Electrophotography – Image formation – Transfer
Reexamination Certificate
2002-09-04
2004-08-03
Braun, Fred L (Department: 2852)
Electrophotography
Image formation
Transfer
C399S343000, C399S350000
Reexamination Certificate
active
06771924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus of an electrophotographic process or the like for forming an image using a plurality of image bearing members (e.g., photosensitive members).
As the image forming apparatus of the electrophotographic process, there are, for example, an electrophotographic copying machine, an electrophotographic printer (e.g., an LED printer and a laser beam printer) and an electrophotographic facsimile machine.
2. Description of the Related Art
In recent years, with the spread of a color image forming apparatus according to the electrophotographic process, a demand for speed-up of color output has been increasing in addition to a demand for a recording quality of a color image. In order to meet these demands, there have been made several proposals with respect to an image forming process.
For example, a color image farming apparatus of a tandem type uses a plurality of photosensitive drums arranged side by side. The color image forming apparatus forms a toner image of each color of black, cyan, magenta and yellow on each photosensitive drum. Then, the toner images are sequentially transferred to a transfer material, which is conveyed by a transfer material conveyor belt, by respective transferring means. Thereafter, the toner images are fixed by a fixing device.
FIGS. 3 and 4
are sectional views of a conventional color image forming apparatus of the tandem type. As shown in
FIGS. 3 and 4
, transfer materials S are set in a sheet feeding cassette
101
inserted in a lower part of an apparatus main body. The transfer materials S are fed by a sheet feed roller
102
and sent to a registration roller pair
104
.
There is provided a transfer material conveyor belt
105
for conveying the transfer materials S on a downstream side in a conveying direction of transfer materials of the registration roller pair
104
. The transfer material conveyor belt
105
is stretched and suspended flatly in the conveying direction of transfer materials (vertical direction of
FIG. 3
) by a plurality of rotation rollers such as a drive roller
106
, a driven roller
107
and a tension roller
108
. An attracting roller
109
is arranged in a most upstream part in the conveying direction of transfer materials of the transfer material conveyor belt
105
. The attracting roller
109
is brought into pressed contact with the driven roller
107
via the transfer material conveyor belt
105
.
A predetermined bias voltage is applied to the attracting roller
109
. Consequently, the transfer material S, which is conveyed onto the transfer material conveyor belt
105
at good timing by the registration roller pair
104
, is electrostatically attracted by the transfer material conveyor belt
105
to be conveyed.
Four photosensitive drums of yellow, magenta, cyan and black
110
y
,
110
m
,
110
c
and
110
k
(hereinafter simply referred to as “photosensitive drums
110
”) are linearly arranged in order from the lower side to the upper side of
FIG. 3
to be opposed to the transfer material conveyor belt
105
.
Primary chargers
111
y
,
111
m
,
111
c
and
111
k
(hereinafter simply referred to as “primary chargers
111
”), developing devices
112
y
,
112
m
,
112
c
and
112
k
(hereinafter simply referred to as “developing devices
112
”) and cleaning means
113
y
,
113
m
,
113
c
and
113
k
(hereinafter simply referred to as “cleaning means
113
”) are arranged around the respective photosensitive drums
110
. In addition, transfer members
114
y
,
114
m
,
114
c
and
114
k
(hereinafter simply referred to as “transfer members
114
”) are arranged opposite to the photosensitive drums
110
across the transfer material conveyor belt
105
.
Toner of each color is contained inside toner containers of the developing devices
112
. Toner images of each color are formed on the photosensitive drums
110
by a well-known image forming process and are sequentially transferred to the transfer material S, which is conveyed by the transfer material conveyor belt
105
, to form a color image.
The transfer material S having the toner image transferred thereon is self-stripped in the position of the drive roller
106
and guided to a fixing roller pair
115
. The transfer material S is subjected to heating and pressurizing processing while it is nipped and conveyed by the fixing roller pair
115
, and the toner image is permanently fixed. Thereafter, the transfer material S is conveyed by a discharge roller pair
116
and discharged onto a discharge tray
117
arranged in the upper part of the apparatus main body.
In the color image forming apparatus as described above, multicolor printing, that is, full color image formation is not always performed but a frequency of performing recording of single color of black, that is, monochrome image formation is also relatively high. Leaving developing rollers in contact with photosensitive drums that do not perform image formation even in such a case contributes to generation of fog or the like and is not preferable.
Therefore, in order to cope with such a method of use, there is proposed a color image forming apparatus of a tandem type that is constituted such that a contact or non-contact state of photosensitive drums and developing rollers can be appropriately switched in association with a case of full color image formation and a case of monochrome image formation.
For example, as shown in
FIG. 3
, image bearing members and developing rollers are in a contact state at the time of full color image formation. On the other hand, at the time of monochrome image formation, as shown in
FIG. 4
, switching means
118
(
118
y
,
118
m
,
118
c
and
118
k
) for switching contact and non-contact of the image bearing members and the developing rollers push up a part of bottoms of developing devices to lift them upward in
FIG. 4
to separate developing rollers
100
from photosensitive drums
110
other than that of black to make them non-contact. Thus, only a black image is recorded.
Constituting the color image forming apparatus in this way, a route of the transfer material S conveyed from the attracting roller
109
to the fixing roller pair
115
through a black image forming portion does not change in the case of full color image formation and the case of monochrome image formation, and a stable conveying performance is realized.
However, in the aforementioned conventional example, if a large number of monochrome images are formed, an abutment state of a cleaning blade tends to be unstable in process cartridges other than that for black. This is because, since the photosensitive drums and the developing rollers are not in contact with each other, toner hardly moves to the photosensitive drums and toner as lubricant decreases in rubbing parts of photosensitive drums and the cleaning blades. When the abutment state of the cleaning blades becomes unstable, it is likely that defective cleaning such as toner slipping or image defectiveness due to contamination of a charging member is caused. In the worst case, it is likely that damages such as tucking of cleaning blades are caused.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above and other drawbacks, and it is an object of the present invention to provide an image forming apparatus in which defective cleaning by cleaning means is prevented.
It is another object of the present invention to provide an image forming apparatus that is capable of performing image formation at a high speed using a plurality of image bearing members.
It is another object of the present invention to provide an image forming apparatus in which an abutment state of an image bearing member, on which an image is not formed, among a plurality of image bearing members and cleaning means is stabilized.
It is another object of the present invention to provide an image forming apparatus in which developer is supplied between an image bearing member on which an image is not formed and cleaning means.
It is yet another object o
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