Laser Printers

Written by Charles Peacock
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Laser printers have always been a mystery to me. How does a cartridge filled with fine black powder turn into printed words that are both waterproof and smear-proof? Judging by the name, some type of laser must be involved. But what exactly happens inside those mysterious laser printers?

How Laser Printers Work

Inside every laser printer is a small drum that is made of photoconductive material (meaning it reacts to light). Tiny spots on this drum can be given either a positive or negative charge, and when you start your printer up, the entire drum is given a positive charge. This is where the laser comes in: a tiny laser beam "cuts" the image of the letters (or whatever you're printing) on the drum, reversing the charge in all of the drawn-on areas to negative.

Once the "last image cutting" has taken place, the drum is then coated with positively charged toner powder. This powder clings (through static electricity) to the parts of the drum that have been given a negative charge by the laser--in other words, the words themselves. A piece of paper is then rolled over the drum, and the toner particles transfer to the paper itself (again using static electricity).

Once the toner is on the paper, it needs to be bonded so that it doesn't just slip off. This bonding is done by the "fuser," which is essentially a pair of heated rollers. They heat up the toner, causing it to bond to the paper. This is why paper coming out of a laser printer always feels slightly warm to the touch.


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