Ricoh FT7770 Service Manual page 90

30
April, '89
-Automatic Image Density Control (Auto ID)-
-When the auto ID is on, the exposure lamp regulator voltage will be Increased
by
4 volts.
limitation.
At the start of the copy cycle, the original sensing mechanism measures the
background density of the original image.
strength of the light reflected from a 50 mm strip at the leading edge of
the original.
on the main board. The photodiode is the input element of the auto ID cir-
cuit.
The CPU checks the voltage output with the auto
has a peak hold function.
mum reflectivity of the original.
base level
(V2)
nal to the power pack. The power pack then applies the proper bias to the
development roller.
As shown in the above table, the ID switch mounted inside the left door
allows operator to add a shift factor
the
The ID switch is set at the factory to the normal position, When the auto ID
input voltage is over 1.38 V, V2' is reduced.
This voltage
cannot exceed 79.75
A fiber optic cable pipes the reflected light to a photodiode
The peak hold voltage corresponds to the maxi-
based on the peak hold voltage and sends a 3-bit control sig-
Auto ID
0.0 to 1.38
over 1.38 V
It does this by measuring the
The CPU then determines the proper bias
input Darker
V
0 v
0 v
(V2') to the
2-34
volts due to lamp regulator
ID circuit. This
Normal
60 V
30 v
base voltage.
bias
circuit
Lighter
120 v
60 V