JP5487046B2 - Fixing apparatus and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a fixing device that heat-fixes a toner image transferred onto a recording medium, and an image forming apparatus including the fixing device.

  An image forming apparatus such as a copying machine, a facsimile, or a printer records, as basic components, an image forming unit that forms an image on an image carrier (for example, a photosensitive drum) and a toner image on the image carrier. A transfer unit that transfers onto a sheet as an example of a medium, and a fixing device that heat-fixes the toner image transferred onto the sheet onto the sheet.

  In order to reduce the warm-up time at startup and to save energy, a number of fixing devices adopting a belt method that can set a small heat capacity are increasing. In addition, an electromagnetic induction heating (IH) method capable of rapid heating and high efficiency heating has attracted attention. In the electromagnetic induction heating method, an induction current is induced in a fixing roller or a fixing belt by a magnetic flux generated by applying a high-frequency current to an induction coil, and the fixing roller or the fixing belt is attached using a resistance of the fixing roller or the fixing belt itself. Joule heat generation (induction heating) is performed, and the toner image is fixed on the sheet (recording medium) at the nip portion between the fixing roller (or the fixing belt) and the pressure roller by the Joule heat. A fixing device combining an electromagnetic induction heating method and a belt method has been commercialized.

  When the belt method and the electromagnetic induction heating method are combined, there are merits such as ease of coil layout, ease of coil cooling, and direct heating of the belt. On the other hand, since the electromagnetic induction heating method has a high heating capacity, there is a problem that the fixing belt and the fixing roller are likely to be overheated.

  Overheating of the fixing belt and the fixing roller tends to occur at both ends in the width direction of the fixing belt (in the case of the fixing roller, both ends in the axial direction). Both ends in the width direction of the fixing belt (both ends in the axial direction of the fixing roller) are non-sheet passing regions that do not contact the sheet at the nip portion when the size in the width direction of the sheet is small. Since heat fixing is not performed in the non-sheet passing area, the temperature rises excessively in the non-sheet passing area when continuous printing is performed on a small size sheet. When printing is performed using a large size paper after printing using a small size paper, the toner is fixed by heat from the portion of the toner image transferred onto the large size paper that contacts the overheated area. It adheres to the overheated area of the belt. The adhered toner adheres to a toner image on a sheet to be fixed next, and causes an image defect, so-called image offset. In addition, the overheated region tends to be thermally deteriorated.

  As a technique for suppressing an excessive temperature rise of a fixing belt or a fixing roller, for example, one disclosed in Patent Document 1 is known. The fixing device of Patent Document 1 includes a fixing belt that is induction-heated by a magnetic field generated by a coil, a pressure roller that forms a nip portion between the fixing belt, an arch core and a side core that form a magnetic path together with the fixing belt, A center core disposed between the arch core and the fixing belt as viewed from the magnetic path, and a magnetic shielding plate attached to the outer surface of the center core.

  The magnetic shielding plate is positioned in the magnetic path along with the rotation of the center core, and shields or suppresses the magnetic flux in the non-sheet passing area, thereby suppressing an excessive temperature rise in the non-sheet passing area of the fixing belt and the fixing roller. It is configured to be possible.

JP 2010-26246 A

  In the fixing device disclosed in Patent Document 1, the magnetic shielding plate is attached to the outer surface of the center core using a silicon-based adhesive. Since it takes time until the adhesive is cured, productivity is lowered. If the application amount of the adhesive is reduced in order to shorten the curing time of the adhesive, the holding force for holding the magnetic shielding plate on the outer surface of the center core is weakened, and a resonance noise may be generated.

Therefore, in view of the above circumstances, the present invention provides a fixing device capable of improving productivity while securing a holding force for the magnetic shielding plate on the outer peripheral surface of the center core, and an image forming apparatus including the same. For the purpose.

In order to achieve the above object, a fixing device according to the present invention includes a magnetic flux generation source that generates magnetic flux, a first rotating body that is induction-heated by the magnetic flux while rotating in a predetermined direction, and a rotation in a predetermined direction. However, a second rotating body that forms a nip portion through which the recording medium carrying the toner image passes is formed between the first rotating body and a magnetic material, and a magnetic path through which the magnetic flux passes is the first rotation. A first core formed together with the body, an outer peripheral surface, made of a magnetic material, disposed between the first core and the first rotating body as viewed from the magnetic path, and rotatable in a predetermined direction. A magnetic shielding plate made of a non-magnetic material attached to the outer peripheral surface of the second core and the second core, wherein the magnetic shielding plate is located in the magnetic path as the second core rotates. Or a magnetic shielding plate to be suppressed and the magnetic shielding plate to the second core And a holding means for holding on said outer peripheral surface, the second core comprises a core pieces adjacent to each other in the axial direction, of the core pieces adjacent ones, the magnetic shield plate on at least one of the core pieces mounted and the magnetic shielding plate, while being held on the outer peripheral surface of the core piece, which extends along the outer peripheral surface, in close contact with the outer peripheral surface and the axial direction of the core pieces A main body having an axial dimension substantially the same as the dimension, and the holding means protrudes in a rib shape from the main body toward the inside of the outer peripheral surface of the core piece , and one of the main body a protrusion extending in the axial direction toward the other end edge from the edge, is formed on the outer peripheral surface of said core pieces, Ri Do and a locking portion capable of locking the protruded portion, the locking Part from one end face of the core piece to the other end face The groove portion extends in the axial direction and into which the protruding portion is inserted, and the protruding portion includes a pair of first protruding pieces and second protruding pieces facing each other in the rotation direction of the second core, The groove portion includes a first groove into which the first protruding piece is inserted and a second groove into which the second protruding piece is inserted .

