JP2010276832A - Fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and image forming apparatus for heating the differential region of paper width, while restricting the heating of common region of different paper widths. <P>SOLUTION: A magnetic flux shielding member 60, located on a route of a magnetic flux acting on a heating roller 53 from an induction heating coil, has a restricted magnetic flux shielding section 60a for forming, on the route of the magnetic flux; a restricted magnetic flux shielding region D3 for passing the magnetic flux through the differential region of different paper width (for example, A3 or A5) and restricting the passage of the magnetic flux through the common region of the paper width. As a result, since the differential region can be heated intensively, while the heating of the common region is restricted, abnormal heating in the common region is prevented, as well as, the region on the member to be heated corresponding to the differential region can be rapidly heated up to a predetermined fixing temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an induction heating type fixing device and an image forming apparatus including the same, and in particular, a fixing device capable of changing a heating target area of a member to be heated (such as a fixing roller) according to a sheet width to be fixed. And an image forming apparatus.

In general, an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine of these uses an induction heating type fixing device that heats a heated member such as a fixing roller by electromagnetic induction. Specifically, in the fixing device, an induction heating coil and a magnetic core are arranged so as to face the maximum sheet passing area of a heated member made of a magnetic material. A magnetic flux is generated by passing a high-frequency current through the induction heating coil. As a result, the magnetic flux generated by the induction heating coil is guided to the member to be heated through the magnetic circuit formed by the magnetic core, and the member to be heated is heated by the eddy current (induction current) generated by electromagnetic induction by the magnetic flux. Is done.
Conventionally, in such an induction heating type fixing device, when a paper having a size smaller than the maximum paper passing area is passed, in order to maintain the paper passing area through which the paper passes at a predetermined fixing temperature, There is a problem that overheating occurs in a non-sheet passing region near the end of the heated member through which the sheet does not pass. Therefore, a configuration in which the width of the heating target region in the heated member can be changed according to the paper size has been studied.
For example, in the configuration described in Patent Document 1, it is possible to adjust the width of the heating target area to the paper size by changing the width of the magnetic flux acting on the member to be heated from the induction heating coil with the magnetic flux shielding member.

JP-A-2005-208624

However, in the configuration in which the width of the heating target area is adjusted to the paper size as described in the cited document 1, the fixing target is used when the paper size is changed from A5 size to A3 size in the continuous printing process. When the paper width is changed from the small size to the large size, the region corresponding to the large size including the region corresponding to the small size that has already been heated to the predetermined fixing temperature becomes the heating target region. For this reason, if the difference area between the small size and the large size on the fixing roller is quickly heated to a predetermined fixing temperature, abnormal heating occurs in the area corresponding to the small size that has already been heated to the predetermined fixing temperature. On the other hand, if an attempt is made to prevent abnormal heating in the area corresponding to the small size, it takes a long time to heat the differential area, and the waiting time until the large-size fixing operation after the change becomes possible becomes long. Occurs.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fixing device capable of heating a differential region of the paper width while restricting heating of a common region of different paper widths. An object is to provide an image forming apparatus.

In order to achieve the above object, the present invention provides an induction heating coil that performs induction heating using a fixing member that melts and fixes toner adhering to a sheet or a heat transfer member that is thermally coupled to the fixing member as a member to be heated, A magnetic flux shielding member that forms on the magnetic flux path one of a plurality of magnetic flux shielding regions corresponding to a plurality of paper widths by a portion interposed on the magnetic flux path acting on the heated member from the induction heating coil; The heating target of the heated member by the induction heating coil is changed by moving the magnetic flux shielding member according to the width of the sheet to be fixed, thereby changing the width of the path of the magnetic flux acting on the heated member from the induction heating coil. And a magnetic flux width changing means for changing the area, wherein the magnetic flux shielding member allows the magnetic flux to pass in different areas of the different paper widths, Configured as a fixing device characterized by comprising a one or more restriction magnetic flux shielding unit limits the magnetic flux shielding region that limits the passage of the magnetic flux is formed on a path of the magnetic flux in the common area of the paper width.
According to the present invention, the heating of the common region can be easily restricted by simply changing the portion of the magnetic flux shielding member positioned on the magnetic flux path to the restricted magnetic flux shielding portion by the magnetic flux width changing means. The difference area can be heated with priority.
For example, it can be considered that the differential shielding portion shields the entire path of the magnetic flux in the common area. In this case, it is possible to heat only the difference area without heating the common area.
Further, the limiting magnetic flux shielding portion shields a part of the path of the magnetic flux in the common area, thereby reducing the amount of magnetic flux passing through the common area from the amount of magnetic flux passing through the difference area. If so, the difference area can be heated while the common area is kept warm.

