Electrophotography – Diagnostics – Document handling
Reexamination Certificate
1999-11-22
2002-02-12
Braun, Fred L (Department: 2852)
Electrophotography
Diagnostics
Document handling
C399S021000, C399S397000
Reexamination Certificate
active
06347196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copier. In particular, the invention relates to an improvement of an image forming apparatus of a type in which a visible image such as a full-color image formed on an image carrying body is transferred collectively to a transfer member.
2. Description of the Related Art
For example, an intermediate transfer type color image forming apparatus is known which is equipped with a latent image carrying body such as a photoreceptor drum on which a toner image of each color component corresponding to an electrostatic latent image is formed according to, for example, the electrophotographic scheme, a belt-like or drum-like intermediate transfer body to which each toner image on the latent image carrying body is transferred intermediately, a first transfer device for sequentially transferring toner images on the latent image carrying body to the intermediate transfer body, and a second transfer device (collective transfer device) for performing collective second transfer, on a transfer member such as a sheet, of the toner images that have been transferred to the intermediate transfer body (refer to Japanese Patent Application Laid-Open No. 5-323704 (1993), for example).
For example, a transfer roller is used as the second transfer device. The transfer roller gives a transfer member charges of the opposite polarity to the toner charging polarity, thereby transferring toner images formed on the intermediate transfer body to the transfer member by electrostatic force.
One example technique for peeling a transfer member from the intermediate transfer body after toner images of the respective color components on the intermediate transfer body have been transferred to the transfer member is a method of forcibly peeling the transfer member by bringing a peeling nail into sliding contact with the intermediate transfer body. Another method is available in which a peeling charge elimination device (e.g., a separation corotron) is provided downstream of the second transfer position and a transfer member is peeled by weakening the electrostatic adsorption force of the transfer member by eliminating charges from the transfer member through an AC corona discharge that is caused by the peeling charge elimination device (refer to Japanese Patent Application Laid-Open No. 8-146707 (1996), for example).
However, the technique in which the peeling nail, for example, is used to peel a transfer member from the intermediate transfer body has a technical problem that a transfer member and the intermediate transfer body are prone to formation of a scratch.
On the other hand, the technique using the peeling charge elimination device has a problem that when charges are eliminated from a transfer member after a second transfer, the amount of charge on the transfer member decreases and the electrostatic adsorption force between toner images on the transfer member and the transfer member is lost, causing toner scattering.
To solve the above problems, a method has already been proposed in which a conductive peeling plate is provided, for example, downstream of the second transfer position. A transfer member is peeled by utilizing a phenomenon that when the transfer member approaches the peeling plate after passing the second transfer position, charges that are reverse in polarity to charges that have been given to the transfer member at the second transfer position are induced on the peeling plate and hence the transfer member is electrostatically adsorbed on the peeling plate (refer to Japanese Patent Publication No. 8-23719 (1996), for example).
However, even in this type of apparatus, if the volume resistivity of the intermediate transfer body becomes, for example, 12 Log &OHgr;·cm or larger because of variations of electric characteristic values of the material of the intermediate transfer body due to environmental variations (i.e., variations in temperature and humidity), after a second transfer a transfer member is given negative charges through a peeling discharge between the transfer member and the intermediate transfer body and positive charges that have been induced by electrostatic polarization remain on the surface of the intermediate transfer body.
At this time, if the volume resistivity of the intermediate transfer body is high, the potential of the surface of the intermediate transfer body becomes, for example, +2,000 V or more and, in addition, the increased volume resistivity markedly elongates the time that is taken until the charges on the intermediate transfer body decrease sufficiently. This results in fear that the electrostatic adsorption force acting on the transfer member that is caused by charges on the intermediate transfer body becomes stronger than the electrostatic adsorption force cased by charges induced on the conductive peeling plate that is provided close to and downstream of the second transfer portion, whereby the transfer member is kept stuck to the intermediate transfer body, that is, a peeling failure occurs.
As described above, after a second transfer the intermediate transfer body continues to hold an electric field in such a direction as to attract a transfer member.
At this time, if a transfer member jams at a location other than the second transfer position, there is a possibility, depending on the timing, that a transfer member is located in a region where a portion of the intermediate transfer body that has been subjected to a second transfer is charged.
In such circumstances, there is fear that the transfer member that has once been peeled from the intermediate transfer body again sticks to the charged portion of the intermediate transfer body.
Conventional image forming apparatuses have no means for preventing such re-sticking of a transfer member; once a transfer member is re-stuck to the intermediate transfer body, it is difficult for a user to realize that fact.
Therefore, there is fear that if such re-sticking of a transfer member occurs, a user does not realize it and the transfer member is transported being stuck to the intermediate transfer body, resulting in a jam at a location that the user is hard to reach to remove the jammed transfer member such as the position of an intermediate transfer body cleaner.
In particular, the possibility of occurrence of the phenomenon of re-sticking of a transfer member to the intermediate transfer body is higher in the case of a transfer member that is easily bent or a transfer member having an extremely large resistivity value (e.g., second-surface copying of a double-sided copying operation in a low-temperature, low-humidity environment).
Although as described above the above technical problems are remarkable in intermediate transfer type image forming apparatus, those problems also occurs in, for example, image forming apparatuses of a type in which a toner image on a photoreceptor belt is directly transferred to a transfer member.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems in the art, and provides an image forming apparatus which effectively prevents a transfer member from re-sticking to an image carrying body at the occurrence of an abnormality such as a jam.
As shown in
FIG. 1
, the image forming apparatus has an image carrying body
1
for carrying a visible image formed by charged particles, a collective transfer unit
2
for collectively transferring the visible image on the image carrying body
1
to a transfer member
3
, a stopping unit
4
for stopping devices during image formation, a transfer member presence judging unit
5
for judging whether the transfer member
3
exists downstream of and in the vicinity of a transfer position of the collective transfer unit
2
, and a pre-stop processing unit
6
for preventing, if the transfer member presence judging unit
5
judges that the transfer member
3
exists when the stopping unit
4
stops the devices, the transfer member
3
from electrostatically sticking to the i
Hayashi Yukio
Hokari Norio
Iseki Shuji
Kawabata Takashi
Komatsu Nobuyoshi
Braun Fred L
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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