JP4878745B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a fixing device installed therein, and in particular, a fixing device using an electromagnetic induction heating method. And an image forming apparatus.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, a fixing device using an electromagnetic induction heating method has been known for the purpose of saving energy by reducing the rise time of the device (see, for example, Patent Document 1). .)

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device mainly includes a support roller (heating roller), a fixing auxiliary roller (fixing roller), and a fixing belt (heat-resistant belt) stretched between the supporting roller and the fixing auxiliary roller. ), Magnetic flux generating means facing the support roller via the fixing belt, and a pressure roller facing the fixing auxiliary roller via the fixing belt. The magnetic flux generation means includes a coil portion extending in the width direction (a direction perpendicular to the recording medium conveyance direction), a core portion (excitation coil core) facing the coil portion, and the like.

The fixing belt is heated at a position facing the magnetic flux generating means. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, a magnetic field is formed around the coil portion, and an eddy current is generated on the surface of the support roller. When an eddy current is generated in the support roller, Joule heat is generated by the electrical resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat.
It is known that a fixing device using such an electromagnetic induction heating method can raise the surface temperature (fixing temperature) of a fixing belt to a desired temperature with a small start-up time with low energy consumption.

On the other hand, Patent Document 2 and Patent Document 3 disclose a fixing device using an electromagnetic induction heating method, and a fixing roller for the purpose of suppressing a temperature rise in a non-sheet passing region in the fixing roller (heating medium). Discloses a technique of providing magnetic flux shielding means for shielding a part of magnetic flux generated from magnetic flux generating means (induction coil) provided in the apparatus.
Specifically, the magnetic flux shielding means changes its position in accordance with the paper passing area in the fixing roller, thereby changing the magnetic flux shielding range. This technique aims to block the magnetic flux reaching the fixing roller in the non-sheet passing area and suppress the temperature rise in the non-sheet passing area.

JP 2002-123106 A Japanese Patent Laid-Open No. 10-74009 JP 2002-83676 A

  The conventional technology described above cannot reliably suppress the temperature rise at both ends in the width direction of the heating member (or the fixing member) that occurs when a recording medium having a short width direction size is continuously fixed. .

Details are as follows.
A general image forming apparatus is configured to form an image on several types of recording media having different sizes in the width direction. Here, the recording media having different sizes in the width direction include recording media of irregular sizes in addition to recording media of various regular sizes in the A and B rows of JIS dimensions. Even in the case of recording media of the same size (for example, A4 size), the transport direction is the short direction (the direction perpendicular to the longitudinal direction) when the longitudinal direction is the transport direction. In some cases, recording media having different sizes in the width direction are handled.

  When fixing such a recording medium having different width direction sizes with the fixing device, the temperature distribution in the width direction of the fixing belt varies depending on the width direction size of the recording medium, resulting in temperature unevenness. was there. For example, when fixing by passing a recording medium having a small size in the width direction, a lot of heat is taken away at the position of the fixing belt corresponding to the size in the width direction of the recording medium (the paper passing area). The fixing temperature is lower than at other positions (non-sheet passing area). Such a phenomenon becomes particularly prominent when a recording medium having a small size in the width direction is continuously fed.

  Therefore, when trying to control the fixing temperature in the entire width direction of the fixing belt with reference to the fixing temperature in the center portion in the width direction of the fixing belt, the fixing temperature in the center portion in the width direction of the fixing belt can be controlled to a desired temperature. The fixing temperature at both ends in the direction will increase. As described above, when a large recording medium in the width direction is fixed in a state where the fixing temperature at both ends in the width direction of the fixing belt is increased, a hot offset occurs on the recording medium corresponding to the temperature increase position. Further, when the fixing temperature at both ends in the width direction exceeds the heat resistance temperature of the fixing belt, it is also conceivable that the fixing belt is thermally damaged.

  On the other hand, if it is attempted to control the fixing temperature in the entire width direction of the fixing belt based on the fixing temperature at both ends in the width direction of the fixing belt, the fixing temperature at both ends in the width direction of the fixing belt can be controlled to a desired temperature. However, the fixing temperature at the center in the width direction is lowered. As described above, when the recording medium is fixed in a state where the fixing temperature at the center portion in the width direction of the fixing belt is lowered, fixing failure or cold offset occurs on the recording medium corresponding to the temperature lowered position.

  In order to solve such a problem, in Patent Document 2 and Patent Document 3 described above, the position of the magnetic flux shielding means is changed according to the size of the recording medium to shield the magnetic flux in the non-sheet passing area. Even when a recording medium having a small size in the width direction is continuously passed, an effect of suppressing the temperature rise in the non-sheet passing area can be expected to some extent.

However, as a result of repeated research, the present inventor has come to know the following matters.
Even if the magnetic flux in the non-sheet passing area is shielded by changing the position of the magnetic flux shielding means according to the size of the recording medium, the heating member (or fixing) is used when continuously passing the recording medium having a small size in the width direction. The heat of the sheet passing area in the member) is gradually transferred to the non-sheet passing area, and the temperature of the non-sheet passing area increases. That is, as the sheet passing time (heating time) increases, heat is transferred from the actively heated sheet passing area to the non-sheet passing area where heating is not scheduled, and the temperature rise in the non-sheet passing area increases. It will occur.

  The present invention has been made to solve the above-described problems, and even when a plurality of recording media are continuously fixed, the temperature rise at both ends of the heating member and the fixing member in the width direction is reliably ensured. An object of the present invention is to provide a fixing device and an image forming apparatus that can be suppressed.

According to a first aspect of the present invention, there is provided a fixing device for fixing a toner image on a recording medium, a magnetic flux generating means for generating a magnetic flux, a heating member induction-heated by the magnetic flux, Based on the magnetic flux adjusting member that reduces the magnetic flux acting on the heating member within a predetermined adjustment range in the width direction, a detecting unit that detects the size of the recording medium that meets the print request, and the size detected by the detecting unit When the magnetic flux adjusting member is driven from the home position to a position corresponding to the size to change the adjustment range for reducing the magnetic flux, and the toner image is continuously fixed to a plurality of recording media. The cumulative heating time since the heating of the heating member is started, and / or the cumulative number of sheets passed since the plurality of recording media are started to pass And a counting means for counting, said varying means, while performing the continuous fixing of the toner image to the plurality of recording media, when the count value of said counting means reaches a predetermined value Further, the magnetic flux adjusting member is driven and controlled so that the adjustment range is varied based on the count value of the counting means so that the adjustment range becomes longer .

