JP2010276835A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing the generation of overcurrent when changing a width of magnetic flux applied from an induction heating coil to a member to be heated, and to provide an image forming apparatus. <P>SOLUTION: After finishing induction heating using the width of a sheet of paper as a heating target area by an induction heating coil, when changing the width of the heating target area to the width of the other sheet of paper which is smaller than the width of the sheet of paper (Yes side at S2), power supply to the induction heating coil is limited at a step S31 prior to the start of moving a magnetic flux shielding member, and after finishing moving the magnetic flux shielding member (S32), a predetermined power previously set according to the other sheet of paper is supplied to the induction heating coil (S33, S34). <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, if the width of the magnetic flux path acting on the member to be heated from the induction heating coil is changed, the induction heating coil is caused by a change in the characteristics of the magnetic circuit formed by the induction heating coil (sudden decrease in saturation magnetic flux, etc.). There is a possibility that the inductance component on the energizing circuit will fluctuate rapidly and an abnormal current increase (overcurrent) may occur on the energizing circuit. In this case, problems such as burning of the induction heating coil and the energizing circuit, operation of an overcurrent protection circuit such as a breaker and a fuse, and flickering of a fluorescent lamp using the same power source occur.
Accordingly, the present invention has been made in view of the above circumstances, and its object is to prevent the occurrence of overcurrent when changing the width of the magnetic flux acting on the member to be heated from the induction heating coil. Another object of the present invention is to provide a fixing device and an image forming apparatus that can be used.

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, Inductive heating control means for controlling power supply to the induction heating coil, and a plurality of magnetic flux shielding regions corresponding to a plurality of paper widths by a portion interposed on a path of magnetic flux acting on the member to be heated from the induction heating coil And a magnetic flux shielding member formed on the magnetic flux path, and moving the magnetic flux shielding member to change the width of the magnetic flux path acting on the member to be heated from the induction heating coil, thereby inducing the induction heating. The present invention is applied to a fixing device comprising a magnetic flux width changing means for changing a heating target area of the member to be heated by a coil, wherein the induction heating control means has one paper width. When the heating target area is changed to another paper width smaller than the one paper width after the induction heating as the heating target area by the induction heating coil is completed, the magnetic flux shielding member by the magnetic flux width changing means is used. The power supply to the induction heating coil is limited before the start of the movement of the sheet, and after the movement of the magnetic flux shielding member by the magnetic flux width changing unit, the predetermined power set in advance corresponding to the other sheet width is applied to the induction heating. The fixing device is configured to be supplied to a coil. Specifically, it is conceivable that the induction heating control means limits the power supply to the induction heating coil by stopping or reducing the power supply to the induction heating coil.
According to the present invention, 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 smaller than the one paper width. Thus, the power supply to the induction heating coil is limited when the magnetic flux shielding member is moved. Therefore, it is possible to prevent the occurrence of overcurrent due to a sudden change in inductance on the energization circuit to which the induction heating coil is connected. As a result, for example, it is possible to prevent the induction heating coil and the energizing circuit from being burned out, the operation of the overcurrent protection circuit such as the breaker and the fuse, and the flickering of the fluorescent lamp using the same power source.

The magnetic flux width changing means includes shielding member moving means for moving the magnetic flux shielding member, and movement control means for controlling the shielding member moving means, and the induction heating control means is connected to the movement control means. It is also conceivable that the power supply to the induction heating coil is stopped by a power cutoff switch that cuts off the power supply to the induction heating coil in accordance with a movement request signal input to the shielding member moving means. As a result, when the magnetic flux shielding member is moved, the power supply to the induction heating coil can be reliably stopped by the power cutoff switch, and the reliability is improved.
Further, in the configuration in which the magnetic flux shielding member changes the magnetic flux shielding region formed on the magnetic flux path in a stepwise manner as the magnetic flux shielding member moves in a predetermined direction, the induction heating control is performed. Means for stepwise supplying power to the induction heating coil in accordance with the movement of the magnetic flux shielding member in the predetermined direction from the start of movement of the magnetic flux shielding member to the end of movement by the magnetic flux width changing means; It is conceivable that this is to be reduced. Even with such a configuration, it is possible to prevent a sudden characteristic change of the magnetic circuit of the induction heating coil during the movement of the magnetic flux shielding member and to prevent the occurrence of an overcurrent.

