Canon LBP-860 Service Manual page 48

2. Control of laser beam intensity (APC
control]
The CPU performs aulomalic power control
diode light. This control can
be classified inlo two types: initial APC and
between-page APC.
a. Initial AE'C
intensity of the laser beam from zero to
The CPU sets Lhc FORCIBLE LASER
ON signal (/LON) Lo "I,", and at the
same time the CPU changes the APCOR
signal (coarse adjustment) and lets the
l o w v a l u e . A s lhe l a s e r currenl
increases. the laser diode (LD) begins
emitting light.
voltage is fed back Lo the CPU as the
signal (APCIN).
signal reaches 70% of the Larget value
CPU. The CPU then does
Lhe
and ends the initial APC when the
become almost equal Lo the larget
b. Between-page
Between-page APC is performed afler
being performed while waiting for the
area, Lo correcl variations in the
he laser printing.
during the unblinking period, described
writing on the image area of the
photosensitive drum.
The CPU sets the UNBLANKING
signal (UBL. used by IC202 and not
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A P C I N
t h e
output externally) to "H" and sets the
FORCIBLE LASER ON signal (/LON) to
The CPU then changes the APCOS
signal (fine adjustment]. compares the
input value of the APCIN signal with
the target value. and optimizes the
CHAPTER 2
2-11