JP2009204717A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of achieving low power supply to an electromagnetic coil, while realizing zero-cross control in PWM control of a switching element, and to provide an image forming apparatus. <P>SOLUTION: By controlling (PWM control) the duty ratio for switching operation of the switching element, to switch whether to supply power to an exciting coil 73, and also adjusting the amount of magnetic flux acting on a heating roller 71 from the exciting coil 73, by changing the distances between a magnetic substance core 74, and the exciting coil 73 and a heating roller 71; and thus, the fixing device that realizes low power supply to the exciting coil 73 is obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device that heats a fixing roller by an electromagnetic induction heating method, and an image forming apparatus including the fixing device, and more particularly to a control technique for realizing low power supply to an electromagnetic coil used for induction heating. is there.

In an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine of these, an electromagnetic induction heating type fixing device that heats a hollow fixing roller made of a magnetic material by electromagnetic induction may be used. Specifically, a magnetic flux acts on the fixing roller by causing an alternating current to flow through an electromagnetic coil disposed with a predetermined gap with respect to the fixing roller. As a result, the fixing roller is heated by electromagnetically induced eddy current (induced current) generated by the magnetic flux.
In general, in an image forming apparatus having a fixing device configured as described above, the temperature of the fixing roller is controlled by controlling the power value supplied to the electromagnetic coil based on the detection result of the temperature sensor that detects the temperature of the fixing roller. Control is performed. At this time, the amount of power supplied to the electromagnetic coil is controlled by so-called PWM control for controlling the duty ratio of a switching element (IGBT or the like) that switches whether power is supplied to the electromagnetic coil. For example, by increasing the ON time of the switching element, the power supply amount increases, and by increasing the OFF time, the power supply amount decreases.

By the way, in the PWM control, as shown in FIGS. 6A to 6C, when the voltage and current applied to the switching element are both substantially zero, zero-cross control for switching ON / OFF of the switching signal is performed. It is desirable to realize. Thereby, power loss in the switching element can be prevented, and overheating and destruction of the switching element can be prevented.
However, for example, when the temperature of the fixing roller is sufficiently high and the power supplied to the electromagnetic coil is reduced, if the ON time of the switching element in the PWM control is made too short, both the voltage and current become zero. Therefore, zero cross control cannot be realized as shown in FIGS. 6D to 6E (see, for example, Patent Document 1).
Therefore, Patent Document 1 discloses a configuration that suppresses power loss in the switching element during low power supply by controlling the presence or absence (ON-OFF) of the switching operation by the switching element in addition to the PWM control. ing. Specifically, the low power supply is realized by fixing the ON time of the switching element in the PWM control to the minimum time and providing the time for stopping the switching operation of the switching element.
JP 2002-231427 A

However, in the configuration disclosed in Patent Document 1, zero-crossing control may not be realized when resuming the switching operation of the switching element, which causes a considerable power loss in the switching element. In addition, when the switching operation of the switching element is resumed, a large ripple is generated, and there is a concern that flicker occurs and affects the power supply. In addition, there is a problem that the response of the temperature control of the fixing roller is lowered due to the increased ripple.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to establish a low power supply to an electromagnetic coil while realizing zero cross control in PWM control of a switching element. An apparatus and an image forming apparatus are provided.