By the way, it is conceivable that 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 opposed to the heated member. In this case, the magnetic flux width changing means only needs to change the 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 present invention can also be understood as an invention relating to an image forming apparatus including the above-described fixing device.

  According to the present invention, when the heating target area is changed to another paper width smaller 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, is completed. Therefore, the power supply to the induction heating coil is limited when the magnetic flux shielding member is moved. Therefore, it is possible to prevent the occurrence of overcurrent due to a sudden fluctuation in inductance on the energizing circuit to which the induction heating coil is connected. As a result, for example, it is possible to prevent the induction heating coil and the energization circuit from being burned out, the operation of the overcurrent protection circuit such as the breaker and the fuse, and the flickering of the fluorescent lamp using the same power source.

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. 3 is a circuit diagram showing a schematic configuration of an induction heating control circuit Y of 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; 9 is a flowchart for explaining another example of the magnetic flux width changing process executed by the copying machine X.

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. The induction heating coil 54 is connected to an induction heating control circuit Y (see FIG. 4), which will be described later, and the control unit 6 controls power supply to the induction heating coil 54 by the induction heating control circuit Y. To do.

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, an example of a shielding member moving unit) 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. The said control part 6 when performing the control process which concerns here corresponds to a movement control means.
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.

FIG. 3 is a schematic diagram for explaining the difference in the heating target area 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 expanded the 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, so that the A3 horizontal (A4 vertical), B4 horizontal (B5 vertical) are formed on the outer peripheral surface of the center core 55. ), A4 horizontal (A5 vertical), B5 horizontal (B6 vertical), A5 horizontal (A6 vertical), and magnetic flux shielding regions D1 to D5 corresponding to the paper widths of various paper sizes. The magnetic flux shielding regions D1 to D5 are regions that allow the magnetic flux to pass through the paper width of the corresponding paper size and shield the passage of the magnetic flux in other regions, and are on the heating roller 53 corresponding to the paper width. This region is used as a heating target region.
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 D1 to D5 is formed.
Therefore, in the copying machine X, the position of the magnetic flux shielding plate 60 is adjusted so that any one of the magnetic flux shielding regions D1 to D5 is formed in the facing portion where the heating roller 53 and the center core 55 are closest to each other. By doing so, it is possible to change the width of the path of the magnetic flux acting on the heating roller 53, that is, the position and width of the heating target region of the heating roller 53.

Specifically, the control unit 6 rotates the center core 55 by the core rotation mechanism (not shown) and rotates (moves) the magnetic flux shielding plate 60, thereby generating magnetic flux acting on the heating roller 53. The part of the magnetic flux shielding plate 60 interposed on the path is changed. For example, when the temperature detected at the end of the heating roller 53 by the temperature sensor (not shown) reaches or exceeds a predetermined temperature, the control unit 6 excludes the end of the heating roller 53 from the heating target region. Therefore, abnormal heating of the end of the heating roller 53 is prevented by moving the position of the magnetic flux shielding plate 60.
Thus, the control unit for moving the magnetic flux shielding plate 60 to change the width of the magnetic flux path acting on the heating roller 53 from the induction heating coil 54 and changing the heating target area of the heating roller 53. 6 and the core rotation mechanism (not shown) are examples of magnetic flux width changing means. If the fixing device 5 is provided with a control means such as an MPU or ASIC, the processing 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.
In addition, in the case of supporting various paper widths (A3 to A6, B3 to B6, postcards, envelopes, etc.), magnetic flux shielding regions corresponding to the different paper widths are formed on the magnetic flux path. What is necessary is just to comprise the said magnetic flux shielding board 60 so that it may obtain. 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.

