JP5158498B2 - 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, electromagnetic induction in which a plurality of pairs of demagnetizing coils and a plurality of arch cores are installed. The present invention relates to a heating type fixing device and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a technique is known in which a demagnetizing coil is installed in an electromagnetic induction heating type fixing device to suppress an excessive temperature rise in a non-sheet passing region of a heating member ( (For example, see Patent Document 1, Patent Document 2, etc.).

In Patent Document 1, etc., a plurality of pairs of degaussing coils are arranged in parallel at both ends in the width direction at positions opposite to the exciting coil, in addition to the exciting coil, in the induction heating portion of the fixing device. The plural pairs of degaussing coils are arranged in parallel at positions corresponding to non-sheet passing areas of recording media of various sizes, and demagnetize the magnetic flux of the exciting coils generated at the opposed positions, thereby preventing the non-sheet passing of the heating member. The overheating of the area is suppressed.
The induction heating unit is provided with a first core (arch core) so as to cover the exciting coil and the demagnetizing coil, and is divided in the width direction so as not to cross the demagnetizing coil in the loop of the exciting coil. Two cores (center core) are extended.

JP 2008-40176 A JP 2007-226126 A

The conventional fixing device described above has a problem that the temperature distribution in the width direction in the sheet passing region of the heat generating member becomes non-uniform. In particular, when a plurality of pairs of degaussing coils are arranged in parallel at both ends in the width direction, a range in which the degaussing coil and the center core are disposed and a range in which the demagnetizing coil is not disposed are generated and should be controlled. Such a problem has become prominent because the magnetic path is complicated.
In order to solve such problems, the inventor of the present application has made researches, and as a result, has optimized the layout (number of installations, positions, etc.) of a plurality of arch cores installed so as to cover the exciting coil and the demagnetizing coil. As a result, the magnetic path formed by the exciting coil and the degaussing coil is finely adjusted, and it has been found that the temperature distribution in the width direction of the heat generating member can be made uniform.

  The present invention has been made to solve the above-described problems. Even when a plurality of pairs of demagnetizing coils are arranged in the width direction, the magnetic path formed by the exciting coils and the degaussing coils is fine. It is an object of the present invention to provide a fixing device and an image forming apparatus that are adjusted so that the temperature distribution in the width direction in the sheet passing region of the heat generating member is made uniform.

According to a first aspect of the present invention, there is provided a fixing device including a heat generating member having a heat generating layer, an exciting coil that opposes the heat generating member, generates a magnetic flux, and induction-heats the heat generating layer with the magnetic flux, A plurality of pairs of demagnetizing coils that are arranged in parallel at both ends in the width direction so as to face the excitation coil, and that generates magnetic fluxes at both ends in the width direction in a direction that cancels the magnetic flux generated by the excitation coil, and the excitation A plurality of center cores arranged in the width direction so as not to intersect the degaussing coil in a loop of the coil, and a direction orthogonal to the width direction so as to cover the excitation coil and / or the degaussing coil and a plurality of arch cores which are bridged, degaussing coils of the plurality of pairs of the opposing distance is differently two height between the exciting coil of the adjacent degaussing coil The demagnetizing coils are arranged so as to overlap each other when viewed from above, and are arranged in the loops of the plurality of pairs of demagnetizing coils of the plurality of center cores. When viewed from above, adjacent portions of the plurality of pairs of degaussing coils are inclined with respect to the width direction so that the center core overlaps with a part of the adjacent center core when viewed from a direction perpendicular to the width direction. The plurality of arch cores are formed so as to be abutted against the plurality of center cores by adjusting the position in the width direction or / and the number of installed arch cores.

The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the plurality of center cores are formed so as to be slidable in the width direction in a state where the arch cores are in contact. The contact part is extended in the width direction.

According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the plurality of arch cores are divided in a direction orthogonal to the width direction so as to sandwich the center core. It is a thing.

According to a fourth aspect of the present invention, there is provided the fixing device according to any one of the first to third aspects, wherein the length of the arch core in the width direction is L1 (mm). When the interval in the width direction between adjacent center cores in the core is L2 (mm),
L1 ≧ L2 × 1/2
This relationship is established.

The fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein the center core is a protrusion formed on a holding member that holds the center core. It has a through hole that engages.

The fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the plurality of pairs of degaussing coils pass through a plurality of types of recording media having different sizes. The heating range in the width direction of the heat generation layer can be varied corresponding to the region.

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

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

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

  The present invention is configured such that even when a plurality of pairs of demagnetizing coils are arranged in parallel in the width direction, the positions and the number of installations in the width direction of the plurality of arch cores are adjusted so as to abut against the plurality of center cores. Therefore, it is possible to provide a fixing device and an image forming apparatus in which the magnetic path formed by the exciting coil and the degaussing coil is finely adjusted, and the temperature distribution in the width direction in the paper passing region of the heat generating member is made uniform. .

