JP6284013B2 - 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 such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a fixing device installed therein, and in particular, a fixing device using an electromagnetic induction heating method, and an image The present invention relates to a forming apparatus.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copiers and printers, a technique using an electromagnetic induction heating type fixing device is widely known for the purpose of reducing the start-up time of the apparatus and saving energy (for example, (See Patent Documents 1 to 3.)

In Patent Document 1, etc., an electromagnetic induction heating type fixing device includes a multi-layered fixing roller having a heat generation layer, an elastic layer, a magnetic flux control layer, and the like, a magnetic flux generation unit (induction heating unit) facing the outer peripheral surface of the fixing roller, It comprises a pressure roller that presses against the fixing roller to form a nip portion.
The fixing roller (heat generation layer) is heated at a position facing the magnetic flux generation unit. The heated fixing roller heats and fixes the toner image on the recording medium transported to the contact position (the fixing nip portion) with the pressure roller. More specifically, an alternating magnetic field is formed around the exciting coil by causing a high-frequency alternating current to flow through the magnetic flux generating section composed of the exciting coil, and an eddy current is generated in the heat generating layer of the fixing roller. When an eddy current is generated in the heat generating layer, Joule heat is generated by the electric resistance of the heat generating layer. The entire fixing roller is heated by this Joule heat.

  Here, in Patent Document 1 or the like, a magnetic flux control layer that controls the magnetic flux when the temperature reaches the Curie temperature is provided around the fixing roller in order to prevent the fixing roller (heat generation layer) from excessively rising in temperature. (Layered). This magnetic flux control layer is formed of a magnetic body (magnetization alloy) having a predetermined Curie temperature.

  On the other hand, in Patent Documents 2, 3 and the like, a heating member (sliding contact with a part of the inner peripheral surface of the fixing belt in the circumferential direction is provided at a position facing the magnetic flux generation unit (excitation coil) via the fixing belt. A technique for installing a fixed plate is disclosed. In such a fixing device, the fixing belt is heated by a heat generating member (fixed plate) electromagnetically heated by the magnetic flux generator, and the fixing belt and the pressure roller are pressed against each other by the heated fixing belt. The toner image on the recording medium is heated and melted at the portion.

  Since the above-described fixing device of Patent Document 1 is provided with a magnetic flux control layer inside the fixing roller (fixing member), an effect of preventing an excessive temperature increase of the fixing roller by self-temperature controllability can be greatly expected. However, since the magnetic flux control layer made of a magnetic shunt alloy has a high material cost and is formed in a circumferential shape (layered shape) according to the roller shape of the fixing roller, the component cost and manufacturing cost (processing) Cost) was high.

  In order to solve such a problem, by applying the techniques of Patent Documents 2 and 3, from a magnetic shunt alloy in a substantially arc shape so as to be in sliding contact with only a part of the inner peripheral surface of the fixing belt (fixing member). A method of providing a magnetic flux control member (magnetic flux control layer) is conceivable. However, in such a case, the fixing belt formed of a relatively soft material is worn and deteriorated due to the sliding contact with the magnetic flux control member, and the sliding resistance of the sliding contact portion due to the sliding contact with the magnetic flux control member is other than that. There is a possibility that a trouble such as heating unevenness occurs in the fixing belt due to the fact that it becomes higher than the portion and the belt in the circumferential direction is deviated.

  The present invention has been made to solve the above-described problems. The cost of the magnetic flux control member is relatively low, and there is a problem that the fixing member is worn and deteriorated or that the fixing member is unevenly heated. It is an object of the present invention to provide a fixing device and an image forming apparatus that are difficult to perform.

The fixing device according to the first aspect of the present invention forms a nip portion where the recording medium is conveyed between the pressure member and travels in a predetermined direction to heat the toner image. The magnetic flux generated from the magnetic flux generator is formed of a fixing member that fixes an image on a recording medium, a magnetic flux generator that generates magnetic flux, and a hollow structure that contacts the fixing member and rotates in a predetermined direction. The heating roller that is heated directly or indirectly by the heating member to heat the fixing member, and the circumferential direction of the inner circumferential surface or outer circumferential surface of the heating roller so that the heating roller is interposed between the magnetic flux generation unit The magnetic flux control member, which is formed between the heating roller and the magnetic flux control member formed so as to be able to vary the flow path of the magnetic flux generated from the magnetic flux generation unit and transmitted through the heating roller. Intervening To face the flux control member so that, and a magnetic flux shielding member for shielding the magnetic flux when the magnetic flux having passed through the heating roller is generated from said magnetic flux generating portion is transmitted through the magnetic flux controlling member The magnetic flux control member is formed by arranging a plurality of magnetic flux control members having different Curie temperatures in the circumferential direction, and the magnetic flux control member having a high Curie temperature passes through the heating roller when the apparatus is started up. Opposite the generator, the apparatus is configured to be movable in the circumferential direction so that a magnetic flux control member having a low Curie temperature is opposed to the magnetic flux generator via the heating roller after the apparatus is started up .

  According to the present invention, there are provided a fixing device and an image forming apparatus in which the cost of the magnetic flux control member is relatively low, and the problem that the fixing member is worn and deteriorated and the problem that the fixing member is unevenly heated are less likely to occur. can do.

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. FIGS. 3A and 3B are configuration diagrams illustrating a main part of a fixing device according to Embodiment 2 of the present invention, in which FIG. 3A is a diagram illustrating a state at startup and FIG. 3B is a diagram illustrating a state after startup. It is a perspective view which shows the magnetic flux control member as the modification 1. It is a block diagram which shows the principal part of the fixing device in Embodiment 3 of this invention. It is a perspective view which shows the magnetic flux control member in Embodiment 4 of this invention. It is a perspective view which shows the magnetic flux control member as the modification 2. It is a block diagram which shows the principal part of the fixing device in Embodiment 5 of this invention. FIG. 10 is a configuration diagram illustrating a main part of a fixing device as a third modification. FIG. 10 is a configuration diagram illustrating a fixing device as a fourth modification.

