Sharp UX-4000M Service Manual - Page 51

STEP 3 (Development): Toner is attached to the latent electrostatic images on the O PC dr um t o form v i s ible images. UX-4000MU FO-2950MU/C On the other hand, when an area of OPC drum which was not exposed to the laser beam and did not lose its charge comes in contact with the developing roller, any residual toner attached to the OPC drum is transferred to the developing roller which is more positively charged. As a result, unnecessary toner on the OPC drum is collected by the developing unit. The operating principle for that case is contrary to that for transfer of toner from the developing roller to the OPC drum surface. (The electric field energy direction is contrary.) STEP 4 (Transfer): Visible images of toner on the OPC drum are transferred to the paper. Developing roller Doctor : Toner (Negatively charged) Scraper Toner supply roller 100V OPC drum Exposed area (Exposed to laser beam) Non-exposed area (Not exposed to laser beam) Grounding sheet DC -310V OPC drum Aluminum layer (Drum base) CGL CTL Paper Aluminum layer (Drum base) CGL CTL Fig. 14 Toner is transported to the scraper area by the toner supply roller and the developing roller. The quantity of toner to be transported to the doctor section is controlled by the scraper. Toner transported to the doctor section is then passed between the developing roller and the doctor to form a thin toner layer on the developing roller by the pressure applied by the doctor. When toner passes between the developing roller and the doctor, it is charged negatively by friction. When an area of OPC drum which was exposed to laser beam and lost its charge comes in contact with the developing roller, toner moves from the developing roller to the OPC drum surface. The principle of toner movement from the developing roller to the OPC drum surface is as follows. The bias voltage of DC-310V is applied to the developing roller. Toner is charged negatively by the difference (electrical energy) between the bias voltage and the OPC drum surface potential and is attracted to the OPC drum surface which is positively charged. At that time, the potential of the area of the OPC drum which was exposed to the laser beam and lost its charge is higher than that of the developing roller. Transfer roller DC+3500V AC600V(P-P) Fig. 15 The high voltage of DC+3500V plus AC600V (P-P) is applied to the transfer roller to generate electric discharge between the roller and the OPC drum, generating positive and negative charges. Positive charges are attracted to the OPC drum and attached to the paper transported between the transfer roller and the OPC drum. Therefore the paper has a strong positive charge. Negatively charged toner on the OPC drum is attracted by the paper which is positively charged, and the visible images of toner are transferred onto the paper. 3 - 8