According to a second aspect of the present invention, in the fixing device according to the first aspect, the variable means is based on a size detected by the detecting means when fixing of the toner image is started. The magnetic flux adjusting member is driven and controlled so that the adjustment range becomes shorter than a range outside the range in the width direction of the recording medium corresponding to the specified heating member.

According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the variable means is detected by the detection means when the count value reaches a predetermined value. The magnetic flux adjusting member is driven and controlled so that the adjustment range becomes longer than a range outside the range in the width direction of the recording medium corresponding to the heating member specified based on the size.

The fixing device according to a fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein the variable means adjusts the magnetic flux stepwise in accordance with an increase in the count value. The member is driven and controlled.

According to a fifth aspect of the present invention, there is provided a fixing device for fixing a toner image onto a recording medium, a magnetic flux generating means for generating a magnetic flux, a heating member induction-heated by the magnetic flux, and the heating A magnetic flux adjusting member that reduces the magnetic flux acting on the member in a predetermined adjustment range in the width direction, a detecting unit that detects a size of a recording medium that meets a print request, and a home based on the size detected by the detecting unit A variable means for changing the adjustment range for reducing the magnetic flux by driving the magnetic flux adjusting member from a position to a position corresponding to the size, and fixing a toner image continuously to a plurality of recording media. And a temperature detecting means for directly or indirectly detecting the temperature of the heating member, and the variable means is continuously applied to the plurality of recording media. While performing fixing of toner image, the temperature detected by said temperature detecting means in which the adjustment range is for driving and controlling said magnetic flux adjusting member to be longer if it becomes more than a predetermined value.

According to a sixth aspect of the present invention, there is provided a fixing device for fixing a toner image onto a recording medium, a magnetic flux generating means for generating a magnetic flux, a heating member induction-heated by the magnetic flux, and the heating A magnetic flux adjusting member that reduces the magnetic flux acting on the member in a predetermined adjustment range in the width direction, a detecting unit that detects a size of a recording medium that meets a print request, and a home based on the size detected by the detecting unit A variable means for changing the adjustment range for reducing the magnetic flux by driving the magnetic flux adjusting member from a position to a position corresponding to the size, and fixing a toner image continuously to a plurality of recording media. And a temperature detecting means for directly or indirectly detecting the temperature of the heating member, and the variable means is continuously applied to the plurality of recording media. While performing fixing of toner image, the temperature detected by said temperature detecting means in which the adjustment range is for driving and controlling said magnetic flux adjusting member to be shorter if it becomes less than a predetermined value.

According to a seventh aspect of the present invention, there is provided the fixing device according to the fifth or sixth aspect , wherein the temperature detecting means is located at a position that does not fall within the adjustment range even if the adjustment range is varied. It is arranged.

The fixing device according to an eighth aspect of the present invention is the fixing device according to the fifth or sixth aspect , wherein the temperature detecting means is always located within the adjustment range even if the adjustment range is varied. Are arranged.

The fixing device according to a ninth aspect of the present invention is the fixing device according to any one of the fifth to eighth aspects, wherein the variable means is the detecting means when fixing of the toner image is started. The magnetic flux adjustment member is driven and controlled so that the adjustment range becomes shorter than the range outside the range in the width direction of the recording medium corresponding to the heating member specified based on the detected size. .

According to a tenth aspect of the present invention, in the fixing device according to any one of the first to ninth aspects, the adjustment range is a range in the width direction of the recording medium corresponding to the heating member. It includes a part or all of the outside range.

According to an eleventh aspect of the present invention, in the fixing device according to any one of the first to tenth aspects, the magnetic flux generating means extends in the width direction so as to face the heating member. A magnetic flux shielding member disposed between the coil portion and the inner core, the coil portion and an inner core facing the coil portion via the heating member. It is a thing.

According to a twelfth aspect of the present invention, in the fixing device according to the eleventh aspect, the magnetic flux shielding member can gradually increase or decrease a range covering the outer periphery of the inner core facing the coil portion. It is formed.

According to a thirteenth aspect of the present invention, in the fixing device according to the twelfth aspect of the present invention, the variable means drives the magnetic flux shielding member so as to gradually increase or decrease the range covering the outer periphery of the inner core. It is a means to do.

The fixing device according to a fourteenth aspect of the present invention is the fixing device according to any one of the eleventh to thirteenth aspects, wherein the magnetic flux generating means is on the side where the coil portion does not face the heating member. The magnetic flux shielding member covers an outer periphery of the inner core facing the center core, the core portion having a center core facing the coil portion.

According to a fifteenth aspect of the present invention, there is provided a fixing device according to any one of the first to fourteenth aspects, wherein the fixing device is stretched by a fixing auxiliary roller and a support roller, and the toner image is melted. The heating member is the support roller, and the magnetic flux generating means is disposed so as to face the support roller via the fixing belt.

According to a sixteenth aspect of the present invention, there is provided a fixing device according to any one of the first to fifteenth aspects, wherein the fixing device is stretched by a fixing auxiliary roller and a support roller and melts a toner image. The heating member is the fixing belt, and the magnetic flux generating means is disposed so as to face the fixing belt.

According to a fifteenth aspect of the present invention, in the fixing device according to the fifteenth aspect or the sixteenth aspect, the fixing auxiliary roller is configured to fix the fixing roller against the pressure roller that presses the conveyed recording medium. It is arrange | positioned so that it may contact | abut via a belt.

A fixing device according to an eighteenth aspect of the present invention is the fixing device according to any one of the first to fourteenth aspects, wherein the fixing device is in contact with a pressure roller that presses the recording medium to be conveyed, and the toner image is displayed. A fixing roller for melting, and the heating member is the fixing roller,
The magnetic flux generation means is disposed so as to face the fixing roller.

An image forming apparatus according to a nineteenth aspect includes the fixing device according to any one of the first to eighteenth aspects.

