JP2011022407A - Magnetic rod, method of manufacturing the same, fixing unit with magnetic rod assembled therein and method of manufacturing center core included in the fixing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic rod that allows temperature spots to be reduced, by reducing the variations in size of the outer periphery outlines of the magnetic rod which is positioned in the vicinity of a coil for generating magnetic flux for heating an object to be heated that is heated through electromagnetic induction, and the object to be heated and by reducing variation in the distance between a magnetic body and the object to be heated, to provide a method of manufacturing the magnetic rod, and to provide a fixing unit with the magnetic rod assembled therein. <P>SOLUTION: The magnetic rod is positioned in the vicinity of the coil for generating the magnetic flux for heating the object to be heated that is heated by electromagnetic induction and the object to be heated. The magnetic rod includes a shaft, a plurality of magnetic cylindrical pieces surrounding the outer circumferential surface of the shaft and a plurality of elastic rings arranged between inner circumferential surfaces of the plurality of magnetic cylindrical pieces and an outer circumferential surface of the shaft. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic rod, a method for manufacturing a magnetic rod, and a fixing unit incorporating the magnetic rod.

  Electromagnetic induction heating can produce rapid heating and highly efficient heating. Therefore, electromagnetic induction heating is used in various devices. Patent Document 1 discloses a fixing device incorporated in an image forming apparatus as an example of an apparatus using electromagnetic induction heating.

  In an apparatus using electromagnetic induction heating, the distance between a magnetic material that allows magnetic flux to pass through and an object to be heated that is electromagnetic induction heated is a very important parameter. For example, as mentioned in Patent Document 1, in the case of a fixing device that uses electromagnetic induction heating, variations in the distance between the magnetic body and the object to be heated cause temperature spots on the object to be heated and fix on the sheet. The quality of the toner image is deteriorated.

International Publication WO2006 / 054658

  For example, the magnetic body that allows the magnetic flux to pass is formed by firing ferrite into small pieces having a predetermined shape and size. When the size of the portion requiring heating is larger than the size of the small piece, a plurality of small pieces are connected to be processed into a magnetic body having a size of the portion requiring heating or larger.

  When there are variations in the outer peripheral contour size of the plurality of connected small pieces, the distance between the magnetic body and the object to be heated varies. Although it is not impossible to fire and mold a long magnetic body having a dimension that requires heating or larger, this method causes deformation such as warping of the molded article after firing. As a result, the variation in the distance between the magnetic body and the object to be heated, which causes the temperature variation of the heated object, is increased. Although it is conceivable to cut the surface of the deformed molded product, this method is not practical from the viewpoint of production cost. Actually, the technique disclosed in Patent Document 1 uses a magnetic material formed by connecting fired small pieces.

  The present invention has been made in order to solve the above-described problem, and a coil for generating magnetic flux for heating a heated object to be heated by electromagnetic induction and an outer periphery of a magnetic rod body positioned near the heated object. Magnetic rod, magnetic rod manufacturing method, and magnetic rod capable of reducing temperature variation by reducing variation in contour dimension and reducing variation in distance between magnetic material and object to be heated An object of the present invention is to provide a fixing unit in which is incorporated.

  A magnetic rod according to one aspect of the present invention that achieves the above object is a magnetic rod disposed near a heated object and a coil that generates a magnetic flux for heating the heated object to be electromagnetically heated. A shaft extending in one direction, a plurality of magnetic cylinder pieces arranged coaxially with respect to a longitudinal axis of the shaft and surrounding an outer peripheral surface of the shaft, and the plurality of magnetic cylinder pieces, And a plurality of elastic rings arranged between the inner peripheral surface of the shaft and the outer peripheral surface of the shaft and press-contacted by the inner peripheral surface of the magnetic cylinder piece and the outer peripheral surface of the shaft, (Claim 1).

  According to the above configuration, the accuracy of the coaxiality between the shaft and the magnetic cylinder piece incorporated in the heating device can be increased, and the magnetic rod body and the object to be heated are caused by variations in the outer peripheral contour size between the plurality of magnetic cylinder pieces. It is possible to minimize the variation in distance.

  The said structure WHEREIN: The said magnetic rod body can further be equipped with the resin layer which covers the outer peripheral surface of these magnetic cylinder pieces. (Claim 2). Thereby, the precision of the coaxiality of a shaft and a magnetic cylinder piece can further be improved. Alternatively, the object disposed on the peripheral surface of the magnetic cylinder piece can be simply and accurately fixed to the peripheral surface of the magnetic cylinder piece. The resin layer is preferably heat-shrinkable (claim 3). In the above configuration, the magnetic rod body may further include an adhesive layer between an inner peripheral surface of at least one of the plurality of magnetic cylindrical pieces and an outer peripheral surface of the shaft. ). Thereby, a magnetic cylinder piece will be stably fixed to a shaft. The fixing position or fixing method of the magnetic cylinder piece is not particularly limited, but in a specific embodiment, an annular storage portion is formed on the inner wall of each end of each of the plurality of magnetic cylinder pieces, and the storage portion The elastic ring body is disposed on the surface (Claim 5). Thereby, while a magnetic cylinder piece is stably fixed to a shaft, attachment to the shaft of a magnetic cylinder piece becomes easy. Note that an O-ring can be suitably used as the elastic ring (claim 6).

  A method of manufacturing a magnetic rod according to another aspect of the present invention that achieves the above object is positioned near a heated object and a coil that generates a magnetic flux for heating the heated object to be electromagnetically heated. It is a manufacturing method of a magnetic rod. This method of manufacturing a magnetic rod includes a step of preparing a shaft and a step of attaching a magnetic cylinder piece to the shaft, and the step of attaching the magnetic cylinder piece externally fits one elastic ring to the shaft. And inserting the shaft to which the one elastic ring is attached into the magnetic cylinder piece and press-contacting the one elastic ring to the outer peripheral surface of the shaft and the inner peripheral surface of the magnetic cylinder piece; The method includes a step of fitting another elastic ring body to the shaft and press-fitting the other elastic ring body into the magnetic cylinder piece (claim 7). In a specific embodiment, the step of attaching the magnetic cylinder piece is repeated a plurality of times (claim 8).

  According to the above configuration, the accuracy of the coaxiality between the shaft and the magnetic cylinder piece incorporated in the heating device can be increased, and the magnetic rod body and the object to be heated are caused by variations in the outer peripheral contour size between the plurality of magnetic cylinder pieces. It is possible to minimize the variation in distance.

  In the above configuration, after the step of attaching the magnetic cylinder piece, a step of forming a heat-shrinkable resin layer on the outer peripheral surface of the magnetic cylinder piece is performed (Claim 9). In a specific embodiment, the heat-shrinkable resin layer is formed by fitting a heat-shrinkable tube to the magnetic cylinder piece (claim 10). After the step of forming the heat-shrinkable resin layer on the outer peripheral surface of the magnetic cylinder piece, a step of heating the heat-shrinkable resin layer and shrinking the heat-shrinkable resin layer is performed (claim 11). . Thereby, the precision of the coaxiality of a shaft and a magnetic cylinder piece can further be improved. Alternatively, the object disposed on the peripheral surface of the magnetic cylinder piece can be simply and accurately fixed to the peripheral surface of the magnetic cylinder piece.

  In the above configuration, the step of attaching the magnetic cylinder piece further includes pressing the one elastic ring body against the outer peripheral surface of the shaft and the inner peripheral surface of the magnetic cylinder piece, and the other elastic member in the magnetic cylinder piece. A step of forming an adhesive layer between the inner peripheral surface of the magnetic cylinder piece and the outer peripheral surface of the shaft may be included during the step of press-fitting the annular body. Thereby, a magnetic cylinder piece will be stably fixed to a shaft.

  A fixing unit according to another aspect of the present invention that achieves the above object provides a toner image on a sheet that passes between a heated object having one rotation center axis and a pressure roller that is in pressure contact with the heated object. At least one coil surface formed by a coil that is arranged along an outer peripheral surface or an inner peripheral surface of the object to be heated and that generates a magnetic field for induction heating the object to be heated; A shaft extending in a direction in which the rotation center axis of the heated body extends, a plurality of magnetic cylinder pieces surrounding the outer peripheral surface of the shaft, and an outer peripheral surface of the shaft and an inner peripheral surface of the magnetic cylinder piece. And a center core including a plurality of elastic ring bodies (claim 13).