In order to achieve the above object, the present invention provides an electromagnetic coil disposed through a predetermined gap with respect to a member to be heated made of a magnetic material, and a magnetic core for guiding magnetic flux from the electromagnetic coil to the member to be heated. And a switching element that supplies power to the electromagnetic coil, and a duty ratio of a switching operation by the switching element flows through the voltage applied to the switching element and the switching element when the switching element is switched ON / OFF The present invention is applied to a fixing device provided with a switching control means for controlling (so-called zero-crossing control) within a range where the current becomes substantially zero, by moving the electromagnetic coil and / or the magnetic core. , A distance between the heated member and the electromagnetic coil and / or the magnetic core, or the electromagnetic Configured to become comprises a distance changing means for changing the distance between yl and the magnetic core as a fixing device according to claim. Here, the member to be heated is, for example, a fixing roller, a fixing belt, a heating roller thermally coupled to the fixing roller, or the like.
In the fixing device configured as described above, the separation distance changing unit is configured to set a separation distance between the heated member and the electromagnetic coil or the magnetic core, or a separation distance between the electromagnetic coil and the magnetic core. By changing, the strength of the magnetic flux acting on the member to be heated can be adjusted.
Therefore, when supplying low power to the electromagnetic coil, the magnetic core is moved while controlling the duty ratio of the switching operation of the switching element within a range where zero cross control is possible, and the heated member Since it is sufficient to weaken the magnetic flux acting on the switching element, it is possible to prevent power loss in the switching element and thermal destruction of the switching element. Further, since the ripple due to the switching operation of the switching element can be suppressed, the responsiveness of the temperature control of the fixing roller is also good.

More specifically, in a configuration comprising supply power value setting means for setting a supply power value to the electromagnetic coil based on the temperature of the fixing roller or the fixing belt, the electromagnetic coil is set by the supply power value setting means. When the power supply value to be set to a predetermined minimum power value or less, the switching control means keeps the duty ratio of the switching operation at the lowest value within the range, and the separation distance changing means It is conceivable to control the power supply value to the electromagnetic coil by changing the separation distance.
In this case, by setting, as the minimum power value, the minimum value of the power value that can be adjusted while the switching control means realizes zero-cross control, the supply power value setting means sets the power value to be equal to or lower than the minimum power value. When set, it is possible to control the power supply value to the electromagnetic coil below the minimum power value while realizing zero cross control by the switching control means.

The present invention can also be understood as an invention of an image forming apparatus that has the same configuration as the fixing device.
That is, a fixing device having an electromagnetic coil disposed through a predetermined gap with respect to a heated member made of a magnetic material, a magnetic core that guides the magnetic flux from the electromagnetic coil to the heated member, and the electromagnetic coil The switching element that supplies the power and the duty ratio of the switching operation by the switching element, the voltage applied to the switching element when the switching element is switched ON / OFF and the current flowing through the switching element are substantially zero. The image forming apparatus includes a switching control unit that controls within a range, and the member to be heated, the electromagnetic coil, and the electromagnetic coil are moved by moving the electromagnetic coil and / or the magnetic core. / Or a separation distance from the magnetic core, or a separation between the electromagnetic coil and the magnetic core. Configured as an image forming apparatus characterized by including the distance changing means for changing the release. Here, the member to be heated is, for example, a fixing roller, a fixing belt, a heating roller thermally coupled to the fixing roller, or the like.
The image forming apparatus also includes supply power value setting means for setting a supply power value to the electromagnetic coil based on the temperature of the fixing roller or the fixing belt, similarly to the fixing device according to the present invention described above. In the configuration provided, when the supply power value to the electromagnetic coil is set below a predetermined minimum power value by the supply power value setting means, the duty ratio of the switching operation is set to the switching control means. What is necessary is just to control the power supply value to the said electromagnetic coil by maintaining the minimum value in the range, and changing the said separation distance by the said separation distance changing means.

  According to the present invention, when low power is supplied to the electromagnetic coil, the separation distance changing means controls the duty ratio of the switching operation of the switching element within a range where zero cross control is possible, By changing the separation distance between the heated member and the electromagnetic coil or the magnetic core, or the separation distance between the electromagnetic coil and the magnetic core, the magnetic flux acting on the heated member may be weakened. , It is possible to prevent power loss in the switching element and thermal destruction of the switching element.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of a copying machine according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing a schematic configuration of a fixing device according to the embodiment of the present invention, and FIG. FIG. 4 is a schematic diagram showing a system configuration of the fixing device according to the embodiment. FIG. 4 is a flowchart for explaining an example of the procedure of the heating control process executed by the fixing device in the copying machine according to the embodiment of the invention. FIG. 6 is a schematic diagram for explaining another example of the fixing device according to the embodiment of the present invention, and FIG. 6 is a diagram for explaining an example of the operation of the switching element.
The copying machine X described in the present embodiment is merely an example of an image forming apparatus according to the present invention. For example, a printer device, a facsimile machine, a multifunction peripheral, and the like also correspond to the image forming apparatus according to 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 various other components that a general electrophotographic copying machine has, but the description thereof is omitted here.
The control unit 6 includes a peripheral device such as a CPU, ROM, and RAM, and controls the copier X in an integrated manner by executing processing according to a predetermined program stored in the ROM.