Next, the induction heating control circuit Y to which the induction heating coil 54 is connected will be described with reference to FIG.
As shown in FIG. 4, the induction heating control circuit Y includes a commercial AC power supply 10, a filter circuit 11, a rectifier circuit 12, the induction heating coil 54, a resonance capacitor 13, an IGBT (insulated gate bipolar transistor) 14, and a drive circuit 15. , Reverse conducting diode 16 and the like. Although not shown, the induction heating control circuit Y is also provided with a protection circuit such as an interlock switch and a thermostat.
In the induction heating control circuit Y, an AC voltage (for example, about AC 100 V) is supplied from the commercial AC power source 10 to the rectifier circuit 12 through the filter circuit 11 including a band pass filter. The commercial AC power supply 10 is also connected to a power supply device (not shown) such as an AC / DC converter that generates a DC voltage supplied from the AC voltage to various electrical components provided in the copying machine X. Yes.
The rectifier circuit 12 converts an AC voltage supplied from the commercial AC power source 10 into a DC voltage and outputs the DC voltage. The rectifier circuit 12 is a diode bridge circuit that performs full-wave rectification of the AC voltage, and a capacitor that functions as a high-frequency filter. Etc. A DC voltage (for example, about DC 500 V) output from the rectifier circuit 12 is supplied toward a resonance circuit formed by the induction heating coil 54 and the resonance capacitor 13.

The drive circuit 15 switches the presence / absence of current input to the base terminal of the IGBT 14 based on the switching signal input from the control unit 6 and switches the presence / absence of energization between the collector and emitter of the IGBT 14. Execute.
The controller 6 controls the power supply to the induction heating coil 54 by controlling the presence / absence of a switching signal input to the drive circuit 15 and the duty ratio. Here, the control unit 6 when performing such control corresponds to induction heating control means. In this embodiment, the case where the control unit 6 executes the control 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 control is performed. A case where the control is executed by means is also conceivable. In this case, the control means of the fixing device 5 corresponds to induction heating control means.

  When a high frequency current is input to the induction heating coil 54 by the switching operation of the IGBT 14, a magnetic flux is generated in the induction heating coil 54, and the heating roller 53 is induction heated by the action of the magnetic flux. The reverse conducting diode 16 connected in parallel to the IGBT 14 is for giving a reverse withstand voltage, and when a reverse blocking insulated gate bipolar transistor is used as the IGBT 14, the reverse conducting diode can be omitted. . The IGBT 14 is merely an example of a switching element, and for example, a transistor or an FET may be used.

By the way, in the induction heating control circuit Y configured as described above, while the electric power is supplied to the induction heating coil 54, the center core 55 and the magnetic flux shielding plate 60 are rotated so that the induction heating coil is rotated. If the width of the magnetic flux path acting on the heating roller 53 is changed from 54, the induction heating coil 54 connected to the induction heating coil 54 is changed due to a change in the characteristics of the magnetic circuit of the induction heating coil 54 (sudden decrease of saturation magnetic flux, etc.). The inductance component on the heating control circuit Y may change abruptly and an overcurrent may occur.
Specifically, when the width of the magnetic flux path is changed from a large size to a small size, an inductance component on the induction heating control circuit Y is rapidly reduced and an overcurrent is generated.

Therefore, in the copying machine X, the induction heating control process (see the flowchart of FIG. 5), which will be described later, is executed by the control unit 6 so that the induction heating control circuit Y on the induction heating control circuit Y caused by the movement of the magnetic flux shielding plate 60 is executed. The occurrence of overcurrent is prevented.
Hereinafter, an example of the procedure of the induction heating control process executed by the control unit 6 in the copying machine X will be described with reference to the flowchart of FIG. In the figure, S1, S2,... Indicate processing procedure (step) numbers.
The induction heating control process is executed when a request for execution of a printing process such as a copying process or a printer process occurs in the copying machine X and a fixing operation is performed in the fixing device 5. Thereafter, the induction heating control process ends with the end of the printing process.

