Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2002-11-18
2004-06-15
Grimley, Arthur T. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S284000, C399S285000
Reexamination Certificate
active
06751423
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus such as a copying machine, a printer, etc., which employs an electrophotographic or electrostatic recording method. It also relates to a developing apparatus suitable for an image forming apparatus employing such a developing apparatus.
In the past, as an electrophotographic employing an electrophotographic or electrostatic recording method, an apparatus having the structure shown in
FIG. 18
has been known.
FIG. 18
is a schematic drawing of an example of image forming apparatus in accordance with the prior art, for showing the basic structure thereof.
In the case of this image forming apparatus, a photoconductive drum 100 is employed as an image bearing member. The photoconductive drum 100 comprises: a cylindrical substrate formed of, for example, aluminum; and a photoconductive layer (organic photoconductive layer, for example) coated on the peripheral surface of the cylindrical substrate. It is rotationally driven. Disposed around the photoconductive drum
100
are a charge roller
101
, an unshown laser beam type scanning optical system, a developing device
102
as a developing means, a transfer roller
111
, and a cleaner
109
, which are listed in order, in terms of the rotational direction of the photoconductive drum
100
.
After the peripheral surface of the photoconductive drum
100
is uniformly charged by the charge roller
101
, it is exposed to the beam of laser light projected in the scanning manner from the unshown optical system. As a result, an electrostatic latent image is formed on the peripheral surface of the photoconductive drum
100
. This electrostatic latent image is visualized (developed) with the use of the toner (developer) in the developing device.
Recording medium, which in this case is a piece of transfer medium P, is fed into the main assembly of an image forming apparatus, through an unshown sheet feeding opening, and is delivered, in synchronism with the above described formation of the visible image (toner image), to the area in which the peripheral surfaces of the photoconductive drum
100
and transfer roller
111
are virtually in contact with each other, and in which the visible image (toner image) is transferred onto the transfer medium P. Thereafter, the image on the transfer medium P is welded to the transfer medium P by a fixing device
110
.
The developing device
102
comprises: a development roller
108
as a developer bearing member; a supply roller
105
for supplying nonmagnetic single-component toner (negative in inherent polarity) to the development roller
103
; a stirring member
106
for conveying the toner within the container to the adjacencies of the supply roller
105
; a development blade
104
as a developer amount regulating member for regulating the amount of the toner on the peripheral surface of the development roller
103
; etc.
Since the development roller
103
is placed in contact with the photoconductive drum
100
, it is formed of elastic substance. The development blade
104
is placed in contact with the peripheral surface of the development roller
103
, with the use of the resiliency of a piece of thin springy metallic plate, generating a small amount of contact pressure against the peripheral surface of the development roller
103
.
In order to transfer the toner from the development roller
103
onto the photoconductive drum
100
, development bias is applied to the development roller
103
from a development bias power source
107
so that the development roller
103
is charged to a predetermined potential level. Further, in order to stabilize the electric charge of the toner, a blade bias power source
108
is connected to the development blade
104
, and blade bias is applied to the development blade
104
so that the development blade
104
is charged to a predetermined potential level (Japanese Laid-open Patent Application 05-011599). There are various blade bias power sources (
108
); for example, those which are identical in potential as the development bias
107
, those which are different in potential from the development bias
107
, etc.
As described above, in the case of an image forming apparatus in accordance with the prior art (which hereinafter may be referred to as a conventional image forming apparatus), fixed DC bias or AC bias is applied to the development blade
104
in an attempt to stabilize the toner in terms of electric charge, manner in which the toner is coated, etc.
However, in the case of a conventional image forming apparatus, it was difficult to stabilize the toner coat while preventing the toner from scattering, preventing the reversal toner from solidifying on the development blade, and also, preventing the toner from welding itself to the development blade.
For example, when an image forming operation was carried out using one of the conventional image forming apparatuses, the following problems could be observed.
Firstly, when the potential of the development bias power source
107
was rendered the same as that of the blade bias power source
108
, the image forming apparatus began to form images irregular in density, more specifically, images having unwanted vertical streaks across the halftone areas thereof, after the formation of approximately 1,000 copies. The streaks similar to the vertical streaks of the images were found also on the portion of the peripheral surface of the development roller
103
, on the immediately downstream side with respect to the development blade
104
, in terms of the rotational direction of the development roller
103
.
The visual examination of the development blade
104
revealed that agglomerations of toner had welded to the area a (area next to downstream border of contact area between development blade
104
and development roller
103
, in terms of rotational direction of development roller
103
) of the development blade
104
. Obviously, the toner particles in the toner layer, the positions of which corresponded to those of the agglomerations of the toner welded to the development blade
104
, were blocked by the agglomerations. As a result, the toner layer on the peripheral surface of the development roller
103
became thinner, across the areas corresponding in position to the areas of the development blade
104
having the toner agglomerations, effecting therefore images suffering from density anomaly in the form of unwanted vertical streaks.
The cause of the above described problem will be described with reference to
FIG. 19
which is a schematic drawing for showing the process in which the toner particles weld in agglomeration to the development blade. Designated by a referential code T are negatively charged nonmagnetic single-component toner particles. The developer is a mixture of the toner particles T and external additive particles G
1
as auxiliary particles.
The toner particles borne on the peripheral surface of the development roller
103
are negatively charged particles. In the normal ambience, after passing the development blade
104
, the potential of the toner layer on the peripheral surface of the development roller
103
is in the range of approximately −20-−50 V (measured with Surface Potentiometer Model 1334: Treck Co., Ltd.). In the contact area between the development roller
103
and development blade
104
, the surface of the development blade
104
is constantly rubbed by the toner particles. Therefore, the external additive particles are not likely to remain adhered to the surface of the development blade
104
.
However, on the downstream side of the contact area between the development roller
103
and development blade
104
(area a in drawing), the distance between the toner layer and the surface of the development blade
104
gradually increases, creating potential gradient.
In other words, even though the development roller
103
and development blade
104
remain the same in potential, the surface portion of the toner layer on the peripheral surface of the development roller
10
Sakaizawa Katsuhiro
Shibata Masahiro
Shinohara Seiichi
Tsuruya Satoshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Gleitz Ryan M
Grimley Arthur T.
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