The operation display unit 1 is a liquid crystal display, a touch panel, or the like for performing various information display and input operations in the copying machine X.
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 applies to document image data read by the image reading unit 2 and document image data input from an information processing apparatus (not shown) connected via a communication network such as a LAN. Various 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 by the configuration relating to the fixing device 5 and will be described in detail below.

2A is a schematic sectional view of the fixing device 5 viewed from the side, FIG. 2B is a schematic view of the fixing device 5 viewed from above, and FIG. 3 is a system of the fixing device 5. It is a schematic diagram which shows a structure.
First, as shown in FIG. 2, the fixing device 5 includes a fixing roller 61 that rotates while pressing the paper conveyed on the paper conveyance path 50 after the toner image is transferred in the image forming unit 4, and an addition roller. The pressure roller 62, a heating roller 71 (an example of a member to be heated) made of a magnetic material such as iron, a fixing belt 72 stretched around the heating roller 71 and the fixing roller 61, and the heating roller 71 are induction-heated. And an exciting coil 73 (an example of an electromagnetic coil) and a magnetic core 74 that is movably supported by a drive mechanism (not shown).
The drive mechanism (not shown) is for moving the magnetic core 74 in the direction of the arrow shown in FIG. 2 by a drive force transmitted from a drive motor 54 (see FIG. 3) described later. For example, the drive mechanism (not shown) includes an arm that rotates the magnetic core 74 about a predetermined rotation axis by a drive force transmitted from a drive motor 54 (see FIG. 3) described later. As an example, a configuration having a rack and a pinion for sliding (sliding) the magnetic core 74 can be considered.

The exciting coil 73 is formed by winding an electric wire with an air core, and is fixed at a position separated from the heating roller 71 by a predetermined interval.
The exciting coil 73 is formed to have a length that extends over at least the entire length of the heating roller 71 in the longitudinal direction (paper width direction). In addition, it can be considered as another embodiment that a plurality of electromagnetic coils are arranged in the longitudinal direction of the heating roller 71 to form the exciting coil 73 over the entire area in the longitudinal direction of the heating roller 71.
In the fixing device 5, an alternating current is supplied to the exciting coil 73 to cause a magnetic flux to act on the heating roller 71 from the exciting coil 73, thereby generating an induced current (eddy current) in the heating roller 71, Induction heating for heating the heating roller 71 is performed.

The fixing belt 72 thermally couples the heating roller 71 and the fixing roller 61, and heats the fixing roller 61 by transferring heat from the heating roller 71 to the fixing roller 61.
The heating roller 71 and the fixing belt 72 may be omitted, and the fixing roller 61 may be formed of a magnetic material so that the fixing roller 61 is inductively heated by the excitation coil 73. . In this case, the fixing roller 61 corresponds to a member to be heated.
Further, a configuration in which the fixing belt 72 is formed of a magnetic material and the fixing belt 72 is induction-heated by the exciting coil 73 is also conceivable. In this case, the fixing belt 72 corresponds to a member to be heated. At this time, in the fixing device 5, the toner image is melted and fixed onto the paper pressed by the fixing roller 61 and the pressure roller 62 by the heat of the fixing belt 72.