(Steps S1 and S2)
First, in step S1, the control unit 6 determines the paper size used in the printing process, the detection result of a temperature sensor (not shown) that detects the temperature of the center or end of the heating roller 53, and the like. The center core 55 and the magnetic flux shielding plate 60 are rotated by the core rotating mechanism (not shown), and the width of the magnetic flux path to the heating roller 53 is adjusted to set the heating target region of the heating roller 53. .
Subsequently, in step S <b> 2, the control unit 6 determines whether it is necessary to change the heating target area of the heating roller 53 in the fixing device 5. Specifically, the control unit 6 changes the paper size used in the printing process and changes the width of the paper to be fixed by the fixing device 5, or the temperature of the end of the heating roller 53 is predetermined. When the temperature reaches or exceeds the upper limit temperature, it is determined that the heating target area of the heating roller 53 needs to be changed.
If it is determined that the heating target area of the heating roller 53 in the fixing device 5 needs to be changed (Yes in S2), the process proceeds to step S3. If it is not necessary to change the heating target area of the heating roller 53 (No side of S2), the process waits in step S2.
In addition, about the process after the said step S3 in the said induction heating control process, performing only in the printing process continuously performed within the space | interval of the preset predetermined time, for example is also considered.

(Steps S3 to S4)
In step S3, the control unit 6 determines whether or not the change of the heating target area is a change from a large size to a small size. Here, when it is determined that the change of the heating target area is a change from the large size to the small size, for example, when the paper size is changed from A3 to A5 (Yes in S3), the process is as follows. The process proceeds to step S31 described later. On the other hand, when it is determined that the change of the heating target area is a change from the small size to the large size, for example, when the paper size is changed from A5 to A3 (No in S3), the process is performed as a step. The process proceeds to S4.
In step S4, the control unit 6 controls the core rotation mechanism (not shown) to rotate the center core 55 and the magnetic flux shielding plate 60, and acts on the heating roller 53 from the induction heating coil 54. The part of the magnetic flux shielding plate 60 located on the path of the magnetic flux to be changed is changed, and the heating target area of the heating roller 53 is changed. For example, when the A5 size is changed to the A3 size, the magnetic flux shielding region D1 corresponding to the A3 size is formed on the magnetic flux path instead of the magnetic flux shielding region D5 corresponding to the A5 size. Then, the magnetic flux shielding plate 60 is rotated, and the heating target area of the heating roller 53 is changed to the sheet width corresponding to the A3 size. Thereby, after that, induction heating is performed with a region corresponding to the A3 size on the heating roller 53 as a heating target region.
In this case, since the inductance component in the induction heating control circuit Y changes in the increasing direction when the magnetic flux shielding plate 60 is moved, the state where the power supply to the induction heating coil 54 is continued. Even so, no overcurrent is generated on the induction heating control circuit Y.

(Steps S31 to S32)
On the other hand, when it is determined that the change of the heating target region is a change from the large size to the small size (Yes side of S3), the control unit 6 switches the switching signal to the drive circuit 15 in the following step S31. Is stopped, the switching operation of the IGBT 14 is stopped. Thereby, the power supply to the induction heating coil 54 is stopped (an example of restriction). Other methods may be adopted as long as the power supply to the induction heating coil 54 can be stopped.
Next, in step S32, the control unit 6 rotates the center core 55 and the magnetic flux shielding plate 60 by the core rotation mechanism (not shown) in a state where power supply to the induction heating coil 54 is restricted. As a result, the part of the magnetic flux shielding plate 60 located on the path of the magnetic flux acting on the heating roller 53 from the induction heating coil 54 is changed, and the width on the path of the magnetic flux, that is, the heating of the heating roller 53 is changed. Change the target area. At this time, since the power supply to the induction heating coil 54 is stopped, no overcurrent is generated in the induction heating control circuit Y.
For example, when the A3 size is changed to the A5 size, the magnetic flux shielding region D5 corresponding to the A5 size is formed on the magnetic flux path instead of the magnetic flux shielding region D1 corresponding to the A3 size. Then, the magnetic flux shielding plate 60 is rotated, and the heating target area of the heating roller 53 is changed to the paper width corresponding to the A5 size.

