JP2009134171A - Fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing occurrence of a magnetic flux unnecessary for induction heating of a fixing roller in response to the paper size by preventing over-heat of an end of the fixing roller, and to provide an image forming apparatus. <P>SOLUTION: In the fixing device 5 (or the image forming apparatus), an electromagnetic coil 80 is wound so that a width proximate at a position where induction heating of a part 511 to be heated of the fixing roller 51 can be performed is different by a rotation position of the electromagnetic coil 80. The fixing device detects the width of a passing region of the paper on the part 511 to be heated of the fixing roller 51, and adjusts the width of the magnetic flux in a width direction of the passing region of the paper acting on the part 511 to be heated from the electromagnetic coil 80 by controlling the rotation position of the electromagnetic coil 80 corresponding to the width. <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 an image forming apparatus including the fixing device, and more particularly to a technique for preventing overheating in the vicinity of an end portion 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, as in Patent Documents 1 and 2, in the configuration in which 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, it is related to the size of the paper. In other words, the same power is always supplied to the electromagnetic coil. Therefore, when using paper of a size smaller than the maximum paper passing size, unnecessary magnetic flux is generated and energy consumption is reduced. There is a problem of inefficiency.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to prevent overheating of the end of the fixing roller and to eliminate magnetic flux unnecessary for induction heating of the fixing roller according to the paper size. It is an object of the present invention to provide a fixing device and an image forming apparatus that can prevent the occurrence of the above-described problem.

In order to achieve the above-mentioned object, the present invention is used when a fixing roller having a heated part made of a magnetic material having a Curie point and induction heating of the heated part by electromagnetic induction, and on the surface of the fixing roller. An electromagnetic coil wound in an intersecting direction, and detecting a width of a sheet passing area in the fixing roller, and detecting the width of the detected sheet passing area from the electromagnetic coil according to the detected width of the sheet passing area. The fixing device is configured to adjust the width of the magnetic flux in the width direction of the sheet passing area acting on the heated portion.
According to the present invention, since it is possible to control the magnetic flux so that it does not act on the outside of the sheet passing area in the fixing roller, it is possible to prevent overheating of the end of the fixing roller and to induce induction heating of the fixing roller. Generation of unnecessary magnetic flux can be prevented. Therefore, it is possible to reduce power consumption required for induction heating of the fixing roller. In addition, in the present invention, it is possible to control so that magnetic flux does not act on the outside of the sheet passing area in the fixing roller by using only one electromagnetic coil without using a plurality of electromagnetic coils.

Specifically, 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 coil in the vicinity of one end or both ends of the fixing roller, and the induced electromotive force By providing an induced electromotive force measuring means for measuring the induced electromotive force generated by the power generating means, the width of the sheet passing area in the fixing roller is detected based on the measurement result by the induced electromotive force measuring means. It becomes possible. Here, it is conceivable that the induced electromotive force generating means is an induction coil in which electromagnetic induction is generated by the magnetic flux.
At this time, it is a condition that one end portion or both end portions of the fixing roller reach the Curie point. However, in the heated portion, the magnetism decreases when the Curie point is exceeded. Is prevented from overheating.
The heated portion may be a magnetic material having a Curie point, but a magnetic shunt alloy having a property that magnetism rapidly decreases when the Curie point is exceeded is used for the magnetic material. Is desirable.

Here, a specific method for adjusting the width of the magnetic flux in the width direction of the sheet passing area acting on the heated portion from the electromagnetic coil will be described.
First, if the electromagnetic coil is wound so that the width close to the position where the heated portion can be induction-heated differs depending on the rotational position of the electromagnetic coil, the rotational position of the electromagnetic coil is controlled. By doing so, it is possible to adjust the width of the magnetic flux in the width direction of the sheet passing area that acts on the heated portion from the electromagnetic coil.
If the electromagnetic coil can be expanded and contracted in the width direction of the paper in the fixing roller, the width of the passage area of the paper acting on the heated portion from the electromagnetic coil is controlled by controlling the expansion and contraction of the electromagnetic coil. It is possible to adjust the width of the magnetic flux in the direction.
Further, if the electromagnetic coil is wound around a magnetic core that can be expanded and contracted in the width direction of the paper in the fixing roller, the electromagnetic coil is controlled to expand and contract by controlling the expansion and contraction of the magnetic core. It is also possible to adjust the width of the magnetic flux in the width direction of the sheet passing area acting on the section.
According to these configurations, if the current applied to the electromagnetic coil is the same, the density of the magnetic flux acting on the heated portion from the electromagnetic coil increases as the width of the paper passage region decreases. Therefore, it is possible to shorten the time required for induction heating of the fixing roller and increase the operation efficiency. On the contrary, if the time for performing the induction heating of the fixing roller is constant, the current applied to the electromagnetic coil can be reduced.