On the other hand, the magnetic core 74 is disposed at the center of the exciting coil 73 and has a width extending over the entire length of the heating roller 71.
The magnetic core 74 is made of a magnetic material such as iron or ferrite and guides the magnetic flux generated by the exciting coil 73 to the heating roller 71. At this time, the amount of magnetic flux guided by the magnetic core 74 varies depending on the distance between the magnetic core 74 and the exciting coil 73 and the distance between the magnetic core 74 and the heating roller 71. Specifically, the smaller the distance between the magnetic core 74 and the exciting coil 73 and the magnetic core 74 and the heating roller 71 is, the smaller the distance between the magnetic core 74 and the heating roller 71 is. The amount of guided magnetic flux increases.

Next, the system configuration of the fixing device 5 will be described with reference to FIG.
As shown in FIG. 3, the fixing device 5 includes a PWM control circuit 51 having electronic parts such as a switching element 511 such as an IGBT for supplying power to the exciting coil 73, and a control device such as a CPU, RAM, and ROM. An IH control microcomputer 52, a temperature sensor 53 such as a thermistor for detecting the temperature of the fixing roller 61, and a drive motor 54 such as a stepping motor connected to the drive mechanism (not shown).
The PWM control circuit 51 controls the switching operation of the switching element 511 by inputting a switching signal to the switching element 511 based on an instruction from the IH control microcomputer 52, and controls the excitation coil 73 and the unillustrated coil. The power supply to a voltage (or current) resonance circuit (not shown) formed by a capacitor or the like is controlled. The inverter circuit composed of the switching element 511, the exciting coil 73, a capacitor (not shown), and the like is the same as the conventional one (see, for example, cited document 1), and thus the description thereof is omitted here.

The temperature sensor 53 detects the temperature of the central portion of the fixing roller 61 and inputs the detection result to the control unit 6. As a result, the control unit 6 controls the excitation coil so that the temperature of the fixing roller 61 becomes a preset fixing temperature (for example, about 200 ° C.) based on the detected temperature input from the temperature sensor 53. The power supply value to 73 is set. Hereinafter, the power supply value set here is referred to as a heating power value. For example, information stored in advance in a predetermined relational expression, a data table, or the like in the internal memory of the control unit 6 is stored in a relationship between the temperature difference between the fixing temperature and the detected temperature and the heating power value. The control unit 6 can set the heating power value according to the temperature difference.
Here, the control unit 6 when setting the heating power value based on the temperature detected by the temperature sensor 53 corresponds to the supply power value setting means. The supply power value setting means realized by the control unit 6 may be realized by the IH control microcomputer 52. That is, it is conceivable that the IH control microcomputer 52 sets the heating power value based on the temperature of the fixing roller 61 detected by the temperature sensor 53.
The heating power value set by the control unit 6 is input to the IH control microcomputer 52.

The IH control microcomputer 52 sets the duty ratio of the switching element 511 in the PWM control circuit 51 based on the heating power value input from the control unit 6. At this time, the IH control microcomputer 52 performs zero-cross control in which the voltage applied to the switching element 511 and the current flowing through the switching element 511 are substantially zero when the switching element 511 is switched ON / OFF. In order to be executed (see FIGS. 6A to 6C), the duty ratio of the switching operation by the switching element 511 is set. Here, the IH control microcomputer 52 when executing such control corresponds to the switching control means. The switching control means may be embodied by the PWM control circuit 51.
The duty ratio set by the IH control microcomputer 52 is transmitted to the PWM control circuit 51. As a result, the PWM control circuit 51 performs ON / OFF switching control of the switching element 511 based on the duty ratio set by the IH control microcomputer 52.

By the way, as shown in FIGS. 6D to 6F, if the heating power value instructed to the IH control microcomputer 52 is too small and the duty ratio in the switching operation of the switching element 511 becomes too low. If the ON width becomes too short, zero cross control (see FIGS. 6A to 6C) cannot be realized in the PWM control circuit 51, and power loss occurs during the switching operation.
Therefore, in the copying machine X according to the embodiment of the present invention, the heating power value is obtained by executing a heating control process (see the flowchart of FIG. 4) described later by the IH control microcomputer 52 in the fixing device 5. Is too small to achieve zero cross control by the PWM control circuit 51, in addition to controlling the duty ratio of the switching element 511, the amount of magnetic flux guided by the magnetic core 74 is adjusted. As a result, the power supply value to the exciting coil 73 is adjusted. Hereinafter, in the fixing device 5, the smallest heating power value within a range in which the zero cross control of the switching element 511 can be realized is referred to as a minimum power value, and the duty ratio at that time is referred to as a minimum duty ratio. The minimum power value, the minimum duty ratio, and the like are known by experiments and simulations performed in advance.

