Electrophotography – Document handling – Copy
Reexamination Certificate
2002-03-18
2004-05-25
Tran, Hoan (Department: 2852)
Electrophotography
Document handling
Copy
Reexamination Certificate
active
06741832
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention is related to a thermal fixing device applied to a device for forming an image by an electrophotographic method.
2. Description of Related Art
The device for forming an image by the electrophotographic method, such as a laser printer, has a thermal fixing device for fixing toner transferred onto a paper. As shown in
FIG. 7
, the thermal fixing device
61
has a heat roller
62
operating as a heater and a pressure roller
63
and applies heat and pressure to a paper
64
passing between the rollers
62
,
63
to melt and fix the toner on the paper
64
.
A guide plate
65
for guiding the paper
63
is arranged in the upstream side of the rollers
62
,
63
relating to the paper feeding direction. The paper
64
is guided by the guide plate
65
and enters a nip portion
66
where the rollers
62
,
63
are in contact and the paper
64
is fed to the downstream side while being heated and pressed.
As shown in
FIG. 8
, the peripheral surface of the heat roller
62
is formed in a reversed arch crown shape and the peripheral surface of the pressure roller
63
is formed in an arch crown shape. A stretching force, in the width direction of the paper
64
, is applied to the paper
64
when entered into the nip portion
66
and the paper
64
so fed is stretched to avoid creasing.
As shown in
FIG. 7
, the guide surface
65
a
that is an upper surface of the guide plate
65
is arranged lower than a surface S extending so as to include a tangent common to the rollers
62
,
63
at the nip portion
66
. The guide surface
65
a
extends almost parallel to the surface S. A front end of the paper
64
is guided by the guide surface
65
a
and the paper
64
enters the nip portion
66
, however, the paper
64
does not contact the guide surface
65
a
when the paper
64
is held by the nip portion
66
. Because the guide plate
65
is heated to an extent by the heat roller
62
, the paper
64
could be preheated when contacting the guide plate
65
. However, if the paper
64
does not contact the guide plate
65
, the paper
64
is not preheated and the toner cannot be fixed certainly.
If the guide surface
65
a
is arranged closer to the heat roller
62
, the paper
64
contacts the guide surface
65
a
and the paper
64
can be preheated. However, the following problems occur if the guide surface
65
a
is arranged too close to the heat roller
62
.
At the beginning of the fixing process, the front end of the paper
64
is held by the nip portion
66
and the rear end of the paper
64
is held between a photosensitive drum and a transfer roller. After the paper
64
proceeds and the rear end of the paper
64
is released from the photosensitive drum and the transfer roller, the paper
64
is lifted by the reaction of the release. The toner on the paper
64
that is not fixed contacts the photosensitive drum and the adjacent portions, and the toner is scattered.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a thermal fixing device for guiding the paper smoothly.
The thermal fixing device of the invention comprises a heater, a pressure member arranged in contact with the heater, a feeder for feeding a medium and a guide member for guiding the medium fed by the feeder to a contact portion where the heater and the pressure member contact, wherein the guide member is arranged so as to guide the medium in contact with the medium between a first surface and a second surface, and the first surface is a surface including a line that links the contact portion and the feeder and the second surface is a surface including a second line that is perpendicular to a first line that links a curvature center in the contact portion of the heater and a curvature center in the contact portion of the pressure member at a point where the first line crosses the contact portion.
The heater is a heat roller that is heated by a heat source and the pressure member is an elastic pressure roller. In this case, the first surface is defined as a surface extending so as to contact a pressure roller side surface of the heat roller and a surface of the feeder. The second surface is defined as a surface including a tangent common to two circles including a circle having a shaft center of the heat roller as a center and a circle having a shaft center of the pressure roller as a center.
A film of an endless belt that is heated by a heat source can be used for the heater. Because the film is very thin and its temperature is easy to increase, the time until the start of the image forming can be shortened.
The guide member can be kept in a float condition electrically to prevent the developer on the medium from being scattered. The guide member can be earthed via a rectifying member (for example, a Zener diode).
The guide member can be urged in the direction of the heater by an urging member. The urging member may be structured to rotate the guide member around a shaft.
The width of the guide member is set smaller than the width of the fed medium.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 5303015 (1994-04-01), Sato
patent: 6108514 (2000-08-01), Nakayama et al.
patent: 6148159 (2000-11-01), Shiraishi
patent: 6564025 (2003-05-01), Sameshima et al.
patent: 2000-137398 (2000-05-01), None
Brother Kogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Tran Hoan
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