Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2003-08-04
2004-12-14
Beatty, Robert (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S301000
Reexamination Certificate
active
06832060
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming apparatus and an image forming method which repeat image create/transfer processing for a plurality of toner colors which are different from each other so that toner images in the respective toner colors are laid one atop the other on a transfer medium, such as a transfer drum and a transfer belt, and a color image is accordingly formed. As herein described, the “image create/transfer processing” refers to a series of processes that after forming a toner image on a photosensitive member while rotating the photosensitive member and a transfer medium in a sub scanning direction, the toner image is transferred onto the transfer medium.
BACKGROUND ART
An image forming apparatus of this type is as that shown in
FIG. 59
, for example. This image forming apparatus allows to form toner images in a plurality of colors which are different from each other, e.g., four colors of yellow (Y), cyan (C), magenta (M) and black (K), on a photosensitive member
21
which is driven to rotate. The respective toner images are primarily transferred onto a transfer medium
41
, such as a transfer belt and a transfer drum, which rotates in synchronization with the photosensitive member
21
. The image forming apparatus comprises a drive source
81
, such as a dynamotor and a pulse motor, in order to drive the photosensitive member
21
and the transfer medium
41
into rotation. Rotational drive force generated by the drive source
81
is applied to the photosensitive member
21
and the transfer medium
41
through a power transmission unit
9
which comprises power transmission members
91
, such as a plurality of gears and a belt, and drives the photosensitive member
21
and the transfer medium
41
into rotation in mutual synchronization.
In this image forming apparatus, toner images in the respective colors are laid one atop the other on the transfer medium
41
through repeated image create/transfer processing for the plurality of colors, and a color image is formed on the transfer medium
41
. Following this, the color image is secondarily transferred onto a sheet member S, such as a copy paper, a transfer paper, a paper and a transparent sheet for an overhead projector, which is fed from a cassette or manual-feed tray.
In order to obtain an excellent color image, it is necessary to lay toner images in the plurality of colors one atop the other while registering the toner images with each other. To this end, in the image forming apparatus described above, a sensor
40
for detecting a reference position of the transfer medium
41
, for instance, is disposed in the vicinity of the transfer medium
41
, and a signal which is outputted from the sensor
40
for every rotation of the transfer medium
41
is used as a reference signal for the image create/transfer processing. More specifically, after a toner image is created on the photosensitive member
21
at predetermined timing for every outputting of the reference signal, the toner images are primarily transferred onto the transfer medium
41
which rotates at a constant speed in synchronization with the photosensitive member
21
. As a result, the toner images in the plurality of colors are laid over with each other accurately. Hence, the transfer medium
41
needs be driven to rotate at a constant speed in synchronization with the photosensitive member
21
until the primary transfer completes since outputting of the reference signal from the sensor
40
.
However, abutting means
400
, such as a secondary transfer roller for secondary transfer onto the transfer medium
41
and a cleaning part for cleaning of the transfer medium
41
, sometimes temporarily comes into contact at proper timing, thereby changing loads upon the transfer medium
41
, the power transmission members
91
, etc. In other words, the contact could hamper the drive rotation of the transfer medium
41
, elastically stretch the transfer medium
41
, elastically bend the power transmission members
91
in a similar manner, or further, change a load upon a driving part (not shown) which drives the transfer medium
41
into rotation. The contact and separation could prevent the transfer medium
41
from rotating at a constant speed.
In an image forming apparatus of this type, in particular, in order to accurately transmit rotational drive force from the drive source
81
to the photosensitive member
21
and the transfer medium
41
, gears formed by a resin material, such as polyacetal (POM), polycarbonate (PC), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT) and polyimide (PI), are often used, and therefore, the gears are elastically deformed as such loads described above change, which is one of main causes of a registration deviation. Further, where the transfer medium
41
is a transfer belt, stretching and shrinking of the transfer medium
41
caused by a change in the loads described above is one of main causes of a registration deviation. A registration deviation which is caused as the abutting means
400
contacts and moves away from the transfer medium
41
will be described in detail in the sections “A-3. Analysis of Causes of Registration Deviation” and “B-3. Analysis of Causes of Registration Deviation” later.
Causes of a registration deviation are not limited to these. A registration deviation may be caused by the following as well. That is, in an image forming apparatus of this type, the photosensitive member
21
and the transfer medium
41
are driven into rotation in mutual synchronization in a sub scanning direction. As the sensor
40
outputs a vertical synchronizing signal using this as a reference, a light beam scans over the photosensitive member
21
in a main scanning direction, which is approximately perpendicular to the sub scanning direction, based on an image signal which is supplied from an external apparatus such as a host computer, whereby an electrostatic latent image which corresponds to the image signal is formed on the photosensitive member
21
.
Further, after the electrostatic latent image is developed by a developer with toner and a toner image is formed, the toner image is transferred onto the transfer medium
41
which is driven into rotation in synchronization with the photosensitive member
21
in the sub scanning direction. Such image create/transfer processing is executed for the respective toner colors (yellow, cyan, magenta and black), so that the respective toner images are laid one atop the other and a color image is created on the transfer medium
41
.
However, in an image forming apparatus of this type, scan timing of the light beam is not synchronous to the vertical synchronizing signal in many cases, sometimes leading to a synchronization error between the vertical synchronizing signal and the scan timing. In this case, a transfer position on the transfer medium
41
becomes deviated by an amount corresponding to the synchronization error. Since synchronization errors become different among the respective toner colors, the toner images become deviated from each other among the respective toner colors, that is, a registration deviation which degrades an image quality is developed.
The present invention has been made in view of the problem above, and accordingly, aims at providing an image forming apparatus and an image forming method with which it is possible to suppress a registration deviation on a transfer medium and form a high-quality image.
SUMMARY OF THE INVENTION
According to the present invention, based on a registration control amount which is needed to correct registration deviations which are caused as image create/transfer processing is repeated for a plurality of toner colors which are different from each other and toner images in the respective toner colors are laid one atop the other on a transfer medium, transfer start positions for toner images in at least one or more of the toner colors are corrected. This eliminates or suppresses relative registration deviations among the toner images on the transfer medium and improves a
Inoue Nozomu
Kowari Tsuyoshi
Nakazawa Yoshio
Taguchi Keiichi
Tanaka Kuniaki
Beatty Robert
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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