JP2008015045A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device for stably preventing excessive temperature increase of width-directional both ends in a heat generation member heated by a magnetic flux generation means, without separating a magnetic flux shielding member from a core, even if reaching a high temperature, and to provide an image forming apparatus. <P>SOLUTION: The fixing means comprises the magnetic flux generation means for generating a magnetic flux; the heat generating member 20 having a heat generation layer heated by the magnetic flux; the core 28 facing the magnetic flux generation means via the heat generating member 20; the magnetic flux shielding member 29 for varying to shield a part of the width direction of the core 28, in the heating range of the width direction of the heat generating member 20 heated by the magnetic flux; and holding members 40A and 40B for unbondedly holding the magnetic flux shielding member 29 on the outer periphery of the core 28. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 composite machine thereof, and a fixing device installed therein, and more particularly to a fixing device and an image forming apparatus using an electromagnetic induction heating method. It is.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, an electromagnetic induction heating type fixing device has been widely used for the purpose of reducing the startup time of the device and saving energy (for example, Patent Document 1). reference.).

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device includes a supporting roller (heating roller) as a heat generating member, a fixing auxiliary roller (fixing roller), a fixing belt stretched between the supporting roller and the fixing auxiliary roller, and a support. It comprises magnetic flux generating means (induction heating unit) facing the roller via the fixing belt, a pressure roller contacting the fixing auxiliary roller via the fixing belt, and the like. The magnetic flux generation means includes a coil portion extending in the width direction (a direction perpendicular to the conveyance direction of the recording medium), a core portion facing the coil portion, and the like. An inner core and a magnetic flux shielding member (shielding member) are installed inside the support roller.

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, an alternating magnetic field is formed around the coil portion, and an eddy current is generated near the surface of the support roller. When an eddy current is generated in the support roller (heat generating member), 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.
Such an electromagnetic induction heating type fixing device has higher heat conversion efficiency than other types such as a heat roller method (heater lamp heating method) because the heat generating member is directly heated by electromagnetic induction. It is known that the surface temperature (fixing temperature) of the fixing belt can be raised to a desired temperature with a small energy consumption and a short start-up time.

  Here, in Patent Document 1 or the like, in order to prevent a problem in which the both ends in the width direction of the heat generating member are excessively heated when small-size paper is continuously passed, it is provided in the support roller. The inner core and the magnetic flux shielding member are rotationally driven to change the heating range of the support roller according to the sheet passing area of the recording medium. In other words, the magnetic flux acting on the range corresponding to the non-sheet passing region in the heat generating member is shielded by the magnetic flux shielding member so that only the sheet passing region becomes the heating range.

JP 2005-258383 A

  In the conventional fixing device described above, the magnetic flux shielding member that changes the heating range of the heat generating member is bonded to the inner core with an adhesive or adhesive tape, and the magnetic flux shielding member is detached from the inner core due to a decrease in the adhesive force due to heat. There was a possibility that a malfunction would occur.

  Specifically, the magnetic flux shielding member is bonded to the surface of the inner core (core) with an adhesive or the like, and further fixed thereon with a resin tape. Therefore, when the ambient temperature of the inner core and the magnetic flux shielding member reaches a high temperature with the operation of the fixing device (induction heating unit), the adhesive force by the adhesive or the fixing force by the resin tape decreases, and the magnetic flux shielding member Sometimes left the inner core. If the magnetic flux shielding member is detached from the inner core, the original function of the magnetic flux shielding member is not exhibited. That is, when small-size paper is continuously passed, a problem arises that the both ends in the width direction of the heat generating member are excessively heated.

  The present invention has been made to solve the above-described problems, and the both ends in the width direction of the heat generating member heated by the magnetic flux generating means without the magnetic flux shielding member being detached from the core even when the temperature reaches a high temperature. It is an object of the present invention to provide a fixing device and an image forming apparatus in which excessive temperature rise is stably suppressed.

  The fixing device according to the first aspect of the present invention is a fixing device that heats and fixes a toner image to a recording medium, and includes a magnetic flux generating means for generating magnetic flux and a heat generating layer heated by the magnetic flux. And a heating range in the width direction of the heat generating member that is heated by the magnetic flux is shielded by changing a part of the core in the width direction. And a holding member for holding the magnetic flux shielding member on the outer peripheral surface of the core in a non-adhesive manner.