  Hereinafter, embodiments 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.
1 and 2, the first embodiment of the present invention will be described in detail.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a tandem color copier as an image forming apparatus, 2 is a writing unit that emits laser light based on input image information, 3 is a document conveying unit that conveys a document D to a document reading unit 4, and 4 is A document reading unit that reads image information of the document D, 7 is a paper feed unit that accommodates a recording medium P such as paper, 9 is a registration roller (timing roller) that adjusts the conveyance timing of the recording medium P, 11Y, 11M, and 11C. , 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, and 13 is each photosensitive drum. Development units 14 for developing the electrostatic latent images formed on 11Y, 11M, 11C, and 11BK, and 14 formed on the photosensitive drums 11Y, 11M, 11C, and 11BK, respectively. Transfer bias roller for transferring superimposed on the recording medium P the over image, 15 denotes each of the photosensitive drums 11Y, 11M, 11C, cleaning unit for collecting the untransferred toner on 11BK, a.

  Reference numeral 16 denotes a transfer belt cleaning unit that cleans the transfer belt 17, reference numeral 17 denotes a transfer belt that conveys the recording medium P so that toner images of a plurality of colors are carried on the recording medium P, and reference numeral 19 denotes the recording medium P. 1 shows an electromagnetic induction heating type fixing device that fixes a toner image (unfixed image) of the toner.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport rollers of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document D placed on the contact glass 5.

  Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light (exposure light) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (this is a charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (development process). .)
Thereafter, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the transfer belt 17. Then, the toner images of the respective colors formed on the photoconductive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the recording medium P on the transfer belt 17 at the position of the transfer bias roller 14 (transfer process). .)

Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

On the other hand, the recording medium P on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are transferred (carrying) is run in the direction of the arrow in the drawing and reaches a position facing the separation charger 18. . Then, the charge accumulated in the recording medium P is neutralized at a position facing the separation charger 18, and the recording medium P is separated from the transfer belt 17 without causing toner dust or the like.
Thereafter, the surface of the transfer belt 17 reaches the position of the transfer belt cleaning unit 16. Then, the deposit adhered on the transfer belt 17 is collected by the transfer belt cleaning unit 16.

Here, the recording medium P transported onto the transfer belt 17 is transported from the paper feeding unit 7 via the registration rollers 9 and the like.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P passes through a conveyance guide (not shown) and is guided to the registration roller 9. The recording medium P that has reached the registration roller 9 is conveyed toward the position of the transfer belt 17 in time.

The recording medium P to which the full color image has been transferred is separated from the transfer belt 17 and then guided to the fixing device 19. In the fixing device 19, the color image (toner) is fixed on the recording medium P at the nip portion between the fixing belt and the pressure roller.
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a discharge roller (not shown), and a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 19 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 19 according to the first embodiment includes a magnetic flux generator 24 (induction heating unit), a fixing belt 20 (belt member) as a fixing member, a heating roller 22 (roller member), and a fixing assist. It comprises a roller 21 (roller member), a pressure roller 30 as a pressure member, a magnetic flux control member 28, a magnetic flux shielding member 29, and the like.

  Here, the fixing auxiliary roller 21 has an outer diameter of about 30 to 40 mm, and a heat-resistant elastic layer such as silicone rubber is formed in a solid or foamed state on the surface of a cored bar made of stainless steel, carbon steel, or the like. It is a thing. The elastic layer of the fixing auxiliary roller 21 is formed to have a thickness of about 3 to 10 mm and an Asker hardness of about 10 to 50 degrees. The auxiliary fixing roller 21 is in pressure contact with the pressure roller 30 (pressure member) via the fixing belt 20 (fixing member) to form a nip portion (fixing nip) where the recording medium P is conveyed. The fixing auxiliary roller 21 rotates in the clockwise direction in FIG. 2 as the fixing belt 20 travels in the arrow direction.

The heating roller 22 is a roller member having a hollow structure. The heating roller 22 is in contact with the fixing belt 20 and rotates in a predetermined direction (clockwise in FIG. 2) by the magnetic flux generated from the magnetic flux generator 24. The fixing belt 20 is heated by being directly (or indirectly) heated. The heating roller 22 includes at least a nonmagnetic layer formed of a nonmagnetic material such as nonmagnetic stainless steel (for example, SUS304) or a liquid crystal polymer that is a high heat resistant resin, and can transmit magnetic flux. It is formed as follows.
Specifically, in the first embodiment, the heating roller 22 is a nonmagnetic material having an outer diameter of about 20 to 30 mm and formed of SUS304 that is a nonmagnetic material. The heating roller 22 may be configured to be indirectly heated by a magnetic flux control member 28 that is electromagnetically heated by the magnetic flux of the magnetic flux generator 24. Further, a copper layer having a layer thickness of about 3 to 15 μm can be formed on the outer peripheral surface of the heating roller 22, and a Ni plating layer (rust preventive layer) can be further formed on the surface.
In the first embodiment, the heating roller 22 includes a magnetic flux control member 28 and a magnetic flux shielding member in order to prevent overheating of the fixing belt 20 by self-temperature controllability (self-temperature control function). 29, which will be described in detail later.

The fixing belt 20 as a fixing member is stretched and supported by a heating roller 22 and a fixing auxiliary roller 21 (two roller members). The fixing belt 20 travels in a predetermined direction (the arrow direction in FIG. 2 and is the clockwise direction) to heat and fix the toner image on the recording medium P. The pressure belt A nip portion between which the recording medium P is conveyed is formed. Thus, all the members (the heating roller 22, the fixing auxiliary roller 21, and the pressure roller 30) that contact the fixing belt 20 rotate at a constant speed together with the fixing belt 20, so that the fixing belt 20 slides locally. The dynamic resistance does not increase, and the members 20 to 22 and 30 are less likely to be deteriorated in wear, and the fixing belt 20 is less likely to be heated due to the belt.
Specifically, the fixing belt 20 (fixing member) has a base layer (base material), an elastic layer, and a release layer (surface layer) laminated from the inner peripheral surface side. The base layer of the fixing belt 20 is formed of a material having sufficient heat resistance in addition to mechanical strength and flexibility as a belt member, and specifically, an insulating and heat resistant resin material. A layer having a thickness of about 30 to 200 μm formed of polyimide, polyimide amide, PEEK, PES, PPS, fluororesin, or the like can be used.
The elastic layer of the fixing belt 20 is provided mainly for forming a uniform fixed image without gloss unevenness, and is formed of silicone rubber or fluorosilicone rubber, and has a rubber hardness (Asker hardness) of 5 to 50 degrees. The layer thickness of about 50 to 500 μm can be used.

  The release layer of the fixing belt 20 includes tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP). ), A mixture of these fluororesins, and those obtained by dispersing these fluororesins in a heat-resistant resin. At this time, in order to achieve both releasability and flexibility, the layer thickness of the release layer is preferably set to about 5 to 50 μm (preferably 10 to 30 μm).

