Epson EPL-N2050 Service Manual page 51

EPSON EPL-N2050
DRIVE & ELECTROPHOTOGRAPHICS
ROS Assy: The ROS (Raster Output Scanner) Assy is the laser
and the scanning hardware. The ROS is made up of
three major components: the Laser Diode Assy, the
Scanner Assy, and the PWBA SOS.
LD Assy (Laser Diode Assy):
Converts electrical signals into optical signals. The
LD Assembly generates the laser beam and
maintains the laser output power at a constant level.
Scanner Assy:
Routes the laser beam to the drum, and scans it
across the drum surface. The Scanner Assy consists
of a fifteen sided Polygon Mirror that is attached to
the Scanner Motor. The Motor rotates at a constant
speed. The spinning Polygon Mirror reflects the
beam, through a series of lens and mirrors, onto the
rotating drum surface. The movement of the
spinning Polygon Mirror scans the beam from one
side of the drum to the other; one scan line per
mirror facet. This process repeats until the controller
stops sending image data to the laser.
The Scanner Motor uses a phase-locked loop (PLL)
for speed control.
The PLL compares the phase of the falling edge of
the output signal from the Schmitt frequency
generator (FG) with the rising edge of the Clock
Signal (CLK). The output of the PLL is a voltage that
is proportional to the differences in the phase of FG
and CLK. The output is the phase detect (PD).
PD pulse duration indicates the amount of signal
deviation observed. The frequency generator
generates 15 pulses during each revolution of the
Scanner Motor. A smoothing filter, using an
integrating amplifier, converts the PD signal into a
Operating Principles Overview
voltage value. The voltage is used as the feed-back
to control the speed of the motor.
The Scanner Motor is driven by a three-phase, full-
wave, linear drive. The current to the motor coil is
switched by a Hall amplifier matrix that uses the
signals from the PD to signal when to switch
phases.
The signal /SCN MOT ON, from the PWBA HKB
MCU, switches the Scanner ON. The signals SPI1
and SPI2 select a ratio of frequency division of the
Clock signal. This ratio switches the resolution of
the scanned image. The signals are always at HIGH,
so the resolution cannot be switched.
PWBA SOS (Start Of Scan):
A sensor that is in-line with the scanning laser
beam. The laser beam strikes the PWBA SOS at the
start of each scan to let the printer control circuitry
know that a new scan is beginning.
Revision B
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