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  1. PRINTERS Introduction:- The printers are one of the most useful output device for use with a computer. In the early days of computing, it was the only source of information about what the computer had done. Printers are used to produce hard copy or permanent record of computer’s output. In computer is a printer is a device that accepts text and graphic output from a computer and transfers the information to paper, usually to standard size sheets of paper. Printers are sometimes sold with computers, but more frequently are purchased separately. Printers are in different sizes,speed,sophistication,and cost. In general, more expensive printers are used for higher-resolution color printing.
  2. Two Categories Of Printers Printers are classified into two main categories1):- Impact Printer 2):-Non-Impact Printers 1( :-.An impact printer is a type of printer that operates by striking a metal or plastic head against the paper, marking the page with the appropriate character, dot, line, or symbol. Impact printers work like typewriters.
  3. Types Of Impact Printers A(:- Dot Matrix Printers B(:- Daisy Wheel Printers C(:- Line Printers Dot Matrix Printer:- Dot matrix printer is an impact printer. Dot matrix printing or impact matrix printing is a type of computer printing which uses a print head that moves back and forth, or in an up and down motion, on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on a typewriter. Each dot is produced by a tiny metal rod, also called a “wire” or “pin”, which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers (pawls(. In a dot matrix printer a letter is formed by the combination of dots. It has 9,18,24 or 32 pins arranged vertically in a print head. It can make pictures also. A normal dot matrix printer has speeds varying from 50 to 600 characters per second. The carriage width of a printer also varies ranging from 80 columns to 132 columns. A standard-width printer prints 80 characters per line.
  4. Daisy Wheel Printers The daisy wheel printer uses a flat disk or wheel with petal like projections each with a different character at the tip. The wheel rotates to bring the desired character into position. A character is formed when hammer strikes the petal under it. Daisy wheels are available in several formats (bold letter, italics etc(. A daisy wheel printer is slower than a dot matrix machine. As print wheel takes more rime to bring the desired petal in position. However produces high-quality print.
  5. Line Printer Daisy wheel printing is an impact printing technology invented in 1969 by David S. Lee at Diablo Data Systems. It uses interchange able pre-formed type element s, each with typicaly96 glyphs, to generate high-quality output comparable to premium typewriters such as the IBM Selectric, but two to three times faster. Daisy wheel printing was used in electronic typewriters, word processors and computers from 1972. The daisy wheel is considered to be so named because of its resemblance to the daisy flower. A number of different types of high speed printers have been developed to satisfy the needs of large computer systems. These are called line printers as they print one complete line at a time. Line printers are also impact printers and may be further divided into drum printers and band or chain printers. Some of these printers can produce over 3000 lines per minute.
  6. Daisy Wheel Printer And Its Printing Page
  7. Drum, Band, And Chain Printer Images
  8. 2(:-Non-Impact Printers:- Non-impact printers have been developed which produce a printed image without striking the paper. These printers use new methods that have improved printing quality and speed. Non-impact printers are noiseless and faster than impact printers. Some types of non-impact printers:- A(:- Electrostatic printers B(:- Electro thermal printers C(:- Ink jet printers D(:- Laser printers
  9. A):- Electrostatic printers:- Electrostatic printers are high-speed non- impact line printers. Electrostatic Printing Process:-Electrostatic printing is a printing technique done without plate, ink or form. The paper is coated with a thin layer of zinc oxide, making it an insulator in the dark and simultaneously a conductor of electricity when exposed to light. These machines are used for printing of geographic maps. With the advancement in technology and higher speed, the machines are also being used to print small books. Electrostatic printers are used for short run printing as they are faster and also do not cost much. Electrostatic printing use a positively charged toner/inks that is attracted to paper which in turn is negatively charged. The paper is moved through a digital ink bath; positively charged particles in ink stick to the negative charge on the paper. The printers print in black and white or color as the case may be, and some handle paper up to six feet wide. Application of Electrostatic Printing:-Electrostatic printers are widely used in different industries for short run printing. They are popular for photocopying jobs both black & white and colored . These printers are faster than inkjet printers.
  10. B):-Electro thermal printers:-Electro thermal printers produce characters on heat sensitive waxy paper. It is an type of printer in which a thermoplastic ink is transferred from a ribbon to the base medium (usually paper or transparent film) by localized heating. The heating occurs as current is passed from discrete electrical contacts on the print head through a resistive layer in the ribbon to a common return layer. Compared with thermal transfer printers, the print quality is less dependent on the surface finish of the receiving medium but the complexity of the ribbon makes the cost of usage higher. Improvements in thermal transfer printers have made electro thermal technology obsolete. These were popular a few years ago because they are portable and low cost. But the drawback is that they require special heat sensitive waxy paper.
  11. C):-Inkjet printers:-Ink jet printers work in the same way as dot matrix printers except that ink jet printers have fine tiny nozzles instead of tiny pins used in dot matrix print head. 1):-Ink jet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto the paper, plastic, or other substrates. Nozzles spray a stream of ink onto the paper. Because the ink is put directly on the paper, therefore, these printers require ink in reservoirs instead of ribbon. Since no mechanical movement is involved, hence these printers are much quieter and have speed of about 200 character per second. Ink jet printers are also available which have more than one ink reservoir, each with a different colour. The colours can be chosen through software to allow the printer to print in rainbow colours. Thus a full colour graphic image from a computer screen can be obtained very quietly on paper. 2):-Ink jet printers are the most commonly used type of printer, and the range from small inexpensive consumer models to expensive professional machines. 3):-The concept of ink jet printing originated in the 19th century, and the technology was first extensively developed in the early 1950s. Starting in late 1970s ink jet printers that could reproduce digital images generated by computers were developed, mainly by Epson, Hewlett-Packard (HP), and Canon.
  12. •D):-Laser printers:-Laser printers are the faster non-impact printers. These printers use laser and electro-photographic technology. Laser printer, a computer printer that produces high-resolution output by means of a process that is similar to photocopying. A bit-mapped image of a page is formed in the computer by software. This is transferred to the printer which activates a laser beam. The laser beam duplicates the image on a rotating drum and forms a charged image on it. The image is transferred on the paper that passes between the drum and positively charged corona wire. The dots of the toner forming the image get fused onto the paper under the combined effect of heat and pressure when passing through the roller. The printed result from a laser printer is impressive and better in quality. •In place of reflected light from an image (as is used in xerography), a laser printer uses data sent from a computer to turn a laser beam on and off rapidly as it scans a charged drum. The drum then attracts toner powder to the area not exposed to the light. Finally, the toner is fused to paper over a belt by heated rollers. In a write-black printer the laser positively charges the printed areas to attract the toner, which gives better detail than a write- white printer. In a write-white printer, the beam charges the areas not to be printed to repel the toner, which gives a denser image. Faster , quieter, and capable of producing more attractive results than standard printers, laser printers have become an important means of printing business documents since they became more generally available in (1984) for personal computers. See also with desktop publishing.. A laser printer have a speed of greater than 20,000 lines per minute.

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