If necessary, a primer layer may be provided between the layers of the fixing belt 20, and a layer for improving durability during sliding may be provided further on the inner peripheral surface side than the base layer. Furthermore, a heat generating layer (for example, a copper layer having a layer thickness of about 3 to 15 μm) that is electromagnetically heated by magnetic flux generated by the magnetic flux generator 24 can be provided on the base layer.
In the first embodiment, the fixing belt 20 is stretched and supported by the two roller members of the heating roller 22 and the auxiliary fixing roller 21. However, the fixing belt 20 is configured by the heating roller 22 and the auxiliary fixing roller. It is also possible to configure such that it is stretched and supported by three or more roller members including 21.

  A pressure roller 30 as a pressure member is formed on a cylindrical member 32 (core metal) made of aluminum, copper or the like, an elastic layer 31 made of silicone rubber or the like, and a release layer (not shown) made of fluororesin or the like. ), Are laminated. The elastic layer 31 of the pressure roller 30 is formed to have a thickness of about 0.3 to 5 mm and an Asker hardness of about 20 to 50 degrees. The release layer of the pressure roller 30 is formed so that the layer thickness is about 10 to 100 μm. The pressure roller 30 is in pressure contact with the auxiliary fixing roller 21 via the fixing belt 20. Then, the recording medium P is conveyed to a contact portion (a nip portion) between the fixing belt 20 and the pressure roller 30.

  The magnetic flux generator 24 generates magnetic flux and faces the outer peripheral surface of the heating roller 22 (within a range of about 1/4 to 1/2 with respect to the entire circumference) via the fixing belt 20. ing. The magnetic flux generation unit 24 includes a coil unit 25 (excitation coil), a core unit 26 (arch core), a coil guide 27, and the like. The coil portion 25 is a litz wire (for example, a wire diameter with an insulation coating of 0) obtained by bundling fine wires on a coil guide 27 disposed so as to cover a part of the outer periphery of the heating roller 22 via the fixing belt 20. About 50 to 500 twisted wires of about 0.05 to 0.2 mm) and wound in the width direction (in the direction perpendicular to the paper in FIG. 2). It is. The coil guide 27 is made of a material such as highly heat-resistant PET or liquid crystal polymer, and holds the coil portion 25. The core portion 26 is made of a soft magnetic material (for example, Mn—Zn ferrite, Ni—Zn ferrite, permalloy, etc.) having a small coercive force, a high magnetic permeability, and a high electrical resistivity. A center core 26a and a side core 26b are provided in order to form an efficient magnetic flux. The core part 26 is installed so as to face the coil part 25 extending in the width direction.

  Although not shown, a thermistor is in contact with the surface of the fixing belt 20. The thermistor is a temperature sensitive element with high thermal responsiveness, and detects the temperature on the fixing belt 20 (fixing temperature). And the amount of heating by the magnetic flux generation part 24 is adjusted based on the detection result by the thermistor.

Here, as shown in FIG. 2, in the fixing device 19 in the first embodiment, a magnetic flux control member 28 and a magnetic flux shielding member 29 are fixed in a non-rotating manner inside the heating roller 22.
The magnetic flux control member 28 has a part in the circumferential direction of the inner peripheral surface of the heating roller 22 (a facing range of the heating roller 22 facing the magnetic flux generation unit 24) so that the heating roller 22 is interposed between the magnetic flux control member 28 and the magnetic flux generation unit 24. This is a range corresponding to. Specifically, the magnetic flux control member 28 is formed in a substantially semi-cylindrical shape so as to have a substantially arc-shaped cross-sectional shape so as to follow the shape of the inner peripheral surface of the heating roller 22, and is slightly in contact with the heating roller 22. They are arranged to face each other with a gap.
The magnetic flux control member 28 is formed such that the flow path of the magnetic flux generated from the magnetic flux generator 24 and transmitted through the heating roller 22 can be varied. Specifically, the magnetic flux control member 28 is a magnetic body (a magnetic shunt alloy) formed so that the Curie temperature becomes 100 to 250 ° C., and controls the magnetic flux when the temperature reaches the Curie temperature. It is a member to do.
Specifically, in Embodiment 1, the magnetic flux control member 28 is formed of a magnetic shunt alloy such as an iron-nickel alloy, a copper-nickel alloy, or a nickel-iron-chromium alloy. The magnetic flux control member 28 made of a magnetic shunt alloy can obtain a desired Curie temperature by adjusting the amount of each material added and the processing conditions. Further, the substantially semi-cylindrical (substantially arched) magnetic flux control member 28 can be formed relatively easily and at low cost by subjecting a plate-shaped magnetic shunt alloy to press working, bending work or the like. In addition, the substantially semi-cylindrical (substantially arched) magnetic flux control member 28 is compared with the case where the magnetic flux control member is formed in a substantially cylindrical shape so as to face the entire circumferential direction of the inner peripheral surface of the heating roller 22. In addition, since the amount of the magnetic shunt alloy (material) to be used can be reduced, the component cost can be relatively reduced. Further, since the magnetic flux control member 28 fixed to the apparatus in a non-rotating manner is not in contact with the rotating heating roller 22, it is possible to reliably prevent the heating roller 22 and the magnetic flux control member 28 from being worn out. .

The magnetic flux shielding member 29 faces the magnetic flux control member 28 so that the magnetic flux control member 28 is interposed between the magnetic roller 28 and the heating roller 22. Specifically, the magnetic flux shielding member 29 is formed in a substantially semi-cylindrical shape (substantially arched) so as to have a substantially arc-shaped cross-sectional shape along the shape of the inner peripheral surface of the heating roller 22 via the magnetic flux control member 28. In this case, the magnetic flux control member 28 is disposed so as to be in non-adhesive contact.
The magnetic flux shielding member 29 is when the magnetic flux generated from the magnetic flux generator 24 and transmitted through the heating roller 22 further passes through the magnetic flux control member 28 (when the temperature of the magnetic flux control member 28 exceeds the Curie temperature). ) To shield the magnetic flux. Specifically, the magnetic flux shielding member 29 has a thickness of about 0.6 to 2.0 mm and is made of a nonmagnetic material such as aluminum having a large magnetic loss. Further, the substantially semi-cylindrical (substantially arched) magnetic flux shielding member 29 can be formed very simply and at low cost by subjecting the sheet metal to press working, bending work or the like.
As described above, the magnetic flux control member 28 having a predetermined Curie temperature (Curie point) is provided close to the heating roller 22, and the magnetic flux shielding member 29 is provided close to the magnetic flux control member 28, thereby ensuring a self-temperature control function. Thus, the fixing belt 20 (heating roller 22) is heated without being excessively heated by electromagnetic induction.

