3.6 AUTOMATIC IMAGE DENSITY SENSING
Light from the exposure lamp is reflected from the original and travels to the
lens [A] via the mirrors. The auto ID sensor [B], a photodiode, is mounted on
the upper front frame. The sensor cover [C] has a hole in it to allow light to
fall directly onto the sensor. Sampling starts 10 millimeters from the leading
edge of the original and continues to 50 millimeters from the leading edge of
original in full size mode. The length of "A" and "B" will vary depending on the
selected reproduction ratio.
The lengths "A" and "B" in each reproduction ratio are calculated as follows:
A
=
10 mm
Reproduction Ratio
(
%
)
x 100
B
=
50 mm
Reproduction Ratio
(
%
)
x 100
The photosensor circuit converts the light intensity to a voltage. The detected
voltage is amplified and sent to the main PCB. The CPU stores the voltage of
each sampled point in RAM. It then computes the image density of the
original from the maximum sample voltage and changes the development
bias accordingly. (See page 2-31 for details.) The exposure lamp voltage is
constant regardless of the image density of the original.
[A]
[C]
[B]
70 mm
B
Sampled area
A
FT4220/4222
2-16
STM
Summary of Contents for FT4215
Page 1: ...FT4220 4222 4215 SERVICE TRAINING MANUAL ...
Page 12: ...SECTION 1 OVERALL MACHINE INFORMATION ...
Page 28: ...8 AC POWER AND DC POWER DISTRIBUTION FT4220 4222 1 16 STM ...
Page 31: ...SECTION 2 DETAILED SECTION DESCRIPTIONS ...
Page 114: ...SECTION 3 DOCUMENT FEEDER ...
Page 138: ...SECTION 4 SORTER ...
Page 157: ...SECTION 5 DUPLEX ...
