112 Theory of operation C7085-90921
Mechanical system
This section discusses each of the imaging units involved in the image formation process.
Photosensitive drum cartridge
The drum drawer assembly is a user-replaceable assembly that contains the photosensitive drum,
primary charging roller, drum memory, and waste toner storage. The drum motor (M4) drives the
drum drive assembly, which in turn drives both the photosensitive drum and the ITB (discussed
later in the mechanical system). Because the primary charging roller’s function was discussed in
the image formation section, only the drum memory and waste storage areas are covered here.
Photosensitive drum life
Located inside the drum cartridge is an EEPROM that stores an identification code along with drum
life and waste toner information. A life threshold value is used as a comparison number to indicate
when the drum has reached its end of life. During printer operation, the DC controller writes to the
drum memory at specific times: when power is deactivated, when the drum drawer is opened, or
whenever 20 pages are printed.
Figure 5-13 Photosensitive drum cartridge
Two messages appear as the drum cartridge reaches its end of life. The first is
DRUM LIFE LOW,
which appears on the control panel when about 85 percent of the drum’s life has expired. When the
drum is 100 percent used, the message
DRUM LIFE OUT appears and the printer stops printing. A
new drum cartridge must be installed at this time.
Waste toner
Inside the drum cartridge are three waste toner reservoirs that store the residual toner left behind
during image formation. As discussed earlier in the image formation section, the residual toner
from the ITB is transferred to the drum. A cleaning blade scrapes the residual toner off the drum’s
surface. The waste toner is then carried by toner feed plates into the waste toner reservoirs for
storage.
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