Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-08-15
2004-07-13
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Fixing
Reexamination Certificate
active
06763218
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fixing apparatus used in copiers, printers, facsimile machines or the like to thermo-compression-bond unfixed toner on a sheet and fix it onto the sheet.
BACKGROUND OF THE INVENTION
In late years, a technique as shown in
FIG. 9
has been developed to a fixing apparatus for electrophotographic systems. In this technique, a belt type fixing apparatus comprises a fixing roller R
1
, a heating/tension roller (hereinafter referred to as “heating roller”) R
3
, a fixing belt B wound around both the fixing and heating rollers, and a pressing roller R
2
for pressing the fixing roller R
1
upward through the fixing belt B. Further, the belt type fixing apparatus is combined with a preheating device of a recording medium D. According to this fixing apparatus, a nip region can be set at a lower temperature by virtue of the preheating of the recording medium D. This allows the heat capacity of the fixing belt B to be reduced. Thus, when passing through the nip region, the fixing belt B is quickly cooled down to provide accelerated aggregation of toner to be released from the fixing belt B at the outlet of the nip region, and consequently enhanced releasability between the fixing belt B and the toner, so that a clear fixed toner image will be obtained without undesirable offset even if no oil or a small amount of oil is applied. This fixing apparatus is known as an effective solution of technical problems in releasability and oil application which have not been solved by a heating roller system.
The structure of the above conventional belt type fixing apparatus will be briefly described bellow. The fixing apparatus comprises the fixing roller R
1
, the pressing roller R
2
disposed below the fixing roller R
1
, the heating roller R
3
disposed on the side of the fixing roller R
1
(on the upstream side along the feeding direction of the recording medium), and the fixing belt B wound around both the fixing roller R
1
and the heating roller R
3
.
An oil coating roller R
4
is provided above an upper belt run of the fixing belt B. Further, a guide plate G serving as a support member for the recording medium is provided below an lower belt run of the fixing belt B with leaving a certain distance therebetween to define a heating passage P for heating the recording medium between the lower belt run of the fixing belt B and the upper surface of the guide plate B. A pressing lever U is adapted to press the heating roller R
3
in the direction causing the heating roller R
3
to get away from the fixing roller R
1
so as to provide a desired tension of the fixing belt B, and the heating roller R
3
is driven by the fixing roller R
1
, so that the fixing belt B can be stably rotated without slipping or sagging.
The belt type fixing apparatus has various features as described above. On the other hand, the belt type fixing apparatus exposes extremely deteriorated releasability as a sheet is large-sized, particularly when used in an electrophotographic machine compatible with A-3 size sheets (or A4 cross-feed), and it transpires that a desired releasability is hardly secured without a separation pawl. Thus, there is a need for improving such a disadvantage.
SUMMARY OF THE INVENTION
In view of the above circumstances, it is therefore an object of the present invention to provide a fixing apparatus capable of reliably releasing a sheet having fixed toner thereon from a fixing belt without any separation pawl even if the sheet is large-sized.
It is another object of the invention to provide a fixing apparatus capable of reliably releasing a sheet having fixed toner thereon from a fixing belt even in an electrophotographic machine compatible with A-3 size sheets.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided a fixing apparatus comprising: a fixing roller; a pressing roller in rotational contact with the fixing roller; a biasing member for applying a biasing force to the pressing roller so as to bring the pressing roller into press contact with the fixing roller at a given pressure; a heating roller disposed apart from the fixing roller; a fixing belt wound around both the heating and fixing rollers in an endless manner; and a heat-generating device embedded in the heating roller to heat the fixing belt so as to heat unfixed toner on a sheet passing through a rotational contact region between the fixing and pressing rollers, whereby when the sheet having unfixed toner on a surface thereof is passed through the rotational contact region along one direction, the unfixed toner is fixed onto the sheet. In this fixing apparatus, an interior angle &thgr; between an axis X and an axis Y is arranged to satisfy the following relationship,
−30°<&thgr;<−80 °
where X is an axis connecting the center of the fixing roller and the center of the pressing roller, and Y is an axis along a biasing direction in which the pressing roller applies the biasing force to the fixing roller in the rotational contact region, wherein on the basis of the axis X, a positive sign is provided to the angle &thgr; when the axis Y is located on a sheet-feed side where the sheet is fed into the rotational contact region, and a negative sign is provided to the angle &thgr; when the axis Y is located on a sheet-discharge side where the sheet is discharged from the rotational contact region.
According to a second aspect of the present invention, there is provided a fixing apparatus comprising: a fixing roller; a pressing roller in rotational contact with the fixing roller; a biasing member for applying a biasing force to the pressing roller so as to bring the pressing roller into press contact with the fixing roller at a given pressure; a heating roller disposed apart from the fixing roller; a fixing belt wound around both the heating and fixing rollers in an endless manner; and a heat-generating device embedded in the heating roller to heat the fixing belt so as to heat unfixed toner on a sheet passing through a rotational contact region between the fixing and pressing rollers, whereby when the sheet having unfixed toner on a surface thereof is passed through the rotational contact region along one direction, the unfixed toner is fixed onto the sheet. In this fixing apparatus, the pressing roller is rotatably pivoted to a swingable member swingably supported on a given pivot shaft, the biasing member being coupled with the swingable member to allow the pressing roller to be brought into press contact with the fixing roller, and an interior angle &thgr; between an axis X and an axis Y being arranged to satisfy the following relationship,
−30°<&thgr;<−80°
where X is an axis connecting the center of the fixing roller and the center of the pressing roller, and Y is an axis along a direction perpendicular to a straight line which passes through the rotational contact region and connects the pivot shaft and the rotational contact region, wherein on the basis of the axis X, a positive sign is provided to the angle &thgr; when the axis Y is located on a sheet-feed side where the sheet is fed into the rotational contact region, and a negative sign is provided to the angle &thgr; when the axis Y is located on a sheet-discharge side where the sheet is discharged from the rotational contact region.
According to a third aspect of the present invention, there is provided a fixing apparatus comprising: a fixing roller; a pressing roller in rotational contact with the fixing roller; and a biasing member for applying a biasing force to the pressing roller so as to bring the pressing roller into press contact with the fixing roller at a given pressure, whereby when a sheet having unfixed toner on a surface thereof is passed through a rotational contact region between the fixing and pressing rollers along one direction, the unfixed toner is fixed onto the sheet. In this fixing apparatus, the fixing roller is disposed to be opposed to the surface of the sheet having unfixed toner, the pressing roller being
Hamada Yasuhide
Higashi Yuichiro
Nitto Kogyo Co. Ltd.
Tran Hoan
Westerman Hattori Daniels & Adrian LLP
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