3.5 ROS ASSY
3.5.1 Major functions
ROS ASSY is an exposure unit that generates laser beams to form electrostatic latent image on the
In this manual, the ROS ASSY is referred to as ROS.
The ROS mainly consists of the following parts:
• LD PWB
• Scanner ASSY
• SOS PWB
• LD PWB
The LD PWB is comprised of four LDs (laser diodes) corresponding to Y, M, C, and K.
Each LD converts the electric signals of incoming image data into laser wave or pulse. In order to
stabilize the laser light quantity during formation of an electrostatic latent image, the LD PWB
always monitors the laser light quantity to adjust it to the appropriate level. This is called "APC
(auto power control)".
• Scanner Assy
The Scanner Assy is comprised of the Scanner Motor that rotates at a constant speed and the
Polygon Mirror that is mounted on the motor shaft.
The laser light output from the LD is irradiated onto the Polygon Mirror via the Mirror.
The Polygon Mirror, provided with six reflecting mirror faces, changes the reflection angle of the
laser light as it rotates by the Scanner Motor, thereby allowing the laser light to scan the drum
along its axial direction. Scanning is performed using one reflecting mirror face for each line.
• SOS PWB
The SOS sensor on the SOS (start of scan) PWB converts an incoming laser beam, upon detec-
tion, to an electric signal as the reference signal for starting scanning and transmits this signal to
the PWBA MCU.
The SOS sensor signals are used to synchronize the starting point of the laser-beam scanning
with the starting point of the image writing.
The laser light reflected from the Polygon Mirror reaches the drum surface via the Lens, Mirror,
and Window. The Lens corrects aberration, the Mirror secures an optical path, and the Window
prevents foreign matters from entering the ROS.
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Chapter 6 Principles of Operation