  The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the core includes a plurality of divided cores divided in the width direction, and the holding member is an outer periphery of the core. And a non-protruding portion that is integrated with the protruding portion and is sandwiched between two adjacent divided cores.

  According to a third aspect of the present invention, in the fixing device according to the second aspect, the magnetic flux shielding member is inserted and held in the holes of the protruding portions of the plurality of holding members. Is.

  According to a fourth aspect of the present invention, in the fixing device according to the second or third aspect, the non-projecting portion is installed on the shaft portion of the core together with the plurality of divided cores. Is.

  The fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the second to fourth aspects, wherein the plurality of divided cores are formed such that there are no gaps between adjacent divided cores. It has been done.

  According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the heating member heats the fixing member that melts the toner image.

  According to a seventh aspect of the present invention, in the fixing device according to the sixth aspect, the fixing member abuts against a pressure roller that presses a recording medium to be conveyed, and at least two roller members. The heat generating member is one of the at least two roller members, and the core is an internal core provided in the one roller member. Is.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to the seventh aspect, wherein the magnetic flux shielding member rotates integrally with the inner core so that the heating range is stepwise or continuous. It is formed so as to gradually increase or decrease.

  A fixing device according to a ninth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the heat generating member is a fixing member that melts a toner image.

  The fixing device according to a tenth aspect of the present invention is the fixing device according to the ninth aspect, wherein the fixing member is a fixing roller that contacts a pressure roller that presses a recording medium to be conveyed. The core is an internal core provided in the fixing roller.

  The fixing device according to an eleventh aspect of the present invention is the fixing device according to the ninth aspect, wherein the fixing member abuts on a pressure roller that presses a recording medium to be conveyed, and at least two roller members. A fixing belt stretched around the roller, wherein the core is an internal core provided in the roller member.

  The fixing device according to a twelfth aspect of the invention is the fixing device according to the tenth or eleventh aspect of the invention, wherein the heating range is stepped by rotating the magnetic flux shielding member integrally with the inner core. It is formed to increase or decrease gradually or continuously.

  An image forming apparatus according to a thirteenth aspect of the present invention includes the fixing device according to any one of the first to twelfth aspects.

  In the fixing device of the electromagnetic induction heating method, the present invention holds the magnetic flux shielding member non-adhered on the outer peripheral surface of the core, so that the magnetic flux shielding member does not leave the core even when the temperature reaches a high temperature. It is possible to provide a fixing device and an image forming apparatus in which excessive temperature rise at both ends in the width direction of the heat generating member heated by the magnetic flux generating means is stably suppressed.

  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.
A 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, reference numeral 1 denotes an apparatus main body of a tandem color copier as an image forming apparatus, 2 a writing unit that emits laser light based on input image information, and 3 an original conveying unit that conveys an original D to an original reading unit 4. 4 is a document reading unit that reads image information of the document D, 7 is a paper feeding unit that accommodates a recording medium P such as transfer paper, 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 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. A developing unit that develops electrostatic latent images formed on 11Y, 11M, 11C, and 11BK, and a toner image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK Transfer bias roller for transferring superimposed on the recording medium P, 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 photosensitive drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (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 between the fixing roller 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.
FIG. 2 is a cross-sectional view showing the fixing device, and FIG. 3 is a cross-sectional view showing a part of the fixing roller 20.

As shown in FIG. 2, the fixing device 19 includes an induction heating unit 24 as a magnetic flux generating unit, a fixing roller 20, a pressure roller 30, an inner core 28 as a core, a magnetic flux shielding member 29, and the like.
Here, the fixing roller 20 (fixing member) as a heat generating member is a multilayer structure in which an elastic layer 22, a heat generating layer 21 and the like are formed on the surface of a hollow core metal 23 made of a nonmagnetic material such as SUS304. .

