EXP Computer C4077-90960 - Manual (Page 101)

Image Writing
During the writing process, a modulated laser diode projects a beam onto a
rotating six-sided scanning mirror. As the scanning mirror rotates, the
beam is directed through a set of focusing lenses to a direction changing
mirror which reflects it through a slot on the top of the toner cartridge, and
onto the photosensitive drum. The beam sweeps across the drum and
discharges the negative potential wherever it strikes the surface. This
creates a latent (invisible) electrostatic image, which is developed into a
visible image as the drum rotates (see Figure 5-10).
Image Writing
Because the beam is sweeping the entire length of the drum and the drum
is rotating, the entire surface area of the drum can be covered. The speed of
the scanner motor (which turns the scanning mirror) and the speed of the
main motor (which turns the drum) are synchronized, and each successive
sweep of the beam is offset 1/600th of an inch. The beam can be turned on
and off to place a dot of light every 1/600th of an inch. This is how the
printer achieves its 600 x 600 dpi resolution. After the writing process, the
drum surface has a latent (invisible) electrostatic image.
At the end of each sweep, the beam strikes the beam detect lens, generating
the Beam Detect Signal (BD). The BD signal is sent to the DC Controller,
where it is converted to an electrical signal used to synchronize the output
of data (VDO) for one sweep (scan line) and to diagnose problems with the
laser diode or scanner motor.
Figure 5-10
5-16 Functional Overview