Electrophotography – Control of electrophotography process
Reexamination Certificate
2000-02-22
2001-11-27
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
C399S167000, C399S303000
Reexamination Certificate
active
06324355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus using the electrophotographic process, and particularly to an image forming apparatus such as a copier, a printer or a facsimile apparatus.
2. Related Background Art
An image forming apparatus adopting the electrophotographic process has a plurality of image forming portions for forming latent images on photosensitive drums which are image bearing members by the utilization of light, magnetism, charges or the like, and visualizing the latent images to thereby obtain visible images, transfer material conveying means for conveying a transfer material to a transfer position of each image forming portion, and fixing means for fixing the image transferred onto the transfer material on the transfer material.
As the transfer material conveying means, use is often made of a belt-shaped conveying member, i.e., a transfer material conveying belt (hereinafter simply referred to as the “conveying belt”) from the viewpoint of the conveying property, and it conveys the transfer material to the transfer position, and further to the fixing device. At this time, the transfer material is retained on the conveying belt by an electrostatic attractive force and is conveyed.
The conveying belt is passed over, supported and moved by a drive roller (drive rotary member) and at least one driven roller (driven rotary member).
Contrivance is made such that the conveying belt is extended with a constant force between the drive roller and the driven roller, and the conveying belt is moved at a constant speed from the most upstream image forming portion to the most downstream image forming portion without slackening between the two rollers.
The transfer material is electrostatically attracted to the conveying belt as previously described, and is conveyed to each image forming portion while being retained on the conveying belt, and a toner image of each color is transferred to the transfer material, and is fixed at fixing means, whereby a full color image can be obtained.
Also, the conveying belt is provided with deviation regulating means for blocking the deviation of the belt (the movement of the belt on the roller shaft in a direction orthogonal to the driving direction) by the extraneous force during long-time rotation or jam clearance to thereby prevent the belt from falling off the rollers.
The image forming process in an image forming apparatus according to the conventional art will now be described specifically with reference to
FIG. 23
of the accompanying drawings.
FIG. 23
schematically shows an example of a full color image forming apparatus according to the conventional art.
First, second, third and fourth image forming portions Pa, Pb, Pc and Pd are juxtaposed in the main body of the image forming apparatus. Below the first to fourth image forming portions Pa to Pd from cassettes
107
a
and
107
b
containing transfer materials therein to a fixing device
111
in the main body of the image forming apparatus, there is provided an endless belt-shaped transfer material conveying means, i.e., a conveying belt
108
, circulatorily moved to convey the transfer material through these image forming portions Pa-Pd. This conveying belt
108
is passed over a driven roller
109
and a drive roller
110
. Further, the driven roller
109
is provided with tension imparting means
109
t
for imparting tension to the conveying belt
108
, and deviation regulating means, not shown.
The conveying belt
108
is a thin belt of a dielectric material driven in the direction indicated by the arrow A by the drive roller
110
rotated by a drive motor, e.g. a stepping motor
120
, and bears thereon the transfer material fed out of the cassette
107
a
or
107
b
and fed in synchronism with image formation by a pair of registration rollers
100
, and the transfer material is conveyed to the afore described image forming portions Pa-Pd in succession. The fixing device
111
receives the transfer material discharged from the drive roller
110
, and collectively fixes toner images of respective colors transferred to the transfer material in superposed relationship with one another at the image forming portions Pa-Pd to thereby form a permanent image.
Each portion of the image forming apparatus will now be described in detail. The image forming portions Pa-Pd have substantially the same construction, and include photosensitive drums
101
a
,
101
b
,
101
c
and
101
d
which are image bearing members rotatively driven in the direction indicated by arrow B, and primary chargers
102
a
,
102
b
,
102
c
and
102
d
for uniformly is charging the photosensitive drums
101
a
-
101
d
, respectively, developing devices
103
a
,
103
b
,
103
c
and
103
d
for developing electrostatic latent images formed on the photosensitive drums
101
a
-
101
d
, respectively, transfer chargers
104
a
,
104
b
,
104
c
and
104
d
for transferring the developed toner images of respective colors to the transfer material, and cleaning devices
105
a
,
105
b
,
105
c
and
105
d
for removing the toners remaining on the photosensitive drums
101
a
-
101
d
, respectively, are successively disposed around the respective photosensitive drums
101
a
-
101
d
in the direction of rotation thereof (the direction indicated by the arrow B). Exposing optical systems
106
a
,
106
b
,
106
c
and
106
d
are provided above the photosensitive drums
101
a
-
101
d
, respectively.
Yellow (Y) toner, magenta (M) toner, cyan (C) toner and black (K) toner are contained in the developing devices
103
a
,
103
b
,
103
c
and
103
d
, respectively.
In the above-described full color image forming apparatus, when a transfer material is placed on the conveying belt
108
, the image forming processes for the corresponding photosensitive drums
101
a
-
101
d
are successively started with the movement of the conveying belt
108
in the direction indicated by the arrow A. That is, a yellow image is formed on the photosensitive drum
101
a
of the first image forming portion Pa, a magenta image is formed on the photosensitive drum
101
b
of the second image forming portion Pb, a cyan image is formed on the photosensitive drum
101
c
of the third image forming portion Pc, and a black image is formed on the photosensitive drum
101
d
of the fourth image forming portion Pd.
The transfer material passes below the photosensitive drums
101
a
-
101
d
in the first to fourth image forming portions Pa-Pd and is conveyed toward the fixing device
111
by the movement of the conveying belt
108
, and the toner images of the respective colors are transferred to the transfer material in superposed relationship with one another by the transfer chargers
104
a
-
104
d
of the image forming portions Pa-Pd, whereby a full color image is formed.
The transfer material passes through the last fourth image forming portion Pd, whereafter it is separated from the conveying belt
108
and is sent to the fixing device
111
, in which the toner images of the respective colors transferred in superposed relationship with one another are fused and fixed, whereafter the transfer material is discharged to a discharge tray
112
.
However, with the ideal conveying speed of the conveying belt
108
as the premise, latent images are formed on the corresponding photosensitive drums
101
a
-
101
d
at exposing time intervals corresponding to desired image information, whereby a desired transferred image ought to be formed on the transfer material, but since there are the following problems, positional deviation may occur to the transferred image to deteriorate the quality of the image.
The following two points become great problems in driving the conveying belt
108
so as to assume an ideal conveying speed.
(1) The conveying speed of the transfer material conveyed by the conveying belt
108
is sequentially changed by the geometrical shape difference or the like of the drive roller
110
or between the drive roller
110
and the driven roller
109
and therefore, in the image sequentially f
Matsui Norio
Munakata Atsushi
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
Tran Hoan
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