Specifically, referring to FIG. 3, the fixing roller 20 has an elastic layer 22, a heat generating layer 21 (consisting of a first nonmagnetic material 21 a and a second nonmagnetic material 21 b), and an antioxidant on a core metal 23. A layer 20b and a release layer 20a are laminated.
The elastic layer 22 is made of an elastic material such as silicone rubber and has a thickness of 50 to 500 μm. Thereby, the heat capacity is not so large, and a good fixed image can be obtained.

As the first nonmagnetic material 21a, SUS304, SUS301, SUS316 (all of which are nonmagnetic stainless steel) or the like as a nonmagnetic material can be used.
As the second nonmagnetic material 21b, copper (Cu) or the like as a nonmagnetic material can be used. The volume resistivity of the second nonmagnetic material 21b is 1.7 × 10 ⁻⁸ Ω · m, which is smaller than the volume resistivity of the first nonmagnetic material 21b. As the second nonmagnetic material 21b, silver (Ag), aluminum (Al), or the like can be used.
The heat generating layer 21 made of the first nonmagnetic material 21a and the second nonmagnetic material 21b is electromagnetically heated by a magnetic flux emitted from the induction heating unit 24 (magnetic flux generating means).

Referring to FIG. 3, the antioxidant layer 20b is formed of nickel (Ni), and the thickness thereof is set to 5 μm or less. The antioxidant layer 20b is for preventing oxidation of the second nonmagnetic material 21b made of copper.
The release layer 20a is made of a fluorine compound such as PFA and has a thickness of 30 μm. The release layer 20a is for improving the toner release property on the surface of the fixing roller 20 with which the toner image (toner) T is in direct contact.
In the first embodiment, the heat generating layer 21 has a two-layer structure of the first nonmagnetic layer 21a and the second nonmagnetic layer 21b. However, the heat generating layer 21 is made of a nonmagnetic metal material such as SUS304 or SUS316. A single layer structure can also be used.

  Referring to FIG. 2, the pressure roller 30 is formed by forming an elastic layer 31 such as fluoro rubber or silicone rubber on a cylindrical member 32 made of aluminum, copper or the like. The elastic layer 31 of the pressure roller 30 is formed to have a thickness of 0.5 to 2 mm and an Asker hardness of 60 to 90 degrees. The pressure roller 30 is in pressure contact with the fixing roller 20. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing roller 20 and the pressure roller 30.

  The induction heating unit 24 as a magnetic flux generation unit includes a coil unit 25 (excitation coil), a core unit 26 (excitation coil core), a coil guide 27, and the like. The coil portion 25 is wound in the width direction (in the direction perpendicular to the paper in FIG. 2) by winding a litz wire bundled with thin wires on a coil guide 27 disposed so as to cover a part of the outer periphery of the fixing roller 20. It is an extension. The coil guide 27 is made of a resin material having high heat resistance and holds the coil portion 25. The core portion 26 is made of a ferromagnetic material such as ferrite (having a relative permeability of about 1000 to 3000), and a center core 26a and a side core 26b are provided to form an efficient magnetic flux toward the heat generating layer 21. It has been. The core part 26 is installed so as to face the coil part 25 extending in the width direction.

Inside the fixing roller 20, an internal core 28 (core) made of a ferromagnetic material such as ferrite and a magnetic flux shielding member 29 covering a part of the outer periphery of the internal core 28 are rotatably installed via a flange 20A. (See also FIG. 4). The rotation drive of the inner core 28 and the magnetic flux shielding member 29 is performed separately from the rotation drive of the fixing roller 20.
The inner core 28 faces the coil portion 25 via the fixing roller 20 and efficiently transmits magnetic flux to the heat generating layer 21 of the fixing roller 20.
The magnetic flux shielding member 29 is made of a good conductor such as copper having a thickness of 1 mm or more. The magnetic flux shielding member 29 is set to have a thickness greater than the skin depth (determined by the volume resistivity and relative permeability of the material and the frequency of the alternating current of the induction heating unit 24). The magnetic flux reaching the heat generating layer 21 from the induction heating unit 24 can be reduced as necessary.

  Although not shown, a thermistor is in contact with the surface of the fixing roller 20. The thermistor is a temperature sensitive element with high thermal responsiveness, and detects the temperature on the fixing roller 20 (fixing temperature). Then, the heating amount by the induction heating unit 24 is adjusted based on the detection result by the thermistor.