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

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is the main body of a tandem type color copier as an image forming apparatus, 2 is a writing unit that emits laser light based on input image information, 4 is a document reading unit that reads image information of a document D, and 7 is A paper supply unit for storing a recording medium P such as transfer paper, 11Y, 11M, 11C, and 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, and 12 is a photosensitive drum. 11Y, 11M, 11C, and 11BK are charged. 13 is a developing unit that develops an electrostatic latent image formed on each photoconductor drum 11Y, 11M, 11C, and 11BK, and 15 is each photoconductor drum 11Y. A cleaning unit that collects untransferred toner on 11M, 11C, and 11BK is shown.
Reference numeral 16 denotes an intermediate transfer belt cleaning unit that cleans the intermediate transfer belt 17, 17 an intermediate transfer belt on which toner images of a plurality of colors are transferred, and 18 a color image formed on the intermediate transfer belt 17 as a recording medium. A secondary transfer roller 19 for transferring the toner image onto P is an electromagnetic induction heating type fixing device for fixing a toner image (unfixed image) on the recording medium P.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, image information of the document D placed on the contact glass 5 is optically read by the document reading unit 4. 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 photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the intermediate transfer belt 17, respectively. Here, a transfer bias roller (not shown) is installed at each facing portion so as to abut on the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photoconductive drums 11Y, 11M, 11C, and 11BK are sequentially transferred to the intermediate transfer belt 17 at the position of the transfer bias roller (primary transfer process). .)

Then, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the primary 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.

Thereafter, the intermediate transfer belt 17 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 18. At this position, the secondary transfer backup roller sandwiches the intermediate transfer belt 17 between the secondary transfer roller 18 and forms a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 17 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip (secondary transfer process). At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 17.
Thereafter, the intermediate transfer belt 17 reaches the position of the intermediate transfer cleaning unit 16. At this position, the untransferred toner on the intermediate transfer belt 17 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 17 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip passes through a transport path K1 in which a paper feed roller 8, a registration roller, and the like are installed from a paper feed unit 7 disposed below the apparatus main body 1. It was transported via.
Specifically, a plurality of recording media P are stored in the paper supply unit 7 in a stacked manner. When the paper feed roller 8 is rotationally driven counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the transport path K1.

  The recording medium P transported to the transport path K1 temporarily stops at the position of the roller nip of the registration roller (not shown) that has stopped rotating. Then, the registration roller is driven to rotate in synchronization with the color image on the intermediate transfer belt 17, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 19. At this position, the color image transferred to the surface is fixed on the recording medium P by heat and pressure generated by the fixing roller and the pressure roller.
The recording medium P after the fixing process is discharged as an output image by the paper discharge roller 9 to the outside of the apparatus main body 1 (moving in the direction indicated by the broken line arrow), 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.
As shown in FIG. 2, the fixing device 19 includes an induction heating unit 25 (magnetic flux generating unit), a fixing roller 20 (fixing member) as a heat generating member facing the induction heating unit 25, and a pressure member that presses the fixing roller 20. As a pressure roller 30, an inlet guide plate 41, a spur 42, a separation plate 43, a guide member 50, and the like.

Here, the fixing roller 20 as a heat generating member is obtained by sequentially laminating a heat insulating elastic layer 22 made of foamed silicone rubber or the like and a sleeve layer 21 on a cored bar 23 made of iron or stainless steel. The outer diameter is about 40 mm.
The sleeve layer 21 of the fixing roller 20 is a multilayer structure in which a base material layer, a first antioxidant layer, a heat generating layer, a second antioxidant layer, an elastic layer, and a release layer are sequentially laminated from the inner peripheral surface side. Specifically, the base material layer is formed of stainless steel having a layer thickness of about 40 μm, and the first antioxidant layer and the second antioxidant layer are formed by strike plating treatment of nickel having a layer thickness of 1 μm or less. The heating layer is made of copper having a layer thickness of about 10 μm, the elastic layer is made of silicone rubber having a layer thickness of about 150 μm, and the release layer has a layer thickness of about 30 μm. It is formed of PFA (tetrafluoroethylene / barfluoroalkyl vinyl ether copolymer).
In the fixing roller 20 (heat generating member) configured as described above, the heat generating layer of the sleeve layer 21 is electromagnetically heated by the magnetic flux generated from the exciting coil 26 of the induction heating unit 25. The configuration of the fixing roller 20 is not limited to that of the first embodiment. For example, the sleeve layer 21 can be separated without being bonded to the heat insulating elastic layer 22 (fixing auxiliary roller). However, when the sleeve layer 21 (fixing sleeve) is separated, it is preferable to install a member for preventing the sleeve layer 21 from moving in the width direction (thrust direction) during operation.

Here, a plurality of spurs 42 are juxtaposed in the width direction at a position facing the fixing roller 20 as a fixing member and upstream of the nip portion (upstream in the transport direction). The spur 42 guides the recording medium P fed into the nip portion to the nip portion. The spur 42 is formed in a saw-tooth shape so that even if it contacts an unfixed image on the recording medium P, the image does not rub.
In addition, a separation plate 43 is installed at a position facing the fixing roller 20 and downstream of the nip portion (downstream in the transport direction). The separation plate 43 is for preventing a problem that the recording medium P after the fixing process sent out from the nip portion is attracted to and wound around the fixing roller 20. That is, when the recording medium P after the fixing process is attracted to the fixing roller 20, the separation member 43 interferes with the leading end of the recording medium P to forcibly separate the recording medium P from the fixing roller 20.
A thermistor 40 (contact temperature detection sensor) is disposed around the fixing roller 20. Then, the temperature on the fixing roller 20 (fixing temperature) is detected by the thermistor 40. And based on the detection result by the thermistor 40, the heating amount by the induction heating part 25 is adjusted. In the first embodiment, a plurality of thermistors 40 are provided in the width direction (see thermistors 40A to 40D in FIG. 4C).