Further, the present invention may be understood as an invention of an image forming apparatus.
That is, a fixing roller having a heated portion made of a magnetic material having a Curie point, and one heated in a direction crossing the surface of the fixing roller, which is used when the heated portion is induction-heated by electromagnetic induction. A fixing device having an electromagnetic coil is provided, detects the width of the sheet passing area in the fixing roller, and acts on the heated portion from the electromagnetic coil according to the detected width of the sheet passing area. The image forming apparatus is configured to adjust the width of the magnetic flux in the width direction of the sheet passage area.

According to the present invention, since it is possible to control the magnetic flux so that it does not act on the outside of the sheet passing area in the fixing roller, it is possible to prevent overheating of the end of the fixing roller and to induce induction heating of the fixing roller. Generation of unnecessary magnetic flux can be prevented. Therefore, it is possible to reduce power consumption required for induction heating of the fixing roller. In addition, in the present invention, it is possible to control so that magnetic flux does not act on the outside of the sheet passing area in the fixing roller by using only one electromagnetic coil without using a plurality of electromagnetic coils.
Specifically, 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 coil in the vicinity of one end portion or both end portions of the fixing roller, and the induced electromotive force An induced electromotive force measuring means for measuring the induced electromotive force generated by the generating means is provided, so that the width of the sheet passing area in the fixing roller is detected based on the measurement result by the induced electromotive force measuring means. Is possible. In this case, it is a condition that one end portion of the fixing roller or both end portions reach the Curie point. However, since the magnetism of the heated portion decreases when the Curie point is exceeded, the Curie of the heated portion is reduced. Overheating beyond the point is prevented.
Further, as the width of the sheet passing area is reduced, the density of magnetic flux acting on the heated portion from the electromagnetic coil is increased, thereby shortening the time required for induction heating of the fixing roller and increasing the operation efficiency. In addition, the current applied to the electromagnetic coil can be reduced.

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. FIG. 4 is a flowchart for explaining an example of the procedure of the magnetic flux width adjustment process executed by the copying machine X. FIG. 5 shows an example of the execution result of the magnetic flux width adjustment process. It is a schematic diagram for demonstrating.

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, a RAM, and the like, and a control unit 6 that generally controls the copying machine X by executing processing according to a predetermined program stored in the ROM. Yes.
The copying machine X has various other constituent elements 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 has various sizes such as A3, B4, A4, and A5 to which a toner image is attached in the image forming unit 4 (not shown) and is conveyed on the paper conveyance path 50. A fixing roller 51 that melts and fixes the toner image on the paper, a pressure roller 51a that rotates while pressing the paper together with the fixing roller 51, and an electromagnetic induction heating method that heats the fixing roller 51 by induction. A heater 52, a temperature sensor 53 such as a thermistor disposed at the center of the fixing roller 51, and induction coils 71 and 72 described later are schematically configured. The fixing roller 51 is formed in a hollow cylindrical shape, and an electromagnetic coil 80 (see FIG. 3), which will be described later, included in the heater 52 is disposed inside the fixing roller 51.
The temperature sensor 53 detects the temperature of the central portion of the fixing roller 51 and inputs the detection result to the control unit 6. As a result, the controller 6 controls the heater 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 temperature sensor 53. 52 is controlled. Note that the fixing temperature control of the fixing roller 51 is not different from that of the conventional apparatus, and the description thereof is omitted here.