  According to the above configuration, it is possible to minimize the variation in the distance between the center core and the object to be heated due to the variation in the outer peripheral contour size between the plurality of magnetic cylinder pieces, and the toner image fixed on the sheet is high. Quality can be maintained.

  The said structure WHEREIN: The at least 1 magnetic shielding member distribute | arranged to the vicinity of the said at least 1 coil surface can be further provided (Claim 14). In this configuration, the center core may further include a shielding plate that is fixed to at least one of the plurality of magnetic cylinder pieces and prevents the magnetic field from passing therethrough (claim 15). In this configuration, when the center core exists at the first position where the shielding plate approaches the at least one magnetic shielding member, the amount of heating to the heating member is determined by separating the shielding plate from the at least one magnetic shielding member. The heating amount when the center core exists at two positions can be made smaller (claim 16).

  The center core of the fixing unit configured as described above includes a step of preparing a shaft, a step of attaching a plurality of magnetic cylinder pieces to the shaft, a step of disposing the shielding plate on the outer peripheral surface of the plurality of magnetic cylinder pieces, A step of forming a heat-shrinkable resin layer on the outer peripheral surface of the shielding plate and the magnetic cylinder piece; and a step of heating and shrinking the heat-shrinkable resin layer, and attaching the plurality of magnetic cylinder pieces. A step of externally fitting one elastic ring to the shaft, and inserting the shaft to which the one elastic ring is attached into the magnetic cylinder piece, and attaching the one elastic ring to the outer peripheral surface of the shaft. And a step of pressing the inner circumferential surface of the magnetic cylinder piece and a step of externally fitting another elastic ring body to the shaft and press-fitting the other elastic ring body into the magnetic cylinder piece. (Claim 17).

  As described above, the magnetic bar, the method for manufacturing the magnetic bar, and the fixing unit incorporating the magnetic bar according to the present invention suitably reduce the problem of temperature spots.

1 is a perspective view of a magnetic bar according to an embodiment of the present invention. It is an expanded sectional view of the magnetic rod shown in FIG. It is a figure explaining the assembly process of the magnetic bar shown in FIG. It is a figure which shows schematic structure of the image forming apparatus incorporating a fixing unit provided with the magnetic rod shown in FIG. FIG. 5 is a diagram illustrating an example of a fixing unit provided in the image forming apparatus illustrated in FIG. 4. FIG. 6 is a perspective view showing a magnetic shielding member provided in the fixing unit shown in FIG. 5. FIG. 6 is a diagram illustrating a retracted position and a shielding position of the center core of the fixing unit illustrated in FIG. 5. It is a figure which shows an example of the other structure of the magnetic shielding member of the fixing unit shown in FIG. FIG. 6 is a schematic configuration diagram of a driving system of the fixing unit shown in FIG. 5. It is a figure which shows the change of the magnetic path in the fixing unit shown in FIG. It is a figure which shows the other fixing unit to which the magnetic rod shown in FIG. 1 is applied. It is a figure which shows the change of the magnetic path in the fixing unit shown in FIG. FIG. 12 is a partially enlarged view of the fixing unit shown in FIG. 11. It is a figure which shows the other fixing unit to which the magnetic rod shown in FIG. 1 is applied. It is a figure which shows the other fixing unit to which the magnetic rod shown in FIG. 1 is applied. It is a figure which shows the other fixing unit to which the magnetic rod shown in FIG. 1 is applied. It is a figure which shows the other fixing unit to which the magnetic rod shown in FIG. 1 is applied. It is a figure which shows an example of a magnetic shielding member. It is a figure explaining the magnetic shielding principle of the magnetic shielding member shown in FIG. It is a figure which shows another example of a magnetic shielding member. It is a figure which shows another example of a magnetic shielding member. It is a figure which shows another example of a magnetic shielding member. It is a figure which shows the magnetic cylinder piece which has a different dimension. It is a figure which shows the distance difference from the heating object surface when the magnetic cylinder piece which has a different dimension is attached to a shaft.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that terms used in the following description, such as “up”, “down”, “left”, “right” and the like, are merely for the purpose of clarifying the explanation and do not limit the present invention. Not what you want. Furthermore, the term “magnetic bar is placed near the coil”, “magnetic bar is placed near the object to be heated”, or similar terms used in the following description, is that the magnetic bar is inductively heated. It is located near the coil or the object to be heated to the extent that it can contribute to the above. The phrase “the magnetic shielding member is disposed near the coil surface” or similar terms means an aspect in which the magnetic shielding member is brought close to the coil surface to such an extent that electromagnetic induction of the coil can be prevented. In addition, the term “annular”, “ring” or similar terms used in the following description is a generic term for not only a perfect circular ring but also an elliptical ring, a rectangular ring, a polygonal ring, etc., and forms an arbitrary closed region. It means the shape of the object.

(Magnetic rod)
FIG. 1 is a perspective view of a magnetic bar according to one embodiment. The magnetic rod 100 includes a shaft 110 extending in one direction, and a plurality of magnetic cylinder pieces 120 that surround the peripheral surface of the shaft 110 and are connected along the shaft 110. The magnetic cylinder piece 120 is molded from ferrite, for example. In the embodiment shown in FIG. 1, the magnetic cylindrical piece 120 has a cylindrical shape, but may have other shapes depending on the purpose of the heating device in which the magnetic rod 100 is incorporated. For example, the magnetic cylinder piece 120 having a polygonal outer peripheral contour and / or inner peripheral contour may be used.

  A nonmagnetic and highly conductive thin plate 130 is fixed to the outer peripheral surface of the magnetic cylinder piece 120 located near both ends of the shaft 110 in the magnetic cylinder 120 shown in FIG. In particular embodiments, the thin plate 130 is formed from oxygen-free copper. In other specific embodiments, lamina 130 is not required. In addition, the thin plate 130 shown in FIG. 1 functions as a shielding plate that prevents the passage of a magnetic field in an embodiment described later. In the embodiment shown in FIG. 1, the thin plate 130 partially covers the outer peripheral surface of two adjacent magnetic cylinder pieces 120 positioned at each end of the shaft 110. The magnetic cylinder piece 120 may be covered. Moreover, the thin plate 130 may cover the entire outer peripheral surface of some of the magnetic cylinders 120 as necessary.

  FIG. 2 is an enlarged view of a cross section at the left end of the magnetic rod 100 shown in FIG. At the end of the shaft 110, for example, a groove 111 for a C-shaped snap ring for fixing a gear or a pulley is formed according to a device in which the magnetic rod 100 is incorporated. The inner diameter of the magnetic cylinder piece 120 is formed larger than the outer diameter of the shaft 110. O-rings (elastic ring bodies) 140 are disposed at both ends of each magnetic cylinder piece 120. The O-ring 140 is pressed against the outer peripheral surface of the shaft 110 and the inner peripheral surface of the magnetic cylinder piece 120. Thereby, each magnetic cylinder piece 120 will be arrange | positioned coaxially with respect to the longitudinal direction axis | shaft of the shaft 110. FIG. In the embodiment shown in FIG. 2, annular concave portions (accommodating portions) 121 are formed at both ends of each magnetic cylinder piece 120, and the O-ring 140 is accommodated in the concave portions 121. In a specific embodiment, an adhesive layer is formed in a gap formed between the outer peripheral surface of the shaft 110 and the inner peripheral surface of the magnetic cylinder piece 120. The O-ring 140 is preferably formed from a heat resistant resin or heat resistant rubber. In a specific embodiment, the O-ring 140 is formed from a fluororesin.

