JP5158497B2 - 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, an electromagnetic induction heating type fixing device and an image provided with a demagnetizing coil. The present invention relates to a 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 FIG. 2, FIG. 3, etc. of Patent Document 1, the induction heating unit of the fixing device is provided with a plurality of pairs of demagnetization coils at both ends in the width direction at positions facing the excitation coil in addition to the excitation coil. Yes. The plural pairs of degaussing coils are arranged at positions corresponding to non-sheet passing regions 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 plural pairs of degaussing coils are stacked in a direction (height direction) facing the exciting coil.
Further, in FIG. 12, FIG. 13 and the like of Patent Document 1, a technique for arranging (adjacent) a plurality of pairs of demagnetizing coils in the width direction is disclosed. Then, in order to correspond to the non-sheet passing area of the recording medium of various sizes, the operating members of the plural pairs of degaussing coils are appropriately combined to suppress the excessive temperature rise in the non-sheet passing area of the heat generating member. Yes.

JP 2008-40176 A JP 2007-226126 A

The above-described conventional fixing device has a problem that the induction heating unit is enlarged in the height direction, a problem that the temperature distribution in the width direction of the heat generating member is not uniform, and the like.
Specifically, when a plurality of pairs of degaussing coils are simply stacked in the height direction as in the fixing device of FIGS. 2 and 3 of Patent Document 1, the guidance increases as the number of recording media of different sizes to be handled increases. As the heating part becomes larger in the height direction, there is a difference in the demagnetization efficiency of the degaussing coils having different facing distances (height positions) from the exciting coils.
In addition, when a plurality of pairs of degaussing coils are arranged in parallel in the width direction as in the fixing device shown in FIGS. 12 and 13 of Patent Document 1, the demagnetizing ability at the boundary portion between adjacent degaussing coils becomes insufficient. In other words, the distance between the center cores installed in the loops of the adjacent degaussing coils becomes long, and the temperature distribution in the width direction of the heat generating member becomes non-uniform.

  In order to solve such problems, a plurality of pairs of degaussing coils are juxtaposed in the width direction, and the height positions of adjacent degaussing coils are changed so that a part of the adjacent degaussing coils overlap when viewed from above. Measures to arrange can be considered. However, even in such a case, since there exist degaussing coils having different height positions, a difference occurs in their demagnetization efficiency, and the temperature distribution in the width direction of the heat generating member becomes non-uniform.

  The present invention has been made to solve the above-described problems, and does not increase the size of the induction heating unit in the height direction, and excitation that occurs in the non-sheet passing regions of a plurality of types of recording media having different sizes. An object of the present invention is to provide a fixing device and an image forming apparatus in which the magnetic flux of the coil is uniformly demagnetized by the degaussing coil, and the temperature distribution in the width direction in the paper passing area of the heat generating member is made uniform.

  The inventor of the present application has conducted research in order to solve the above problems, and as a result, the layout (the number of arrangement, position, etc.) of the plurality of cores (magnetic cores) installed in the induction heating unit is degaussing of the degaussing coil. It has been found that the efficiency (which is a rate of suppressing the heat generation of the heat generating member by demagnetization) greatly affects. A plurality of pairs of degaussing coils are arranged in parallel at both ends in the width direction, and a plurality of cores are provided for each degaussing coil having a different height position even when the height positions of adjacent degaussing coils are changed. (The multiple cores are arranged so that the degaussing efficiency of the degaussing coil with a short facing distance to the exciting coil is equal to the demagnetizing efficiency of the demagnetizing coil with a long facing distance to the exciting coil.) The degaussing efficiency of the degaussing coils with different height positions is adjusted, and the magnetic flux of the exciting coil generated in the non-sheet passing area of multiple types of recording media of different sizes is uniformly degaussed by the degaussing coil and the degaussing coil is operated It has been found that the temperature distribution in the width direction in the paper passing area of the heat generating member is made uniform even when the heating member is not used.