  In the present invention, the adjustment range in which the magnetic flux acting on the heating member is reduced is varied while a plurality of recording media are continuously fixed. Accordingly, it is possible to provide a fixing device and an image forming apparatus that can reliably suppress a temperature rise at both ends in the width direction of the heating member and the fixing member.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a main body of a laser printer as an image forming apparatus, 3 is an exposure unit that irradiates a photosensitive drum 18 with exposure light L based on image information, and 4 is detachably installed on the apparatus main body 1. A process cartridge as an image forming unit; 7, a transfer unit for transferring a toner image formed on the photosensitive drum 18 to a recording medium P; 10, a paper discharge tray on which an output image is placed; A paper feeding unit in which a recording medium P such as paper is stored, 13 is a registration roller that conveys the recording medium P to the transfer unit 7, 15 is a manual paper feeding unit, and 20 is a fixing unit that fixes an unfixed image on the recording medium P. Indicates the device.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, exposure light L such as laser light based on image information is emitted from the exposure unit 3 (writing unit) toward the photosensitive drum 18 of the process cartridge 4. The photosensitive drum 18 rotates counterclockwise in the figure, and a toner image corresponding to image information is formed on the photosensitive drum 18 through a predetermined image forming process (charging process, exposure process, development process). Is done.
Thereafter, the toner image formed on the photosensitive drum 18 is transferred onto the recording medium P conveyed by the registration roller 13 in the transfer unit 7.

On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows.
First, one of the plurality of paper feeding units 11, 12, and 15 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 11 is selected). To do.) Each of the plurality of paper feeding units 11 and 12 stores a recording medium P having a different size and a recording medium P having the same size and different transport directions.

  Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 11 is transported toward the position of the transport path K. Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller 13. Then, the recording medium P that has reached the position of the registration roller 13 is conveyed toward the transfer unit 7 at the same timing in order to align with the toner image formed on the photosensitive drum 18.

After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt and the pressure roller, and the toner image is fixed by the heat received from the fixing belt and the pressure received from the pressure roller. The recording medium P on which the toner image has been fixed is sent from between the fixing belt and the pressure roller, and then is discharged from the image forming apparatus main body 1 as an output image and placed on the paper discharge tray 10.
Thus, a series of image forming processes is completed.

Next, the configuration / operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIG.
As shown in FIG. 2, the fixing device 20 mainly includes a fixing auxiliary roller 21, a fixing belt 22, a support roller 23 (heating roller), an induction heating unit 24, a pressure roller 30, a thermopile 37, a thermistor 38, and an oil application roller. 34, a guide plate 35, a separation plate 36, and the like.

Here, the fixing auxiliary roller 21 has an elastic layer such as silicone rubber formed on the surface thereof, and is driven to rotate counterclockwise in FIG. 2 by a driving unit (not shown).
The support roller 23 is a cylindrical body made of a nonmagnetic material such as SUS304 and rotates counterclockwise in the figure. An inner core 28 made of a ferromagnetic material such as ferrite and a magnetic flux shielding member 29 covering a part of the outer periphery of the inner core 28 are rotatably installed inside the support roller 23. The inner core 28 faces the coil portion 25 through the fixing belt 22 and the support roller 23. The rotational drive of the inner core 28 and the magnetic flux shielding member 29 is performed separately from the rotational drive of the support roller 23. The configuration and operation of the support roller 23 provided with the inner core 28 and the magnetic flux shielding member 29 will be described in detail later.

The fixing belt 22 as a fixing member is stretched and supported by a support roller 23 and a fixing auxiliary roller 21. The fixing belt 22 is a multi-layered endless belt in which a heating layer, an elastic layer, and a release layer are formed on a base material.
The base material of the fixing belt 22 is made of a heat-resistant resin material. For example, polyimide, polyamideimide, PEEK (polyetheretherketone), PES (polyethersulfone), PPS (polyphenylene sulfide), fluororesin, or the like can be used. . As the heating layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy composed of a plurality of these metals, or the like can be used. As the elastic layer, silicone rubber, fluorosilicone rubber, or the like can be used. As the release layer, fluorine resins such as tetrafluoroethylene resin (PTFE) and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (FEP), or a mixture of these resins can be used.

  In the first embodiment, the base material of the fixing belt 22 and the heating layer are mixed layers. Specifically, three heating layers made of silver are formed at intervals in a base material made of polyimide. Then, an elastic layer and a release layer are sequentially formed on the hybrid layer.

The induction heating unit 24 as a magnetic flux generation unit includes a coil unit 25, a core unit 26, a coil guide 27, and the like.
Here, the coil portion 25 is wound around a litz wire in which fine wires are bundled so as to cover the outer peripheral surface of the fixing belt 22 wound around the support roller 23 and is in the width direction (in the direction perpendicular to the paper surface of FIG. 2). It is extended. The coil guide 27 is made of a highly heat-resistant resin material or the like, and holds the coil part 25 and functions as a frame of the induction heating part 24. The core part 26 is made of a ferromagnetic material such as ferrite having a relative permeability of about 2500, and is provided with a center core part 26a and a side core 26b. The core part 26 is installed so as to face the coil part 25 extending in the width direction. The center core 26a is at a substantially central position in the circumferential direction of the coil portion 25, and is a position where the density of magnetic flux formed around the coil portion 25 is the highest. The coil unit 25 is connected to a high frequency power supply unit (not shown), and an alternating current of 10 k to 1 MHz is applied from the high frequency power supply unit.

  The pressure roller 30 is formed by forming an elastic layer such as fluorine rubber or silicone rubber on a cylindrical member made of aluminum, copper, stainless steel or the like. The elastic layer of the pressure roller 30 has a thickness of 1 to 5 mm and an Asker hardness of 20 to 50 degrees. The pressure roller 30 is in contact with the fixing auxiliary roller 21 via the fixing belt 22. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure roller 30.

A guide plate 35 for guiding the conveyance of the recording medium P is disposed on the entrance side of the contact portion between the fixing belt 22 and the pressure roller 30.
A separation plate 36 that guides conveyance of the recording medium P and promotes separation of the recording medium P from the fixing belt 22 is disposed on the exit side of the contact portion between the fixing belt 22 and the pressure roller 30.

  An oil application roller 34 is in contact with a part of the outer peripheral surface of the fixing belt 22. The oil application roller 34 supplies oil such as silicone oil onto the fixing belt 22. Thereby, the toner releasability on the fixing belt 22 is further ensured. The oil application roller 34 is in contact with a cleaning roller 33 that removes dirt on the surface.

A thermopile 37 serving as a non-contact type temperature detecting unit is installed at a position facing the outer peripheral surface of the fixing belt 22 and in a central portion in the width direction (a position that does not become an adjustment range described later). . Further, a thermistor 38 as a temperature detecting means is installed at a position in contact with the outer peripheral surface of the fixing belt 22 and in an end portion in the width direction (a position to be an adjustment range described later).
The surface temperature (fixing temperature) on the fixing belt 22 is detected by the thermopile 37 and the thermistor 38, and the output in the induction heating unit 24 having an inverter circuit is adjusted. Thus, the fixing temperature on the fixing belt 22 is kept constant. Further, the magnetic flux acting on both ends of the support roller 23 in the width direction is adjusted based on the temperature detected by the thermopile 37 and the thermistor 38. This will be described in detail later.