  FIG. 3 is a diagram showing a manufacturing process of the magnetic rod 100 shown in FIGS. 1 and 2. As shown in FIG. 3A, first, the shaft 110 is prepared. Thereafter, as shown in FIG. 3B, the O-ring 140 is fitted on the shaft 110 and attached to a predetermined position of the shaft 110. Further, as shown in FIG. 3C, the shaft 110 is inserted into the magnetic cylinder piece 120, and the O-ring 140 is accommodated in a recess 121 formed at one end of the magnetic cylinder piece 120. Thereafter, an O-ring 140 is further press-fitted into the recess 121 formed at the other end of the magnetic cylinder piece 120 (FIG. 3D). Note that an adhesive is injected into the gap formed between the inner peripheral surface of the magnetic cylindrical piece 120 and the outer peripheral surface of the shaft 110 between the step shown in FIG. 3C and the step shown in FIG. Then, an adhesive layer may be formed. By repeating the steps shown in FIGS. 3B to 3D, a plurality of magnetic cylinder pieces 120 can be attached to the shaft 110 (FIG. 3E). After that, if necessary, the thin plate 130 can be attached to the recessed area formed on the outer peripheral surface of some of the magnetic cylinder pieces 120 (FIG. 3F). For attachment of the thin plate 130, a silicon-based adhesive can be used. However, as shown in FIGS. 3G and 3H, the thin plate 130 can be fixed by a heat-shrinkable resin layer. Even when the thin plate 130 is fixed using the heat-shrinkable resin layer, the thin plate 130 and the outer peripheral surface of the magnetic cylinder piece 120 can be fixed with an adhesive. A tube 150 formed of a heat-shrinkable material is fitted on the magnetic cylinder 120 provided continuously (FIG. 3G), the tube 150 is heated, the tube 150 is heat-shrinked, and the outer periphery of the magnetic cylinder 120 A heat-shrinkable resin layer can be formed on the surface.

(Image forming device)
FIG. 4 is a schematic diagram showing a configuration of an image forming apparatus including a fixing unit in which the magnetic rod 100 described with reference to FIGS. 1 to 3 is incorporated. The principle of the magnetic rod described with reference to FIGS. 1 to 3 is, for example, a printer, a copying machine, a facsimile machine, a multifunction machine having these functions, or printing paper based on image information inputted from the outside. The present invention can also be applied to other apparatuses that perform printing by transferring a toner image onto the surface of the print medium or other apparatuses that incorporate an electromagnetic induction heating system. The image forming apparatus shown in FIG. 4 is a tandem type color printer.

  The image forming apparatus 1 includes a square box-shaped main body 2. A color image is formed (printed) on the paper inside the apparatus main body 2. A paper discharge unit 3 is provided on the upper surface of the apparatus main body 2, and the paper discharge unit 3 discharges a sheet on which a color image is printed.

  The apparatus main body 2 includes a paper feeding cassette 5 that supplies paper, a stack tray 6 that is located above the paper feeding cassette 5 and that feeds manual paper, and an image forming unit 7 that is located above the stack tray 6. The image forming unit 7 forms an image on a sheet based on image data such as characters and designs transmitted from the outside of the image forming apparatus 1.

  A first transport path 9 is disposed on the left side of the apparatus main body 2 shown in FIG. 4, and the paper fed from the paper feed cassette 5 is transported to the image forming section 7 through the first transport path 9. . A second transport path 10 is disposed above the paper feed cassette 5. Through the second conveyance path 10, the sheet fed from the stack tray 6 moves from the left side to the right side of the apparatus main body 2 and reaches the image forming unit 7. In the upper left part of the apparatus main body 2, a fixing unit 14 that performs a fixing process on a sheet on which an image is formed by the image forming unit 7, and a third unit that conveys the sheet on which the fixing process has been performed to the sheet discharge unit 3. The transport path 11 is provided.

  In order to replenish paper, the paper feed cassette 5 is formed to be able to be pulled out of the apparatus main body 2 (for example, on the right side in FIG. 4). The paper feed cassette 5 includes a storage unit 16 in which at least two types of paper having different sizes in the paper feed direction can be selectively stored. Note that the sheets stored in the storage unit 16 are fed one by one toward the first transport path 9 by the sheet feeding roller 17 and the separating roller 18.

  The stack tray 6 is formed to be rotatable up and down between a closed position along the outer surface of the apparatus main body 2 and an open position (shown in FIG. 4) protruding from the outer surface of the apparatus main body 2. In the manual feed section 19 of the stack tray 6, manual feed sheets are placed one by one or a plurality of manual feed sheets are stacked. The sheets placed on the manual feed unit 19 are fed out one by one by the pickup roller 20 and the separating roller 21 toward the second conveyance path 10.

  The first conveyance path 9 and the second conveyance path 10 merge before the registration roller 22. The paper that has reached the registration roller 22 stops here, and is sent to the secondary transfer unit 23 after skew adjustment and timing adjustment. The full color toner image on the intermediate transfer belt 40 is secondarily transferred to the sheet sent to the secondary transfer unit 23. After the secondary transfer, the paper is sent to the fixing unit 14 and the toner image is fixed on the paper. If necessary, after the toner image is fixed on the sheet, the sheet is transferred to the fourth transport path 12 in order to perform secondary transfer of the full-color toner image on the other side using the secondary transfer unit 23. Can be sent out and reversed. A new toner image is fixed using the fixing unit 14, and then discharged to the paper discharge unit 3 through the third conveyance path 11 by the discharge roller 24.

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

  Each of the image forming units 26 to 29 includes a photosensitive drum 32, a charging unit 33 disposed so as to face the peripheral surface of the photosensitive drum 32, and a periphery of the photosensitive drum 32 on the downstream side of the charging unit 33. A laser scanning unit 34 for irradiating a laser beam to a specific position on the surface, and a development disposed downstream of the laser beam irradiation position from the laser scanning unit 34 and facing the peripheral surface of the photosensitive drum 32 And a cleaning unit 36 disposed on the downstream side of the developing unit 35 and facing the circumferential surface of the photosensitive drum 32.

  The photosensitive drums 32 of the image forming units 26 to 29 shown in FIG. 4 are rotated counterclockwise by a drive motor (not shown). In each toner box 51 of the developing unit 35 of each image forming unit 26 to 29, black toner, yellow toner, cyan toner, and magenta toner are respectively stored.

  The intermediate transfer unit 30 includes a rear roller (drive roller) 38 disposed near the image forming unit 26, a front roller (driven roller) 39 disposed near the image forming unit 29, and a rear roller. 38, the intermediate transfer belt 40 extending between the front roller 39 and the photosensitive drum 32 of each of the image forming units 26 to 29. The intermediate transfer belt 40 is located on the downstream side of the developing unit 35 and is interposed via the intermediate transfer belt 40. And four transfer rollers 41 disposed so as to be capable of being pressed.

  At the position of the transfer roller 41 of each of the image forming units 26 to 29, the toner images for the respective colors are transferred onto the intermediate transfer belt 40 in a superimposed manner, and finally a full-color toner image is formed.

  The first conveyance path 9 extends toward the intermediate transfer unit 30, and the sheet fed from the paper feed cassette 5 reaches the intermediate transfer unit 30 through the first conveyance path 9. The first transport path 9 is disposed in front of the plurality of transport rollers 43 disposed at a predetermined position in the apparatus main body 2 and the intermediate transfer unit 30, and the image forming operation of the image forming unit 7. A registration roller 22 is provided for timing the sheet feeding operation.

  The toner image transferred onto the paper by the image forming unit 7 is not fixed on the paper. The fixing unit 14 heats and pressurizes a toner image having an unfixed image, and fixes the toner image on a sheet. The fixing unit 14 includes, for example, a roller pair including a pressure roller 44 and a heating type fixing roller 45. The pressure roller 44 includes, for example, a metal core material and an elastic surface layer (for example, silicon rubber), and the fixing roller 45 includes a metal core material and an elastic surface layer (for example, silicon sponge) and a mold release. A layer (eg, PFA) can be provided. A heat roller 46 is provided adjacent to the fixing roller 45, and a heating belt 48 is wound around the heat roller 46 and the fixing roller 45.

  A conveyance path 47 is provided on each of the upstream side and the downstream side of the fixing unit 14 in the sheet conveyance direction. The sheet conveyed through the intermediate transfer unit 30 is introduced into the nip between the pressure roller 44 and the fixing roller 45 / heating belt 48 through the upstream conveyance path 47, and the toner image is fixed on the sheet. The The paper that has passed between the pressure roller 44 and the fixing roller 45 is guided to the third conveyance path 11 through the conveyance path 47 on the downstream side.