The fixing device 19 configured as described above operates as follows.
When the auxiliary fixing roller 21 is driven to rotate clockwise in FIG. 2 by a drive motor (not shown), the fixing belt 20 and the heating roller 22 are also rotated in the clockwise direction, and the pressure roller 30 is driven in the counterclockwise direction. Rotate. The fixing belt 20 as a fixing member is heated by the magnetic flux generated from the magnetic flux generator 24 at a position facing the magnetic flux generator 24.

  Specifically, the magnetic field lines are formed so as to alternately switch in both directions in the loop of the coil unit 25 by flowing a high-frequency alternating current of 10 kHz to 1 MHz from the power source unit (not shown) to the coil unit 25. By forming the alternating magnetic field in this way, an eddy current is generated in the heating roller 22 (and the magnetic flux control member 28), Joule heat is generated, and the heating roller 22 (and the magnetic flux control member 28) is electromagnetically induced. Heated. The fixing belt 20 receives heat from the heated heating roller 22 and is heated.

Thereafter, the surface of the fixing belt 20 heated by the magnetic flux generator 24 reaches a contact portion (nip portion) with the pressure roller 30. Then, the toner image T (toner) on the recording medium P conveyed to the nip portion is heated and melted.
The surface of the fixing belt 20 that has passed through the fixing position then reaches the position facing the magnetic flux generator 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed into the nip portion between the fixing belt 20 and the pressure roller 30 while being guided by a guide plate (not shown) ( It is the movement in the conveyance direction of the broken line arrow Y1.) The toner image T is fixed on the recording medium P by the heat received from the fixing belt 20 and the pressure received from the pressure roller 30, and the recording medium P is sent out from the nip portion between the fixing belt 20 and the pressure roller 30. .
On the other hand, the surface of the fixing belt 20 that has passed through the nip portion thereafter reaches the position facing the magnetic flux generation portion 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

In such a fixing process, when the temperature of the magnetic flux control member 28 exceeds the Curie temperature, the heat generation of the heating roller 22 is limited.
That is, when the temperature of the magnetic flux control member 28 heated by the magnetic flux generation unit 24 exceeds the Curie temperature, the magnetic flux control member 28 loses magnetism, and eddy currents are generated near the surface of the heating roller 22. Limited. Thereby, the generation amount of Joule heat in the heating roller 22 is reduced, and excessive temperature rise is suppressed.
Specifically, when the temperature of the magnetic flux control member 28 does not reach the Curie temperature, the magnetic flux generated from the magnetic flux generator 24 passes from the heating roller 22 through the inside of the magnetic flux control member 28 and again passes through the heating roller 22. Thus, a flow path (magnetic path) returning to the magnetic flux generation unit 24 is drawn. As a result, the heating roller 22 is heated by electromagnetic induction and rises to a predetermined temperature. On the other hand, when the temperature of the magnetic flux control member 28 reaches the Curie temperature, the magnetic flux generated from the magnetic flux generator 24 penetrates the magnetic flux control member 28 from the heating roller 22 and passes through the magnetic flux shield member 29. Such a flow path (magnetic path) is drawn. At this time, since the magnetic flux is shielded by the magnetic flux shielding member 29, the heating roller 22 is not heated by electromagnetic induction, and the heating roller 22 (fixing belt 20) is prevented from being overheated. In the first embodiment, the Curie temperature of the magnetic flux control member 28 is set so that the temperature (fixing temperature) of the fixing belt 20 is about 170 ° C.

  As described above, in the first embodiment, the heating roller 22 is interposed between the heating roller 22 that contacts the fixing belt 20 (fixing member) and heats the fixing belt 20 and the magnetic flux generator 24. The magnetic flux control member 28 that opposes a part of the inner peripheral surface of the heating roller 22 in the circumferential direction and the magnetic flux generated from the magnetic flux generator 24 and transmitted through the heating roller 22 pass through the magnetic flux control member 28. And a magnetic flux shielding member 29 for shielding the magnetic field. As a result, the cost of the magnetic flux control member 28 is relatively low, and it is possible to make it difficult to cause a problem that the fixing belt 20 is worn and deteriorated or a problem that the fixing belt 20 is unevenly heated.

  In the first embodiment, the magnetic flux shielding member 28 is disposed in a non-contact manner with respect to the heating roller 22. However, the magnetic flux shielding member 28 may be disposed in contact with the heating roller 22. Even in such a case, since the heating roller 22 is formed of a metal material, the heating roller 22 is slid by contact with the magnetic flux shielding member as compared with the case where the magnetic flux shielding member is slidably contacted with the soft fixing belt. The degree of wear deterioration is very small.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 3A is a cross-sectional view showing a state when the fixing device 19 in the second embodiment is started up, and FIG. 3B is a view showing a state after the fixing device 19 is started up. FIG. 4 is a perspective view showing a magnetic flux control member 28 installed in the fixing device 19 as a modification thereof.
The fixing device 19 in the second embodiment is different from that in the first embodiment in that a plurality of magnetic flux control members 28A and 28B are arranged in the circumferential direction.

  Referring to FIG. 3, the fixing device 19 according to the second embodiment also has a magnetic flux generator 24, a fixing belt 20 (fixing member), a heating roller 22, and a fixing auxiliary roller 21, as in the first embodiment. , A pressure roller 30 (pressure member), magnetic flux control members 28A and 28B, a magnetic flux shielding member 29, and the like.

Here, the fixing device 19 according to the second embodiment is different from the first embodiment in that two magnetic flux control members 28A and 28B having different Curie temperatures are arranged in parallel in the circumferential direction.
When the fixing device 19 is started up (when the fixing temperature is raised from a sufficiently low state, such as when the main power supply of the apparatus main body 1 is turned on), the magnetic flux control member having a high Curie temperature (the first temperature control member). 1 magnetic flux control member 28A) is opposed to the magnetic flux generator 24 via the heating roller 22 and the fixing device 19 is started up (after the fixing temperature is sufficiently raised). The magnetic flux control member (the second magnetic flux control member 28 </ b> B) having a low temperature is configured to be movable in the circumferential direction so as to face the magnetic flux generator 24 via the heating roller 22.

