toner is added to the drum and another sheet of paper is charged, passed by the drum,
and fused. If only one copy is being printed of the page, any remaining toner is removed
from the drum, the drum is recharged, and the process begins again.
A quick word about the toner used in a laser printer before I go into more detail about
the EP process. Laser printer toner is made up of plastic-coated iron particles. Toner is a
dry powder that consists of iron particles coated with a plastic resin. The toner is applied
to the drum as it rotates and attaches to the dot row just completed by the laser immedi-
ately after it scans a row.
The EP laser printing process can be organized into six separate phases, as follows:- Charging The entire drum is uniformly charged to –600V by the primary
corona wire (also known as the main corona) located inside the toner cartridge. - Exposing The laser printer’s controller uses a laser beam and one or more
mirrors to create the image of the page on the drum. The laser beam is turned
on and off to create a series of small dots on the drum to match the document
to be printed. Where the light of the laser contacts the photosensitive drum,
the charge at that spot is reduced to about –100V. After the entire image of the
document has been transferred to the drum, the controller starts a sheet feeding
through the printer, stopping it at the registration rollers. - Developing Inside the developing roller, which is also located inside the toner
cartridge, is a magnet that attracts the iron particles in the toner. As the developing
roller rotates by the drum, the toner is attracted to the areas of the drum that
have been exposed by the laser, creating a mirror image of the document on
the drum. - Transferring The back of the paper sheet is given a positive charge. As the
paper passes the drum, the negatively charged toner is attracted from the drum
onto the paper. The paper now has the image of the document on it, but the toner,
held in place by simple magnetism, is not bonded to it. - Fusing The fusing rollers apply heat and pressure to the toner, melting and
pressing it into the paper to create a permanent bond. The fusing rollers are
covered with Teflon and a light silicon oil to keep the paper and toner from
sticking to them. - Cleaning Before the next page is started, the drum is swept free of any
lingering toner with a rubber blade and a fluorescent lamp removes any
electrical charge remaining on the drum. Any toner removed in this step
is not reused but is put into a used-toner compartment on the cartridge.
Hewlett Packard (HP) Process
The Hewlett Packard laser printing process is the same as the EP process except in the
first two phases. The charging phase of the EP process is adjusted to become a condition-
ing phase, and the exposing phase is replaced with the writing phase. The HP process(^426) PC Hardware: A Beginner’s Guide