Brother DCP-8020, Service Manual

Page: 80 / 353

CHAPTER 3 THEORY OF OPERATION
3-24
2.7.3 Developing
Developing causes the toner to be attracted to the electrostatic image on the drum so as to
transform it into a visible image.
The developer consists of a non-magnetic toner. The development roller is made of
conductive rubber and the supply roller (which is also made of conductive sponge) rotate
against each other. The toner is charged and carried from the supply roller to the development
roller. The toner adheres to the development roller and is conveyed to the photosensitive drum
at an even thickness controlled by the blade. The toner is nipped between the development
roller and the drum and developed onto the latent image on the drum. The electrostatic field
between the drum and the development roller, which is DC-biased from the high-voltage power
supply, creates the electrostatic potential to attract toner particles from the development roller
to the latent image area on the drum surface.
Fig. 3-37
2.7.4 Transfer
(1) Transfer process
After the drum has been charged and exposed, and has received a developed image, the
toner formed is transferred onto the paper by applying a negative charge to the back of
the paper. The negative charge applied to the paper causes the positively charged toner
to leave the drum, and adhere to the paper. As a result, the image is visible on the paper.
(2) Cleaning process of transfer roller
If the toner is not transferred onto the paper perfectly it is possible that there may be
residual toner on the drum which will adhere to the transfer roller. The transfer voltage
changes to a positive voltage during non-printing rotation of the drum. Therefore the
transfer roller is cleaned by returning the positively charged toner adhering to the transfer
roller onto the photo-conductive drum.
Photosensitive drum
Corona wire
Development roller
Blade
Supply roller Transfer roller