Ricoh FT6645 Manual page 49

DRUM UNIT 23 April 1993
2.4.2 Lead Edge and Trail Edge Erase
The entire line of LEDs turns on when the main motor turns on. They stay on
until the erase margin slightly overlaps the lead edge of the original image on
the drum (lead edge erase margin). It prevents the shadow of the original
lead edge from appearing on the copy paper. This lead erase margin is also
necessary for the lead edge of the copy paper to separate from the hot roller.
The width of the lead edge erase margin can be adjusted by SP mode
( SP Adjustment mode: PAGE 3).
1
When the scanner reaches the return position, the charge corona, the grid
bias, and the exposure lamp turn off. However, the charged area on the drum
surface is a little longer than the actual original length in order to have the
entire latent image of the original.
The entire line of LEDs turn on when the trail edge of the latent image has
passed under the erase lamp unit. This prevents developing unnecessary
parts of the drum surface, reducing toner consumption and drum cleaning
load.
The LEDs stay on to erase the lead edge of the latent image in the next copy
cycle. After the final copy, the erase lamps turn off at the same time as the
main motor.
2.4.3 Side Erase
Based on the combination of copy paper size and the reproduction ratio data,
the LEDs turn on in blocks. This prevents the shadow of the original side
edge and unexposed front and rear sides of the drum surface in reduction
mode from being developed. This reduces toner consumption and drum
cleaning load.
In the DJF mode, the horizontal original standard position on the exposure
glass is 5 mm away from the rear scale.
In the RDH mode, the horizontal center of the original is aligned with the
center of the exposure glass.
On the other hand, the horizontal original standard position on the exposure
glass in the platen cover mode is the rear scale edge.
To erase the shadow made by the edge of the rear scale in platen cover
mode, one more LED at the front side turns on. This is in addition to the
LED's on in DJF and RDH modes.
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