JP2008256939A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in which the energy of a leakage magnetic-flux from the vicinity of the end part of a fixing roller can be used for heating the vicinity of the central part of the fixing roller; and to provide an image forming apparatus. <P>SOLUTION: The fixing device 5 is configured by including: the fixing roller 51 having a part 511 to be heated made of magnetic shunt alloy (one example of a magnetic material) having a Curie point; and an electromagnetic induction heating system heating heater 52 for heating the part 511 to be heated by electromagnetic induction. The fixing device 5 further includes: electromagnetic coils 71 and 72 for generating an induced electromotive force by the magnetic flux after passing through the part 511 to be heated from the electromagnetic coil 82 of the heating heater 52, in the vicinity of both end parts of the fixing roller 51; and a resistance heating element 73 for heating the vicinity of the central part of the fixing roller 51 by the induced electromotive force generated in the electromagnetic coils 71 and 72. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device that heats a fixing roller by an electromagnetic induction heating method, and more particularly to a technique for preventing overheating near the end of the fixing roller.

An image forming apparatus such as a printer, a copying machine, a facsimile machine, or a complex machine of these may use an electromagnetic induction heating type fixing device that heats a fixing roller by electromagnetic induction.
Specifically, an electromagnetic coil is arranged inside a hollow fixing roller made of a magnetic material, and a magnetic flux is generated by passing an alternating current through the electromagnetic coil. As a result, in the fixing roller, eddy current (inductive current) is generated by electromagnetic induction due to magnetic flux (magnetic field) of the electromagnetic coil, and heat is generated. In general, in the image forming apparatus configured as described above, the temperature of the fixing roller is controlled by controlling the alternating current applied to the electromagnetic coil based on the detection result of the temperature sensor that detects the temperature of the fixing roller. .

Conventionally, when print output is performed using a small-size sheet, there is a problem that overheating occurs in a non-sheet passing area near the end of the fixing roller through which the sheet does not pass. Therefore, for example, Patent Document 1 discloses a configuration that uses a magnetic shunt alloy for the fixing roller to prevent overheating of a non-sheet passing region in the fixing roller. Here, the magnetic shunt alloy has a characteristic that the magnetism rapidly decreases when the Curie point is reached.
In such a configuration, when the temperature of the non-sheet-passing region of the fixing roller exceeds the Curie point of the magnetic shunt alloy, the magnetism in the non-sheet-passing region rapidly decreases, and the eddy current generated by electromagnetic induction rapidly increases. Will be reduced. Therefore, overheating of the non-sheet passing area of the fixing roller can be prevented without using a temperature sensor or a thermostat.
On the other hand, for example, Patent Document 2 discloses a configuration in which a metal having diamagnetism such as copper is provided on the outer periphery of a fixing roller made of a magnetic material. Here, diamagnetism is a property of being magnetized in a direction opposite to the direction of magnetic flux. Therefore, in such a configuration, when the magnetic flux leaks from the electromagnetic coil through the fixing roller, the leakage magnetic flux is canceled out by the diamagnetic metal, so that leakage to the outside is prevented.
JP 2004-325678 A Japanese Patent Laid-Open No. 2003-223063

However, in Patent Documents 1 and 2, the temperature of the non-sheet passing region of the fixing roller rises, and the magnetic flux leaking from the fixing roller is released or canceled out as it is, and the energy of the magnetic flux is wasted. There is a problem of being consumed.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to use the energy of leakage magnetic flux from the vicinity of the end portion of the fixing roller for heating near the center portion of the fixing roller. It is an object of the present invention to provide a fixing device or an image forming apparatus capable of performing the above.

