JP2009237403A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve reduction in a warm-up time and space saving while attaining lower heat capacity, by reducing the number of members arranged in a heating roller or the like in a fixing unit for an image forming apparatus. <P>SOLUTION: The fixing unit 14 includes: an induction heating coil 52 arranged along an outer surface of a heating belt 48; arch cores 54 and side cores 56 forming magnetic paths on both sides of the center of the coil; a center core 58 arranged at the center of the coil; a ring circuit fixing unit 80 arranged along a winding area of the induction heating coil 52; and a ring circuit movable unit 90. A comb-shaped open fixed ring circuit 82 is formed in the ring circuit fixing unit 80. By bringing a movable ring circuit 94 into contact with the fixed ring circuit 82, a closed circuit is formed to cancel magnetic field, thereby dealing with a change of sheet size. <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 is disposed along the outer surface of the heating member, and generates a magnetic field for induction heating the heating member in an axial direction orthogonal to the paper conveyance direction, and on the opposite side of the heating member across the coil. A first core that is disposed and forms a magnetic path around the coil, and a plurality of peripheral circuits that are disposed in the vicinity of the coil and that are formed around the through-path of the magnetic field generated by the coil. A plurality of peripheral circuits together with the conductive member and the first conductive member, and a second conductive member provided to be movable relative to the first conductive member; By moving the second conductive member and switching the second conductive member to either the contact or non-contact state with respect to the first conductive member in accordance with this movement, the plurality of peripheral circuits are opened and closed. A drive mechanism that individually controls the state Those were example.

  As described above, the present invention employs a method (outside IH) in which the heating member (or another heating element) is induction-heated by the magnetic field generated by the coil of the fixing unit to heat and melt the toner image. There is no need to provide a special member inside the heating member. Further, since the core is merely disposed around the coil in order to form a magnetic path for guiding the magnetic field generated by the coil, the space occupied as a whole is not inadvertently increased in size.

  In particular, in the present invention, a plurality of peripheral circuits are formed in the vicinity of the coil by the first and second conductive members, so that a demagnetizing field is generated by the induced current generated by the magnetic field penetrating the inside, and the magnetic field of the coil Is offset to prevent overheating of the heating member. Note that the plurality of peripheral circuits can correspond in advance to a range that is a non-sheet passing area in accordance with a change in the paper size. For example, if the paper size on which the image is fixed is changed in various ways, the range that becomes the non-sheet passing area changes, and accordingly, the peripheral circuit is appropriately closed to adjust the magnetic field of the coil within the non-sheet passing area. By canceling, overheating of the heating member is suppressed.

  The plurality of peripheral circuits can control the open / close state by moving the second conductive member relative to the first conductive member. That is, when the drive mechanism moves the second conductive member to control the peripheral circuit to be in an open state, the magnetic field generated by the coil penetrates as it is to generate an eddy current in the heating member, thereby performing magnetic induction heating. it can. On the other hand, when the drive mechanism moves the second conductive member to control the peripheral circuit to the closed state, the magnetic field of the coil is canceled by the demagnetizing field from the peripheral circuit, and the amount of heat generated by the heating member can be reduced.

  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, the plurality of closed circuits are formed in the axial direction of the heating member, and the second conductive member is a part of the plurality of peripheral circuits extending in the axial direction of the heating member. The drive mechanism is configured to move the second conductive member in a direction orthogonal to the axial direction of the heating member, thereby reducing the number of peripheral circuits that are closed among the plurality of peripheral circuits. Can be changed.

  With such an aspect, the range in which the magnetic field is canceled can be changed according to the amount of movement of the second conductive member, so that it is possible to quickly cope with a change in the paper size.

  Alternatively, in the above aspect, the drive mechanism may move the second conductive member in the axial direction of the heating member to change the number of peripheral circuits that are closed among the plurality of peripheral circuits. Good. In this case as well, the range for canceling the magnetic field can be changed according to the amount of movement of the second conductive member, so that it is possible to quickly respond to the change in the paper size.

  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 outer package IH, the movable object is only the movement of the second conductive member, 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. Can do.

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 for irradiating a laser beam to a specific position on the upper side; a developing unit 35 provided on the downstream side 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 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.

