LASER PRINTERS

6/16/2000

Laser Printers: Laser printers work by projecting the image of information to be printed onto a photosensitive drum that has previously been given a strong electrical charge. The charge that remains after exposure is used to attract a colored toner -- typically black. The toner is rolled onto the paper or other material to be printed onto. Then heat is used to melt (fuse) the toner to the medium.

Laser printers are not much different than photocopiers except that the image to be printed is created electronically rather than being scanned. The parts of a laser printer consist of a light source -- usually an infrared laser; a rotating photosensitive drum; a high voltage corona wire that charges the drum; a toner store that meters out toner and a magnetic carrier onto the charged drum; motors and gears that rotate the drum and drive the paper over it. Another corona wire in back of the paper moves the toner to the paper. A third corona wire is used in some designs to separate the paper from the drum. The paper is then moved to a Teflon coated roller that contains a heat lamp. Meanwhile a mechanical scraper removes any toner left on the drum and a bright light is used to remove any residual charge.

Laser printers are complex and relatively expensive, but they produce high quality copies cheaply and quickly. Many laser printers bundle most of the components into a user replaceable "toner cartridge" that includes not only the toner, but the drum, toner spreader ("doctor blade"), toner scraper, and other parts.

For the most part, Laser Printers printers operate as page printers downloading a picture of a page to print then printing it. Most laser printers will not print within 6mm of the paper edges. While the printers will print on a wide variety of material, gummed labels and very heavy stock are not recommended for printers that have convoluted paper paths. Many early laser printers are incompatible with mechanical printer switches. Transparent stock is available for laser printers and copiers, but feeding an arbitrarily selected sheet of plastic may result in its melting in the fuser.

ftp://ftp.unina.it/pub/electronics/repairfaq/REPAIR.250a/F_Printer.html

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