  The third transport path 11 transports the paper on which the fixing process has been performed by the fixing unit 14 to the paper discharge unit 3. For this reason, a transport roller 49 is disposed at an appropriate position in the third transport path 11. A discharge roller 24 is disposed at the exit of the third transport path 11.

(Fusing unit)
FIG. 5 shows the structure of the fixing unit 14 in which the magnetic rod 100 described with reference to FIGS. 1 to 3 is incorporated. The magnetic rod 100 described with reference to FIGS. 1 to 3 is used as a center core in the fixing unit 14. FIG. 5A is a cross-sectional view showing the fixing unit 14 shown in FIG. 4 turned about 90 ° counterclockwise. FIG. 5B is a plan view of the fixing unit 14 shown in FIG. Although the paper conveyance direction shown in FIG. 4 is directed from the bottom to the right, the paper conveyance direction shown in FIG. 5 is from the right to the left. Note that the term “sheet passing width” used in connection with the description of the fixing unit means the width dimension of the sheet passing through the image forming apparatus 1 described above, and generally in the image forming apparatus. It means the size of the paper in the direction perpendicular to the paper transport direction. Generally, the sheet passing width is determined by industrial standards (ISO, JIS, DIN, etc.), but the present invention is not limited to these. Further, the term “maximum sheet passing width” used in the following description means the maximum width of the sheet that the image forming apparatus 1 allows to pass through. The term “maximum sheet passing width” of the image forming apparatus 1 described with reference to FIG. In this case, it means the maximum width of paper that can be accommodated in the image forming apparatus 1 and can be transported from the paper cassette 5 or the maximum width of paper that is allowed to be transported from the stack tray 6. In addition, the term “minimum sheet passing width” used in the following description means the minimum width dimension of the sheet that the image forming apparatus 1 allows to pass through, and the image forming apparatus 1 described with reference to FIG. In this case, it means the minimum width of paper that can be transported from the paper feed cassette 5 of the image forming apparatus 1 or the minimum width of paper that is allowed to be transported from the stack tray 6.

  The fixing unit 14 includes a pressure roller 44, a fixing roller 45, a heat roller (object to be heated) 46, and a heating belt (object to be heated) 48. An elastic layer of silicon sponge is formed on the surface layer of the fixing roller 45, and a flat nip is formed between the heating belt 48 and the fixing roller 45.

  The base material of the heating belt 48 is made of a ferromagnetic material (for example, Ni). A thin elastic layer (for example, silicon rubber) is formed on the surface layer of the heating belt 48. The surface layer of the heating belt 48 is covered with a release layer (for example, PFA). When the heating belt 48 does not have a heat generating function, the heating belt 48 may be a resin belt such as PI. The core of the heat roller 46 is made of a magnetic metal (for example, Fe, SUS). The surface of the metal core of the heat roller 46 is covered with a release layer (for example, PFA).

  The metal core material of the pressure roller 44 can be formed using, for example, Fe, Al or the like. A Si rubber layer can be formed on the core material, and a fluororesin layer can be formed on the surface of the Si rubber layer. For example, a halogen heater 44 a may be provided inside the pressure roller 44.

  The fixing unit 14 further includes an IH coil unit 50 outside the heat roller 46 and the heating belt 48. The IH coil unit 50 includes an induction heating coil 52, a pair of arch cores 54, a pair of side cores 56, and a center core 58 (magnetic rod 100).

  In the embodiment shown in FIG. 5, the arc-shaped portions of the heat roller 46 and the heating belt 48 are target areas to be induction heated. The induction heating coil 52 generates a magnetic flux for induction heating the target area. The induction heating coil 52 is disposed on an arc surface along the arc-shaped outer surface of the heat roller 46 and / or the heating belt 48. For example, a resin bobbin 500 is disposed outside the heat roller 46 and the heating belt 48, and the induction heating coil 52 is disposed on the bobbin 500 in a winding shape. As a result, the induction heating coil 52 is continuously provided along the arc surface of the bobbin 500 to form an arc-shaped coil surface 520. The induction heating coil 52 draws a loop on the heat roller 46 in plan view. In the example shown in FIG. 5, the upper half of the heat roller 46 is surrounded by the induction heating coil 52. Accordingly, the coil surfaces 520 are formed on the left and right sides of the heat roller 46. The left and right coil surfaces 520 extend in the longitudinal direction of the heat roller 46. The bobbin is molded into a semi-cylindrical shape along the outer surface of the heat roller 46. The bobbin is preferably made of a heat resistant resin (for example, PPS, PET, LCP). Note that the bobbin 500 is omitted in the drawings other than FIG. 5 in order to avoid unnecessarily obscuring the description.

  The center core 58 is positioned on a straight line connecting the rotation center axes of the pressure roller 44, the fixing roller 45 and the heat roller 46. The pair of arch cores 54 and the pair of side cores 56 are disposed symmetrically about the center core 58. The pair of arch cores 54 are ferrite cores formed in an arch shape in cross section. The total length of each arch core 54 is longer than the winding region (coil surface 520) of the induction heating coil 52. The pair of side cores 56 are ferrite cores formed in a block shape. Each side core 56 is connected to one end (the lower end in FIG. 5) of each arch core 54. The arch core 54 and the side core 56 cover the outside of the winding region (coil surface 520) of the induction heating coil 52.

  The arch core 54 is formed from, for example, arch core pieces 540 arranged at a plurality of positions at intervals in the longitudinal direction of the heat roller 46. The side cores 56 are continuously arranged in the longitudinal direction of the heat roller 46 without a gap. The total length of the side core 56 corresponds to the length of the winding region (coil surface 520) of the induction heating coil 52. The arrangement of the cores 54 and 56 is determined according to the magnetic flux density (magnetic field strength) distribution of the induction heating coil 52, for example. In the portion where the arch core piece 540 does not exist, the side core 56 compensates the magnetic field focusing effect, and makes the magnetic flux density distribution (temperature difference) in the longitudinal direction uniform. For example, a resin core holder (not shown) is provided outside the arch core 54 and the side core 56. The arch core 54 and the side core 56 are supported by the core holder. The material of the core holder is also preferably a heat resistant resin (for example, PPS, PET, LCP).

  The fixing unit 14 shown in FIG. 5 includes a thermistor 62 installed inside the heat roller 46. The thermistor 62 is preferably disposed in a portion where the amount of heat generated by induction heating is large. Further, a thermostat (not shown) may be disposed inside the heat roller 46. Thereby, the safety | security at the time of abnormal temperature rise can be improved.

  The magnetic rod 100 described with reference to FIGS. 1 to 3 is used as the center core 58. As with the heat roller 46, the center core 58 has a length sufficient to correspond to the maximum sheet passing width of the sheet. Although not shown in FIG. 5, it is connected to the drive mechanism via the shaft 110 of the center core 58. With this drive mechanism, the center core 58 can rotate around the rotation center axis extending in the longitudinal direction of the center core 58. The center core 58 extends parallel to the rotation center axis of the heat roller 46 and is positioned near the upper surface of the heat roller 46 / heating belt 48 and near the longitudinal edge of the coil surface 520 arranged on the left and right.

  The thin plate 130 described with reference to FIGS. 1 to 3 functions as the movable shielding member 60 in the fixing unit 14. The movable shielding member 60 has a thin plate shape and is formed to be curved in an arc shape as a whole. Note that the movable shielding member 60 may be disposed in a recessed region formed on the outer peripheral surface of the center core 58 as described with reference to FIGS. 1 to 3, or may be attached to the outer surface of the center core 58. It may be attached. The movable shielding member 60 rotates together with the center core 58 and plays a role of switching a magnetic field path (magnetic path) generated by the induction heating coil 52.

  The movable shielding member 60 is preferably formed from a nonmagnetic and highly conductive material, for example, oxygen-free copper. When a magnetic field perpendicular to the surface of the movable shielding member 60 penetrates, an induced current is generated. This induced current generates a reverse magnetic field and cancels the interlaced magnetic flux (perpendicular penetrating magnetic field). As a result, the movable shielding member 60 can shield the magnetic field. The movable shielding member 60 formed of a highly conductive member can further suppress Joule heat generation due to the induced current and efficiently shield the magnetic field. The conductivity of the movable shielding member 60 can be improved by forming the movable shielding member 60 with a material having a small specific resistance or by forming the movable shielding member 60 thick. Specifically, the plate thickness of the movable shielding member 60 is preferably 0.5 mm or more, and in this embodiment, for example, a thickness of 1 mm is used.

