Oce 3121 Technical & Service Manual page 196

Development
blade
Blade
The static image on the surface of the OPC is made visible by the application
of toner.
As shown in the figure , the developing assembly consists of a developing cyl-
inder (made of a fixed magnet and a cylinder rotating around it) and a magnetic
blade.
The main ingredients of the toner are magnetite and resins. The toner has insu-
lating properties and is charged to a negative potential by friction against the
cylinder.
The Océ 3121 deposits toner over the areas on the surface of the drum whose
charges have been neutralised by a laser beam (light areas); for this reason, the
polarity of the toner is negative, which is the same as the polarity of primary
charging.
blade
Blade
magnetic
Concentrated
field
magnetic field
magnet
Magnet
A concentrated magnetic field occurs from the magnet to the edge of the blade,
attracting toner.
Once inside the field, the toner becomes virtually immobile because of the
strong bond with the blade so that, when deposited, it forms an even, thin layer
on the cylinder.
An AC bias and a DC bias (negative component) are applied to the developing
cylinder and the blade at the same time (developing bias); the negative compo-
nent of the developing bias is stronger than the positive component.
DC bias
DC bias
During copying, toner is attracted to the image areas on the OPC. The latent
image is then a visible image created by the negatively charged toner. The ex-
cess toner is removed from the OPC. This is due to the positive bias on the de-
veloping roller and the surface potential on the OPC.
ed.1
cylinder
Cylinder
magnet
Magnet
developing cyl-
Developing
cylinder
inder
developer
Developer
Magnet
magnet
positive component
Positive component
negative component
Negative component
General operation 7