Referring to FIG. 2, a pressure roller 30 as a pressure member is formed on a cylindrical member 32 made of aluminum, copper or the like, an elastic layer 31 made of silicone rubber or the like, a release layer made of PFA or the like (not shown). Is formed). The elastic layer 31 of the pressure roller 30 is formed to have a thickness of 1 to 5 mm. The release layer of the pressure roller 30 is formed so that the layer thickness is 20 to 50 μm. The pressure roller 30 is in pressure contact with the fixing roller 20. Then, the recording medium P is conveyed to a pressure contact portion (a nip portion) between the fixing roller 20 and the pressure roller 30.
In the first embodiment, a heater 33 (electric member) such as a halogen heater is provided in the pressure roller 30 in order to increase the heating efficiency of the fixing roller 20. By supplying electric power to the heater 33 as an electric member, the pressure roller 30 is heated by the radiant heat of the heater 33, and the surface of the fixing roller 20 is heated via the pressure roller 30.

Here, an inlet guide plate 41 is installed at a position facing the pressure roller 30 and upstream of the nip portion. The inlet guide plate 41 guides the recording medium P fed into the nip portion to the nip portion.
A guide member 50 is installed at a position facing the pressure roller 30 and downstream of the nip portion (a position facing the non-fixing surface of the recording medium P fed from the nip portion). Yes. The guide member 50 is for guiding the recording medium P sent from the nip portion after the fixing process toward the conveyance path after the fixing process.

The induction heating unit 25 includes an exciting coil 26, a plurality of pairs of demagnetizing coils 27A to 27C, core portions 28, 29, and 35, a coil guide 36 (holding member), and the like.
The exciting coil 26 is formed by winding a litz wire bundled with fine wires on a coil guide 36 disposed so as to cover a part of the outer peripheral surface of the fixing roller 20 (heat generating member) having a heat generating layer (FIG. 2). (It is also possible to refer to FIGS. 4 and 8). The exciting coil 26 facing the fixing roller 20 generates a magnetic flux, and the heat generation layer of the fixing roller 20 is electromagnetically heated by the magnetic flux.

A plurality of pairs of degaussing coils 27A to 27C are arranged in parallel at both ends in the width direction so as to face the exciting coil 26 (see also FIG. 4). The degaussing coils 27 </ b> A to 27 </ b> C generate a magnetic flux in a direction that cancels the magnetic flux generated by the exciting coil 26 at both ends in the width direction.
Specifically, as shown in FIG. 3A, when the changeover switch 60 is opened (when the degaussing coils 27A to 27C do not operate), the magnetic flux generated from the exciting coil 26 (shown by a thick line arrow in the figure). This forms a magnetic circuit that passes through the heat generating layer 21 of the fixing roller 20. Therefore, an induced current flows through the heat generating layer, and the heat generating layer generates heat due to Joule heat.
On the other hand, as shown in FIG. 3B, when the changeover switch 60 is closed (a part or all of a plurality of pairs of degaussing coils 27A to 27C are operated), it is generated from the exciting coil 26. The magnetic flux (indicated by a thick arrow in the figure) is canceled by the magnetic flux (indicated by the thick broken line arrow in the figure) generated from the degaussing coils 27A to 27C, and becomes a very weak magnetic flux. In this way, the magnetic flux that heats the heat generating layer becomes very weak, and the heating amount of the fixing roller 20 can be reduced at positions facing the degaussing coils 27A to 27C (both ends in the width direction). In addition, although illustration is abbreviate | omitted, the changeover switch 60 is each installed independently with respect to the 1st degaussing coil 27A, the 2nd degaussing coil 27B, and the 3rd degaussing coil 27C.

In the first embodiment, referring to FIG. 4, three pairs of degaussing coils 27A to 27C correspond to the B4 size, A4 size (or B5 size), and postcard size recording media P in the width direction ( (It is the horizontal direction of FIG. 4). Then, the heating range in the width direction of the heat generating layer is varied by the three pairs of degaussing coils 27A to 27C in correspondence with the sheet passing areas of a plurality of types of recording media P having different sizes. Specifically, when an A3 size recording medium P (A3 length (hereinafter, “vertical” is simply referred to as “T”)) is passed in the vertical direction, all of the three pairs of degaussing coils 27A to 27C are used. When the changeover switch 60 is opened and the B4 size recording medium P (B4T) is passed in the vertical direction, only the changeover switch 60 of the first degaussing coil 27A is closed and the A4 size recording medium P (A4T) is closed. Is switched in the vertical direction, the changeover switch 60 of the first degaussing coil 27A and the second degaussing coil 27B is closed, and three pairs of postcard-size recording media P (H) are passed through. All the changeover switches 60 of the degaussing coils 27A to 27C are closed.
Here, since the dimensional difference between the B5 size and the A4 size is relatively small, in the first embodiment, when the B5 size recording medium P (B5T) is passed in the vertical direction, the A4 size Similarly to the case where the recording medium P (A4T) is passed in the vertical direction, the changeover switch 60 of the first degaussing coil 27A and the second degaussing coil 27B is closed. In the first embodiment, the demagnetizing coil used when the B5-size recording medium P (B5T) is passed in the vertical direction is used, and the A4 size recording medium P (A4T) is passed in the vertical direction. However, it is also possible to add a degaussing coil separately for the B5 size.