Specifically, the heating target area is larger than the one paper width before the preset set time elapses after the induction heating in which one paper width is set as the heating target area by the induction heating coil. When the fixing operation is performed by changing to another sheet width, it can be considered that the common area is sufficiently hot and only the temperature of the difference area is low. Therefore, in such a case, the magnetic flux shielding member is arranged so that the magnetic flux width changing means interposes the limiting magnetic flux shielding portion corresponding to the one paper width and the other paper width on the path of the magnetic flux. Can be considered. As a result, the limiting magnetic flux shielding area corresponding to the one paper width and the other paper width is formed on the magnetic flux path, so that the difference area is focused while restricting heating of the common area. Heating can be performed, and abnormal heating in the common region can be prevented, and a region on the heated member corresponding to the difference region can be rapidly heated to a predetermined fixing temperature.
Also, after the induction heating in which one paper width is set as the heating target area by the induction heating coil, the heating target area is changed to another paper width larger than the one paper width and the fixing operation is performed. In addition, when the temperature of the region corresponding to the common region of the one sheet width and the other sheet width in the heated member is equal to or higher than a preset temperature, the magnetic flux width changing unit similarly It is conceivable to move the magnetic flux shielding member so that the limiting magnetic flux shielding portions corresponding to the one paper width and the other paper width are interposed on the path of the magnetic flux.

On the other hand, if the state where the heating of the common area is limited continues, the temperature of the common area eventually becomes lower than a predetermined fixing temperature. Therefore, in such a case, it is necessary to set a width equivalent to the width of the other paper in the member to be heated as a heating target region.
Accordingly, the magnetic flux width changing means is configured to change the other magnetic flux width when a predetermined time or more has elapsed since the limiting magnetic flux shielding portion corresponding to the one paper width and the other paper width is interposed on the magnetic flux path. It is conceivable that the magnetic flux shielding member is moved so that the magnetic flux shielding region corresponding to the paper width of the paper is formed on the path of the magnetic flux. That is, when it is estimated that the temperature of the common area has reached a predetermined fixing temperature or less, a width equivalent to the other sheet width is set as the heating target area.
Further, the magnetic flux width changing means includes the restrictive magnetic flux shielding portion corresponding to the one paper width and the other paper width on the path of the magnetic flux, and then the one paper width in the heated member. When the temperature of the area corresponding to the common area with the other paper width reaches a predetermined temperature, the magnetic flux shielding area corresponding to the other paper width is formed on the path of the magnetic flux. It is also conceivable to move the magnetic flux shielding member.

Here, it is conceivable that the magnetic flux shielding member is provided on the outer peripheral surface of a cylindrical magnetic core that forms part of the path of the magnetic flux by being opposed to the heated member. In this case, the magnetic flux width changing means can change the portion of the magnetic flux shielding member interposed on the path of the magnetic flux by rotating the magnetic core and rotating the magnetic flux shielding member. .
The present invention may also be understood as an invention of an image forming apparatus provided with the fixing device.

According to the present invention, the heating of the common region can be easily restricted by simply changing the portion of the magnetic flux shielding member positioned on the magnetic flux path to the restricted magnetic flux shielding portion by the magnetic flux width changing means. The difference area can be heated with priority.
Specifically, after the end of induction heating in which one sheet width is set as a heating target region by the induction heating coil, before the set time set in advance, or the one sheet width in the heated member Fixing operation by changing the heating target area to another paper width larger than the one paper width in a state where the temperature of the area corresponding to the common area with the other paper width is equal to or higher than a preset temperature. Is performed, the heating of the common area can be performed while restricting the heating of the common area, thereby preventing abnormal heating in the common area and the heated member corresponding to the differential area. The upper area can be quickly heated to a predetermined fixing temperature.

1 is a block diagram showing a schematic configuration of a copying machine X according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing a schematic configuration of a fixing device 5 according to an embodiment of the present invention. 4 is a schematic diagram for explaining an example of a magnetic flux shielding plate 60 included in the fixing device 5. FIG. 6 is a flowchart for explaining an example of a magnetic flux width changing process executed by the copying machine X; FIG. 6 is a schematic diagram for explaining another example of a magnetic flux shielding plate 60 included in the fixing device 5.

