Toshiba DP-5550, Руководство по обслуживанию, Страница: 156 / 404

e-STUDIO555/655/755/855 © 2009 - 2011 TOSHIBA TEC CORPORATION All rights reserved
LASER OPTICAL UNIT
7 - 8
7.2.3 f
θ
lenses 1 and 2
These two lenses perform the following adjustment on the laser beams reflected by the polygonal
mirror.
7.2.4 H-sync detection PC board (SNS board)
Laser beam which has started to be scanned from one of the reflected faces of the polygonal mirror is
reflected by the H-sync detection mirror and goes into the PIN diode on the H-sync detection PC board
(SNS). The primary scanning synchronizing signal is generated based on this reflected laser beam.
For the e-STUDIO755/855, the rudder sensor is attached to the H-sync sensor to space out evenly
(42.3 µm), the intervals of the secondary scanning of the 1st and 2nd beams by its detection value.
7.2.5 Laser driving board (LDR1/LDR2 board)
This control board has the following functions:
a. APC control function (adjusts disparity of the laser intensity caused by temperature)
b. Laser ON/OFF function
7.2.6 Slit glass
Slit glass is located where the laser beams are output from the laser optical unit, and it protects the unit
from dust.
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 f
θ lenses help to correct this difference,
making all the dot-to-dot pitches equal on the
drum surface.
Fig. 7-7
b. Face tilt connection
The reflecting face of the polygonal mirror is
tilted slightly to one side against the perfect
vertical.
Horizontal deviation of the laser beam which is
caused by the tilt is corrected.
Fig. 7-8
c. Sectional shape of laser beam
The shape of the laser beam spotted on the
drum is adjusted.
Wider
Narrower
Drum
f Lens-1
f Lens-2
Same intervals
Mirror plane is tilted.
Deviation