Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2000-02-22
2001-11-27
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S299000, C399S314000, C430S126200
Reexamination Certificate
active
06324359
ABSTRACT:
The invention is based on Japanese patent application No. H11-42880 (42880/1999) Pat. filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of applying a transfer voltage to each of a plurality of transfer members, which are opposed to image carriers carrying toner images, respectively, for transferring the toner images on the image carriers onto an image transfer target member to be moved through positions between the image carriers and the transfer members.
The invention also relates to an image forming apparatus, in which a plurality of transfer members are opposed to image carriers carrying toner images, respectively, and a transfer voltage is applied to each transfer member for transferring the toner images on the image carriers onto an image transfer target member to be moved through positions between the image carriers and the transfer members.
2. Description of the Background Art
An example of a structure of a color image forming apparatus in the prior art is schematically shown in FIG.
15
.
An image forming apparatus Ap shown in
FIG. 15
is an electrophotographic color image forming apparatus of the tandem type.
The image forming apparatus Ap includes four image forming units PC, PM, PY and PK. The image forming units PC, PM, PY and PR can form cyan, magenta, yellow and black images of toner on a record sheet, respectively.
The image forming units PC, PM, PY and PK are disposed at respective positions opposed to an outer peripheral surface of a sheet transporting belt
98
which can carry and transport the record sheet.
The image forming unit PC has a photosensitive member
91
C. Around the photosensitive member
91
C, there are arranged is a charger
92
C, a laser exposing device
93
C, a developing device
94
C containing cyan toner, a transfer roller
95
C, a cleaning device
96
C and an eraser lamp
97
C aligned in this order.
The image forming units PM, PY and PK likewise have photosensitive members
91
M,
91
Y and
91
K, around which devices similar to those of the image forming unit PC are successively arranged, respectively.
In the image forming apparatus Ap, a color toner image based on the original image is formed on the record sheet in the following manner.
Toner images in cyan, magenta, yellow and black are formed on the photosensitive members
91
C,
91
M,
91
Y and
91
K, respectively, and then are successively transferred onto the record sheet R transported by the sheet transporting belt
98
so that the color image is formed on the record sheet R.
The toner images formed on the photosensitive members
91
C,
91
M,
91
Y and
91
K are electrostatically transferred onto the record sheet by applying transfer voltages onto the transfer rollers
95
C,
95
M,
95
Y and
95
K, respectively. In the transferring operation, the record sheet R is transported by the sheet transporting belt
98
through a path between the photosensitive members and the transfer rollers.
The transfer roller is supplied with the transfer voltage which is, e.g., a DC voltage. It is already proposed to use, as the transfer voltage, a sinusoidal AC voltage which is superimposed on a DC voltage, and therefore has a central voltage shifted from 0 volts. It is also proposed to apply, as the transfer voltage, a pulse AC voltage superimposed on a DC voltage.
However, when the toner images formed on the respective photosensitive members are transferred onto the record sheet by applying the transfer voltages to the transfer rollers, interfere of the transfer currents flowing through the record sheet may occur in the respective transfer regions, where the transfer rollers are opposed to the photosensitive members, respectively. In particular, if the record sheet is a paper sheet which has taken up moisture, the interference of the transfer current is likely to occur. When the interference of the transfer current occurs, transfer failure such as irregular transfer occurs so that good color toner images can not be formed on the record sheet.
The transfer failure due to the interference of the transfer current occurs not only in the image forming apparatus such as an image forming apparatus Ap, which is configured to transfer the toner images formed on the respective photosensitive members directly onto the record sheet, but also in an image forming apparatus which is configured to transfer temporarily the toner images formed on the respective photosensitive members onto an intermediate transfer member, and then transfer collectively all the transferred images onto the record sheet in a secondary transfer operation.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method of applying a transfer voltage in an image forming apparatus for transferring toner images respectively formed on a plurality of image carriers onto an image transfer target member to be moved successively through positions where a plurality of transfer members are respectively opposed to the image carriers by applying the transfer voltages to the respective transfer members, and particularly to provide the transfer voltage applying method in which interference of the transfer current between the transfer regions is suppressed, and good transfer can be performed in each of the transfer regions.
Another object of the invention is to provide an image forming apparatus, in which toner images respectively formed on a plurality of image carriers are transferred onto an image transfer target member to be moved successively through positions where a plurality of transfer members are respectively opposed to the image carriers by applying the transfer voltages to the respective transfer members, and particularly to provide the image forming apparatus in which interference of the transfer current between the transfer regions is suppressed, and good transfer can be performed in each of the transfer regions so that a good toner image can be formed on the record sheet.
The invention provides a transfer voltage applying method in an image forming apparatus for transferring toner images formed respectively on a plurality of image carriers onto an image transfer target member to be moved successively through positions where a plurality of transfer members are respectively opposed to the image carriers by applying transfer voltages to the transfer members, respectively, wherein
the transfer members are supplied with predetermined AC voltages, respectively, so as that the successively neighboring at least two transfer members are supplied with the AC voltages having phases shifted from each other, respectively, and the successively neighboring at least two transfer members are not simultaneously supplied with the maximum voltages, each in absolute value, of the AC voltages.
The invention also provides an image forming apparatus for forming a toner image based on an original image on a record sheet, comprising:
a plurality of image carriers;
a plurality of image forming devices provided for the image carriers, respectively, and each provided for forming a toner image on the corresponding image carrier;
a plurality of transfer devices provided for the image carriers, respectively, each including a transfer member opposed to the corresponding image carrier, and each provided for transferring the toner image on the corresponding image carrier onto an image transfer target member to be moved successively through positions between the image carriers and the transfer members by applying a transfer voltage to the transfer member; and
a transfer power source device for applying predetermined AC voltages as the transfer voltages to the transfer members, respectively; wherein
the transfer power source device supplies the AC voltages having phases shifted from each other to the successively neighboring at least two transfer members, respectively, so as that the successively neighboring at least two transfer members are not simultaneously supplied with the maximum voltages, each in absolute value, of the AC voltages.
The f
Chen Sophia S.
McDermott & Will & Emery
Minolta Co. , Ltd.
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