The fixing device 19 configured as described above operates as follows.
When the fixing roller 20 is driven to rotate clockwise in FIG. 2 by a drive motor (not shown), the pressure roller 30 also rotates counterclockwise. The fixing roller 20 as a fixing member is heated by the magnetic flux generated from the induction heating unit 24 at a position facing the induction heating unit 24.

  Specifically, by supplying a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) from the power supply unit (not shown) to the coil unit 25, both lines of magnetic force are generated between the core unit 26 and the inner core 28. It is formed so as to switch alternately in the direction. By forming an alternating magnetic field in this way, an eddy current is generated in the heat generating layer 21 of the fixing roller 20, and the heat generating layer 21 is inductively heated by generating Joule heat due to its electric resistance. Thus, the fixing roller 20 is heated by induction heating of the heat generating layer 21 of itself.

Thereafter, the surface of the fixing roller 20 heated by the induction heating unit 24 reaches a contact portion with the pressure roller 30. Then, the toner image T (toner) 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 roller 20 and the pressure roller 30 while being guided by a guide plate (not shown) (arrow). Y1 movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing roller 20 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing roller 20 and the pressure roller 30.

The surface of the fixing roller 20 that has passed through the fixing position 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.

Next, the configuration and operation of the inner core 28 and the magnetic flux shielding member 29 will be described in detail with reference to FIGS.
FIG. 4 is a view of the fixing roller 20 installed in the fixing device 20 of FIG. 2 as viewed in the width direction from the induction heating unit 24 side, and shows the inside of the fixing roller 20. FIG. 5 is a perspective view showing the inner core 28, FIG. 6 is a perspective view showing the structure of the split core 28 </ b> A and the holding member 40, and FIG. 7 is a front view showing the holding member 40.

  As shown in FIG. 4, an inner core 28 and a magnetic flux shielding member 29 (magnetic flux shielding plate) are installed inside the fixing roller 20. Specifically, flanges 20 </ b> A made of heat resistant resin are inserted at both ends of the fixing roller 20. A shaft portion 28B of the inner core 28 that holds the magnetic flux shielding member 29 is rotatably supported on the flange 20A of the fixing roller 20.

  Magnetic flux shielding members 29 made of copper are held in non-adhesion 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 so as to continuously increase or decrease the range of shielding the outer peripheral surface of the inner core 28 from the end surface side. Specifically, the developed shape of the magnetic flux shielding member 29 is substantially triangular (see the perspective view of FIG. 5). Thereby, by rotating the inner core 28 together with the magnetic flux shielding member 29, the shielding 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, when the 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 shielding member 29 is not present. The regular magnetic flux formed is weakened. Thereby, at the position of the fixing roller 20 through which the magnetic flux shielding member 29 is interposed, the heating efficiency is lowered as the acting magnetic flux is reduced.

  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 heating range on the fixing roller 20 can be varied in the range of L1 to L2 in FIG. That is, the adjustment range (shielding range) is varied in the range of 0 to (L1-L2).

  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) connected to the shaft portion 28B of the inner core 28. This stepping motor is a drive system different from a drive motor (not shown) that drives the fixing roller 20.

Specifically, the inner core 28 and the magnetic flux shielding member 29 are rotated by a predetermined angle (predetermined number of steps) 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.
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.

Then, the magnetic flux shielding member 29 is rotationally driven by the stepping motor so that the width direction range (sheet passing region) of the recording medium P with respect to the fixing roller 20 matches the heating range of the fixing roller 20. Note that the range in the width direction of the recording medium P with respect to the fixing roller 20 is determined based on the detection result of a size detection sensor (detection means) that detects the size of the recording medium P.
In the first embodiment, the magnetic flux shielding member 29 is formed so as to continuously increase or decrease the range of shielding the outer peripheral surface of the inner core 28 from the end surface side. However, the outer peripheral surface of the inner core 28 is shielded from the end surface side. The magnetic flux shielding member 29 can be formed so as to increase or decrease the range to be performed stepwise (for example, three steps).