Next, a configuration related to induction heating of the fixing device 5 will be described with reference to a schematic diagram of FIG. FIG. 3A is a schematic diagram of the main part when the inside of the fixing roller 51 is viewed from the front, and FIG. 3B is a schematic diagram of the main part when the inside of the fixing roller 51 is viewed from the side.
As shown in FIG. 3, the fixing roller 51 has 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.). The heated portion 511 is provided along the circumference of the fixing roller 51.
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.
Therefore, when the heated portion 511 of the fixing roller is induction-heated by the heater 52 and the temperature of a certain area of the heated section 511 rises and exceeds the Curie point, the magnetism rapidly decreases in that area. As a result, eddy currents generated by electromagnetic induction are drastically reduced and overheating is prevented.

On the other hand, the heater 52 controls, as shown in FIG. 3, one electromagnetic coil 80 used for induction heating of the heated portion 511 by electromagnetic induction, and AC power supplied to the electromagnetic coil 80. And a drive circuit 81. The drive circuit 81 is provided with an inverter circuit for controlling an alternating current applied to the electromagnetic coil 80, for example.
In the heater 52, the drive circuit 81 is controlled by the controller 6, and a magnetic flux is generated in the electromagnetic coil 80, so that an eddy current (induced current) due to electromagnetic induction is generated in the heated portion 511 of the fixing roller 51. Is generated, and the heated portion 511 is heated. 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. In addition, the electromagnetic coil 80 may be provided at a plurality of locations in the fixing roller 51 as another embodiment.

The electromagnetic coil 80 is formed of an electric wire wound in a direction crossing the surface of the heated portion 511, and is rotatably supported by a drive shaft connected to a drive motor (not shown). . The electromagnetic coil 80 may be wound around an air core, or may be wound around a magnetic core such as an iron core.
The electromagnetic coil 80 is wound so that the width of the electromagnetic coil 80 close to the position where the heated portion 511 can be induction-heated differs depending on the rotational position of the electromagnetic coil 80. Specifically, the electromagnetic coil 80 has a trapezoidal shape when viewed from the front as shown in FIG. 3A and a semicircular shape when viewed from the side as shown in FIG. It is rolled up. That is, in the electromagnetic coil 80, the winding width (width in the longitudinal direction) is gradually reduced in the direction of the arrow R1 shown in FIG. 3, and the density of the wire is increased. In such a configuration, if the part of the electromagnetic coil 80 adjacent to the heated part 511 is different, the width of the magnetic flux acting on the heated part 511 from the electromagnetic coil 80 is also different.

Therefore, in the fixing device 5, the controller 6 controls a drive motor (not shown) of the electromagnetic coil 80 and adjusts the rotational position of the electromagnetic coil 80, so that the heated portion is heated from the electromagnetic coil 80. The width of the magnetic flux acting on 511, that is, the induction heating region in the heated portion 511 can be adjusted. The controller 6 adjusts the rotational position of the electromagnetic coil 80 according to the number of steps of the drive motor and the drive time.
Here, in the copying machine X, information on the rotational position of the electromagnetic coil 80 for the width of the magnetic flux acting on the heated portion 511 from the electromagnetic coil 80 to be the same as the width of each of the plurality of sizes of paper. (Hereinafter referred to as “rotational position correspondence information”) is stored in the internal memory of the control unit 6. The rotation position correspondence information is referred to by the control unit 6 in a magnetic flux width adjustment process (see the flowchart of FIG. 4) described later, and is used to specify the rotation position of the electromagnetic coil 80 corresponding to the paper size. The rotational position correspondence information is not limited to the internal memory of the control unit 6, but may be stored in a storage unit such as a ROM that can be read by the control unit 6.

On the other hand, in the fixing device 5, as shown in FIG. 3, on the outer periphery of the fixing roller 51, electromagnetic induction by magnetic flux that has passed through the heated portion 511 from the electromagnetic coil 80 near both ends of the fixing roller 51. Inductive coils 71 and 72 (an example of induced electromotive force generating means) for generating induced electromotive force (inductive current) are provided. The induction coils 71 and 72 are formed to have the same length as at least the interval between the maximum width and the minimum width of the electromagnetic coil 80. Although FIG. 3 shows a state in which the induction coils 71 and 72 are wound with an air core, they may be wound around a magnetic core such as an iron core.
The induction coils 71 and 72 are connected in series to the input port of the control unit 6, and the induced electromotive force generated by the induction coils 71 and 72 is input to the control unit 6. The induced electromotive force generated in the induction coils 71 and 72 is measured as a voltage value (or current value) by a voltage measurement circuit (or current measurement circuit) (not shown) provided in the control unit 6. Here, the voltage measurement circuit (or voltage measurement circuit) when performing such measurement is an example of the induced electromotive force measurement means. It is also conceivable as another embodiment that the induced electromotive force generated in the induction coils 71 and 72 is individually input to the control unit 6.
Here, the induced electromotive force generated by the induction coils 71 and 72 varies depending on the size of the sheet passing through the fixing roller 51. Hereinafter, this point will be described with reference to FIG.

