Toshiba e-STUDIO453 Service Manual page 161

(3) fθ lenses-1 and -2
These two lenses perform the following adjustment on the laser beam reflected by the polygonal
mirror.
a. Uniform-velocity scanning
Since the polygonal mirror is rotating at a
uniform velocity, the laser beam reflected
from the mirror scans over the drum
surface at a uniform angular velocity;
namely, the pitch between the dots on
the drum is wider at both ends than at
the center of the scanning range. The
fθ lenses help to correct this difference,
making all the dot-to-dot pitches equal on
the drum surface.
b. Face tilt correction
The reflecting face of the polygonal mir-
ror is tilted slightly to one side against the
perfect vertical. Horizontal deviation of
the laser beam which is caused by the tilt
is corrected.
c. Sectional shape of laser beam
The shape of the laser beam spotted on
the drum is adjusted.
(4) H-Sync signal detection PC board
The laser beam which is started to be scanned from one of the reflected plane of the polygonal
mirror is reflected by the H-Sync detection mirror and enters the PIN diode on the H-Sync signal
detection PC board. The primary scanning synchronizing signal is generated based on this reflec-
tion.
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fØ Lens-
Fig. 8-203
Mrror plane s tlted.
Fig. 8-204
8 - 5 e-STUDIO350/352/353/450/452/453
Wder
Narrower
Drum
fØ Lens-2
Same ntervals
Devaton
LASER OPTICAL UNIT
8