Ricoh FT 4015 Service Manual page 37

20 December 1996
5.4.2 Base Bias Voltage Factor in Automatic Image Density (ADS) Mode
The bias voltage for ADS mode depends on the background image density of
the original which is measured by the ADS sensor. (See "Automatic Image
Density Sensor" for more information about the ADS sensor.)
The CPU checks the voltage output from the automatic ID circuit. This circuit
has a peak hold function. The peak hold voltage is the maximum ADS sensor
output voltage, which corresponds to the maximum reflectivity of the original.
The CPU then determines the proper base bias level by comparing this
voltage (read from the original) with the standard ADS reference voltage.
The table below shows the relationship between the original background
density (ADS voltage ratio) and the base bias voltage.
ADS Voltage Ratio [
80 to 100 (light)
75 to 79
70 to 74
60 to 69
29 to 59
0 to 28 (dark)
ADS Voltage Ratio [α]
: Standard ADS Reference Voltage (2.5 ± 0.1 V)
V
ADS0
Using SP34, the base bias voltage and the exposure lamp setting can be
increased or decreased for the ADS mode as follows:
SP Setting Setting
0 Normal
1 Lighter
2 Darker
3 Lightest
4 Darkest
5.4.3 Drum Residual Voltage (V
During the drum's life, drum residual voltage (V
compensate for this, the bias voltage is increased by –20 V every 5 k copies.
The V correction is done up to 20 k copies. The V
R
change after 20 k copies.
α
] (%)
Maximum ADS Output Voltage
=
V
Dev. Bias
0
–40 V
+40 V
–40 V
+40 V
) Correction Factor
R
2-23
Bias Voltage
–200 V
–240 V
–280 V
–320 V
–360 V
–380 V
ADS0
Exposure Lamp
0
0
0
+4 steps
–4 steps
(Default Setting: 0)
) will gradually increase. To
R
correction will not
R
DEVELOPMENT