As shown in FIG. 2B, when the paper size is different, the paper passing area in the fixing roller 51 is different, and the width of the non-paper passing area where the paper does not pass at both ends of the fixing roller 51 is also different. For example, the width of the non-sheet passing region at both ends of the fixing roller 51 is wider when the A4 size paper passes than when the B4 size paper passes.
Therefore, when performing induction heating of the fixing roller 51 using the position of the maximum width of the electromagnetic coil 80, when the non-sheet passing area at both ends of the fixing roller 51 exceeds the Curie point, the non-sheet passing area The amount of magnetic flux leaking from the sheet is greater when A4 size paper is used than when B4 size paper is used.
As described above, in the fixing device 5, when induction heating of the fixing roller 51 is performed using the position of the maximum width of the electromagnetic coil 80, the amount of magnetic flux acting on the induction coils 71 and 72 is determined by the fixing roller. 51 differs depending on the width of the sheet passage area. For this reason, the magnitude of the induced electromotive force generated by the induction coils 71 and 72 also varies depending on the width of the sheet passing area in the fixing roller 51.

Accordingly, the relationship between the magnitude (for example, voltage value) of the induced electromotive force generated in the induction coils 71 and 72 and the width of the sheet passage area (sheet size) in the fixing roller 51 is previously tested and simulated. The control unit 6 stores the magnitude of the induced electromotive force input from the induction coils 71 and 72 by storing it in a storage means such as a ROM that can be read by the control unit 6. Based on this, it is possible to detect the width of the sheet passing area in the fixing roller 51.
Hereinafter, as the relationship between the magnitude of the induced electromotive force generated by the induction coils 71 and 72 and the width of the sheet passing area in the fixing roller 51, the induction corresponding to the sheet size of each of A3, B4, A4, and A5. It is assumed that information about the predetermined range of the voltage value of the electromotive force (hereinafter referred to as “width correspondence information”) is stored in the internal memory of the control unit 6.
In the copying machine X according to the embodiment of the present invention, leakage from both ends of the fixing roller 51 is performed by the control unit 6 performing a magnetic flux width adjustment process (see the flowchart of FIG. 4) described later. The width of the sheet passing area in the fixing roller 51 is detected according to the magnitude of the induced electromotive force generated by the magnetic flux, and the width of the magnetic flux acting on the heated portion 511 from the electromagnetic coil 80 corresponding to the width. Is adjusted.

Hereinafter, according to the flowchart of FIG. 4, an example of the procedure of the magnetic flux width adjustment process executed by the control unit 6 in the copying machine X will be described, and then a specific operation example will be described with reference to FIG. Here, S1, S2,... Shown in FIG. 4 represent processing procedure (step) numbers.
The magnetic flux width adjustment process is executed by the control unit 6 when a print job is requested to the copying machine X, and the process is started from step S1. The said control part 6 when performing the magnetic flux width adjustment process which concerns here corresponds to an induction heating control means.
The magnetic flux width adjustment process executed by the control unit 6 may be executed by a control circuit (not shown) such as an ASIC provided in the fixing device 5. In this case, the control circuit (not shown) ) Corresponds to induction heating control means.

First, in step S1, the control unit 6 causes the electromagnetic coil 80 to have a position where the maximum width of the electromagnetic coil 80 corresponding to the maximum sheet size A3 size is closest to the heated portion 511. The drive control of a drive motor (not shown) is performed.
At this time, the control unit 6 controls the rotational position of the electromagnetic coil 80 by controlling the amount of rotation of the drive motor (not shown), for example, according to the number of steps and the energization time. Further, a sensor for detecting the rotational position of the electromagnetic coil 80 may be provided, and the amount of rotation may be controlled according to the detection result of the sensor. In addition, if the site | part of the maximum width in the said electromagnetic coil 80 is already arrange | positioned in the position nearest to the said to-be-heated part 511, the said drive motor (not shown) will not be driven.

