BROTHER HL-1660
Manual de Servicio

3.2.2

Developing stage Development places particles of toner onto the areas of the drum that have been cleared of charge by the laser beam. This makes a visible image. This printer uses the toner projection development method with a single-component toner.

Step 3

Development
Blade

Photosensitive drum

Stirrer

AC bias DC bias

Developing cylinder Cylinder Magnet

Figure 2.11 Note: The charges on the light areas on the photosensitive drum are shown as positive in this figure. Actually they are negative, but they are more positive than the developing cylinder and explanation is simplified by regarding them as positive. As shown in Figure 2.11, the developing unit consists of a developing cylinder and 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 by friction due to the rotation of the 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 onto them. This is called toner projection, and the latent image on the drum becomes visible.
Developing cylinder surface potential +V 0
Voltage (V)

Drum surface potential (exposed area) DC bias

-V Time t

Drum surface potential (unexposed area)

Figure 2.12 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 IMAGE DENSITY ADJUSTMENT signal (sent from the Engine CPU to the high-voltage power supply) changes the DC bias, and thus the potential difference between the cylinder and drum. This changes the density of the print. This printer has a stirring mechanism to supply toner in the cartridge smoothly to the cylinder. II - 8