Drum; Selenium Drum Characteristics; Handling The Drum - Ricoh FT5540 Service Manual

1. DRUM

1.1 SELENIUM DRUM CHARACTERISTICS

Selenium has the following characteristics:
• Accepts a high positive electrical charge in the dark. (The electrical resistance of selenium
is high in the absence of light.)
• Dissipates the electrical charge when exposed to light. (Exposure to light greatly enhances
the conductivity of selenium.)
• Dissipates the electrical charge in direct proportion to the intensity of the light.
That is, where stronger light is directed to the selenium surface, a smaller voltage
remains on the selenium.
The sensitivity of selenium changes slightly with variations in the surface temperature of the
drum. (Under cool conditions, the drum conductivity decreases. This will result in background
or excessive image density.) As a countermeasure, the development bias is changed to
compensate for temperature variations around the drum. Also, while the copier is off, the drum
heater warms the drum.
Drum sensitivity also depends on how long the drum has rested between copy runs. The
copier's CPU compensates for changes in drum sensitivity due to rest time by changing the
development bias. This prevents variations in image density at the beginning of copy runs.
The selenium drum used in this model has high sensitivity, good color reproduction, and good
reproduction of low contrast originals (pencil originals, etc.)

1.2 HANDLING THE DRUM

Never touch the drum surface with bare hands.
Store the drum in a cool, dry place away from heat.
When cleaning the drum, always wear a pair of gloves. Do not throw away cotton
used for cleaning. Bring it back to the service depot for disposal according to local
regulations.
Prime the drum with setting powder when the drum, cleaning blade, or cleaning brush are
replaced. Do this within one minute in a location not exposed to strong light.
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31 August 1989