Printhead Unit (Exposure Section) - Epson EPL N2700 Service Manual

EPL-N2700

2.1.5 Printhead Unit (Exposure Section)

The print head unit incorporates a laser diode that emits the laser beam
corresponding to the print image data. The spot of the laser beam
emitted from the laser diode is shaped in a circle through the collimator
lens. Then, it is applied to the heptagonal polygon mirror via the
cylindrical lens. The polygon mirror is turned by the polygon motor in the
print head unit in the direction as shown by the arrow.
The reflected laser beam by the rotating polygon mirror passes the
three lenses, producing a parallel scanning laser beam. The scanning
laser beam scans on the PC drum from left to right for producing an
electrostatic latent image on the surface of the PC drum.
Collimator Lens
Cylindrical Lens
Rotational
direction
Heptagonal Polygon
Mirror
Figure 2-19. Printhead Unit Mechanism
Operating Principles
Laser Diode
SOS Sensor
Scanning direction
PC Drum
Printer Mechanism Operating Principles


Operation of the SOS Sensor
To maintain the printing density constant, it is required to emit a
laser beam at constant laser power. To control the laser power to be
constant is called APC (Automatic Power Control).
The SOS sensor incorporated in the print head unit is used to detect
whether the laser power reaches certain laser power for printing.
The SOS sensor is located outside of the printing area. When
printing starts, it takes 1 or 2 scans to obtain the SOS sensor output.
During printing, the SOS sensor output is monitored in every
scanning for controlling the laser power constant.
Revision A
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