(Steps S33 to S34)
In step S33, the control unit 6 applies the predetermined electric power determined in advance according to the heating target area of the heating roller 53 after the change in step S32, that is, the changed small paper width, to the induction heating. The setting of the duty ratio of the switching signal input to the drive circuit 15 is changed so as to be supplied to the coil 54. Here, the predetermined power is a value that decreases as the paper width decreases, and when the paper width is set as a heating target area of the heating roller 53, no overcurrent is generated on the induction heating control circuit Y. In addition, the value is preset based on the experimental result or the simulation result.
Thereafter, in step S34, the control unit 6 resumes the switching operation of the IGBT 14 by the drive circuit 15 by resuming the input of the switching signal to the drive circuit 15, and the power to the induction heating coil 54 is resumed. Restart supply.
At this time, the power supplied to the induction heating coil 54 is lower than that in the case where induction heating is performed using the magnetic flux shielding region D1 corresponding to the A3 size, and the power value corresponding to the A5 size is used. Therefore, the occurrence of overcurrent in the induction heating control circuit Y is prevented.

As described above, in the copying machine X, when the induction heating control process is executed by the control unit 6, after the induction heating in which one paper width is set as the heating target area by the induction heating coil 54 is completed. When the heating target area is changed to another sheet width smaller than the one sheet width, the induction heating coil 53 in step S31 is started before the movement of the magnetic flux shielding plate 60 in step S32. The power supply to the induction heating coil 53 is limited (stopped), and after the movement of the magnetic flux shielding plate 60 is completed, a predetermined power set in advance corresponding to the other paper width is supplied to the induction heating coil 53 (S34).
Therefore, it is possible to prevent the occurrence of overcurrent due to a sudden change in inductance on the induction heating control circuit Y to which the induction heating coil 54 is connected.
As a result, for example, the induction heating coil 54 and the induction heating control circuit Y are burned out, the overcurrent protection circuit such as a breaker and a fuse is activated, the flickering of lighting equipment such as a fluorescent lamp using the same power source as the copying machine X, etc. Can be prevented.

In the present embodiment, the power supply to the induction heating coil 54 is stopped by stopping the switching signal to the drive circuit 15 in the step S31. The means for cutting off the power supply is not limited to this.
For example, a movement request signal input from the control unit 6 to the core rotation mechanism (not shown) on the energization path of the drive current from the drive circuit 15 to the IGBT 14 or the energization path to the induction heating coil 54. It is conceivable as another embodiment to provide a power cut-off switch that operates in accordance with the power supply and cuts off the energization path. As described above, in the configuration in which the power supply to the induction heating coil 54 is cut off by the power cut-off switch, the power supply to the induction heating coil 54 is surely stopped when the magnetic flux shielding plate 60 is moved. Can improve reliability.

Furthermore, in the present embodiment, the case where the power supply to the induction heating coil 54 is stopped in step S31 has been described as an example. However, in step S31, it is caused by the movement of the magnetic flux shielding plate 60. In another embodiment, the power supply can be reduced to a power level that does not cause overcurrent.
In this case, the power value after the reduction is the width of the heating roller 53 after the change of the heating target region, the difference width before and after the change, or the heating target region through which the heating roller 53 is changed during the change of the heating target region. In accordance with the width or the like, it may be set in advance based on experimental results or simulation results so that no overcurrent is generated when the magnetic flux shielding plate 60 is moved.

In this embodiment, another example of the induction heating control process (see the flowchart of FIG. 5) will be described. FIG. 6 is a flowchart for explaining another example of the induction heating control process executed by the control unit 6. In addition, the same code | symbol is attached | subjected about the process similar to the said induction heating control process demonstrated in the said embodiment, and the description is abbreviate | omitted.
In the copying machine X, the magnetic flux shielding plate 60 changes the magnetic flux shielding area formed on the magnetic flux path to D1 to D5 in a stepwise manner as the magnetic flux shielding plate 60 moves in a predetermined direction. It is. In such a configuration, the electric power is supplied to the induction heating coil 54 stepwise as the magnetic flux shielding plate 60 moves in the predetermined direction before the magnetic flux shielding plate 60 starts moving and ends. By reducing it to the above, generation of overcurrent on the induction heating control circuit Y can be prevented. The process will be described below with reference to the flowchart of FIG.

