Electrophotography – Image formation – Fixing
Reexamination Certificate
1999-06-24
2001-03-06
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Fixing
C399S330000
Reexamination Certificate
active
06198901
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a heating apparatus for heating a sheet of recording medium or the like. In particular, it relates to a heating apparatus which employs a heat generating system based on electromagnetic induction. This type of heating apparatus is employed, as a fixing apparatus, in an image forming apparatus, for example, a copying machine, a printer, a facsimile machine, or the like.
Usually, an image forming apparatus such as a copying machine, a printer, or a facsimile machine, is equipped with a heating apparatus.
A heating apparatus is used as a fixing apparatus, or a surface treating apparatus. In the case of the latter usage, it is used to heat a sheet of recording medium comprising a surface layer of porous high polymer, to melt the porous high polymer surface layer after an image is formed on the sheet with the usage of, for example, an ink jet system.
Next, a case in which a heating apparatus is employed as a fixing apparatus will be described.
An electrophotographic copying machine or the like is equipped with a fixing apparatus which fixes a toner image to a sheet of recording medium, for example, recording paper, after the toner image is transferred onto the sheet.
Such a fixing apparatus comprises a fixing roller for thermally melting the toner on a sheet of recording medium, and a pressure roller for holding the sheet against the fixing roller with a predetermined pressure. The fixing roller is sometimes called a heating roller.
The fixing roller comprises a hollow cylinder, and a heating member disposed in the cylinder. They are concentrically supported with the central axis of the fixing roller.
The heating member consists of a tubular heater such as a halogen lamp or the like, and generates heat as a predetermined voltage is applied to the heating member.
Since the heating member, or a halogen lamp, is concentrically supported, along with the cylinder of the heating roller, by the central axis of the heating roller, the radiant heat from the halogen lamp is uniformly distributed across the internal surface of the cylinder of the fixing roller. As a result, the temperature distribution of the cylinder of the fixing roller becomes uniform in terms of the circumferential direction of the cylinder.
The cylinder of the fixing roller is heated until its temperature reaches a specific temperature suitable for image fixation (for example, 150°-120°).
The fixing roller, the temperature of which is within the above range, and the pressure roller are rotated in the directions opposite to each other while being in contact with each other, and hold between them a sheet of recording medium on which a toner image has been temporarily adhered.
The toner on the sheet is melted by the heat from the fixing roller, and is fixed to the sheet by the pressure generated by the two rollers, in their interface (hereinafter, “nip”).
However, in the case of a fixing apparatus such as the above described one equipped with a heating member consisting of a halogen lamp or the like, the fixing roller is heated with the use of radiant heat from a halogen lamp or the like, and therefore, the time necessary for the temperature of the fixing roller to reach the predetermined temperature suitable for image fixation after a power source is turned on (hereinafter, “warmup time”), is relatively long.
In other words, a user has to wait for a relatively long time without being able to use the copying machine during this warmup period, which is a problem.
There is a method for reducing the length of the warmup time so that the operational efficiency of the apparatus is improved, according to which a large amount of electric power is given to the fixing roller. However, this method increases the electrical power consumption of the fixing apparatus, which is a problem in terms of energy conservation.
Thus, recently, more attention has been paid to reducing the amount of energy consumed by a fixing apparatus while improving operational efficiency (quick print capability), so that the commercial value of such merchandise as a copying machine can be further improved.
As for an apparatus which meets such a requirement, there is an induction heating based fixing apparatus disclosed in Japanese Laid-Open Patent Application No. 33,787/1984, according to which a high frequency induction system is used as a heating generating source.
The aforementioned induction heating based fixing apparatus comprises a hollow roller formed of electrically conductive metal, and a coil disposed in the hollow roller, concentrically with the hollow roller. In operation, eddy current is induced in the hollow roller by a high frequency magnetic field generated by flowing high frequency electric current through the coil, and heat (joule heat) is directly generated within the hollow roller by the induced current and the electrical resistance of the hollow roller.
The inductive heat generation system is very high in electrothermal conversion efficiency, and therefore, its employment makes it possible to substantially reduce the warmup time of a fixing apparatus.
Further, combining the coil with a core formed of magnetic material (magnetic field shielding material) can improve the efficiency with which high frequency magnetic field is generated.
In particular, the employment of a core with a T-shaped cross section reduces the amount of electric power necessary to generate a given amount of heat required by a fixing apparatus, because the core with a T-shaped cross section is effective in focusing high frequency magnetic fluxes, and also shielding the magnetic field so that the magnetic field is confined in the heat generating area.
However, the aforementioned conventional technology had the following problems.
That is, in the case of an inductive heat generation based fixing apparatus such as the one described above, the temperature of the magnetic core itself increased due to the inward heat radiation from the fixing roller, which was one of the problems.
More specifically, as the temperature of the magnetic core increased beyond the Curie-point of the magnetic material of the core, the heat generation efficiency decreased, which resulted in fixation failure, which in turn resulted in the production of inferior images.
Thus, various proposals for preventing the temperature increase of the magnetic core were made. According to one of the proposals, disclosed in Japanese Laid-Open Patent Application No. 39/645/1979, a cooling mechanism such as a means for sending air into the interior of the fixing roller was provided to reduce the amount of the coil temperature increase.
However, the provision of a cooling mechanism resulted in the increase in the apparatus size, as well as the complication of the apparatus.
The inventors of the present invention proposed a simple structure which was capable of preventing the temperature increase of the magnetic core without increasing the apparatus size. According to this proposal, the supporting member for fixing the core and the coil to the side plate or the like of a fixing apparatus was formed of highly heat conductive material such as aluminum, so that heat was conducted out of the fixing roller through the supporting member.
However, such a structure was only theoretically successful in allowing heat to escape outward through the highly heat conductive material such as aluminum so that the core remained cool. More specifically, the surface of the core formed of magnetic material with the use of extruding, grinding, or the like production method did not fit tightly with the supporting member (hereinafter, “stay”) due to design error or the like. Therefore, heat was not allowed to efficiently escape from the core to the stay.
SUMMARY OF THE INVENTION
The primary object of the present invention is to prevent the temperature increase of the magnetic member, so that it becomes possible to provide an image heating apparatus capable of reliably heating an image.
Another object of the present invention is to provide an image forming apparatus equip
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
LandOfFree
Image heating apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image heating apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image heating apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2496871