The fixing device 20 configured as described above operates as follows during normal operation.
By the rotation driving of the auxiliary fixing roller 21, the fixing belt 22 rotates in the direction of the arrow in FIG. 2, the support roller 23 also rotates counterclockwise, and the pressure roller 30 also rotates in the direction of the arrow. The fixing belt 22 is heated at a position facing the induction heating unit 24. Specifically, the magnetic field lines are alternately switched between the core part 26 and the inner core 28 by passing a high-frequency alternating current through the coil part 25. At this time, an eddy current is generated on the surface of the support roller 23 and the heating layer of the fixing belt 22, and Joule heat is generated by the electrical resistance of the support roller 23 and the heating layer. Thus, the fixing belt 22 is heated by the heat received from the heat-generating support roller 23 and the heat generated by its own heating layer. That is, the support roller 23 functions as a heating member, and the fixing belt 22 functions as a heating member as well as a member to be heated.

Thereafter, the surface of the fixing belt 22 heated by the induction heating unit 24 passes through the position of the thermistor 38 and then reaches the contact portion with the pressure roller 30. Then, the toner image T on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing belt 22 and the pressure roller 30 while being guided by the guide plate 35 (indicated by the arrow Y). It is movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing belt 22 and the pressure roller 30.

The surface of the fixing belt 22 that has passed through the position of the pressure roller 30 sequentially passes through the positions of the oil application roller 34 and the thermopile 37, and then reaches the position facing the induction heating unit 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

The configuration and operation of the support roller 23 will be described in detail with reference to FIG.
FIG. 3 is a front view of the support roller 23 installed in the fixing device 20 of FIG. 2 as viewed in the width direction from the induction heating unit 24 side.
As shown in FIG. 3, an inner core 28 and a magnetic flux shielding member 29 are rotatably installed in the cylindrical body of the support roller 23.

  Magnetic flux shielding members 29 made of a diamagnetic material such as copper are integrally installed at both ends in the width direction of the cylindrical inner core 28 made of a ferromagnetic material. The magnetic flux shielding member 29 is formed with an inclined portion 29a so as to gradually decrease (or gradually increase) the range of shielding the outer peripheral surface of the inner core 28 from the end surface side. Thereby, by rotating the inner core 28 together with the magnetic flux shielding member 29, the shielding range (adjustment range) in the width direction of the inner core 28 facing the coil portion 25 of the induction heating unit 24 can be varied.

  Specifically, referring to FIG. 4, when a magnetic flux shielding member 29 is interposed between the center core 26a (the position where the magnetic flux density is highest) of the induction heating unit 24 and the inner core 28, the magnetic flux A normal magnetic flux (indicated by a broken line B in FIG. 4) formed when there is no shielding member 29 is weakened. Thereby, in the position of the support roller 23 which has arrange | positioned the magnetic flux shielding member 29, a heating efficiency falls with the fall of the magnetic flux which acts.

  Here, the range in the width direction (adjustment range) for reducing the magnetic flux can be varied by changing the posture of the magnetic flux shielding member 29 facing the coil portion 25. Specifically, by rotating and driving (drive control) the magnetic flux shielding member 29 together with the inner core 28, the adjustment range for reducing the magnetic flux can be varied within the range of L1 to L2 in FIG. That is, the length of the adjustment range (shielding range) can be changed from 0 to (L1-L2). Thus, the magnetic flux shielding member 29 functions as a magnetic flux adjusting member that reduces the magnetic flux acting on the support roller 23 (or the fixing belt 22) in the adjustment range in the width direction.

  The rotational drive (drive control) of the inner core 28 and the magnetic flux shielding member 29 is performed by a stepping motor (not shown) as variable means connected to the shaft portion of the inner core 28. The stepping motor is a drive system different from a drive motor (not shown) that drives the auxiliary fixing roller 21, the fixing belt 22, the support roller 23, and the like.

Specifically, the inner core 28 and the magnetic flux shielding member 29 are rotated by a predetermined angle in the circumferential direction so that the maximum range of the magnetic flux shielding member 29 is opposed to the center core 26a. At this time, the adjustment range in which the magnetic flux is reduced is maximized, and the outside of the adjustment range (the region of the center width L2) is the main heating range of the fixing belt 22. This state is suitable for fixing the recording medium P whose width direction size is L2.
On the other hand, the inner core 28 and the magnetic flux shielding member 29 are further rotated by a predetermined angle in the circumferential direction so that the magnetic flux shielding member 29 does not face the center core 26a. At this time, the adjustment range in which the magnetic flux is reduced becomes zero, and the entire range (the region of the width L1) becomes the main heating range of the fixing belt 22.

The fixing device 20 configured in this way, when continuously fixing the toner image T to a plurality of recording media P (during continuous paper passing and continuous fixing), during the paper passing. Also, the adjustment range by the magnetic flux shielding member 29 is varied.
Hereinafter, based on the flowchart of FIG. 5, the control at the time of continuous paper feeding will be described in detail with reference to FIGS. 6 to 8 as appropriate.
FIG. 6 is a schematic diagram showing a positional relationship in the width direction of the magnetic flux shielding member 29, the center core 26a, the recording medium P, the adjustment range N, and the heating range M when the magnetic flux shielding member 29 is driven and controlled. .

  First, when the power source of the apparatus main body 1 is turned on (steps S1 and S2), the home position of the magnetic flux shielding member 29 as a magnetic flux adjusting member is detected (step S3). That is, drive control is performed so that the position (posture) of the magnetic flux shielding member 29 matches the initial position (home position). Specifically, referring to FIG. 6 (A), the home position of magnetic flux shielding member 29 is a position that opens the entire width of the inner core, and at this time, adjustment range N is zero and the entire width is the heating range. M.

Thereafter, the switch of the inverter power supply (high frequency power supply unit) of the fixing device 20 is turned on, and heating by the induction heating unit 24 is started (step S4). Then, after reloading (step S5), it is determined whether there is a print request (a print command by the user) (step S6).
As a result, if it is determined that there is no print request, the process goes through a standby state (step S7), and the flow after step S6 is performed again.

