Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2002-06-13
2004-03-16
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C399S075000, C399S299000
Reexamination Certificate
active
06708013
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus. More specifically, the invention relates to a so-called tandem type color image forming apparatus provided with a plurality of monochromatic toner image carriers on an intermediate transfer belt or a recording medium delivery belt which is to be circulated, and serving to sequentially transfer toner images having different colors which are formed by a monochromatic toner image carrier to a recording medium delivered through the intermediate transfer belt or the recording medium delivery belt, thereby forming a color image. In particular, the invention relates to a driving system for rotating each monochromatic toner image carrier.
Japanese Patent Publication No. 61-156159A discloses a conventional tandem type color image forming apparatus.
As shown in
FIG. 10A
, the conventional color image forming apparatus comprises a recording medium delivery belt
1
to be circulated, three photosensitive members
2
Y,
2
M and
2
C to be monochromatic toner image carriers (for three colors of yellow (Y), magenta (M) and cyan (C)) provided on the recording medium delivery belt
1
, and a gear train
3
(see
FIG. 10B
) for rotating the monochromatic toner image carriers, and serves to sequentially transfer toner images carried by the three monochromatic toner image carriers
2
Y,
2
M and
2
C to a recording medium P supplied through a paper feeding roller
4
and delivered through the recording medium delivery belt
1
, thereby forming a color image on the recording medium P.
A driving gear
3
a
(Y, C, M) is provided on the end of each of the monochromatic toner image carriers
2
Y,
2
M and
2
C.
Intermediate gears
3
b
and
3
b
are provided between the driving gears
3
a
(Y, C, M), and the driving gears
3
a
(Y, C, M) and the intermediate gears
3
b
and
3
b
are provided in a line to constitute a gear train
3
.
A driving source gear
5
a
to be rotated by a motor
5
is engaged with the driving gear
3
a
(Y) positioned on the end of the gear train
3
. Consequently, each of the monochromatic toner image carriers
2
(Y, M, C) is rotated through the gear train
3
.
Thus, the driving gears
3
a
(Y, C, M) and the intermediate gears
3
b
and
3
b
are arranged in a line so that each of the monochromatic toner image carriers
2
(Y, C, M) can be rotated at a minimum gear number.
In the conventional apparatus, as shown in
FIG. 10B
, since the centers of the rotation of the driving gears
3
a
(Y, C, M) and the centers of the rotation of the intermediate gears
3
b
and
3
b
in the gear train
3
are arranged on a straight line SL, the following problem arises.
More specifically, the driving gear
3
a
and the intermediate gear
3
b
have manufacturing errors respectively and are swollen by a rise in a temperature in the apparatus. In some cases, therefore, the sizes of the driving gear
3
a
and the intermediate gear
3
b
are increased to be greater than desirable dimensions.
In such a situation, if the centers of the rotation of the driving gears
3
a
(Y, C, M) and the centers of the rotation of the intermediate gears
3
b
and
3
b
are arranged on the straight line SL, the gears
3
a
and
3
b
are pressed in the direction of the straight line SL and receive an unstable load when the sizes of the gears
3
a
and
3
b
are increased to be greater than the desirable dimensions due to the manufacturing error or the rise in the temperature.
Such an unstable load, particularly, an unstable load acting on the driving gear
3
a
unstably moves each of the monochromatic toner image carriers
2
(Y, C, M) in the direction of the straight line SL, causing an uneven rotation or a color shift. As a result, obtained image quality is deteriorated.
In the conventional apparatus, with respect to the drive gear
3
a
(M) for driving the image carrier
2
M, a driving force F sent from the intermediate gear
3
b
on the upstream side and a driving reaction force R sent from the intermediate gear
3
b
on the downstream side act.
On the other hand, since developing rollers
6
(Y, C, M) abut on the image carrier
2
, an abutment force Fd acts on the image carrier
2
.
In this configuration, since the driving force F, the driving reaction force R and the abutment force Fd sent from the developing roller (abutment member)
6
are sent in one direction (downward in FIG.
10
B), a resultant force thereof acts as a great radial force on the bearing portion of the image carrier.
For this reason, the conventional apparatus has a problem in that a driving torque is increased and the bearing portion is apt to be deteriorated by a wear so that the rotation blurring of the image carrier is apt to be generated and image quality is thereby deteriorated easily.
Moreover, since the image carrier gear is provided on only one end of the image carrier, the great radial force acts on one end side thereof. The radial force on one end side (therefore, the imbalance of the radial force on both ends of the image carrier) causes the skew of the image carrier. When the image carrier skews, image forming conditions in an axial direction are changed. Therefore, there is a problem in that the image quality is deteriorated (the image quality in a transverse direction seen in the direction of delivery of the recording medium P is apparently varied).
The problems arise in a color image forming apparatus having one image carrier and a monochrome image forming apparatus as well as a tandem type image forming apparatus in which a plurality of image carriers are provided, and remarkably arise in a tandem type image forming apparatus in which a plurality of image carriers are provided.
As in the conventional apparatus, in the case in which the gear train
3
for driving a plurality of monochromatic toner image carriers
2
(Y, C, M) is constituted in a line, a color formed and transferred by the image carrier positioned in the final stage of the power transmission path causes a color shift or a jitter (a stripe-shaped density unevenness generated by a fluctuation in the speed of the image carrier) most easily by the accumulation of the manufacturing errors of the gears
3
a
(Y, C, M) and
3
b
constituting the gear train
3
.
Moreover, in the case in which the gear train
3
is constituted in a line as shown in
FIG. 10B
, a driving force F sent from the intermediate gear
3
b
provided on the upstream side and a driving reaction force R sent from the intermediate gear
3
b
provided on the downstream side act on the driving gear (for example,
3
a
(M)) positioned on the way of the power transmission path, while only the driving force F sent from the intermediate gear
3
b
provided on the upstream side acts on the driving gear
3
a
(C) positioned in the final stage of the power transmission path. Therefore, the driving gears
3
a
(Y) and
3
a
(M) positioned on the way of the power transmission path and the driving gear
3
a
(C) positioned in the final stage are deformed differently.
For this reason, a color formed and transferred by the image carrier positioned in the final stage of the power transmission path causes the color shift or the jitter most easily.
Under such a situation, in the conventional apparatus, the driving gear
3
a
(C) of the image carrier
2
(C) for cyan to be a relatively remarkable color is provided in the final stage of the power transmission path in the gear train
3
. Therefore, the color shift and the jitter of the cyan image are easily remarkable in such a state that the toner images having a plurality of colors are superposed on the recording medium P. As a result, there is a problem in that the image quality of the whole color image is deteriorated.
As shown in
FIG. 11
, Japanese Patent Publication No. 11-231754A discloses a color image forming apparatus of such a type (an intermediate transfer type) comprising an intermediate transfer belt
6
, and a plurality of monochromatic toner image carriers
2
(Y, M, C, K (black)) provided on the intermediate transfer belt
6
, and serving to sequentially trans
Chen Sophia S.
Seiko Epson Corporation
Sughrue & Mion, PLLC
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