[First structural example]
FIG. 2 is a longitudinal sectional view showing a first structure 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. Since the elastic layer of silicon sponge is formed on the surface layer of the fixing roller 45 as described above, 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, an arch core 54, a pair of side cores 56, and a center core 58. Furthermore, in this embodiment, the ring circuit fixing unit 80 and the ring circuit movable unit 90 are included in the IH coil unit 50 as components. Hereinafter, each component will be described.

〔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).

〔core〕
As shown in FIG. 2, the center core 58 is located at the center, and the arch core 54 and the side core 56 are arranged around the center core 58. The arch core 54 is a ferrite core formed in a cross-sectional arch shape (semi-circular shape) as a whole, and its entire length is 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 respectively connected to both ends (lower end in FIG. 2) of the 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.

[Ring circuit fixing unit]
The ring circuit fixing unit 80 includes, for example, a resin-made fixing base 81, and the fixing base 81 has a curved shape along the outside of the winding region of the induction heating coil 52. Although the side surface shape is shown in FIG. 2, the fixed base 81 has a certain length in the axial direction of the heat roller 46.

[First conductive member]
On the fixed base 81, for example, a comb-shaped (substantially E-shaped in a plan view) fixed ring circuit 82 is provided. The fixed ring circuit 82 has a curved shape along the fixed base 81. Yes. Although only a part of the side surface is shown in FIG. 2, the comb-shaped fixing ring circuit 82 extends to a certain extent in the axial direction of the heat roller 46, like the fixing base 81.

[Second conductive member]
The ring circuit movable unit 90 includes a movable base 92 made of, for example, resin, and the movable base 92 extends in the axial direction of the heat roller 46. Although only the side surface is shown in FIG. 2, the movable base 92 has a certain length in the axial direction of the heat roller 46 and has a rod shape as a whole. A movable ring circuit 94 is provided on the lower surface of the movable base 92, and this movable ring circuit 94 also extends in the axial direction of the heat roller 46.

  FIG. 3 is a diagram showing in detail the arrangement of the fixed ring circuit 82 and the movable ring circuit 94 with respect to the induction heating coil 52. 3A shows the IH coil unit 50 and the heat roller 46 extracted from FIG. 2, and FIG. 3B shows the fixing at one end as viewed in the axial direction of the heat roller 46. The top view of the ring circuit 82 and the movable ring circuit 94 is shown. The ring circuit fixing unit 80 and the ring circuit movable unit 90 are provided at both ends as viewed in the axial direction of the heat roller 46.

  In particular, as shown in FIG. 3B, the fixed ring circuit 82 is an open circuit having a comb-like shape (substantially E-shape) as a whole, and each comb-teeth (E-shaped horizontal axis) In addition to a plurality of (four in each case) corresponding conductive members 82a, 82b, 82c, and 82d, a conductive member 82e corresponding to the root of the comb (vertical axis of E-shape) is provided. The plurality of conductive members 82a to 82d are arranged in parallel at intervals in the axial direction of the heat roller 46, and the plurality of conductive members 82a to 82d are mutually connected by the conductive member 82e at one end position. It is connected to the.

  Although not shown in FIG. 2 and FIG. 3A, insulating layers 84, 85, 86 are formed on the upper surface of the fixed ring circuit 82, and these insulating layers 84, 85, 86 are fixed respectively. A part of the ring circuit 82 is covered. Of these, one insulating layer 84 covers the other end portion (the tip portion of the comb teeth) of the conductive member 82a closest to the center of the heat roller 46 (the center of the sheet passing region). Another insulating layer 85 covers the other end of the adjacent conductive member 82b. When viewed in the longitudinal direction of each conductive member 82a, 82b, the insulating layer 84 closest to the center of the heat roller 46 has a wider range than the other insulating layer 85. The entire conductive member 82e and the other end portions of the comb-shaped conductive members 82a to 82d are covered (protected) by the insulating layer 86. The insulating layers 84, 85, 86 are made of, for example, a resin material.