The present invention is based on the matters described above. That is, the fixing device according to the first aspect of the present invention is configured to generate a magnetic flux while facing the heat generating member having the heat generating layer and the heat generating member. And an excitation coil for inductively heating the heat generating layer by the magnetic flux, and parallel to both ends in the width direction so as to face the excitation coil, and a magnetic flux in a direction to cancel the magnetic flux generated by the excitation coil. comprising a plurality of pairs degaussing coils to be generated in the opposite end portions, and a plurality of cores that control the magnetic path by the exciting coil or / and said demagnetizing coil, degaussing coils of said plurality of pairs of the adjacent degaussing coil opposing distance between the excitation coil is disposed alternately differently in two height positions, said plurality of cores, said degaussing coil a loop of the exciting coil A plurality of center cores that are divided in the width direction so as not to make a difference, and a plurality of arch cores that are installed in a direction orthogonal to the width direction so as to cover the excitation coil and / or the degaussing coil, The height position where the facing distance to the exciting coil becomes long without providing the arch core at the position of the degaussing coil disposed at a height position where the facing distance to the exciting coil becomes short The arch core is disposed at the position of the degaussing coil disposed on the surface .

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 pairs of degaussing coils are arranged such that a part of the adjacent degaussing coils overlap when viewed from above. It has been done.

According to a third aspect of the present invention, in the fixing device according to the first or second aspect of the present invention, the plurality of cores are disposed at a height position at which a facing distance from the exciting coil is shortened. The degaussing efficiency of the degaussing coil is set to be equal to the degaussing efficiency of the degaussing coil arranged at a height position where the facing distance to the exciting coil becomes long.

  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 exciting coil has both ends in the width direction as compared with the number of coil turns in the center portion in the width direction. It is formed so that the number of coil turns of the part increases.

  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 plurality of pairs of degaussing coils are used to pass 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 sixth 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.

  A fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the heating member is a heating member that heats a fixing member that melts a toner image. Is.

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

  In the present invention, a plurality of pairs of degaussing coils are arranged in parallel at different heights at both ends in the width direction, and the degaussing efficiency of the degaussing coil having a short facing distance to the exciting coil is long and the demagnetizing coil having a long facing distance to the exciting coil The arrangement of a plurality of cores is optimized so as to be equivalent to the demagnetization efficiency of the core. As a result, the induction heating unit does not increase in size in the height direction, and the magnetic flux of the excitation coil generated in the non-sheet passing regions of the plurality of types of recording media having different sizes is uniformly demagnetized by the degaussing coil. It is possible to provide a fixing device and an image forming apparatus in which the temperature distribution in the width direction in the paper passing region 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.
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, 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, a plurality of cores 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 can also refer to FIG. 4). 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 plurality of cores 28, 29, and 35 are made of a ferromagnetic material such as ferrite (relative 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. For the purpose of forming an efficient magnetic flux toward the heat generation layer of the fixing roller 20. As shown in FIGS. 2 and 4, the plurality of cores includes a plurality of center cores 28, a plurality of arch cores 29, and two side cores 35. The characteristic configurations of the plurality of cores 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 and the degaussing coils 27 </ b> A to 27 </ b> C on the side facing the fixing roller 20.
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 7.
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).

As shown in FIG. 4, the three pairs of degaussing coils 27 </ b> A to 27 </ b> C are disposed at at least two height positions where the facing distance to the exciting coil 26 is different. Specifically, the three pairs of degaussing coils 27 </ b> A to 27 </ b> C are alternately arranged at two height positions so that the facing distance between adjacent degaussing coils (the facing distance to the excitation coil 26) is different. Specifically, the second demagnetizing coil 27B is disposed at a height position close to the exciting coil 26, and the first demagnetizing coil 27A and the third degaussing coil 27C (demagnetizing coils adjacent to the second degaussing coil 27B). Is disposed at a height position away from the exciting coil 26 by a distance Z.
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 opposing distance between the first degaussing coil 27A (or the third degaussing coil 27C) and the exciting coil 26 is set. 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.
The demagnetization efficiency of the degaussing coils 27A and 27C disposed at a height position where the facing distance to the exciting coil 26 is shortened, and the facing distance to the exciting coil 26 is increased. It arrange | positions so that it may become equivalent to the degaussing efficiency of the degaussing coil 27B arrange | positioned in the height position.
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 plurality of cores 28, 29, 35 installed in the induction heating unit 25 (in particular, the number and positions of the arch cores 29) is demagnetization efficiency of the demagnetizing coil (the heat generation of the fixing roller 20 due to demagnetization). This is because it greatly affects

