Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-10-18
2004-09-21
Lee, Susan (Department: 2852)
Electrophotography
Image formation
Fixing
C399S069000, C399S329000
Reexamination Certificate
active
06795681
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of controlling a fixing device, the fixing device and an image forming apparatus equipped with the fixing device.
In general, electro-photographic image forming apparatus is equipped with a hot-press type fixing device to fix toner images that are formed but unfixed on transfer sheets or recording materials. Among such hot-press type fixing devices, a well-known fixing device that provides a comparatively stable fixability (also referred to as fixing performance) comprises, for example, a heating roller containing a heat source such as a heater lamp, a supporting roller that is in parallel with the heating roller with a space between them, a fixing belt that is trained about the heating roller and the supporting roller, and a pressing roller that is placed to form a nipping area between the fixing belt and the pressing roller and gives a pressing force to the heating roller or the supporting roller via the fixing belt.
In the fixing device of this belt type, the pressing roller comprises a core bar made of metal such as aluminum and an elastic layer made of elastic material such as silicone rubber that covers the surface of the core bar.
This kind of fixing device is equipped with a temperature detecting means for detecting the temperature of the pressing roller. The fixing device sets the target temperature of the heating roller for optimum fixing according to temperature information sent from the temperature detecting means, causes a proper controlling mechanism to control turning on and off the heater lamp in the heating roller, and thus keeps the temperature of the nipping area at a preset temperature.
However, this controlling method that sets the target temperature of the heating roller from only temperature information sent from the temperature detecting means cannot keep the expected fixability (fixing performance) steadily as the hardness of the elastic material constituting the elastic layer around the surface of the pressing roller goes down when the fixing device is used for a long time or when the operating environment of the fixing device such as ambient temperature and humidity changes. Consequently, this kind of fixing device cannot be free from a problem that the formed images may have uneven glossiness.
Further, when a fixing condition such as the moving speed of the fixing belt or the fixing load changes, the fixing performance cannot be the same. Therefore, the fixing device cannot form images of even glossiness independently of the fixing process conditions.
Further, the conventional fixing devices have problems as explained below.
Glossiness of fixed images is one of the most significant image characteristics. As the glossiness of fixed images is dependent upon the fixing process conditions, the optimum fixing condition is set according to the expected glossiness of the fixed images. However, to change the glossiness of the fixed images, it is necessary to determine another optimum fixing process conditions by trial and error. This is a complicated and time-consuming work.
Even when an optimum fixing condition is set, for example, the hardness of the elastic material covering the pressing roller goes lower as the fixing device is used longer and the nipping width and the nipping surface pressure vary. In other words, the fixing process condition varies substantially. Therefore, it is difficult to form fixed images of the expected glossiness.
Further, the fixing device cannot be free from a problem that fixed images do not have uniform glossiness when the operating environment such as ambient temperature and humidity of the fixing device varies.
SUMMARY OF THE INVENTION
In view of the foregoing, a first object of the invention is to provide a method of controlling a fixing device to steadily retain a desired fixability (fixing performance) for a long time independently of a change or fluctuation in the fixing process condition or change in the operating condition.
A second object of the invention is to provide a fixing device that steadily retains a desired fixability (fixing performance) for a long time independently of a change or fluctuation in the fixing process condition or change in the operating condition.
A third object of the invention is to provide an image forming apparatus that steadily retains a desired fixability (fixing performance) for a long time independently of a change or fluctuation in the fixing process condition or change in the operating condition and steadily forms images of uniform glossiness.
A fourth object of the invention is to provide a method of controlling a fixing device that forms fixed images of a desired glossiness easily and steadily for a long time and that steadily forms fixed images of a desired glossiness independently of changes in the operating environment or the like.
A fifth object of the invention is to provide a fixing device that forms fixed images of a desired glossiness easily and steadily for a long time and that steadily forms fixed images of a desired glossiness independently of changes in the operating environment or the like.
A sixth object of the invention is to provide an image forming apparatus that forms fixed images of a desired glossiness easily and steadily for a long time and that steadily forms fixed images of a desired glossiness independently of changes in the operating environment or the like.
The above-described first through third objects can be accomplished by one of the structures below.
A method of controlling a fixing device comprising a heating roller containing a heat source, at least one supporting roller that is in parallel with the heating roller with a space between them, a fixing belt that is trained about the heating roller and the supporting roller, and a pressing roller that is placed to form a nipping area between the fixing belt and the pressing roller and gives a pressing force to the heating roller or the supporting roller via the fixing belt, wherein said method comprises the steps of (i) detecting the temperature of said pressing roller, (ii) calculating a target heating roller temperature (a) from a detected temperature (b) of the pressing roller obtained in said step (i), a loaded nipping time (c) calculated by Expression (1) below, a false nipping time (d) calculated by Expression (2) below, and a loaded nipping surface pressure (e) calculated by Expression (3) below, and (iii) controlling the operating status of the heat source in said heating roller from the target heating roller temperature (a) obtained in step (ii).
Loaded nipping time (
c
)=
L
1/
V
Expression (1)
False nipping time (
d
)=
L
2/
V
Expression (2)
Loaded nipping surface pressure (
e
)=
P
/(
L
1×
W
) Expression (3)
In Expressions (1) to (3), L1 is the width of the fixing belt along the movement of the fixing belt in the surface area of the fixing belt sandwiched by the pressing roller and the supporting roller or the heating roller, L2 is the width of the fixing belt in the area in contact with the pressing roller only along the movement of the fixing belt, V is the moving speed of the fixing belt, W is the width of the fixing belt perpendicular to the movement of the fixing belt in the surface area of the fixing belt sandwiched by the pressing roller and the supporting roller or the heating roller, and P is the load (pressure) applied to the area sandwiched by the pressing roller and the supporting roller or the heating roller.
In the fixing device controlling method of the present invention, the target heating roller temperature (a) that satisfies Expression (4) below is preferably calculated in step (iii).
A
×target heating roller temperature (
a
)+
B
×detected pressure roller temperature (
b
)+
C
×loaded nipping time (
c
)+
D
×false nipping time (
d
)+
E
×loaded nipping surface pressure (
e
)+
F=
0, Expression (4)
wherein A, B, C, D, E, and F are all constants.
Further in the fixing
Fuma Hiroshi
Hamada Jun-ichi
Onodera Masahiro
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
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