Here, with reference to FIG. 4 and FIG. 5, in the first embodiment, the magnetic flux shielding member 29 is held non-adhering on the outer peripheral surface of the inner core 28 by the holding members 40 </ b> A and 40 </ b> B.
Specifically, the inner core 28 as a core is composed of a plurality of divided cores 28A divided in the width direction (in the first embodiment, there are 14 divided cores 28A having a length in the width direction of 10 to 30 mm. ). Referring to FIG. 6, the holding member 40 includes a protruding portion 40 a that protrudes on the outer peripheral surface of the inner core 28 (divided core 28 </ b> A), and two adjacent divided cores 28 </ b> A that are integrated with the protruding portion 40 a and adjacent to each other. And a non-projecting portion 40b sandwiched between the two. The protrusion 40a of the holding member 40 is formed with a hole 40a1 for holding the magnetic flux shielding member 29 in a non-adhesive manner.

  Specifically, both ends of the magnetic flux shielding member 29 are inserted and held in the hole portions 40a1 of the protruding portions 40a of the two holding members 40A and 40B. As shown in FIG. 7A, the hole 40a1 of the holding member 40A installed at the center in the width direction of the inner core 28 is formed to be relatively small, and the tip of the magnetic flux shielding member 29 is inserted. The On the other hand, the hole 40a1 of the holding member 40B installed at the widthwise end of the inner core 28 is formed to be relatively large as shown in FIG. Is inserted.

With such a configuration, the magnetic flux shielding member 29 is not adhered to the outer peripheral surface of the inner core 28 without using an adhesive or a tape. The problem of leaving from 28 is suppressed.
As a material for the holding members 40A and 40B, it is preferable to use a nonmagnetic material that does not disturb the magnetic flux formed toward the inner core 28.
Moreover, in order to further improve the holding force with respect to the magnetic flux shielding member 29, the magnetic flux shielding member 29 inserted into the hole 40a1 of the protruding portion 40a can be welded to the protruding portion 40a.

Here, referring to FIG. 6, in the first embodiment, a portion other than the protruding portion 40 a of the holding member 40 (the portion where the magnetic flux shielding member 29 is inserted and held) is the surface of the inner core 28. The non-projecting part 40b does not project. As a result, unnecessary protrusions are not formed on the surface of the inner core 28, thereby preventing a problem that the magnetic flux formed toward the inner core 28 is disturbed.
Here, the plurality of divided cores 28A are preferably formed so as not to have a gap between the adjacent divided cores 28A. Specifically, the thickness of the non-projecting portion 40b of the holding member 40 can be reduced, or the split core 28A can be formed so that the portion where the non-projecting portion 40b is sandwiched is concave. As a result, unnecessary gaps are not formed on the surface of the inner core 28, so that a problem that the magnetic flux formed toward the inner core 28 is disturbed is suppressed.

  With reference to FIG. 6, the non-projecting portion 40 b of the holding member 40 is installed on the shaft portion 28 </ b> B of the inner core 28 together with the plurality of divided cores 28 </ b> A. Thereby, in the inner core 28, the holding member 40 is positioned with high accuracy, and the magnetic flux shielding member 29 is stably held.

  As described above, in the first embodiment, in the electromagnetic induction heating type fixing device, the magnetic flux shielding member 29 is held on the outer peripheral surface of the inner core 28 (core) without being bonded. Thereby, even if it reaches high temperature, the magnetic flux shielding member 29 is not detached from the inner core 28, and even when a small size paper is continuously passed, the induction heating unit 24 (magnetic flux generating means). An excessive temperature rise at both ends in the width direction of the fixing roller 20 (heat generating member) to be heated is stably suppressed.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 8 is a cross-sectional view showing the fixing device 19 according to the second embodiment, and FIG. 9 is a cross-sectional view showing a part of the fixing belt 60 installed in the fixing device 19. The fixing device 19 of the second embodiment is different from that of the first embodiment in which the fixing belt 60 is used as the fixing member, and the fixing roller 20 is used as the fixing member.

  As shown in FIG. 8, the fixing device 19 according to the second embodiment includes an induction heating unit 24, a fixing belt 60 (fixing member) as a heat generating member, and a support roller 41 (roller member) that functions as a heat generating member together with the fixing belt 60. ), A fixing auxiliary roller 50 (roller member), a pressure roller 30, and the like.