According to the fixing device of the present invention, the rib-like protruding portion protruding from the main body portion of the magnetic shielding plate toward the outer peripheral surface of the second core is engaged with the locking portion formed on the outer peripheral surface of the second core. The magnetic shielding plate can be firmly held on the outer peripheral surface of the second core only by stopping. This reduces the time required to hold the magnetic shielding plate on the outer peripheral surface of the second core as compared to the configuration in which the magnetic shielding plate is held on the outer peripheral surface of the second core using an adhesive. Productivity is improved. Moreover, since the main-body part of a magnetic shielding board is hold | maintained in the state of contact | adhering to the outer peripheral surface of the 2nd core, generation | occurrence | production of a resonance sound can be suppressed. Moreover, according to this structure, a magnetic shielding board can be hold | maintained on the outer peripheral surface of a 2nd core by the simple process of forming a groove part in the outer peripheral surface of a 2nd core. Further, according to this configuration, the first projecting piece and the second projecting piece are formed to face the rotation direction of the second core, and the first groove and the second groove are also formed to face the rotation direction of the second core. Has been. Therefore, the magnetic shielding plate can resist the centrifugal force generated by the rotation of the second core.

A fixing device according to another aspect of the present invention includes a magnetic flux generation source that generates magnetic flux, a first rotating body that is induction-heated by the magnetic flux while rotating in a predetermined direction, and a toner that rotates in a predetermined direction. A second rotating body that forms a nip portion through which a recording medium carrying an image passes is formed between the first rotating body and a magnetic material, and a magnetic path through which the magnetic flux passes is formed together with the first rotating body. A first core, a second core having an outer peripheral surface, made of a magnetic material, disposed between the first core and the first rotating body as viewed from the magnetic path, and rotatable in a predetermined direction; A magnetic shielding plate made of a nonmagnetic material attached to the outer peripheral surface of the second core, wherein the magnetic shielding plate is located in the magnetic path as the second core rotates and shields or suppresses the magnetic flux. A shielding plate and the magnetic shielding plate on the outer peripheral surface of the second core; Holding means, and the magnetic shielding plate has a main body portion that extends along the outer peripheral surface and is in close contact with the outer peripheral surface while being held on the outer peripheral surface of the second core. The holding means is formed on the outer peripheral surface of the second core and a protruding portion that protrudes in a rib shape from the main body portion toward the outer peripheral surface of the second core, and locks the protruding portion. it consists of a possible locking portion, the second core comprises a core pieces adjacent to each other in the axial direction, of the core pieces adjacent ones, and said magnetic shielding plate is at least one of the core pieces are attached The magnetic shielding plate has a coupling piece protruding in the axial direction of the second core, and the other core piece of the adjacent core pieces has a fitting portion into which the coupling piece is fitted. .

  According to this configuration, the coupling piece of the magnetic shielding plate is fitted into the fitting portion of the other core piece, so that the magnetic shielding plate is adjacent to the one core piece to which the magnetic shielding plate is attached. It is also held by a piece. Thereby, a magnetic shielding board can be hold | maintained still more firmly.

  In still another preferred embodiment of the present invention, the other core piece has an end surface facing the one core piece, and the fitting portion is a hole formed in the end surface.

  According to this configuration, the magnetic shielding plate can be held on the other core piece by a simple process of forming a hole in the end face of the other core piece.

In still another preferred embodiment of the present invention, the fixing device further includes a sheet material that is elastic and is disposed between the main body portion of the magnetic shielding plate and the outer peripheral surface of the second core. .

According to this structure, the main-body part of a magnetic shielding board is hold | maintained in the state which adhered further to the outer peripheral surface of the 2nd core via the sheet | seat material. Thereby, generation | occurrence | production of a resonance sound can be suppressed further.

  An image forming apparatus according to the present invention includes an image carrier on which a toner image is formed, an image forming unit that forms the toner image on the image carrier, and a transfer unit that transfers the toner image onto a recording medium. A fixing device for fixing the toner image on the recording medium, and the fixing device having the above-described configuration is used as the fixing device.

According to the fixing device and the image forming apparatus including the same according to the present invention, the protrusion is formed on the magnetic shielding plate, the engaging portion is formed on the outer peripheral surface of the second core, and the protruding portion is used as the engaging portion. With the configuration of locking, it is possible to improve productivity while securing a holding force for the magnetic shielding plate.

1 schematically shows an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a longitudinal sectional view of the fixing device, showing a state where the magnetic shielding plate is in a retracted position. FIG. 3 is a longitudinal sectional view of the fixing device, showing a state where the magnetic shielding plate is in a shielding position. It is the top view which looked at the magnetic shielding board and the center core from the heat roller side, when a magnetic shielding board exists in a shielding position. It is a perspective view of a 1st shielding board part. It is a perspective view of the 1st core piece. It is a perspective view which shows the state which attached the 1st shielding board part to the 1st core piece. It is a front view which shows the state which attached the 1st shielding board part to the 1st core piece. It is a front view which shows an example of the attachment to the 3rd core piece of a 3rd shielding board part. It is a front view which shows the other example of attachment to the 3rd core piece of a 3rd shielding board part. It is a figure which shows the structure which has arrange | positioned the elastic sheet material between the 1st shielding board and the 1st core piece.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 has, for example, a printer, a copier, a facsimile apparatus, and the like which perform printing by transferring a toner image onto the surface of a sheet as an example of a recording medium based on image information input from the outside. It can take the form of a multifunction machine or the like.

  An image forming apparatus 1 shown in FIG. 1 is a tandem color printer, for example. The image forming apparatus 1 includes a square box-shaped apparatus main body 2 that forms a color image on paper inside, and a discharge tray 3 for discharging the paper on which the color image is printed is provided on the upper surface of the apparatus main body 2. Is provided. In the lower part of the apparatus main body 2, a paper feed cassette 5 for storing paper is disposed. Further, a stack tray 6 on which manual paper is placed is disposed on the right side surface of the apparatus main body 2 in FIG. An image forming unit 7 is provided on the upper part of the apparatus main body 2, and the image forming unit 7 forms an image on a sheet based on image data such as characters and patterns transmitted from the outside of the apparatus.

