Laser Exposure; Overview - Gestetner A294 Service Manual

2.4 LASER EXPOSURE

2.4.1 OVERVIEW

[A]
This machine uses four laser diodes to produce electrostatic images on an OPC
drum. The four parallel beams write four lines at once.
The laser diode unit converts image data from the SICU board into laser pulses,
and the optical components direct these pulses to the drum.
Exposure of the drum by the laser beam creates the latent image. The laser beam
makes the main scan while drum rotation controls the sub scan.
The strength of each beam is 10 mw on the drum surface at a wavelength of 785
nm.
The polygon motor speed is 29,528 rpm.
There are up to 4 image density levels for each pixel. To realize this, this machine
uses a form of pulse width modulation. In this machine, pulse width modulation
consists of the following processes:
• Laser diode pulse positioning
• Laser diode power/pulse width modulation
Laser diode power and pulse width modulation is done by the laser diode drive
board (LDR). Briefly, the width of the laser pulse for a pixel depends on the output
level (from 0 to 3) required for the pixel.
There are two fan motors, the polygonal motor cooling fan [A] and LDB cooling fan
[B], for removing heat in the laser unit.
SM
CÓPIA NÃO CONTROLADA
[B]
2-33
CÓPIA NÃO CONTROLADA
LASER EXPOSURE
A294D103.WMF
A294/A295