In this way, the energization of the three pairs of degaussing coils 27A to 27C is changed depending on the paper size of the recording medium P to be passed. Here, as a method of detecting the paper size of the recording medium P, for example, a method of directly determining the paper size based on paper size information (input signal) input by the user, or the width direction of the fixing roller 20 A method of detecting the temperature distribution of the paper and indirectly determining the paper size can be used.
In the first embodiment, referring to FIG. 4, a method is used in which the paper size is indirectly determined by detecting the temperature distribution in the width direction of the fixing roller 20. Specifically, a plurality of thermistors 40A to 40D as temperature detection sensors are arranged in the width direction so as to face (contact) the fixing roller 20 in accordance with the end positions of various recording media P in the paper size. Yes. More specifically, the thermistor 40A is arranged at the center, and the first to third thermistors 40B to 40D are arranged at positions corresponding to the first to third demagnetizing coils 27A to 27C, respectively. The temperature distribution in the width direction of the fixing roller 20 is detected by the four thermistors 40A to 40D. In the sheet passing area, the heat of the fixing roller 20 is taken away by the recording medium P, and in the non-sheet passing area, the temperature of the fixing roller 20 is maintained higher than that in the sheet passing area. The paper size of the recording medium P being passed can be determined from the temperature distribution. A demagnetizing coil to be energized is determined according to the detected temperature information (temperature distribution).

Note that when using a method for determining the paper size based on the paper size information input by the user, the degaussing coil is already energized at the start of paper passing, so There is a possibility that the heat at the end is deprived by the non-sheet passing area where the temperature rise is suppressed by demagnetization, and the end temperature in the sheet passing area falls. In such a case, poor fixing occurs on the output image.
On the other hand, according to the paper size detection method based on the temperature distribution of the first embodiment described above, all the degaussing coils 27A to 27C are not energized until a predetermined time elapses from the start of paper feeding. Therefore, such a fixing failure does not occur. Even when a method of determining the paper size based on the paper size information input by the user is used, control is performed so that the degaussing coils 27A to 27C are not energized until a predetermined time has elapsed from the start of paper feeding. By doing so, the above-described problems can be solved.
Here, in the first embodiment, the thermistors 40A to 40D (contact-type temperature detection sensors) are used as the temperature detection sensors for detecting the temperature distribution, but non-contact like a thermopile is used as the temperature detection sensor for detecting the temperature distribution. A mold temperature detection sensor can also be used.

The core portions 28, 29, and 35 are made of a ferromagnetic material such as ferrite (relative magnetic permeability is about 2500), and are magnetic paths (paths in which magnetic flux is formed) by the excitation coil 26 and the demagnetization coils 27A to 27C. .) Is controlled to form an efficient magnetic flux toward the heat generating layer of the fixing roller 20. As shown in FIGS. 2 and 4, the core portion is composed of a plurality of center cores 28, a plurality of arch cores 29, and two side cores 35. The characteristic configurations of the core portions 28, 29, and 35 and the degaussing coils 27A to 27C will be described in detail later.
The coil guide 36 is made of a heat-resistant resin material or the like, and holds the exciting coil 26, the degaussing coils 27A to 27C, and the core portions 28, 29, and 35 (see also FIG. 8).
The induction heating unit 25 is configured to be separable from the main part of the fixing device 19. The main part of the fixing device 19 is separated from the induction heating unit 25 and taken out from the image forming apparatus main body 1 in a state where the door 100 is opened (the movement to the right in FIG. 1). .)

The fixing device 19 configured as described above operates as follows.
The fixing roller 20 is driven to rotate counterclockwise in FIG. 2 by a drive motor (not shown), and the pressure roller 30 is rotated clockwise accordingly. The sleeve layer 21 (heat generation layer) of the fixing roller 20 is heated by the magnetic flux generated from the induction heating unit 25 (excitation coil 26) at a position facing the induction heating unit 25.

  Specifically, the oscillation circuit passes a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) from the power supply unit (not shown) whose frequency is variable to the excitation coil 26, so The magnetic field lines are formed so as to alternately switch in both directions toward the sleeve layer 21 of the fixing roller 20. By forming an alternating magnetic field in this manner, an eddy current is generated in the heat generating layer of the sleeve layer 21, and the heat generating layer generates Joule heat due to its electric resistance and is induction-heated. Thus, the sleeve layer 21 (fixing roller 20) is heated by induction heating of its own heat generation layer.

