HP LaserJet 5000gn User Manual download pdf (Page 115)

5-24 Functional Information

Writing the Image

During the writing process, a modulated laser diode projects the

beam onto the rotating six-sided scanning mirror. As the mirror

rotates, the beam reflects off the mirror, through a set of focusing

lenses, through a slot in the rear of the Toner Cartridge, and onto the

photosensitive drum. The beam sweeps the drum from left to right,

discharging the negative potential wherever the beam strikes the

surface. This creates a latent electrostatic image, which later is

developed into a visible image.

Figure 5-11 Writing the Image

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 by

1/1200th of an inch. The beam can be turned on and off to place a dot

of light every 1/1200th of an inch. This is how the printer achieves its

1200x1200 dpi resolution. After the writing process, the drum surface

has an invisible (latent) 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 Board, 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.

Photosensitive Drum

BD Mirror

BDIC PCB

BD Lens

Focusing

Lens

Scanning Mirror

(Hexahedron)

Scanner

Motor

Laser Driver

Cylindrical Lens

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HP LaserJet 5000gn User Manual Page 115