  The IH coil unit 50 further includes a pair of magnetic shielding members 90. The magnetic shielding member 90 is disposed between the induction heating coil 52 and the arch core 54 and is disposed symmetrically about the center core 58. Referring to FIG. 5, the pair of magnetic shielding members 90 are arranged symmetrically with respect to the coil center of the induction heating coil 52. Each magnetic shielding member 90 is fixedly disposed between the induction heating coil 52 and the heating belt 48 (heat roller 46). Further, each magnetic shielding member 90 is disposed so as to be inserted into a part of the gap formed between the induction heating coil 52 and the heating belt 48, and the entire gap formed between the induction heating coil 52 and the heating belt 48. Is not inserted to occupy. As described above, the magnetic shielding member 90 is disposed near the coil surface 520 and thereby plays a role of shielding the magnetic field generated from the coil surface 520.

  FIG. 6 is a perspective view showing an example of the magnetic shielding member 90. The magnetic shielding member 90 has a curved plate shape as a whole. The total length of the magnetic shielding member 90 is substantially equal to the total length of the heat roller 46. Moreover, the thickness of the magnetic shielding member 90 is 0.5 mm, for example, Preferably, it is the range of 0.5 mm-3.0 mm. The magnetic shielding member 90 is bonded (fixed) to the inner surface of the resin bobbin 500 as shown in FIG.

  FIG. 7 is a diagram illustrating the arrangement of the magnetic shielding member 90. The movable shielding member 60 shown in FIG. 7A is in the retracted position and is located outside the magnetic path. The movable shielding member 60 shown in FIG. 7B is moved from the retracted position shown in FIG. 7A to the shielding position by the rotation of the center core 58. In the shielding position, the movable shielding member 60 is located in the magnetic path. A side view of the center core 58 and the magnetic shielding member 90 is drawn on the upper side of FIG. 7, and a bottom view of the center core 58 and the magnetic shielding member 90 is drawn on the lower side of FIG. In FIG. 7, the outer surface of the center core 58 is represented by a shaded area. At the retracted position, the center core 60 extends in the longitudinal direction of the center core 60 and is at a position farthest from a surface connecting the edges of the magnetic shielding members adjacent to each other. On the other hand, at the shielding position, the center core 60 is located closest to a surface extending in the longitudinal direction of the center core 60 and connecting edges of the magnetic shielding members adjacent to each other.

  The center core 58 has a total length substantially equal to or longer than the maximum sheet passing width W3. The movable shielding member 60 is divided into two pieces and arranged along the longitudinal direction of the center core 58. The divided pieces of the movable shielding member 60 are symmetrical to each other. Each piece of the movable shielding member 60 has, for example, a triangular shape in plan view or bottom view, and the sharpest corner of each piece of the movable shielding member 60 is positioned closer to the center of the center core 58. Therefore, at the position closer to the center of the center core 58, the arc length of the movable shielding member 60 is the shortest, and the arc length gradually increases toward both side ends of the center core 58.

  Further, most of the movable shielding member 60 is located in both outer regions of the region of the minimum sheet passing width W1 orthogonal to the sheet passing direction, and only a small portion of the movable shielding member 60 exists in the region of the minimum sheet passing width W1. do not do. The movable shielding member 60 protrudes slightly outward from the region of the maximum sheet passing width W3 at both ends of the center core 58. The minimum sheet passing width W1 and the maximum sheet passing width W3 are determined by the minimum or maximum size sheet that can be printed by the image forming apparatus 1.

  The ratio of the arc length of the movable shielding member 60 to the outer peripheral length of the center core 58 varies depending on the axial position (longitudinal position) of the center core 58. Here, when the ratio of the arc length (Lc) of the movable shielding member 60 to the outer peripheral length (L) of the center core 58 is the coverage (= Lc / L), the coverage is closer to the axial center position of the center core 58. It becomes smaller and becomes larger toward the outside (both ends) in the axial direction. Specifically, the coverage is minimum in the vicinity of the area of the minimum sheet passing width W 1 and is maximum at both ends of the center core 58.

  The magnetic path can be switched by changing the position of the movable shielding member 60 between the shielding position (first position) and the retracted position (second position). As a result, the generated magnetic flux can be controlled, and the amount of heating can be adjusted according to the paper size (paper passing width). The rotation angle (rotational displacement amount) of the center core 58 is changed according to the paper size (paper passing width) so that the magnetic shielding amount is reduced as the paper size is larger, and conversely, the shielding amount is increased as the paper size is smaller. By doing so, it is possible to prevent excessive temperature rise at both ends of the heat roller 46 and the heating belt 48. In FIG. 7, only the rotation in the counterclockwise direction is indicated by an arrow, but the center core 58 may be rotated in the clockwise direction. Further, the paper passing direction may be opposite to the direction shown in FIG.

  FIG. 8 illustrates another structure of the magnetic shielding member 90. In the example shown in FIG. 8, each magnetic shielding member 90 shown in FIG. 7 is divided into two pieces, and each divided piece is arranged in the longitudinal direction (paper width direction). The magnetic shielding member 90 mainly covers the outside of the area with the minimum sheet passing width W1, and hardly shields the area with the minimum sheet passing width W1. The magnetic shielding member 90 shown in FIG. 8 does not contribute to magnetic shielding within the region of the minimum sheet passing width W1. However, since the fixing operation is always performed within the area of the sheet passing width W1, there is no particular problem even with the arrangement as shown in FIG.

  FIG. 9 is a front view showing the configuration of the drive mechanism 64 of the center core 58. The drive mechanism 64 plays a role of rotating the center core 58 around the shaft 110 and moving the movable shielding member 60 to the shielding position or the retracted position. Thereby, switching of a magnetic path is performed. The drive mechanism 64 includes, for example, a stepping motor 66 and a speed reduction mechanism 68 that decelerates the rotation of the stepping motor 66. The shaft 110 of the center core 58 is connected to the speed reduction mechanism 68. The stepping motor 66 drives the shaft 110 and rotates the center core 58. For example, a worm gear is used as the speed reduction mechanism 68, but the present embodiment is not limited to this. The drive mechanism 64 further detects the disk 72 with the slit fixed to the end of the shaft 110 and the rotation angle of the disk 72 with the slit (that is, the rotation angle of the center core 58 (rotational displacement amount from the reference position)). A photo interrupter 74 is provided.

  The rotation angle of the center core 58 can be controlled by, for example, the number of drive pulses applied to the stepping motor 66, and the drive mechanism 64 includes a control circuit 640 that controls the rotation of the stepping motor 66. The control circuit 640 includes, for example, a control IC 641, an input driver 642, an output driver 643, a semiconductor memory 644, and the like. A detection signal from the photo interrupter 74 is input to the control IC 641 through the input driver 642. Based on the input signal, the control IC 641 detects the current rotation angle (position) of the center core 58. On the other hand, an information signal regarding the current paper size is transmitted to the control IC 641 from the image formation control unit 650 included in the image forming apparatus 1. After receiving the information signal from the image formation control unit 650, the control IC 641 reads information on the rotation angle suitable for the paper size from the semiconductor memory (ROM) 644, and drives pulses for reaching the target rotation angle. Is output at regular intervals. The drive pulse is applied to the stepping motor 66 through the output driver 643. The stepping motor 66 operates according to the driving pulse. In the case where it is necessary to detect only the reference position when controlling the stepping motor 66, the slit disk 72 may be used as an index member, and the index member may be detected by the photo interrupter 74 at the reference position.

  FIG. 10 is a view for explaining the effect of suppressing the excessive temperature rise accompanying the rotation of the center core 58. Hereinafter, the action of suppressing excessive temperature rise will be described with reference to FIGS. 10 (a) and 10 (b).

  FIG. 10A shows a case where the center core 58 is rotated and the movable shielding member 60 is moved to the retracted position. The induction heating coil 52 generates a magnetic field, and this magnetic field passes through the heating belt 48 and the heat roller 46 through a first path (thick solid line in the drawing) including the side core 56, the arch core 54, and the center core 58. . At this time, eddy currents are generated in the heating belt 48 and the heat roller 46 which are ferromagnetic materials, Joule heat is generated according to the specific resistance of each material, and the heating belt 48 and the heat roller 46 are heated.