Thereafter, the surface of the fixing roller 20 heated by the induction heating unit 25 reaches a contact portion (nip 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 sent between the fixing roller 20 and the pressure roller 30 while being guided by the entrance guide plate 41 (or the spur 42). (The movement in the transport direction of the arrow Y1.) The toner image T is fixed on 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 out between the fixing roller 20 and the pressure roller 30 ( This is the movement in the transport direction of the arrow Y2.)
The surface of the fixing roller 20 that has passed through the nip portion then reaches the position facing the induction heating unit 25 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

Hereinafter, the configuration and operation of the fixing device 19, which is characteristic in the first embodiment, will be described in detail with reference to FIGS. 4 to 8.
4A is a schematic top view illustrating the induction heating unit 25, FIG. 4B is a schematic side view illustrating the induction heating unit 25, and FIG. 4C illustrates the induction heating unit 25 and the A3 size. It is a figure which shows the positional relationship of the width direction with the recording medium of postcard size. 4C also shows the positional relationship in the width direction between the fixing roller 20 and the thermistors 40A to 40D that are in contact with the fixing roller 20. FIG. FIG. 5 is a cross-sectional view showing the X1-X1 cross section (the cross section at the position of the first degaussing coil 27A and the third degaussing coil 27C) in FIG. FIG. 6 is a cross-sectional view showing a cross section taken along line X2-X2 of FIG. 4A (the cross section at the position of the second degaussing coil 27B). Further, FIG. 7 is a perspective view showing the center core 28 and the arch core 29. FIG. 8 is a schematic side view showing the induction heating unit 28.

As shown in FIG. 4, the three pairs of degaussing coils 27 </ b> A to 27 </ b> C are alternately arranged at two height positions so that the facing distances of adjacent degaussing coils (the facing distances with the exciting coil 26) are different. Has been. Specifically, the second degaussing coil 27B is disposed at a height position close to the exciting coil 26, and the first degaussing coil 27A and the third degaussing coil 27C (demagnetizing coils adjacent to the second degaussing coil 27B). It is disposed at a height position away from the exciting coil 26 by a distance Z.
Specifically, in the first embodiment, the opposing distance between the second degaussing coil 27B and the exciting coil 26 is set to about 2 mm, and the first degaussing coil 27A (or the third degaussing coil 27C) and the exciting coil 26 are separated from each other. The facing distance is set to about 5 mm.

  Further, the three pairs of degaussing coils 27 </ b> A to 27 </ b> C are disposed so that adjacent degaussing coils partially overlap when viewed from above. That is, referring to FIG. 4A, the inner portion of the first degaussing coil 27A on the inner side (width direction center portion) is above the outer portion of the second degaussing coil 27B on the outer side of the loop (width direction end portion side). It is arranged so as to overlap (upward in the direction perpendicular to the paper surface of FIG. 4A). Similarly, the portion of the third degaussing coil 27C on the loop outer side (width direction end portion side) is arranged to overlap the portion of the second degaussing coil 27B on the loop inner side (width side central portion side). .

  With such a configuration, the induction heating unit 25 becomes large in the height direction (the direction perpendicular to the paper surface in FIG. 4A), and the demagnetizing ability at the boundary portion between adjacent degaussing coils is insufficient. Defects that become are suppressed. Further, since the three pairs of degaussing coils 27A to 27C are arranged such that a part of the adjacent degaussing coils overlap when viewed from above, the center cores 28 installed in the loops of the adjacent degaussing coils , And the temperature distribution in the width direction of the fixing roller 20 is made uniform.

In the first embodiment, a plurality of center cores 28 are arranged in the width direction so as not to cross the degaussing coils 27A to 27C in the loop of the exciting coil 26. Specifically, the center core 28 is disposed within the loop of the exciting coil 26 and the first degaussing coil 27A, the center core 28 is disposed within the loop of the exciting coil 26 and the second degaussing coil 27B, and the exciting coil 26. And the one disposed in the loop of the third degaussing coil 27C and the one disposed only in the loop of the exciting coil 26 (the center core disposed in the central portion in the width direction). Yes.
Furthermore, a plurality of arch cores 29 (indicated by a one-dot chain line in FIG. 4A) are installed in a direction orthogonal to the width direction so as to cover the exciting coil 26 and the demagnetizing coils 27A and 27C. Specifically, the arch core 29 is constructed so as to cover only the excitation coil 26 (an arch core disposed in the center in the width direction), and the arch core 29 so as to cover the excitation coil 26 and the demagnetizing coil. There is something.
These arch cores 29 are at a height position where the demagnetization efficiency of the degaussing coils 27A and 27C disposed at the height position where the facing distance to the exciting coil 26 is shortened is such that the facing distance from the exciting coil 26 is long. It arrange | positions so that it may become equivalent to the degaussing efficiency of the arranged degaussing coil 27B.
Specifically, as shown in FIGS. 4A and 5, the first degaussing coil 27 </ b> A and the third degaussing coil 27 </ b> C disposed at a height position where the facing distance to the exciting coil 26 becomes long. Is provided with an arch core 29. On the other hand, as shown in FIGS. 4A and 6, an arch core 29 is disposed at the position of the second degaussing coil 27B disposed at a height position where the facing distance to the exciting coil 26 is shortened. Not set up.

