Electrophotography – Control of electrophotography process – Control of charging
Reexamination Certificate
2001-03-06
2003-04-22
Tran, Hoan (Department: 2852)
Electrophotography
Control of electrophotography process
Control of charging
Reexamination Certificate
active
06553192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus employing an electrophotographic system therein, and in particular relates to an image forming apparatus for use in copying machines and facsimile machines, etc., for example.
2. Description of the Related Art
Recently, a so-called tandem-type image forming apparatus has been proposed as a multicolored or full-colored electrophotographic apparatus, in which plural photosensitive drums are arranged in a line. Each drum corresponds to a different color, and a toner image formed on each drum is sequentially overlaid on a recording member to form a color image thereon.
FIG. 7
is a schematic block diagram showing an example of a conventional full-colored tandem-type image forming apparatus employing an electrophotographic system therein.
The image forming apparatus comprises four image forming sections (image forming units) which are an image forming section
101
M for forming a magenta image, an image forming section
101
C for forming a cyan image, an image forming section
101
Y for forming a yellow image, and an image forming section
101
Bk for forming a black image. These four image forming sections are arranged in a line and spaced at predetermined intervals.
These image forming sections
101
M,
101
C,
101
Y, and
101
Bk are provided with photosensitive drums
102
a
,
102
b
,
102
c
, and
102
d
, respectively. Around the photosensitive drums
102
a
,
102
b
,
102
c
, and
102
d
, charging rollers
103
a
,
103
b
,
103
c
, and
103
d
, developing devices
104
a
,
104
b
,
104
c
, and
104
d
, transfer rollers
105
a
,
150
b
,
105
c
, and
105
d
, and drum cleaning devices
106
a
,
106
b
,
106
c
, and
106
d
are arranged, respectively. In upper portions between the charging rollers
103
a
,
103
b
,
103
, and
103
d
and the developing devices
104
a
,
104
b
,
104
c
, and
104
, exposure devices
107
a
,
107
b
,
107
c
, and
107
d
are arranged, respectively. In the developing devices
104
a
,
104
b
,
104
c
, and
104
d
, magenta toner, cyan toner, yellow toner, and black toner are stored, respectively.
In order to form an image on a recording member, each toner image formed on each photosensitive drum is transferred to the recording member which is carried on and conveyed by a conveying belt, thereby sequentially overlaying each toner image thereon. Then, using a fuser, the toner image is fixed on the recording member and the recording member is separated from the conveying belt and discharged from the apparatus.
By the way, when using the above-mentioned color image forming apparatus, not only full-colored printing, but also mono-colored (black) printing is frequently performed, and the rate of the latter case tends to increase recently.
However, in the above-mentioned conventional color image forming apparatus, even during the mono-colored (black) image forming, the four image forming sections (image forming units)
101
M,
101
C,
101
Y, and
101
BK are activated. Accordingly, the surfaces of the photosensitive drums
102
a
,
102
b
, and
102
c
of the image forming sections
101
M,
101
C, and
101
Y which do not form images are mechanically ground just like during the full-colored printing due to the friction of the charging rollers
103
a
,
103
b
, and
103
c
, the developing devices
104
a
,
104
b
, and
104
c
, the drum cleaning devices
106
a
,
106
b
, and
106
c
, and a recording member P. That is, during the mono-colored printing, the losses of the surfaces of the photosensitive drums
102
a
,
102
b
, and
102
c
of the image forming sections
101
M,
101
C, and
101
Y which do not form images are also caused by abrasion.
Also, in order to equalize the charge on the entire surface of the photosensitive drum when charging it by using the charging roller, in the voltage applied to the charging roller, a DC voltage is superposed on an AC voltage. In such a structure, due to the AC voltage, the surfaces of the photosensitive drums
102
a
,
102
b
, and
102
c
, which do not form images may be degraded, thereby reducing an endurance life thereof. This is mainly because the degradation of the photosensitive drum is caused by the electric discharge that occurs between the charging roller and the photosensitive drum due to the AC voltage.
Moreover, in recent color image forming apparatuses, a process cartridge may be used for improving usability, in which the charging device, the developing device, a toner container, etc., are integrated into the photosensitive drum. When mono-colored (black) printing is frequently performed in such an image forming apparatus, the degradation of the photosensitive drum may be advanced even when color toner is not consumed in the process cartridge. Thus, the life of the photosensitive drum can end before the color toner is fully consumed, thereby causing the remaining toner to be undersirably abandoned.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an image forming apparatus capable of increasing the life of an image carrier.
REFERENCES:
patent: 4935787 (1990-06-01), Maeda et al.
patent: 5426487 (1995-06-01), Stelter et al.
patent: 5596393 (1997-01-01), Kobayashi et al.
patent: 5991557 (1999-11-01), Kunishi et al.
patent: 6324374 (2001-11-01), Sasamoto et al.
patent: 362220977 (1987-09-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Tran Hoan
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