  In the left position of the image forming unit 7 in FIG. 1, a first transport path 9 for transporting the sheet fed from the paper feed cassette 5 to the image forming unit 7 is disposed. A second transport path 10 that guides the paper placed on the stack tray 6 to the first transport path is disposed above the paper feed cassette 5. Each of the first conveyance path 9 and the second conveyance path 10 is provided with a conveyance roller pair 43 for conveying a sheet. In the upper left part of the apparatus main body 2, a fixing device 14 that performs a fixing process on a sheet on which an image is formed by the image forming unit 7, and a sheet that has been subjected to the fixing process are conveyed to a discharge tray 3. 3 conveyance paths 11 are arranged.

  The paper feed cassette 5 can be inserted into and removed from the apparatus main body 2 and has a storage unit 16. The storage unit 16 can selectively store at least two types of sheets having different sizes in the paper feeding direction. The paper stored in the storage unit 16 is fed out to the first transport path 9 one by one by the paper feed roller 17 and the pair of roller rollers 18.

  The stack tray 6 can be opened and closed with respect to the apparatus main body 2, and a sheet is placed on the manual feed surface 19. The sheets placed on the manual feed surface 19 are fed out to the second conveyance path 10 one by one by the pickup roller 20 and the pair of roller rollers 21.

  The first conveyance path 9 and the second conveyance path 10 join before the registration roller pair 22. The paper supplied to the registration roller pair 22 waits here, performs skew adjustment and timing adjustment, and then is sent to the secondary transfer unit 23. The full color toner image on the intermediate transfer belt 40 is secondarily transferred to the sheet by the secondary transfer unit 23 on the sent sheet. Thereafter, the sheet on which the toner image is fixed by the fixing device 14 is reversed in the fourth conveyance path 12 as necessary, and the full-color toner image is secondarily transferred to the opposite side surface by the secondary transfer unit 23. Is done. Then, after the toner image on the opposite surface is fixed by the fixing device 14, the toner image is discharged to the discharge tray 3 by the discharge roller pair 24 through the third conveyance path 11.

  The image forming unit 7 is formed by four image forming units 26 to 29 that form toner images of black (B), yellow (Y), cyan (C), and magenta (M), and image forming units 26 to 29. And an intermediate transfer unit 30 that synthesizes and carries the toner images of the respective colors.

  Each of the image forming units 26 to 29 includes a photosensitive drum 32 (image carrier), a charger 33 disposed to face the peripheral surface of the photosensitive drum 32, and the rotation of the photosensitive drum 32 with respect to the charger 33. A laser scanning unit 34 that irradiates a laser beam to a specific position on the circumferential surface of the photosensitive drum 32 on the downstream side in the direction, and a downstream side in the rotational direction of the photosensitive drum 32 with respect to the laser beam irradiation position from the laser scanning unit 34. A developing device 35 disposed opposite to the circumferential surface of the photosensitive drum 32 and a downstream side of the developing device 35 in the rotation direction of the photosensitive drum 32 and opposed to the circumferential surface of the photosensitive drum 32. And a cleaner 36 provided.

  The photosensitive drums 32 of the image forming units 26 to 29 are rotated in the counterclockwise direction in the drawing by a drive motor (not shown). The developing device 35 of each of the image forming units 26 to 29 includes a developing container 51 that stores a two-component developer that includes black toner, yellow toner, cyan toner, and magenta toner.

  The intermediate transfer unit 30 includes a driving roller 38 disposed near the image forming unit 26, a driven roller 39 disposed near the image forming unit 29, and a space between the driving roller 38 and the driven roller 39. A tension roller 42 disposed at a position, a driving roller 38, a driven roller 39, an intermediate transfer belt 40 disposed across the tension roller 42, and the photosensitive drum 32 of each of the image forming units 26 to 29 are intermediate. And four transfer rollers 41 disposed so as to be capable of being pressed through the transfer belt 40.

  In the intermediate transfer unit 30, the toner images of the respective colors are transferred from the photosensitive drum 32 onto the intermediate transfer belt 40 at the position of the transfer roller 41 of each of the image forming units 26 to 29, and full color toner is transferred. An image is formed.

  A transport path 47 is provided on the upstream side and the downstream side of the fixing device 14 in the paper transport direction. The sheet conveyed through the secondary transfer unit 23 is guided to the fixing device 14 through the upstream conveyance path 47. Then, the sheet subjected to the fixing process is guided to the third conveyance path 11 through the conveyance path 47 on the downstream side.

  The third transport path 11 guides the paper on which the fixing process has been performed by the fixing device 14 to the discharge tray 3. The third transport path 11 is provided with a transport roller pair 49 for transporting the paper to the discharge tray 3 and the discharge roller pair 24 is disposed at the outlet thereof.

  Hereinafter, the fixing device 14 will be described with reference to FIG. FIG. 2 is a longitudinal sectional view of the fixing device 14. The fixing device 14 performs a fixing process for fixing the toner image on the paper by heating and pressing the toner image transferred onto the paper. The fixing device 14 includes a pressure roller 44 (second rotating body), a fixing belt 48 (first rotating body), a fixing roller 45, a heat roller 46, and a coil unit 50.

  The pressure roller 44 is a roller member that can rotate counterclockwise in FIG. 2, for example, a cylindrical core material made of SUS, an elastic layer made of silicone rubber laminated on the core material, and an elastic layer. And a PFA surface release layer laminated thereon. A heat source such as a halogen heater may be disposed inside the core member 46. The elastic layer 48 can be heated by a heat source.