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.
First, a schematic configuration of the copying machine X according to the embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, a copying machine X according to an embodiment of the present invention includes an operation display unit 1, an image reading unit 2, an image processing unit 3, an image forming unit 4, a fixing device 5, a control unit 6, and the like. In general, it is structured. The copying machine X has other paper feeding cassettes and other various components that other general electrophotographic copying machines have. However, these are not different from the conventional ones, so the description thereof is omitted here. To do. The present invention is not limited to a copying machine, and can be applied to, for example, an electrophotographic image forming apparatus such as a printer, a facsimile machine, and a multifunction machine having these functions and a scanner function.
The control unit 6 has a CPU, peripheral devices such as a ROM and a RAM, and controls the copier X in an integrated manner by executing various processes in accordance with a predetermined program stored in the ROM. To do.
The operation display unit 1 includes a liquid crystal display that displays various types of information in accordance with instructions from the control unit 6, a touch panel for performing various operation inputs such as the start of copying processing to the control unit 6, and the like. Have.

The image reading unit 2 reads an image of a document set on a document table or an ADF (automatic conveyance device), and the image data read by the image reading unit 2 is input to the image processing unit 3. The
The image processing unit 3 performs various operations on image data of a document read by the image reading unit 2 and image data of a document input from an information processing apparatus (not shown) via a communication network such as a LAN. Image processing is performed. The image data that has been subjected to image processing by the image processing unit 3 is input to the image forming unit 4.
The image forming unit 4 includes a photosensitive drum, a charger, a developing device, an LSU, and the like. A toner image (developer) is applied to a sheet based on image data of a document input from the image processing unit 3. To form.
The fixing device 5 melts and fixes the toner image on the paper on which the toner image is formed by the image forming unit 4. The copying machine X according to the embodiment of the present invention is characterized in the configuration and operation related to the fixing device 5 and will be described in detail below with reference to FIGS.

As shown in FIG. 2, the fixing device 5 includes a fixing roller 51 and a pressure roller that rotate while pressing a sheet conveyed on the sheet conveying path 50 after the toner image is transferred in the image forming unit 4. 51a, a fixing belt 52 (an example of a fixing member) stretched between the fixing roller 51 and a heating roller 53 described later, and a driving force transmitted from the fixing roller 51 via the fixing belt 52. Heating roller 53 (an example of a heat transfer member), an induction heating coil 54 that performs induction heating using the heating roller 53 as a member to be heated, and a path that guides the magnetic flux generated by the induction heating coil 54 to the heating roller 53 ( A center core 55 and an outer core 56 forming a magnetic circuit.
The fixing roller 51 is connected to driving means such as a stepping motor (not shown), and is rotationally driven by the driving means. When the fixing roller 51 is rotationally driven, the fixing belt 52 travels by the driving force, and the heating roller 53 rotates by the driving force transmitted from the fixing belt 52. The heating roller 53 is made of a magnetic material such as iron or a magnetic shunt alloy.

The induction heating coil 54 is wound in the direction of the rotation axis (the depth direction in FIG. 2), which is the width direction of the heating roller 53, and the longitudinal width of the heating roller 53 (approximately the maximum sheet passing width). And the same width).
The center core 55 and the outer core 56 are made of a ferromagnetic material such as ferrite, and have a width substantially the same as the width of the heating roller 53 in the same manner as the induction heating coil 54. Is formed. The center core 55 and the outer core 56 form a path (see the thick arrow in FIG. 2) that guides the magnetic flux generated by the induction heating coil 54 to the heating roller 53.
In the fixing device 5, the magnetic flux generated in the induction heating coil 54 by supplying power to the induction heating coil 54 is guided to the heating roller 53 by the center core 55 and the external core 56, and the surface of the heating roller 53 When the eddy current (inductive current) is generated, the heating roller 53 is heated (induction heating). The power supply to the induction heating coil 54 is controlled by the control unit 6. Specifically, the control unit 6 supplies power to the induction heating coil 54 based on a temperature detected by a temperature sensor (not shown) that detects the temperature of the center or end of the fixing roller 51 or the heating roller 53. Control the supply.

