Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2000-06-16
2002-11-26
Beatty, Robert (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S314000
Reexamination Certificate
active
06487380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic system. For example, the present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile.
2. Related Background Art
There have conventionally known image forming apparatuses using an electrophotographic system or an electrographic recording system such as a copier, a facsimile, and a printer. For example, an image forming apparatus of electrophotographic system will be described. This type of image forking apparatus obtains an image by uniformly charging a surface of, e.g., a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “a photosensitive drum”) used as an image bearing member, then exposing the surface in accordance with image information to form an electrostatic latent image, visualizing this electrostatic latent image with developer (including toner) to form so called a toner image which is a visible image, and subsequently transferring this toner image from the photosensitive drum to a recording material and then fixing it.
Further, various image forming apparatuses having a plurality of image forming portions have been provided which form differently colored toner images in the respective image forming portions and transfer the toner images by sequentially superimposing them on the same recording material to form a color image. In this type of image forming apparatus, a recording material is fed to each image informing portion using an endless recording material bearing member. Such a color electrophotographic image forming apparatus is used for high speed recording in a color copier or the like.
FIG. 1
shows a schematic configuration of an example of an color image forming apparatus using electrophotographic system.
In the image forming apparatus of
FIG. 1
, first, second, third and fourth image forming portions Pa, Pb, Pc and Pd are provided together. In the respective image forming portions differently colored (cyan, magenta, yellow and black in this example) toner images are separately formed by being subjected to the respective processes of forming a latent image by charging and exposure, of forming a toner image by developing, and of transferring the image. A transfer belt
130
that is a belt-shaped recording material bearing member is provided adjacently to photosensitive drums
3
a,
3
b,
3
c
and
3
d
used as the image bearing members provided on the respective image forming portions while being stretched around a driving roller
13
and supporting rollers
14
and
15
, and toner images of the respective colors formed on the respective photosensitive drums
3
a
to
3
d
are transferred onto a recording material S borne and fed by the transfer belt
130
.
Surfaces of the photosensitive drums
3
a
to
3
d
which the image forming portions Pa to Pd have respectively are uniformly charged with drum chargers
2
a,
2
b,
2
c
and
2
d
which are charging means provided on the respective outer peripheries of the photosensitive drums
3
a
to
3
d.
After that, a laser beam emitted from a light source device (not shown) is scanned by turning a polygon mirror
117
, the scanned light flux is deflected with a reflecting mirror in a light-guiding means
116
and is further condensed on the generatrix of the respective photosensitive drums
3
a
to
3
d
with an f&thgr; lens to expose them, and latent images according to the image information are formed on these photosensitive drums
3
a
to
3
d.
Additionally, the outer peripheries of the respective photosensitive drums
3
a
to
3
d
are also provided with light exposure lamps
111
a,
111
b,
111
c
and
111
d
and electric potential sensors
113
a,
113
b,
113
c
and
113
d,
respectively.
Developing devices
1
a,
1
b,
1
c
and
1
d
provided along the outer peripheries of the respective photosensitive drums
3
a
to
3
d
are replenished with a given amount of cyan, magenta, yellow and black toner, respectively, as developers by supply devices (not shown) and the respective developing devices
1
a
to
1
d
develop the electrostatic latent images formed on the respective photosensitive drums
3
a
to
3
d
as mentioned above to form a cyan toner image, a magenta toner image, an yellow toner image and a black toner image, which are visible images.
On the other hand, the recording material S is contained in a recording material cassette
10
, is supplied from here onto the transfer belt
130
through a plurality of feeding rollers and registration rollers
12
, and is borne and fed with the transfer belt
130
so as to be sequentially sent to transfer portions that are opposite to the photosensitive drums
3
a
to
3
d.
The transfer belt
130
is made of a dielectric material sheet such as polyethylene terephthalate resin sheet (PET resin), polyvinylidene fluoride resin sheet, or polyurethane resin sheet. As the transfer belt
130
, an endless belt in which both ends were overlapped and joined together, or a seamless belt is used.
When this transfer belt
130
is turned with the driving roller
13
and it is confirmed the transfer belt
130
is at a given position, the recording material S is fed from the registration rollers
12
to the transfer belt so that the recording material S is fed toward the transfer portion (an opposed portion between the photosensitive drum
3
a
and the transfer belt
130
) of the first image forming portion Pa. At the same time, an image writing signal is turned ON and an image formation is performed as described above on the photosensitive drum
3
a
of the first image forming portion Pa at desired timing with reference to this signal. Then, by imparting electric field or charge at the transfer portion on the lower side of the photosensitive drum
3
a
in
FIG. 1
with transfer means
24
a,
a toner image of first color formed on the photosensitive drum
3
a
is transferred onto the recording material S.
This transfer causes the recording material S securely borne on the transfer belt
130
by electrostatic attractive force and the recording material S is fed to the second image forming portion Pb and downstream thereof.
As the transfer means
24
a
to
24
d
a non-contact charger such as corona discharge, or a contact charger using a transfer charging member such as a blade, roller or brush is used. The non-contact charger has problems that the charger generates ozone and is weak to variations in temperature and humidity circumstances of the air because of charging through air so that images are not formed stably. On the other hand, the contact charger has merits of being ozoneless, strong against the variations in temperature and humidity circumstances, capable of producing a high quality image, etc.
In the second to fourth image forming portions Pb to Pd, toner images are transferred on the recording material S while being superimposed in the same way as mentioned above. After that, the recording material S to which four colored toner images were transferred is separated from the transfer belt
130
by reducing the electrostatic attractive force by eliminating the residual charge with a separation charger
32
, downstream in the feeding direction of the transfer belt
130
. Usually, the driving roller
13
is grounded for performing stable separation. Further, as the separation charger
32
a non-contact charger is used because the recording material S is charged before a toner image is fixed thereto.
The recording material S to which four colored toner images have been transferred and which has been separated from the transfer belt
130
is fed to a fixing device
9
by a feeding portion
62
and is heated and pressurized at the fixing device
9
so that mixing of toner images and fixing thereof to the recording material S are performed. The fixing device
9
is composed of a fixing roller
51
, a pressure roller
52
, heat resistant cleaning members
54
and
55
for cleaning the rollers
51
and
52
, respectively, roller heaters
56
and
57
provided in th
Beatty Robert
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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