Hereinafter, an example of the procedure of the heating control process executed by the fixing device 5 in the copying machine X will be described with reference to the flowchart of FIG. Here, S1, S2,... In the figure represent processing procedure (step) numbers.
The heating control process is executed by the IH control microcomputer 52 when induction heating of the fixing roller 61 provided in the fixing device 5 is performed, such as during image formation in the multifunction device X or during standby. In addition, when the said IH control microcomputer 52 and the said control part 6 are embodied by one control part, the said heating control process is performed by this control part.
First, in step S1, the IH control microcomputer 52 determines whether or not the heating power value set by the control unit 6 is less than or equal to the predetermined minimum power value. That is, here, whether the heating power value is a value that can realize the zero cross control of the switching element 511 when the supply of the heating power value is realized only by the switching control of the switching element 511. Has been determined.
Here, when it is determined that the heating power value is less than or equal to the minimum power value (Yes side of S1), the process proceeds to step S2, and the heating power value is greater than the minimum power value. If it is determined (No side of S1), the process proceeds to step S11.

(Steps S11 and S12)
First, the case where it is determined that the heating power value is larger than the minimum power value (No side of S1) and the process proceeds to step S11 will be described.
In step S11, the drive motor 54 is controlled by the IH control microcomputer 52, so that the magnetic core 74 is moved to an initial position (for example, a solid line position shown in FIG. 2). If the magnetic core 74 is already in the initial position, the state is maintained. Here, the initial position is, for example, a position where the amount of magnetic flux acting on the heating roller 71 from the exciting coil 73 is the largest, and is determined in advance by experiments or simulations. The position of the magnetic core 74 may be determined based on a detection result by a position detection sensor (not shown) such as a limit switch, a drive history of the drive motor 54, or the like.
Subsequently, in step S12, the IH control microcomputer 52 sets the duty ratio of the switching operation of the switching element 511 based on the heating power value, and transmits the duty ratio to the PWM control circuit 51. As a result, the PWM control circuit 51 controls the switching operation of the switching element 511 based on the duty ratio instructed from the IH control microcomputer 52, thereby realizing the output of the heating power value. Here, since the heating power value is larger than the minimum power value and the duty ratio of the switching operation of the switching element 511 is larger than the minimum duty ratio, zero-crossing control is realized in the switching operation of the switching element 511. Therefore, no power loss occurs in the switching element 511.

(Step S2)
Next, a case will be described in which it is determined that the heating power value is equal to or less than the minimum power value (Yes side of S1), and the process proceeds to step S2.
First, in step S2, the drive motor 54 is controlled by the IH control microcomputer 52, whereby the magnetic core 74 is moved away from the exciting coil 73 and the heating roller 71 (for example, FIG. 2). The position of the broken line shown in
At this time, the IH control microcomputer 52 controls the moving distance of the magnetic core 74 based on the heating power value, so that the separation distance between the magnetic core 74 and the excitation coil 73, the magnetic body The distance between the core 74 and the heating roller 71 is changed, and the amount of magnetic flux guided from the exciting coil 73 to the heating roller 71 by the magnetic core 74 is controlled. Here, the IH control microcomputer 52 for performing such control corresponds to the separation distance changing means.
Specifically, the IH control microcomputer 52 supplies the heating power value to the excitation coil 73 when the PWM control circuit 51 performs the switching operation of the switching element 511 based on the minimum duty ratio. The magnetic core 74 is moved to a position where it can be realized. For example, by previously storing information in which the relationship between the heating power value and the position of the magnetic core 74 is set in a predetermined relational expression or a data table in the internal memory of the IH control microcomputer 52, the IH The control microcomputer 52 can set the amount of movement of the magnetic core 74 according to the heating power value. Note that the position of the magnetic core 74 may be determined based on a detection result by a position detection sensor (not shown) such as a limit switch, a drive history of the drive motor 54, or the like as described above.

