PRINTERS WORK WITH COMPUTER

DOT MATRIX PRINTERS

In dot matrix printer, each letter is formed with a series of dots. Standard characters are produced by a pin printer or 24 pin printer. A normal dot matrix printer has speeds varying form 50 to 600 characters per seconds. The carriage width of a printer also varies ranging from 80 columns to 132 columns. Thus standard width printer print 80 characters per line while the wide carriage printer prints 132 characters per line.

DAISY WHEEL PRINTERS

This printer uses a print mechanism in the form of a series of petals arranged on a petal wheel. A character is contained at the end of each petal. The wheel rotates to bring the desired character into position. An image formed when a hammer strike the desired character. Daisy wheels are available in several formats (bold letter, italics etc.). A daisy wheel printer is slower than a dot matrix machine because of the time required to turn the print wheel. However it produces high quality print.

LINE PRINTERS

Line Printers are used with minicomputers and mainframe computers. They print at very fast speed. Line printers print one complete line at a time and at speeds greater than 1000 lines per minute. Line printers may be further divided into drum printers and band or chain printers.

NON IMPACT PRINTERS

New methods are being used in the computer printer technology in order to attain better quality and higher speed. A number of non impact printer have been developed which produce a printed image without striking the paper. Non impact printer are much faster has impact printers and produce much less noise and print high quality characters. Some of the non impact type of printers are:

• Electrostatic Printers
• Electro Thermal Printers
• Ink jet Printers and
• Laser Printers

ELECTROSTATIC PRINTERS

Electrostatic printer are high speed line printers. On scanning by electric field, a charged image is formed on paper. This paper is passed through an inkfog. The ink adhered at charged spots, which is fixed on passing through the heated rollers, producing the final printed sheet.

ELECTRO THERMAL PRINTERS

Thermal printers are inexpensive, small and require low voltage or battery power to operate. Their drawbacks are that these are slow and can only print on a special heat sensitive waxy paper. The image formed on the waxy paper is burned by the printer. Moreover this burned in image fades with time on prolonged exposure to sunlight. Thermal printers were popular a few years ago and are still available because of their protable nature and low cost.

INK JET PRINTERS

Work in the same way as dot matrix printers except that ink jet printer have fine spray nozsles instead of tiny pins used in dot matrix print head. Nozzles spray a stream of ink onto the paper. Because the ink is put directly on the paper, therefore, these printers require ink in a reservoirs instead of ribbon. Since no mechanical movement is involved, hence these printers are much quieter and have speed of about 200 characters 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 a rainbow colour. Thus a full colour graphinc image from a computer screen can be obtained very quietly on paper.

LASER PRINTER

Laser printers are the fastes machines in the printer industry. These printers use laser and electrophotographic technology to achieve printing speeds greater than 20,000 lines per minutes. In laser printing, a software creates a bitmapped image of the page in the computer. This image is processed and transferred to the printer which activates a laser beam to secan image on positively charged photoconductive surface of a rotating drum. The spots written by the laser take up a negative electric charge. A positive charged toner material is attracted by the negatively charged area of the drum written by the laser beam. This develops an image on the drum. As the paper passes between the drum and a positively charged wire called the corona wire, the image is transferred on the paper. The paper then passed between two rollers where the dots of the toner forming the image get fused onto the paper under the combined effect of heat and pressure. The printed result from a laser printer is impressive and better than letter quality. An advantage of laser printers over daisy wheel printers is their ability to produce graphic. Depending upon the software graphic and text can be merged on one page. As far as noise is concerned, laser printers are quieter and much faster.

DOT MATRIX, DAISY WHEEL, LINE PRINTERS