Canon PC720 Service Manual - Page 72

measurements

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OPERATIONS AND TIMING 2. Operation To measure the density of an original, the scanning lamp is turned on at a specific intensity to expose the original during initial rotation with the scanner at the home position. The light reflected by the area shown in Figure 3-317 is checked by the AE sensor (photodi- ode), whose output is amplified and sent to the microprocessor on the DC controller PCB as the AE signal. The microprocessor on the DC controller PCB checks the AE signal four times, and averages the measurements to compute the developing DC bias which best matches the averaged density of the original; it then sends the developing DC bias signal and the developing DC bias on signal to the microprocessor on the composite power supply PCB. The microprocessor on the composite power supply PCB generates the developing DC bias control signal (DCBPWM) based on the value of the DC bias. 20 mm 28 mm (approx.) (approx.) Center of imAge 56 mm (approx.) : AE sensor reading area Figure 3-317 3. Basic Sequence of Operations (AE measurement) Copy Start key ON STBY INTR SCFW SCRV SCFW iSCRV LSTR Main motor (M-I) Scanner motor (M2) Scanning lamp (FU) AE sensor input "sRuevmerse Pre-heating 11 Figure 3-318 3 - 32 COPYRIGHT © 1994 CANON INC. CANON PC7201740501170 REV.O AUG.1994 PRINTED IN JAPAN (Ink AU JAPAN)

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OPERATIONS
AND
TIMING
2.
Operation
To
measure
the
density
of
an
original,
the
scanning
lamp
is
turned
on
at
a
specific
intensity
to
expose
the
original
during
initial
rotation
with
the
scanner
at
the
home
position.
The
light
reflected
by
the
area
shown
in
Figure
3-317
is
checked
by
the
AE
sensor
(photodi-
ode),
whose
output
is
amplified
and
sent
to
the
microprocessor
on
the
DC
controller
PCB
as
the
AE
signal.
The
microprocessor
on
the
DC
controller
PCB
checks
the
AE
signal
four
times,
and
aver-
ages
the
measurements
to
compute
the
developing
DC
bias
which
best
matches
the
averaged
density
of
the
original;
it
then
sends
the
developing
DC
bias
signal
and
the
developing
DC
bias
on
signal
to
the
microprocessor
on
the
composite
power
supply
PCB.
The
microprocessor
on
the
composite
power
supply
PCB
generates
the
developing
DC
bias
control
signal
(DCBPWM)
based
on
the
value
of
the
DC
bias.
20
mm
28
mm
(approx.)
(approx.)
Center
of
imAge
56
mm
(approx.)
:
AE
sensor
reading
area
Figure
3-317
3.
Basic
Sequence
of
Operations
(AE
measurement)
Copy
Start
key
ON
Main
motor
(M
-
I)
Scanner
motor
(M2)
Scanning
lamp
(FU)
AE
sensor
input
STBY
INTR
SCFW
SCRV
SCFW
iSCRV
LSTR
Reverse
"sum
Pre
-heating
11
Figure
3-318
3
-
32
COPYRIGHT
©
1994
CANON
INC.
CANON
PC7201740501170
REV.O
AUG.1994
PRINTED
IN
JAPAN
(Ink
AU
JAPAN)