  Inside the magnetic path that passes through the heating belt 48 and the heat roller 46 through the side core 56, the arch core 54, and the center core 58, the magnetic shielding member 90 is, for example, a shortcut magnetic flux that attempts to leak from the arch core 54 (thick dashed-dotted line in the figure). Shield. However, since such a short-cut magnetic flux is small and hardly contributes to heat generation, the magnetic shielding member 90 does not hinder full width heating.

  FIG. 10B shows a case where the movable shielding member 60 is moved to the shielding position. FIG. 10B is a cross-sectional view of a region outside the region having the minimum sheet passing width W1. As shown in FIG. 10 (b), the movable shielding member 60 is located on the magnetic path indicated by the solid line in FIG. 10 (a). Since the movable shielding member 60 and the magnetic shielding member 90 form a shielding surface that prevents passage of the magnetic field on the path toward the heating belt 48 and the heat roller 46 via the center core 58, the magnetic path does not pass through the center core 58. The route is switched to route 2 (thick broken line in the figure). As a result, the amount of heat generated outside the region of the minimum sheet passing width W1 can be suppressed, and excessive heating of the heating belt 48 and the heat roller 46 can be prevented.

  The magnetic shielding member 90 can supplement the shielding effect of the movable shielding member 60 and shield the magnetic flux that is about to leak from the arch core 54 after being switched to the second path. For this reason, in this embodiment, a sufficient magnetic shielding effect can be obtained in the non-sheet passing region (the region where the paper does not pass) without excessively increasing the area of the movable shielding member 60. Therefore, excessive heating of the heating belt 48 and the heat roller 46 can be suppressed as compared with the prior art. Even when the movable shielding member 60 is in the shielding position, a weak magnetic flux (magnetic flux as indicated by a thick dashed line in FIG. 10A) that circulates small inside the arch core 54 is generated. Such a weak magnetic flux is continuously shielded by the fixed magnetic shielding member 90 even after the movable shielding member 60 moves from the retracted position to the shielding position.

  FIG. 11 illustrates the structure of another fixing unit 14. The fixing unit shown in FIG. 11 has the same structure as the fixing unit 14 described with reference to FIG. 5 except that a magnetic shielding member 90 is disposed between the arch core 54 and the induction heating coil 52.

  Each magnetic shielding member 90 is disposed symmetrically about the coil center of the induction heating coil 52, and is fixed between the arch core 54 and the induction heating coil 52 (in this example, the inner surface of the arch core 54). Each magnetic shielding member 90 covers a part of the inner surface area of the arch core 54, not the entire inner surface area.

  FIG. 12 is a diagram showing an action of suppressing excessive temperature rise accompanying rotation of the center core 58 of the fixing unit 14 shown in FIG. Hereinafter, the action of suppressing excessive temperature rise will be described with reference to FIGS. 12 (a) and 12 (b).

  FIG. 12A shows a case where the center core 58 is rotated and the movable shielding member 60 is moved to the retracted position. The induction heating coil 52 generates a magnetic field, and this magnetic field passes through the heating belt 48 and the heat roller 46 through a first path (thick solid line in the drawing) including the side core 56, the arch core 54, and the center core 58. . At this time, eddy currents are generated in the heating belt 48 and the heat roller 46 which are ferromagnetic materials, Joule heat is generated according to the specific resistance of each material, and the heating belt 48 and the heat roller 46 are heated.

  Inside the magnetic path that passes through the heating belt 48 and the heat roller 46 through the side core 56, the arch core 54, and the center core 58, the magnetic shielding member 90 is, for example, a shortcut magnetic flux that attempts to leak from the arch core 54 (thick dashed-dotted line in the figure). Shield. However, since such a short-cut magnetic flux is small and hardly contributes to heat generation, the magnetic shielding member 90 does not hinder full width heating.

  FIG. 12B shows a case where the movable shielding member 60 is moved to the shielding position. FIG. 12B is a cross-sectional view of a region outside the region having the minimum sheet passing width W1. As shown in FIG. 12B, the movable shielding member 60 is located on the magnetic path indicated by the solid line in FIG. Since the movable shielding member 60 and the magnetic shielding member 90 form a shielding surface that prevents passage of the magnetic field on the path toward the heating belt 48 and the heat roller 46 via the center core 58, the magnetic path does not pass through the center core 58. The route is switched to route 2 (thick broken line in the figure). As a result, the amount of heat generated outside the region of the minimum sheet passing width W1 can be suppressed, and excessive heating of the heating belt 48 and the heat roller 46 can be prevented. Similarly to the other structural examples, while being switched to the second path, the magnetic shielding member 90 shields the magnetic flux that is about to leak from the arch core 54, and supplements the shielding effect by the movable shielding member 60. it can.

  FIG. 13 shows the positional relationship between the center core 58 and the magnetic shielding member 90. The magnetic shielding member 90 is preferably arranged as close to the center core 58 as possible, and a gap (reference numeral G in FIG. 13) between the outer peripheral surface of the center core 58 and the edge of the magnetic shielding member 90 is set to 0, for example. About 5 mm is preferable.

  FIG. 14 illustrates another structure of the fixing unit 14. Unlike the fixing unit 14 shown in FIG. 5, the fixing unit 14 shown in FIG. 14 does not include a heating belt, and uses a fixing roller (object to be heated) 45 and a pressure roller 44 to fix a toner image. For example, a magnetic material similar to the heating belt 48 of the fixing unit 14 shown in FIG. 5 is wound around the outer periphery of the fixing roller 45. Using the induction heating coil 52, the wound magnetic body is induction heated. The thermistor 62 is disposed outside the fixing roller 45 and faces the magnetic layer. Other structures are the same as those of the fixing unit 14 shown in FIG. The magnetic shielding member 90 may be disposed between the induction heating coil 52 and the fixing roller 45 or may be fixed to the inner surface of the arch core 54.

  FIG. 15 illustrates another structure of the fixing unit 14. The heat roller 46 of the fixing unit 14 shown in FIG. 14 is formed of a nonmagnetic metal (for example, SUS: stainless steel). A center core 58 is disposed inside the heat roller 46. Further, a pair of left and right arch cores 54 are connected at the center of the fixing roller 14. An intermediate core 55 is installed on the lower surface (center position) of the arch core. The magnetic shielding member 90 is disposed between the induction heating coil 52 and the heating belt 48.

  When the heat roller 46 is made of a nonmagnetic metal, the magnetic field generated by the induction heating coil 52 passes through the side core 56, the arch core 54 and the intermediate core 55, passes through the heat roller 46, and reaches the internal center core 58. The heating belt 48 is induction-heated by a penetrating magnetic field.

  When the fixing unit 14 shown in FIG. 15 is used, the position where the movable shielding member 60 is separated from the intermediate core 55 is the retracted position (position shown in FIG. 15). While the movable shielding member 60 is in the retracted position, the heating belt 48 is induction-heated in the region of the maximum sheet passing width W3 without the magnetic shielding effect. On the other hand, when the movable shielding member 60 is moved to a position closest to the intermediate core 55 (shielding position), the magnetic path is switched to the second path, and excessive temperature rise is suppressed outside the sheet passing area.

  FIG. 16 is a longitudinal sectional view illustrating another structure of the fixing unit 14. The fixing unit 14 shown in FIG. 16 includes a so-called inclusion IH type IH coil unit 50. The heat roller 46 is made of a non-magnetic metal (for example, SUS) having a relatively large diameter (for example, 40 mm). An induction heating coil 52 and a center core 58 are accommodated in the heat roller 46. The fixing unit 14 shown in FIG. 16 does not include the arch core 54 and the side core 56 outside the heat roller 46. A release layer (PFA) is formed on the surface of the heat roller 46. The magnetic shielding member 90 is fixedly disposed between the induction heating coil 52 and the inner surface of the heat roller 46.