In order to achieve the above object, the present invention provides a fixing device comprising a fixing roller having a heated portion made of a magnetic material having a Curie point, and electromagnetic induction heating means for heating the heated portion by electromagnetic induction. One or a plurality of induced electromotive force generations that generate an induced electromotive force by a magnetic flux that has passed through the heated portion from the electromagnetic induction heating means in the vicinity of one end portion or both end portions of the fixing roller And a one or a plurality of induced electromotive force heating means for heating the vicinity of the center portion of the fixing roller by the induced electromotive force generated by the induced electromotive force generating means. Is done.
In the configuration of the present invention, for example, the temperature of the non-sheet passing region where the sheet in the vicinity of the end of the fixing roller does not pass exceeds the Curie point, and the magnetism of the heated portion in the non-sheet passing region is drastically reduced. When magnetic flux leaks from the electromagnetic induction heating means through the heated portion, an induced electromotive force is generated by the induced electromotive force generating means due to the magnetic flux, and the induction electromotive force heating means causes the vicinity of the center portion of the fixing roller. Is heated. That is, according to the present invention, the energy consumption efficiency can be improved by utilizing the energy of the magnetic flux leaking from the vicinity of the end portion of the fixing roller for heating the central portion of the fixing roller.

Here, the heated portion may be a magnetic material having a Curie point, and a magnetic shunt alloy having a characteristic that magnetism rapidly decreases when the Curie point is exceeded is used for the magnetic material. It is desirable.
For example, an electromagnetic coil may be used as the induced electromotive force generating means. In the electromagnetic coil, an induced electromotive force (inductive current) is generated by the magnetic flux that has passed through the heated portion from the electromagnetic induction heating means.
On the other hand, the induction electromotive force heating means may be, for example, a resistance heating element or a halogen heater. In this resistance heating element, halogen heater, or the like, the vicinity of the center portion of the fixing roller is heated by the induced electromotive force.

  Further, the present invention may be understood as an invention of an image forming apparatus. An image forming apparatus comprising a fixing roller having a heated portion made of a magnetic material having a Curie point and an electromagnetic induction heating means for heating the heated portion by electromagnetic induction, One or a plurality of induced electromotive force generating means for generating an induced electromotive force by magnetic flux that has passed through the heated portion from the electromagnetic induction heating means in the vicinity of one end or both ends of the fixing roller, and the induced electromotive force generating means One or a plurality of induced electromotive force heating means for heating the vicinity of the central portion of the fixing roller by the generated induced electromotive force is configured as an image forming apparatus.

  According to the present invention, for example, the temperature of the non-sheet passing region where the sheet in the vicinity of the end of the fixing roller does not pass exceeds the Curie point, and the magnetism of the heated portion in the non-sheet-passing region is rapidly reduced. When magnetic flux leaks from the electromagnetic induction heating means through the heated portion, an induced electromotive force is generated by the induced electromotive force generating means due to the magnetic flux, and the induction electromotive force heating means causes the vicinity of the center portion of the fixing roller. Is heated. That is, according to the present invention, the energy consumption efficiency can be improved by utilizing the energy of the magnetic flux leaking from the vicinity of the end portion of the fixing roller for heating the central portion of the fixing roller.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of a copying machine X according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing a schematic configuration of a fixing device 5 according to the embodiment of the present invention, and FIG. 4 is a schematic diagram showing an internal configuration of the fixing device 5 according to the embodiment of the present invention, and FIG. 4 is a conceptual schematic diagram for explaining a state of magnetic flux in the fixing device 5 according to the embodiment of the present invention.
As shown in FIG. 1, a copying machine X according to an embodiment of the present invention includes an operation display unit 1 such as a liquid crystal display and a touch panel for displaying and inputting various information in the copying machine X, a document table, An image reading unit 2 that reads an image of a document set on an ADF (automatic conveyance device), image data of the document read by the image reading unit 2, and a not-shown image connected via a communication network such as a LAN. The image processing unit 3 performs various image processing on the image data of the document input from the information processing apparatus, and includes a photosensitive drum, a charger, a developing device, an LSU, and the like. An image forming unit 4 that forms a toner image (developer) on a sheet based on the input document image data, and a fixing device 5 that melts and fixes the toner image formed on the sheet by the image forming unit 4 on the sheet. And C U and a peripheral device such as a ROM and a RAM, and a control unit 6 that controls the copying machine X in an integrated manner by executing processing according to a predetermined program stored in the ROM. ing.
Further, the copying machine X has various components that a general electrophotographic copying machine has, but the description thereof is omitted here. The copying machine X is merely an example of an image forming apparatus according to the present invention. For example, a printer apparatus, a facsimile apparatus, a multifunction peripheral, and the like correspond to the image forming apparatus according to the present invention. The copying machine X according to the embodiment of the present invention is characterized by the configuration relating to the fixing device 5 and will be described in detail below.

