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HARDCOPY DEVICES

Hardcopy Device : Printer


The printer is an important accessory of any computer system, specially for a graphicssystem. This is because most of the graphics creation using computer graphics has itsultimate utilization in printed form – for documentation, exhibition or publication in printmedia or books. It is the quality of printed output that finally matters in many businesses.


Hardcopy Device : Dot Matrix Printer 

A dot matrix printer refers to a type of computer printer with a print head (usually containing9 to 24 pins) that runs back and forth on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter. Unlike a typewriter or daisywheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrarygraphics can be produced. Because the printing involves mechanical pressure, these printerscan create carbon copies. The print head normally prints along every raster row of theprinter paper and the colour of print.


Hardcopy Device : Line Printer

The line printer is a form of high speed impact printer in which a line of type is printed at a time.In a typical design, a fixed font character set is engraved onto the periphery of anumber of print wheels, the number matching the number of columns (letters in a line).The wheels spin at high speed and paper and an inked ribbon are moved past the print position. As the desired character for each column passes the print position, a hammerstrikes the paper and ribbon causing the desired character to be recorded on the continuouspaper. Printed type is set at fixed positions and a line could consist of any number of character positions with 132 columns as the most common, but 80 column, 128 column and 160 column variants are also in use. Other variations of line printer have the type on moving bars or a horizontal spinning chain.


Hardcopy Device : Inkjet Printer 

An inkjet printer is a non-impact printer that places extremely small droplets of ink onto thepaper to create an image. These printers are popular because they less costly but generateattractive graphic output.

The dots sprayed on paper are extremely small (usually between 50 and 60 microns indiameter), and are positioned very precisely, with resolutions of up to 1440 × 720 dpi. The dots can have different colours combined together to create photo-quality images.

Hardcopy Device : Laser Printer 

The laser printer employs technology similar to that of a photocopy machine. A laser beamfocuses a positively charged selenium-coated rotating drum. The laser gun removes the positive charge from the drum except for the area to be printed (black portion of thepaper). In this way, the laser draws the letters and images to be printed as a pattern ofelectrical-charges — an electrostatic image. The negatively-charged black toner powder first adheres to this positively-charged area (image) on the drum from where it is transferred to the rolling white paper. Before the paper rolls under the drum, it is given a positive chargestronger than the positive charge of the electrostatic image, so the paper can pull the toner powder away. The paper is then subjected to mild heating to melt and fix the loose toner onthe paper. The laser printer is mainly a bilevel printer. In case of colour lasers, this process is repeated three times.


Hardcopy Device : Electrostatic Printer

In inkjet printers, the single printing head moves left-to-right and prints as it is traveling. In contrast, the electrostatic printer has many print heads, actually covering the entire 36" media width. So instead of a single print head moving across the width of the media, the electrostatic printer prints an entire width of the page at one time. The media (paper,vellum, film) is electrostatically charged (energized). The toner solution is circulated past the media and ‘sticks’ to the energized portion of the media, thus producing a very fast high quality image. 


Hardcopy Device : Plotter 

In contrast to the printer which is primarily a raster scan device, the plotter is a vector device. In colour plotters the carriage accommodates a number of pens with varying colours and widths. The microprocessor in the plotter receives instructions from the host computer and executes commands like ‘move’ (moving the carriage to a given position with pens up) and ‘draw’ (drawing geometric entities like point, line, arc, circle etc. with pens down). Since the plotter is a vector device it can directly reach specific positions on printer paper without following raster row sequence. In flat bed plotter the paper lies flat and stationary while the pen moves from one location to another on the paper. But in drum plotters the paper itself slides on a cylindrical drum and the pen moves over the drum. 
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