  The fixing belt 48 is an endless belt wound around a fixing roller 45 and a heat roller 46 described later, and can rotate clockwise in FIG. The pressure roller 44 is pressed toward the fixing belt 48 by a biasing member (not shown) to form a nip portion NP between the fixing belt 55 through which a sheet carrying a toner image is passed. The fixing belt 48 has a width-direction dimension in a direction orthogonal to the conveyance direction T of the sheet passing through the nip portion NP.

  The fixing belt 48 is laminated on an electroformed nickel base material positioned on the fixing roller 45 side, an elastic layer made of silicone rubber laminated on the base material on the side opposite to the fixing roller 45, and the elastic layer. And a PFA surface release layer located on the pressure roller 44 side.

  The fixing roller 45 is a roller member that is disposed in the fixing belt 48 in parallel to the pressure roller 44 and is rotatable in the clockwise direction that is the same as the rotation direction of the fixing belt 48. The fixing roller is, for example, a cylindrical core material made of SUS, an elastic layer made of silicone rubber laminated on the core material, and a surface release layer made of PFA laminated on the elastic layer and contacting the fixing belt 48. Including. The fixing roller 45 rotates while contacting the inner surface of the fixing belt 55 at a position corresponding to the nip portion NP. As a result, the fixing belt 48 rotates while being sandwiched between the fixing roller 45 and the pressure roller 44 at the nip portion NP.

  The heat roller 46 is a roller member disposed in the fixing belt 48 in parallel to the fixing roller 45 at a position opposite to the pressure roller 44 with the fixing roller 45 interposed therebetween. It can be rotated. The heat roller 46 includes a cylindrical core material made of magnetic metal such as SUS, and a surface release layer made of PFA laminated on the core material.

  Each of the pressure roller 44, the fixing roller 45, and the heat roller 46 has an axial dimension that is set larger than the maximum width dimension of the paper that is passed through the nip portion NP, and the width dimension of the fixing belt 48 is It is set to be larger than the maximum width dimension of the paper.

  The coil unit 50 induction-heats the fixing belt 48 at a position where the fixing belt 48 is wound around the heat roller 46. The coil unit 50 includes a coil 52 (magnetic flux generation source), a bobbin 53, and a center core 58 (second core). Core), a plurality of pairs of arch cores 54, a pair of side cores 56, and a magnetic shielding plate 60.

  The bobbin 53 is a member that holds the coil 52, and extends along the axial direction of the heat roller 46 (that is, the width direction of the fixing belt 48). The bobbin 53 is a member formed in a semi-cylindrical shape so as to extend along the fixing belt 48 at a position opposite to the fixing roller 45. The bobbin 53 extends over the width of the fixing belt 48 and substantially half of the circumferential length of the fixing belt 48. The bobbin 53 is separated from the fixing belt 48 by a predetermined distance. The material of the bobbin 53 is a heat resistant resin (for example, PPS, PET, LCP).

  The coil 52 is arranged in a winding shape on the semi-cylindrical bobbin 53 along the extending direction of the bobbin 53. The winding region of the coil 52 is set to a size that exceeds the dimension in the width direction of the fixing belt 48. The coil 52 is attached to the bobbin 53 by, for example, a silicone adhesive. Further, an AC bias power source V is connected to the coil 52, and when an AC bias is applied to the coil 52, the coil 52 generates a magnetic flux.

  The center core 58 is a cylindrical core made of a magnetic material such as ferrite. In FIG. 2, the center core 58 is disposed on the opposite side of the heat roller 46 with the bobbin 53 interposed therebetween, and extends parallel to the heat roller 46. The center core 58 faces the area where the coil 52 does not exist in the bobbin 53. A rotation shaft member 59 is inserted through the center core 58, and the rotation of the rotation shaft member 59 causes the center core 58 to rotate clockwise or counterclockwise. The rotating shaft member 59 is made of, for example, a nonmagnetic metal (AL or the like) or a heat resistant resin (PPS, PET, LCP, or the like), and is rotated by a driving source (not shown).

  The arch core 54 and the side core 56 are made of a magnetic material such as ferrite, and form a magnetic path along with the fixing belt through which the magnetic flux generated by the coil 52 passes. The arch core 54 is paired so as to surround the coil 52 from both sides around the center core 58. The arch core 54 is formed in an arch shape with the center core 58 interposed therebetween in a paired state. In practice, a plurality of pairs of arch cores 54 are arranged along the axial direction of the center core 58 as shown in FIG. The plurality of arch cores 54 are arranged over a region exceeding the winding region of the coil 52.

  In FIG. 2, the center core 58 is disposed between the upper ends of the arch cores 54 that make a pair. On the other hand, a side core 56 extending along the extending direction of the bobbin 53 is connected to the lower end of the arch core 54. The arch core 54 and the side core 56 are held by a core holder (not shown) made of a heat resistant resin (for example, PPS, PET, LCP). In the present embodiment, the arch core 54 and the side core 56 constitute a first core.

  The magnetic flux generated by the coil 52 passes through a magnetic path formed between the fixing belt 48, the side core 56, the arch core 54 and the center core 58. The center core 58 is located between the arch core 54 and the fixing belt 48 as viewed from the magnetic path, and a magnetic shielding plate 60 is attached to the outer peripheral surface of the center core 58.

  The magnetic shielding plate 60 is a thin plate member made of a nonmagnetic and highly conductive material, for example, oxygen-free copper. The magnetic shielding plate 60 can rotate between the shielding position and the retracted position as the center core 58 rotates. FIG. 2 shows a state where the magnetic shielding plate 60 is in the retracted position, and FIG. 3 shows a state where the magnetic shielding plate 60 is in the shielding position. When the magnetic shielding plate 60 is in the shielding position (FIG. 3), it is located in the magnetic path formed between the fixing belt 48, the side core 56, the arch core 54 and the center core 58, that is, facing the fixing belt 48. , Shield or suppress magnetic flux. On the other hand, when the magnetic shielding plate 60 is in the retracted position (FIG. 2), it retracts from the magnetic path, that is, moves to a position not facing the fixing belt 48, and does not shield or suppress the magnetic flux.

