Phaser 4500/4510 Service Manual 2-19
Theory of Operation
Laser Assembly
The laser assembly scans the surface of the drum with a laser beam. The
laser assembly consists of three components: the laser diode (LD) assembly,
the scanner assembly, and the start of scan (SOS) board.
Laser diode (LD) assembly The LD assembly produces a laser beam that is
turned on and off according to the print data signal. A single LD is used for
600 dpi, and a dual LD is used for 1200 dpi, generating one beam for 600 dpi
and two beams for 1200 dpi.
Scanner assembly This assembly consists of a 12-sided polygonal mirror
mounted on the shaft of the scanner motor. As this mirror rotates, it reflects
the beam onto the drum surface through lenses and mirrors to scan the beam
across the drum.
Start of scan (SOS) board When the laser beam strikes the sensor on the SOS
board, the signal generated indicates the initial position of the scan. The initial
position where a scan is started on each line is detected. Depending on the
print resolution selected, either one beam creates one line, or two beams
create two lines at a time.
When the laser beam scans from one end of the drum surface to the other
while being turned off and on, one line of a latent image is created. The
resolution in the scanning direction (from right to left) is determined by the
rotational speed of the scanner motor and by the speed at which the laser is
modulated. The resolution in the process direction (from top to bottom) is
determined by the number of the scan beams and the rotational speed of the
print drum.
Conceptual Diagram of Image Creation by Scanning
s4500-011
Paper Path
600 Dots/Inch
600 Scans/Inch
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