  In the inclusion IH type fixing unit 14 shown in FIG. 16, the magnetic field generated by the induction heating coil 52 is guided by the center core 58 inside the heat roller 46 so that the heat roller 46 is induction heated. FIG. 16 shows the movable shielding member 60 in the retracted position, and the movable shielding member 60 is at a position farthest from the induction heating coil 52. While the movable shielding member 60 is in the retracted position, the heating belt 48 is induction-heated in the region of the maximum sheet passing width W3 without the magnetic shielding effect. On the other hand, when the movable shielding member 60 is moved to a position close to the induction heating coil 52 (shielding position), the magnetic path is switched to the second path, and excessive temperature rise is suppressed outside the sheet passing area.

  FIG. 17 illustrates another structure of the fixing unit 14. In the fixing unit 14 shown in FIG. 17, the flat portion between the heat roller 46 and the fixing roller 45 is induction-heated instead of the portion where the heating belt 48 is curved in an arc shape. The magnetic shielding member 90 is not curved and has a planar shape. For example, as indicated by a solid line in FIG. 17, the induction heating coil 52 and the heating belt 48 may be installed. Alternatively, as shown by a two-dot chain line in FIG. 17, the magnetic shielding member 90 is fixed along the inner surface of the arch core 54 extending along the planar portion of the heating belt 48, and the arch core 54 and the induction heating coil 52 are fixed. You may install between.

  As described above, the magnetic rod described with reference to FIGS. 1 to 3 can be incorporated into the fixing unit 14 in various structures. Various modifications can be made to the fixing unit according to the above description.

  FIG. 18 shows another structure of the magnetic shielding member 90. The movable shielding member 60 shown in FIG. 18A is in the retracted position and is located outside the magnetic path. The movable shielding member 60 shown in FIG. 18B is moved from the retracted position shown in FIG. 18A to the shielding position by the rotation of the center core 58. In the shielding position, the movable shielding member 60 is located in the magnetic path. The side view of the center core 58 and the magnetic shielding member 90 is drawn on the upper side of FIG. 18, and the bottom view of the center core 58 and the magnetic shielding member 90 is drawn on the lower side of FIG. In FIG. 18, the outer surface of the center core 58 is represented by a shaded area.

  18, the magnetic shielding member 90 includes a plurality of rectangular loops, and the plurality of rectangular loops are aligned in the longitudinal direction of the center core 58. The magnetic shielding member 90 can be formed by punching out the magnetic shielding member 90 made of a nonmagnetic metal (for example, oxygen-free copper) shown in FIG. 6 and arranging a plurality of rectangular holes in parallel. As shown in the upper diagram of FIG. 18, the magnetic shielding member 90 is formed to be curved in an arc shape as a whole.

  Each rectangular loop includes a pair of linear portions 90a extending in the longitudinal direction of the center core 58 and a pair of arc portions 90b extending in the sheet passing direction. 18 is bonded to the inner surface of the resin bobbin 500. The magnetic shielding member 90 shown in FIG.

  When the magnetic shielding member 90 is divided into a plurality of loops, each of the loops independently exhibits a magnetic shielding effect. Each loop of the magnetic shielding member 90 aligned in the longitudinal direction of the center core exhibits a magnetic shielding effect. For this reason, each loop is provided at a position corresponding to the sheet passing widths W1, W2, and W3.

  FIG. 19 is a conceptual diagram for explaining the loop characteristics of the magnetic shielding member 90. In FIG. 19, for clarity of explanation, one of a plurality of loops of the magnetic shielding member 90 is taken out, but the phenomenon described below is applied to all the loops of the magnetic shielding member 90. Is.

  Reference is made to FIG. FIG. 19A shows a unidirectional penetrating magnetic field (complex magnetic flux) penetrating at right angles to the loop plane (virtual plane). This interlaced magnetic flux produces an induced current that flows along the loop. Due to the electromagnetic induction caused by the induced current, a magnetic field (demagnetizing field) opposite to the penetrating magnetic field is generated. As a result, the complex magnetic flux and the demagnetizing field cancel each other, canceling the magnetic field. In the present embodiment, when the movable shielding member 60 is moved to the shielding position and the magnetic path is switched to the second path, the magnetic shielding member 90 supplements the magnetic shielding effect by using this magnetic field canceling effect. .

  Reference is made to FIG. In the upper diagram of FIG. 19B, a bidirectional penetrating magnetic field (interlaced magnetic flux) penetrating at right angles to the loop surface (virtual plane) is shown. It is assumed that the total sum (balance) of the interlaced magnetic flux is approximately 0 (± 0). In this case, almost no induced current is generated in the loop of the magnetic shielding member 90. Therefore, each loop hardly exhibits the magnetic field canceling effect, and the bidirectional magnetic field passes through the magnetic shielding member 90. This is the same when the magnetic field directed in the U-turn direction passes through the inside of the loop, as shown in the lower diagram of FIG.

  When the magnetic shielding member 90 includes a plurality of loops, the magnetic shielding member 90 does not inhibit heat generation as long as the balance of the magnetic flux flowing out / inflowing inside the loop is zero. Therefore, while the movable shielding member 60 is in the retracted position, the magnetic shielding member 90 has no influence on the magnetic flux that makes a U-turn through the loop of the magnetic shielding member 90. Therefore, it can be said that the magnetic shielding member 90 prevents the heat generation effect from being reduced as much as possible.

  Reference is made to FIG. FIG. 19C shows a magnetic field (interlaced magnetic flux) substantially parallel to the loop surface. In this case as well, as in the case shown in FIG. 19B, almost no induced current is generated in each loop. Therefore, the magnetic field canceling effect does not occur.

  FIG. 20 shows another structure of the magnetic shielding member 90. Note that the movable shielding member 60 shown in FIG. 20 is in the shielding position. The movable shielding member 60 is composed of a plurality of loops that are independently arranged. Note that the loops are not electrically connected to each other. Further, each loop can be arranged so as to correspond to the sheet passing widths W1, W2, and W3 that differ depending on the sheet size. For example, when the sheet size is the minimum (minimum sheet passing width W1), the magnetic shielding effect can be obtained by the loops of the magnetic shielding members 90, three from each of the outer sides (total 12). At this time, a strong magnetic flux does not flow into the loop of the magnetic shielding member 90 located inside the minimum sheet passing width W1, and the magnetic shielding effect does not occur. Further, when the paper size is in the range from the minimum to the middle (minimum sheet passing width W1 to intermediate sheet passing width W2), two loops of the magnetic shielding member 90 from each outside (a total of eight) are used, The magnetic shielding effect can be supplemented. When the paper size is the maximum (maximum paper passing width W3), no induction current is generated in the loops of all the magnetic shielding members 90, and the influence on the magnetic field generated by the induction heating coil 52 can be eliminated.

  FIG. 21 shows another structure of the magnetic shielding member 90. The magnetic shielding member 90 shown in FIG. 21 is obtained by removing the magnetic shielding member 90 inside the minimum sheet passing width W1 from the magnetic shielding member 90 shown in FIG. Others are the same as those of the magnetic shielding member 90 shown in FIG.

  FIG. 22 shows another structure of the magnetic shielding member 90. A magnetic shielding member 90 shown in FIG. 22 is obtained by dividing the magnetic shielding member 90 shown in FIG. 18 into two pieces, and these two pieces are respectively arranged on both outer sides of the region of the minimum sheet passing width W1. is there. Others are the same as those of the magnetic shielding member 90 shown in FIG.

  FIG. 23 shows a magnetic cylinder piece obtained by the molding process. In FIG. 23, three magnetic cylinder pieces are shown, but the inner diameter dimension and the outer diameter dimension are different. Among the three magnetic cylinder pieces, a magnetic cylinder piece having an intermediate inner diameter dimension and an outer diameter dimension is indicated by a symbol A, a magnetic cylinder piece having a maximum inner diameter dimension and an outer diameter dimension is indicated by a symbol B, and a minimum inner diameter dimension is indicated. In addition, a magnetic cylinder piece having an outer diameter is indicated by a symbol C.

  The magnetic cylinder piece is generally molded using a mold of the same size, but due to differences in process environment (temperature, humidity, etc.) during the cooling process, the outer diameter dimension and inner diameter dimension of the obtained magnetic cylinder piece are reduced. Make a difference. As a rule of thumb, it has been found that the inner and outer circles of the magnetic cylinder piece maintain high coaxial accuracy. As described above, since the shaft 110 is inserted into the magnetic cylinder piece, the dimension of the prepared magnetic cylinder piece must be larger than the outer diameter dimension of the shaft 110.

