Toshiba e-STUDIO163 Service Manual page 116

3) fT lenses 1 and 2
These two lenses perform the following adjustment on the laser beams reflected by the polygonal
mirror.
a. Uniform-velocity scanning
Since the polygonal mirror is rotating at a uni-
form 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 fT 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 mirror is
tilted slightly to one side against the perfect
vertical. Horizontal deviation of the laser light
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 (SNS)
The laser light which is started to be scanned from one of the reflected plane of the polygonal mirror
is reflected by the H-Sync returning mirror and enters the PIN diode on the H-Sync signal detection
PC board (SNS). The primary scanning synchronizing signal is generated based on this reflection.
5) Slit glass
Slit glass is located where the laser beams are output from the laser optical unit, and it protects the
unit from dust.
e-STUDIO163/203
LASER OPTICAL UNIT
Mirror plane is tilted.
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8 - 4
Drum
fθ Lens-1
fθ Lens-2
Same intervals
Fig. 8-5
Fig. 8-6
Wider
Narrower
Deviation