Canon LBP 2460 Service Manual - Page 84

CHAPTER 2 As shown in Figure 2-4-8, the developing unit consists of a developing cylinder and a rubber blade. The developing cylinder rotates around a fixed internal magnet. The single-component toner consists of magnetite and a resin binder, and is held to the cylinder by magnetic attraction. The toner is an insulator, and acquires a negative charge from friction of the rotating cylinder. The areas on the drum that were exposed to the laser beam have a higher potential (are less negative) than the negatively charged toner particles on the developing cylinder. When these areas approach the cylinder, the potential difference projects the toner particles to them. This is called toner projection, making the latent image on the drum visible. Voltage (V) Developing cylinder surface potential + V Drum surface potential (exposed area) 0 DC bias - V Time t Drum surface potential (unexposed area) Figure 2-4-9 An AC bias is applied to the developing cylinder to help project the toner particles to the drum surface and improve the contrast of the printed image. The center voltage of the AC bias (1600 Vp-p) varies with the DC bias voltage. The change in the DC bias changes the potential difference between the cylinder and drum so the density of the print can be adjusted. It can be done through a command from an external device. This printer has a stirring mechanism in the cartridge to ensure that toner is applied smoothly to the cylinder. 3. Transfer stage In the transfer stage, the toner image is transferred from the drum surface to the paper. Step 4 Transfer Photosensitive drum Paper Transfer charging roller Figure 2-4-10 A positive charge applied to the back of the paper attracts the negatively charged toner particles to the paper. 2 - 38