  FIG. 24 is a view showing a state in which the magnetic cylinder pieces A, B, and C shown in FIG. In FIG. 24, the set of magnetic cylinder pieces A, B, and C shown on the left side portion of the shaft 110 is attached to the shaft 110 using the O-ring 140 according to the method described with reference to FIGS. It has been. The magnetic cylinder pieces A, B, and C shown on the right side portion of the shaft 110 are attached to the shaft 110 without using the O-ring 140. In addition, a heating target surface H having a flat outline is shown below the shaft 110.

As shown in FIG. 24, the O-ring 140 absorbs a dimensional difference generated between the magnetic cylinder pieces A, B, and C. Therefore, magnetic cylindrical piece to the shaft 110 A, B, and C, when mounted with an O-ring 140, magnetic cylindrical pieces A, B, the maximum difference in distance d ₁ to the heating target surface between the C is the following It is expressed by a formula. Incidentally, d _b is the outer diameter of the magnetic cylindrical piece B having the largest outer diameter, d _c is the outer diameter of the magnetic cylindrical piece C having the minimum outer diameter.

On the other hand, when the magnetic cylinder pieces A, B, and C are attached to the shaft 110 without using the O-ring 140, the outer diameter dimensional difference absorbing action by the O-ring 140 cannot be obtained. , C, the maximum distance difference d ₂ to the surface to be heated is expressed by the following equation.

The value of the distance difference d ₂ is not may be possible to reduce the skill of use or skilled assemblers of any fixture, it does not fall below the value of the distance difference d _1. Therefore, in this embodiment, when the magnetic rod 100 is incorporated in an arbitrary electromagnetic induction heating device, the distance difference between the magnetic cylinder pieces A, B, and C from the surface H to be heated is kept to a minimum. It can be said that it guarantees.

  The present invention is applicable to a heating device that performs electromagnetic induction heating and a device that incorporates a heating device that performs electromagnetic induction heating. In particular, the present invention can be applied to various image forming apparatuses such as a color printer, a printer, a copier, a facsimile machine, and a multifunction machine having these functions.

14 .... Fixing unit 100 ... Magnetic rod 110 ... Shaft 120 ... Magnetic cylinder 130 ... Thin plate (shielding plate)
140 ... O-ring (elastic ring)
46... Heat roller (object to be heated)
48 ... Heating belt (object to be heated)
520 ... Coil surface 58 ... Center core 90 ... Magnetic shielding member

Claims (17)

A magnetic rod disposed near the object to be heated and a coil for generating a magnetic flux for heating the object to be heated by electromagnetic induction heating,
A shaft extending in one direction;
A plurality of magnetic cylinder pieces arranged coaxially with respect to the longitudinal axis of the shaft and surrounding the outer peripheral surface of the shaft;
A plurality of elastic rings disposed between the inner peripheral surface of each of the plurality of magnetic cylinder pieces and the outer peripheral surface of the shaft and pressed against the inner peripheral surface of the magnetic cylinder piece and the outer peripheral surface of the shaft And a magnetic rod characterized by comprising:   The magnetic bar according to claim 1, further comprising a resin layer covering an outer peripheral surface of the plurality of magnetic cylinder pieces.   The magnetic rod according to claim 2, wherein the resin layer is heat-shrinkable.   4. The magnetic rod body further comprises an adhesive layer between an inner peripheral surface of at least one of the plurality of magnetic cylindrical pieces and an outer peripheral surface of the shaft. 2. A magnetic rod according to claim 1. An annular housing portion is formed on the inner wall of each end of each of the plurality of magnetic cylinder pieces,
The magnetic rod according to any one of claims 1 to 4, wherein the elastic ring body is disposed in the housing portion.   The magnetic rod body according to claim 1, wherein the elastic ring body is an O-ring. A method of manufacturing a magnetic rod positioned near a heated object and a coil that generates magnetic flux for heating the heated object to be electromagnetically heated,
Preparing a shaft;
Attaching the magnetic cylinder piece to the shaft, and attaching the magnetic cylinder piece externally fitting one elastic ring to the shaft;
Inserting the shaft to which the one elastic ring body is attached into the magnetic cylinder piece, and press-contacting the one elastic ring body to an outer peripheral surface of the shaft and an inner peripheral surface of the magnetic cylinder piece;
A method of manufacturing a magnetic rod, comprising: fitting another elastic ring to the shaft; and press-fitting the other elastic ring into the magnetic cylinder piece.   8. The method of manufacturing a magnetic rod according to claim 7, wherein the step of attaching the magnetic cylinder piece is repeated a plurality of times.   9. The method of manufacturing a magnetic rod according to claim 7, further comprising a step of forming a heat-shrinkable resin layer on an outer peripheral surface of the magnetic cylinder piece after the step of attaching the magnetic cylinder piece.   The magnetic rod body according to claim 9, wherein the step of forming the heat-shrinkable resin layer on the outer peripheral surface of the magnetic cylinder piece includes a step of fitting a heat-shrinkable tube to the magnetic cylinder piece. Production method.   The method further comprises the step of heating the heat-shrinkable resin layer and shrinking the heat-shrinkable resin layer after the step of forming the heat-shrinkable resin layer on the outer peripheral surface of the magnetic cylinder piece. Item 11. A method for producing a magnetic rod according to Item 9 or 10.   The step of attaching the magnetic cylinder piece further includes press-contacting the one elastic ring body to the outer peripheral surface of the shaft and the inner peripheral surface of the magnetic cylinder piece, and press-fitting the other elastic ring body into the magnetic cylinder piece. 12. The magnetism according to claim 7, further comprising a step of forming an adhesive layer between an inner peripheral surface of the magnetic cylinder piece and an outer peripheral surface of the shaft during the step of forming the magnetic cylinder piece. A method for manufacturing a rod. A fixing device that fixes a toner image on a sheet that passes between a heated object having one rotation center axis and a pressure roller that is in pressure contact with the heated object,
At least one coil surface formed by a coil that is arranged along an outer peripheral surface or an inner peripheral surface of the object to be heated and that generates a magnetic field for induction heating the object to be heated;
A shaft extending in the extending direction of the rotation center axis of the heated body, a plurality of magnetic cylindrical pieces surrounding the outer peripheral surface of the shaft, and an outer peripheral surface of the shaft and an inner peripheral surface of the magnetic cylindrical piece are pressed against each other. And a center core including a plurality of elastic rings.   The fixing unit according to claim 13, further comprising at least one magnetic shielding member disposed near the at least one coil surface.   15. The fixing unit according to claim 13, wherein the center core further includes a shielding plate that is fixed to at least one of the plurality of magnetic cylinder pieces and prevents the magnetic field from passing therethrough. The center core further includes a shielding plate fixed to at least one of the plurality of magnetic cylinder pieces and preventing passage of the magnetic field,
When the center core is present at a first position where the shielding plate approaches the at least one magnetic shielding member, a heating amount to the heating member is at a second position where the shielding plate is separated from the at least one magnetic shielding member. The fixing unit according to claim 14, wherein the fixing unit is smaller than a heating amount when the center core exists. A method for manufacturing the center core used in the fixing unit according to any one of claims 13 to 16,
Preparing a shaft;
Attaching a plurality of magnetic cylinder pieces to the shaft;
Disposing the shielding plate on the outer peripheral surface of the plurality of magnetic cylinder pieces;
Forming a heat-shrinkable resin layer on the outer peripheral surface of the shielding plate and the magnetic cylinder piece;
Heating and shrinking the heat-shrinkable resin layer,
The step of attaching the plurality of magnetic cylinder pieces includes a step of externally fitting one elastic ring body to the shaft, and inserting the shaft having the one elastic ring body attached thereto into the magnetic cylinder piece, Pressing the elastic ring body with the outer peripheral surface of the shaft and the inner peripheral surface of the magnetic cylinder piece; and fitting another elastic ring body with the shaft; and the other elastic ring within the magnetic cylinder piece A method of manufacturing a center core, comprising the step of repeating a step of press-fitting a body.

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