  The movable ring circuit 94 has a single bar shape as described above. The total length of the movable ring circuit 94 is set to be substantially the same as or slightly longer than the conductive member 82e. The movable ring circuit 94 can be translated in the longitudinal direction of the conductive members 82a to 82d, and is crimped to the fixed ring circuit 82 along with this movement. Thereby, the adjacent conductive members 82a to 82d are connected (conducted), and the peripheral circuit is switched to the closed state. In this example, a maximum of three ring circuits (circumferential circuits) can be formed by crimping the fixed ring circuit 82 and the movable ring circuit 94.

  In the present embodiment, the fixed ring circuit 82 and the movable ring circuit 94 are made of, for example, a copper plate, and the thickness is, for example, about 1 mm and the width is about 5 mm. In both the fixed ring circuit 82 and the movable ring circuit 94, the thickness direction of the copper plate is the radial direction of the heat roller 46.

  FIG. 4 is a diagram showing the configuration of the ring circuit movable unit 90 more specifically. 4A shows the ring circuit fixed unit 80 together with the ring circuit movable unit 90 in a plan view, and FIG. 4B shows the ring circuit movable unit 90 in a side view. In FIG. 4B, the ring circuit movable unit 90 is shown in a horizontal state, but actually, as shown in FIG. 2, the ring circuit movable unit 90 along the peripheral surface of the heat roller 46. Are arranged in an inclined manner.

(Drive mechanism)
The movement of the movable ring circuit 94 is realized by a drive mechanism 95. For example, the drive mechanism 95 drives the stepping motor 96 to rotate the pinion 97 and transmits the rotation to the movable base 92 from the rack 98 to move the movable ring circuit 94 as described above.

  Next, switching of the stop position of the movable ring circuit 94 by the drive mechanism 95 will be described. In this embodiment, the stop position of the movable ring circuit 94 is switched to the following four types.

(1) Retraction position (reference position)
This retracted position is a position where the movable ring circuit 94 is not in contact with the fixed ring circuit 82, and specifically corresponds to the position shown in FIG. In a state where the movable ring circuit 94 is in the retracted position, a closed circuit by the fixed ring circuit 82 and the movable ring circuit 94 is not formed (all peripheral circuits are open).

  When the movable ring circuit 94 is stopped at the retracted position, the magnetic field penetrates the entire winding region of the induction heating coil 52, so that the eddy currents are generated in the entire area of the heat roller 46 and the heating belt 48 in the axial direction. Joule heat is generated by the specific resistance of the material and heating is performed. Thus, the image can be fixed with the maximum sheet passing width W4.

(2) Closed Circuit 1 Forming Position This position is a position at which the movable ring circuit 94 is partially brought into contact with the fixed ring circuit 82. Specifically, by stopping the movable ring circuit 94 at the position of the right end indicated by the two-dot chain line in FIG. 4A, two conductive members 82c from both end positions in the axial direction of the heat roller 46. , 82d can be connected to each other. In this case, one closed circuit is formed by the movable ring circuit 94 and the conductive members 82c, 82d, and 82d (one peripheral circuit is in a closed state). At this time, since the movable ring circuit 94 is insulated by the two insulating layers 84 and 85, the other two conductive members 82a and 82b are not connected.

  When the movable ring circuit 94 is stopped at the position where the closed circuit 1 is formed, a closed current is generated in one closed circuit, and a demagnetizing field opposite to the penetrating magnetic field is generated. Therefore, when viewed in the axial direction of the winding region of the induction heating coil 52, the generation of the magnetic field is partially suppressed (cancelled by the demagnetizing field) on both outer sides of the conductive member 82c. As a result, the amount of heat generated on both outer sides of the intermediate sheet passing width W3 can be suppressed, and excessive heating of the heating belt 48 and the heat roller 46 can be prevented.

(3) Closed Circuit 1 and 2 Forming Position This position is also a position at which the movable ring circuit 94 is partially brought into contact with the fixed ring circuit 82. Specifically, in FIG. By stopping the movable ring circuit 94 at the center position indicated by the chain line, the three conductive members 82b, 82c, and 82d can be connected to each other from both end positions in the axial direction of the heat roller 46. In this case, two closed circuits are formed by the movable ring circuit 94 and the conductive members 82b, 82c, 82d, and 82e (two peripheral circuits are closed). At this time, since the movable ring circuit 94 is continuously insulated by the insulating layer 84, the remaining one conductive member 82a is not connected.

