HP 4600 Service Manual - Page 169

Photosensitive drum cleaning A cleaning blade inside the print cartridge clears the remaining toner on the photosensitive drum as the drum rotates past the blade. This waste toner is moved into the waste-toner container in the top of the print cartridge. Figure 5-29 Drum cleaning illustrates this step. Figure 5-29 Drum cleaning During the printing process, toner adheres to the primary charging roller and the toner charging roller. To prevent print quality defects, this toner needs to be cleaned. The DC controller alternately applies negative bias in different values to the primary charging roller and the toner charging roller when one of the following occurs: ■ The printer is turned on ■ The covers are closed ■ At the start of a print operation ■ After printing a specified number of pages Applying bias removes the toner from each roller. The toner on the primary charging roller is transferred to the photosensitive drum, and the toner on the toner charging roller is transferred to the developing cylinder. Then the cleaning blade scrapes the toner on the photosensitive drum into the waste-toner container, as described above. The toner on the developing cylinder is returned to the toner case. Figure 5-30 Primary charging roller and toner charging roller cleaning illustrates this process. ENWW Image-formation system 153