Toshiba DP1600 Service Manual page 149

(3) Lenses 1 and 2
These lenses perform the following compensations on the laser light reflected by the polygonal mirror.
Equidistant scanning
The reflected laser light on the polygonal
mirror is scanned at the same angle, be-
cause the polygonal mirror is rotated at the
same speed. That is, when the scan is com-
pleted, the dot-pitch on the drum becomes
the wide spaces at the both edges and the
narrow spaces in the center. So, in order to
regularize intervals of dots, laser light is
compensated so that it is scanned on the
drum at equal speeds.
Pyramidal error compensation
The reflected face on polygonal mirror is
tilted in either of two directions for the per-
fect vertical direction. Deviation of the laser
light (for the perfect horizontal) caused by
this reflected face's pyramidal error is com-
pensated.
The section's shape of the laser beam on
the drum is compensated.
(4) HSYNC detection
The laser light, which is scanned by the any reflected face on the polygonal mirror, is reflected by the
HSYNC detection mirror, and becomes incident to the PIN diode on the laser drive PWA. Then, the
primary scanning synchronizing is formed by detection of the laser light.
1600/2000/2500 PRINTING
Fθ lens 1
8 - 4
Wide
Narrow
Fθ lens 2
Equidistant
Fig. 8-2-3
Mirror plane is tilted Deviation
Fig. 8-2-4
December 2000 © TOSHIBA TEC
09-02-03
09-02-04