Specifically, the two magnetic flux control members 28A and 28B are both made of a magnetic shunt alloy, but the addition amount of each material and processing conditions are different, and the Curie temperature of the first magnetic flux control member 28A is It is formed to be higher than the Curie temperature of the second magnetic flux control member 28B. Specifically, the Curie temperature of the first magnetic flux control member 28A is set to a temperature higher than the target fixing temperature (about 170 ° C.), and the Curie temperature of the second magnetic flux control member 28B is set to the target fixing temperature ( It is about 170 ° C.) It is set in the vicinity.
The first magnetic flux control member 28A is installed on the upstream side with respect to the rotation direction of the heating roller 22, and the second magnetic flux control member 28B is installed adjacent to the downstream side with respect to the first magnetic flux control member 28A. Has been. A magnetic flux shielding member 29 is installed on the inner peripheral surface side of the two magnetic flux control members 28A and 28B so as to come into contact with both magnetic flux control members 28A and 28B. The magnetic flux control members 28A and 28B, together with the magnetic flux shielding member 29, are configured to be rotatable in the clockwise and counterclockwise directions in FIG. 3 by a rotation mechanism (not shown) regardless of the rotation of the heating roller 22. Yes.

  When the fixing device 19 is started up, as shown in FIG. 3A, the rotation mechanism is configured so that the first magnetic flux control member 28A having a high Curie temperature faces the magnetic flux generator 24 via the heating roller 22. As a result, the magnetic flux control members 28A and 28B and the magnetic flux shielding member 29 are rotated. On the other hand, after the fixing device 19 is started up, the second magnetic flux control member 28B having a low Curie temperature is opposed to the magnetic flux generator 24 via the heating roller 22, as shown in FIG. In addition, the magnetic flux control members 28A and 28B and the magnetic flux shielding member 29 are rotated by the rotation mechanism.

As a result, at the time of start-up where a shortening of the start-up time is required, the threshold at which self-temperature control acts is set high, and the fixing belt 20 (heating roller 22) can be rapidly heated. In addition, after the start-up, rapid temperature rise is unnecessary and it is desired to prevent over-temperature rise with good responsiveness. Therefore, the threshold at which the self-temperature control acts is set near the target fixing temperature.
With such a configuration and operation, the fixing device 19 according to the second embodiment has a start-up time (warm-up) while preventing overheating of the fixing belt 20 equally as compared with the first embodiment. Time).
While rapid temperature rise is required at startup, self-temperature control as after startup is not necessarily required. Therefore, as the first magnetic flux control member 28A, a magnetic material having a roughly high Curie temperature, such as ferrite, can be used instead of the magnetic shunt alloy having a desired Curie temperature.

Here, in the second embodiment, referring to FIG. 4, a plurality of magnetic flux control members 28 having the same Curie temperature and different lengths in the width direction (in the direction of the double arrow in FIG. 4). The magnetic flux control members 28A and 28B arranged in parallel in the circumferential direction can also be used. In that case, the magnetic flux control member having a length in the width direction corresponding to the size in the width direction of the recording medium P conveyed to the nip portion (fixing nip) is opposed to the magnetic flux generation portion 24 via the heating roller 22. It is configured to be movable in the circumferential direction.
Specifically, referring to FIG. 4, the two magnetic flux control members 28A and 28B both have a Curie temperature at the center portion in the width direction (sheet passing portions 28A1 and 28B1) at both end portions in the width direction (non-passage). The paper portions 28A2 and 28B2) are formed so as to be higher than the Curie temperature. Specifically, the Curie temperature of the paper passing portions 28A1 and 28B1 is set near or higher than the target fixing temperature (about 170 ° C.), and the Curie temperature of the non-paper passing portions 28A2 and 28B2 is the target temperature. It is set at a temperature lower than the fixing temperature or near the fixing temperature.
In the first magnetic flux control member 28A, the paper passing portion 28A1 corresponds to a paper passing area of small size paper (for example, a postcard size recording medium P), and the non-paper passing portion 28A2 is small size paper. It is formed so as to correspond to the non-sheet passing area. On the other hand, in the second magnetic flux control member 28B, the paper passing portion 28B1 corresponds to the paper passing area of large size paper (for example, A4 size recording medium P), and the non-paper passing portion 28B2 is large. It is formed so as to correspond to a non-sheet passing region of size paper.
The first magnetic flux control member 28A is installed on the upstream side with respect to the rotation direction of the heating roller 22, and the second magnetic flux control member 28B is installed adjacent to the downstream side with respect to the first magnetic flux control member 28A. Has been. Although not shown, a magnetic flux shielding member 29 is installed on the inner peripheral surface side of the two magnetic flux control members 28A and 28B so as to contact both magnetic flux control members 28A and 28B. The magnetic flux control members 28A and 28B, together with the magnetic flux shielding member 29, are configured to be rotatable in the clockwise and counterclockwise directions in FIG. 3 by a rotation mechanism (not shown) regardless of the rotation of the heating roller 22. Yes.

  Then, when the small size paper is passed, the magnetic flux control member 28A, by the rotation mechanism so that the first magnetic flux control member 28A corresponding to the small size paper faces the magnetic flux generation unit 24 via the heating roller 22. 28B and the magnetic flux shielding member 29 are rotated. On the other hand, when large-size paper is passed, the rotation mechanism controls the magnetic flux so that the second magnetic flux control member 28B corresponding to the large-size paper faces the magnetic flux generator 24 via the heating roller 22. The members 28A and 28B and the magnetic flux shielding member 29 are rotated.

Thus, even when the recording medium P having a different size in the width direction is passed (especially during continuous feeding), the heat of the non-sheet passing area of the fixing belt 20 (heating roller 22) is recorded. It is possible to prevent a problem that the non-sheet passing area is excessively heated without being taken away by the medium P. That is, the rotational positions of the magnetic flux control members 28A and 28B are determined so as to match the non-sheet passing area of the recording medium P having different sizes, and the self-temperature control is surely performed in the portion corresponding to the non-sheet passing area of the recording medium P. Therefore, it is possible to prevent an excessive temperature rise in the non-sheet passing region in the fixing belt 20 (heating roller 22).
It should be noted that the self-temperature controllability as in the non-sheet-passing portions 28A2 and 28B2 is not necessarily required since the sheet passing portions 28A1 and 28B1 are not easily heated due to the recording medium P and are not heated excessively. Therefore, as the paper passing portions 28A1 and 28B1, a magnetic material having a roughly high Curie temperature such as ferrite can be used instead of the magnetic shunt alloy having a desired Curie temperature.

