November 2003 © TOSHIBA TEC 8 - 5 e-STUDIO350/450 LASER OPTICAL UNIT
8
(3) f
θ
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 sur-
face 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 f
θ
lenses help to cor-
rect this difference, making all the dot-to-
dot pitches equal on the drum surface.
b. Face tilt correction
The reflecting face of the polygonal mirror
is tilted slightly to one side against the per-
fect 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.
Fig. 8-203
Fig. 8-204
Wider
Narrower
Drum
f
Ø
Lens-1
f
Ø
Lens-2
Same intervals
Mirror plane is tilted. Deviation
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