As shown in FIG. 2, the outer core 56 is composed of a pair of U-shaped and inverted U-shaped magnetic cores surrounding both sides of the heating roller 53 and the center core 55. A path of magnetic flux is formed between the heating roller 53 and the center core 55 that passes outside the induction heating coil 54. The outer core 56 is not limited to the one continuously formed over the entire longitudinal width of the heating roller 53 and the center core 55. For example, the outer core 56 is not limited to the longitudinal direction of the heating roller 53 and the center core 55. It may have a plurality of plate-like cores arranged at predetermined intervals over the entire width.
On the other hand, the center core 55 is a cylindrical roller member disposed to face the heating roller 53 through a hollow portion of the induction heating coil 54. The center core 55 is interposed between the outer core 56 and the heating roller 53, thereby forming a magnetic flux path between the induction heating coil 54 and the heating roller 53. The center core 55 is rotatably supported by a core rotation mechanism (not shown) that rotates the center core 55 independently of the heating roller 53.

The core rotation mechanism (not shown) includes a transmission system such as a rotation shaft and a gear connected to the center core 55, and a drive system such as a stepping motor and a servo motor connected to the rotation shaft and the gear. Yes. The presence / absence of drive of the core rotation mechanism (not shown), the drive amount, and the like are controlled by the control unit 6 and the like.
Specifically, when a stepping motor that rotates by a predetermined amount in accordance with the number of input steps is used as the drive system, the control unit 6 includes a stepping motor or the like previously stored in a ROM or the like of the control unit 6. The rotation position of the center core 55 can be controlled based on the relationship between the rotation amount (such as the number of steps) of the drive system and the rotation amount of the center core 55 by the core rotation mechanism (not shown). Of course, a sensor for detecting the rotational position of the center core 55 or the magnetic flux shielding plate 60 described later may be provided, and the amount of rotation of the center core 55 may be controlled based on the detection result of the sensor. . The drive system may be configured using, for example, a clutch or a solenoid.

When the heating roller 53 is heated by the induction heating coil 54, the fixing belt 52 is heated by heat conduction from the heating roller 53 to the fixing belt 52 thermally coupled to the heating roller 53. The As a result, on the paper contacting the fixing belt 52, the toner adhering to the paper is melted and fixed.
A configuration in which the fixing belt 52 is made of a magnetic member and the fixing belt 52 is directly heated by the magnetic flux from the induction heating coil 54 is also conceivable. It is also conceivable that the fixing roller 51 is directly induction-heated by the magnetic flux from the induction heating coil 54 without the heating roller 53 or the fixing belt 52. In these cases, the fixing belt 52 and the fixing roller 51 to be heated correspond to the heated member.

In the fixing device 5, the longitudinal direction of the heating roller 53 is arranged on the outer peripheral surface of the center core 55 on the path of magnetic flux acting on the heating roller 53 from the induction heating coil 54 (thick line arrow in FIG. 2). Is provided with a magnetic flux shielding plate 60 (an example of a magnetic flux shielding member) having a shape in which the width corresponding to is changed in a plurality of stages.
The magnetic flux shielding plate 60 is made of a material such as silver, copper, or aluminum having a function of shielding magnetic flux. The magnetic flux shielding plate 60 is attached to the outer peripheral surface of the center core 55 and rotates (moves) as the center core 55 rotates.
Specifically, in the present embodiment, the control unit 6 rotates (moves) the magnetic flux shielding plate 60 by rotating the center core 55 by the core rotation mechanism (not shown). The part of the magnetic flux shielding plate 60 interposed on the path of the magnetic flux acting on the roller 53 is changed.

Here, the magnetic flux shielding plate 60 will be described with reference to FIG. 3A to 3D are schematic diagrams for explaining the difference in the heating target region of the heating roller 53 depending on the position where the magnetic flux shielding plate 60 and the heating roller 53 face each other. The state which expand | deployed the magnetic flux shielding board 60 and the said center core 55 is shown.
As shown in FIG. 3, the magnetic flux shielding plate 60 is attached to the outer peripheral surface of the center core 55 to form four magnetic flux shielding regions D0 to D3 on the outer peripheral surface of the center core 55. is there.
The magnetic flux shielding plate 60 has a magnetic flux on the magnetic flux path by a portion interposed on the magnetic flux path acting on the heating roller 53 from the induction heating coil 54, that is, a portion closest to the heating roller 53. One of the shielding regions D0 to D3 is formed.
Therefore, in the copying machine X, as shown in FIGS. 3A to 3D, any one of the magnetic flux shielding regions D0 to D3 is located at the facing portion where the heating roller 53 and the center core 55 are closest to each other. By adjusting the position of the magnetic flux shielding plate 60 to be formed, the width of the magnetic flux path acting on the heating roller 53, that is, the position and width of the heating target region of the heating roller 53 can be changed. It is.

