- HP All-in-One Printer Manual

120 Theory of operation Q2431-90912
Electrostatic latent-image formation
Forming the electrostatic latent image on the photosensitive drum requires applying a uniform
negative charge (bias) to the surface of the drum and then the exposing it to the laser beam. The
laser beam naturalizes the section of the drum so that it attracts toner during the developing
operation.
Primary charging
The conditioning process consists the primary charging roller applying a uniform negative charge
on the surface of the drum. The primary charging roller is coated with conductive rubber that has
an ac bias applied. This erases any residual charges and maintains a constant drum surface
charge. The print density setting modifies the amount of dc voltage.
Figure 51. Primary charging of the photosensitive drum
ac bias
dc bias
Primary charging roller
Photosensitive drum