  When the movable ring circuit 94 is stopped at the position where the closed circuits 1 and 2 are formed, a closed current is generated in the two closed circuits, and generation of a magnetic field is partially suppressed on both outer sides of the conductive member 82b. As a result, the amount of heat generated on both outer sides of the intermediate sheet passing width W2 can be suppressed, and excessive heating of the heating belt 48 and the heat roller 46 can be prevented.

(4) Closed Circuit 1, 2, 3 Formation Position This position is a position where the movable ring circuit 94 is brought into contact with the fixed ring circuit 82 as a whole. Specifically, all four conductive members 82a, 82b, 82c, and 82d are mutually connected by stopping the movable ring circuit 94 at the left end position indicated by the two-dot chain line in FIG. Can be connected. In this case, three closed circuits are formed by the movable ring circuit 94 and the conductive members 82a, 82b, 82c, 82d, and 82e (three peripheral circuits are closed).

  When the movable ring circuit 94 is stopped at the positions where the closed circuits 1, 2, and 3 are formed, a closed current is generated in the three closed circuits, and the generation of a magnetic field is suppressed from the conductive member 82a across the entire outer sides. Thereby, the amount of heat generated on both outer sides 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.

(Control method)
Switching of the movable ring circuit 94 to the stop positions (1) to (4) by the drive mechanism 95 can be controlled by the following method. That is, a position detection unit 92a is provided at one end of the movable base 92, and four photo interrupters 100a to 100d are installed on the side of the rack 98 along the moving direction. The four photo interrupters 100a to 100d correspond to the four stop positions of the movable ring circuit 94. When the movable base 92 moves as the rack 98 moves, the position detector 92a is moved by the photo interrupters 100a to 100d. It is to be detected.

  A control circuit (not shown) is connected to the drive mechanism 95, and the operation of the stepping motor 96 can be controlled by this control circuit. The control circuit includes, for example, a control IC, an input / output driver, a semiconductor memory, and the like. Detection signals from the photo interrupters 100a to 100d are input to the control IC through an input driver, and the control IC detects the current position of the movable ring circuit 94 based on the detection 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 the position information of the movable ring circuit 94 (above-mentioned stop positions (1) to (4)) suitable for the paper size from the semiconductor memory (ROM), and corresponds to the position information at that time. A drive pulse corresponding to the moving direction and moving distance of the rack 98 is output. The drive pulse is applied to the stepping motor 96 through the output driver, and the stepping motor 96 operates in response to the drive pulse.

  FIG. 5 is a table showing detection states (light transmission / light shielding) of the photo interrupters 100a to 100d at the stop positions (1) to (4). The control circuit drives the stepping motor 96 with reference to the detection states of the photo interrupters 100a to 100d when switching the stop position of the movable ring circuit 94 corresponding to the paper size (paper passing widths W1 to W4).

[Second structural example]
Next, FIG. 6 is a longitudinal sectional view and a partial plan view showing a second structure example of the fixing unit 14. In the second structure example, the structures of the ring circuit fixing unit 80 and the ring circuit movable unit 90 are different from those of the first structure example. Hereinafter, the description will focus on differences from the first structure example.

  6A: In the second structural example, the ring circuit movable unit 90 is disposed at the center position of the ring circuit fixing unit 80 (in the vicinity of the center core 58) in the circumferential direction of the heat roller 46. FIG. Further, the ring circuit movable unit 90 moves in the axial direction instead of the circumferential direction of the heat roller 46.

  6B: In the second structural example, the comb-shaped fixed ring circuit 82 (first conductive member) is formed symmetrically across the axis (coil center line) of the heat roller 46. The comb-shaped fixing ring circuit 82 is disposed in a state where one end portions of the conductive members 82a to 82d face each other, and one end portion of each of the conductive members 82a to 82d is in the same direction (paper passing region). Is bent in the center direction). Thereby, the one end parts of the conductive members 82a to 82d facing each other can function as crimp terminals due to their elasticity. Note that one end portions of the respective conductive members 82a to 82d are not in contact with each other in a natural (no load) state, and an appropriate gap (gap) is formed in each. Further, one end of each of the conductive members 82a to 82d may have a shape curved in an R shape in addition to a shape bent in a bowl shape as shown in the figure.