Here, out of the magnetic flux shielding regions D0 to D3, the magnetic flux shielding region D0 corresponds to the paper width of A3 size (an example of one paper width), and the paper width of A3 size in the heating roller 53. Is used to make the region corresponding to the heating target region.
The magnetic flux shielding area D1 corresponds to a sheet width of A5 size (an example of another sheet width) smaller than the sheet width of A3 size, and corresponds to the sheet width of A5 size in the heating roller 53. It is used to set the region as a heating target region.
The magnetic flux shielding region D2 is used when the entire path of the magnetic flux acting on the heating roller 53 from the induction heating coil 54 is shielded, such as when induction heating of the heating roller 53 is unnecessary.

The magnetic flux shielding area D3 allows the magnetic flux to pass through the difference area (both ends) of the A3 size and A5 size paper width, and restricts the passage of the magnetic flux in the common area (center portion) of the paper width. , Corresponding to the restricted magnetic flux shielding region. The magnetic flux shielding area D3 is formed by a restricted magnetic flux shielding portion 60a corresponding to the position of the common area of the A3 size and A5 size paper width provided on the magnetic flux shielding plate 60. The limiting magnetic flux shielding unit 60a shields the entire path of the magnetic flux in the common area.
In the present embodiment, a case will be described in which the sheet width to be fixed by the fixing device 5, that is, the heating target area of the heating roller 53 corresponds to two different A3 size and A5 size sheet widths. When the sheet width to be fixed by the fixing device 5 corresponds to various sheet widths (A3 to A6, B3 to B6, postcards, envelopes, etc.), the magnetic flux shielding corresponding to the different sheet widths. What is necessary is just to comprise the said magnetic flux shielding board 60 so that an area | region can be formed on the path | route of the said magnetic flux. In this case, it is conceivable to provide a plurality of the restricted magnetic flux shielding areas corresponding to the different paper widths.
The fixing device 5 is based on the premise that the sheet is transported so that the center of the heating roller 53 in the width direction coincides with the center of the sheet. Similarly, the present invention can be applied to a configuration in which is conveyed.

In the copying machine X, the control unit 6 executes a magnetic flux width changing process (see the flowchart of FIG. 4) described later, whereby the magnetic flux shielding plate 60 is changed according to the paper width to be fixed by the fixing device 5. It is rotated (moved), the width of the path of the magnetic flux acting on the heating roller 53 from the induction heating coil 54 is changed, and the heating target area of the heating roller 53 by the induction heating coil 54 is changed.
Thus, the said control part 6 and the said core rotation mechanism (not shown) when moving the said magnetic flux shielding board 60 are examples of a magnetic flux width change means. In the present embodiment, the case where the control unit 6 performs the magnetic flux width changing process will be described as an example. However, when the fixing device 5 is provided with a control unit such as an MPU or an ASIC. The magnetic flux width changing process may be executed by the control means. In this case, the control means of the fixing device 5 constitutes a magnetic flux width changing means.

Hereinafter, a specific example of the magnetic flux width changing process executed by the control unit 6 will be described with reference to the flowchart of FIG. Here, S1, S2,... Shown in the figure indicate processing procedure (step) numbers.
The magnetic flux width changing process is started when a request for executing a printing process such as a copying process or a printer process is generated in the copying machine X, and is terminated when the printing process is completed.
Further, in addition to the processing procedure described here, the control unit 6 performs the operation of the heating roller 53 when the temperature detected at the end of the heating roller 53 by the temperature sensor (not shown) reaches or exceeds a predetermined temperature. A process of adjusting the position of the magnetic flux shielding plate 60 so as to exclude the end portion from the heating target region is also executed. Thereby, abnormal heating of the end portion of the heating roller 53 is prevented.

(Steps S1, S11)
First, in step S1, the control unit 6 determines whether or not the paper size used for printing processing such as copying processing or printer processing, that is, the paper size to be fixed by the fixing device 5 is A3 size.
If it is determined that the paper size is A3 size (Yes side of S1), the process proceeds to step S2 described later, and if it is determined that the paper size is not A3 size (S1). No)), the process proceeds to step S11.
In step S <b> 11, the control unit 6 controls the core rotation mechanism (not shown) so that the magnetic flux shielding region D <b> 1 is formed on the magnetic flux path between the center core 55 and the heating roller 53. Then, the center core 55 and the magnetic flux shielding plate 60 are rotated. Thereby, the width of the path of the magnetic flux acting on the heating roller 53 from the induction heating coil 54, that is, the heating target area of the heating roller 53 is set to the A5 size paper width (see FIG. 3B). Therefore, abnormal heating at both ends of the heating roller 53 is prevented.