  On the other hand, if it is determined that there is a print request, the size of the recording medium P that matches the print request is detected by the detecting means (step S8). That is, the width direction size (or size and transport direction) of the recording medium P that is continuously passed (continuously fixed) is detected by the detection unit. Here, the width-direction size of the recording medium P detected by the detecting means specifies the width-direction range (sheet passing area) of the recording medium P corresponding to the support roller 23 and the fixing belt 22. That is, in the support roller 23 and the fixing belt 22, a non-sheet passing region that may overheat is specified. Further, the detection means detects the size in the width direction of the recording medium P based on a size detection sensor installed in the paper feeding units 11, 12, 15, input information requested by the user, or the like.

  Thereafter, the magnetic flux shielding member 29 is driven and controlled based on the size of the recording medium P detected by the detecting means (step S9). At this time, the adjustment range N that is varied by the magnetic flux shielding member 29 is controlled to be shorter than the range (non-sheet passing region) outside the range of the recording medium P detected by the detection unit. That is, referring to FIG. 6B, the adjustment range N is set shorter by a predetermined length X2 from the end of the recording medium P through which the paper is passed, and the heating range M is set longer.

  This is because the temperature of the non-sheet passing area of the support roller 23 and the fixing belt 22 does not rise immediately after the start of heating, and instead of reducing the magnetic flux in the entire non-sheet passing area, the area near the boundary with the sheet passing area is not. This is because the temperature becomes too low.

Thereafter, continuous paper feeding is started (step S10). At this time, the counting means counts the heating time for continuous paper feeding (the cumulative time during which power is supplied from the high-frequency power supply unit to the induction heating unit) and the cumulative number of papers to be passed.
Then, when the count value (heating time or paper passing time) counted by the counting means reaches a predetermined value, the adjustment range N set at the start of heating becomes longer (the heating range M becomes shorter). Drive control of the magnetic flux shielding member 29 is performed (step S11).

Specifically, the magnetic flux shielding member 29 set at the position of FIG. 6B at the start of heating is driven and controlled so that the length of the adjustment range N increases stepwise as the count value increases. Then, with the predetermined count value as a boundary, the adjustment range N becomes longer than the non-sheet passing region, and the heating range M becomes shorter than the sheet passing region. In FIG. 6C, the adjustment range N is longer than the non-sheet passing region by the length X3.
Referring to FIG. 7, the relationship between the count value and adjustment range N is stored in advance as a table in the control unit. That is, the magnetic flux shielding member 29 is driven and controlled so that the length of the adjustment range N increases stepwise as the number of sheets to be passed and the heating time increase.

This is due to the fact that the heat in the heating range M is gradually transferred to the adjustment range N that is not actively heated as the continuous paper feeding starts and the heating time (or the number of papers to be passed) increases. That is, when the adjustment range N in which the magnetic flux is reduced during continuous paper feeding is fixed, an excessive temperature rise occurs at a position close to the heating range M in the adjustment range N.
In the first embodiment, the adjustment range N is controlled to become gradually longer according to the heating time (or the number of sheets to be passed), so that the non-sheet passing area is excessively increased due to heat transfer from the heating range M. Temperature can be suppressed.

  Thereafter, when the continuous sheet passing is completed (step S12), the home position of the magnetic flux shielding member 29 is detected again (step S13). And the switch of an inverter power supply (high frequency power supply part) is turned off, and the heating by the induction heating part 24 is stopped (step S14). Thus, a series of control flow ends (step S15).

FIG. 8 is a graph showing the temperature distribution in the width direction on the fixing belt 22 in the fixing device of the first embodiment.
In FIG. 8, the horizontal axis indicates the position in the width direction of the fixing belt 22, and the vertical axis indicates the temperature of the fixing belt 22 (fixing temperature). Here, “0” in the width direction position on the horizontal axis indicates the center position in the width direction of the fixing belt 22. A solid line R1 indicates a temperature distribution when the recording medium P having a width direction size L1 is continuously fed. A solid line R2 indicates a temperature distribution when the recording medium P having a width direction size L2 is continuously fed.

  By finely adjusting the adjustment range N by the magnetic flux shielding member 29 over time, the temperature distribution of the fixing belt 22 can be maintained as shown in FIG. Thereby, in the range exceeding the sheet passing width of the recording medium P, the temperature of the fixing belt 22 does not increase, and thermal damage to the fixing belt 22 is suppressed.

  As described above, in the first embodiment, the magnetic flux acting on the fixing belt 22 and the support roller 23 is reduced while a plurality of recording media P are continuously fixed (during continuous paper feeding). The adjustment range N is variable. As a result, the temperature rise at both ends in the width direction of the fixing belt 22 and the support roller 23 can be reliably suppressed.

  In the first embodiment, the fixing belt 22 having a heating layer and the support roller 23 are used as heating members. On the other hand, only one of the fixing belt 22 and the support roller 23 can be used as a heating member. Even in this case, the same effect as in the first embodiment can be obtained by optimizing the adjustment range N by the magnetic flux shielding member 29 from the start of heating to the completion of paper passing.

  In the first embodiment, a halogen heater can be installed inside the pressure roller 30. Further, a thermistor or an oil application roller can be brought into contact with the outer peripheral surface of the pressure roller 30. In the first embodiment, the present invention is applied to the monochrome image forming apparatus 1. However, the present invention can also be applied to a color image forming apparatus. In these cases, the same effect as in the first embodiment can be obtained.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 9 is a flowchart illustrating control performed by the fixing device 20 according to the second embodiment. In the second embodiment, the magnetic flux shielding member 29 is driven and controlled based on the temperature detected by the thermopile 37 as the temperature detecting means. The magnetic flux shielding member 29 is based on the count value counted by the counting means. This is different from that of the first embodiment in which the drive is controlled.

In the flowchart of FIG. 9, the control flow from step S1 to step S10 is the same as that described in FIG. 5 of the first embodiment.
In step S10, after the continuous paper feeding is started, the temperature on the fixing belt 22 during the continuous paper feeding is detected by the thermopile 37 (step S21). Here, the thermopile 37 faces substantially the center in the width direction of the fixing belt 22. This position is a position that is not included in the adjustment range N even if the adjustment range N changes in the subsequent control. Thereby, the temperature fluctuation of the fixing belt 22 outside the adjustment range N can be detected.

  Thereafter, it is determined whether the detected temperature of the thermopile 37 is equal to or lower than a predetermined value D (step S22). As a result, when it is determined that the detected temperature is equal to or lower than the predetermined value D, the magnetic flux shielding member 29 is driven and controlled to be shorter than the adjustment range N adjusted in step S9 (step S23). As a result, heat in the heating range M is transmitted to the adjustment range N side, and an excessive increase in temperature in the non-sheet passing area is suppressed, and a temperature drop at both ends of the sheet passing area is suppressed.

