
For touchscreens to be effective input devices, users must be able to accurately select targets and avoid accidental selection of adjacent targets. The design of touchscreen interfaces should reflect technical capabilities of the system, ergonomics, cognitive psychology and human physiology.
Guidelines for touchscreen designs were first developed in the 2000s, based on early research and actual use of older systems, typically using infrared grids—which were highly dependent on the size of the user's fingers. These guidelines are less relevant for the bulk of modern touch devices which use capacitive or resistive touch technology.[114][115]
From the mid-2000s, makers of operating systems for smartphones have promulgated standards, but these vary between manufacturers, and allow for significant variation in size based on technology changes, so are unsuitable from a human factors perspective.[116][117][118]
Much more important is the accuracy humans have in selecting targets with their finger or a pen stylus. The accuracy of user selection varies by position on the screen: users are most accurate at the center, less so at the left and right edges, and least accurate at the top edge and especially the bottom edge. The R95 accuracy (required radius for 95% target accuracy) varies from 7 mm (0.28 in) in the center to 12 mm (0.47 in) in the lower corners.[119][120][121][122][123] Users are subconsciously aware of this, and take more time to select targets which are smaller or at the edges or corners of the touchscreen.[124]
This user inaccuracy is a result of parallax, visual acuity and the speed of the feedback loop between the eyes and fingers. The precision of the human finger alone is much, much higher than this, so when assistive technologies are provided—such as on-screen magnifiers—users can move their finger (once in contact with the screen) with precision as small as 0.1 mm (0.004 in).[125]
Hand position, digit used and switching[edit]
Users of handheld and portable touchscreen devices hold them in a variety of ways, and routinely change their method of holding and selection to suit the position and type of input. There are four basic types of handheld interaction: