JP2009237401A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten warm-up time and to save occupancy space by reducing the number of members such as a heating roller to be arranged inside arranged inside a heating member, thereby reducing the heat capacity in a fixing unit of an image forming apparatus. <P>SOLUTION: The fixing unit 14 includes: an induction heating coil 52 disposed along the outer surface of a heating belt 48; arch cores 54 and side cores 56 forming magnetic paths on both sides of the coil center; a center core 58 disposed in the coil center; and a shielding member 60 disposed along the outer surface of the center core. The center core 58 is divided into a plurality of bock cores 58a and 58b in the axial direction. These block cores 58a and 58b are separately rotated, thereby individually controlling them to switch between the shielding member where the shielding member 60 shields magnetism and a retracted position where the passage of magnetism is allowed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus provided with a fixing unit that heats and melts unfixed toner to a sheet while passing the paper carrying a toner image between a heated roller pair or a nip between a heating belt and a roller. It is.

  In recent years, in this type of image forming apparatus, a belt system capable of setting a small heat capacity has attracted attention because of demands for shortening the warm-up time in the fixing unit and saving energy (for example, see Patent Document 1). In recent years, the electromagnetic induction heating method (IH) having the possibility of rapid heating and high-efficiency heating has been attracting attention. From the viewpoint of energy saving when fixing a color image, the electromagnetic induction heating is combined with the belt method. Many things have been commercialized. When combining the belt method and electromagnetic induction heating, many cases are adopted in which electromagnetic induction devices are arranged outside the belt because of the coil layout and ease of cooling, and the advantage that the belt can be directly heated (so-called). Outer package IH type).

  In the above-mentioned electromagnetic induction heating method, various technologies have been developed to prevent overheating in the non-sheet passing area according to the width of the sheet size (sheet passing width) that is passed through the fixing unit. In particular, there are the following prior arts as size switching means in the outer package IH (see, for example, Patent Documents 2 and 3).

  In the first prior art (Patent Document 2), a magnetic member is divided into a plurality of pieces and arranged in the sheet passing width direction, and a part of the magnetic member is placed on the exciting coil in accordance with the sheet size (sheet passing width) to be passed. To be separated. In this case, it is considered that the heat generation efficiency is lowered by separating the magnetic member from the exciting coil in the non-sheet passing area, and the heat generation amount is smaller than the area corresponding to the sheet having the minimum sheet passing width.

In the second prior art (Patent Document 3), another conductive member is disposed outside the minimum sheet passing width inside the heat generating roller, and the position of the conductive member is switched within or outside the magnetic field range. It is. In this prior art, first, the conductive member is positioned outside the magnetic field range, and the heat generating roller is heated by electromagnetic induction. When the heat generating roller rises to near the Curie temperature due to the temperature rise, the conductive member is brought into the magnetic field range. By moving, the magnetic flux is leaked from the heat generating roller outside the minimum sheet passing width to prevent overheating.
JP-A-6-31801 Japanese Patent Laying-Open No. 2003-107941 (FIGS. 2 and 3) Japanese Patent No. 3527442 (FIG. 10)

  However, since the first prior art has a large movable range of the magnetic member and requires an extra space, there is a problem that the entire apparatus is inadvertently enlarged. On the other hand, the second prior art can save space because the size switching member is arranged inside the heat generating roller. However, the inside of the heat generating roller is in a high temperature environment, and when a certain member is arranged there, it is necessary to set the Curie temperature high, and there is a problem that a member having a large heat capacity prolongs the warm-up time.

  Therefore, the present invention provides a technique capable of reducing the heat capacity by reducing the number of members arranged inside the heating member, reducing the warm-up time, and realizing space saving.

  According to the present invention, a sheet on which a toner image has been transferred by an image forming unit is transported by being sandwiched between a heating member and a pressure member, and in this transport process, the toner image is fixed on the sheet by at least heat from the heating member. An image forming apparatus including a fixing unit. The fixing unit in the image forming apparatus of the present invention is disposed along the outer surface of the heating member, and a coil that generates a magnetic field for induction heating the heating member over the maximum sheet passing area of the conveyed paper, and sandwiches the coil The fixed core disposed on the opposite side of the heating member and forming a magnetic path around the coil, and the magnetic path along with the fixed core disposed between the fixed core and the heating member as viewed in the direction of magnetic field generation by the coil. A block-shaped core that is formed and arranged in a plurality of divided directions in the width direction of the conveyed paper, and a shielding member that is provided along the outer surface of the block-shaped core and shields magnetism in a magnetic field generated by a coil By rotating the plurality of block-shaped cores individually around the axis intersecting the magnetic field passage direction, the shield member is shielded from the shield position, and the passage of magnetism is allowed. And a magnetic shielding amount adjusting means for performing an operation to switch to the that retracted position independently for each of the plurality of block-shaped core.

  As described above, the present invention employs a method (outside IH) in which the heating member is induction-heated by the magnetic field generated by the coil to heat and melt the toner image, so that a special member is provided inside the heating member. There is no need to provide it. The fixed core is arranged around the coil in order to form a magnetic path for guiding the magnetic field generated by the coil, and the block-shaped core divided into a plurality is also arranged between the fixed core and the heating member. Therefore, the space occupied as a whole is not inadvertently increased in size.

  In particular, in the present invention, the amount of heat generated by the heating member can be adjusted simply by rotating the block-shaped core. That is, when the magnetic shielding amount adjusting means rotates a plurality of block-shaped cores and moves the shielding member to the retracted position, the magnetic field generated by the coil is guided to the fixed core and the block-shaped core to generate an eddy current in the heating member. And magnetic induction heating. On the other hand, when the magnetic shielding amount adjusting means rotates the block-shaped core and moves the shielding member to the shielding position, the magnetic resistance in the magnetic path increases, the magnetic field strength decreases, and the heating value of the heating member decreases. Can do.

  Further, in the present invention, the block-shaped core is installed in a plurality in a state of being divided in the width direction of the paper, and by individually rotating these, the position of the shielding member is switched independently for each block-shaped core, The heat generation amount of the heating member can be adjusted corresponding to various paper sizes (paper passing widths). For example, when the paper size is the smallest, with respect to the block-like core positioned outside the minimum paper passing area in the paper width direction, the heating member is excessively heated by performing control to switch the shielding member to the shielding position. Temperature can be prevented. In addition, if the paper size is changed, heating is performed while quickly responding to the paper size change by performing control to switch the shielding member of the block core positioned outside the necessary paper passing area at that time to the shielding position. It is possible to reliably prevent overheating of the member.

  Thus, in the present invention, it is not necessary to separate the core from the heating member when adjusting the amount of heat generated by the heating member, and space saving can be achieved accordingly. In addition, since it is not necessary to provide a magnetic induction core or a magnetic field adjusting conductive member inside the heating member, it is possible to suppress an increase in heat capacity and contribute to a reduction in warm-up time.

  In the present invention, at least two block-like cores positioned at both ends as viewed in the width direction of the sheet conveyed by the fixing unit can be integrally rotated while being attached to the same rotation shaft member. It is preferable that the block-like cores at other positions are provided so as to be individually rotatable with respect to the rotary shaft member.

  According to such an aspect, the respective shielding members can be simultaneously switched to the shielding position by rotating the two block-shaped cores at both end positions in the width direction of the sheet integrally. Accordingly, it is possible to easily shield the magnetic field on the outermost side of the sheet passing width, and it is possible to quickly cope with the change in the sheet size.

  In the present invention, it is preferable that the shielding member is provided on a block-shaped core positioned outside the minimum sheet passing area in the width direction of the sheet conveyed by the fixing unit.

  As described above, the plurality of block-shaped cores are arranged over the maximum sheet passing area of the sheet. Among them, the block shape positioned outside the minimum sheet passing area is required to correspond to the switching of the sheet size. Just the core. For this reason, by not providing a shielding member on the block-shaped core in the minimum sheet passing area, it is possible to always transmit the magnetic flux to the heating member without shielding the magnetism by the shielding member by the rotation. .

  The image forming apparatus of the present invention does not need to provide a magnetic shielding mechanism inside the heating member, and can reduce the heat capacity accordingly, so that it is possible to reduce the warm-up time of the fixing unit. Even in the case of the envelope IH, the movable object is only the rotation of the block-shaped core, so that the movable range as a whole can be reduced, and the fixing unit and thus the entire image forming apparatus can be reduced in size.

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 includes a printer, a copier, a facsimile machine, and a multifunction machine having both functions of transferring a toner image onto the surface of a printing medium such as printing paper based on image information input from the outside. Or the like.

  An image forming apparatus 1 shown in FIG. 1 is, for example, a tandem color printer. The image forming apparatus 1 includes a square box-shaped apparatus main body 2 that forms (prints) a color image on a sheet therein, and discharges the sheet on which the color image is printed on the upper surface of the apparatus main body 2. Paper discharge section (discharge tray) 3 is provided.

  In the apparatus main body 2, a paper feed cassette 5 for storing paper is provided at the lower part thereof. A stack tray 6 for supplying manually fed sheets is provided at the center of the apparatus main body 2. An image forming unit 7 is provided on the upper part of the apparatus main body 2. 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 apparatus.

  As shown in FIG. 1, a first transport path 9 for transporting paper fed from the paper feed cassette 5 to the image forming unit 7 is provided on the left side of the apparatus main body 2. A second transport path 10 is provided for transporting paper fed from the stack tray 6 to 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 sheet that has been subjected to the fixing process are conveyed to the sheet discharging unit 3. 3 conveyance paths 11 are provided.

  The paper feed cassette 5 can be replenished by pulling it out of the apparatus main body 2 (for example, the front side in FIG. 1). 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 paper stored in the storage unit 16 is fed out to the first transport path 9 side by sheet by the paper feed roller 17 and the separating roller 18.

  The stack tray 6 can be opened and closed on the outer surface of the apparatus main body 2, and manual sheets are loaded one by one or a plurality of sheets are stacked on the manual feed portion 19. Note that 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 to the second conveyance path 10 side.

  The first transport path 9 and the second transport path 10 merge before the registration roller 22, and the paper supplied to the registration roller 22 waits here for a while, and after adjusting skew and timing, It is sent out toward the next transfer unit 23. The full color toner image on the intermediate transfer belt 40 is secondarily transferred onto the sheet by the secondary transfer unit 23 on the fed sheet. Thereafter, the sheet on which the toner image is fixed by the fixing unit 14 is reversed in the fourth conveyance path 12 as necessary, and a full-color toner image is also formed on the surface opposite to the first by the secondary transfer unit 23. Secondary transferred. After the toner image on the opposite surface is fixed by the fixing unit 14, the toner image passes through the third conveyance path 11 and is discharged to the paper discharge unit 3 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. The intermediate transfer unit 30 is configured to synthesize and carry the toner images of the respective colors formed in 29.

  Each of the image forming units 26 to 29 includes a photosensitive drum 32, a charging unit 33 provided to face the circumferential surface of the photosensitive drum 32, and a circumferential surface of the photosensitive drum 32 on the downstream side of the charging unit 33. A laser scanning unit 34 that irradiates a laser beam to a specific position above, and a developing unit 35 that is provided on the downstream side of the laser beam irradiation position from the laser scanning unit 34 and that faces the peripheral surface of the photosensitive drum 32; And a cleaning unit 36 provided on the downstream side of the developing unit 35 and facing the peripheral surface of the photosensitive drum 32.

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

  The intermediate transfer unit 30 includes a rear roller (drive roller) 38 provided in the vicinity of the image forming unit 26, a front roller (driven roller) 39 provided in the vicinity of the image forming unit 29, and a rear roller 38. An intermediate transfer belt 40 provided across the front roller 39 and a position downstream of the developing unit 35 in the photosensitive drum 32 of each of the image forming units 26 to 29 are provided so as to be capable of being pressed through the intermediate transfer belt 40. And four transfer rollers 41.

  In the intermediate transfer unit 30, the toner images of the respective colors are superimposed and transferred onto the intermediate transfer belt 40 at the positions of the transfer rollers 41 of the image forming units 26 to 29. Become.

  The first conveyance path 9 conveys the sheet fed from the sheet feeding cassette 5 to the intermediate transfer unit 30 side, and includes a plurality of conveyance rollers 43 provided at predetermined positions in the apparatus main body 2. A registration roller 22 is provided in front of the intermediate transfer unit 30 for timing the image forming operation and the paper feeding operation in the image forming unit 7.

  The fixing unit 14 performs processing for fixing the unfixed toner image on the paper by heating and pressurizing the paper on which the toner image has been transferred by the image forming unit 7. The fixing unit 14 includes, for example, a roller pair including a heating pressure roller 44 and a fixing roller 45, and the pressure roller 44 includes a metal core and an elastic surface layer (for example, silicon rubber). The fixing roller 45 has a metal core, an elastic surface layer (for example, silicon sponge), and a release layer (for example, PFA). 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. The detailed structure of the fixing unit 14 will be described later.

  When viewed in the sheet conveyance direction, conveyance paths 47 are provided on the upstream side and the downstream side of the fixing unit 14, and the sheet conveyed through the intermediate transfer unit 30 is pressurized through the upstream conveyance path 47. It is introduced into the nip between the roller 44 and the fixing roller 45. 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, the third conveyance path 11 is provided with a conveyance roller 49 at an appropriate position, and the discharge roller 24 is provided at the outlet thereof.

[Details of fixing unit]
Next, details of the fixing unit 14 applied to the image forming apparatus 1 of the present embodiment will be described.

  FIG. 2 is a longitudinal sectional view showing a structural example of the fixing unit 14. In FIG. 2, the orientation is turned counterclockwise by about 90 ° from the state in which the image forming apparatus 1 is mounted. Accordingly, the sheet conveying direction from the bottom to the top as viewed in FIG. 1 is from right to left as viewed in FIG. In addition, when the apparatus main body 2 is larger (multifunction machine etc.), it may be mounted in the direction shown in FIG. As another layout, the fixing unit 14 may be arranged in a posture inclined left or right from the state shown in FIG.

  The fixing unit 14 includes the pressure roller 44, the fixing roller 45, the heat roller 46, and the heating belt 48 as described above. As described above, since the elastic layer of silicon sponge is formed on the surface layer of the fixing roller 45, a flat nip is formed between the heating belt 48 and the fixing roller 45.

  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, and a release layer (for example, PFA) is formed on the outer surface thereof. Has been. In the case where the heating belt 48 does not have a heat generation function, a resin belt such as PI may be used. Further, the core of the heat roller 46 is a magnetic metal (for example, Fe, SUS), and a release layer (for example, PFA) is formed on the surface thereof.

  More specifically, for the pressure roller 44, for example, Fe, Al, or the like is used for the metal core, and a Si rubber layer is formed on the core, and a fluororesin layer is formed on the surface layer. Is. Note that, for example, a halogen heater 44 a may be provided inside the pressure roller 44.

  In addition, the fixing unit 14 includes an IH coil unit 50 outside the heat roller 46 and the heating belt 48 (not shown in FIG. 1). The IH coil unit 50 includes an induction heating coil 52, a pair of arch cores 54, and a pair of side cores 56 and a center core 58.

〔coil〕
In the example of FIG. 2, the induction heating coil 52 is disposed on a virtual arcuate surface along the arcuate outer surface in order to perform induction heating in the arcuate portions of the heat roller 46 and the heating belt 48. Actually, for example, a resin bobbin 53 is disposed outside the heat roller 46 and the heating belt 48, and the induction heating coil 52 is disposed on the bobbin 53 in a winding shape. The bobbin 53 is formed in a semi-cylindrical shape along the outer surface of the heat roller 46. The material of the bobbin 53 is preferably a heat resistant resin (for example, PPS, PET, LCP).

[Fixed core]
As shown in FIG. 2, the center core 58 is located in the center, and the arch core 54 and the side core 56 are arranged so as to make a pair on both sides thereof. Of these, the arch cores 54 on both sides are ferrite cores (fixed cores) formed in a cross-sectional arch shape that is symmetrical to each other, and each has a total length longer than the winding region of the induction heating coil 52. The side cores 56 on both sides are ferrite cores (fixed cores) formed in a block shape. The side cores 56 on both sides are connected to one end (lower end in FIG. 2) of each arch core 54, and these side cores 56 cover the outside of the winding region of the induction heating coil 52. Of these, the arch cores 54 are disposed at a plurality of positions, for example, at intervals in the longitudinal direction of the heat roller 46. Further, the side cores 56 are continuously arranged in the longitudinal direction of the heat roller 46 without being spaced apart, and the total length thereof corresponds to the length of the winding region of the induction heating coil 52. The arrangement of the cores 54 and 56 is determined in accordance with, for example, the magnetic flux density (magnetic field strength) distribution of the induction heating coil 52. The side core 56 compensates for the magnetic field focusing effect and leveles the magnetic flux density distribution (temperature difference) in the longitudinal direction. For example, a resin core holder (not shown) is provided outside the arch core 54 and the side core 56, and 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).

  In the example of FIG. 2, a thermistor 62 is installed inside the heat roller 46. The thermistor 62 can be disposed inside a portion of the heat roller 46 that generates a large amount of heat, particularly due to induction heating. In addition, a thermostat (not shown) can be arranged inside the heat roller 46 to improve safety when the abnormal temperature rises.

[Block core]
The center core 58 is, for example, a ferrite core having a cylindrical cross section, and a rotation shaft member 59 is inserted in the center thereof in the axial direction. The rotary shaft member 59 is formed of, for example, a nonmagnetic metal (AL or the like) or a heat resistant resin (PPS, PET, LCP, or the like). Although only one cross section is shown in FIG. 2, the center core 58 is divided into a plurality of parts in the axial direction, and each one is configured as a block-like core (indicated by reference numeral 58 a in the drawing). . In addition, about the center core 58, the structure as a block-shaped core divided | segmented into plurality is further mentioned later.

  As shown in FIG. 2, a driving roller 80 and a driving motor 82 are installed above the center core 58 (in the direction opposite to the heat roller 46). For example, a rubber layer is formed on the surface of the driving roller 80, and the outer peripheral surface thereof is in contact with one block-shaped core 58a. The driving roller 80 presses the rubber layer on the surface to the surface of the block-shaped core 58a with an appropriate load by an elastic force such as a spring (not shown). The driving roller 80 is rotated (driven) by the power of the driving motor 82, and the block-shaped core 58a that is in contact with the driving roller 80 can be rotated by frictional force. The rotation of the block-shaped core 58a by the driving roller 80 will be further described later.

(Shielding member)
A shielding member 60 is attached to the center core 58 along the outer surface of each block-shaped core 58a. The shielding member 60 has a thin plate shape and is formed to be curved in an arc shape as a whole. In addition, the shielding member 60 may be installed in a state of being embedded in a thick portion of the block-shaped core 58a as illustrated, or may be installed in a state of being attached to the outer surface of the block-shaped core 58a. . The shielding member 60 can be attached using, for example, a silicon-based adhesive.

  As a structure of said shielding member 60, a nonmagnetic and highly conductive member is preferable, for example, oxygen free copper etc. are used. The shielding member 60 generates a reverse magnetic field by an induced current caused by the penetration of a magnetic field perpendicular to the surface thereof, and shields it by canceling the complex magnetic flux (perpendicular magnetic field). Further, by using a highly conductive member, Joule heat generation due to an induced current can be suppressed and a magnetic field can be efficiently shielded. In order to improve the conductivity, for example, methods such as (1) selecting a material with as low a specific resistance as possible and (2) increasing the thickness of the member are effective. Specifically, the plate thickness of the shielding member 60 is preferably 0.5 mm or more, and in this embodiment, for example, a thickness of 1 mm is used.

[Magnetic shielding amount adjusting means]
As shown in FIG. 2, when the shielding member 60 is in a position (shielding position) close to the surface of the heating belt 48, the magnetic resistance increases around the induction heating coil 52 and the magnetic field strength decreases. On the other hand, when the block-shaped core 58a rotates 180 ° (the direction is not particularly limited) from the state shown in FIG. 2 and the shielding member 60 moves to the position (retracted position) farthest from the heating belt 48, the induction heating coil 52 is moved. Around the center core 58, a magnetic path is formed through the arch core 54 and the side cores 56 on both sides centering on the center core 58, and a magnetic field acts on the heating belt 48 and the heat roller 46.

[Details of Center Core]
FIG. 3 is a plan view showing in detail the configuration of the center core 58 divided in the axial direction. The center core 58 extends in the width direction orthogonal to the sheet passing direction (the arrow direction in FIG. 3), and the total length is slightly larger than the maximum sheet passing width (for example, A3 length, A4 width). The center core 58 includes a total of four block-shaped cores 58a, two block-shaped cores 58b at both end positions in the width direction, and one block-shaped core 58c at the center position in the width direction. Are arranged respectively. Of these, the block-shaped cores 58b at both end positions are each provided with the shielding member 60, but the block-shaped core 58c at the center position is not provided with the shielding member 60.

  These block-shaped cores 58a, 58b, and 58c are arranged at predetermined positions in the paper width direction. If the size of the block-shaped core 58c becomes too large, it may be further divided into a plurality of blocks in the axial direction for convenience of manufacturing. However, in terms of function, five blocks can be considered as one block-shaped core 58c. Therefore, in the following, they are unified as the block-shaped core 58c.

[Blocks at both ends and center]
As described above, the rotary shaft member 59 extends through the entire center core 58 in the axial direction, and its overall length is longer than that of the center core 58. Of the block-shaped cores 58a, 58b, and 58c, the two block-shaped cores 58b positioned at both ends in the width direction and the one block-shaped core 58c positioned at the center are all fixed to the rotating shaft member 59. Attached. For this reason, the three block-shaped cores 58 b and 58 c rotate as the rotation shaft member 59 rotates.

  The IH coil unit 50 is provided with another drive motor 66, and the rotating shaft member 59 is rotated by the power of the drive motor 66. Therefore, a driven gear 59a is attached to one end portion of the rotating shaft member 59, and the output gear 66a of the driving motor 66 is engaged with the driven gear 59a. When the driving motor 66 is driven, the rotary shaft member 59 is rotated by the power, and the three block cores 58b and 58c can be rotated integrally.

[Independent block]
On the other hand, each of the other four block-shaped cores 58 a has a rotating shaft member 59 passing through in the axial direction, but is supported so as to be rotatable relative to the rotating shaft member 59. Therefore, by driving the driving motor 82 as described above, each block-shaped core 58a can be individually rotated independently.

  FIG. 4 is a diagram illustrating an operation example accompanying rotation of the center core 58 (particularly, the block-shaped cores 58a and 58b). Each will be described below.

  FIG. 4A shows an example of operation when the shielding member 60 is switched to the retracted position as the block-shaped cores 58a and 58b rotate. In this case, the magnetic field generated by the induction heating coil 52 passes through the heating belt 48 and the heat roller 46 through the side core 56, the arch core 54, and the block-shaped cores 58a and 58b. At this time, eddy currents are generated in the heating belt 48 and the heat roller 46, which are ferromagnetic materials, and Joule heat is generated due to the specific resistance of each material, and heating is performed.

  FIG. 4B shows an operation example when the shielding member 60 is switched to the shielding position. In this case, since the shielding member 60 is located on the magnetic path at the position of each block-shaped core 58a, 58b in the width direction, the generation of the magnetic field is partially suppressed. As a result, the amount of heat generation is suppressed at the positions of the respective block-like cores 58a and 58b, and excessive heating of the heating belt 48 and the heat roller 46 can be prevented.

(Rotation control method)
Next, a method for individually controlling the rotation of the center core 58 for each block-shaped core 58a, 58b, 58c will be described. FIG. 5 is a side view showing one end portion of the center core 58 and a partial cross-sectional view (longitudinal cross-section along the line BB) showing the operation thereof.

  5A: A position detecting member 73 is attached to the other end of the rotating shaft member 59 so as to protrude in the radial direction from the outer surface. In addition, two photo interrupters 74 are installed on the other end portion of the rotating shaft member 59 so as to be divided into upper and lower portions (refer to FIG. 4 as appropriate). In the present embodiment, by controlling the stop position of the drive motor 66 based on the detection signal from the photo interrupter 74, the block-shaped cores 58b and 58c at both end positions and the center position are rotated by 180 °, and the shielding member 60 is rotated. The position of can be switched. In addition, since the shielding member 60 is not provided in the block-shaped core 58c at the center position, the switching of the position of the shielding member 60 is performed for the block-shaped core 58b at both end positions. Each block-shaped core 58a has a position detecting member 84 attached to the outer peripheral surface thereof, and this position detecting member 84 projects radially from the outer peripheral surface of the block-shaped core 58a (see FIG. 4 for details). Is also shown.)

  In FIG. 5B, for this reason, the block cores 58a are also controlled by controlling the stop positions of the individual drive motors 82 based on the detection signals from the photo interrupters 86 on both sides. Similarly, the position of the shielding member 60 (the shielding position or the retracted position) can be switched independently by rotating 180 degrees individually.

  The shielding position and the retracted position correspond to opposite positions rotated by 180 °, and the rotation direction of the driving roller 80 is different between when the shielding member 60 is moved to the shielding position and when the shielding member 60 is moved to the retracted position. It has been switched between forward and reverse. For example, when the shielding member 60 is moved to the shielding position, if the block-shaped core 58a is rotated in the clockwise direction in FIG. 5B, the position detecting member 84 is detected by one photo interrupter 86. At the same time, the overrun of the block-shaped core 58a is regulated by the position detecting member 84. On the other hand, when the shielding member 60 is moved to the retracted position, the position detection member 84 is detected by the other photo interrupter 86 at the same time by rotating the block-shaped core 58a counterclockwise. The overrun of the block-shaped core 58a is regulated by the member 84.

  Here, the two photointerrupters 86 and 74 are used for each of the block-shaped cores 58a and 58b. However, the position detection member 73 in this state with the shield position of each of the block-shaped cores 58a and 58b as a reference position. , 84 may be arranged one by one at the position where each is detected. In this case, the stop position of each of the drive motors 82 and 66 can be controlled with the position where each of the block cores 58a and 58b is rotated by 180 ° from the reference position (shielding position) as the retracted position.

[Individual control circuit]
In the present embodiment, each of the drive motors 66 and 82 is constituted by a stepping motor, for example, and the operation of each of the drive motors 66 and 82 is controlled by a control circuit (not shown). This control circuit can be constituted by, for example, a control IC, an input / output driver, a semiconductor memory, and the like. Detection signals from the photo interrupters 74 and 86 are input to the control IC through the input driver, and the control IC detects the current rotation angle (position) of each of the drive motors 66 and 82 based on this signal. On the other hand, the control IC is notified of information relating to the current paper size from an image formation control unit (not shown). In response to this, the control IC reads position information (shielding position or retracted position) of the shielding member 60 suitable for the paper size from the semiconductor memory (ROM), and a rotation angle (180 °) corresponding to the position information at that time. Minute drive pulse is output. The drive pulses are applied to the drive motors 66 and 82 through the output driver, and the drive motors 66 and 68 are operated in response to the drive pulses.

[Individual control example]
Next, individual control of each block-shaped core 58a, 58b, 58c performed according to the paper size will be described. In the present embodiment, each of the block-shaped cores 58a, 58b, and 58c is designed to have a size corresponding to each sheet passing width corresponding to, for example, A5 length, A4 length, B4 length, and A4 width.

  FIG. 6 is a diagram illustrating a control example corresponding to each of the minimum sheet passing width and the maximum sheet passing width. In the figure, halftone dots are provided on the outer surfaces of the block-shaped cores 58a, 58b, and 58c. Hereinafter, each control example will be described.

[Minimum paper feed width]
In FIG. 6, (A): When image formation is performed with the minimum sheet passing width W1 (for example, A5 length), the blocking member 60 is set to the blocking position for the block-shaped core 58b at both ends and the other four block-shaped cores 58a. In the switched state, the stop position (rotation angle) of the drive motors 66 and 82 is controlled. In this case, induction heating of the heat roller 46 is performed within the range of the minimum sheet passing width W1, but heat generation is suppressed on both outer sides of the minimum sheet passing width W1, and thus excessive heating of the heat roller 46 is prevented.

[Maximum paper feed width]
In FIG. 6, (B): On the other hand, when image formation is performed with the maximum sheet passing width W4 (for example, A4 width, A3 length), both of the block-shaped cores 58b at the both ends and the other four block-shaped cores 58a. With the shielding member 60 switched to the retracted position, the stop position (rotation angle) of the drive motors 66 and 82 is controlled. In this case, since the induction heating of the heat roller 46 is performed within the entire range of the maximum sheet passing width W4, it is possible to reliably fix the image on the maximum size sheet.

[In the case of intermediate paper width]
FIG. 7 is a diagram illustrating a control example corresponding to the intermediate sheet passing width. (B)-(G) in FIG. 7 shows the cross section which follows the BB line-GG line of (A) in FIG. 7, respectively. In the following description, a change from the state shown in FIG. 6B is taken as an example.

  In FIG. 7, (A): When image formation is performed with an intermediate sheet passing width W2 (for example, A4 length) that is one size larger than the minimum sheet passing width W1, two adjacent block cores together with the block cores 58b at both ends. With regard to 58a, the stop positions (rotation angles) of the drive motors 66 and 82 are controlled while the shielding member 60 is switched to the retracted position. Each will be specifically described below.

[Blocks at both ends]
7B and 7G: At this time, the block-shaped cores 58b at the both end positions are rotated together with the rotary shaft member 59 by 180 ° by driving the drive motor 66, so that both the shielding members 60 are moved. It has been switched to the shielding position.

[Two blocks near both ends]
In FIG. 7, (C) and (F): The two block cores 58a adjacent to the block cores 58b at both end positions are individually rotated by 180 ° by the respective drive motors 82, and the shielding member 60 is moved. It has been switched to the shielding position.

[Two blocks near the center]
In FIG. 7, (D) and (E): On the other hand, the two block-shaped cores 58a adjacent to the block-shaped core 58c at the center position are stopped while the shielding member 60 is switched to the retracted position.

  Next, FIG. 8 is a diagram illustrating another control example corresponding to the intermediate sheet passing width. (B)-(G) in FIG. 8 shows the cross section which follows the BB line-GG line of (A) in FIG. 8, respectively. In the following description, for example, a change from the state shown in FIG. 7 is taken as an example.

  In FIG. 8, (A): When image formation is performed with an intermediate sheet passing width W3 (for example, B4 length) that is one size larger than the previous intermediate sheet passing width W2 and one size smaller than the maximum sheet passing width W4, a block shape at both end positions. For the core 58b, the stop position (rotation angle) of the drive motor 66 is controlled so as to switch the shielding member 60 to the retracted position, and for the other four block-shaped cores 58a, the shielding member 60 is switched to the shielding position. Thus, the stop position (rotation angle) of the individual drive motor 82 is controlled. Each will be specifically described below.

[Blocks at both ends]
In FIG. 8, (B) and (G): At this time, the block-shaped cores 58b located at both end positions are stopped while both the shielding members 60 are switched to the shielding positions.

[Two blocks near both ends]
In FIG. 8, (C) and (F): On the other hand, the two block-shaped cores 58a adjacent to the block-shaped cores 58b at both end positions are individually rotated by 180 ° by the respective drive motors 82, and the shielding member 60 is switched to the retracted position.

[Two blocks near the center]
In FIG. 8, (D), (E): The two block cores 58a adjacent to the block core 58c at the center position are stopped while the shielding member 60 is switched to the retracted position.

[Magnetic shielding amount adjusting means]
As described above, in this embodiment, each block-shaped core 58a is individually rotated, and the position of each shielding member 60 is independently controlled, so that the optimum magnetic shielding is achieved in accordance with various intermediate sheet passing widths W2 and W3. The amount can be adjusted. For this reason, it is possible to accurately control the heating range of the heat roller 46 in accordance with a predetermined paper size (sheet passing width), and it is possible to reliably prevent an excessive temperature rise outside the sheet passing width. In the figure, the clockwise and counterclockwise rotations are indicated by arrows, but each of the block cores 58a and 58b may rotate only in one direction. Further, the sheet passing direction may be opposite to the illustrated direction.

[Other structural examples]
FIG. 9 is a diagram illustrating another structure example of the fixing unit 14. In this structural example, the toner image is fixed by the fixing roller 45 and the pressure roller 44 without using the heating belt. For example, a magnetic material similar to that of the above-described heating belt is wound around the outer periphery of the fixing roller 45, and the magnetic material is induction-heated by the induction heating coil 52. In this case, the thermistor 62 is provided outside the fixing roller 45 at a position facing the magnetic layer. The rest is the same as described above, and each block-like core 58a, 58b can be rotated to cope with a change in paper size.

  Next, FIG. 10 is a diagram illustrating another example of the structure of the IH coil unit 50. In this structural example, the induction heating is performed not at the arcuate position of the heating belt 48 but at a planar position between the heat roller 46 and the fixing roller 45. In this case as well, each block-like core 58a, 58b can be rotated to cope with a change in the paper size.

  The present invention can be implemented with various modifications without being limited to the above-described embodiments. For example, the cross-sectional shape of each block-shaped core 58a, 58b, 58c is not limited to a cylinder or a column, but may be a polygonal shape. Further, the lengths of the block-shaped cores 58a, 58b, and 58c in the axial direction are not particularly limited, and can be appropriately set according to the paper size to be used.

  In addition, the specific form of each part including the arch core 54 and the side core 56 is not limited to the illustrated one, and can be appropriately modified.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. FIG. 3 is a longitudinal sectional view showing a structural example of a fixing unit. It is a top view which shows in detail the structure of the center core divided | segmented into the axial direction. It is a figure which shows the operation example accompanying rotation of a block-shaped core. It is the side view which shows the one end part of a center core, and the fragmentary sectional view (vertical section which follows the BB line) which shows the operation | movement. It is a figure which shows the example of control corresponding to the minimum paper passing width and the maximum paper passing width, respectively. It is a figure which shows the example of control corresponding to an intermediate paper passing width. It is a figure which shows another example of control corresponding to an intermediate paper passing width. It is a figure which shows the other structural example of a fixing unit. It is a figure which shows the other structural example of an IH coil unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 14 Fixing unit 50 IH coil unit 52 Induction heating coil 54 Arch core 56 Side core 58 Center core 58a, 58b, 58c Block-shaped core 59 Rotating shaft member 60 Shielding member 66 Driving motor 80 Driving roller 82 Driving motor

Claims (3)

A fixing unit that fixes the toner image onto the sheet by at least heat from the heating member is conveyed by sandwiching the sheet on which the toner image is transferred in the image forming unit between the heating member and the pressure member. An image forming apparatus comprising:
The fixing unit includes:
A coil that is disposed along the outer surface of the heating member and generates a magnetic field for inductively heating the heating member over a maximum sheet passing area of the conveyed paper;
A fixed core disposed on the opposite side of the heating member across the coil and forming a magnetic path around the coil;
Arranged between the fixed core and the heating member as viewed in the direction of generation of the magnetic field by the coil to form a magnetic path with the fixed core, and divided into a plurality of sections in the width direction of the paper to be conveyed A block-shaped core,
A shielding member that is provided along an outer surface of the block-shaped core and shields magnetism in a magnetic field generated by the coil;
By individually rotating the plurality of block-shaped cores around an axis intersecting the magnetic field passage direction, the shield member is shielded from the shield position, and the retracted position is allowed to pass the magnetism. An image forming apparatus comprising: a magnetic shielding amount adjusting unit that performs an operation of switching to each of the plurality of block cores independently. The image forming apparatus according to claim 1,
At least two of the block-like cores positioned at both ends as viewed in the width direction of the sheet conveyed by the fixing unit can be integrally rotated while being attached to the same rotating shaft member, and are at other positions. The block-shaped core is provided so as to be individually rotatable with respect to the rotating shaft member. The image forming apparatus according to claim 1, wherein
The shielding member is
An image forming apparatus, wherein the image forming apparatus is provided on the block-shaped core positioned outside a minimum sheet passing area in a width direction of a sheet conveyed by the fixing unit.

Images