(Steps S2, S21)
In step S2, the control unit 6 determines whether or not the paper size has been changed from A5 size to A3 size, that is, whether or not the paper size having a small paper width has been changed to a paper size having a large paper width. In order to make this determination, the control unit 6 stores the sheet size to be fixed in the previously executed printing process.
If it is determined that the paper size has been changed from A5 size to A3 size (Yes side of S2), the process proceeds to step S3 described later, and the paper size has been changed from A5 size to A3 size. If it is determined that there is not (No in S2), the process proceeds to step S21.
In step S21, the controller 6 controls the core rotation mechanism (not shown) so that the magnetic flux shielding region D0 is formed on the magnetic flux path between the center core 55 and the heating roller 53. Then, the center core 55 and the magnetic flux shielding plate 60 are rotated. Thereby, the width of the path of the magnetic flux acting on the heating roller 53 from the induction heating coil 54, that is, the heating target area of the heating roller 53 is set to the A3 size paper width (see FIG. 3D).

(Steps S3 and S21)
In step S3, the control unit 6 determines whether or not a preset set time has elapsed after the induction heating of the heating roller 53 by the induction heating coil 54 is finished with the A5 size paper width as the heating target region. to decide.
The set time is previously determined as a determination index for determining whether or not the temperature of the area corresponding to the A5 size paper width in the heating roller 53 is sufficiently high (for example, in the vicinity of a predetermined fixing temperature). It is a set value. In order to make the determination, the control unit 6 stores the paper size to be fixed in the previously executed printing process and from the end of the induction heating of the heating roller 53 to fix the paper size. Timekeeping processing that counts the elapsed time is executed.
Here, when it is determined that the set time has elapsed (Yes side of S3), it is considered that the temperature of the region corresponding to the A5 size paper width of the heating roller 53 is not sufficient. In step S21, as described above, the heating target area of the heating roller 53 is set to the sheet width of A3 size (see FIG. 3D).

(Step S4)
On the other hand, if it is determined that the paper size has been changed from A5 size to A3 size before the set time elapses (No side of S3), an area corresponding to the A5 size paper width of the heating roller 53 Is sufficiently high and it is considered that there is no need to heat the area corresponding to the sheet width, and therefore the process proceeds to step S4.
In step S4, the control unit 6 interposes the limiting magnetic flux shielding unit 60a on the magnetic flux path between the center core 55 and the heating roller 53, and the magnetic flux shielding area on the magnetic flux path. The center core 55 and the magnetic flux shielding plate 60 are rotated by controlling the core rotation mechanism (not shown) so that D3 is formed. Thereby, the width of the path of the magnetic flux acting on the heating roller 53 from the induction heating coil 54, that is, the heating target area of the heating roller 53 is set to the difference area between the A3 size and A5 size paper width (FIG. 3). (See (c)).
As a result, the heating of the central portion of the heating roller 53, which is a common area of the A3 size and A5 size paper width, which is already at a sufficiently high temperature, is not limited, and the heating that is the difference area of the paper width is not performed. Since only both ends of the roller 53 can be heated, abnormal heating in the common area can be prevented, and an area on the heating roller 53 corresponding to the differential area can be rapidly heated to a predetermined fixing temperature. it can.

(Step S5)
However, if the state where the heating of the common region is limited as described above continues, the temperature of the common region will eventually decrease. Therefore, in such a case, it is necessary to set a width equivalent to the width of the other paper in the member to be heated as a heating target region.
Therefore, the control unit 6 executes a time counting process for counting an elapsed time since the heating of the common area is limited by setting the magnetic flux shielding area D3. In the subsequent step S5, the magnetic flux shielding area D3 is executed. It is determined whether or not a predetermined time has elapsed since the heating of the common area was limited to D3. Note that the predetermined time is set in advance as a determination index for determining that the temperature of the common area corresponding to the A5 size paper width in the heating roller 53 has decreased and that the common area needs to be heated. Value.
If it is determined that the predetermined time has elapsed (Yes in S5), it is determined that the common area needs to be heated, and the process proceeds to step S21. As a result, the heating target area of the heating roller 53 is set to the A3 size paper width, and induction heating of the entire paper width corresponding to the A3 size is performed (see FIG. 3D).
On the other hand, when the predetermined time has not elapsed (No side of S5), it is determined that the temperature of the common region is maintained at a sufficiently high state, and the state of heating only the difference region is continued. , Processing proceeds to step S6.

