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Impact printers, which mostly have been superseded by ink-jet and laser printers, use a mechanical hammering device to produce each character. A formed character printer forces metal or plastic characters against an inked ribbon to produce a sharp image on paper; the characters may be on a moving bar, a rapidly rotating chain, a rotatable ball, or wheel spokes. A dot matrix printer uses a matrix of tiny pegs that, when hit from behind against a ribbon, impart a set of dots to form a character on the paper; a wide variety of characters and graphics is created using different dot combinations. Although noisy, impact printers can produce multiple copies of business forms simultaneously using carbon or carbonless techniques.
Nonimpact printers use thermal and electrostatic, rather than mechanical, techniques. Ink-jet printers, including bubble-jet printers, squirt heated ink through a matrix of holes to form characters or images. Laser printers form an image of the output on a selenium-coated drum using laser light that is turned on and off by data from the computer and then transfer the output from the drum using photocopying techniques. Thermal-wax-transfer printers and dye-sublimation printers use heat to transfer color pigment from a ribbon to a special paper to produce photographic-quality color images. Nonimpact printers are quieter than impact printers and produce higher quality output, especially of graphics, but at a greater cost per page.
See also laser printer.
in computer technology, a part of a computer hardware or a functionally independent device that records the results of data processing on paper or another recording medium in an alphabetic, numeric, or graphic form suitable for visual perception. In the most commonly used printers a symbol, or character, is mechanically imprinted on the paper by the pressure, or impact, of a raised typeface through an inked ribbon. In some printer designs, however, the type is not pressed against the paper but the paper is pressed by a special smooth “hammer” against the raised surface of an immobile type through an inked ribbon. Printers that use xerographic, electromagnetic, photographic, ink-jet, or other techniques are less common. Printers may write data on separate sheets of paper or on continuous strips of paper that can be subsequently folded and cut into separate sheets. Two types of printers exist with respect to the movement of the recording medium: printers with continuous feed, where printed characters are written on a moving medium, and printers with noncontinuous feed, where the recording medium is stationary at the moment of printing.
The basic element of a mechanical printer is the printing mechanism, which includes the printing element—typebars or a
spherical head or wheel with raised typefaces (see Figure 1)— and a drive system. To print a character, the printer automatically converts the character code received from the computer into an electrical signal that sets the appropriate type bar in motion, turns the spherical printing head so that the necessary character is facing the paper, or sets the digital wheel in the position where the needed character is opposite the hammer. Mechanical printers work relatively slowly; their operating speeds are determined by the inertia of the moving elements and, depending on the design, reach 20 characters a second for character serial printers and 200–300 lines a minute for line printers. The weight of the moving elements is much less in matrix, or wire, printers, wherein the printed character is formed as a set of points that are printed by moving forward selected members of an array of wires.
In nonmechanical printers the image of the characters being printed is formed automatically either on the screen of a cathode ray tube or by optical or other special means and then transferred to paper optically or electrically. The image obtained in this way is fixed by burning through the paper (spark printing), by chemical or thermal means using photo- or heat-sensitive paper, or by applying an inking powder that settles on electrically charged sections of the paper and is fixed thermally or chemically. The speed of such printers ranges from 100 to 3,000 characters a second depending on the design and technological characteristics.
REFERENCESSaveta, N. N. Ustroistva vvoda i vyvoda informatsii universal’nykh elektronnykh tsifrovykh vychislitel’ nykh mashin. Moscow, 1971.
Alferov, A. V., I. S. Reznik, and V. G. Shorin. Orgatekhnika. Moscow, 1973.
M. G. GAAZE-RAPOPORT
Compare plotter. See also Braille printer, tree-killer.
printerA device that converts computer output into printed images. Following is an overview of the various technologies. For more details, look up the individual entries.
Serial Printers (Character Printers)
Serial printers print one character at a time moving across the paper. Electrosensitive, direct thermal, older daisy wheel and even inkjet printers could be cataloged in this group; however, the primary desktop serial printer is the serial dot matrix printer, with speeds ranging from 200 to 400 cps, which is about 90 to 180 lines per minute (lpm).
Line printers print a line at a time from approximately 400 to 2,000 lpm and are commonly found in datacenters and industrial environments. Earlier technologies included drum, chain, train and dot band matrix technologies. The surviving technologies use band and line matrix mechanisms.
Page printers print a page at a time from four to more than 800 ppm. Laser, LED, solid ink and electron beam imaging printers fall into this category. All of these printers adhere toner or ink onto a drum which is transferred to the entire page in one cycle for black and white and multiple cycles for color.
Serial Dot Matrix
A desktop printer that uses a moving printhead of wire hammers. It forms characters and graphics by impacting a ribbon and transferring dots of ink onto the paper. See dot matrix printer.
A type of line printer that uses an oscillating row of print hammers. The hammers form characters and graphics by impacting a ribbon and transferring dots of ink onto the paper. See line matrix printer.
Band (Line Character)
A type of line printer that uses a fixed set of characters attached to a continuously revolving metal band. A set of hammers (one for each column) hit the paper, pushing it into the ribbon and against the character image on the band. See band printer.
Earlier Impact Technologies
Impact printers were developed for the first computers, and several earlier technologies have gone by the wayside.
Chain, train and drum printers were precursors to band printers. They all used actual shaped characters, or type slugs, to print a fixed size and style of letter and digit. Daisy wheel printers were desktop impact printers used in the 1970s and 1980s. Dot band matrix printers used a combination of band printer and dot matrix methods. See chain printer, train printer, drum printer, daisy wheel and dot band matrix printer.
Laser & LED
Laser printers and LED printers employ the electrophotographic method used in copy machines. Both technologies are available from small desktop units to high-speed digital printing presses, ranging in speed from four to more than 700 ppm, and color units from three to 75 ppm. See laser printer, LED printer and electrophotographic.
Inkjets have become the most popular form of desktop personal printer, and all units print in color. Inkjets propel droplets of ink directly onto the paper. See inkjet printer.
IRIS printers use inkjet technology, but are in a class by themselves. They achieve a perceived 1,800 dpi resolution and can print on fabric as well as paper. See IRIS printer.
Solid ink printers use sticks of wax ink that are melted into a liquid. The ink is directed onto a drum, similar to a laser printer, and then transferred onto the paper to produce high-quality output. See solid ink printer.
Electron Beam Imaging
A technology somewhat similar to a laser printer, except that electricity is used to create the image instead of light. This evolved from ion deposition and is used in very high-speed page printers exceeding 800 ppm. See electron beam imaging.
Thermal Wax Transfer & Dye Sublimation
Dots of ink or dye are transferred from a ribbon onto paper by passing the ribbon and the paper across a line of heating elements. Thermal wax is used for barcode and other types of labels as well as medium-resolution graphics. Dye sublimation is used for photorealistic color output. See thermal wax transfer printer and dye sublimation printer.
A dot matrix printhead charges dots on aluminum-coated silver paper, usually in a serial fashion. The charge removes the coating, leaving a black image. See electrosensitive printer.
Used in barcode and other specialty printers as well as in earlier fax machines, dots are burned onto a type of coated paper that darkens when heat is applied to it. See direct thermal printer.
Dots are charged onto a coated paper, typically a line at a time. A toner is attracted to the paper and made permanent by pressure or heat. See electrostatic plotter.