With such a configuration, the three pairs of demagnetizing coils 27A to 27C are arranged in parallel at both ends in the width direction, and the height positions are different even when they are arranged with different height positions of adjacent demagnetizing coils. The degaussing efficiency of the degaussing coil is made uniform, and the magnetic flux of the exciting coil 26 generated in the non-sheet passing areas of the plurality of types of recording media P having different sizes is uniformly degaussed by the degaussing coil (evenly demagnetized with the same demagnetizing efficiency). ) Further, since the demagnetization unevenness in the width direction does not occur when the demagnetizing coils 27A to 27C are operated, the demagnetizing coils 27A to 27C are not operated (when the A3 size is passed), and the like. The temperature distribution in the width direction in the paper passing area is made uniform.
This is because the layout of the core portions 28, 29, and 35 (particularly the number and positions of the arch cores 29) installed in the induction heating unit 25 is the uniformity of the temperature distribution in the width direction of the fixing roller 20 and the demagnetizing coil. This greatly affects the demagnetization efficiency (the ratio of suppressing the heat generation of the fixing roller 20 by demagnetization).

  Here, the induction heating unit 25 according to the first embodiment is configured to abut against the plurality of center cores 28 by adjusting the position in the width direction and the number of installations of the plurality of arch cores 29. Specifically, referring to FIG. 7 and the like, the center core 28 can be slid in the width direction (the direction of the double arrow in FIG. 7 and the left-right direction in FIG. 4) with the arch core 29 abutting against the center core 28. The abutting portion 28a (formed in a convex shape) formed in this manner extends in the width direction. Such an abutting portion 28a is also provided in the center core 28 installed in the loop of the plural pairs of degaussing coils 27A to 27C, and to the center core 28 (not installed in the loop of the plural pairs of degaussing coils 27A to 27C). It is also provided in the center core disposed in the center in the width direction.

With such a configuration, the layout (the number and position of installation) of the plurality of arch cores 29 is optimized, and the magnetic path formed by the exciting coil 26 and the demagnetizing coils 27A to 27C is finely adjusted. The temperature distribution in the width direction of the roller 20 can be made uniform.
For example, when the fixing temperature at both ends in the width direction of the fixing roller 20 is slightly lower than the fixing temperature at the center in the width direction, the arch core 29 installed at the position of the first degaussing coil 27A is moved to the end in the width direction. The arch core 29 can be added to the position of the first degaussing coil 27A. Further, when the demagnetization efficiency at the position of the third degaussing coil 27C is slightly lower than the demagnetization efficiency at the other position, the arch core 29 installed at the position of the second degaussing coil 27C or at another position is moved to the end in the width direction. It is possible to slide a small distance, to add the arch core 29 at the position of the second degaussing coil 27C, or to remove the arch coil 29 installed at other positions. At this time, since the abutting portion 28a of the center core 28 extends in the width direction, the arch core 29 can be easily moved and added while maintaining the contact state between the center core 28 and the arch core 29. It will be. In this way, the temperature distribution in the width direction of the fixing roller 20 can be made uniform by adjusting and controlling the entire magnetic path.

In the first embodiment, referring to FIGS. 5 and 7, the plurality of arch cores 29 are divided in a direction perpendicular to the width direction so as to sandwich the center core 28. The divided arch cores 29 are abutted against the abutting portions 28a formed in a convex shape at both ends of the center core 28, respectively.
With such a configuration, the layout of the divided arch core 29 can be adjusted independently, so that the adjustment control of the entire magnetic path can be performed with fine accuracy.

Referring to FIG. 8, the induction heating unit 25 in the first embodiment is provided with a coil guide 36 as a holding member. The coil guide 36 (holding member) holds the exciting coil 26, the degaussing coils 27A to 27C, and the center core 28. Furthermore, the plurality of arch cores 29 are held in the coil guide 36 after the positions and the number of installations are adjusted.
Specifically, the assembly procedure at the time of manufacture is as follows.
First, the exciting coil 28 and the center core 28 not disposed in the loop of the degaussing coils 27 </ b> A to 27 </ b> C are fixed on the coil guide 36. Thereafter, a plurality of pairs of degaussing coils 27 </ b> A to 27 </ b> C and a center core 28 disposed in the loop of the degaussing coils 27 </ b> A to 27 </ b> C are fixed on the coil guide 36. Finally, a plurality of arch cores 29 whose layout has been determined by performing adjustment control of the entire magnetic path are fixed on the coil guide 36 by bonding or the like.

7 and 8, the center core 28 is formed with a through hole 28b (a positioning hole and a long hole) that engages with a protrusion 36b formed in the coil guide 36. ing. Thereby, the position of the center core 28 in the induction heating unit 25 is accurately determined.
In FIG. 8, the protrusion 36b and the through hole 28b are shown only at the position of the third degaussing coil 27C, and the protrusion 36b and the through hole 28b at other positions are not shown.

  As described above, in the first embodiment, even when a plurality of pairs of degaussing coils 27A to 27C are arranged in parallel in the width direction, the positions and the number of installations of the plurality of arch cores 29 are adjusted. Since it is configured to abut against the plurality of center cores 28, the magnetic path formed by the exciting coil 26 and the demagnetizing coils 27A to 27C is finely adjusted, and the fixing roller 20 (heat generating member) in the paper passing area. The temperature distribution in the width direction can be made uniform.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 9 is a schematic diagram illustrating an induction heating unit of the fixing device according to the second embodiment, and corresponds to FIG. 4 according to the first embodiment. FIG. 10 is a schematic view of the center core 28 disposed in the loop of the degaussing coils 27A to 27C when viewed from the K viewing direction of FIG.
In the fixing device according to the second embodiment, the configuration of the center core 28 and the degaussing coils 27A to 27C is different from that of the first embodiment.

