HP 4550 Service Manual - Page 109

Transfer During transfer, the toner image is transferred from the drum surface to the ITB (primary transfer) and then from the ITB to the paper (secondary transfer). Primary transfer The ITB has a primary transfer roller that provides a positive bias that pulls the toner image from the drum to the ITB. This process is repeated four times (one time for each toner cartridge). The positive bias applied by the transfer roller increases with each pass to compensate for increasing layers of toner. As shown in Figure 5-6, the toner particles still maintain their negative charge. Only the transfer belt is charged positively. Figure 5-6 Primary transfer Secondary transfer Once the entire print image is on the intermediate transfer belt, the secondary transfer roller is lifted into position. At the appropriate time, a sheet of media is pulled into the transfer area. With the secondary transfer roller biased at a positive potential, the toner on the ITB is pulled onto the media as the ITB passes over the secondary transfer roller. C7085-90921 Chapter 5 Theory of operation 107