Oki B6200 Maintenance Manual page 623

ROS ASSY
The ROS (Raster Output Scanner) scans the surface of the drum with a laser beam. The ROS
ASSY consists of the following three components, i.e., LD (Laser Diode) Assembly, Scanner
Assembly, and SOS PWB.
• LD Assembly
The LD Assembly produces a laser beam. This beam is turned ON and OFF according to a print
data signal.
The maximum nominal output of the semiconductor laser diode used as the laser light source, is
listed below.
34PPM
24PPM
• Scanner Assemblyy
The Scanner Assembly consists of a Polygon Mirror (12 facets for 34PPM, and 6 facets for
24PPM) and a Scanner Motor. The Polygon Mirror is mounted to the shaft of the Scanner Motor.
The Scanner Motor rotates the Polygon Mirror at a specified speed. The rotating Polygon Mirror
reflects the beam to the drum surface through lenses and mirrors, to scan the beam from one
end to the other of the drum. One scan is made with one facet of the mirror.
The Scanner Motor is driven by three-phase, full-wave current linear drive. The current through
the winding of each phase is switched by a Hall amplifier matrix. The signal from the phase
detection terminal of the Motor is used.
• SOS PWB
When the laser beam hits the SOS Sensor of the SOS PWB, the beam is converted into an
electrical signal (SOS signal), and the initial position where a scan is started on each line is
detected.
When the laser beam is scanned across the drum surface from one end to the other while turning
ON and OFF the beam, one line of latent image is created. If the scanning by the laser beam is
repeated while rotating the drum, a two-dimensional image is created. The resolution in the
scanning direction (from right to left) is determined by the rotational speed of the Scanner Motor and
by the speed at which the laser is adjusted. The resolution in the process direction (from top to
bottom) is determined by the rotational speed of the Scanner Motor. (If the scanning speed is
increased, the next row to be scanned can be started earlier accordingly.)
Conceptual diagram of image creation by scanning
600dpi Mode
10mW
5mW
6 - 19
Chapter 6 Principle of Operation
1200dpi Mode
10mW
10mW