(Step S6)
In step S6, the controller 6 determines whether or not the paper size has been changed from A3 size to A5 size, that is, whether or not the paper size having a large paper width has been changed to a paper size having a small paper width.
If it is determined that the paper size has been changed to A5 size (Yes in S6), the process proceeds to step S11. As a result, the heating target area of the heating roller 53 is set to the A5 size paper width, and induction heating of the paper width corresponding to the A5 size is performed (see FIG. 3B).
On the other hand, if the paper size has not been changed to A5 size (No side of S6), the state of heating only the difference area is continued, and the process returns to step S5.

As described above, in the copying machine X, the control unit 6 executes the magnetic flux width changing process (see the flowchart of FIG. 4), so that the fixing device 5 can set the A5 size paper width to be fixed. When the fixing operation for fixing the A3 size paper width is performed immediately after the fixing operation is performed, the heating roller 53, which is the difference area between the A3 size and A5 size paper width, is used. Only both ends are induction-heated, and induction heating of the central portion of the heating roller 53, which is a common area thereof, is limited, so that abnormal heating in the common area is prevented and the heating roller corresponding to the differential area The area on 53 can be quickly heated to a predetermined fixing temperature.
In the present embodiment, as shown in FIG. 3, the magnetic flux shielding plate 60 is composed of a single plate member that can form the magnetic flux shielding regions D0 to D3 on the outer peripheral surface of the center core 55. Although the case has been described, it may be configured by a plurality of plate members corresponding to the magnetic flux shielding regions D0 to D3. Further, the arrangement order of the magnetic flux shielding regions D0 to D3 formed by the magnetic flux shielding plate 60 in the circumferential direction of the center core 55 is not limited to this. For example, the magnetic flux shielding areas D0, D3, D1, and D2 may be formed in this order. In this case, when changing from the magnetic flux shielding area D1 to the magnetic flux shielding area D0, the center core 55 and the magnetic flux shielding area are formed. By rotating the plate 60 sequentially in one direction, the change to the magnetic flux shielding region D0 can be performed via the magnetic flux shielding region D3.

In step S3, it is determined whether or not a preset time has elapsed after the end of induction heating in which the A5 size paper width is set as the heating target area by the induction heating coil 53. Instead, the temperature detected by a temperature sensor (not shown) that detects the temperature of the central portion of the heating roller 53 corresponding to the common area of the A3 size and A5 size paper width is equal to or higher than a preset set temperature. It can be considered as another embodiment to determine whether or not. In this case, when the temperature of the common region is equal to or higher than the set temperature (No side of S3), the process proceeds to step S4, and when the temperature of the common region is lower than the set temperature (S3 Yes side), the process proceeds to step S21.
Furthermore, when one of the conditions that the set time has elapsed and the temperature of the common area is lower than the set temperature is satisfied, the process may be shifted to step S21.

In step S5, a predetermined time is elapsed after the magnetic flux limiting portion 60a is interposed on the magnetic flux path, that is, the heating target region of the heating roller 53 is limited to the differential region by the magnetic flux shielding region D3. Although it has been determined whether or not the above has elapsed, instead of this, a temperature sensor (not shown) for detecting the temperature of the central portion of the heating roller 53 corresponding to the common area of the A3 size and A5 size paper width. It can be considered as another embodiment to determine whether or not the detected temperature by is in a state below the predetermined temperature. In this case, when the temperature of the common area is lower than the predetermined temperature (Yes side of S5), the process proceeds to step S21, and when the temperature of the common area is equal to or higher than the predetermined temperature (S5). No), the process proceeds to step S6.
Furthermore, it is also conceivable that the process proceeds to step S21 when one of the conditions that the predetermined time has elapsed and the temperature of the common region is lower than the predetermined temperature is satisfied.

In the first embodiment, another example of the magnetic flux shielding plate 60 will be described with reference to FIG.
As shown in FIG. 5A or FIG. 5B, the magnetic flux shielding plate 60 according to the first embodiment is provided on the restricted magnetic flux shielding portion 60a corresponding to the common area of the A3 size and the A5 size paper width. , Notches 61 or 62 through which magnetic flux passes are formed.
As a result, the limited magnetic flux shielding unit 60a reduces the amount of magnetic flux passing through the common region to be less than the amount of magnetic flux passing through the differential region. Therefore, when the magnetic flux shielding region D3 is formed on the path of the magnetic flux by interposing the limiting magnetic flux shielding part 60a on the path of the magnetic flux acting on the heating roller 53 from the induction heating coil 54, Only a part of the path of the magnetic flux in the common area is shielded, and the remaining magnetic flux passes through the notches 61 or 62.
Accordingly, as shown in FIGS. 5A and 5B, the heat-retention heating (temperature decrease) at the center of the heating roller 53, which is a common area of the A3 size and A5 size paper width, which is already at a sufficiently high temperature. The two ends of the heating roller 53, which is the difference region of the sheet width, can be heated with priority.