  Here, the fixing auxiliary roller 50 is formed by forming an elastic layer such as silicone rubber on the surface of a cored bar made of stainless steel or the like. The elastic layer of the auxiliary fixing roller 50 is formed so as to have a thickness of 1 to 5 mm and an Asker hardness of 30 to 60 degrees.

The support roller 41 as a heat generating member has a heat generating layer composed of a first nonmagnetic material 41a made of SUS304 (nonmagnetic stainless steel) and a second nonmagnetic material 41b made of a copper plating layer. The configurations of the first nonmagnetic material 41a and the second nonmagnetic material 41b of the support roller 41 are substantially the same as the configurations of the first nonmagnetic material 21a and the second nonmagnetic material 21b of the fixing roller 20 in the first embodiment. is there. Although not shown, a nickel layer that functions as an anti-oxidation layer and an anti-wear layer is formed on the heat generation layers 41 a and 41 b of the support roller 41. Further, flanges (made of a heat resistant resin) as support members are inserted at both ends of the support roller 41.
The support roller 41 rotates in the clockwise direction in FIG. The heat generating layers 41 a and 41 b of the support roller 41 are induction heated by the magnetic flux generated from the induction heating unit 24.

The fixing belt 60 including the heat generating layer is stretched and supported by a support roller 41 and a fixing auxiliary roller 50 (two roller members).
Referring to FIG. 9, the fixing belt 60 includes, from the inner peripheral surface side, a heat generating layer (consisting of a first nonmagnetic material 61 a and a second nonmagnetic material 61 b), an oxidation preventing layer 60 b made of nickel, An elastic layer 62 made of silicone rubber or the like and a release layer 60a made of a fluorine compound are laminated. The configuration of each layer of the fixing belt 60 is substantially the same as the configuration of each layer of the fixing roller 20 in the first embodiment.
The fixing belt 60 travels clockwise in FIG. The heat generating layers 61 a and 61 b of the fixing belt 60 are induction heated by the magnetic flux generated from the induction heating unit 24.

Inside the support roller 41, 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 via a flange. 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 41.
The inner core 28 faces the coil portion 25 via the fixing belt 60 and the support roller 41, and efficiently transmits magnetic flux to the support roller 41 and the heat generating layers 61 a and 61 b of the fixing belt 60.
The magnetic flux shielding member 29 is set so that its thickness is larger than the skin depth, and the magnetic flux reaching the support roller 41 and the heat generating layers 61a and 61b of the fixing belt 60 from the induction heating unit 24 as necessary. Can be reduced.
Here, also in the second embodiment, similarly to the first embodiment, the magnetic flux shielding member 29 is held on the outer peripheral surface of the inner core 28 by a plurality of holding members (not shown) in a non-adhesive manner. ing.

The fixing device 19 configured as described above operates as follows.
By the rotation driving of the auxiliary fixing roller 50, the fixing belt 60 rotates in the clockwise direction in FIG. 8, the support roller 41 also rotates in the clockwise direction, and the pressure roller 30 also rotates in the counterclockwise direction. The fixing belt 60 is heated at a position facing the induction heating unit 24.

  Specifically, by supplying a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) from the power supply unit (not shown) to the coil unit 25, both lines of magnetic force are generated between the core unit 26 and the inner core 28. It is formed so as to switch alternately in the direction. By forming the alternating magnetic field in this way, eddy currents are generated on the surface of the support roller 41 and the heat generating layers 61a and 61b of the fixing belt 60, and Joule heat is generated by the electric resistance of the support roller 41 and the heat generating layers 61a and 61b. Occurs and the support roller 41 and the heat generating layers 61a and 61b are heated. Thus, the fixing belt 60 is heated by the heat received from the heated support roller 41 and the heat generated by the heat generating layers 61a and 61b.

Thereafter, the surface of the fixing belt 60 heated by the induction heating unit 24 reaches a contact portion with the pressure roller 30. Then, the toner image T (toner) on the conveyed recording medium P is heated and melted.
The surface of the fixing belt 60 that has passed the fixing position 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.

