Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-11-01
2002-03-19
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S040000, C399S231000, C399S299000, C399S306000
Reexamination Certificate
active
06360070
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus in which a printing medium is supported and conveyed by a conveyer and transfer belt which abuts the transfer area surface of the rotationally driven image bearer (photosensitive drum), with a predetermined positional relationship so that the toner image formed on the image bearer is transferred to and reproduced on the printing medium. More detailedly, the present invention relates to an image forming apparatus in which the image bearer is controlled so that it stops with a predetermined positional relationship when it is stopped to thereby become ready for subsequent image formation with precision.
(2) Description of the Prior Art
Conventionally, color image forming apparatus have been known in which a color image is transferred as image data of YMCK components to the recording portion whereby the color image is reproduced by forming color separations of the image and successively superimposing them one over another. So, color image forming apparatus of this type suffer from the problem in that a correct color image cannot be reproduced if each color separation cannot be exactly laid over the others. Therefore, how this problem is handled is the key to the technical development of this field.
In the image forming apparatus having a large number of parts, each part has small variations in precision. Further, individual image forming apparatus present variations in the assembly accuracy when these parts are assembled.
To deal with this, a configuration has been known conventionally, which forms trial color-separated pattern images and checks the positional relationship between these color separated pattern images to perform registration adjustment to image forming positions for individual component color image formations (c.f. Japanese Patent Application Laid-Open Sho 63 No. 286864).
Though it was possible to compensate for ‘color misregistration’ due to ‘deviations of the start-position of writing of individual images’ by the execution of the aforementioned registration adjustment, it was impossible to correct the color misregistration attributed to the irregular speed variations of the photosensitive drums which are caused by periodic driving irregularities of the drive system, of drive gears etc. for driving the photosensitive drums.
Actually, the image forming apparatus of this kind has conventionally suffered from periodic driving unevenness in different recording portions. Due to the occurrence of the periodic driving unevenness in individual recording portions, the image forming apparatus has the problem of color misregistration arising when the images recorded with different coloring matters are sequentially superimposed one over another to reproduce a color image, making it impossible to reproduce a correct color image.
To deal with this, in the conventional color image forming apparatus, in order to synchronize the behavior of each photosensitive drum due to the driving unevenness when the images formed on the photosensitive drum in individual recording portions are transferred at in their transfer stations, arrangement of the image forming system has been manipulated in such a geometry that the distance (time) from the position of image recording to one photosensitive drum to its transfer position is set equal to N times (N is an integer) of the cycle period of the driving unevenness of the driving mechanism (see Japanese Patent Application Laid-Open Sho 62 No.129873 and Japanese Patent Application Laid-Open Sho 63 No.11965).
FIG. 1
shows a configuration of image forming portions and a conveyer and transfer belt and thereabout for transferring the images formed in the individual image forming portions in a conventional color image forming apparatus using the above technique.
In
FIG. 1
, photosensitive drums
322
a
,
322
b
,
322
c
and
322
d
, constitute the recording portions for black, cyan, magenta and yellow, from the right to left. The images of different colors formed on these photosensitive drums
322
a
to
322
d
are transferred, sequentially from black, onto the printing medium supported and conveyed by conveyer and transfer belt
316
, at the transfer areas A where photosensitive drums
322
a
to
322
d
are located close to conveyer and transfer belt
316
.
Here, photosensitive drums
322
a
to
322
d
are adapted to start rotating simultaneously and are attached in such an arrangement that the behavior of rotational driving unevenness is in phase with each other.
As an illustrative example, the driving gears (not shown) are fitted on the shafts of photosensitive drums
322
a
to
322
d
so that certain references (for example, keyhole shaped holes ha shown in
FIG. 1
) indicating the phase of the driving unevenness are oriented in the same direction. By this arrangement, photosensitive drums
322
a
to
322
d
will rotate with their driving unevenness always in phase if they are started simultaneously.
Therefore, when the distance L′ between transfer areas A as to photosensitive drums
322
a
to
322
d
is set so that
L′=N&pgr;d . . . (N is an integer)
where d is the diameter of each photosensitive drum
322
a
to
322
d
, in the image transfer process at each transfer area A of the four photosensitive drums
322
a
to
322
d
arranged in parallel to each other, images of different colors will be sequentially superimposed one over another with their behavior of the driving unevenness always being harmonized with respect to the printing medium. As result, it is possible to eliminate color misregistration due to driving unevenness.
However, in an image forming apparatus having a large number of parts, each part has small variations in precision. Or, individual image forming apparatus present variations in the assembly accuracy when these parts are assembled. Further, in the above configuration, the recording portions arranged in parallel to each other have to be arranged with their distances set in conformity with the periodic driving variations. So, when the recording portions are set with their distance from one to the next in conformity with the periodic driving variations, even with an integer N equal to 1, the distance at least needs to be equal to the circumference of the photosensitive drum. As a result, the image forming apparatus itself becomes bulky, in contrast to the user's demands for downsizing. In particular, this problem is markedly significant in an image forming apparatus having four photosensitive drums of component colors Y, M, C and Bk, as stated above.
In the conventional apparatus shown in
FIG. 1
, in order to reduce the friction between the photosensitive drums and the conveyer and transfer belt as low as possible, photosensitive drums
322
a
to
322
d
start and stop rotating simultaneously. Further, in order to suppress the appearance of the driving unevenness derived from the driving system of the photosensitive drums, the start-position or behavior of driving unevenness in each photosensitive drum relative to conveyer and transfer belt
316
is kept in phase with that of the others so that photosensitive drums
322
a
to
322
d
start and stop rotating from their reference positions keeping the positional relationship between the drums and the conveyer and transfer belt
316
constant.
However, it is impossible to start and stop the movements of photosensitive drums
322
a
to
322
d
and conveyer and transfer belt
316
for the transfer operation, completely in synchronism. The time lag of the rotation and stoppage will impart a large contact friction to the delicate surfaces of the photosensitive drums around their reference positions. Thus, repetitions of the contact friction promotes damage to the surfaces of the photosensitive drums around the reference positions and consequently, a duplicated image degrades at the corresponding position, so the photosensitive drums have to be replaced in spite of their partial damage.
In connection with this, the damage around the referenc
Fukutome Shoichi
Harada Yoshikazu
Manabe Nobuo
Sakagami Hidekazu
Taka Kyosuke
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Grainger Quana M.
Sharp Kabushiki Kaisha
Tucker Davis A.
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