Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2001-06-26
2002-10-22
Ngo, Hoang (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S281000, C399S285000
Reexamination Certificate
active
06470153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing device and a developing method, and in particular to an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer, and a developing device and a developing method that are applied to such an image forming apparatus.
2. Description of the Related Art
Conventionally, as an electrophotographic method, there is a method of utilizing a photoconductive material to form an electric latent image on a photosensitive drum by various ways, subsequently developing the latent image with toner to visualize it, transferring a toner image on a transfer material such as a sheet depending on a situation, and then fixing the toner image by heat, pressure or the like to obtain a copy.
On the other hand, since improvement of image resolution, definition, and the like is currently required, development of a method of forming a thin layer of toner and an apparatus for the method is essential, and several measures have been proposed to fulfill the requirement.
In recent years, a contact single component developing method has been proposed, which performs development with a configuration for pressing against a surface layer of a photosensitive drum using a semiconductive developing roller or a developing roller having a dielectric layer formed on its surface.
Here, a schematic sectional view of a conventional image forming apparatus using a DC contact single component developing method is shown in FIG.
17
. In this method, a photosensitive drum
61
and a developing roller
65
abut each other. First, the photosensitive drum
61
is charged by a charging roller
62
, and a latent image is formed on the photosensitive drum
61
by a laser beam from an exposing unit
63
.
Then, the latent image is visualized by a developing device
64
. Thereafter, toner
68
on the developed image is transferred to a transfer material
13
by a transferring roller
9
. The toner
68
that was not transferred and remains on the photosensitive drum
61
is scraped off by a cleaning blade
10
and contained in a cleaning container
69
.
This developing device
64
has an elastic roller
66
that is in pressurized contact with the developing roller
65
at a position on the upstream side in the rotating direction of the developing roller
65
from an elastic blade
67
inside a developer container
60
containing nonmagnetic toner
68
as a single component developer. The elastic roller
66
rotates in the direction of an arrow D to supply the toner
68
on the developing roller
65
. The toner
68
supplied on the developing roller
65
is conveyed in accordance with the rotation of the developing roller
65
and is given a charge by friction at the abutment part of the elastic blade
67
and the developing roller
65
to form a thin layer.
Then, the toner
68
forming the thin layer is conveyed by the developing roller
65
and is supplied for development of an electrostatic latent image at the abutment part with the photosensitive drum
61
. Thereafter, the toner
68
that was not used for development in the abutment part of the photosensitive drum
61
and the developing roller
65
and remains on the developing roller
65
is scraped off by the elastic roller
66
.
In addition, new toner
68
is supplied to the developing roller
65
by the elastic roller
66
as described above, and the above-mentioned actions are repeated. In addition, the above-mentioned single component developer consists of toner prepared by internally or externally adding an auxiliary agent to base resin according to necessity. An auxiliary agent to be internally added is represented by a charging polarity agent, and an auxiliary agent to be externally added is represented by a plasticizer.
Further, in the developing method using the DC contact single component developing method, it is necessary to convey sufficiently charged toner to a developing region and visualize a latent image by such toner in order to form a visualized image with high quality of a predetermined density.
However, it is extremely difficult to convey sufficiently charged toner to a developing region over a long period. This is because triboelectric property is lowered due to deterication of a developing roller, an elastic blade and an elastic roller resulting from a multiplicity of times of frictions, and toner is deteriorated due to separation of externally added agent.
Therefore, in recent years, a method of using means for electrically charging toner using a toner charging roller for the purpose of high triboelectric stability and fog reduction has been proposed as disclosed in Japanese Patent Application Laid-open No. Hei 11-119546 and Japanese Patent Application Laid-open No. Hei 11-119547.
Here, a developing method using a toner charging roller is shown in FIG.
18
.
FIG. 18
is a schematic sectional view of a developing device of a contact developing method using a conventional toner charging roller. This developing device is an apparatus of the above-mentioned method to which a toner charging roller
72
is attached. The developing device has an elastic roller
76
that is in pressurized contact with a developing roller
75
at a position on the upstream side of the rotating direction of the developing roller
75
from an elastic blade
73
inside a developer container
70
containing nonmagnetic toner
74
as a single component developer. The elastic roller
76
rotates in the direction of an arrow D to supply the toner
74
on the developing roller
75
.
The toner
74
supplied on this developing roller
75
is conveyed in accordance with the rotation of the developing roller
75
and is given charge by friction at the abutment part of the elastic blade
73
and the developing roller
75
to form a thorn layer.
Moreover, the toner
74
is given charge electrically by discharge of the toner charging roller
72
. Then, the toner
74
to which charge is given is conveyed by the developing roller
75
and is supplied or development of an electrostatic latent image at the abutment part with a photosensitive drum
71
.
Thereafter, the toner
74
that was not used for development at the abutment part of the photosensitive drum
71
and the developing roller
75
and remains on the developing roller
75
is scraped off by the elastic roller
76
. In addition, new toner
74
is supplied to the developing roller
75
by the elastic roller
76
as described above, and the above-mentioned actions are repeated.
If the above-mentioned toner charging roller is used, toner can be conveyed to a developing region of sufficiently charged toner even it an amount of toner charge (hereinafter referred to as a toner charge amount) decreases due to use over a long period, and an image defect such as a fog can be prevented.
However, even if a toner charging roller is used, a toner charge amount changes over time due to separation of an externally added agent of toner, etc. As a result, there is a problem in that an image quality varies in such a case in which image densities at an initial time of use and after a long term use are different.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above and other drawbacks, and it is an object of the present invention to provide a developing device and a developing method that are capable of steadily supplying sufficiently charged toner over a long period of time and always giving a high image quality.
In order to solve the above problem, a developing device in accordance with the present invention comprises: a developer bearing member for bearing and conveying a developer in order to apply the developer to an image bearing member, wherein a first voltage is applied to the developer bearing member; further comprising a developer charging member for charging the developer born by the developer bearing member, a second voltage is applied to the developer charging member and controlling means for variably controlling a potential difference between the first voltage and the
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