  Thereafter, it is determined that the number of sheets for which printing has been requested has been completed (step S26). As a result, if it is determined that the requested number of sheets has not been completed, the flow after step S21 is repeated. On the other hand, if it is determined that the requested number of sheets has been completed, the flow after step S12 similar to that of the first embodiment is performed, and this control flow is ended (step S15). .

If it is determined in step S22 that the detected temperature is not lower than the predetermined value D, it is further determined whether the detected temperature is higher than the predetermined value E (step S24). The predetermined value E is larger than the predetermined value D.
As a result, when it is determined that the detected temperature is equal to or higher than the predetermined value E, the magnetic flux shielding member 29 is driven and controlled to be longer than the adjustment range N adjusted in step S9 (step S25). As a result, the rate at which heat in the heating range M is transferred to the adjustment range N side is reduced, and excessive temperature rise in the non-sheet passing region is suppressed.

Thereafter, it is determined that the number of sheets for which printing has been requested has been completed (step S26). Similarly, if it is determined in step S24 that the detected temperature is not equal to or higher than the predetermined value E, it is determined that the number of sheets for which printing has been requested has been completed (step S26).
As a result, if it is determined that the requested number of sheets has not been completed, the flow after step S21 is repeated. On the other hand, if it is determined that the requested number of sheets has been completed, the flow after step S12 similar to that of the first embodiment is performed, and this control flow is ended (step S15). .

  As described above, in the second embodiment, the magnetic flux acting on the fixing belt 22 and the support roller 23 is reduced while a plurality of recording media P are continuously fixed (during continuous paper feeding). The adjustment range N is varied based on the temperature fluctuation at the center in the width direction of the fixing belt 22. As a result, the temperature rise at both ends in the width direction of the fixing belt 22 and the support roller 23 can be reliably suppressed.

In the second embodiment, the temperature of the fixing belt 22 as the heating member is directly detected and the adjustment range N is varied based on the detection result. However, the temperature of the support roller 23 as the heating member is directly changed. The adjustment range N can be varied based on the detection result.
Further, when the fixing belt 22 functions only as a member to be heated (when no heating layer is provided), the temperature of the fixing belt 22 is detected, and the adjustment range N is varied based on the detection result. You can also. In that case, the temperature of the heating member is indirectly detected.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 10 is a flowchart showing the control performed by the fixing device 20 according to the third embodiment. In the third embodiment, the magnetic flux shielding member 29 is driven and controlled based on the temperature variation at the widthwise end portion of the fixing belt 22. The magnetic flux shielding is performed based on the temperature variation at the central portion in the width direction of the fixing belt 22. This is different from the second embodiment in which the member 29 is driven and controlled.

In the flowchart of FIG. 10, the control flow from step S1 to step S10 is the same as that described in FIG. 9 of the second embodiment.
In step S10, after the continuous paper feeding is started, the temperature on the fixing belt 22 during the continuous paper feeding is detected by the thermistor 38 (step S31). Here, the thermistor 38 is in contact with the end of the fixing belt 22 in the width direction. This position is always included in the adjustment range N even if the adjustment range N changes in the subsequent control. As a result, the temperature fluctuation of the fixing belt 22 within the adjustment range N can always be detected.

  Thereafter, it is determined whether the detected temperature of the thermistor 38 is equal to or higher than a predetermined value F (step S32). As a result, when it is determined that the detected temperature is equal to or higher than the predetermined value F, the magnetic flux shielding member 29 is driven and controlled to be longer than the adjustment range N adjusted in step S9 (step S33). As a result, the rate at which heat in the heating range M is transferred to the adjustment range N side is reduced, and excessive temperature rise in the non-sheet passing region is suppressed.

  Thereafter, it is determined that the number of sheets for which printing has been requested has been completed (step S26). As a result, if it is determined that the requested number of sheets has not been completed, the flow after step S31 is repeated. On the other hand, if it is determined that the requested number of sheets has been completed, the flow after step S12 similar to that of the second embodiment is performed, and this control flow is ended (step S15). .

If it is determined in step S32 that the detected temperature is not higher than the predetermined value F, it is further determined whether the detected temperature is lower than the predetermined value G (step S34). The predetermined value F is larger than the predetermined value G.
As a result, when it is determined that the detected temperature is equal to or lower than the predetermined value G, the magnetic flux shielding member 29 is driven and controlled so as to be shorter than the adjustment range N adjusted in step S9 (step S35). As a result, heat in the heating range M is transmitted to the adjustment range N side, and an excessive increase in temperature in the non-sheet passing area is suppressed, and a temperature drop at both ends of the sheet passing area is suppressed.

Thereafter, it is determined that the number of sheets for which printing has been requested has been completed (step S26). Similarly, if it is determined in step S34 that the detected temperature is not equal to or lower than the predetermined value G, it is determined that the number of sheets for which printing has been requested has been completed (step S26).
As a result, if it is determined that the requested number of sheets has not been completed, the flow after step S31 is repeated. On the other hand, if it is determined that the requested number of sheets has been completed, the flow after step S12 similar to that of the second embodiment is performed, and this control flow is ended (step S15). .

FIG. 11 is a graph showing an example of the relationship between the number of continuously passing sheets (horizontal axis) and the fixing temperature (vertical axis) when the magnetic flux shielding member 29 is not installed. In FIG. 11, the solid line S1 indicates the temporal variation of the fixing temperature in the paper passing region (the central portion in the width direction), and the solid line S2 indicates the temporal variation of the fixing temperature in the non-paper passing region (the end portion in the width direction). Indicates.
In FIG. 11, in the paper passing area, the fixing temperature is low at the start of heating, but thereafter the fixing temperature is stable. On the other hand, in the non-sheet passing region, the fixing temperature is low at the start of heating, and the fixing temperature is not stable thereafter.
The control according to the third embodiment is particularly effective when such a tendency increases. That is, by varying the adjustment range N based on the temperature fluctuation at the width direction end where the fixing temperature is not stable, it is possible to stabilize the fixing temperature at both ends in the width direction and suppress overheating.

  As described above, in the third embodiment, the adjustment range N for reducing the magnetic flux acting on the fixing belt 22 and the support roller 23 while the plurality of recording media P are continuously fixed is set as the fixing belt. It is variable based on the temperature fluctuation at the end in the width direction of 22. As a result, the temperature rise at both ends in the width direction of the fixing belt 22 and the support roller 23 can be reliably suppressed.