Next, in step S <b> 2, the control unit 6 gives a control instruction to the drive circuit 81 to apply an alternating current to the electromagnetic coil 80. Thereby, a magnetic flux acts on the heated part 511 from the electromagnetic coil 80, and the heated part 511 is induction-heated by electromagnetic induction by the magnetic flux. When the fixing roller 51 is heated to a predetermined fixing temperature, the printing process in the copying machine X is executed.
At this time, if the temperature of the heated part 511 does not reach the Curie point, the magnetic flux generated in the electromagnetic coil 80 does not pass through the heated part 511, and therefore the induced electromotive force is generated in the induction coils 71 and 72. Does not occur. Specifically, when the printing process is executed using A3 size paper corresponding to the maximum width of the electromagnetic coil 80, the temperature of the heated portion 511 does not reach the Curie point.

In subsequent step S3, the control unit 6 determines whether or not the temperatures at both ends of the heated portion 511 have reached the Curie point, depending on whether or not the induced electromotive force is input from the induction coils 71 and 72. To do.
Here, if the induced electromotive force is not input (No side of S3), it is determined that the temperature of the heated portion 511 has not reached the Curie point, and the process proceeds to step S3 until the print job is completed. Waiting at.

On the other hand, when the printing process is repeatedly performed using a paper having a size (B4, A4, A5, etc.) smaller than the A3 size paper corresponding to the maximum width of the electromagnetic coil 80, the fixing roller does not pass the paper. In some cases, the non-sheet passing region in the vicinity of both ends of 51 may reach the Curie point. When the non-sheet passing area reaches the Curie point, an induced electromotive force is input from the induction coils 71 and 72 to the control unit 6.
Therefore, in step S3, it is determined that the induced electromotive force has been input (Yes side of S3), and the process proceeds to step S4.
At this time, since the magnetism of the non-sheet passing region in the heated portion 511 is rapidly reduced, the induced current generated in the non-sheet passing region is rapidly decreased, and the temperature rise in the non-sheet passing region is further increased. 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.
However, in this case, at both ends of the heating roller 51, the magnetic flux from the electromagnetic coil 80 is radiated wastefully through the heated portion 511, and power consumption for generating the magnetic flux is low. It is useless. Therefore, in the magnetic flux width adjustment process, the width of the magnetic flux acting on the heated portion 511 from the electromagnetic coil 80 is adjusted in accordance with the width of the sheet passing area in the fixing roller 51, thereby reducing unnecessary magnetic flux. It prevents the occurrence and saves power.

First, in step S4, the control unit 6 measures the magnitude of the induced electromotive force input from the induction coils 71 and 72 by the voltage measurement circuit (not shown), and the fixing roller according to the measurement result. The width of the paper passage area at 51 is detected. Here, the control unit 6 when executing the detection process corresponds to a sheet passing area detecting unit.
Specifically, the control unit 6 determines the sheet size corresponding to the voltage value of the induced electromotive force input from the induction coils 71 and 72 based on the width correspondence information stored in the internal memory as described above. The width of the paper passage area is detected by specifying
In the present embodiment, a case where the paper size is detected according to the magnitude of the induced electromotive force input from the induction coils 71 and 72 will be described as an example. It is also conceivable as another embodiment to acquire the paper size from the paper setting data for the printing process, the type of the paper feed cassette used in the printing process, and the like. Further, a plurality of temperature sensors corresponding to positions of a plurality of sheet sizes are provided in the sheet width direction of the fixing roller 51, and any size sheet passes based on the temperature detected by each of the temperature sensors. It is also possible to detect whether or not

In step S5, the width of the paper passage area detected in step S4 and the width of the portion of the electromagnetic coil 80 adjacent to the heated portion 511 are the same by the control unit 6. The rotational position of the coil 80 is specified.
Specifically, the control unit 6 is detected in step S4 based on the rotation position correspondence information (information indicating the correspondence between the paper size and the rotation position) stored in the internal memory as described above. The rotational position of the electromagnetic coil 80 corresponding to the paper size is specified.

