HP LaserJet M9040/M9050 Service Manual - Page 154

Image formation system The image formation system consists of the print cartridge, the transfer charging roller, and the fuser. When the formatter sends a print command, the image formation system completes the following process: 1. The main motor rotates the photosensitive drum, the primary charging roller, the developing cylinder, the transfer charging roller, and the pressure roller. 2. The primary charging roller applies a uniform negative charge to the photosensitive drum surface. 3. The laser beams, modulated by signals from the formatter, focus on the photosensitive drum surface to form a latent image. 4. Toner on the developing cylinder converts the latent image into a visible image, which is transferred onto media by the transfer charging roller. 5. The fuser applies heat and pressure to the toner image on the media to make the image permanent. 6. The cleaning blade scrapes residual toner from the photosensitive drum. 7. The primary charging roller applies a new charge to the photosensitive drum for the next image. Figure 5-31 Image formation process The image formation process Table 5-12 Image formation process Step process Conditioning (primary charging) The primary charging roller, which is made of conductive rubber, is located inside the print cartridge. An AC bias applied to it erases residual charges from the previous image. Then a negative DC bias applied to it creates a uniform negative potential on the photosensitive drum. Writing Two laser diodes project laser beams onto a rotating scanning mirror. As the scanning mirror rotates, it reflects the beams through a set of focusing lenses and onto another mirror, which reflects the beams through a slot in the top of the print cartridge and onto the photosensitive drum. The beams sweep from left to right on the drum discharging the negative potential wherever they strike the surface. This creates the latent electrostatic image on the drum. Developing The developing drum inside the toner cartridge receives a negative charge from the negative DC supply and charges the toner as it rotates. With the negative charge, the toner is attracted to the 136 Chapter 5 Theory of operation ENWW