Embodiment 4 FIG.
A fourth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 12 is a diagram illustrating the support roller 23 of the fixing device according to the fourth embodiment, and corresponds to FIG. 3 according to the first embodiment. The support roller 23 of the fourth embodiment is different from that of the first embodiment in the shape of the magnetic flux shielding member 29 provided inside.

  As shown in FIG. 12, an inner core 28 and a magnetic flux shielding member 29 are installed inside the support roller 23. Unlike the first embodiment, the magnetic flux shielding member 29 according to the fourth embodiment is made of a plurality of copper materials having different lengths in the width direction. The magnetic flux shielding member 29 is attached to the outer peripheral surface of the inner core 28. Copper materials having different lengths in the width direction in the magnetic flux shielding member 29 are formed so as to gradually decrease (or gradually increase) the range of shielding the outer peripheral surface of the inner core 28 from the end surface side. Thus, as in the above-described embodiments, the inner core 28 is rotated together with the magnetic flux shielding member 29, thereby shielding the width direction shielding range (adjustment range) of the inner core 28 facing the coil portion 25 of the induction heating unit 24. Can be varied.

  As described above, also in the fourth embodiment, the magnetic flux acting on the fixing belt 22 and the support roller 23 while the plurality of recording media P are continuously fixed, as in the above embodiments. The adjustment range N to be lowered is varied. As a result, the temperature rise at both ends in the width direction of the fixing belt 22 and the support roller 23 can be reliably suppressed.

Embodiment 5 FIG.
A fifth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 13 is a development view showing the magnetic flux shielding member 29 of the support roller 23 in the fifth embodiment. In the fifth embodiment, the shape of the magnetic flux shielding member 29 is different from that of the first embodiment.

As shown in FIG. 13, the magnetic flux shielding member 29 according to the fifth embodiment is formed with a slope portion 29 a for changing the adjustment range N in a step shape. The magnetic flux shielding member 29 is also formed so as to gradually decrease (or gradually increase) the range of shielding the outer peripheral surface of the inner core 28 from the end surface side in the same manner as in the above embodiments.
In the fifth embodiment as well, as in each of the embodiments described above, the magnetic flux shielding member so as to finely adjust the adjustment range N in the width direction for reducing the magnetic flux according to the heating time, the temperature of the fixing belt 22, and the like. 29 is driven and controlled.

  As described above, also in the fifth embodiment, the magnetic flux that acts on the fixing belt 22 and the support roller 23 while the plurality of recording media P are continuously fixed, as in the above embodiments. The adjustment range N to be lowered is varied. As a result, the temperature rise at both ends in the width direction of the fixing belt 22 and the support roller 23 can be reliably suppressed.

Embodiment 6 FIG.
A sixth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 14 is a development view showing the magnetic flux shielding member 29 of the support roller 23 in the sixth embodiment. In the sixth embodiment, the shape of the magnetic flux shielding member 29 is different from that of the first embodiment.

As shown in FIG. 14, the magnetic flux shielding member 29 of the sixth embodiment is obtained by sticking a plurality of copper materials having different lengths in the width direction to the support roller 23 in order to vary the adjustment range N. The plurality of copper inclined portions 29a are formed in a tapered shape. The magnetic flux shielding member 29 is also formed so as to gradually decrease (or gradually increase) the range of shielding the outer peripheral surface of the inner core 28 from the end surface side in the same manner as in the above embodiments.
Also in the sixth embodiment, similarly to each of the embodiments described above, the magnetic flux shielding member so as to finely adjust the adjustment range N in the width direction in which the magnetic flux is reduced according to the heating time, the temperature of the fixing belt 22, and the like. 29 is driven and controlled.

  As described above, also in the sixth embodiment, the magnetic flux acting on the fixing belt 22 and the support roller 23 while the plurality of recording media P are continuously fixed, as in the above embodiments. The adjustment range N to be lowered is varied. As a result, the temperature rise at both ends in the width direction of the fixing belt 22 and the support roller 23 can be reliably suppressed.

Embodiment 7 FIG.
A seventh embodiment of the present invention will be described in detail with reference to FIG.
FIG. 15 is a sectional view showing the fixing device 20 according to the seventh embodiment. In the fixing device according to the seventh embodiment, the fixing roller 31 is used as the heating member and the fixing member, and the fixing belt is used as the fixing member using the support roller and the fixing belt as the heating member. It differs from one.

As shown in FIG. 15, the fixing device 20 of the seventh embodiment mainly includes a fixing roller 31 (fixing member), a pressure roller 30, an induction heating unit 24, and the like.
The fixing roller 31 includes a heat generating layer 31a, an elastic layer made of silicone rubber, a release layer made of a fluorine compound, and the like. The inside of the fixing roller 31 has a hollow structure, and the inner core 28 and the magnetic flux shielding member 29 are rotatably installed.

The induction heating unit 24 includes a coil unit 25, a core unit 26, a coil guide 27, and the like, as in the first embodiment. Then, when an alternating current of 10 k to 1 MHz is supplied to the coil portion 25, magnetic lines of force are formed between the core portion 26 and the inner core 28, and the fixing roller 31 is heated by electromagnetic induction. In this way, the heated fixing roller 31 heats and melts the toner image on the recording medium P conveyed from the arrow Y direction, and fixes the toner image on the recording medium P.
Also in the seventh embodiment, similarly to each of the embodiments described above, the magnetic flux shielding member so as to finely adjust the adjustment range N in the width direction in which the magnetic flux is reduced according to the heating time, the temperature of the fixing roller 31, and the like. 29 is driven and controlled.

  As described above, in the seventh embodiment, the adjustment range N for reducing the magnetic flux acting on the fixing roller 31 is varied while the plurality of recording media P are continuously fixed. Thereby, the temperature rise at both ends in the width direction of the fixing roller 31 can be reliably suppressed.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a view showing a support roller installed in the fixing device of FIG. 2. FIG. 3 is an enlarged view showing the vicinity of an induction heating unit in the fixing device of FIG. 2. 3 is a flowchart showing control performed by the fixing device of FIG. 2. It is a schematic diagram which shows the positional relationship when a magnetic flux shielding member operate | moves. It is a figure which shows the table used by control of FIG. 3 is a graph showing a temperature distribution in a width direction on a fixing belt in the fixing device of FIG. 2. It is a flowchart which shows the control performed with the fixing device in Embodiment 2 of this invention. It is a flowchart which shows the control performed with the fixing device in Embodiment 3 of this invention. 6 is a graph showing an example of a change in fixing temperature during continuous paper feeding. It is a figure which shows the support roller installed in the fixing device in Embodiment 4 of this invention. It is an expanded view which shows the magnetic flux shielding member installed in the support roller in Embodiment 5 of this invention. It is an expanded view which shows the magnetic flux shielding member installed in the support roller in Embodiment 6 of this invention. It is sectional drawing which shows the fixing device in Embodiment 7 of this invention.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20 fixing device, 21 fixing auxiliary roller,
22 fixing belt (heating member, fixing member, heated member),
23 support roller (heating member),
24 induction heating part (magnetic flux generating means), 25 coil part,
26 core part, 26a center core, 26b side core,
28 inner core,
29 magnetic flux shielding member (magnetic flux adjusting member), 30 pressure roller,
31 fixing roller (heating member, fixing member),
37 thermopile (temperature detection means), 38 thermistor (temperature detection means),
N adjustment range, P recording medium.

