Electrophotography – Image formation – Development
Reexamination Certificate
2000-09-18
2002-07-16
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Development
C399S255000, C399S256000
Reexamination Certificate
active
06421516
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing device and an image forming apparatus in which an electrostatic latent image is formed on an image carrier with a electrophotographic process or an electrostatic recording process, for example, and then developed using a two-component developer. Further, the present invention relates to a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is mounted in a detachable manner.
Herein, the terms “image forming apparatus” and “electrophotographic image forming apparatus” include, for example, copying machines, printers (such as an LED printer and a laser beam printer), facsimiles, word processors, etc.
Also, the term “process cartridge” implies not only an integral unit comprising at least one of a charging means, developing means, and cleaning means, and an electrophotographic photoconductor, which are constructed in the form of a cartridge, the cartridge being detachably mounted to a body of an electrophotographic image forming apparatus, but also implies an integral unit comprising at least a developing means and an electrophotographic photoconductor which are constructed in the form of a cartridge, the cartridge being detachably mounted to the body of the electrophotographic image forming apparatus.
2. Description of the Related Art
Hitherto, the so-called two-component developing method has been employed in many apparatuses. The two-component developing method utilizes a two-component developer, which is made up of a nonmagnetic toner (hereinafter referred to simply as a “toner”) and a magnetic carrier (hereinafter referred to simply as a “carrier”), as a developer to visualize an electrostatic latent image formed on an image carrier.
According to the two-component developing method, a two-component developer is agitated by a developer agitating and transporting means (hereinafter referred to simply as an “agitating means”) disposed in a developer container for containing the developer, so that the toner is electrically charged as a result of friction. Thereafter, the developer is transported to a developing sleeve that serves as a developer carrier and includes a stationary magnet roller disposed therein. Then, the developer is borne on the surface of the developing sleeve and transported with the rotation of the developing sleeve. The developer is thereby supplied to an electrostatic latent image formed on an image carrier for developing the latent image.
A two-component developing device employing the two-component developing method is advantageous in that it has a longer useful life and a lower operating cost because the device can be used repeatedly by replenishing only the toner from a toner resupply unit provided separately. Accordingly the two-component developing device has been widely used.
A process cartridge scheme is also known in which an electrophotographic photoconductor and at least one process means acting on the electrophotographic photoconductor are constructed into an integral unit in the form of a cartridge, and the cartridge is detachably mounted to a body of an image forming apparatus. This process cartridge scheme enables a user to carry out maintenance of the apparatus without the need for a serviceman, and hence can achieve a noticeable improvement in operability. For that reason, this process cartridge scheme has been widely used in electrophotographic image forming apparatuses.
FIG. 7
schematically shows a cross-section of a typical conventional two-component developing device. A developer container
50
for accommodating a two-component developer includes, as a developer carrier, a developing sleeve
51
rotatable in the direction of arrow “y”. The developing sleeve
51
is a hollow metallic sleeve including a magnet roller
52
disposed therein, which serves as a magnetic field generating means. As shown in
FIG. 7
, a doctor blade
53
serving as a developer layer thickness restricting means is provided closely below the developing sleeve
51
. As the developing sleeve
51
rotates in the direction of arrow “y”, the developer transported to a gap between the developing sleeve
51
and the doctor blade
53
is formed into a thin layer by the doctor blade
53
.
In the developer container
50
, an A screw
54
is disposed as a first agitating means to extend substantially parallel with the longitudinal direction of the developing sleeve
51
. As the A screw rotates in the direction of the arrow “x” in
FIG. 7
, it transports and agitates the developer. On the opposite side of the developing sleeve
51
to the A screw
54
, a B screw
55
is disposed as a second agitating means rotatably in the direction of arrow “z” in FIG.
7
.
Also, a toner density sensor
56
serving as a developer amount detecting means is provided on a wall surface of the developer container
50
which faces the B screw
55
on the side opposite to the A screw
54
. A sensor surface
56
a
of the toner density sensor
56
is positioned near the B screw
55
and arranged to lie perpendicularly to a line connecting a rotary shaft of the B screw
55
and the toner density sensor
56
. The reason why the sensor surface
56
a
is so arranged with respect to the B screw
55
is for preventing buildup of the developer on the sensor surface
56
a
. If the toner is built up on the sensor surface
56
a
, the toner density sensor
56
will fail to precisely detect a toner density (i.e., a mixing ratio of the carrier and the toner) in the developer.
FIG. 8
schematically shows the construction of the developing device of
FIG. 7
as viewed from above. The A screw
54
and the B screw
55
are arranged substantially parallel with each other, and an inner wall
57
is provided between both the screws
54
,
55
as a partition to prevent the developer from moving directly from one of both screws
54
,
55
to the other. However, the inner wall
57
is not provided in areas corresponding to longitudinal opposite portions of the A screw
54
and the B screw
55
, allowing the developer to move between both screws
54
,
55
. The A screw
54
and the B screw
55
are rotated in the directions of their respective arrows shown in
FIG. 7
to transport the developer in the opposite longitudinal directions, i.e., in the directions of respective arrows X and Y shown in FIG.
8
. Thus, a circulation path for the developer is formed within the developer container
50
to ensure continuous developer circulation.
The toner density sensor
56
is disposed in the upstream side of the B screw
55
in the direction of transport of the developer. The reason for arranging the toner density sensor
56
in the upstream side of the B screw
55
in the direction of transport of the developer is for enabling toner density detection to be immediately made on the developer that has been subjected to image formation using the toner and has a reduced toner density. More specifically, the developer residing in the A screw
54
side (hereinafter referred to as a “development chamber
50
A”) of the developer container
50
partitioned by the inner wall
57
is borne by the developer carrier and employed for image formation. Thereafter, the developer is sent to the B screw
55
side (hereinafter referred to as an “agitation chamber
50
B”) of the developer container
50
partitioned by the inner wall
57
following the above-described circulation path, and the toner density is immediately detected by the toner density sensor
5
. In accordance with a detected result, an appropriate amount of the developer is replenished from a toner resupply unit
59
(FIG.
7
), which is provided adjacent to the developer container
50
and communicated with it, through a toner resupply port
58
positioned downstream of the toner density sensor
56
in the direction of transport of the developer. Consequently, the toner density of the developer is kept constant.
As seen from the above, the circulation of the developer is particularly important in the two-component developing device.
The ab
Adachi Motoki
Kinoshita Masahide
Yamaguchi Seiji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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