Electrophotography – Image formation – Development
Reexamination Certificate
2000-03-29
2001-11-27
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Development
C399S119000, C399S256000, C399S263000
Reexamination Certificate
active
06324369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus of electrophotographic type or electrostatic recording type such as a copying machine, a page printer and the like, and more particularly, it relates to a developing apparatus, and a process cartridge and an image forming apparatus which have such a developing apparatus.
2. Related Background Art
In such developing apparatus, since charging ability for toner is very good in an electrophotographic process, a developing apparatus using two component developer developing agent including toner and carrier (referred to as “two-component developing apparatus” hereinafter) has widely been used.
FIG. 5
is a sectional view showing a conventional two-component developing apparatus.
As shown in
FIG. 5
, the two-component developing apparatus has a developer container
110
containing two-component developer, and a developing sleeve
102
as a developer bearing member.
The developing sleeve
102
is a rotatable hollow metallic sleeve in which a magnet roller (magnetic field generating means)
103
is fixed and which serves to bear the developer in the developer container
110
.
An A screw (first agitating means)
105
having an axis substantially parallel with an axial direction of the developing sleeve
102
is disposed within the developing container
110
and serves to convey and agitate the developer in the developer container
110
in a direction shown by the arrow in FIG.
8
.
Further, a B screw (second agitating member)
106
is disposed at an opposite side of the developing sleeve
102
with respect of the A screw
105
.
FIG. 8
is a top view of the two-component developing apparatus shown in FIG.
5
.
As shown in
FIG. 8
, the A screw
105
and B screw
106
are arranged so that their axes become substantially parallel with each other, and the developer container
110
is partitioned by an inner wall (partition member)
107
for dividing the interior of the developer container
110
into two chambers, which inner wall is provided at its both ends (in the axial direction of the developing sleeve
102
) with openings for permitting the developer to move between the A screw
105
and the B screw
106
.
Further, since the A screw
105
and B screw
106
convey the developer in opposite directions, a circulating path for circulating developer without discontinuity is defined within the developer container
110
.
The developer container
110
is provided at its upper part with a replenishing port
108
for replenishing the developer in the developer container
110
.
When toner (developer) density in the developer is decreased as a result that the toner is consumed during image formation, a proper amount of toner is replenished in the developer container
110
through the replenishing port
108
by means of a toner replenishing mechanism
109
so that the toner density of the developer is always maintained to a constant value.
However, in such a developing apparatus, it is very difficult to design the developing apparatus so that the developer is well circulated, and, thus, it is desirable that the two-component developing apparatus satisfies the following three conditions or requirements.
First, it is preferable that a surface of the developer within the developer container near the A screw (referred to as “agent surface” hereinafter) is above an uppermost part of the A screw.
The reason is that, since the A screw
105
is positioned near the developing sleeve, as shown in
FIG. 6
, if the agent surface is lowered below the uppermost part of the A screw, the developer supplied to the developing sleeve between uneven (i.e., increased or decreased) in dependence upon a pitch of vanes of the A screw, with the result that density unevenness of an image may occur due to the pitch of the screw (referred to as “screw pitch unevenness”).
So long as the agent surface near the A screw in the developer container is positioned above the uppermost part of the A screw, since the developer is supplied to the developing sleeve relatively uniformly, the screw pitch unevenness is hard to generate.
Second, it is preferable that an agent surface near the B screw in the developer container is below an uppermost part of the B screw.
The reason is that, the side of the B screw in the developer container has a purpose for agitating the developer in the developer container, and, thus, if the agent surface is increased above the uppermost part of the B screw, the agent above the B screw is hard to be agitated.
Particularly, as shown in
FIG. 7
, if the toner is replenished when the agent surface near the B screw is above the uppermost part of the B screw, the toner having specific weight smaller than the developer may be floating on the agent surface.
In such a case, the toner is hard to be mixed with the developer, with the result that non-charged toner is supplied to the developing sleeve, thereby causing fog or poor density.
However, in the case where the agent surface near the B screw within the developer container is below the uppermost part of the B screw, even when the toner is replenished, the toner is semiforcibly entered into the developer by rotation of the B screw to be agitated adequately, thereby preventing the fog and the poor density.
Third, the agent surfaces near the B screw and the A screw within the developer container may be horizontal at their screw areas.
The reason is that, if the agent surface near the A screw within the developer container is inclined in a longitudinal direction, the amount of the developer supplied to the developing sleeve becomes uneven in the longitudinal direction, with the result that difference in density may occur along the longitudinal direction.
On the other hand, if the agent surface near the B screw within the developer container is inclined in the longitudinal direction, the charging ability due to agitation may be reduced.
In order to satisfy these requirements, it is necessary to perform delicate adjustments of the shape of the developer container, the amount of the developer, the pitch between the vanes of the screw, rotational speeds of the screws and the like.
However, if the amount of the developer container is decreased, as shown in
FIG. 6
, the uppermost part of the A screw will be come out from the agent surface; whereas, if the amount of the developer is increased, as shown in
FIG. 7
, the B screw will be lowered below the agent surface.
Further, in order to satisfy the first and second requirements, if a conveying speed of the B screw is merely increased, the upstream side (in the conveying direction) of the agent surface of the A screw will be higher than the downstream side thereof, with the result that the third requirement cannot be satisfied. Consequently, the difference in density occurs in the longitudinal direction. Thus, very delicate adjustment is requested to make the design of the developing apparatus very difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a developing device, a process cartridge having such a developing apparatus, and an image forming apparatus having such a developing apparatus, which can maintain high image quality.
Another object of the present invention is to provide a developing device, a process cartridge having such a developing apparatus, and an image forming apparatus having such a developing apparatus, in which design can easily be attained, developer can stably be circulated in a developer contained by first and second agitating means, and density unevenness, fog and poor density can be prevented.
A further object of the present invention is to provide a developing apparatus comprising a developer container for containing developer, a developer bearing member for bearing the developer within the developer container and for conveying the developer to a position opposed to an image bearing member, a first agitating member for agitating the developer within the developer container, a second agitating member for agitating the developer within the developer con
Kinoshita Masahide
Yamaguchi Seiji
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ngo Hoang
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