  As described above, also in the second embodiment, similarly to the first embodiment, in the electromagnetic induction heating type fixing device, the magnetic flux shielding member 29 is not bonded to the outer peripheral surface of the inner core 28 (core). Since the magnetic flux shielding member 29 is not separated from the inner core 28 even when the temperature reaches a high temperature, the width of the fixing belt 60 and the support roller 41 heated by the induction heating unit 24 (magnetic flux generating means). Overheating at both ends in the direction is stably suppressed.

  In the second embodiment, the fixing belt 60 and the support roller 41 are used as heat generating members. On the other hand, only one of the fixing belt 60 and the support roller 41 can be used as a heat generating member. Even in this case, the same effect as in the second embodiment can be obtained.

  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.

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 cross-sectional view showing a part of a fixing roller. FIG. 2 is a schematic view showing the inside of a fixing roller. It is a perspective view which shows an internal core. It is a perspective view which shows the structure of a division | segmentation core and a holding member. It is a front view which shows a holding member. It is sectional drawing which shows the fixing device in Embodiment 2 of this invention. FIG. 3 is a cross-sectional view illustrating a part of a fixing belt.

Explanation of symbols

1 image forming apparatus body (apparatus body),
19 fixing device,
20 fixing roller (fixing member, heating member),
21 exothermic layer,
24 induction heating part (magnetic flux generating means), 25 coil part, 26 core part,
28 inner core (core),
28A split core, 28B shank,
29 magnetic flux shielding member,
30 pressure roller,
40, 40A, 40B holding member,
40a protruding part, 40a1 hole part, 40b non-protruding part,
41 Support roller (heat generating member, roller member),
50 Fixing auxiliary roller (roller member),
60 Fixing belt (fixing member, heating member).

Claims (13)

A fixing device that heats and fixes a toner image to a recording medium,
Magnetic flux generating means for generating magnetic flux;
A heat generating member having a heat generating layer heated by the magnetic flux;
A core facing the magnetic flux generation means via the heating member;
A magnetic flux shielding member that varies a heating range in the width direction of the heat generating member heated by the magnetic flux by shielding a part of the core in the width direction;
A holding member that holds the magnetic flux shielding member on the outer peripheral surface of the core in a non-adhering manner;
A fixing device comprising: The core is composed of a plurality of divided cores divided in the width direction,
The holding member includes a protruding portion that protrudes on an outer peripheral surface of the core, and a non-projecting portion that is integrated with the protruding portion and is sandwiched between two adjacent divided cores. The fixing device according to claim 1.   The fixing device according to claim 2, wherein the magnetic flux shielding member is inserted and held in a hole portion of the protruding portion of the plurality of holding members.   The fixing device according to claim 2, wherein the non-projecting portion is installed on a shaft portion of the core together with the plurality of divided cores.   The fixing device according to claim 2, wherein the plurality of divided cores are formed so as not to have a gap between adjacent divided cores.   6. The fixing device according to claim 1, wherein the heat generating member heats a fixing member that melts the toner image. The fixing member is a fixing belt that abuts on a pressure roller that presses a recording medium to be conveyed and is stretched between at least two roller members,
The heating member is one of the at least two roller members,
The fixing device according to claim 6, wherein the core is an internal core provided in the one roller member.   The fixing device according to claim 7, wherein the magnetic flux shielding member is formed so that the heating range gradually increases or decreases stepwise or continuously by rotating integrally with the inner core.   The fixing device according to claim 1, wherein the heat generating member is a fixing member that melts a toner image. The fixing member is a fixing roller that contacts a pressure roller that presses a recording medium to be conveyed,
The fixing device according to claim 9, wherein the core is an internal core provided in the fixing roller. The fixing member is a fixing belt that abuts on a pressure roller that presses a recording medium to be conveyed and is stretched between at least two roller members,
The fixing device according to claim 9, wherein the core is an internal core provided in the roller member.   The said magnetic flux shielding member is formed so that the said heating range may increase or decrease gradually or continuously by rotating integrally with the said inner core, The Claim 10 or Claim 11 characterized by the above-mentioned. Fixing device. An image forming apparatus comprising the fixing device according to claim 1.

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