What Is a Laser Printer Fuser?by Fred Decker
Laser printers are unmatched in their ability to generate crisp, sharp text at high speeds. The basic technology is derived from photocopiers -- a laser printer is essentially a copier that works with digital originals, rather than pieces of paper. The final step in the printing process requires a high-temperature fuser, which is why newly printed pages are often warm to the touch.
Toner and Fuser
You're probably familiar with toner, the remarkably fine black powder that gets absolutely everywhere if you have the misfortune to drop the cartridge while you're changing it. When subjected to heat and pressure, the microscopic grains of toner adhere, or "fuse," to the surface of the paper. That's the role the fuser plays in converting your files to printed pages.
Creating the Image
When you send a page to the printer, the printer driver and the printer's own onboard software collaborate to translate your text and graphics into a pattern of microscopically tiny dots. On entry-level printers, there might be just 300 dots per inch, or dpi, while higher-end printers often cram in 2,400 dpi. A microprocessor-controlled laser relays those dots to the printer's drum, an aluminum cylinder with a photosensitive coating. The drum itself has a positive electrical charge, which becomes negative where it's touched by the laser. The toner is positively charged, so it's repelled by most of the drum but attracted by the laser-imprinted areas.
Printing the Image
The printer's sheet feeder rolls a sheet of paper into the print mechanism, where the rotating drum presses firmly against it and transfers the dry toner to the page. At this point the finished page is recognizable, but the dry toner would simply rub off if it was removed from the printer. Instead, the page is passed between the fuser and another roller, which apply the heat and pressure needed to make the image permanent. As the page heads toward your output tray, a rotating brush cleans away any loose leftover toner and recycles it for later use.
Laser printers are subject to a number of print-quality issues, some of which involve the fuser unit. For example, if your printed page is freckled or spotted with loose toner, your fuser might need cleaning. Business-supply stores sell special drum/fuser cleaning sheets you can run through the printer for easy cleaning. Some especially rough or textured pages might print poorly, with "dropouts," or areas with little or no toner. Check your printer's settings for a "high-toner" mode, which compensates for this with extra toner. That same setting might also be necessary if your finished page has areas of dry, unfused toner that can easily be rubbed off. Many papers have a rough and a smooth side, so printing on the smooth side is also helpful.
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