  Next, the center core 58 and the magnetic shielding plate 60 will be further described with reference to FIG. FIG. 4 is a plan view of the magnetic shielding plate 60 and the center core 58 viewed from the heat roller 46 side when the magnetic shielding plate 60 is in the shielding position. The center core 58 is actually divided into a plurality of parts in the axial direction, and an intermediate core piece 580 corresponding to an intermediate portion of the center core 58 and a pair of first core pieces positioned outside the intermediate core piece 580 in the axial direction. 581, a pair of second core pieces 582 positioned axially outward of the intermediate core piece 580 relative to the first core piece 581, and positioned axially outward of the intermediate core piece 580 relative to the second core piece 582. It consists of a pair of third core pieces 583. The intermediate core piece 580, the first core piece 581, the second core piece 582, and the third core piece 583 are adjacent to each other in the axial direction of the center core 58, and the third core piece 583 is the endmost in the axial direction of the center core 58. It is a core piece located in. The rotary shaft member 59 is inserted through all of the intermediate core piece 580, the first core piece 581, the second core piece 582, and the third core piece 583, and the intermediate core piece 580, the first core piece 581, the second core. The piece 582 and the third core piece 583 rotate together.

  The magnetic shielding plate 60 is also divided corresponding to the center core 58. Specifically, the magnetic shielding plate 60 includes a first shielding plate portion 60a attached to the outer peripheral surface of the first core piece 581 and a second shielding plate portion 60b attached to the outer peripheral surface of the second core piece 582. And the third shielding plate 60c attached to the outer peripheral surface of the third core piece 583. The magnetic shielding plate 60 is not attached to the intermediate core piece 580.

  The first shielding plate portion 60a, the second shielding plate portion 60b, and the third shielding plate portion 60c have substantially the same width as the axial dimension of the corresponding first core piece 581, second core piece 582, and third core piece 583. Has directional dimensions. The first shielding plate portion 60a extends in the circumferential direction of the first core piece 581 over an angular range of 80 °, and the second shielding plate portion 60b extends around the second core piece 582 over an angular range of 160 °. The third shielding plate part 60c extends in the circumferential direction of the third core piece 583 over an angle range of 280 °. Therefore, the circumferential direction length of the 1st shielding board part 60a is the smallest, and the circumferential direction length of the 3rd shielding board part 60c is the largest.

  The division of the center core 58 and the division of the magnetic shielding plate 60 are determined according to the size of the sheet passing through the nip portion NP. Specifically, the axial dimension of the intermediate core piece 580 is determined so as to correspond to the paper P1 (for example, A5 paper) having the minimum width size. The axial dimension from one first core piece 581 to the other first core piece 581 is determined so as to correspond to a sheet P2 (for example, A4 sheet lengthwise) having an intermediate width size. The axial dimension from one second core piece 582 to the other second core piece 582 is determined so as to correspond to the paper P3 (for example, A3 paper) having the maximum width size. The axial dimension from one third core piece 583 to the other third core piece 583, that is, the axial dimension of the center core 58 is set to exceed the width size of the paper P3.

  As described above, the pair of arch cores 54 is arranged along the axial direction of the center core 58, and the arrangement density of the pair of arch cores 54 is determined in accordance with the magnetic flux density (magnetic field strength) distribution of the coil 52. . By appropriately arranging the arch core 54 and the side core 56, the magnetic flux density distribution (temperature difference) in the axial direction of the heat roller 46 (the width direction of the fixing belt 48) is made uniform.

  Next, the fixing operation by the fixing device 14 configured as described above will be described. When an AC bias is applied to the coil 52 from the AC bias power source V, the coil 52 generates a magnetic flux. The magnetic flux passes through a magnetic path formed between the fixing belt 48, the side core 56, the arch core 54, and the center core 58. When the magnetic flux passes through the fixing belt 48, an induced current is induced. When the induced current flows through the fixing belt 48, Joule heat is generated by the resistance of the fixing belt 48 itself, that is, the fixing belt 48 is induction heated. The entire fixing belt 48 generates heat as the fixing roller 45 rotates.

  At this time, the center core 58 is appropriately rotated by the rotating shaft member 59 according to the width direction size of the sheet, and the first shielding plate portion 60a to the third shielding plate portion 60c of the magnetic shielding plate 60 are shielded in the magnetic path. The position is switched to the retracted position retracted from the magnetic path.

  For example, when the sheet passing through the nip portion NP is the sheet P1 having the minimum width size, the center core 58 has the rotation shaft member 59 so that all of the first shielding plate portion 60a to the third shielding plate portion 60c take the shielding position. Is rotated by. Therefore, only the sheet passing area where the fixing belt 48 contacts the sheet P1 at the nip NP is induction-heated, while the non-sheet passing area where the fixing belt 48 does not contact the sheet P1 at the nip NP is not induction-heated, or Heating is suppressed.

  When the sheet passing through the nip portion NP is the sheet P2 having an intermediate width size, the center core 58 has the second shielding plate portion 60b and the third shielding plate portion 60c while the first shielding plate portion 60a takes the retracted position. Is rotated by the rotary shaft member 59 so as to take the shielding position. Therefore, only the paper passing area where the fixing belt 48 contacts the paper P2 at the nip portion NP is induction-heated, while the non-paper passing area where the fixing belt 48 does not contact the paper P2 at the nip portion NP is not induction heated, or Heating is suppressed.