As shown in FIG. 6, in the induction heating control process according to the present embodiment, steps S41 to S43 are executed instead of the steps S31 to S34.
First, in step S41, the control unit 6 controls the switching signal input to the drive circuit 15 to reduce the power supplied to the dielectric heating coil 54 by one step. The electric power after the reduction in step S41 is a value set in advance based on an experimental result or a simulation result as a value that does not generate an overcurrent even if the magnetic flux shielding plate 60 is moved one step in the next step S42. .
Next, in step S42, the control unit 6 rotates the magnetic flux shielding plate 60 by one step by controlling the core rotation mechanism (not shown). For example, the rotation amount at this time switches the magnetic flux shielding regions D1 to D5 formed by the magnetic flux shielding plate 60 in one step.
In step S43, the control unit 6 determines whether or not the change of the heating target area of the heating roller 53 due to the movement of the magnetic flux shielding plate 60 is completed. Here, when it is determined that the magnetic flux shielding plate 60 has been moved to a position that becomes a target heating target region (Yes side of S43), the processing is returned to Step S2.
On the other hand, when it is determined that the magnetic flux shielding plate 60 has not been moved to a position that becomes the target heating target region (No side of S43), the process returns to step S41. As a result, again, the power supplied to the induction heating coil 54 is reduced by one step (S41), and the magnetic flux shielding plate 60 is moved by one step (S42).

As described above, in the induction heating control process according to the present embodiment, the induction heating coil is moved along with the movement of the magnetic flux shielding plate 60 in the predetermined direction from the start of the movement of the magnetic flux shielding plate 60 to the end of the movement. The power supply to 54 is gradually reduced. Even with such a configuration, it is possible to prevent the occurrence of overcurrent in the induction heating control circuit Y when the magnetic flux shielding plate 60 is moved.
In addition, here, the magnetic flux shielding regions D1 to D5 are switched one step at a time by the movement of the magnetic flux shielding plate 60, and the power supply to the induction heating coil 54 is reduced accordingly. For example, the power supply to the induction heating coil 54 may be reduced by a predetermined value every time the stepping motor provided in the core rotation mechanism (not shown) reaches a predetermined number of steps. Is considered.

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)
D1 to D5 ... Magnetic flux shielding area X ... Copying machine (an example of an image forming apparatus)

Claims (6)

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, and controls power supply to the induction heating coil One of a plurality of magnetic flux shielding regions corresponding to a plurality of paper widths is formed on the magnetic flux path by an induction heating control means and a portion interposed on the magnetic flux path acting on the member to be heated from the induction heating coil. A magnetic flux shielding member that changes the width of a magnetic flux path that acts on the member to be heated from the induction heating coil by moving the magnetic flux shielding member, and a region to be heated of the member to be heated by the induction heating coil A fixing device comprising a magnetic flux width changing means for changing,
When the induction heating control means changes the heating target area to another paper width smaller 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. Restricts the power supply to the induction heating coil before the movement of the magnetic flux shielding member by the magnetic flux width changing means, and corresponds to the other paper width after the movement of the magnetic flux shielding member by the magnetic flux width changing means is completed. Then, a predetermined power set in advance is supplied to the induction heating coil.   The fixing device according to claim 1, wherein the induction heating control unit is configured to limit power supply to the induction heating coil by stopping or reducing power supply to the induction heating coil. The magnetic flux width changing means comprises shielding member moving means for moving the magnetic flux shielding member and movement control means for controlling the shielding member moving means,
The induction heating control means supplies power to the induction heating coil by a power cut-off switch that cuts off power supply to the induction heating coil in response to a movement request signal input from the movement control means to the shielding member moving means. The fixing device according to claim 2, wherein the fixing device is stopped. The magnetic flux shielding member changes the magnetic flux shielding region formed on the magnetic flux path in a stepwise manner as the magnetic flux shielding member moves in a predetermined direction,
The induction heating control means supplies power to the induction heating coil in accordance with the movement of the magnetic flux shielding member in the predetermined direction before the movement of the magnetic flux shielding member by the magnetic flux width changing means until the movement is completed. The fixing device according to claim 1, wherein the fixing device is reduced stepwise. 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,
5. The magnetic flux width changing means changes a 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 fixing device according to any one of the above.   An image forming apparatus comprising the fixing device according to claim 1.