  Referring to FIG. 9, the fixing device according to the second embodiment also has an exciting coil 26, three pairs of degaussing coils 27 </ b> A to 27 </ b> C, a center core 28, an arch core 29, and a side core, as in the first embodiment. An induction heating unit 25 composed of 35, etc. is installed. Also in the second embodiment, the three pairs of degaussing coils 27A to 27C are alternately arranged in parallel at two height positions so that the opposing distances between the adjacent degaussing coils and the exciting coil 26 are different. Further, the three pairs of degaussing coils 27A to 27C are arranged so that a part of the adjacent degaussing coils overlap when viewed from above. The center core 28 is provided with a projecting abutment portion 28a so that the center core 28 can be abutted against the plurality of center cores 28 by adjusting the position in the width direction and the number of installed arch cores 29. Yes.

  Here, in the second embodiment, referring to FIGS. 9A and 10, the center core 28 disposed in the loop of the three pairs of demagnetizing coils 27 </ b> A to 27 </ b> C among the plurality of center cores 28. When viewed from above, three pairs of demagnetizing coils 27 </ b> A to 27 </ b> A are viewed so that a part of the adjacent center cores 28 overlap when viewed from the direction orthogonal to the width direction (when viewed from the K viewing direction in FIG. 10). The adjacent portion of 27C is formed to be inclined with respect to the width direction. Specifically, as shown in FIG. 9A, when viewed from above, the first demagnetizing coil 27A and the center core 28 installed in the loop are formed in a substantially triangular shape, and the second demagnetizing coil 27B and the third demagnetizing coil 27B The degaussing coil 27C and the center core 28 installed in those loops are formed in a substantially parallelogram.

  Thus, even if there is a gap between the center cores 28 disposed in the adjacent degaussing coils, they are adjacent when viewed from the direction orthogonal to the width direction (K viewing direction) as shown in FIG. A part of the center core 28 is formed so as to overlap. Therefore, the effect of efficiently controlling the magnetic path by the center core 28 is exhibited uniformly over the width direction. Accordingly, by finely adjusting the position in the width direction and the number of installations of the plurality of arch cores 29 and further finely adjusting the magnetic path formed by the excitation coil 26 and the demagnetization coils 27A to 27C, the demagnetization by the demagnetization coils 27A to 27C. Is further uniformly performed in the width direction, and the temperature distribution in the width direction in the sheet passing region of the fixing roller 20 (heat generating member) is further uniformized. That is, when the demagnetizing coils 27A to 27C and the center core 28 disposed in the loop are configured as in the second embodiment, the position and the number of the arch cores 29 in the width direction can be adjusted. The effect by having comprised in becomes large.

Referring to FIG. 9, in the second embodiment, the length in the width direction of arch core 29 is L1 (mm), and the interval in the width direction between adjacent center cores 28 in a plurality of center cores 28 is L2. (Mm)
L1 ≧ L2 × 1/2
Is set to hold. With such a configuration, it is possible to sufficiently secure the installation location of the arch core 29 on the abutting portion 28a of the center core 28 while maintaining the function of controlling the magnetic path of the arch core 29.

  As described above, even in the second embodiment, similarly to the first embodiment, even when a plurality of pairs of degaussing coils 27A to 27C are arranged in the width direction, the width direction of the plurality of arch cores 29 is determined. Therefore, the fixing roller 20 is finely adjusted to adjust the magnetic path formed by the exciting coil 26 and the demagnetizing coils 27A to 27C. The temperature distribution in the width direction in the paper passing region of the (heating member) can be made uniform.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 11 is a cross-sectional view showing the induction heating unit of the fixing device in the third embodiment, and corresponds to FIG. 5 in the first embodiment. In the fixing device according to the third embodiment, the configuration of the arch core 29 is different from that of the first embodiment.

  Referring to FIG. 11, the fixing device according to the third embodiment also has an exciting coil 26, three pairs of demagnetizing coils 27 </ b> A to 27 </ b> C, a center core 28, an arch core 29, and a side core, as in the above embodiments. An induction heating unit 25 composed of 35, etc. is installed. Also in the third embodiment, the three pairs of degaussing coils 27A to 27C are alternately arranged in parallel at two height positions so that the facing distances between the adjacent degaussing coils and the exciting coil 26 are different. Further, the three pairs of degaussing coils 27A to 27C are arranged so that a part of the adjacent degaussing coils overlap when viewed from above.

  Here, also in the third embodiment, the center core 28 is extended in a convex shape so that the position and the number of installations in the width direction of the plurality of arch cores 29 are adjusted and abutted against the plurality of center cores 28. An abutting portion 28a is provided. In the third embodiment, as shown in FIG. 11, in order to increase the contact area between the abutting portion 28a of the center core 28 and the arch core 29, the tip portion of the arch core 29 (abuts against the abutting portion 28a). Step) is provided with a stepped portion. Thereby, the adhesiveness of the arch core 29 with respect to the center core 28 increases, and the positioning accuracy of the arch core 29 improves.