  Further, in the second structural example, the movable ring circuit 94 (second conductive member) moves linearly in the axial direction of the heat roller 46, so that the movable ring circuit 94 (second conductive member) enters between the one end portions of the conductive members 82a to 82d. Crimping (electrically connecting) can form a closed circuit. Further, when the movable ring circuit 94 comes out from between one end portions of the conductive members 82a to 82d, the ring circuit is opened by the gap.

  In the second structural example, only the insulating layer 86 is formed on the upper surface of the fixed ring circuit 82, and these insulating layers 86 cover the portions other than one end portions of the respective conductive members 82a to 82d.

  FIG. 7 is a plan view showing more specifically the configuration of the ring circuit movable unit 90 in the second structural example. In the second structure example, the drive mechanism 95 drives the stepping motor 96 to rotate the pinion 97, and this rotation is transmitted from the rack 98 to the movable base 92, so that the movable ring circuit 94 is connected to the heat roller 46 as described above. Can be moved in the axial direction.

  Also in the second structure example, the stop position of the movable ring circuit 94 is switched to the following four types.

(1) Retraction position (reference position)
This retracted position is a position where the movable ring circuit 94 is not in contact with the fixed ring circuit 82. In a state where the movable ring circuit 94 is in the retracted position, a closed circuit by the fixed ring circuit 82 and the movable ring circuit 94 is not formed (all peripheral circuits are open).

  Also in the second structural example, when the movable ring circuit 94 is stopped at the retracted position, the magnetic field penetrates the entire winding region of the induction heating coil 52, so that the heat roller 46 and the heating belt 48 are swirled in the entire axial direction. Electric current is generated, and Joule heat is generated by the specific resistance of each material, and heating is performed. Thus, the image can be fixed with the maximum sheet passing width W4.

(2) Closed Circuit 1 Forming Position This position is a position at which the movable ring circuit 94 is partially brought into contact with the fixed ring circuit 82. Specifically, by stopping the movable ring circuit 94 at the position shown in FIG. 7, the two sets of conductive members 82 c and 82 d can be connected to each other from both end positions of the heat roller 46. In this case, the movable ring circuit 94 and the conductive members 82c and 82d form two closed circuits with the movable ring circuit 94 interposed therebetween (one set of peripheral circuits on both sides is closed). Note that one end portions of the other two conductive members 82a and 82b are not connected to each other.

  When the movable ring circuit 94 is stopped at the position where the closed circuit 1 is formed, a closed current is generated in a pair of closed circuits on both sides, and a demagnetizing field in a direction opposite to the penetrating magnetic field is generated. Therefore, when viewed in the axial direction of the winding region of the induction heating coil 52, the generation of the magnetic field is partially suppressed (cancelled by the demagnetizing field) on both outer sides of the conductive member 82c. As a result, the amount of heat generated on both outer sides of the intermediate sheet passing width W3 can be suppressed, and excessive heating of the heating belt 48 and the heat roller 46 can be prevented.

(3) Closed circuit 1 and 2 formation positions This position is located at both ends in the axial direction of the heat roller 46 by stopping the movable ring circuit 94 at a position where the movable ring circuit 94 has been moved one step further from the previous closed circuit 1 formation position The three sets of conductive members 82b, 82c, and 82d can be connected to each other. In this case, a total of four closed circuits are formed by the movable ring circuit 94 and the conductive members 82b, 82c, 82d, and 82e (two sets of peripheral circuits on both sides are closed). The remaining set of conductive members 82a is not connected to each other.

  When the movable ring circuit 94 is stopped at the position where the closed circuits 1 and 2 are formed, a closed current is generated in the two sets of closed circuits on both sides, and generation of a magnetic field is partially suppressed on both outer sides of the conductive member 82b. As a result, the amount of heat generated on both outer sides of the intermediate sheet passing width W2 can be suppressed, and excessive heating of the heating belt 48 and the heat roller 46 can be prevented.

(4) Closed Circuit 1, 2, 3 Formation Position This position is a position where the movable ring circuit 94 is brought into contact with the fixed ring circuit 82 as a whole. Specifically, by stopping the movable ring circuit 94 at a position that is most advanced from the center of the sheet passing area, all four sets of the conductive members 82a, 82b, 82c, and 82d can be connected to each other. . In this case, six closed circuits are formed by the movable ring circuit 94 and the conductive members 82a, 82b, 82c, 82d, and 82e (three sets of peripheral circuits on both sides are closed).