  Further, when the paper passing through the nip portion NP is the paper P3 having the maximum width size, the center core 58 has the third shielding plate 60c while the first shielding plate 60a and the second shielding plate 60b take the retracted position. Is rotated by the rotary shaft member 59 so as to take the shielding position. Therefore, only the sheet passing area where the fixing belt 48 contacts the sheet P3 at the nip NP is induction-heated, while the non-sheet passing area where the fixing belt 48 does not contact the sheet P3 at the nip NP is not induction-heated, or Heating is suppressed.

  In this way, the center core 58 is appropriately rotated so as to shield the first shielding plate portion 60a to the third shielding plate portion 60c so that the non-sheet passing region in the fixing belt 48 is not induction heated or suppressed. By switching between the position and the retracted position, excessive temperature rise in the non-sheet passing area is suppressed. Note that the positional relationship between the first shielding plate portion 60a to the third shielding plate portion 60c is such that the first shielding plate portion 60a to the third shielding plate portion 60c appropriately set the shielding position or the retracted position according to the sheets P1 to P3. It is set to be able to take.

  When the sheets P1 to P3 enter the nip portion NP along the transport direction T, the toner images on the sheets P1 to P3 are heated from the fixing belt 48 while being sandwiched between the fixing belt 48 and the pressure roller 44. receive. As a result, the toner image is fixed on the paper.

  A thermistor 62 is disposed in the heat roller 46. The thermistor 62 detects the surface temperature of the heat roller 46. The detected surface temperature is transmitted to a control unit (not shown), and the control unit controls the AC bias power source V based on the surface temperature to adjust the density of magnetic flux generated by the coil 52.

  Next, attachment of the magnetic shielding plate 60 to the outer peripheral surface of the center core 58 will be described with reference to FIGS. 5 to 8 illustrate the attachment of the first shielding plate portion 60a to the first core piece 581. FIG. FIG. 5 is a perspective view of the first shielding plate portion 60a. FIG. 6 is a perspective view of the first core piece 581. FIG. 7 is a perspective view showing a state in which the first shielding plate 60 a is attached to the first core piece 581. FIG. 8 is a front view showing a state in which the first shielding plate 60 a is attached to the first core piece 581.

  The first shielding plate portion 60a is a main body formed in an arc shape so as to extend along the outer peripheral surface 581a and be in close contact with the outer peripheral surface 581a when held on the outer peripheral surface 581a of the first core piece 581. Part 61. The widthwise dimension of the main body 61 is substantially the same as the axial dimension of the first core piece 581.

  The first shielding plate portion 60a further includes a pair of rib-shaped first projecting pieces 62 and a rib-shaped second projecting toward the outer peripheral surface 581a while being held on the outer peripheral surface 581a of the first core piece 581. A protruding piece 64 is provided. The main body 61 has a pair of edges facing the circumferential direction of the first core piece 581 and extending in the axial direction of the first core piece 581. The first protruding piece 62 protrudes from one edge, A second protruding piece 64 protrudes from the other edge. Accordingly, the first protruding piece 62 and the second protruding piece 64 face each other in the rotation direction of the first core piece 581. In this embodiment, the 1st protrusion piece 62 and the 2nd protrusion piece 64 comprise the protrusion part.

  The first shielding plate 60 a further protrudes from the first protruding piece 62 in the axial direction of the first core piece 581 and from the second protruding piece 64 to the axial direction of the first core piece 581. And a second coupling piece 65. The first coupling piece 63 and the second coupling piece 65 extend in parallel to each other. A step is formed between the first and second coupling pieces 63 and 65 and the main body 61.

  The 1st core piece 581 has a groove part which consists of a pair of 1st groove | channel 581b and 2nd groove | channel 581c formed in the outer peripheral surface 581a. The first groove 581b and the second groove 581c extend in the axial direction of the first core piece 581 from one end face of the first core piece 581 to the other end face. The 1st protrusion piece 62 is inserted in the 1st groove | channel 581b, and the 2nd protrusion piece 64 is inserted in the 2nd groove | channel 581c. The first groove 581b and the second groove 581c may have any shape as long as the first projecting piece 62 and the second projecting piece 64 can be fitted therein. The first groove 581b and the second groove 581c are formed by using a mold when the first core piece 581 is fired, for example. In this embodiment, the 1st groove | channel 581b and the 2nd groove | channel 581c comprise the latching | locking part which latches a protrusion part (the 1st protrusion piece 62 and the 2nd protrusion piece 64). The first core piece 581 has a through hole 581d through which the rotary shaft member 59 is inserted.

  7 and 8, the first protruding piece 62 of the first shielding plate portion 60a is fitted into the first groove 581b of the first core piece 581, and the second protruding piece 64 is inserted into the second groove 581c. When fitted, the main body 61 of the first shielding plate 60 a is held in close contact with the outer peripheral surface 581 a of the first core piece 581. In the present embodiment, the first protruding piece 62 and the second protruding piece 64, the first groove 581b and the second groove 581c hold the first shielding plate portion 60a on the outer peripheral surface 581a of the first core piece 581. Means.

  When the first shielding plate portion 60a is held on the outer peripheral surface 581a of the first core piece 581, the pair of first coupling pieces 63 and the second coupling piece 65 of the first shielding plate portion 60a become the first core. In this state, the first core piece 581 protrudes from the end face of the piece 581 in the axial direction. The intermediate core piece 580 adjacent to the first core piece 581 has a fitting portion into which the first coupling piece 63 and the second coupling piece 65 can be fitted. Specifically, the intermediate core piece 580 has an end surface 580a facing the first core piece 581 in the axial direction, and the first hole 580b into which the first coupling piece 63 can be inserted into the end surface 580a, A second hole 580c into which the two coupling pieces 65 can be fitted is formed. The first hole 580b and the second hole 580c are formed, for example, using a mold when the intermediate core piece 580 is fired.