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 51a ... Pressure roller 52 ... Fixing belt (fixing member) One case)
53 ... Heating roller (an example of a heat transfer member and a member to be heated)
54 ... induction heating coil 55 ... center core 56 ... outer core 60 ... magnetic flux shielding plate (an example of magnetic flux shielding member)
60a ... Limiting magnetic flux shielding portions 61, 62 ... Notches D0 to D3 ... Magnetic flux shielding region X ... Copier (an example of an image forming apparatus)

Claims (9)

An induction heating coil that performs induction heating using a fixing member that melts and fixes the toner adhering to the paper or a heat transfer member that is thermally coupled to the fixing member as a heated member, and acts on the heated member from the induction heating coil A magnetic flux shielding member that forms on the magnetic flux path one of a plurality of magnetic flux shielding regions corresponding to a plurality of paper widths by a portion interposed on the magnetic flux path to be fixed, and the magnetic flux shielding according to the paper width to be fixed Magnetic flux width changing means for changing the heating target area of the member to be heated by the induction heating coil by changing the width of the path of the magnetic flux acting on the member to be heated from the induction heating coil by moving the member. A fixing device comprising:
One or a plurality of restrictions that the magnetic flux shielding member forms a restricted magnetic flux shielding area on the path of the magnetic flux that allows the magnetic flux to pass in the difference area of the different paper widths and restricts the passage of the magnetic flux in the common area of the paper widths A fixing device having a magnetic flux shielding portion.   When the magnetic flux width changing means sets one paper width as the heating target area by the induction heating coil, the heating target area changes to the one paper width before the preset set time elapses after the end of induction heating. When the fixing operation is performed by changing to another paper width larger than that, the limiting magnetic flux shielding portion corresponding to the one paper width and the other paper width is interposed on the magnetic flux path. The fixing device according to claim 1, wherein the magnetic flux shielding member is moved.   The magnetic flux width changing unit changes the heating target area to another paper width larger than the one paper width after the induction heating in which the one paper width is set as the heating target area by the induction heating coil, and is fixed. When the operation is performed, if the temperature of the region corresponding to the common region of the one sheet width and the other sheet width in the heated member is equal to or higher than a preset temperature, the one 3. The fixing device according to claim 1, wherein the magnetic flux shielding member is moved so that the limiting magnetic flux shielding portion corresponding to the paper width and the other paper width is interposed on the path of the magnetic flux. .   When a predetermined time or more has elapsed since the magnetic flux width changing means has interposed the restricted magnetic flux shielding portion corresponding to the one paper width and the other paper width on the path of the magnetic flux, The fixing device according to claim 2, wherein the magnetic flux shielding member is moved so that the magnetic flux shielding region corresponding to a sheet width is formed on the path of the magnetic flux.   After the magnetic flux width changing means interposes the limiting magnetic flux shielding portion corresponding to the one paper width and the other paper width on the path of the magnetic flux, the one paper width in the heated member and the When the temperature of the area corresponding to the common area with the other sheet width reaches a predetermined temperature, the magnetic flux shielding area corresponding to the other sheet width is formed on the magnetic flux path. The fixing device according to claim 2, wherein the magnetic flux shielding member is moved.   The limiting magnetic flux shielding unit shields a part of the path of the magnetic flux in the common area, thereby reducing the amount of magnetic flux passing through the common area from the amount of magnetic flux passing through the difference area. The fixing device according to claim 1.   The fixing device according to claim 1, wherein the limiting magnetic flux shielding portion shields the entire path of the magnetic flux in the common area. The magnetic flux shielding member is provided on the outer peripheral surface of a cylindrical magnetic core that forms a part of the path of the magnetic flux by being disposed opposite to the member to be heated,
The magnetic flux width changing means changes a part of the magnetic flux shielding member interposed on the magnetic flux path by rotating the magnetic core and rotating the magnetic flux shielding member. The fixing device according to any one of the above.   An image forming apparatus comprising the fixing device according to claim 1.