How laser printing works

Have you ever looked inside a laser printer and wondered just how it takes what’s on your computer screen and puts it on paper? Oddly, in this age of fancy digital devices, static electricity is the key to making a laser printer work.

It all starts with a computer file that is sent to the printer, either over a parallel or USB cable or via a wired or wireless network.

First, the printer’s processor turns the data into what’s called a raster image that is composed of millions of tiny dots on a line by line basis. For instance, a solid area for a 300 dot per inch image requires 90,000 dots per square inch, or 8 million dots for a sheet of paper. Up the resolution to 600 dots per inch and that number rises to 360,000 dots per square inch or 32 million per page.

Next, a precise laser beam scans back and forth over the printer’s photoconductive drum as the printer draws in a clean sheet of paper. A special rotating mirror does the hard work of sending the beam to where it needs to be. The key is that wherever the laser’s beam hits the drum, it selectively removes the static charge on the drum on that exact spot. Some printers use light emitting diodes instead of a laser to imprint the image on the drum.

To get this latent image onto the page, the drum next selectively picks up toner where the drum remains charged. This creates a reverse image of what was on the drum. This image is then transferred to the paper.

Finally, a hot roller squeezes the page, melting the toner’s polymer to fuse it with the surface of the paper. This creates a permanent image on the page.

In this process, the toner is a key player and has to work perfectly with the rest of the printer. Generic toner or using a remanufactured cartridge can make the printer unreliable and turn out shoddy pages. In other words, it just isn’t good enough.

This story, "How laser printing works" was originally published by ITworld.

Copyright © 2010 IDG Communications, Inc.

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