Claims (19)

A fixing device for fixing a toner image on a recording medium,
Magnetic flux generating means for generating magnetic flux;
A heating member that is induction-heated by the magnetic flux;
A magnetic flux adjusting member that reduces the magnetic flux acting on the heating member for a predetermined adjustment range in the width direction;
Detection means for detecting the size of the recording medium that matches the print request;
Variable means for varying the adjustment range for reducing the magnetic flux by driving the magnetic flux adjusting member from a home position to a position corresponding to the size based on the size detected by the detecting means;
When continuously fixing toner images on a plurality of recording media, the cumulative heating time from the start of heating of the heating member or / and the passing of the plurality of recording media is started. Counting means for counting the cumulative number of sheets passed since then,
With
The variable means is configured to increase the adjustment range when the count value of the counting means reaches a predetermined value while continuously fixing toner images to the plurality of recording media. A fixing device, wherein the magnetic flux adjusting member is driven and controlled so that the adjustment range is varied based on a count value of a counting means. The variable means is for a range outside the range in the width direction of the recording medium corresponding to the heating member specified based on the size detected by the detection means when fixing of the toner image is started. The fixing device according to claim 1, wherein the magnetic flux adjusting member is driven and controlled so that the adjustment range is shortened. The variable means is for a range outside the range in the width direction of the recording medium corresponding to the heating member specified based on the size detected by the detection means when the count value reaches a predetermined value. The fixing device according to claim 1, wherein the magnetic flux adjusting member is driven and controlled so that the adjustment range becomes longer. The fixing device according to claim 1, wherein the variable unit drives and controls the magnetic flux adjusting member in a stepwise manner in accordance with an increase in the count value. A fixing device for fixing a toner image on a recording medium,
Magnetic flux generating means for generating magnetic flux;
A heating member that is induction-heated by the magnetic flux;
A magnetic flux adjusting member that reduces the magnetic flux acting on the heating member for a predetermined adjustment range in the width direction;
Detection means for detecting the size of the recording medium that matches the print request;
Variable means for varying the adjustment range for reducing the magnetic flux by driving the magnetic flux adjusting member from a home position to a position corresponding to the size based on the size detected by the detecting means;
Temperature detecting means for directly or indirectly detecting the temperature of the heating member while continuously fixing toner images on a plurality of recording media;
With
The variable means is configured to increase the adjustment range when the temperature detected by the temperature detecting means exceeds a predetermined value while continuously fixing toner images on the plurality of recording media. The fixing device is characterized in that the magnetic flux adjusting member is driven and controlled. A fixing device for fixing a toner image on a recording medium,
Magnetic flux generating means for generating magnetic flux;
A heating member that is induction-heated by the magnetic flux;
A magnetic flux adjusting member that reduces the magnetic flux acting on the heating member for a predetermined adjustment range in the width direction;
Detection means for detecting the size of the recording medium that matches the print request;
Variable means for varying the adjustment range for reducing the magnetic flux by driving the magnetic flux adjusting member from a home position to a position corresponding to the size based on the size detected by the detecting means;
Temperature detecting means for directly or indirectly detecting the temperature of the heating member while continuously fixing toner images on a plurality of recording media;
With
The variable unit is configured to shorten the adjustment range when the temperature detected by the temperature detection unit becomes a predetermined value or less while the toner images are continuously fixed to the plurality of recording media. The fixing device is characterized in that the magnetic flux adjusting member is driven and controlled. The fixing device according to claim 5 , wherein the temperature detection unit is disposed at a position that does not fall within the adjustment range even if the adjustment range is varied. The fixing device according to claim 5 , wherein the temperature detection unit is disposed at a position that is always within the adjustment range even if the adjustment range is varied. The variable means is for a range outside the range in the width direction of the recording medium corresponding to the heating member specified based on the size detected by the detection means when fixing of the toner image is started. The fixing device according to any one of claims 5 to 8, wherein the magnetic flux adjusting member is driven and controlled so that the adjustment range is shortened. The fixing device according to claim 1, wherein the adjustment range includes a part or all of a range outside a range in a width direction of the recording medium corresponding to the heating member. . The magnetic flux generating means includes a coil portion extending in the width direction so as to face the heating member, and an inner core facing the coil portion via the heating member,
The fixing device according to claim 1, wherein the magnetic flux adjusting member is a magnetic flux shielding member disposed between the coil portion and the inner core. The fixing device according to claim 11, wherein the magnetic flux shielding member is formed so that a range covering an outer periphery of the inner core facing the coil portion can be gradually increased or decreased. The fixing device according to claim 12, wherein the variable unit is a unit that drives the magnetic flux shielding member so as to gradually increase or decrease a range covering an outer periphery of the inner core. The magnetic flux generating means includes a core portion having a center core and facing the coil portion on the side where the coil portion does not face the heating member,
The fixing device according to claim 11, wherein the magnetic flux shielding member covers an outer periphery of the inner core facing the center core. A fixing belt that is stretched by a fixing auxiliary roller and a supporting roller and that melts a toner image,
The heating member is the support roller,
The fixing device according to claim 1, wherein the magnetic flux generation unit is disposed to face the support roller with the fixing belt interposed therebetween. A fixing belt that is stretched by a fixing auxiliary roller and a supporting roller and that melts a toner image,
The heating member is the fixing belt,
The fixing device according to claim 1, wherein the magnetic flux generation unit is disposed so as to face the fixing belt. 17. The fixing according to claim 15, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. apparatus. A fixing roller that contacts a pressure roller that presses the recording medium to be conveyed and melts the toner image;
The heating member is the fixing roller,
The fixing device according to claim 1, wherein the magnetic flux generation unit is disposed so as to face the fixing roller. An image forming apparatus comprising the fixing device according to claim 1.

Images