  As described above, also in the second embodiment, similarly to the first embodiment, the heating roller 22 that contacts the fixing belt 20 (fixing member) and heats the fixing belt 20, the magnetic flux generation unit 24, and the like. Magnetic flux control members 28A and 28B facing a part in the circumferential direction of the inner peripheral surface of the heating roller 22 so that the heating roller 22 is interposed therebetween, and the magnetic flux generated from the magnetic flux generator 24 and transmitted through the heating roller 22 Includes a magnetic flux shielding member 29 that shields the magnetic flux when the magnetic flux passes through the magnetic flux control members 28A and 28B. As a result, the costs of the magnetic flux control members 28A and 28B are relatively low, and it is possible to make it difficult to cause a problem that the fixing belt 20 is worn and deteriorated or a problem that the fixing belt 20 is unevenly heated.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 5 is a configuration diagram illustrating a main part of the fixing device 19 according to the third embodiment, and corresponds to FIG. 3 according to the second embodiment.
The fixing device 19 according to the third embodiment is different from that according to the first embodiment in that the magnetic flux shielding member 29 is movably moved toward and away from the magnetic flux control member 28.

  Referring to FIG. 5, the fixing device 19 in the third embodiment also has a magnetic flux generator 24, a fixing belt 20 (fixing member), a heating roller 22, and a fixing auxiliary roller 21, as in the above embodiments. , A pressure roller 30 (pressure member), a magnetic flux control member 28, a magnetic flux shielding member 29, and the like.

Here, the fixing device 19 in the third embodiment is different from that in the first embodiment when the magnetic flux shielding member 29 is other than that when the fixing device 19 (image forming apparatus 1) is started up ( It is configured to be movable so as to be separated from the magnetic flux control member 28 that is in a contact state (the state of FIG. 2) mainly during the fixing step.
Specifically, the magnetic flux shielding member 29 is configured to be movable so as to be able to contact and separate from the magnetic flux control member 28 by a moving mechanism (not shown). When the apparatus is started up, as shown in FIG. 5, when the magnetic flux shielding member 29 moves away from the magnetic flux control member 28 in the direction of the black arrow and is separated, the magnetic flux control member 28 reaches the Curie temperature. The self-temperature control function is reduced. On the other hand, after the fixing device 19 is started up and in the normal fixing process (when paper is passed), the magnetic flux shielding member 29 that has been separated is in contact with the magnetic flux control member 28 (FIG. 2). The self-temperature control function when the magnetic flux control member 28 reaches the Curie temperature is secured.

As a result, at the time of start-up where a shortening of the start-up time is required, the self-temperature control is set so as not to act easily, and the fixing belt 20 (heating roller 22) can be rapidly heated. In addition, after the start-up, rapid temperature rise is unnecessary and it is desired to prevent excessive temperature rise with good responsiveness, so that the self-temperature control is set to act reliably.
With such a configuration and operation, the fixing device 19 according to the third embodiment has a startup time (warm-up) while preventing overheating of the fixing belt 20 as compared with the first embodiment. Time).
In order to prevent local deformation of the pressure roller 30 and the auxiliary fixing roller 21, a moving mechanism for separating the pressure roller 30 from the fixing belt 20 when not in operation is installed. By using the moving mechanism to perform the above-described contact / separation operation of the magnetic flux shielding member 29, the apparatus is made compact.

In the present embodiment, the magnetic flux shielding member 29 is configured to move away from the magnetic flux control member 28 that is in a contact state at other times when the apparatus is started up.
On the other hand, at the time of starting up the apparatus, the magnetic flux shielding member 29 can be moved so that the separation distance from the magnetic flux control member 28 that is in a non-contact state at other times becomes large. That is, at the time of normal paper passing (during the fixing process), the magnetic flux shielding member 29 is spaced apart from the magnetic flux control member 28 with a slight gap so that the self-temperature control function of the magnetic flux control member 28 is ensured. doing. Then, when the apparatus is started up, the magnetic flux shielding member 29 is moved so that the separation distance is increased so that the self-temperature control of the magnetic flux control member 28 becomes difficult to act.
Even in this case, the same effect as that of the third embodiment can be obtained.

  As described above, also in the third embodiment, the heating roller 22 that contacts the fixing belt 20 (fixing member) and heats the fixing belt 20, the magnetic flux generation unit 24, and the like, as in the above embodiments. The magnetic flux control member 28 that opposes a part of the inner circumferential surface of the heating roller 22 in the circumferential direction so that the heating roller 22 is interposed therebetween, and the magnetic flux generated from the magnetic flux generator 24 and transmitted through the heating roller 22 is the magnetic flux. And a magnetic flux shielding member 29 that shields the magnetic flux when transmitted through the control member 28. As a result, the cost of the magnetic flux control member 28 is relatively low, and it is possible to make it difficult to cause a problem that the fixing belt 20 is worn and deteriorated or a problem that the fixing belt 20 is unevenly heated.

Embodiment 4 FIG.
6 and 7, the fourth embodiment of the present invention will be described in detail.
FIG. 6 is a perspective view showing the magnetic flux control member 28 of the fixing device 19 according to the fourth embodiment. FIG. 7 is a perspective view showing a magnetic flux control member 28 as a modification thereof.
The fixing device 19 in the fourth embodiment is different from that in the first embodiment in that a plurality of slits 28 a are formed in the magnetic flux control member 28.

  In the fixing device 19 according to the fourth embodiment, the magnetic flux generator 24, the fixing belt 20 (fixing member), the heating roller 22, the fixing auxiliary roller 21, and the pressure roller 30 (additional roller) are also provided in the same manner as in the above embodiments. Pressure member), a magnetic flux control member 28, a magnetic flux shielding member 29, and the like.

Here, referring to FIG. 6, the fixing device 19 in the fourth embodiment is different from that in the first embodiment in that a plurality of slits 28 a are formed in the magnetic flux control member 28 in the width direction. .
Thus, as shown in FIG. 6, the eddy current X that flows when the magnetic flux control member 28 is electromagnetically heated by the magnetic flux generator 24 is formed so as to circulate around the entire surface of the magnetic flux control member 28. However, it is formed so as to circulate within a small width region partitioned by the slits 28a. Thus, by making the eddy current X small, the heating loss due to the eddy current is reduced, and the heating efficiency of the magnetic flux control member 28 can be increased.

