HP 2100 Service Manual - Page 93

Writing Stage Figure 5-11 Laser Scanner System At the writing station, a laser beam focuses laser light onto the photosensitive drum to discharge the drum's negative potential. This creates a latent electrostatic image, which later is developed into a visible image. A small laser diode beam shines onto a rotating, 6-sided mirror. As the mirror rotates, the beam reflects off the mirror and sweeps the page from left to right. A set of lenses and mirrors focuses the horizontal sweeping beam through the laser beam access slot in the rear of the toner cartridge and onto the photosensitive drum. Because the beam sweeps the entire length of the drum while the drum rotates, the entire circumference of the drum can be covered. Each successive sweep of the beam is offset 1/1200th of an inch. This is how the printer achieves its 1200 dpi resolution. At the beginning of each sweep (before the beam reaches the drum), the beam detect mirror reflects the beam. The momentary pulse of light goes to the Engine Controller Assembly, which converts the light to an electrical signal used to synchronize other activities in the printer and to diagnose problems with the laser scanner assembly. Portions of the drum not exposed to the laser still contain the uniform negative potential (placed there by the primary charging roller), but those portions exposed to light have been discharged to ground to form the latent electrostatic image. C4170-90959 Image Formation System 83