Monday, November 12, 2007

Printers

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Printer

Printer is an output device. The most common method of producing human readable out put is using printers. Printed output is usually referred to as hard copy. Printers provide information in a permanent readable form. They produce printed output of results, programs and data. Printers are classified as follows:

1.       Character printers – They prints one character of the text at a time.

2.       Line printers         - They prints one line of the text at a time.

3.       Page printers        - They prints one page of the text at a time.

 

Above classifications of printers are based on how they print. Besides these printers can also be classified on the basis of technology used in their manufacture.

i.e.

·              Impact printers-

They use electromechanical mechanism that causes hammers or pins to strike against a ribbon and paper to print the text. e.g. dot-matrix, daisy wheel.

·              Non Impact printers-

They don't use electromechanical printing head to strike against ribbon and paper. But they use thermal, chemical, electrostatic, laser beam or inkjet technology for printing the text.e.g. Laser printers, inkjet printers, thermal printers.

 

 

Types of Printers:

1.             Character Printers:

Character printers print one character at a time. They are low speed printers. Their printing speed is 300-600 characters per second depending upon the type of the printer. Characters to be printed are sent serially to the printer. There are two types of character printers.

a)             Dot Matrix Impact Type Character Printers –

A character is printed by printing the selected number of dots from a matrix of dots. The formation of a character has been shown using 5-dot rows and 7-dot columns. This pattern is called 5x7    dot matrix. A dot matrix printer is faster than a letter quality printer. Dot matrix printers are very flexible. They don't have fixed character font. The term font is used to refer to a character set of printer. As the fonts are not fixed, a dot matrix printer can print any shape of a character by the software. To print graphics the dot pattern for each column of dots are sent out to the print head from the memory. Its print quality is not as good as that of a letter quality printer. It is a noisy printer.

b)   Letter Quality Impact Character Printers –

     A daisy wheel type letter quality printer was used in the past for good quality printing. It is no longer    used .It has embossed characters just like those of a type writer. The characters are embossed on leaves placed on a wheel. An electric motor is used to rotate the wheel rapidly. When the desired character comes in the correct position a solenoid-driven hammer strikes against the ribbon to print the character on the paper.

2. Ink-Jet Printers:

    These works in a similar manner to a dot-matrix printer, but instead of pressing a dry ink against the page, the print head sprays drops of liquid ink onto the page. Ink jet and bubble jet printers have better image quality and are faster than dot-matrix printers; however, printouts have a tendency to smear if gotten wet.

3. Laser Printers:

    These work in a manner similar to a photocopier. A roller is charged with electricity, and then a laser is used to remove the charge from portions of the roller. Powdered ink (toner) sticks to the parts of the roller that were hit by the laser, and this toner is transferred from the roller to the paper. Then the ink is baked into the paper using a heater. Laser printers produce very high quality output and are very fast.

4. Line Printers:

    A line printer prints one line of the text at a time. A non impact type line printer may use electrostatic, thermal, thermal-wax transfer or solid ink technology. Whether a non impact printers using above mentioned technology is a line printer or character printer depends on its mechanical arrangements. If several points causing impressions are in row, the printer put dots in horizontal line by scanning process and print a line at a time are line printers. The impact type line printers are of the following types:

     a) Drum Printer

     b) Chain Printer

     c) Band Printer

a) Drum Printer:

    A line printer in which the type is mounted on a rotating drum that contains a full character set for each printing position is called Drum Printer. Each character position along the text line contains a band of raised character set. There is a magnetically driven hammer in each character position of the line. The printers receive all characters to be printed in one line of the text from the processor. The hammer hit the paper and ribbon against the desired character on the drum when it comes in the printing position. Its noise level is high and its speed varies from 200 to 2000 lines per minute.

b) Chain Printer:

     An impact printer that carries the type slugs by links of a revolving chain is called chain printer. Each link of the chain is character font. Magnetically driven hammers are there in each print position. The printers receive all the characters to be printed in one line from the processor. Printers print one line at a time. When the desired character comes in the print position the hammer strikes the ribbon and paper against the character. The noise level of this printer is high and its speed lies in the range of 400-2400 lines/min.

 

 

c) Band Printer:

      Band printers are just like chain printers. They contain fast rotating scalloped steel print band in place of a chain. The print bands contain raised character set. Hammers strike the ribbon and the paper against the character to print the character. Some printers can print up to 3000 lines/min.Their noise level is high.

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