In the fourth embodiment, as shown in FIG. 7, the magnetic flux control member 28 can be divided into a plurality of parts in the width direction. That is, the magnetic flux control member 28 can also be configured by a divided magnetic flux control unit 28b that is divided into a plurality (seven in the example of FIG. 7) in the width direction.
Even in such a case, as shown in FIG. 7, the eddy current X flowing when the magnetic flux control member 28 is electromagnetically heated by the magnetic flux generator 24 circulates around the entire surface of the magnetic flux control member 28. Instead of being formed, the divided magnetic flux control unit 28b is formed so as to circulate in a region having a small width, so that the heating loss due to the eddy current is reduced, and the magnetic flux control member The heating efficiency of 28 can be increased.
In the example of FIG. 7, the entire magnetic flux control member 28 can be configured as one member by providing and connecting an insulating member between the adjacent divided magnetic flux control unit 28 b and the divided magnetic flux control unit 28 b. .

  As described above, also in the fourth embodiment, the heating roller 22 that contacts the fixing belt 20 (fixing member) and heats the fixing belt 20, the magnetic flux generation unit 24, and the like, as in the above embodiments. The magnetic flux control member 28 that opposes a part of the inner circumferential surface of the heating roller 22 in the circumferential direction so that the heating roller 22 is interposed therebetween, and the magnetic flux generated from the magnetic flux generator 24 and transmitted through the heating roller 22 is the magnetic flux. And a magnetic flux shielding member 29 that shields the magnetic flux when transmitted through the control member 28. As a result, the cost of the magnetic flux control member 28 is relatively low, and it is possible to make it difficult to cause a problem that the fixing belt 20 is worn and deteriorated or a problem that the fixing belt 20 is unevenly heated.

Embodiment 5. FIG.
A fifth embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 8 is a configuration diagram illustrating a main part of the fixing device 19 according to the fifth embodiment, and corresponds to FIG. 3 according to the second embodiment. FIG. 9 is a block diagram showing a main part of a fixing device 19 as a modified example, and FIG. 10 is a block diagram showing a fixing device 19 as still another modified example.
The fixing device 19 according to the fifth embodiment is different from that according to the first embodiment in that the magnetic flux control member 28 and the magnetic flux shielding member 29 are disposed so as to face the outer peripheral surface side of the fixing belt 20. Is different.

  In the fixing device 19 according to the fifth embodiment, the magnetic flux generator 24, the fixing belt 20 (fixing member), the heating roller 22, the fixing auxiliary roller 21, and the pressure roller 30 (heating roller) are added in the same manner as in the above embodiments. Pressure member), a magnetic flux control member 28, a magnetic flux shielding member 29, and the like.

Here, referring to FIG. 8, the fixing device 19 in the fifth embodiment differs from that in the first embodiment in that the magnetic flux control member 28 (and the magnetic flux shielding member 29) is connected to the magnetic flux generator 24. The heating roller 22 is opposed to a part of the outer circumferential surface of the heating roller 22 in the circumferential direction so as to have a substantially arc-shaped cross-sectional shape so as to follow the shape of the outer circumferential surface of the heating roller 22. Is formed. That is, the magnetic flux control member 28 and the magnetic flux shielding member 29 are fixed on the outer peripheral surface side of the heating roller 22, and the magnetic flux generator 24 is fixed on the inner peripheral surface side of the heating roller 22.
Even when configured in this manner, substantially the same effects as those of the first embodiment can be obtained.

As a modification of the fixing device 19 in the first embodiment, as shown in FIG. 9, a plurality of substantially rectangular parallelepiped magnetic fluxes instead of one substantially semi-cylindrical magnetic flux control member 28 and magnetic flux shielding member 29. The control member 28 and the magnetic flux shielding member 29 can be juxtaposed in the circumferential direction.
Even when configured in this manner, substantially the same effects as those of the first embodiment can be obtained. In particular, since the substantially rectangular parallelepiped magnetic flux control member 28 and the magnetic flux shielding member 29 have very simple shapes, their manufacturing costs (processing costs) can be further reduced.

As a modification of the fixing device 19 in the first embodiment, as shown in FIG. 10, a fixing roller 23 can be used as a fixing member instead of using the fixing belt 20 as a fixing member. The fixing roller 23 has a layer as a fixing member formed on the outer peripheral surface of the heating roller 22 in the first embodiment, and the fixing member and the heating roller are integrated.
Specifically, the fixing roller 23 is a roller member having a hollow structure, and is a cylindrical body formed of a non-magnetic material such as SUS304 (a portion corresponding to the heating roller 22 in the first embodiment, which is a fixing belt). The elastic layer and the release layer are laminated on top of each other (the portion corresponding to the fixing belt 20 in the first embodiment). A substantially semi-cylindrical magnetic flux control member 28 and a magnetic flux shielding member 29 are installed on the inner peripheral surface side of the fixing roller 23, and a magnetic flux generator 24 is installed on the outer peripheral surface side of the fixing roller 23. .
When the fixing roller 23 is rotationally driven in the clockwise direction in FIG. 10 by a drive motor (not shown), the pressure roller 30 is also rotated in the counterclockwise direction. The fixing roller 23 is electromagnetically heated by the magnetic flux generated from the magnetic flux generation unit 24 at a position facing the magnetic flux generation unit 24 and is recorded at the position of the nip portion (fixing nip) with the pressure roller 30. The toner image T on P is fixed by heating and melting.
Even when configured in this manner, substantially the same effects as those of the first embodiment can be obtained.

  As described above, also in the fifth embodiment, the heating roller 22 that contacts the fixing belt 20 and heats the fixing belt 20 (or the fixing roller 23 in which the fixing member and the heating roller are integrated); Generated from the magnetic flux generation member 24 and the magnetic flux control member 28 facing a part in the circumferential direction of the outer circumferential surface (or inner circumferential surface) of the heating roller 22 so that the heating roller 22 is interposed between the magnetic flux generation unit 24 and the magnetic flux generation unit 24. A magnetic flux shielding member 29 is provided for shielding the magnetic flux when the magnetic flux transmitted through the heating roller 22 passes through the magnetic flux control member 28. As a result, the cost of the magnetic flux control member 28 is relatively low, and it is possible to make it difficult to cause a problem that the fixing belt 20 is worn and deteriorated or a problem that the fixing belt 20 is unevenly heated.

