Oki B930 Service Manual page 21

ROS ASSY
The ROS ASSY-12 scans the drum surface with a laser beam. It consists of four main com-
ponents: LD (Laser Diode) PWB, ROS MOTOR, POLYGON MIRROR, and SOS PWB.
(1) LD PWB
The LD PWB generates a laser beam with the two LDs of LD1 and LD2. The beam is turned
ON or OFF according to a print data signal.
(2) ROS MOTOR / POLYGON MIRROR
The Polygon Mirror is mounted to the shaft of the ROS Motor, and is rotated at a high speed
by the ROS Motor. The mirror rotation shifts the incidence and reflection angles of a laser
beam to scan the laser beam in the drum axial direction. The laser beam reached the Poly-
gon Mirror passes through the Lens L1, Lens L2 and Window, and then arrives at the drum
surface.
(3) SOS PWB
When a laser beam hits the SOS Sensor on the SOS PWB, the beam is converted to an
electrical signal (SOS signal), and detects the initial position where a scan starts on each
line.
When a 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 scan-
ning direction (from right to left) is determined by the rotational speed of the ROS Motor, depend-
ing on how quickly the laser is adjusted. The resolution in the process direction (from top to
bottom) is determined by the rotational speed of the ROS Motor. (The higher the scanning speed
becomes, the earlier scanning of the next row can be started.)
Conceptual diagram of image creation by scanning:
CRU
2-12
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