  When the first coupling piece 63 of the first shielding plate portion 60a is fitted into the first hole 580b of the intermediate core piece 580 and the second coupling piece 65 is fitted into the second hole 580c, the first shielding plate portion 60a is The state is held not only by the first core piece 581 but also by the intermediate core piece 580.

  In addition, although the attachment to the 1st core piece 581 of the 1st shielding board part 60a was demonstrated with reference to FIGS. 5-8, the 2nd shielding board part 60b is also the 2nd shielding piece part 582 of the 2nd core piece 582 by the same holding means. It is attached to the outer peripheral surface.

  Next, attachment of the third shielding plate 60c to the third core piece 583 will be described with reference to FIGS. FIG. 9 is a front view illustrating an example of attachment of the third shielding plate portion 60c to the third core piece 583, and FIG. 10 illustrates another attachment of the third shielding plate portion 60c to the third core piece 583. It is a front view which shows an example.

  First, an example of attachment shown in FIG. 9 will be described. In FIG. 9, the third shielding plate portion 60 c is attached to the outer peripheral surface 583 b of the third core piece 583 using the elasticity of the third shielding plate portion 60 c. As described above, the third shielding plate portion 60c is a copper plate having a circular arc cross section made of oxygen-free copper, and extends over an angle range of 280 °. In addition, the inner diameter of the third shielding plate portion 60 c is set to be appropriately smaller than the outer diameter of the third core piece 583. When attaching the 3rd shielding board part 60c to the 3rd core piece 583, the 3rd shielding board part 60c is covered with the outer peripheral surface 583b of the 3rd core piece 583, elastically deforming the 3rd shielding board part 60c. Is externally fitted to the outer peripheral surface 583b of the third core piece 583. As a result, the third shielding plate portion 60 c is in close contact with the outer peripheral surface 583 b of the third core piece 583.

  Next, a mounting example shown in FIG. 10 will be described. In FIG. 10, the third shielding plate portion 60c is placed on the outer peripheral surface 583b of the third core piece 583 by means similar to the holding means for holding the first shielding plate portion 60a on the outer peripheral surface 581a of the first core piece 581. It is attached. In other words, the third shielding plate portion 60c has a pair of protruding pieces 66 that face each other in the rotation direction of the third core piece 583, and the third core piece 583 has a pair of grooves into which the pair of protruding pieces 66 can be fitted. 583a. When attaching the 3rd shielding board part 60c to the 3rd core piece 583, the 3rd shielding board part 60c is made into the 3rd by inserting the protrusion piece of the 3rd shielding board part 60c in the groove | channel of the 3rd core piece 583. The outer peripheral surface 583b of the core piece 583 is externally fitted. As a result, the third shielding plate portion 60 c is in close contact with the outer peripheral surface 583 b of the third core piece 583.

  In this embodiment, in order to further improve the adhesion between the first shielding plate portion 60a to the third shielding plate portion 60c and the first core piece 581 to the third core piece 583, the elastic sheet material 70 is used. be able to. The elastic sheet material 70 will be described with reference to FIG. 11 illustrating the attachment of the first shielding plate portion 60a to the first core piece 581. The elastic sheet material 70 includes a body portion 61 of the first shielding plate portion 60a and an outer circumferential surface 581a of the first core piece 581 in a state where the first shielding plate portion 60a is held on the outer circumferential surface 581a of the first core piece 581. It is arranged between. The elastic sheet material 70 is made of a material having heat resistance, for example, PTFE. When the first projecting piece 62 and the second projecting piece 64 of the first shielding plate portion 60a are fitted into the first groove 581b and the second groove 581c of the first core piece 581, the elastic sheet material 70 becomes the first shielding plate. It is sandwiched between the main body portion 61 of the portion 60a and the outer peripheral surface 581a of the first core piece 581 while being elastically deformed. Therefore, the formation of a gap between the main body 61 and the outer peripheral surface 581a is suppressed. Thereby, the adhesiveness between the main-body part 61 and the outer peripheral surface 581a increases.

  In the fixing device 14 according to the present embodiment described above, for example, the first protruding piece 62 and the second protruding piece 64 protruding from the main body portion 61 of the first shielding plate portion 60a are replaced with the outer peripheral surface 581a of the first core piece 581. The first shielding plate portion 60a can be firmly held on the outer peripheral surface 581a of the first core piece 581 simply by being fitted into the first groove 581b and the second groove 581c formed in FIG. This reduces the time required to hold the magnetic shielding plate 60 on the outer peripheral surface of the center core 58 as compared with the conventional configuration in which the magnetic shielding plate is held on the outer peripheral surface of the core using an adhesive. Productivity is improved.

  Further, according to the fixing device 14 according to the present embodiment, the first shielding plate portion 60a to the third shielding plate portion 60c are held in close contact with the outer peripheral surfaces of the first core piece 581 to the third core piece 583. The generation of resonance noise can be suppressed. Furthermore, the elastic sheet material 70 is disposed between the first shielding plate portion 60a to the third shielding plate portion 60c and the outer peripheral surfaces of the first core piece 581 to the third core piece 583, thereby the first shielding plate portion 60a. -The 3rd shielding board part 60c can be stuck further to the outer peripheral surface of the 1st core piece 581-the 3rd core piece 583. FIG. Thereby, generation | occurrence | production of a resonance sound can be suppressed further.

  Furthermore, according to the fixing device 14 according to the present embodiment, the first shielding plate portion 60a and the second shielding plate portion 60a can be obtained by a simple mold process in which grooves are formed on the outer peripheral surfaces of the first core piece 581 and the second core piece 582. The shielding plate portion 60b can be held on the outer peripheral surfaces of the first core piece 581 and the second core piece 582.