  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 embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

  In the present specification and the like, the “width direction” is defined as a direction orthogonal to the conveyance direction of the recording medium P and a direction that coincides with the rotation axis direction of the heating roller.

1 image forming apparatus (image forming apparatus main body),
19 fixing device,
20 fixing belt (fixing member),
21 Fixing auxiliary roller (roller member),
22 Heating roller (roller member),
23 fixing roller (fixing member, heating roller),
24 Magnetic flux generation part (induction heating part),
28 magnetic flux control member,
28A first magnetic flux control member, 28B second magnetic flux control member,
28A1, 28B1 Paper passing part, 28A2, 28B2 Non-paper passing part,
28a slit,
28b split magnetic flux control unit,
29 magnetic flux shielding member,
30 Pressure roller (pressure member), P recording medium.

JP 2008-46531 A JP 2010-2603 A JP 2012-3187 A

Claims (10)

A fixing member that forms a nip portion between which the recording medium is conveyed and a pressure member, travels in a predetermined direction, heats the toner image, and fixes the toner image to the recording medium;
A magnetic flux generator for generating magnetic flux,
A heating roller that has a hollow structure, contacts the fixing member, rotates in a predetermined direction, and is heated directly or indirectly by the magnetic flux generated from the magnetic flux generation unit to heat the fixing member;
It is generated from the magnetic flux generator and passes through the heating roller so as to face a part of the inner circumferential surface or outer circumferential surface of the heating roller so that the heating roller is interposed between the magnetic flux generator and the magnetic flux generator. A magnetic flux control member formed so that the flow path of the magnetic flux can be varied;
When the magnetic flux generated from the magnetic flux generator and transmitted through the heating roller is transmitted through the magnetic flux control member so as to face the magnetic flux control member so that the magnetic flux control member is interposed between the magnetic roller and the heating roller. A magnetic flux shielding member that shields the magnetic flux;
Equipped with a,
The magnetic flux control member is
A plurality of magnetic flux control members having different Curie temperatures are arranged in the circumferential direction,
When the apparatus is started up, a magnetic flux control member having a high Curie temperature is opposed to the magnetic flux generation part via the heating roller, and after the apparatus is started up, a magnetic flux control member having a low Curie temperature is passed through the heating roller through the heating roller. A fixing device configured to be movable in a circumferential direction so as to face a generation unit . A fixing member that forms a nip portion between which the recording medium is conveyed and a pressure member, travels in a predetermined direction, heats the toner image, and fixes the toner image to the recording medium;
A magnetic flux generator for generating magnetic flux,
A heating roller that has a hollow structure, contacts the fixing member, rotates in a predetermined direction, and is heated directly or indirectly by the magnetic flux generated from the magnetic flux generation unit to heat the fixing member;
It is generated from the magnetic flux generator and passes through the heating roller so as to face a part of the inner circumferential surface or outer circumferential surface of the heating roller so that the heating roller is interposed between the magnetic flux generator and the magnetic flux generator. A magnetic flux control member formed so that the flow path of the magnetic flux can be varied;
When the magnetic flux generated from the magnetic flux generator and transmitted through the heating roller is transmitted through the magnetic flux control member so as to face the magnetic flux control member so that the magnetic flux control member is interposed between the magnetic roller and the heating roller. A magnetic flux shielding member that shields the magnetic flux;
With
The magnetic flux control member is
A plurality of magnetic flux control members having the same Curie temperature and different lengths in the width direction are arranged in parallel in the circumferential direction,
A magnetic flux control member having a length in the width direction corresponding to the size in the width direction of the recording medium conveyed to the nip portion is configured to be movable in the circumferential direction so as to face the magnetic flux generation portion via the heating roller. A fixing device characterized by that. The magnetic flux shielding member moves away from the magnetic flux control member that is in a contact state at other times when the apparatus is started up, or the magnetic flux that is in a non-contact state at other times. The fixing device according to claim 1, wherein the fixing device moves so as to increase a separation distance from the control member. A fixing member that forms a nip portion between which the recording medium is conveyed and a pressure member, travels in a predetermined direction, heats the toner image, and fixes the toner image to the recording medium;
A magnetic flux generator for generating magnetic flux,
A heating roller that has a hollow structure, contacts the fixing member, rotates in a predetermined direction, and is heated directly or indirectly by the magnetic flux generated from the magnetic flux generation unit to heat the fixing member;
It is generated from the magnetic flux generator and passes through the heating roller so as to face a part of the inner circumferential surface or outer circumferential surface of the heating roller so that the heating roller is interposed between the magnetic flux generator and the magnetic flux generator. A magnetic flux control member formed so that the flow path of the magnetic flux can be varied;
When the magnetic flux generated from the magnetic flux generator and transmitted through the heating roller is transmitted through the magnetic flux control member so as to face the magnetic flux control member so that the magnetic flux control member is interposed between the magnetic roller and the heating roller. A magnetic flux shielding member that shields the magnetic flux;
With
The magnetic flux shielding member moves away from the magnetic flux control member that is in a contact state at other times when the apparatus is started up, or the magnetic flux that is in a non-contact state at other times. A fixing device which moves so as to increase a separation distance from a control member . The magnetic flux control member is formed so as to have a substantially arc-shaped cross-sectional shape so as to follow the shape of the inner peripheral surface or outer peripheral surface of the heating roller, and is disposed so as not to contact the heating roller. The fixing device according to any one of claims 1 to 4, wherein the fixing device is characterized in that: 6. The fixing device according to claim 1, wherein the magnetic flux control member is a magnetic body formed to have a Curie temperature of 100 to 250 ° C. 6.   6. The fixing according to claim 1, wherein the magnetic flux control member is formed with a plurality of slits in a width direction or divided into a plurality of slits in the width direction. apparatus.   The fixing device according to claim 1, wherein the heating roller includes at least a nonmagnetic layer formed of a nonmagnetic material. A fixing auxiliary roller that presses against the pressure member via the fixing member to form the nip portion;
The fixing device according to claim 1, wherein the fixing member is a fixing belt stretched by a plurality of roller members including at least the heating roller and the fixing auxiliary roller. .   An image forming apparatus comprising the fixing device according to claim 1.

Images