Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-03-02
2003-01-07
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
C399S328000, C399S122000, C399S330000, C399S331000
Reexamination Certificate
active
06505028
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, such as a printer, a facsimile machine or a copy machine, which is capable of forming a toner image on a recording medium, such as a paper sheet, by the electrophotography technique. More particularly, the invention relates to a fixing device for use with the image forming apparatus.
Generally, the image forming apparatus for forming a toner image on a recording medium by the electrophotography technique includes a photosensitive member to be driven to rotate, an exposure mechanism for forming an electrostatic latent image on the surface of the photosensitive member, a developing mechanism for developing the latent image into a toner image, a transfer mechanism for transferring the toner image onto a recording medium, and a fixing device for fusing and fixing the toner image on the recording medium in a manner that the recording medium having the toner image transferred thereto by the transfer mechanism is moved to pass therethrough.
The fixing device, usually, includes a first rotary member to be heated and a second rotary member pressed against the first rotary member. A recording medium having a toner image thereon is moved to pass through a press nip between the first and second rotary members. When passing through the press nip, the recording medium is compressed by those rotary members and heated, whereby the toner image is fused and permanently fixed onto the recording medium.
In the fixing device thus constructed, if a peripheral speed difference is present between the two rotary members, a toner image on the recording medium passing through the press nip (press contact portion) between the rotary members is blurred and the image is disturbed or disarranged. For this reason, the prior technique does not employ such a drive method as to drive and rotate both the rotary members, and instead, employs such a drive method that one of the rotary members is driven to rotate, while the other is rotated as a follower.
In a case where the rotary member to be heated consists of a roller, a long time is consumed for the initial heating of the roller. In connection with this, there is known a belt fixing device in which an endless belt is used for the rotary member to be heated, whereby the initial heating time is reduced.
FIG. 32
is a diagram showing an example of the belt fixing device (JP-A-9-138600).
The belt fixing device includes an endless heat-resistant belt endless heat-resistant belt
6
, rollers
7
a
and
7
b
for supporting the belt
6
on the inner side thereof, a roller
8
for heating the belt endless heat-resistant belt
6
, and an pressure application roller
9
in contact with the outer peripheral surface of the belt endless heat-resistant belt
6
. The pressure application roller
9
is driven by a motor M to rotate in the direction of an arrow “a”, while the belt
6
follows the pressure application roller
9
in rotation.
A recording medium having a toner image formed thereon is moved in the direction of an arrow “b” to pass through a press contact portion N between the belt
6
and the pressure application roller
9
. When passing the press contact portion N, the toner image is heated and fused, and permanently fixed on the recording medium.
FIG. 58
is a diagram showing another example of the belt fixing device (JP-A-8-334997).
In the belt fixing device, a fixing belt
1
extends around a fixing roller
2
driven to rotate and a heating roller
3
containg a heater. An pressure application roller
4
is pressed against the fixing roller
2
with the fixing belt
1
being interposed therebetween. A recording medium S having a toner image T formed thereon is moved in the direction of an arrow to pass through a pressure contact portion N therebetween, whereby the toner image T is fused and permanently affixed onto the recording medium S.
The heating roller
3
includes guide rings
3
a
as restricting portions which come in contact with the side ends
1
b
of the fixing belt
1
to restrict such a behavior of the fixing belt
1
as to move aside.
To prevent such a phenomenon that toner is transferred from the recording medium onto the surface of the fixing belt
1
(called offset phenomenon), the fixing device includes an oil coating roller
5
for coating the surface of the fixing belt
1
with release oil, such as silicone oil, as release agent.
The conventional belt fixing device shown in
FIG. 57
has the following problem. When a recording medium S that relatively easily slips, for example, a synthetic resin sheet, is supplied to the press contact portion N between the pressure application roller
9
to be driven to rotate and the belt
6
which follows the pressure application roller in rotation, a slip will occur between the pressure application roller
9
of the drive side and the recording medium and/or the recording medium and the belt
6
of the follower side because of the presence of the easily slidable recording medium. As a result, a peripheral speed of the belt
6
is different from that of the pressure application roller
9
. Further, a stable operation of the fixing device will be lost.
The conventional belt fixing device shown in
FIG. 58
has the following problem. When a recording medium S that relatively easily slips is supplied to the press contact portion N between the belt
1
to be driven and the pressure application roller
4
which follows the belt in rotation, and as a result, a slip will occur between the belt
1
of the drive side and the recording medium an/or the recording medium and the pressure application roller
4
of the follower side because of the presence of the easily slidable recording medium. As a result, a peripheral speed of the belt
1
is different from that of the pressure application roller
4
. Further, a stable operation of the fixing device will be lost.
Particularly in the belt fixing device shown in
FIG. 58
, the surface of the belt
1
is coated with release oil. Because of the coating of the release oil, the above slip is more likely to occur. The release oil that has been applied to the surface of the belt
1
gradually moves to the ends N′ of the press contact portion N to reduce a friction force acting between the a fixing roller
2
and the pressure application roller
4
at the ends N′. Further the release oil that will move the ends N′ of the press contact portion N also moves to between the belt
1
and the fixing roller
2
, to thereby reduce a friction force between the belt
1
and the fixing roller
2
. As a result, there is a fear that the fixing operation of the fixing device will be more instable.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to solve the above-mentioned problems of the conventional fixing devices for use with an image forming apparatus and to provide a fixing device which stably operates.
According to the present invention, there is provided a first image forming apparatus having a fixing device constructed such that the fixing device includes an endless belt to be heated and a rotary member to be in pressing contact with the endless belt, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium,
wherein a high grip portion is provided at a portion of the endless belt which is not pressed by the recording medium but pressed by the rotary member.
The present invention provides a second image forming apparatus having a fixing device constructed such that the fixing device includes an endless belt to be heated and a rotary member to be in pressing contact with the endless belt, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass th
Fujisawa Kazutoshi
Kagami Takao
Mori Shuhei
Okumura Naoyuki
Takeda Yoshiyuki
Ngo Hoang
Seiko Epson Corporation
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