  As described above, also in the third embodiment, similarly to the above embodiments, even when a plurality of pairs of degaussing coils 27A to 27C are arranged in the width direction, the width direction of the plurality of arch cores 29 is determined. Therefore, the fixing roller 20 is finely adjusted to adjust the magnetic path formed by the exciting coil 26 and the demagnetizing coils 27A to 27C. The temperature distribution in the width direction in the paper passing region of the (heating member) can be made uniform.

In each of the above embodiments, the present invention is applied to a fixing device using the fixing roller 20 as the fixing member and the pressure roller 30 as the pressure member. However, a fixing belt or a fixing film is used as the fixing member. The present invention can also be applied to the electromagnetic induction heating type fixing device used and the electromagnetic induction heating type fixing device using a pressure belt or a pressure pad as a pressure member.
Further, in each of the above embodiments, the present invention is applied to the fixing device using the fixing member (fixing roller 20) as the heat generating member that is induction-heated by the induction heating unit 25. However, the fixing member is heated as the heat generating member. The present invention can also be applied to a fixing device using a heating member. For example, a heating roller (heat generating member) that stretches a fixing belt as a fixing member is provided with a heat generating layer, and the fixing roller indirectly heats the fixing belt by induction heating the induction roller 25. The present invention can be applied even to an apparatus.
In these cases, the same effects as those in the above embodiments can be obtained.

  In each of the above embodiments, three pairs of degaussing coils 27A to 27C are used. However, the present invention can be applied even when two or less pairs or four or more pairs of degaussing coils are installed. . Even in this case, the same effects as those of the above embodiments 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. 2 is a configuration diagram illustrating a fixing device. FIG. It is a figure which shows the state of the magnetic flux generated by the induction heating part. It is the schematic which shows an induction heating part. It is sectional drawing which shows the X1-X1 cross section of FIG. It is sectional drawing which shows the X2-X2 cross section of FIG. It is a perspective view which shows a center core and an arch core. It is a schematic side view which shows an induction heating part. It is the schematic which shows the induction heating part of the fixing device in Embodiment 2 of this invention. It is the schematic which shows the K view direction of FIG. It is sectional drawing which shows the induction heating part of the fixing device in Embodiment 3 of this invention.

Explanation of symbols

1 image forming apparatus body (apparatus body),
19 fixing device,
20 fixing roller (fixing member, heating member),
25 induction heating unit,
26 Excitation coil,
27A-27C degaussing coil,
28 Center core,
28a butting part, 28b through hole,
29 Arch Core,
30 pressure roller (pressure member),
35 side core,
36 Coil guide (holding member),
36b protrusion,
40, 40A-40D thermistor, 60 selector switch.

Claims (9)

A heating member having a heating layer;
An exciting coil that opposes the heat generating member and generates a magnetic flux to inductively heat the heat generating layer with the magnetic flux;
A plurality of pairs of demagnetizing coils that are arranged in parallel at both ends in the width direction so as to face the excitation coil, and that generate magnetic flux in the direction opposite to the magnetic flux generated by the excitation coil at both ends in the width direction,
A plurality of center cores arranged in the width direction so as not to intersect the degaussing coil in a loop of the excitation coil;
A plurality of arch cores constructed in a direction orthogonal to the width direction so as to cover the exciting coil or / and the demagnetizing coil;
With
The plurality of pairs of degaussing coils are alternately arranged at two height positions so that the opposing distances of the adjacent degaussing coils to the excitation coil are different, and a part of the adjacent degaussing coils when viewed from above. Are arranged to overlap,
When viewed from above so that the center cores disposed in the loops of the plurality of pairs of demagnetizing coils of the plurality of center cores overlap with a part of the adjacent center cores when viewed from the direction orthogonal to the width direction. Adjacent portions of the plurality of pairs of degaussing coils are inclined with respect to the width direction,
A fixing device configured to be abutted against the plurality of center cores by adjusting a position or / and the number of installations in the width direction of the plurality of arch cores. 2. The fixing device according to claim 1, wherein the plurality of center cores have abutting portions extending in the width direction so as to be slidable in the width direction in a state in which the arch core is abutted. The fixing device according to claim 1, wherein the plurality of arch cores are divided in a direction orthogonal to a width direction so as to sandwich the center core. When the length in the width direction of the arch core is L1 (mm) and the interval in the width direction between adjacent center cores in the plurality of center cores is L2 (mm),
L1 ≧ L2 × 1/2
The fixing device according to claim 1, wherein the relationship is established. The fixing device according to claim 1, wherein the center core includes a through hole that engages with a protrusion formed on a holding member that holds the center core. 2. The plurality of pairs of degaussing coils are arranged so that a heating range in a width direction of the heat generating layer can be varied corresponding to a sheet passing area of a plurality of types of recording media having different sizes. The fixing device according to claim 5. The fixing device according to claim 1, wherein the heat generating member is a fixing member that melts a toner image. The fixing device according to claim 1, wherein the heat generating member is a heating member that heats a fixing member that melts a toner image. An image forming apparatus comprising the fixing device according to claim 1.

Images