Scanner Drive; Driving The Scanner - Canon LBP-CX Series Service Manual

The drum is rotating at a constant speed. In the
time that the beam takes to cross the drum and
return to its original position, the drum's surface has
shifted downward 1/240 of an inch (240 raster lines/
inch model; about 106 µ), 1/300 of an inch (300
raster lines/inch model; about 8 5 µ), 1 /400 of an inch
(400 raster lines/inch model; about 64 µ).
To the front left of the drum is a small, station-
ary mirror which reflects the beam to the beam
position sensor, which then sends the reflected beam
through an optic fiber to the photodiode of the
horizontal sync generator (a part of the DC controller
PCB). The horizontal sync generator produces a beam
detect pulse (IBD) just before each line is scanned.
The IBD pulse informs the microcomputer in the
printer that the laser beam is at home position.
C. Scanner Drive
r------------------------,
: . Scanner
I
1
S~annmg
motor
I
I
mirror
I
l
Scanner
SCi\i5N
DC
I
driver (SCANNER controller
: :DRIVE
: Scanner •command)
L ____
u_n~t_
_______________
J
Figure 2-8 Driving the scanner
The heart of the scanner unit is a mirror with six
rectangular faces of equal size spaced equally around
an axis. (It is a regular hexagon when viewed from the
end.) It is manufactured with extreme precision. This
mirror rotates at a carefully controlled speed and
deflects the stationary laser beam across the rotating
drum. The scanner mechanism that provides such
precise rotation is a self-contained unit. When required
for making a printing sequence, the DC controller
outputs a TRUE SCNON, command and the scanner
driver generates a TRUE SMD signal to cause the
scanner motor to rotate, turning the scanning mirror.
COPYRIGHT
©
BY CAllOll lllC. CANON LBP·CX SERIES REY.2 JULY 1985 PRINTED IN JAPAll (IMPRIME Aii jiiPOll)
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