Epson EPL-N1600 Service Manual page 47

EPSON EPL-N1600
XEROGRAPHIC MODULES
Rev. A
ROS ASSY: The ROS (Raster Output Scanner) Assembly
scans a laser beam on the drum surface. The
ROS Assembly consists of two major
components: PWBA LD and Scanner Assembly.
Basic Operation:
The Laser Diode (LD) of the PWBA LD emits
laser light. The LD is switched on and off
according to the print image signal during
printing. The power of the laser light is
monitored by the monitor circuit and controlled
to be a constant power. The laser light from the
LD is shaped and converged into a very thin
beam by means of a slit and a Cylinder Lens,
and directed to a Polygon Mirror. The Polygon
Mirror has six facets and is rotated at a constant
speed by the Scanner Motor. These facets
reflect the laser beam in turn as the Polygon
Mirror rotates. The laser beam reflected by the
Polygon Mirror passes through a Correction
Lens L1 and is reflected by a Mirror M1 onto the
drum surface, moving from one end of the Drum
to the other. The laser beam is thus scanned
one line by each facet of the Polygon Mirror.
LD Output Power Control:
The drive current of the LD is switched on and
off by the Current Switching Circuit in the LDD
(Laser Diode Driver) according to the print
image signal (/PDATA) from the engine control
circuit. The LD drive current while the LD is on is
precisely determined by the two DC voltage
signals (VLI and VL2) from HMCU. The laser
power is monitored using a monitor signal (MO),
Chapter 2 Operating Principles
48