Thereafter, in step S6, the control unit 6 controls the rotational drive of a drive motor (not shown) of the electromagnetic coil 80 so that the rotational position of the electromagnetic coil 80 becomes the rotational position specified in step S5. To do. As a result, the width of the sheet passage area in the fixing roller 51 and the width of the magnetic flux acting on the heated portion 511 from the electromagnetic coil 80 are adjusted to be the same.
Thus, in the copying machine X, the magnitude of the leakage magnetic flux from the vicinity of the end of the fixing roller 51 is measured by the induced electromotive force generated in the induction coils 71 and 72, and according to the measured value, The rotational position of the electromagnetic coil 80 is adjusted so as not to generate unnecessary magnetic flux for induction heating of the fixing roller 51.
Accordingly, overheating of the end portion of the fixing roller 51 can be prevented, and generation of magnetic flux unnecessary for induction heating of the fixing roller 51 can be prevented according to the sheet size. Accordingly, it is possible to appropriately reduce the power consumption required for induction heating of the fixing roller 51. For example, when a small size paper is used, induction heating is performed only on the paper passing area in the heated portion 511 by a portion where the density of the electric wire in the electromagnetic coil 80 is high. That is, it is possible to shorten the energization time to the electromagnetic coil 80.
In the present embodiment, the sheet passing through the fixing roller 51 has been described as an example of a configuration in which the sheet is conveyed toward the center, but the sheet passing through the fixing roller 51 is the fixing roller 51. In the image forming apparatus of the type that passes along one of the end portions, the electromagnetic coil 80 may be formed so that the width gradually increases from one end portion to the other end portion.

Next, an example of the operation of the fixing device 5 when a print job using A5 size paper, which is the minimum paper size in the copying machine X, is executed will be described with reference to FIG. For understanding.
First, when energization of the electromagnetic coil 80 is started (S2 in FIG. 4), as shown in FIG. 5A, a magnetic flux in the direction of the arrow shown by the electromagnetic coil 80 is generated. An eddy current (inductive current) flows through the heated portion 511 of the fixing roller 51 by the magnetic flux generated by the electromagnetic coil 80, and the heated portion 511 is heated.
At this time, since the size of the sheet passing through the fixing roller 51 is A5, the width of the sheet passing area in the fixing roller 51 is larger than the width of the magnetic flux acting on the heated portion 511 from the electromagnetic coil 80. short. For this reason, the temperature of the non-sheet passing region R where the sheet of the fixing roller 51 does not pass gradually increases.

After that, the printing process is continuously executed, and when the temperature of the non-sheet passing region R of the fixing roller 51 reaches the Curie point, the magnetism of the heated portion 511 in the non-sheet passing region R rapidly decreases. As shown in FIG. 5B, the magnetic flux from the electromagnetic coil 80 passes through the heated portion 511 and leaks to the outside.
At this time, magnetic flux leaked to the outside from both ends of the heated portion 511 acts on the induction coils 71 and 72, so that an induced electromotive force is generated in the induction coils 71 and 72. The induced electromotive force generated by the induction coils 71 and 72 is input to the control unit 6.
Here, when the controller 6 detects the input of the induced electromotive force from the induction coils 71 and 72 (Yes side of S3), it passes through the fixing roller 51 according to the magnitude of the induced electromotive force. It is detected that the paper size is A5 (S4), and the rotational position of the electromagnetic coil 80 corresponding to the A5 size is specified (S5).

  Then, the controller 6 adjusts the rotational position of the electromagnetic coil 80 to a rotational position corresponding to A5 which is the size of the sheet passing through the fixing roller 51 (S6). As a result, in the fixing device 5, as shown in FIG. 5C, the electromagnetic coil 80 exists only in the paper passage area in the heated portion 511, so that only the paper passage area is inductively heated. Will be. Accordingly, the magnetic flux does not act on the non-sheet passing region R in the vicinity of both end portions of the fixing roller 51 as in the case where induction heating is performed using the maximum width portion of the electromagnetic coil 80, and wasteful energy consumption is achieved. Can be prevented.