FIG. 7 is a graph showing the relationship between the opposing distance between the degaussing coil 27 and the exciting coil 26 and the demagnetizing efficiency when the arch core 29 is installed and not installed.
In FIG. 7, the horizontal axis represents the facing distance between the demagnetizing coil 27 and the exciting coil 26, and the vertical axis represents the demagnetizing efficiency. In FIG. 7, the solid line graph is a graph showing the relationship between the opposing distance and the demagnetization efficiency when the arch core 29 covering the demagnetizing coil is installed (as shown in FIG. 5). It is a graph which shows the relationship between the opposing distance and the demagnetization efficiency when not installing the arch core 29 which covers a demagnetizing coil (it is a form like FIG. 6).
As shown in FIG. 7, the demagnetization efficiency decreases as the opposing distance between the degaussing coil and the excitation coil becomes longer, whether the arch core 29 is installed or the arch core 29 is not installed. However, when the arch core 29 is not installed, the demagnetization efficiency is lower as a whole compared to the case where the arch core 29 is installed. In the first embodiment, by utilizing such a property, the height position (opposite distance) and the arch core 29 are arranged so that the demagnetization efficiency of the demagnetization coils having different height positions (opposite distance) is substantially the same. The presence or absence is adjusted.

  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), the exciting coil 26, Is set to about 5 mm, and the arch coil 29 is not installed for the second demagnetizing coil 27B. Therefore, the difference in demagnetization efficiency δ1 between the three pairs of degaussing coils 27A to 27C is determined as the second demagnetizing coil. The difference in demagnetization efficiency δ2 when the arch coil 29 is installed can be made extremely small with respect to the coil 27B (δ1 << δ2).

  As described above, in the first embodiment, a plurality of pairs of degaussing coils 27A to 27C are arranged in parallel at both ends in the width direction, and the demagnetizing coil 27B having a short facing distance from the exciting coil 26 is provided. The arrangement of the plurality of cores 29 is optimized so that the demagnetization efficiency is equal to the demagnetization efficiency of the degaussing coils 27 </ b> A and 27 </ b> C having a long opposing distance to the excitation coil 26. Thereby, the magnetic flux of the exciting coil 26 generated in the non-sheet passing region of the plural types of recording media P having different sizes is uniformly demagnetized by the degaussing coils 27A to 27C without the induction heating unit 25 becoming large in the height direction. Thus, the temperature distribution in the width direction in the sheet passing area of the fixing roller 20 (heat generating member) can be made uniform.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 8 is a schematic diagram illustrating an induction heating unit of the fixing device according to the second embodiment. In the fixing device according to the second embodiment, the configuration of the exciting coil 26 is different from that of the first embodiment.

  Referring to FIG. 8, in the fixing device according to the second embodiment, as in the first embodiment, excitation coil 26, three pairs of demagnetization coils, center core 28, arch core 29, side core 35, coil An induction heating unit 25 composed of a guide or the like 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. The arch core 29 is disposed at the position of the first demagnetizing coil 27A and the third demagnetizing coil 27C, and the arch core 29 is not disposed at the position of the second demagnetizing coil 27B. Adjustments are made to be equivalent. In FIG. 8, the degaussing coil is not shown for easy understanding.

Here, in the second embodiment, as shown in FIG. 8, the exciting coil 26 is a coil at both ends in the width direction (the range K in FIG. 8) compared to the number of coil turns at the center in the width direction. The number of turns is increased.
With such a configuration, when any one of the three pairs of degaussing coils 27A to 27C is not operated (as in the case of FIGS. 4A and 4C in the first embodiment, the size other than the postcard size). In the case where the recording medium P is passed through), the presence of the degaussing coil that does not perform the degaussing operation causes the temperature at both ends in the width direction of the heating range of the fixing roller 20 heated by the excitation coil 26 to be the center in the width direction. The malfunction which becomes low compared with can be suppressed. Therefore, it is possible to reliably suppress the problem that the fixing unevenness in the width direction occurs in the fixed image on the recording medium P.

  As described above, also in the second embodiment, similarly to the first embodiment, a plurality of pairs of demagnetizing coils 27A to 27C are arranged in parallel at the height positions at both ends in the width direction, and the exciting coil 26 is arranged. The arrangement of the cores 29 is optimized so that the demagnetizing efficiency of the degaussing coil 27B with a short facing distance is equal to the demagnetizing efficiency of the degaussing coils 27A and 27C with a long facing distance with the exciting coil 26. Thereby, the magnetic flux of the exciting coil 26 generated in the non-sheet passing region of the plural types of recording media P having different sizes is uniformly demagnetized by the degaussing coils 27A to 27C without the induction heating unit 25 becoming large in the height direction. Thus, the temperature distribution in the width direction in the sheet passing area of the fixing roller 20 (heat generating 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. 9 is a schematic diagram illustrating an induction heating unit of the fixing device according to the third embodiment, and corresponds to FIG. 4 according to the first embodiment. The fixing device according to the third embodiment is different from that of the first embodiment in the configuration of the center core 28 and the degaussing coils 27A to 27C.

