Service manual

The seven image-formation processes
Paper Pickup
Figure 4-5 Image formation-block diagram
1 Conditioning stage (primary charging)—This process applies a uniform negative charge to the
surface of the drum with the primary charging roller, which is located in the print cartridge. The
primary charging roller is coated with conductive rubber. An ac bias is applied to the roller to erase
any residual charges from any previous image. In addition, the primary charging roller applies a
negative dc bias to create a uniform negative potential on the drum surface. The print density setting
modifies the dc voltage.
2 Writing stage (scanning exposure)—During this process, a modulated laser diode projects the
beam onto a rotating scanning mirror. As the mirror rotates, the beam reflects off the mirror, first
through a set of focusing lenses, then off a mirror, and finally through a slot in the top of the print
cartridge, and onto the photosensitive drum. The beam sweeps the drum from left to right,
discharging the negative potential wherever the beam strikes the surface. This creates a latent
electrostatic image, which later is developed into a visible image. Because the beam sweeps the
entire length of the drum while the drum rotates, the entire surface area of the drum can be covered.
At the end of each sweep, the beam strikes the beam-detect lens, generating the beam-detect signal
(BD signal). The BD signal is sent to the ECU where it is converted to an electrical signal used to
synchronize the output of the next scan line of data.
3 Developing stage—During this process, the latent electrostatic image is present on the drum. The
toner particles obtain a negative surface charge by rubbing against the developing cylinder, which
is connected to a negative dc supply. The negatively charged toner is attracted to the discharged
(exposed, grounded) areas of the drum, and it is repelled from the negatively charged (unexposed)
areas.
4 Transfer stage—During this process, the toner image on the drum surface is transferred to the
media. The transfer roller applies a positive charge to the back of the media, which attracts the
negatively charged toner on the drum surface to the media. After separation, the drum is cleaned
and conditioned for the next image.
5 Separation stage—During this process, the media separates from the drum. To stabilize the feed
system and prevent toner dropouts on the printed image at low temperature and humidity, the static
eliminator reduces the charge on the back of the media.
ENWW Printer functions 55