Sharp FO IS125N Service Manual - Page 78

FO-IS125N 7.6. Image forming operation STEP 1 (Cleaning, Charging): Residual toner the OPC drum is stirred and negative charges are scattered evenly on the OPC drum. (The OPC drum surface is evenly charged.) The main charger is a rotating brush roller. The main charger removes residual toner from the OPC drum by its rotating sweeping action and causes it to stick to the brush. At the same time, a high voltage of -950V is applied to the main charger roller to generate a discharge of electricity between the roller and the OPC drum, generating positive and negative charges. The negative charges are attracted to the OPC drum, and evenly distributed on the OPC drum. (The OPC drum surface is evenly charged.) STEP 2 (Exposure): Laser beam scanning light corresponding to the print data is radiated on the OPC drum. Positive and negative charges are generated in the OPC drum CGL exposed with the laser beam. Positive charges generated in the CGL are attracted toward the OPC drum surface (negative charges), and negative charges toward the aluminum layer (positive charges). Therefore, the positive and negative charges neutralize each other in the laser-exposed area of the OPC drum surface and the aluminum layer, decreasing the potential of the OPC drum surface. The area which is not exposed to laser beam has no change, and the OPC drum surface remains negatively charged to keep a high potential. As a result, latent electrostatic images are formed on the OPC drum. Main charger brush Residual toner AC760V (P-P) OPC drum CTL Aluminum layer (drum base) CGL DC-950V Fig. 12 Laser beam Exposed area CTL CGL Aluminum layer (Drum base) Non-exposed area CTL CGL Aluminum layer (Drum base) Fig. 13 3 - 8