By the way, in the magnetic flux width adjusting process (see FIG. 4), the initial setting of the rotational position of the electromagnetic coil 80 is set to a position where the maximum width portion of the electromagnetic coil 80 is close to the heated portion 511. Then, an induced electromotive force detected when induction heating is performed using the portion is measured, and the rotational position of the electromagnetic coil 80 is adjusted according to the measurement result. , 72 to measure the induced electromotive force and adjust the rotational position of the electromagnetic coil 80 as necessary.
For example, when an induced electromotive force is still generated in the induction electromagnetic coils 71 and 72 after the rotation position of the electromagnetic coil 80 is changed, the rotation position of the electromagnetic coil 80 is further changed. It can be considered that the width of the electromagnetic coil 80 is adjusted to be smaller. In this case, the configuration may be such that only the presence or absence of the induced electromotive force generated in the induction coils 71 and 72 can be detected by the presence or absence of driving of a relay (relay) or a transistor, for example. It is possible to simplify the circuit by omitting the voltage measurement circuit (or the current measurement circuit).

Further, a method in which the maximum width portion of the electromagnetic coil 80 is not initially set is also conceivable. For example, a plurality of temperature sensors corresponding to positions corresponding to a plurality of paper size widths are provided at both end portions (or one end portion) of the fixing roller 51, and the temperature detected by the temperature sensor and the induction coils 71 and 72 are set. It is conceivable to adjust the rotational position of the electromagnetic coil 80 based on both of the induced electromotive force generated in step (b).
In this configuration, for example, in the printing process using A5 size paper, after performing the induction heating of the heated portion 511 using a portion of the electromagnetic coil 80 having the same width as the width of the A5 size paper, When executing printing processing using B4 size paper, the rotational position of the electromagnetic coil 80 is set to B4 size on condition that the temperature detected by the temperature sensor corresponding to B4 size paper has not reached the fixing temperature. It is possible to adjust so that a part having the same width as the width of the paper is close to the heated portion 511.

Hereinafter, in the first and second embodiments, another structure for adjusting the width of the magnetic flux acting on the heated portion 511 from the electromagnetic coil 80 will be described.
FIG. 6 is a schematic diagram showing the internal configuration of the fixing device 5 ′ according to the first embodiment of the present invention, and the inside of the fixing device 5 ′ is viewed from the front. In the fixing device 5 ′ according to the first embodiment, the same components as those of the fixing device 5 described in the embodiment are denoted by the same reference numerals, and the description thereof is omitted.
As shown in FIG. 6, in the heating device 52 ′ provided in the fixing device 5 ′, both ends of the electromagnetic coil 80 are supported by a movable rack 91, and the rack 91 is rotated by a motor (not shown). It is meshed with a pinion gear 92 connected to the shaft.
According to such a configuration, the position of the rack 91 is changed by controlling the rotation direction and amount of rotation of the pinion gear 92 by the motor by the control unit 6, so that the electromagnetic coil 80 is The fixing roller 51 can be expanded and contracted in the paper width direction. That is, in the fixing device 5 ′, the control unit 6 expands and contracts the electromagnetic coil 80 to adjust the width of the electromagnetic coil 80, so that the magnetic flux acting on the heated portion 511 from the electromagnetic coil 80 is adjusted. It is possible to adjust the width.

FIG. 7 is a schematic diagram showing the internal configuration of the fixing device 5 ″ according to the second embodiment of the present invention, and the inside of the fixing device 5 ″ is viewed from the front. For the fixing device 5 ″ according to the second embodiment, the same reference numerals are given to the same configurations as those of the fixing device 5 described in the above embodiment, and the description thereof is omitted.
As shown in FIG. 7, in the heating device 52 ″ provided in the fixing device 5 ″, the electromagnetic coil 80 has a magnetic core such as an iron core that can expand and contract in the width direction of the paper in the fixing roller 51. No. 93. In this case, the width of the magnetic flux generated by the electromagnetic coil 80 varies depending on the length of the magnetic core 93.
Here, the magnetic core 93 has a double tube structure in which the inner tube 93b is inserted into the inside from both ends of the outer tube 93a. And the said inner pipe | tube 93b is comprised so that insertion / removal in the said outer pipe | tube 93a is possible. For example, it is conceivable to connect a rack that performs linear motion to the end of the inner pipe 93b by rotation of a pinion gear connected to a motor as shown in the first embodiment. Thus, by controlling the rotation of the motor, the magnetic core 93 can be expanded and contracted by adjusting the amount of protrusion of the inner tube 93b from the outer tube 93a. The structure for inserting / removing the inner tube 93b is not limited to this.
As described above, in the fixing device 5 ″, the control unit 6 changes the protruding amount of the inner tube 93b from the outer tube 93a to expand and contract the magnetic core 93, thereby the electromagnetic coil 80. It is possible to adjust the width of the magnetic flux acting on the heated portion 511.