  Further, according to the fixing device 14 according to the present embodiment, the first projecting piece 62 and the second projecting piece 64 are formed so as to face the rotation direction of the first core piece 581 (second core piece 582), and the first projecting piece 62 and the second projecting piece 64 are formed. The groove 581b and the second groove 581c are also formed to face the rotation direction of the first core piece 581 (second core piece 582). Therefore, the 1st shielding board part 60a (2nd shielding board part 60b) can resist the centrifugal force which arises by rotation of the 1st core piece 581 (2nd core piece 582).

  Furthermore, according to the fixing device 14 according to the present embodiment, for example, the first coupling piece 63 and the second coupling piece 65 of the first shielding plate portion 60a are formed in the first hole 580b and the second hole 580c of the intermediate core piece 580. By being inserted, the first shielding plate part 60a is also held by the intermediate core piece 580 adjacent to the first core piece 581 to which the first shielding plate part 60a is attached. Thereby, the 1st shielding board part 60a can be hold | maintained still more firmly.

  Furthermore, according to the fixing device 14 according to the present embodiment, the first shielding plate portion 60a is placed in the middle by a simple mold processing in which the first hole 580b and the second hole 580c are formed in the end surface 580a of the intermediate core piece 580. The core piece 580 can be held.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 14 Fixing apparatus 44 Pressure roller (2nd rotary body)
45 Fixing roller 46 Heat roller 48 Fixing belt (first rotating body)
50 Coil unit 52 Coil 54 Arch core 56 Side core 58 Center core 60 Magnetic shielding plate 60a First shielding plate portion 60b Second shielding plate portion 60c Third shielding plate portion 61 Body portion 62 First protruding piece (protruding portion)
63 1st coupling piece 64 2nd protrusion piece (protrusion part)
65 Second coupling piece 70 Elastic sheet material 580 Intermediate core piece 581 First core piece 581a Outer peripheral surface 581b First groove 581c Second groove 582 Second core piece 583 Third core piece NP Nip portion P1 to P3 Paper (recording medium)

Claims (5)

A magnetic flux generation source for generating magnetic flux;
A first rotating body that is induction-heated by the magnetic flux while rotating in a predetermined direction;
A second rotating body that forms a nip portion with the first rotating body through which a recording medium carrying a toner image passes while rotating in a predetermined direction;
A first core made of a magnetic material and forming a magnetic path through which the magnetic flux passes together with the first rotating body;
A second core having an outer peripheral surface, made of a magnetic material, disposed between the first core and the first rotating body as viewed from the magnetic path, and rotatable in a predetermined direction;
A magnetic shielding plate made of a non-magnetic material attached to the outer peripheral surface of the second core, wherein the magnetic shielding is located in the magnetic path with the rotation of the second core and shields or suppresses the magnetic flux. The board,
Holding means for holding the magnetic shielding plate on the outer peripheral surface of the second core;
With
The second core includes core pieces adjacent in the axial direction,
The magnetic shielding plate is attached to at least one of the adjacent core pieces,
The magnetic shielding plate extends along the outer peripheral surface while being held on the outer peripheral surface of the core piece , is in close contact with the outer peripheral surface , and is substantially the same as the axial dimension of the core piece. Having a body portion with axial dimensions ,
The holding means protrudes in a rib shape from the main body portion toward the inner side of the outer peripheral surface of the core piece and extends in the axial direction from one end edge of the main body portion to the other end edge. the formed on the outer peripheral surface of the core piece, Ri Do and a locking portion capable of locking the protruded portion,
The locking portion extends from the one end surface of the core piece to the other end surface in the axial direction, and is a groove portion into which the protruding portion is inserted,
The protruding portion includes a pair of first protruding pieces and second protruding pieces facing each other in the rotation direction of the second core,
The fixing device includes a first groove into which the first protruding piece is inserted and a second groove into which the second protruding piece is inserted . A magnetic flux generation source for generating magnetic flux;
A first rotating body that is induction-heated by the magnetic flux while rotating in a predetermined direction;
A second rotating body that forms a nip portion with the first rotating body through which a recording medium carrying a toner image passes while rotating in a predetermined direction;
A first core made of a magnetic material and forming a magnetic path through which the magnetic flux passes together with the first rotating body;
A second core having an outer peripheral surface, made of a magnetic material, disposed between the first core and the first rotating body as viewed from the magnetic path, and rotatable in a predetermined direction;
A magnetic shielding plate made of a non-magnetic material attached to the outer peripheral surface of the second core, wherein the magnetic shielding is located in the magnetic path with the rotation of the second core and shields or suppresses the magnetic flux. The board,
Holding means for holding the magnetic shielding plate on the outer peripheral surface of the second core;
With
The magnetic shielding plate has a body portion that extends along the outer peripheral surface and is in close contact with the outer peripheral surface while being held on the outer peripheral surface of the second core,
The holding means is formed on the outer peripheral surface of the second core and a protruding portion that protrudes in a rib shape from the main body portion toward the outer peripheral surface of the second core, and locks the protruding portion. Consisting of possible locking parts,
The second core includes core pieces adjacent in the axial direction,
The magnetic shielding plate is attached to at least one of the adjacent core pieces,
The magnetic shielding plate has a coupling piece protruding in the axial direction of the second core,
The other core piece of the adjacent core pieces is a fixing device having a fitting portion into which the coupling piece is fitted. The fixing device according to claim 2 ,
The other core piece has an end surface facing the one core piece,
The fixing device, wherein the fitting portion is a hole formed in the end face. In the fixing device according to any one of claims 1 to 3 ,
Further, the fixing device includes a sheet material that has elasticity and is disposed between the main body portion of the magnetic shielding plate and the outer peripheral surface of the second core. An image carrier on which a toner image is formed;
An image forming unit that forms the toner image on the image carrier;
A transfer portion for transferring the toner image onto a recording medium;
A fixing device for fixing the toner image on the recording medium;
With
Examples fixing device, an image forming apparatus to which a fixing device is used according to any one of claims 1-4.

Images