HP Pro 4300 C9H70UT C9H70UT#ABA manual Developing the image

Developing the image

The developing process makes the latent electrostatic image a visible image on the drum. The developing unit consists of a metallic cylinder that rotates around a fixed magnetic core inside the toner cavity. Toner is a powdery substance made of black plastic resin bound to iron particles, which is uniformly attracted to the magnetic core of the cylinder.

The toner particles obtain a negative surface charge by rubbing against the developing cylinder, which is connected to a negative dc supply. The negatively charged toner is attracted to the discharged (exposed, grounded) areas on the drum. An ac potential is applied to the developing cylinder to decrease the attraction between the toner and the magnetic core of the cylinder, and to increase the repelling action of the toner against the areas of the drum that have not been exposed to the laser beam. This ac potential improves density and contrast.

Photosensitive

drum

Blade

Stirring unit

Stirring plate

Developing cylinder

Cylinder magnet

ac bias

dc bias

Figure 53. Developing the image

The print-density control in the print-quality menu adjusts the dc bias of the developing cylinder by changing the force of attraction between the toner and drum. A change in the dc bias causes either more or less toner to be attracted to the drum, which in turn either increases or decreases the print density. Both the primary and developer dc bias voltages are changed in response to the density setting.

122 Theory of operation Q2431-90912