(Step S3)
When the magnetic core 74 is moved, the IH control microcomputer 52 transmits the minimum duty ratio corresponding to the minimum power value to the PWM control circuit 51 in the subsequent step S3. Thus, the PWM control circuit 51 controls the switching operation of the switching element 511 based on the minimum duty ratio instructed from the IH control microcomputer 52.
Thus, the IH control microcomputer 52 sets the duty ratio of the switching operation by the switching element 511 to the minimum duty ratio when the power supply value to the excitation coil 73 is set to be equal to or lower than the minimum power value. In addition, the distance between the magnetic core 74 and the exciting coil 73 and the heating roller 71 is changed to reduce the amount of magnetic flux guided by the magnetic core 74, thereby supplying the exciting coil 73 to the exciting coil 73. Control is performed so that the power value becomes the heating power value. Here, the IH control microcomputer 52 for performing such control corresponds to the supply power value control means.
As described above, the fixing device 5 can weaken the magnetic flux acting on the heating roller 71 from the exciting coil 73 by separating the magnetic core 74, so that in the switching operation of the switching element 511. While realizing zero-cross control (see FIGS. 6A to 6C), it is possible to realize power supply to the exciting coil 73 that is equal to or lower than the minimum power value. As a result, power loss when the switching element 511 is turned on / off can be prevented, and thermal destruction of the switching element 511 can be prevented.

In the present embodiment, the case where the magnetic core 74 is arranged in the center of the exciting coil 73 has been described as an example. Of course, the shape of the magnetic core 74 is not limited to this. Absent.
For example, as shown in FIG. 5, in addition to the magnetic core 74, a configuration including magnetic cores 74a and 74b supported so as to be movable outside the excitation coil 73 is conceivable.
In this case, the magnetic cores 74, 74a, 74b are integrally connected, and the magnetic cores 74a, 74b are moved together with the magnetic core 74, or the magnetic cores 74, 74a, 74b are respectively moved. Can be moved independently in the direction of the arrow shown by an individual drive mechanism. In the configuration in which the magnetic cores 74, 74a, and 74b can be individually moved, the amount of magnetic flux guided from the exciting coil 73 to the heating roller 71 can be adjusted in more detail.

By the way, in the said embodiment, although the structure which moves the said magnetic body core 74 was demonstrated, the structure which moves the said excitation coil 73 is demonstrated here.
In the fixing device 5, the excitation coil 73 is separated from the magnetic core 74 and the heating roller 71, so that the degree of electromagnetic coupling between the excitation coil 73 and the magnetic core 74, the excitation coil 73, By changing the degree of electromagnetic coupling of the heating roller 71, the amount of magnetic flux acting on the heating roller 71 from the exciting coil 73 can be adjusted.
Therefore, the excitation coil 73 is supported by the drive mechanism instead of the magnetic core 74, and in the heating control process executed by the IH control microcomputer 52, a supply power value equal to or lower than the minimum power value is set. In this case, the duty ratio of the switching operation by the switching element 511 is maintained at the minimum duty ratio, and the excitation coil 73 is moved to separate the excitation coil 73 and the heating roller 71 from each other, It can be considered that the amount of magnetic flux acting on the heating roller 71 from the excitation coil 73 is reduced by changing the distance between the excitation coil 73 and the magnetic core 74. Here, the IH control microcomputer 52 for executing such control corresponds to the separation distance changing means and the supplied power value control means.
Even with such a configuration, in the fixing device 5, power loss in the switching element 511 can be prevented, and thermal destruction of the switching element 511 can be prevented.
Needless to say, the exciting coil 73 and the magnetic core 74 (74a, 74b) may be moved in a direction away from the heating roller 71. For example, if the magnetic core 74 (74a, 74b) is integrally formed by winding an electric wire to form the exciting coil 73, the magnetic core 74 (74a, 74b) and the exciting coil 73 are formed. Can be moved simultaneously.

