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2011-10-12

A+: Laser printer fundamentals

The laser ('electrophotographic') printer was invented in 1971, and first sold in 1984. It uses 'toner', a black or colored substance mixed with iron oxide so electrostatic charges can move it, plus a polyester resin which melts into the paper.


Toner cartridges add a developer/carrier as well as contain the toner. A drum or belt is also normally built into the cartridge, along with a scraper blade which removes excess toner. When a laser beam strikes the drum or belt, a photo-sensitive coating gives up a charge, so the toner will stick to the drum or belt where needed. The drum/belt not hit by the laser beam are statically charged so toner won't stick to it. A high voltage power supply in the laser printer generates the charge; that power supply is dangerous, can threaten your life, and should never be opened up.


A transfer corona wire or roller (roller-based systems are faster) moves the toner from the drum to the paper. A static eliminator strip drains the charge from the paper once the toner is fused to the paper.


Okidata and Panasonic created LED printers to compete with laser printers. They're less expensive and less complicated, but also print at a lower resolution (300 dpi instead of the 600 dpi or above of lasers and better bubble jet printers). The charging roller and erasing lamp are not in the toner cartridge, and are instead in a separate replacable assembly. The laser assembly is replaced by a row of LEDs which blink on and off as the belt or drum turns.

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