First, the schematic configuration of the fixing device 5 will be described with reference to the schematic diagram of FIG. 2A is a view of the fixing device 5 seen from the side, and FIG. 2B is a view of the fixing device 5 seen from above.
As shown in FIG. 2, the fixing device 5 includes a fixing roller 51 that melts and fixes the toner image on sheets of various sizes such as A3 to A5 to which the toner image is attached in the image forming unit 4 (not shown). , A pressure roller 51 a that rotates while pressing the sheet together with the fixing roller 51, and an electromagnetic induction heating heater 52 (electromagnetic) that is provided inside the fixing roller 51 and heats the fixing roller 51 by electromagnetic induction. An example of induction heating means), a central temperature sensor 53 such as a thermistor disposed in the vicinity of the central part of the fixing roller 51, and electromagnetic coils 71 and 72 (an example of induction electromotive force generation means) described later. It is roughly structured.
The central temperature sensor 53 detects the temperature in the vicinity of the central portion of the fixing roller 51 and inputs the detection result to the control unit 6. In the controller 6, the heater 52 is set so that the temperature of the fixing roller 51 becomes a preset fixing temperature (for example, about 200 ° C.) based on the detected temperature input from the central temperature sensor 53. The drive control is performed. Note that the temperature control of the fixing roller 51 is not different from the conventional apparatus, and the description thereof is omitted here.

Next, the details of the fixing device 5 will be described with reference to FIG. 3A is a longitudinal sectional view of the heater 52, and FIG. 3B is a cross-sectional view taken along the line AA in FIG. 3A.
As shown in FIG. 3, the fixing roller 51 is formed in a hollow cylindrical shape and includes a heated portion 511 formed of a magnetic shunt alloy (an example of a magnetic material) having a Curie point (for example, about 220 ° C.). Have. It is conceivable that the magnetic shunt alloy is an alloy such as iron, nickel, or chromium. As described above, the magnetic shunt alloy has a characteristic that the magnetism rapidly decreases when the temperature reaches the Curie point. The magnetic shunt alloy is not limited, and other magnetic materials having a Curie point may be used.
In the fixing device 5, for example, print output is performed using a sheet whose size is smaller than the maximum sheet passing width of the fixing roller 51, and the temperature of the non-sheet passing region near the end of the fixing roller 51 rises, causing a curie. When the point is exceeded, the magnetism in the non-sheet passing region decreases rapidly, and the eddy current generated by electromagnetic induction decreases rapidly. Thereby, without using a temperature sensor or the like for detecting the temperature in the vicinity of the end portion of the fixing roller 51, it is possible to prevent overheating in the vicinity of the end portion and ensure safety.

On the other hand, the heater 52 includes an electromagnetic coil 82 wound around a plurality of iron cores 81, a drive circuit 83 (see FIG. 4) for applying an alternating current to the electromagnetic coil 82, and the like.
The heater 52 applies an alternating current to the electromagnetic coil 82 from the drive circuit 83 (see FIG. 4), thereby generating a magnetic flux (magnetic field) in the electromagnetic coil 82, and a heated portion of the fixing roller 51. The heated portion 511 is heated by generating an eddy current (induced current) due to electromagnetic induction with respect to 511. The fixing roller 51 is rotationally driven by a driving unit (not shown) so that the entire circumference is uniformly heated by the heater 52.

