Ricoh FT8880 Service Manual page 12

5 June 1992
6. DEVELOPMENT
6.4.3 Bias for the ID Sensor Pattern
ID Sensor
Reduction
The ID sensor pattern cannot always be used for the image density detection
due to the position of the ID sensor and both the positioning and size of the
ID sensor pattern on the drum.
The outside of the exposure glass (no light) is exposed on the drum and used
as the ID sensor pattern in reduction mode.
The potential of the drum in these cases, the no light and the ID sensor
pattern exposure, is not the same. So the ID sensor bias (V
using two base voltages, V
V (no light) = --360 + V
BP
V (ID Pattern) = --360 + Vd
BP
The Vd value which is determined during the process control data
initialization will be used.
V and V , which are explained in the process control section, are used for
01 02
the V calculation as the V
BP
The V can be changed by the SP mode (Toner Density Correction).
BP
The following compensation will be applied to the above V
Setting L
(V) --60
Full Size
Enlargement
Exposure Glass
for the no-light condition and Vd for the pattern.
0
(Reproduction ratio < 77%)
0
(Reproduction ratio ≥ 77%)
(drum potential after the charge corona) value.
0
N H VH
0 +60 +120
Default: H (+60 V)
2-1
DEVELOPMENT
V Pattern
L
ID Sensor Pattern
Outside
) is determined
BP
.
BP