Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2000-10-27
2002-02-12
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S306000, C399S308000, C399S309000
Reexamination Certificate
active
06347200
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to image forming apparatus employing an electro-photographic method, such as copiers, printers, facsimile devices, etc., in which a charging means, an image writing means and a developing means are disposed around the circumferential surface of an image bearing member to form a toner image, which is transferred and fixed on a transfer sheet, and specifically relates to a duplex image forming apparatus which can form images on both sides of a transfer sheet by employing an intermediate transfer belt.
In a conventional duplex image forming apparatus, a toner image of one side, formed on the image bearing member, is transferred and fixed on the transfer sheet to be temporarily stored in the reversible feeding device after the fixing operation. Then, the transfer sheet is fed from the reversible feeding device, synchronized with another toner image formed again on the image-bearing member, to transfer and fix the other toner image onto the other side of the transfer sheet.
In the conventional duplex image forming apparatus, since the transfer sheet should be conveyed to the reversible feeding device and should be pass through the fixing device twice, as mentioned above, the transfer sheet is compelled to pass through a very complicated conveyance path, which deteriorates a reliability of the conveying operation for the transfer sheet and causes jams and wrinkles of the transfer sheet.
To overcome the abovementioned problems, the duplex image forming apparatus, in which toner images, formed on the both sides of the transfer sheet by employing both the image bearing member and the intermediate transfer member, are fixed onto the transfer sheet at a time, are set forth in Tokkaishou 49-37538, Tokkaishou 54-28740, Tokkaihei 1-44457 and Tokkaihei 4-21576.
Further, the present inventors have disclosed the method and apparatus for forming duplex color images set forth in Tokkaihei 9-258492 and Tokkaihei 9-258516, in which a plurality of sets, each of which is comprised of a charging means, an image writing means and a developing means, are arranged around the circumferential surface of the photoreceptor drum, and the superimposed color toner image formed on the photoreceptor drum is collectively transferred onto the intermediate transfer member, and then, the transfer sheet is conveyed on the intermediate transfer member, synchronizing with the superimposed color toner image formed again on the photoreceptor drum and the toner image already transferred on the intermediate transfer member, and during the conveying operation of the transfer sheet, the toner image formed again on the photoreceptor drum is transferred onto one side of the transfer sheet as the obverse side image while the toner image already transferred on the intermediate transfer member is transferred onto the other side of the transfer sheet as the reverse side image, and then, the transfer sheet is separated from the intermediate transfer member to fix the toner images onto the transfer sheet at a time, and thus, the duplex color images can be formed.
In the duplex image forming apparatus which forms images on both sides of the transfer sheet by employing an intermediate transfer belt, serving as a belt-shaped intermediate transfer member as mentioned above, there are provided a transfer sheet charging means for charging the transfer sheet, such as a recording sheet, etc., to convey the transfer sheet along the intermediate transfer belt while the transfer sheet is electro-statically adhering onto it, a first transfer means for transferring a toner image, formed on the image bearing member, onto the intermediate transfer belt or the obverse side of the transfer sheet, and a second transfer means for re-transferring the toner image, already transferred on the intermediate transfer belt, onto the reverse side of the transfer sheet.
When the transfer sheet is conveyed on the intermediate transfer belt during the duplex image forming operation, a bias voltage is applied to the transfer sheet charging means, the first transfer means and the second transfer means, in order to transfer good toner images onto the both sides of the transfer sheet. Incidentally, in the system for forming the abovementioned duplex images, the transfer sheet charging means, the first transfer means and the second transfer means are disposed at positions as described in the following.
Initially, the first transfer means is disposed at a position backside the intermediate transfer belt, where the photoreceptor drum opposes to the intermediate transfer belt, to supply electronic charge onto the backside surface of the intermediate transfer belt (for instance, the lower side surface of the transfer sheet shown in FIG.
1
). In this configuration, a toner image formed on the photoreceptor drum is transferred onto one side of the transfer sheet (for instance, the upper side surface of the transfer sheet shown in FIG.
1
), which is conveyed by the intermediate transfer belt while electro-statically adhering on it.
On the other hand, the second transfer means is disposed at a position, located downstream the position of the first transfer means and at a front-side of the intermediate transfer belt, to directly supply electronic charge onto the opposite side surface of the transfer sheet (for instance, the upper side surface of the transfer sheet shown in FIG.
1
), which is conveyed by the intermediate transfer belt while electro-statically adhering on it. In this configuration, a toner image already transferred on the intermediate transfer belt is transferred onto the other side of the transfer sheet (for instance, the lower side surface of the transfer sheet shown in FIG.
1
).
Further, the transfer sheet charging means is disposed at a position, located upstream the position of the first transfer means and at a front-side the intermediate transfer belt, to directly supply electronic charge onto the upper side surface of the transfer sheet, shown in
FIG. 1
, which is fed on the intermediate transfer belt, so that the transfer sheet electro-statically adheres onto the intermediate transfer belt.
Accordingly, in the system for forming the duplex images on the both sides of the transfer sheet at a time, the first transfer means indirectly supplies electronic charge to one side of the transfer sheet with putting the intermediate transfer belt between them, while the second transfer means or the transfer sheet charging means directly supplies electronic charge to the other side (opposite side) of the transfer sheet.
The present inventors have found a problem that the electronic charge, applied to one side of the transfer sheet, and the other electronic charge, applied to the other side of the transfer sheet, interfere each other in the system mentioned above. Namely, the present inventors have found that, since the relative position of the transfer sheet, with respect to the positions of the transfer sheet charging means, the first transfer means and the second transfer means, varies depending on the current position of the transfer sheet as convying with the intermediate transfer belt, presence or absence of the interference between electronic charges supplied to the both sides of the transfer sheet considerably affects the quality of the toner images.
Specifically in the duplex image forming apparatus, incorporating the intermediate transfer belt, it is also found that a delicate variation of the electronic resistance of the transfer sheet or that of the intermediate transfer belt considerably affects the interfering action between electronic charges residing on the both sides of the transfer sheet. The abovementioned interfering action gives far greater influences to the transfer sheet than that in image forming apparatus, which forms a toner image on only one side of the transfer sheet.
Owing to the interfering action in the abovementioned duplex image forming apparatus, there has been a problem that an unevenness of the density like a stripped pattern is generated in the transferred images, when
Haneda Satoshi
Nagase Hisayoshi
Sato Yotaro
Shigeta Kunio
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Konica Corporation
Lee Susan S. Y.
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