  When the movable ring circuit 94 is stopped at the position where the closed circuits 1, 2, and 3 are formed, a closed current is generated in the three closed circuits on both sides, and the generation of a magnetic field is suppressed from the conductive member 82a to the entire outer sides. . Thereby, the amount of heat generated on both outer sides 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.

  Also in the second structure example, the stop position of the movable ring circuit 94 can be controlled by the control circuit. In addition, the detection states (light transmission / light shielding) of the photo interrupters 100a to 100d at the stop positions (1) to (4) are the same as the table shown in FIG.

[Third structure example]
FIG. 8 is a diagram illustrating a third structure example of the fixing unit 14. In the third structure 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. Others are the same as described above, and the entire center core 58 can be rotated together with the rotating shaft member 59 to cope with the change in the paper size.

  Here, the ring circuit fixing unit 80 and the ring circuit movable unit 90 mentioned in the first structure example are shown, but those mentioned in the second structure example may be adopted.

[Fourth structural example]
Next, FIG. 9 is a diagram illustrating a fourth structure example of the fixing unit 14. In the fourth structure example, 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 the fourth structure example, the ring circuit movable unit 90 is formed in a flat shape instead of an arc shape, and is arranged in parallel with the flat portion of the heating belt 48.

  In addition, although the thing similar to the ring circuit fixed unit 80 and the ring circuit movable unit 90 mentioned in the 1st structural example is shown here, you may employ | adopt what was mentioned in the 2nd structural example.

  The present invention can be implemented with various modifications without being limited to the above-described embodiments. The structures of the ring circuit fixing unit 80, the ring circuit fixing unit 80, the drive mechanism 95, and the like described in the embodiment are merely examples, and these may be modified as appropriate.

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 first structure example of a fixing unit. It is the figure which showed arrangement | positioning of a fixed ring circuit and a movable ring circuit in detail. It is a figure which shows the structure of a ring circuit movable unit more concretely. It is a table | surface which shows the detection state of each photo interrupter in each stop position (1)-(4). FIG. 6 is a longitudinal sectional view and a partial plan view showing a second structural example of the fixing unit. It is a top view which shows more specifically the structure of the ring circuit movable unit in a 2nd structural example. It is a figure which shows the 3rd structural example of a fixing unit. It is a figure which shows the 4th structural example of a fixing 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 80 Ring circuit fixed unit 82 Fixed ring circuit 90 Ring circuit movable unit 94 Movable ring circuit 95 Drive mechanism

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 an outer surface of the heating member, and that generates a magnetic field for induction heating the heating member in an axial direction orthogonal to a paper conveyance direction;
A core disposed on the opposite side of the heating member across the coil and forming a magnetic path around the coil;
A first conductive member disposed in the vicinity of the coil and partially constituting a plurality of peripheral circuits formed by surrounding a magnetic field generated by the coil;
A second conductive member that partially constitutes the plurality of peripheral circuits together with the first conductive member, and that is movable relative to the first conductive member;
By moving the second conductive member and switching the second conductive member to either a contact state or a non-contact state with respect to the first conductive member with the movement, An image forming apparatus comprising: a drive mechanism that individually controls an open / close state of a peripheral circuit. The image forming apparatus according to claim 1,
The plurality of closed circuits are arranged in the axial direction of the heating member,
The second conductive member constitutes a part of the plurality of peripheral circuits extending in the axial direction of the heating member,
The drive mechanism moves the second conductive member in a direction orthogonal to the axial direction of the heating member, thereby changing the number of peripheral circuits in the closed state among the plurality of peripheral circuits. An image forming apparatus. The image forming apparatus according to claim 1,
The plurality of closed circuits are arranged in the axial direction of the heating member,
The second conductive member constitutes a part of the plurality of peripheral circuits extending in the axial direction of the heating member,
The drive mechanism is configured to change the number of closed peripheral circuits among the plurality of peripheral circuits by moving the second conductive member in the axial direction of the heating member. apparatus.

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