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. 6 is a flowchart for explaining an example of a procedure of magnetic flux width adjustment processing executed by the copier according to the embodiment of the present invention. FIG. 5 is a schematic diagram for explaining an example of the execution result of magnetic flux width adjustment processing executed by the copier according to the embodiment of the present invention. 1 is a schematic diagram illustrating an internal configuration of a fixing device according to Embodiment 1 of the present invention. FIG. FIG. 6 is a schematic diagram illustrating an internal configuration of a fixing device according to a second embodiment of the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Operation display part 2 ... Image reading part 3 ... Image processing part 4 ... Image forming part 5, 5 ', 5''... Fixing device 6 ... Control part 50 ... Paper conveyance path 51 ... Fixing roller 511 ... Heated part 52 , 52 ', 52''... heater 53 ... temperature sensor 71, 72 ... induction coil (an example of induced electromotive force generating means)
80 ... Electromagnetic coil 81 ... Drive circuit 91 ... Rack 92 ... Pinion gear 93 ... Magnetic core X ... Copying machine

Claims (8)

A fixing roller having a heated portion made of a magnetic material having a Curie point;
One electromagnetic coil used in induction heating of the heated portion by electromagnetic induction and wound in a direction intersecting the surface of the fixing roller;
Paper passage area detecting means for detecting the width of the paper passage area in the fixing roller;
Induction heating control means for adjusting the width of the magnetic flux in the width direction of the paper passing area acting on the heated portion from the electromagnetic coil according to the width of the paper passing area detected by the paper passing area detecting means; ,
A fixing device comprising: Generated by one or a plurality of induced electromotive force generating means for generating an induced electromotive force by the magnetic flux that has passed through the heated portion from the electromagnetic coil in the vicinity of one end or both ends of the fixing roller, and the induced electromotive force generating means And an induced electromotive force measuring means for measuring the induced electromotive force.
The fixing device according to claim 1, wherein the paper passage area detection unit detects a width of a paper passage area in the fixing roller based on a measurement result by the induced electromotive force measurement unit.   The fixing device according to claim 2, wherein the induced electromotive force generating means is an induction coil that generates electromagnetic induction by the magnetic flux.   The fixing device according to claim 1, wherein the magnetic material is a magnetic shunt alloy. The electromagnetic coil is wound such that the width of the electromagnetic coil close to the position where induction heating of the heated portion is different depends on the rotation position of the electromagnetic coil,
2. The induction heating control means adjusts the width of the magnetic flux in the width direction of the sheet passing area acting on the heated portion from the electromagnetic coil by controlling the rotational position of the electromagnetic coil. The fixing device according to any one of? The electromagnetic coil is extendable in the width direction of the paper in the fixing roller;
The said induction heating control means adjusts the width of the magnetic flux in the width direction of the passage area of the paper that acts on the heated portion from the electromagnetic coil by controlling expansion and contraction of the electromagnetic coil. 5. The fixing device according to any one of 4 above. The electromagnetic coil is wound around a magnetic core that can expand and contract in the width direction of the paper in the fixing roller,
2. The induction heating control means adjusts the width of a magnetic flux in the width direction of a sheet passing region acting on the heated portion from the electromagnetic coil by controlling expansion and contraction of the magnetic core. The fixing device according to any one of? A fixing roller having a heated portion made of a magnetic material having a Curie point, and an electromagnetic coil wound when the heated portion is induction-heated by electromagnetic induction and wound in a direction crossing the surface of the fixing roller A fixing device having
Paper passage area detecting means for detecting the width of the paper passage area in the fixing roller;
Induction heating control means for adjusting the width of the magnetic flux in the width direction of the paper passing area acting on the heated portion from the electromagnetic coil according to the width of the paper passing area detected by the paper passing area detecting means; ,
An image forming apparatus comprising:

Images