Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-06-28
2002-10-08
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000, C219S619000, C399S328000, C399S334000, C399S333000
Reexamination Certificate
active
06463252
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a fixing apparatus employing an induction heating method (an electromagnetic inducing heating method) to press, heat and fix toner images, which are obtained by developing electrostatic latent images with thermally meltable toner.
Conventionally, for image forming apparatuses, which are used for high speed, high image quality copiers and printers, frequently employed is a method of developing electrostatic latent images, typified by an electrophotographic method.
In this method, electrostatic images are developed with thermally meltable toner, and after the obtained toner images are transferred onto a recording medium, the toner images are fixed with heat and pressure. As a heat source used in a fixing apparatus, a halogen lamp has been commonly used.
However, in recent years, an apparatus applying an electromagnetic induction system, which is characterized by direct heating of a heat receiving member (a heat roller, etc.) and high heating efficiency, has been extensively studied. (For example, as described in Tokkaihei 11-190950.) However, it has become more and more apparent that an electromagnetic induction fixing apparatus has some problems and without countermeasures, the apparatus is not likely to come into practical use.
Conventionally, as heat-receiving members, an electro conductive roller, a magnetic metal roller, or a roller comprised of multi layers of Ni and Cu, etc. on insulating body have been used. However, there are many cases where ferromagnetic materials have low electric conductivity, or materials of high electric conductivity have low relative magnetic permeability, and large eddy current cannot be obtained, and heating efficiency is not so high as expected.
Further, in cases of using a halogen lamp, temperature of the heat-receiving member is measured and power supply is cut off in accordance with the measured value in order to control the temperature. In this case, if the power supply is cut off after the temperature reaches a predetermined value, a large overshoot is often caused by a delay of the action. Also, in electromagnetic induction fixing, wherein material with exceedingly higher Curie temperature, than usual fixing temperature, is used for the heat receiving member and core, a large overshoot as aforementioned cases arises in cases where, a heat receiving material with low thermal capacity is used and high electrical power is supplied, aiming for a rapid temperature rise.
Alternatively, in cases where correct temperature cannot be detected because of failure in a temperature sensor, a thermal runaway occurs and neighboring parts would be damaged, and in the worst case, would be burned. For these cases, decreasing the overshoot as far as possible, and in the case of overheating, restricting a heat generating rate to low levels are important subjects.
Further, depending on the size of the recording medium (or recording paper), required heat distribution is different, and this causes an abnormal increase of temperature at areas distant from the center of the heat-receiving member, therefore, equalization of this temperature distribution is another subject.
Furthermore, in an apparatus wherein a conventional way of winding an induction coil is applied, uneven temperature distribution is caused in the circumferential direction of the heat-receiving member, therefore in order to equalize the temperature, increasing the previous revolutions of the heat-receiving member (fixing roller, etc.) is required. Still more, when a thick heating roller with large heat capacity is used, a long warming up time is needed, and when a thin heating roller or a roller with low heat conductivity is used, unevenness of temperature tends to be caused.
The present invention is performed to overcome the above-described shortcomings.
Namely, the first object of the present invention is to provide an inducing heating type fixing apparatus with short warming up time (WUT) by using high magnetic permeability and high electrical conductivity alloy which generates eddy current effectively.
The second object of the present invention is to provide an inducing heating type fixing apparatus, wherein temperature overshoot is minimized, and in case of overheating the heat generation rate is suppressed.
The third object of the present invention is to provide an inducing heating type fixing apparatus in which temperature unevenness in the circumferential direction of a heat-receiving member (fixing roll, etc.) is decreased.
Incidentally, the fixing apparatus utilizing electromagnetic induction usually comprises a heating means and a pressure means, and both means contact each other to grip and transport the toner image bearing recording medium and fix the image. Said heating means comprises roll or belt-shaped rotatable heat receiving member in which provided a helical coil or a vertically wound coil, and a core if necessary. Alternating current, whose frequency is preferably 5 kHz or higher, is supplied to said coil to generate an alternating magnetic field, and eddy current is induced in said heat receiving member, then, the eddy current loss causes a heat generation in the heat receiving member. With this heat, cooperating with pressure, which is applied elastically by said pressure means, toner images are fixed onto the recording medium.
The above fixing apparatus utilizing the electromagnetic induction has superior characteristics to a fixing apparatus, which uses an infrared heater or a nichrome wire heater, in that; the apparatus can be made in small size and light weight, and almost free from a fear of fire, the power consumption loss is small, a warm up time is very short after starting a supply of high frequency alternating current, etc. Therefore, studies and developments of the fixing apparatus utilizing the electromagnetic induction have been performed recently. For example, in Tokkaisyo 54-39645(official report 1), and Tokkaihei 9-106207(official report 2), etc., various technologies concerning the fixing apparatus utilizing the electromagnetic induction are proposed.
Said official report 1 relates to a heating means for a fixing apparatus wherein high frequency AC current is supplied to a helically wound coil, and eddy current is induced in a heat-receiving member, which is made of electro conductive ferromagnetic material and rotatably provided around the coil, and generated heat is used for fixing. And the official report 1 describes that, said coil in the heating means is wound coarsely at the area near the center in the longitudinal direction of the heating means, and wound thickly at the area near the side ends, and the heat-receiving member is evenly heated in the longitudinal direction.
Further, the official report 2 relates to a fixing apparatus wherein high frequency AC power is supplied to a plurality of coils wound vertically around divided cores, and eddy current is induced in a heat-receiving member, which is made of electro conductive ferromagnetic material and rotatably provided around the coil, and the generated heat is used for fixing. And the report 2 describes that said coils provided near the center in the longitudinal direction of the heat receiving member are connected in parallel, and coils provided near the ends are connected in series to said coils connected in parallel, and by this configuration, the temperature distribution of the heat-receiving member in the longitudinal direction is equalized.
However, conventional fixing apparatuses utilizing an electromagnetic induction described in the official report 1 and 2, etc. are aiming for an equalization of the temperature distribution in a certain fixed operation mode, and can not deal with the cases of various modes in the process of forming fixed images where various power consumption distributions are required, such as a warming up mode, a large sized paper transporting mode, a small sized paper transporting mode, and a standby mode, etc. Especially, there have been problems such that, in a large sized paper transporting mode, tempera
Omoto Tetsuko
Toyoda Miho
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
Ngo Hoang
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