Specifications

5.4.2 Base Bias Voltage Factor In Automatic Image Density Control
In automatic image density control mode, the base exposure lamp voltage is
fixed to Vo. (See page 2-18 for more information.) Image density is controlled
by changing only the base bias voltage.
The base bias voltage depends on the background image density of the
original, which is measured using the original ID sensor. (See page 2-18 for
more information.)
The CPU checks the voltage output from the automatic ID circuit. This circuit
has a peak hold function. The peak hold voltage corresponds to the
maximum reflectivity of the original. The CPU then determines the proper
base bias level with reference to the peak hold voltage.
The following table gives the base bias voltages at each ADS output level.
When the automatic density level is set to darker by SP mode #34, the base
bias voltage shifts +40 volts as shown in the following table.
K
Base Bias Voltage
Normal or Lighter
(SP mode #34 = 0 or 2)
Darker
(SP mode #34 = 1)
K ≥ TH1
TH1 > K ≥ TH2
TH2 > K ≥ TH3
TH3 > K
–200 volts
–260 volts
–320 volts
–380 volts
–160 volts
–220 volts
–280 volts
–340 volts
K =
ADS Output Voltage (Peak Hold Voltage)
ADS Adjusted Voltage (SP #56)
TH1 to 3: Threshold level (See the following table.)
To maintain the correct image density, the lamp data is incremented when
the reproduction ratio is changed and/or drum wear correction is done. This
increment in the lamp data increases the intensity of light reflected from the
original. Therefore, the ADS output voltage also changes.
In order to maintain a constant voltage for the same original when the lamp
data is incremented, the threshold levels are shifted with each increment in
the lamp data as shown in the following table.
Increase of
lamp data
+0 +1 +2 +3 +4 +5 +6 +7 +8 +9
TH1 0.70 0.75 0.80 0.85 0.89 0.94 0.98 1.03 1.08 1.12
TH2 0.66 0.70 0.74 0.78 0.83 0.87 0.91 0.96 1.00 1.04
TH3 0.29 0.31 0.33 0.35 0.37 0.39 0.41 0.43 0.45 0.48
1 December 1990
2-30