Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2002-02-01
2004-09-21
Brase, Sandra L. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C399S176000, C399S313000
Reexamination Certificate
active
06795669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer.
2. Description of the Related Art
There is known an image forming apparatus as an apparatus in which a toner image formed on a photoconductive drum is transferred to a sheet of recording paper so as to form an image on the sheet of recording paper. Conventionally, an image forming apparatus capable of obtaining high quality printed image is desired.
FIG.
6
A and
FIG. 6B
show part of an image forming apparatus
1
in accordance with the conventional technique.
FIG. 6A
is a cross sectional view and
FIG. 6B
shows a simplified model. As shown in
FIG. 6A
, a photoconductive drum
2
is composed of a hollow cylindrical photoconductive drum elementary pipe portion
43
and a pair of drum flanges
6
which cover openings at both ends of the photoreceptor drum elementary pipe portion
43
. Further, a drum shaft
8
, which penetrates the photoconductive drum
2
in the axial direction, is provided on the same shaft as that of the photoconductive drum
2
. Then, the drum shaft
8
is rotatably supported by a pair of shaft bearings
41
provided at both ends of the drum shaft.
A transfer roller
3
has a cylindrical shape, and an axis A
2
thereof is arranged in parallel with an axis A
1
of the photoconductive drum
2
. Further, a roller shaft
7
, which penetrates the transfer roller
3
in the axial direction, is provided on the same shaft as that of the transfer roller
3
, and is rotatably supported by a pair of shaft bearings
42
provided at both ends of the roller shaft. Further, the roller shaft
7
comes in contact with a pair of spring members
5
having elasticity in the axial direction, a pair of tracking rolls
4
, which are a control means according to the invention, are provided. The roller shaft
7
is pressed against the drum shaft
8
with the spring members
5
. The gap H is made between the photoconductive drum
2
and the transfer roller
3
at a proper value by allowing each tracking roll
4
to come in contact with the photoconductive drum
2
. Such conventional image forming apparatus
1
is disclosed in Japanese Unexamined Patent Publication JP-A 9-218549 (1997).
Such an image forming apparatus
1
is configured to make the gap between a circumferential surface of the photoconductive drum and a circumferential surface of the transfer roller. Accordingly, the photoconductive drum and the transfer roller can move without friction, so that abrasion and peeling of the photoreceptive layer in the circumferential surface of the photoreceptor drum can be prevented. Consequently, the toner image can be finely transferred to the recording paper, thereby preventing fluctuation of image.
Further, in addition to the above mentioned image forming apparatus which is configured to keep the gap between a circumferential surface of the photoconductive drum and a circumferential surface of the transfer roller at a proper value by the controlling means such as a tracking roll, there is another image forming apparatus, which is configured so as to press the circumferential surface of the photoconductive drum and the circumferential surface of the transfer roller with a specific pressure by the controlling means. Such conventional technique is disclosed in Japanese Unexamined Patent Publication JP-A 2-165173 (1990).
According to the image forming apparatus, by bringing the circumferential surface of the photoconductive drum into contact with the circumferential surface of the transfer roller, and by pressing them at a steady specific pressure, there is no need to further increase the transfer electric field (or potential difference) which functions between the circumferential surface of the photoconductive drum and the circumferential surface of the transfer drum. Further, problems such that letters are missing in the middle part due to high pressure is not raised. Consequently, the toner image can be finely transferred to the recording paper.
The foregoing conventional technique has the following problems, in which the positional relationship between the outer circumference of an image carrier which supports a toner image, such as a photoconductive drum, a photoconductor belt, and an intermediate transfer, and the circumferential surface of the transfer roller which transfers the toner image on the image carrier to the recording paper, is controlled to be a predetermined positional relationship by spring members and the controlling means.
When inserting a sheet of recording paper between the surface of the image carrier and the surface of the transfer roller, the interval between the photoconductive drum and the transfer roller further increases in comparison with the case where sheets of recording paper are not housed in the space between the surface of the image carrier and the surface of the transfer roller. After discharging the recording paper from the space between the surface of image carrier and the surface of the transfer roller, the positional relationship is reset to its original position by the spring members. At the time, an impact caused by insertion and withdrawal of the recording paper, is transmitted to the image carrier. In particular, when inserting a recording paper having a certain thickness and unevenness, the impact is increased.
An impact is transmitted to the image carrier, thereby causing displacement of the image carrier in a short time and creating vibrations on the toner image supported on the image carrier and unfixed toner image which is transferred to the recording paper. Consequently, there is problems that blot and blur of image are generated due to vibrations and high quality image cannot be obtained. In a particular case where the image carrier and the transfer roller have a hollow, when an impact is transmitted to the outer circumference of the portion having a hollow inside, vibrations created by the image carrier is further increased.
Further, according to the copying machine, which is one example of the image forming apparatus, after fixing an image of a developing material such as a toner on the circumferential surface of the photoconductive drum, which is one example of the image carrier, the toner image is transferred to transfer materials such as a transfer sheet, thereby printing the image. At the time, in the periphery of the photoconductive drum, rotating bodies are provided, namely, a charging roller which applies static charges to the photoconductive drum, a developing roller which forms a toner image on the circumferential surface of the photoconductive drum, and a transfer roller which transfers the toner image by pressing against the circumference of the photoconductive drum. At this time, to obtain an image having a certain quality, these rotating bodies provided in the periphery are required to keep the interval between shafts or the interval between circumferential surfaces with regard to the photoconductive drum with high accuracy.
In response to the needs, the following technique is proposed in, for example, JP-A 2-165173 and Japanese Unexamined Patent Publication JP-A 8-63043 (1996). A guide portion is provided on the peripheral rotating body such as the transfer roller and the circumference or the rotation axis of the image carrier such as the photoconductive drum, and the guide portion comes in contact with the circumference of the image carrier or the peripheral rotating body, thereby keeping the interval between shafts of the image carrier and the peripheral rotating body and the interval between the circumferences to a proper value.
Further, according to the technique disclosed in Japanese Unexamined Patent Publication JP-A 4-175779 (1992), a ring-shaped spacer roller provided on the peripheral rotating body are brought into contact with support members of the image carrier, thereby the interval between shafts of the image carrier and the peripheral rotating body and the interval between the circumferences can be kept t
Inoue Tatsuya
Kida Hiroshi
Masuda Yoshiaki
Takeda Shinichi
Yamauchi Hirokazu
Birch Stewart Kolasch & Birch, LLP.
Brase Sandra L.
Sharp Kabushiki Kaisha
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