Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
1999-12-29
2001-05-29
Pendegrass, Joan (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C399S222000, C399S265000
Reexamination Certificate
active
06240268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a laser printer, a copying machine, or a facsimile, that employs electrophotographic technology. More particularly, the present invention relates to a member for retaining a gap between an image bearing member and a developer bearing member.
2. Description of the Related Art
Referring to
FIGS. 2 and 3
, an image forming apparatus
1
that employs electrophotographic technology selectively exposes a photosensitive drum
20
, which is an image bearing member and has been uniformly charged by a charging device
30
, by an exposure device
3
to thereby form a latent image on the photosensitive drum
20
. The latent image is developed using a developer or toner T, and the developed image is transferred to a recording medium P, such as paper or OHT. Then, the transferred image on the recording medium P is pressed and thermally fixed using a fixing device
9
so as to record the image. Upon completion of transferring the image toner, the toner remaining on the photosensitive drum
20
is removed by a cleaning device
50
before another cycle of the image forming process beginning with electrical charging is started.
As the photosensitive drum
20
used with such an image forming apparatus, a photosensitive drum has been known, in which a conductive base material, such as aluminum, is employed as a base member
21
, and a photoconductive material providing a photosensitive layer
22
is coated on the base member
21
as shown in FIG.
5
. Conventionally used photoconductive materials include inorganic photoconductive materials, such as selenium, cadmium sulfide, and zinc oxide, and organic photoconductive materials, such as polyvinyl carbazole, oxadiazole, and phthalocyanine. When using an organic photoconductive material, in particular, it has been known to use, for the purpose of sensitization, the photosensitive layer
22
formed of a laminate of an electric charge generating layer
22
a
and an electric charge transporting layer
22
b
to separately provide different functions. The electric charge transporting
22
b
serving as a surface layer that uses polycarbonate as a binder has been put in practical use.
A developing device
40
that has been put in practical use is constituted by a toner chamber
45
holding a toner T, a developer supply chamber
44
, a developer bearing member or a developing roller
41
, and a developer restricting member or a developing blade
42
as shown in FIG.
3
.
The developing roller
41
is formed of a conductive material, such as aluminum, and rotatably retained with a predetermined gap, preferably 0.2 mm to 0.5 mm, from the photosensitive drum
20
. The developing roller
41
incorporates therein a magnet roller
43
having a plurality of magnetic poles. The magnet roller
43
is retained by a developing device frame
46
so that it does not rotate as shown in FIG.
5
.
The developing blade
42
is secured to the developing device frame
46
such that one end thereof is pressed against an outer peripheral surface of the developing roller
41
.
As shown in
FIG. 3
, the toner T of the toner chamber
45
is carried from the toner chamber
45
to the developer supply chamber
44
by its own weight or a carrying means (not shown), and drawn to the vicinity of the developing roller
41
by a magnetic force of the magnet roller
43
. The toner T carried to the vicinity of the developing roller
41
is carried toward the developing blade
42
by the rotation of the developing roller
41
, restricted in its layer thickness by the developing blade
42
, then carried toward the photosensitive drum
20
. At this point, a predetermined level of electric charge is imparted to the toner T having its layer thickness restricted when passing through a nipped portion between the developing blade
42
and the developing roller
41
.
In the aforesaid developing device
40
, means for stably holding the developing roller
41
and the photosensitive drum
20
with a predetermined gap therebetween is formed of polyacetal, and has substantially cylindrical gap retaining members or spacer rollers
60
having a wall thickness of, for example, 0.2 mm to 0.5 mm. The spacer rollers
60
are rotatably fitted at both ends of the developing roller
41
, and the developing roller
41
is pressed toward the photosensitive drum
20
by a compression spring
54
functioning as an urging means, as shown in
FIGS. 1 and 4
. Two typical examples are shown in FIG.
1
.
Extended use of the image forming apparatus
1
requires supply of the toner T and adjustment, cleaning, or replacement of the photosensitive drum
20
and other means for implementing diverse processes. Such maintenance and service have been difficult in practice for people other than servicemen with expertise.
To overcome the difficulty mentioned above, a process cartridge
2
shown in
FIG. 2
, for example, has been devised and put in practical use. The process cartridge
2
combines processing means, such as the toner T, the photosensitive drum
20
, the developing device
40
, the charging device
30
, and the cleaning device
50
, into one unit. The process cartridge
2
is detachably installed on the image forming apparatus
1
, thus improving maintainability.
With recent dissemination of the image forming apparatus
1
, there have been demands for a reduced size, a reduced noise, and lower cost of the image forming apparatus (apparatus main body)
1
. The reduction of noise and cost has been studied and achieved by obviating the need for an exhaust fan. As other measures for achieving the lower cost, the material used for a main body frame
1
a
has been changed from a sheet metal to a resin to permit one-piece molding. However, an attempt to achieve the reduced size, the controlled noise, and the lower cost of the apparatus main body
1
employing the conventional spacer rollers
60
has been facing difficulties set forth below.
The apparatus main body
1
includes various heat generating sources, including the fixing device
9
. Making the apparatus main body
1
smaller would cause the temperature in the apparatus main body
1
to rise more easily. Especially in the case of the apparatus main body
1
not equipped with an exhaust fan, the temperature in the apparatus main body
1
would rise more easily.
The spacer rollers
60
are repeatedly subjected to compressive stress. Hence, if the apparatus main body
1
is made smaller or not provided with an exhaust fan, then the spacer rollers
60
will be repeatedly subjected to compressive stress at a high temperature. In the case of an apparatus that employs the spacer rollers
60
that can be fitted at the ends of the developing roller
41
as shown in
FIG. 1
, there has been a danger in that the spacer rollers
60
incur rolling deformation. As a result, prolonged use of the apparatus may cause the spacer rollers
60
to fail to maintain a proper gap.
In addition, the outer peripheries of the spacer rollers
60
are usually pressed against the photosensitive layer
22
of the photosensitive drum
20
. The spacer rollers
60
are repeatedly brought into contact with and moved away from the photosensitive layer
22
, and the friction from sliding against each other causes the outer peripheral surface of the spacer rollers
60
to be easily charged.
The photosensitive layer
22
of the photosensitive drum
20
is preferably short from the viewpoint of manufacturing process and cost. For this reason, it is desirable to expose the base member
21
of the photosensitive drum
20
at both end areas not involved in formation of images as shown in
FIG. 5
rather than providing those end areas also with the photosensitive layer
22
.
Because of the exposed areas, there have been cases where the surfaces of the spacer rollers
60
are charged, and the electric charges are discharged to exposed portions
21
a
of the base member of the photosensitive drum
20
, radiating a field emission voltage. There has been a danger in that the field emission
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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