1 is a block diagram showing a schematic configuration of a copier according to an embodiment of the present invention. 1 is a schematic diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. 1 is a schematic diagram showing a system configuration of a fixing device according to an embodiment of the present invention. 6 is a flowchart for explaining an example of a procedure of heating control processing executed by the fixing device in the copying machine according to the embodiment of the present invention. FIG. 6 is a schematic diagram for explaining another example of a fixing device according to an embodiment of the present invention. The figure for demonstrating an example of operation | movement of a switching element.

Explanation of symbols

1: Operation display unit 2: Image reading unit 3: Image processing unit 4: Image forming unit 5: Fixing device 6: Control unit 50: Paper transport path 51: PWM control circuit 511: Switching element 52: IH control microcomputer 53: Temperature Sensor 54: Drive motor 61: Fixing roller (an example of a member to be heated)
62: Pressure roller 71: Heating roller (an example of a member to be heated)
72: fixing belt (an example of a member to be heated)
73: Excitation coil (an example of an electromagnetic coil)
74, 74a, 74b: Magnetic cores S1, S2,...: Processing procedure (step) number X: Copying machine (an example of an image forming apparatus)

Claims (6)

An electromagnetic coil arranged with a predetermined gap with respect to a heated member made of a magnetic material, a magnetic core for guiding a magnetic flux from the electromagnetic coil to the heated member, and power supply to the electromagnetic coil The switching element and the duty ratio of the switching operation by the switching element are controlled within a range in which the voltage applied to the switching element and the current flowing through the switching element are substantially zero when the switching element is switched ON / OFF. A fixing device comprising a switching control means,
By moving the electromagnetic coil and / or the magnetic core, a separation distance between the heated member and the electromagnetic coil and / or the magnetic core, or a separation distance between the electromagnetic coil and the magnetic core is set. A fixing device comprising a changing distance changing means for changing.   The fixing device according to claim 1, wherein the member to be heated is any one of a fixing roller, a fixing belt, and a heating roller thermally coupled to the fixing roller. Supply power value setting means for setting a supply power value to the electromagnetic coil based on the temperature of the fixing roller or the fixing belt;
When the supply power value to the electromagnetic coil is set below a predetermined minimum power value by the supply power value setting means, the switching control means sets the duty ratio of the switching operation to the minimum value within the range. A power supply value control means for controlling the power supply value to the electromagnetic coil by changing the separation distance by the separation distance changing means;
The fixing device according to claim 2, further comprising: An electromagnetic coil disposed with respect to a heated member made of a magnetic material via a predetermined gap, a fixing device having a magnetic core for guiding the magnetic flux from the electromagnetic coil to the heated member, and power to the electromagnetic coil The switching element to be supplied and the duty ratio of the switching operation by the switching element are within a range in which the voltage applied to the switching element and the current flowing through the switching element are substantially zero when the switching element is switched ON / OFF. An image forming apparatus comprising a switching control means controlled by
By moving the electromagnetic coil and / or the magnetic core, a separation distance between the heated member and the electromagnetic coil and / or the magnetic core, or a separation distance between the electromagnetic coil and the magnetic core is set. An image forming apparatus comprising a separation distance changing means for changing.   The image forming apparatus according to claim 4, wherein the member to be heated is any one of a fixing roller, a fixing belt, and a heating roller thermally coupled to the fixing roller. Supply power value setting means for setting a supply power value to the electromagnetic coil based on the temperature of the fixing roller or the fixing belt;
When the supply power value to the electromagnetic coil is set below a predetermined minimum power value by the supply power value setting means, the switching control means sets the duty ratio of the switching operation to the minimum value within the range. A power supply value control means for controlling the power supply value to the electromagnetic coil by changing the separation distance by the separation distance changing means;
The image forming apparatus according to claim 5, further comprising:

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