HP 4600 Service Manual - Page 159

Electrostatic-latent-image-formation block The image formation process begins in the electrostatic-image formation block (see Figure 5-14 Image-formation process), where the electrostatic latent image is formed on the photosensitive drum. This block consists of three steps: ■ Primary exposure ■ Primary charging ■ Laser-beam exposure After the last step is complete, areas of the drum surface that have not been exposed to the laser beam retain a negative charge. The areas that have been exposed to the laser are neutralized. This neutralized image is called an electrostatic latent image because it is invisible to the eye. Step 1: Primary exposure To prepare for primary charging, light from the primary exposure LED strikes the photosensitive drum surface. This eliminates any residual charge on the drum surface in order to avoid inconsistent charge density. Figure 5-20 Primary exposure illustrates this step. Figure 5-20 Primary exposure ENWW Image-formation system 143