Further, as shown in FIG. 3, the fixing device 5 is induced on the outer periphery of the fixing roller 51 by magnetic flux that has passed through the heated portion 511 from the electromagnetic coil 82 in the vicinity of both ends of the fixing roller 51. Electromagnetic coils 71 and 72 for generating electric power and a resistance heating element 73 connected in series with the electromagnetic coils 71 and 72 are provided. Here, the electromagnetic coils 71 and 72 may be connected either in series or in parallel. Further, connecting the electromagnetic coils 71 and 72 to separate resistance heating elements 73 is also conceivable as another embodiment. 3 shows a state in which the electromagnetic coils 71 and 72 are wound with an air core, they may be wound around a magnetic body such as an iron core.
The resistance heating element 73 is disposed in the vicinity of the center portion of the fixing roller 51, and generates heat by the induced electromotive force generated in the electromagnetic coils 71, 72 to heat the vicinity of the center portion of the fixing roller 51. It is an example of an electromotive force heating means. Instead of the resistance heating element 73, a heating means such as a halogen heater may be used.

The electromagnetic coils 71 and 72 are provided corresponding to the position of the iron core 81 in the heater 52. In FIG. 3, a configuration in which three sets of the electromagnetic coils 71 and 72 are provided is shown as an example, but the electromagnetic coils 71 and 72 may be at least one set or more. Further, in an image forming apparatus in which the sheet passing through the fixing roller 51 passes along one end portion of the fixing roller 51, an electromagnetic coil may be provided in the vicinity of the one end portion.
In the fixing device 5 configured as described above, when magnetic flux leaks from the vicinity of the end of the fixing roller 51, an induced electromotive force (induced current) is generated in the electromagnetic coils 71 and 72 due to the leaked magnetic flux.

Hereinafter, the state of magnetic flux in the fixing device 5 will be described with reference to FIG. 4A shows the case where the temperature near the both ends of the fixing roller 51 is lower than the Curie point, and FIG. 4B shows the case where the temperature near the both ends of the fixing roller 51 reaches the Curie point. It is a conceptual schematic diagram which shows the magnetic flux in.
First, when the temperature near the end of the fixing roller 51 is lower than the Curie point, as shown in FIG. 4A, the fixing roller 51 is caused by the magnetic flux generated by the electromagnetic coil 82 (see the arrow in the drawing). An eddy current (induced current) due to electromagnetic induction flows through the entire heated portion 511, and the entire heated portion 511 is heated.
However, when the printing process is repeatedly performed using a sheet having a width smaller than the maximum sheet passing size of the fixing roller 51, that is, the sheet does not pass, the sheet does not pass near the both ends of the fixing roller 51. The temperature of the region R is higher than the temperature near the center.
Here, in the copying machine X, the heater 52 is set so that the temperature in the vicinity of the center of the fixing roller 51 detected by the center temperature sensor 53 becomes a preset fixing temperature (for example, about 200 ° C.). Therefore, only the temperature of the non-sheet passing region R near the end of the fixing roller 51 continues to rise.

Thereafter, when the temperature of the non-sheet passing region R in the vicinity of both ends of the fixing roller 51 rises and the temperature of the heated portion 511 in the non-sheet passing region R reaches a Curie point (for example, about 220 ° C.), The magnetism of the heated portion 511 in the non-sheet passing region R is abruptly lowered.
And as shown in FIG.4 (b), the magnetic flux (refer arrow to illustrate) from the said electromagnetic coil 82 leaks outside. Therefore, the eddy current generated by electromagnetic induction in the heated portion 511 in the non-sheet passing region R is rapidly reduced, and further temperature rise in the non-sheet passing region R is prevented. Thus, in the fixing device 5, overheating above the Curie point of the heated portion 511 is prevented by using a magnetic shunt alloy as the magnetic material having the Curie point in the heated portion 511.

