HP LaserJet 4100 Manuel de service télécharger pdf (Page 115)

EN Chapter 5 Theory of operation 113

Developing the image

The developing process develops the latent electrostatic image into 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 not exposed to laser light.

This AC potential improves density and contrast.

Figure 24. 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.

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HP LaserJet 4100 Manuel de service Page 115