Electrophotography – Image formation – Development
Reexamination Certificate
2000-11-22
2002-03-19
Grainger, Quna M. (Department: 2852)
Electrophotography
Image formation
Development
C399S256000
Reexamination Certificate
active
06360066
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing apparatus, and more particularly, to a developing apparatus for an image formation apparatus such as a copying unit, a printer, a facsimile unit, etc.
2. Description of the Prior Art
Conventionally, as a developing apparatus that is generally used for an image formation apparatus, there has been known a developing apparatus of the type that has a development roller, a developer restricting member, and a plurality of developer stirring shafts within the development casing.
As the developer stirring shafts disposed within the developing apparatus, there have been widely employed developer stirring shafts that have approximately elliptic stirring vanes (elliptic vanes) formed on the rotational axis or that have a screw-shaped spiral vane formed on the rotational axis.
For example, some developing apparatuses have a structure that a plurality of developer stirring shafts
1
are disposed adjacently in parallel with each other, each developer stirring shaft
1
having a plurality of elliptic vanes
2
installed on the slant at a predetermined angle on a rotational axis
3
, as shown in
FIGS. 1A and 1B
.
Some other developing apparatuses have a structure that a plurality of developer stirring shafts are disposed adjacently in parallel with each other, each developer as stirring shaft
10
having a screw-shaped spiral vane
12
installed on a rotation axis
3
, as shown in FIG.
2
. Some other developing apparatuses have a structure that a plurality of a set of developer stirring shafts
20
and
21
are disposed adjacently in parallel with each other, the two developer stirring shafts
20
and
21
having spiral vanes
22
and
23
respectively having mutually different pitches. Further, some other developing apparatuses have a structure that a plurality of a set of developer stirring shafts are configured to oppose with each other so that pitches of spiral vanes of developer stirring shafts are shifted one-half pitch with respect to each other.
According to the structure of the developer stirring shafts having elliptic vanes formed on the rotational axis, the distribution of a developer becomes dense at portions where tip portions of the stirring vanes on the stirring shafts oppose with each other. However, at other portions, the shafts oppose with each other, and therefore, the distribution of the developer becomes coarse. As a result, uneven stirring of the developer tends to be emphasized.
Therefore, when the developer stirring shafts within the development casing have all the same shapes, the developer may be maldistributed at only one side within the development casing depending on the combination of the rotational direction. Thus, there has been a problem that the distribution of the developer is influenced by tilt of the development casing.
Further, as the developer conveying force is strong in the radial direction of the developer stirring shafts, some portion of the developer is supplied to the developing section without obtaining a sufficient stirring period within the development casing. Therefore, there has been a problem that this becomes a cause of a defect in the picture quality.
Further, when a plurality of developer stirring shafts
30
having the same shapes are disposed, each developer stirring shaft having elliptic vanes
32
formed in the same pitches, as shown in FIG.
4
A and
FIG. 4B
, the tip portions of the elliptic vanes oppose with each other. At these portions where the tip portions opposes with each other, the developer is stirred strongly, and the conveying force of the developer becomes strong. On the other hand, at portions between the elliptic vanes, that is, at portions where the rotational shafts oppose with each other, the developer is stirred weakly, and the conveying force of the developer becomes weak.
Therefore, when the developer stirring shafts are disposed in such a way that the tip portions of the elliptic vanes coincide with each other between the adjacent developer stirring shafts, the stirring of the developer emphasizes the peak and bottom at the interface of the developer. As a result, uneven stirring of the developer tends become significant, due to occurrence of dense distribution portions and coarse distribution portions of the developer.
Further, when the machine is placed at a slanted position, the distribution of the developer becomes uneven and the developer is maldistributed at one end portion within the development casing. In this case, when the side at which the developer is shifted and the direction to which the developer is conveyed in the axial direction of the developer stirring shafts are the same, there is a problem that the maldistribution of the developer becomes more significant.
On the other hand, in the case of the structure of the developer stirring shafts that have screw-shaped spiral vanes installed on the rotation axes, the developer conveying force in the axial direction is secured. However, there has been a problem that the developer conveying force in the radial direction is inadequate. Further, since the developer conveying force in the axial direction is strong, stagnation of the developer and pressure increase thereof may be caused at the end portions in the conveying direction. Thus, the developer is subjected to a stress. Then, the developer may enter bearing portion which is disposed at the end portions of the conveying direction. As a result there has been a problem that the rotational shafts are blocked by the developer. Meanwhile, in the case of the structure of the developer stirring shafts that have spiral vanes of different pitches installed on the rotational axes, there has been a further problem that the shapes of the parts of the stirring shafts become complex.
In order to improve the stirring and the conveying performance of the developer in the developing apparatus having the above-described conventional structures, there have been the following proposals. In the case of the structure of the developer stirring shafts having elliptic vanes formed on the rotational axes, as disclosed in Japanese Patent Application Laid-open Hei 6 No. 89061 there has been proposed the following structure. That is to say, the developer stirring shafts have two spiral vanes of different pitches, with different external diameters, the external diameter becoming gradually larger toward one direction, or further having one stirring shafts installed with an angle.
Further, there has been proposed a structure of developer stirring shafts having a plurality of elliptic disks installed on the stirring shafts, with brushes provided uniformly between the disks, as disclosed in Japanese Patent Application Laid-open Hei 7 No. 168431.
Further, there has been proposed the following structure of developer stirring shafts, as disclosed in Japanese Patent Application Laid-open Hei 8 No. 95359. That is to say, developer stirring shafts are formed in a semi-cylindrical shape, with a plurality of plate-shaped outside-stirring vanes provided on the slant on the external periphery, and with a plurality of plate-shaped inside-stirring vanes provided on the slant on the inner periphery of the semi-cylinders, in the opposite direction to the slanting angle of the outside-stirring vanes. Further, there is provided a structure of these developer stirring shafts having their flat portions fixed to oppose with each other, and with the far end of each semi-cylinder cut open to communicate inside of each with.
On the other hand, in the case of the structure of the developer stirring shafts having screw-shaped vanes formed on the rotational axes, there has been proposed the following structure, as disclosed in Japanese Patent Application Laid-open Hei 9 No. 106154. The developer stirring shafts have a plurality of stirring vane shafts, with winding directions of spiral vanes at one side formed reversed to those of spiral vanes at the other side with the center portion of each rotational axis as the boundary. Based on this structure, the dev
Ishiguro Yasuyuki
Kato Keiji
Kawahito Hiroshi
Nagata Tsutomu
Nishino Toshio
Grainger Quna M.
Sharp Kabushiki Kaisha
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