  Referring to FIG. 9, 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 first embodiment. 35, an induction heating unit 25 composed of a coil guide and the like 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. The arch core 29 is disposed at the position of the first demagnetizing coil 27A and the third demagnetizing coil 27C, and the arch core 29 is not disposed at the position of the second demagnetizing coil 27B. Adjustments are made to be equivalent.

Here, in the third embodiment, referring to FIG. 9A, the center core 28 disposed in the loop of the three pairs of demagnetizing coils 27A to 27C among the plurality of center cores 28 is arranged in the width direction. The adjacent portions of the three pairs of degaussing coils 27A to 27C are arranged in the width direction so that a part of the adjacent center cores 28 overlap each other when viewed from a direction orthogonal to (a short direction in FIG. 4A). It is formed so as to be inclined with respect to it. 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.
As described above, even if there is a gap between the center cores 28 disposed in the adjacent demagnetizing coils, a part of the adjacent center cores 28 overlaps when viewed from the direction orthogonal to the width direction. Therefore, the effect of efficiently controlling the magnetic path by the center core 28 is uniformly exhibited over the width direction. Therefore, the demagnetization by the demagnetizing coils 27A to 27C is further uniformly performed in the width direction, and the temperature distribution in the width direction in the sheet passing area of the fixing roller 20 (heating member) is further uniformized.

  As described above, also in the third embodiment, a plurality of pairs of degaussing coils 27A to 27C are arranged in parallel at both ends in the width direction, and the exciting coil 26, as in the above embodiments. The arrangement of the cores 29 is optimized so that the demagnetizing efficiency of the degaussing coil 27B with a short facing distance is equal to the demagnetizing efficiency of the degaussing coils 27A and 27C with a long facing distance with the exciting coil 26. Thereby, the magnetic flux of the exciting coil 26 generated in the non-sheet passing region of the plural types of recording media P having different sizes is uniformly demagnetized by the degaussing coils 27A to 27C without the induction heating unit 25 becoming large in the height direction. Thus, the temperature distribution in the width direction in the sheet passing area of the fixing roller 20 (heat generating 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, even when two pairs or four or more pairs of degaussing coils are installed, a plurality of pairs of degaussing coils are arranged at a height position. The arrangement of multiple cores is optimized so that the degaussing efficiency of the degaussing coil with a short facing distance to the exciting coil 26 is equivalent to the demagnetizing efficiency of the demagnetizing coil with a long facing distance to the exciting coil 26. By achieving the same effect, it is possible to obtain the same effects as those of the above embodiments.

  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 graph which shows the relationship between the opposing distance of a degaussing coil and an exciting coil, and a degaussing efficiency. 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 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,
29 Arch Core,
30 pressure roller (pressure member),
35 side cores, 36 coil guides,
40, 40A-40D thermistor, 60 selector switch.

Claims (8)

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 cores for controlling a magnetic path by the excitation coil and / or the degaussing 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 ,
The plurality of cores cover 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, and the excitation coil and / or the degaussing coil. A plurality of arch cores constructed in a direction perpendicular to the width direction as described above,
The demagnetizing coil disposed at a height where the facing distance to the exciting coil is shortened is not disposed at the height position where the facing distance from the exciting coil is increased without disposing the arch core. The fixing device according to claim 1, wherein the arch core is disposed at a position of the degaussing coil . The fixing device according to claim 1, wherein the plurality of pairs of degaussing coils are arranged so that a part of adjacent degaussing coils overlap when viewed from above. The plurality of cores are disposed at a height position where the demagnetizing efficiency of the degaussing coil disposed at a height position where the facing distance to the exciting coil is shortened, and the facing distance from the exciting coil is increased. The fixing device according to claim 1, wherein the fixing device is disposed so as to be equivalent to a demagnetizing efficiency of the degaussing coil.   The said exciting coil was formed so that the coil winding number of the width direction both ends might be larger than the coil winding number of the width direction center part, The Claim 1 characterized by the above-mentioned. Fixing device.   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 4.   The fixing device according to claim 1, wherein the heat generating member is a fixing member that melts a toner image.   6. 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