On the other hand, as shown in FIG. 4B, in the non-sheet passing region R in the vicinity of both end portions of the fixing roller 51, the electromagnetic coil 82 of the heater 52 passes through the heated portion 511 and leaks to the outside. The magnetic flux acts on the electromagnetic coils 71 and 72.
Thereby, in the electromagnetic coils 71 and 72, an induced electromotive force (inductive current) is generated by the magnetic flux leaking from the heated portion 511. The induced electromotive force generated in the electromagnetic coils 71 and 72 flows to the resistance heating element 73.
Therefore, the resistance heating element 73 generates heat due to the induced electromotive force generated in the electromagnetic coils 71 and 72, and the heated portion 511 near the center portion of the fixing roller 51 is heated.

As described above, in the fixing device 5, the resistance heat generation that auxiliary heats the vicinity of the center portion of the fixing roller 51 with the energy of the leakage magnetic flux from the vicinity of the end portion of the fixing roller 51 that has been conventionally wasted. By using it for the body 73, energy required for controlling the temperature in the vicinity of the center of the fixing roller 51 to a preset fixing temperature can be reduced. Specifically, the operation load of the heater 52 can be reduced.
In the present embodiment, the case where the electromagnetic coil 82 is wound in the same direction as the circumferential direction of the fixing roller 51 has been described as an example. However, the electromagnetic coil 82 is not fixed to the fixing roller 51. The present invention can be similarly applied to a configuration in which the roller 51 is wound in the longitudinal direction.

1 is a block diagram showing a schematic configuration of a copier according to an embodiment of the present invention. 1 is a schematic diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating an internal configuration of a fixing device according to an embodiment of the present invention. FIG. 3 is a conceptual schematic diagram for explaining a state of magnetic flux in the fixing device according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Operation display part 2 ... Image reading part 3 ... Image processing part 4 ... Image forming part 5 ... Fixing device 6 ... Control part 50 ... Paper conveyance path 51 ... Fixing roller 511 ... Heated part 52 ... Heater 53 ... Central part Temperature sensors 71, 72 ... electromagnetic coils (an example of induced electromotive force generating means)
73 ... Resistance heating element (an example of induction electromotive force heating means)
81 ... Iron core 82 ... Electromagnetic coil 83 ... Drive circuit

Claims (5)

A fixing device comprising: a fixing roller having a heated portion made of a magnetic material having a Curie point; and electromagnetic induction heating means for heating the heated portion by electromagnetic induction,
One or a plurality of induced electromotive force generating means for generating an induced electromotive force by magnetic flux that has passed through the heated portion from the electromagnetic induction heating means in the vicinity of one end portion or both end portions of the fixing roller;
One or more induced electromotive force heating means for heating the vicinity of the center portion of the fixing roller by the induced electromotive force generated by the induced electromotive force generating means;
A fixing device comprising:   The fixing device according to claim 1, wherein the magnetic material is a magnetic shunt alloy.   The fixing device according to claim 1, wherein the induced electromotive force generating means is an electromagnetic coil.   The fixing device according to claim 1, wherein the induction electromotive force heating means is a resistance heating element or a halogen heater. An image forming apparatus comprising: a fixing roller having a heated portion made of a magnetic material having a Curie point; and a fixing device having electromagnetic induction heating means for heating the heated portion by electromagnetic induction,
One or a plurality of induced electromotive force generating means for generating an induced electromotive force by magnetic flux that has passed through the heated portion from the electromagnetic induction heating means in the vicinity of one end portion or both end portions of the fixing roller;
One or more induced electromotive force heating means for heating the vicinity of the center portion of the fixing roller by the induced electromotive force generated by the induced electromotive force generating means;
An image forming apparatus comprising:

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