Xerox Phaser 6128MFP Service Manual page 78

Theory of Operation
2-24
The Laser Unit is an exposure unit that generates laser beams to form an
electrostatic latent image on the drum surface. The Laser Unit consists of the
following components: laser diode (LD) board, scanner, start of scan (SOS) board,
lenses, mirrors, and windows.
• Laser Diode Board
The laser diode board consists of four laser diodes (LDs) corresponding to C,
M, Y, and K. Each LD converts the electric signals of incoming image data into
laser waves. In order to stabilize the laser light quantity during formation of
an electrostatic latent image, the laser diode board monitors the intensity of
the laser beam to adjust it to the appropriate level. This process is called auto
power control (APC).
• Scanner
The scanner consists of a scanner motor that rotates at a constant speed and
a polygon mirror that is mounted on the motor shaft. The laser light output
from the LD is directed onto the polygon mirror. The polygon mirror, provided
with six reflecting mirror faces, changes the reflection angle of the laser light
as it rotates, thereby allowing the laser light to scan the drum along its axial
direction. Scanning is performed using one reflecting mirror face for each line.
• Start of Scan (SOS) Board
The SOS Sensor on the SOS Board converts incoming laser beam, upon
detection, to an electric signal as reference for starting scanning, and
transmits this signal to the MCU Board. The SOS sensor signals are used to
synchronize the starting point of the laser beam scanning with the starting
point of the image writing.
• Lenses
The laser light reflected from the polygon mirror reaches the drum surface via
the lenses, mirror, and window. The Lenses correct aberration.
• Mirror
The mirror directs the laser beam to the Imaging Unit.
• Window
The window is the area where the laser beams exit the Laser Unit.
Phaser 6128MFP Service Manual