Electrophotography – Image formation – Development
Reexamination Certificate
1999-09-10
2001-07-24
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Image formation
Development
C399S267000
Reexamination Certificate
active
06266507
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a developing device which performs development of the static latent image formed on the static latent image bearer, by rotating a developer support that incorporates a magnetic field forming means having multiple magnetic poles fixed at predetermined positions and that supports a developer thereon so as to supply the static latent image with the developer.
(2) Description of the Prior Art
When a dual-component developer is used, toner concentration unevenness will occur in the dual-component developer layer after development of a static latent image in the developing area. To deal with this, in a conventional developing device for dual-component developer, two magnetic poles, namely the first and second poles, of a similar polarity are arranged adjacent to each other inside the developer sleeve using fixed magnets, on the downstream side of the developing portion with respect to the rotational direction of the developer sleeve, so that a repulsive magnetic field formed by these two magnetic poles will remove the developer from the developer sleeve. The thus removed developer is agitated by a rotational agitator disposed in the repulsive magnetic field to make the toner concentration uniform, and then the developer with the toner density made uniform is conveyed by the rotating agitator to the developer sleeve on its second magnetic pole side. Thus, the density unevenness in the developed image due to development hysteresis can be prevented.
However, under the formation of a repulsive magnetic field alone, it is not possible to completely remove the developer from the developer sleeve, so some part of the developer is conveyed whilst adhering to the developer sleeve, from the first magnetic pole side to the second magnetic side. Particularly, when the toner is a micro particle toner and/or the magnetic carrier is a micro particle carrier, the tribo-charge amount on the developer per unit weight becomes relatively large so that the developer adheres to the developer sleeve with a greater electrostatic attraction. Therefore, it is difficult for the repulsive magnetic field to fully remove the developer from the developer sleeve.
So that, when the developer having passed through the developing area cannot be removed from the developer sleeve and hence re-enter the developing area, the developed image may have density unevenness and cannot offer a high, fine quality. Further there is the problem in that if the developing device has been run for a long period of time without the developer fully removed from the developer sleeve, degradation of the developer is accelerated causing density lowering and background fogging in the developed image.
As countermeasures against these problems, for example, Japanese Patent Application Laid-Open Hei 6 No.194962 has offered a method in which the developer is removed from the developer support by using a magnetic brush formed between the developer support and the magnetic element, by providing a magnetic element in the developer flow path under the influence of a repulsive magnetic field. Another method has been also proposed in Japanese Patent Application Laid-Open Hei 5 No.289523, in which the developer is removed from the developer support by providing a cleaning member in the developer flow path in the repulsive magnetic field so that the cleaning member comes into frictional contact with the developer support.
However, a small-diametric developer sleeve configuration in combination with the scheme of Japanese Patent Application Laid-Open Hei 6 No.194962 where the removal of the developer is performed by using lowering of the developer support's retention force by formation of a repulsive magnetic field, has a disadvantage in terms of cost because the fixed magnets incorporated in the developer sleeve need to be magnetized with a high precision.
Further, provision of a magnetic element or a cleaning member in the developer flow path will disturb the flowing state of the developer in the developing hopper, inducing a high risk of degradation of the image quality. In particular, in the illustration of Japanese Patent Application Laid-Open Hei 6 No.194962, the magnetic element is located between the developer sleeve and rotational agitator. However, originally the developer conveyance pressure and the toner concentration are high at this point, so that the conveyance pressure is further increased if a magnetic element is laid out in such a position, which may possibly cause problems of toner aggregation, toner filming over the developer sleeve surface and/or spent toner.
Moreover, the arrangement of a cleaning member in direct and frictional contact with the developer support surface, produces excessive stress on the developer, which may result in increasing of the driving torque and heat generation of the developing unit.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a developing device, which can prevent the occurrence of turbulence of the developer flow accompanied by addition of extra elements in the developer hopper and which will not cause excessive stress on the developer and/or the developing device and hence is free from the problems of toner aggregation, sleeve filming, spent toner etc., and wherein the developer in the developing hopper can be smoothly circulated by achieving easy removal of the developer after development from the developer sleeve and easy supplying of the developer thus removed to the rotational agitator.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a developing device includes:
a magnetic field forming means having multiple number of magnetic poles fixed at predetermined positions;
a developer support which rotatably encloses the magnetic field forming means for conveying the developer whilst supporting it on the surface thereof by magnetism of the magnetic field forming means;
a regulating element for regulating the thickness of the developer layer supported on the developer support surface; and
a rotational agitating means which is disposed adjacent to the developer support and receives the developer from the developer support and supplies the developer to the surface of the developer support, wherein the developer support, as it rotates, supplies and develops the static latent image on a static latent image bearer with the developer supported on the developer support, and is characterized in that a magnetic element is arranged opposing the developer support and outside the developer flow path.
In accordance with the second aspect of the present invention, the developing device having the above first feature is characterized in that the longitudinal dimension, perpendicular to the developer conveying direction, of the magnetic element is almost equal to, or shorter than, the magnetized width of the developer conveyance magnetic pole of the magnetic field forming means.
In accordance with the third aspect of the present invention, the developing device having the above first feature is characterized in that the magnetic element is arranged out of the influence of the magnetic field of the development magnetic pole of the magnetic field forming means.
In accordance with the fourth aspect of the present invention, the developing device having the above first feature is characterized in that the magnetic element is arranged out of contact with the developer circulating inside the developing device.
In accordance with the fifth aspect of the invention, a developing device includes:
a magnetic field forming means having multiple number of magnetic poles fixed at predetermined positions;
a developer support which rotatably encloses the magnetic field forming means for conveying the developer whilst supporting it on the surface thereof by magnetism of the magnetic field forming means;
a regulating element for regulating the thickness of the developer layer supported on the developer sup
Nagahama Hitoshi
Nishino Toshio
Sumida Katsuaki
Lee Susan S. Y.
Sharp Kabushiki Kaisha
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