(^428) PC Hardware: A Beginner’s Guide
There is a liquid crystal pixel for each of the tiny dots on the drum that can be dis-
charged to create a document. So, if the printer is rated for 1200dpi, 1200 liquid crystals
are used in each inch of the light source. As the drum rotates past the light source, the
crystals are opened and closed to create the dots on the drum for each line of pixels in the
document’s image.
Inside the Laser Printer
Laser printers use toner to create the image on the printed page. Toner is supplied to the
printer in a removable cartridge that typically also contains many of the most important
components of the printing process (see Figure 17-14). Located inside the toner cartridge
are the photosensitive drum, a charging mechanism, typically a corona wire, used to con-
ditionthedrum,adevelopingrollerusedtodeposittoneronthedrum,and,ofcourse,the
toner. Including these parts of the process in the toner cartridges provides the printer
with a fresh drum each time the toner cartridge is changed, preventing drum imaging
problems common to older photocopiers, which includes scratches or grooves being
etched into the drum by paper bits, staples, or other foreign bodies that fall into the print
drum area. These types of problems are avoided when the drum is new and sealed inside
the cartridge.Figure 17-14. A laser printer toner cartridge