Electrophotography – Image formation – Development
Reexamination Certificate
2002-05-29
2004-05-11
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06735410
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing device of an image forming apparatus for forming an image using the electrophotographic system and, more specifically, to a developing device of an image forming apparatus such as a copying machine, a printer and a facsimile machine.
2. Description of Related Art
Conventionally, for example, in an image forming apparatus such as a copying machine and a laser beam printer using the electrophotographic system, an electrostatic latent image is formed on a surface of an electrophotographic photosensitive member (photosensitive drum), for example, of a cylindrical shape functioning as an image bearing member, the electrostatic latent image is developed by a developing device and the developed image is transferred to a recording material and then fixed thereon by a fixing device to form an image on the recording material.
FIG. 12
shows a schematic structure of a copying machine as an example of a conventional image forming apparatus of the electrophotographic system. In such an image forming apparatus, an image of an original is read by an image reading portion
8
, exposure is applied to a surface of a photosensitive drum
1
functioning as an image bearing member from an image writing portion
9
according to an instruction from a controller (not shown) based on data of the read image to form an electrostatic latent image on the photosensitive drum
1
. The surface of the photosensitive drum
1
is uniformly charged at a predetermined potential by a charging device
2
before the exposure by the image writing portion
9
. Then, a laser beam or the like is irradiated from the image writing portion
9
onto the uniformly charged photosensitive drum
1
, whereby an electrostatic latent image is formed on the photosensitive drum
1
.
The electrostatic latent image formed on the photosensitive drum
1
is developed as a so-called toner image by a developing device
3
using developer. Thereafter, the developed toner image is carried to a portion opposed to a transfer device
4
(transfer portion) by the rotation of the photosensitive drum
1
.
A recording material P such as a recording sheet is fed one by one from a recording material containing cassette
12
by a pickup roller
13
in response to the carrying of the toner image on the photosensitive drum
1
and, at the same time, is transported to a part where the photosensitive drum
1
and the transfer device
4
oppose each other while timing being taken by a registration roller pair
14
. Then, when the recording material P passes the part where the photosensitive drum
1
and the transfer device
4
oppose each other, the toner image on the photosensitive drum
1
is transferred onto the recording material P by an action of the transfer device
4
.
The recording material P having the toner image transferred thereon is transported to a fixing device
7
by a predetermined transport device
6
. The fixing device
7
is provided with a fixing roller pair consisting of a fixing roller
7
a
and a pressure roller
7
c
. The recording material P is pressurized by the fixing roller pair
7
and, at the same time, heated by a heater
7
b
provided in the fixing roller
7
a
. Thus, unfixed toner on the recording material P is fused and fixed on the recording material P.
Thereafter, the recording material P having the toner image fixed thereon is delivered to a tray
15
provided outside an apparatus main body by a transport roller pair
10
, a delivery roller pair
11
and so on.
On the other hand, the surface of the photosensitive drum
1
after the toner image is transferred to the recording material P is subject to removal of transfer residual toner or the like by a cleaner
5
and serves image formation repeatedly. Thus, a series of image forming processes is completed.
An electrostatic latent image such as the one described above that is formed on, for example, the photosensitive drum
1
functioning as an image bearing member by a well-known electrostatic latent image technique is developed by the developing device
3
. The developing device
3
is generally provided with a rotatable cylindrical developing sleeve
31
functioning as a developer bearing member in a position opposed to the photosensitive drum
1
. That is, the developing device
3
is provided with a developing container
32
for containing developer and defining a developing device main body. A position of the developing container
32
opposed to the photosensitive drum
1
opens along a longitudinal direction of the photosensitive drum
1
(a direction perpendicular to a transport direction of the recording material P). The developing sleeve
31
is positioned in the opening portion and supported rotatably with respect to the developer container
32
. The developer in the developing device
3
forms a thin layer of a uniform thickness to be borne on the surface of the developing sleeve
31
and is fed to a developing area where the photosensitive drum
1
and the developing sleeve
31
oppose each other by the rotation of the developing sleeve
31
. Then, in the developing area, the toner on the developing sleeve
31
moves to the surface of the photosensitive drum
1
, whereby an electrostatic latent image is developed.
FIG. 13
shows a schematic sectional view of an example of a conventional developing device. As illustrated, the photosensitive drum
1
and the developing sleeve
31
are arranged while maintaining a microscopic gap (hereinafter referred to as “SD gap”) between them constant. Thus, predetermined development can be performed.
The developer is fed to the developing sleeve
31
by developer agitating and feeding members (agitating members)
37
and
38
provided inside the developing container
32
.
FIG. 14
shows an arrangement of the developing sleeve
31
in its axial direction (longitudinal direction). As illustrated, the SD gap can be guaranteed by providing two spacer rollers (abutting rollers)
20
, whose outer circumferences abut against the outer circumference of the photosensitive drum
1
, functioning as spacer members at both end portions in the longitudinal direction of the developing sleeve
31
. The two spacer rollers
20
provided in both ends of the developing sleeve
31
are substantially circular in their cross sections and are arranged such that their rotational centers are concentric with the rotational center of the developing sleeve
31
. An outer diameter of the spacer rollers
20
is formed larger than an external diameter of the developing sleeve
31
by a size of the SD gap. In addition, the developing container
32
is pressurized by pressurizing means such as pressurizing springs
51
, whereby the spacer rollers
20
are always brought into contact with the outer circumference of the photosensitive drum
1
. According to such a structure, the photosensitive drum
1
and the developing sleeve
31
are arranged while keeping the predetermined SD gap.
In general, the spacer rollers
20
are provided with ball bearings (hereinafter referred to simply as “bearings”)
20
a
inside the spacer rollers
20
. Thus, the outer circumferences of the spacer rollers
20
rotate following the rotation of the photosensitive drum
1
, and the inner circumferences of the bearings
20
a
provided inside the spacer rollers
20
is rotated by the rotation of the developing sleeve
31
.
Parts of the spacer rollers
20
abutting against the photosensitive drum
1
are formed of a material that is excellent in slidability, hard to be worn and unlikely to scratch the photosensitive drum
1
. In general, a POM-based resin or an ultrahigh molecular weight polyethylene resin is used as the material.
As shown in
FIG. 14
, the developing sleeve
31
is supported at its both ends rotatably with respect to the developing container
32
of the developing device
3
via the bearings
21
. In the illustrated example, the developing sleeve
31
is supported with respect to the developing container
32
on the inner side inside positions in which the spacer
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