Understanding Working Principles

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UNDERSTANDING

WORKING PRINCIPLESLASER PRINTER

BY:RASHMI CHAUHAN


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LASER PRINTERS

INTRODUCTION:

A laser printer is a common type of computer printer that rapidlyproduces high quality text and graphics on plain paper. Laser printersemploy a xerographic printing process.

A laser beam projects an image of the page to be printed onto anelectrically charged rotating drum coated with selenium or, morecommon in modern printers, organicphotoconductors.Photoconductivity removes charge from the areas exposed to light.

Dry ink (toner) particles are then electrostatically picked up by the

drum's charged areas. The drum then prints the image onto paper bydirect contact and heat, which fuses the ink to the paper.


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WORKING IN DETAIL

Typically seven steps involved in the laser printing process:

1. Raster image processing- Each horizontal strip of dotsacross the page is known as a raster line or scan line.

Creating the image to be printed is done by a Raster

Image Processor (RIP), typically built into the laser printer.The RIP uses the page description language to generate abitmap of the final page in the raster memory.

1. Charging - a corona wire positioned parallel to thedrum, or in more recent printers, a primary charge roller,

projects an electrostatic charge onto the photoreceptor ,a revolving photosensitive drum or belt, which is capableof holding an electrostatic charge on its surface while it isin the dark.


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An AC bias is applied to the primary charge rollerto remove any residual charges left by previousimages. The roller will also apply a DC bias on thedrum surface to ensure a uniform negative

potential.


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3. Exposing -The laser is aimed at arotating polygonal mirror, which directsthe laser beam through a system of lenses

and mirrors onto the photoreceptor. Thecylinder continues to rotate during thesweep and the angle of sweepcompensates for this motion. The

stream of rasterized data held in memoryturns the laser on and off to form the dotson the cylinder. Lasers are used becausethey generate a narrow beam over greatdistances. The laser beam neutralizes (or


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4. Developing -The surface with thelatent image is exposed to toner, fineparticles of dry plastic powder mixed with

carbon black or coloring agents. Thecharged toner particles are given anegative charge, and are electrostaticallyattracted to the photoreceptor's latent

image, the areas touched by the laser.Because like charges repel, the

negatively charged toner will not touchthe drum where the negative chargeremains.


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6. Fusing - The paper passes through rollers inthe fuser assembly where heat (up to 200 Celsius)and pressure bond the plastic powder to thepaper. One roller is

usually a hollow tube (heat roller) and the other isa rubber backing roller (pressure roller). A radiantheat lamp is suspended in the center of the hollowtube, and its infrared energy uniformly heats theroller from the inside. For proper bonding of thetoner, the fuser roller must be uniformly hot.


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7. Cleaning - When the print is complete, anelectrically neutral soft plastic blade cleans anyexcess toner from the photoreceptor and deposits itinto a waste reservoir, and a discharge lamp

removes the remaining charge from thephotoreceptor.


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THANK YOU

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Understanding Working Principles