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A. Outline
External device
Video controller
,BD
t
,SCNON APCIN i"DATA ,ENBL LON APCOUTiBDl
Figure 2-7
The DC controller receives the VIDEO
signal (/VDO) from the video conlroller and
sends it to the laser driver in the
laser/scanner unil as the /VDATA signal.
The laser driver lurns the laser diode on
and off according to the /VDATA signal
and generates the modulated laser beam
only when the VIDEO DATA ENABLE
signal
from the DC controller is
(/ENBId)
"L"
The laser activates the laser diode in
response to the AUTOMATIC POWER
CONTROL OUTPUT signal @PCOUT] when
the FORCIBLE LASER ON signal (/LON)
from the DC controller goes "L", delects the
laser beam with the pholodiode adjoining
the laser diode, and sends an output
proportional to the intensity of the laser
b e a m t o t h e D C c o n t r o l l e r a s t h e
AUTOMATIC POWER CONTROL INPUT
signal.
RF'CIN)
II
/"DO
,"SYNC
t
t
Photosensitive
drum
The DC controller controls the APCOU'I
signal to set the APCIN signal to the
specified value to stabilize the intensity of
the laser beam. (Control of laser beam
intensity: APC control)
The modulated laser beam is formed by
a collimator lens and a cylindrical lens into
a parallel beam that strikes the scanning
mirror, which is rotating at constant speed.
The beam is reflected from this mirror,
then brought to a focus on the photo-
sensitive drum by the focusing lens in front
of the scanning mirror. The path of the
beam passing through the focusing lens is
changed by a mirror.
As the scanning mirror rotates al
constant speed, the beam is scanned
across the photosensitive drum. which also
r o t a t e s a t c o n s t a n t s p e e d . A s t h e
photosensitive drum rotates, the laser
beam successively scans across its
surface. Thus the laser beam builds up the
latent image on the surface of the
photosensitive drum.
CHAPTERS
2-7
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