C7085-90921 Chapter 5 Theory of operation 113
Figure 5-14 Waste toner
As the waste toner reservoirs fill, a waste toner sensor (PS13) monitors the level of waste toner. Light
from a photo sensor emitter moves along a light guide to a window on the drum. The light passes
through one of the waste toner reservoirs, as shown in Figure 5-14, to the receiving side of the waste
toner sensor. A stirrer rotates past the window to clean away waste toner to prevent false readings.
As the reservoir fills, the length of time the window remains clear shortens. The DC Controller
monitors this time and when the threshold is reached the
WASTE TONER FULL message is displayed
on the front panel. At this point, the printer stops printing and the drum cartridge must be replaced.
Under normal printing conditions the
DRUM LIFE OUT message will be seen first. Only when printing
full-color pages with a high percentage of coverage or when a lot of waste toner is removed from the
ITB will the
WASTE TONER FULL message be displayed before the DRUM LIFE OUT message.
Intermediate transfer belt
The entire print image forms on the intermediate transfer belt (ITB) before being transferred to the
media. The image formation section of this chapter includes a description of this process and
discusses operation of the motors and other items associated with the ITB. Figure 5-15 shows the
components associated with the ITB.
Figure 5-15 Transfer unit function
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