Electrophotography – Image formation – Development
Reexamination Certificate
2001-01-03
2002-07-02
Braun, Fred L (Department: 2852)
Electrophotography
Image formation
Development
C258S005000
Reexamination Certificate
active
06415126
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing unit for use in an image forming apparatus such as a laser printer, a copier, facsimile machine or the like and, in particular, relates to a toner replenishing device for replenishing, as required, a developing hopper as a part of the developing unit, with the toner for image development.
2. Description of the Related Art
An image forming apparatus such as a laser printer, a copier, a facsimile machine, or the like, utilizing an electrophotographic technique, has an image forming portion for forming a desired image on a sheet for recording. In this image forming portion, the surface of a photosensitive member as an image bearer is uniformly electrified with charges of a particular polarity and then is illuminated with an optical image to form a static latent image corresponding to the image. For the purpose of visualizing this static latent image, the image forming portion includes a developing unit and other components. The developing unit is composed of developer hopper holding a developer and having a developing roller and the like for supplying the developer to the developing position where the developing roller opposes the photosensitive member. Further, since the toner in the developing hopper is consumed, the developing unit is provided, adjacent to the developing hopper, with a toner replenishing device for replenishing the developing hopper, if necessary, with the toner which is a developer.
In the developing unit described above, if the toner reserve container for replenishing the developing hopper with the developer is arranged on the top, the developing unit would be bulky as to its height and hence a waste space would arise inside the image forming apparatus, thus making the whole image forming apparatus bulky. For this reason, the toner reserve container is horizontally arranged adjacent to the developing hopper to reduce the height of the developing unit, thus making the developing unit into a low profile and at the same time making an image forming apparatus as a whole compact by eliminating the unnecessary space which would arise inside the image forming apparatus.
For example, an example of such a developing unit is disclosed in Japanese Patent Application Laid-Open Hei 10 No. 123815. A toner replenishing device has a rotatable toner conveying unit for agitating the toner and conveying the toner at the same time in a toner reserve container (toner hopper) for reserving the toner. This toner conveying unit has the function of securing the performance of conveying the toner and the function of preventing a degradation in the toner (flocculation or the like) by agitating the toner.
The toner conveying unit described above is conventionally constituted by an agitator which is a rotary member usually formed of a considerably hard material (metal, resin or the like), and firmly formed like a ladder, as disclosed in Japanese Patent Application Laid-Open Hei 10 No. 301377, for example, and a flexible conveying sheet provided at an end portion of the agitator so as to convey the toner.
As described above, since the toner reserve container is provided with the toner conveying unit made up of the agitator and the conveying sheet, the toner stored in the toner reserve container is completely conveyed without being stagnated by the above-mentioned toner conveying unit with sufficient conveyance even if the amount of the toner becomes smaller. For example, in the toner conveying unit disclosed in Japanese Patent Application Laid-Open Hei 6 No. 236110, an elastic sheet (corresponding to the conveying sheet) is provided at the tip of the agitator. The elastic sheet is put into sliding contact with the inside of the toner reserve container by rotating the agitator to sufficiently agitate and convey the toner having the tendency to accumulate on the bottom and the like. Therefore, even if the amount of toner becomes smaller, the performance of conveying the toner can be sufficiently secured and problems such as toner stagnation and the like are not presented and hence the toner can be effectively used.
Also, in the toner conveying unit disclosed in Japanese Patent Application Laid-Open Hei 10 No.301377 a ladder-shaped toner agitator provided with a rectangular film (corresponding to the conveying sheet) produces the same effect as is disclosed in the Japanese Patent Application Laid-Open Hei 6 No.236110.
Further, in Japanese Patent Application Laid-Open Hei 10 No.123815 proposed by the present inventor is also disclosed a conveying unit including an agitator and a film-shaped conveying sheet fixed to the agitator, wherein the tip end portion of the conveying sheet is in sliding contact with the inside of a toner reserve container to secure toner conveyance to stably convey the toner. In this conveying sheet, in order to further secure the toner conveyance, the tip end of the conveying sheet is bent in the rotational direction to increase the toner conveyance.
In the configuration of the conventional toner replenishing device described above, the agitator arranged in the toner reserve container is provided with the conveying sheet made of a flexible sheet or film for sufficiently securing toner conveyance even when the quantity of toner becomes smaller.
However, if the toner storage capacity of the toner reserve container is large, the toner stored in the toner reserve container can not completely be conveyed unless the conveying sheet fixed to the agitator is elongated. In this case, the strength and rigidity of the conveying sheet or the like is a big problem. For example, if a large amount of toner is stored in the toner reserve container, the conveying sheet is largely deformed to reduce the toner conveyance. To overcome the problem, it is recommended that a conveying sheet having sufficient rigidity be used, but because the conveying sheet is in sliding contact with the toner reserve container, it loses flexibility and can not be largely curved, thereby applying large load to a driving motor and to the conveying sheet itself, resulting its shorter life.
Further, the above conveying sheet is made of, for example, a polyethylene terephthalate (PET) film or a polyester film or the like so that it has good flexibility and has a tolerance against deformation and curving. For this reason, if the conveying sheet is repeatedly curved and deformed, the conveying sheet may be plastically deformed and bent and unable to reset its curvature and deformation and hence lose its toner conveying performance and its toner agitating performance.
Then, in Japanese Patent Application Laid-Open Hei 10 No. 301377 is disclosed a technique for reducing the force applied to a resin conveying sheet (film) during its rotation by making a plurality of holes in the conveying sheet fixed to an agitator. This technique can prevent the toner from applying a rotational load to the conveying sheet and, at the same time, can prevent a decrease in life caused by deformation or the like to some extent, even if the amount of toner is large.
However, it is thought that the toner conveying performance is reduced because the rigidity of the film is reduced by many holes made in the film, as described above. Also, if a plurality of holes are only made, the amount of toner conveyed by the conveying sheet is reduced as well. In particular, if many holes are formed in the portion for conveying the toner, they tend to reduce the total amount of conveyed toner.
Further, since the holes are formed uniformly in the whole area of the conveying sheet, the toner conveying performance is reduced at the tip end of the conveying sheet, whereby part of toner is left in the toner reserve container and the toner can not completely effectively conveyed.
SUMMARY OF THE INNOVATION
In view of the above problems, it is an object of the present invention to provide a toner replenishing device capable of making effective use of a toner stored in a toner reserve container and always securing a stable toner conveying performance and the suf
Araki Hiroshige
Ishiguro Yasuyuki
Kaneshige Masatoshi
Nagata Tsutomu
Nishino Toshio
Braun Fred L
Sharp Kabushiki Kaisha
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