JP2011197501A - Fixing device and image forming apparatus loaded with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device in which nonuniform cooling of a coil as viewed from the axial direction of a heating member is prevented, and to provide an image forming apparatus loaded with the fixing device.SOLUTION: The fixing device includes: the coil (52) disposed along the periphery of the heating member (46), extending in the axial direction of the heating member, and used to generate an electromagnetic field for induction heating the heat member; a core portion disposed opposite from the heating member with the coil therebetween, covering the coil by extending in a direction intersecting the axial direction of the heating member, having a plurality of arch cores (54), and forming a magnetic path around the coil, the arch cores being spaced in the axial direction of the heating member; a cooling means having an upstream side (80) and a downstream side (82) oblique to the disposition of the arch cores, and used to cool the coil with a flow of cooling air flowing from the upstream side; laminar flowing means (76 and 77) provided on a plurality of support members (72) supporting the respective arch cores, and used to eliminate turbulent flow caused downstream of the support members and to generate a flow of a cooling air flowing to the downstream side from the upstream side via the coil.

Description

  The present invention relates to a fixing device that heats and melts unfixed toner on a recording medium while passing a recording medium carrying a toner image between a nip between a fixing roller pair or a heating belt and a roller, and an image equipped with the fixing device. The present invention relates to a forming apparatus.

  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 device and saving energy. In recent years, the electromagnetic induction heating method (IH) that has the potential for rapid heating and high-efficiency heating has attracted attention. From the viewpoint of energy saving when fixing color images, electromagnetic induction heating is combined with the belt method. Many products have been commercialized.

  Specifically, in this electromagnetic induction heating method, a structure (so-called envelope IH) in which a coil that generates a magnetic field for electromagnetic induction is arranged outside the belt is disclosed (for example, refer to Patent Document 1). Then, the cooling air from the fan cools the coil through the duct. This is because the coil is heated not only by its own electrical resistance but also by heat conduction from the heat roller, and the temperature rise of the coil causes damage to the fixing device.

JP 2006-285126 A

By the way, in the above-mentioned conventional technology, a duct for directly connecting the fan and the IH coil unit is provided. However, this duct increases the number of parts, saves space in the image forming apparatus, and reduces cooling air from the fan. There is a structure in which the duct is omitted from the viewpoint of effective use for other components.
Specifically, an upstream side cooling fan that supplies cooling air to the coil and a downstream side exhaust fan that exhausts the airflow that has taken away the heat of the coil are arranged diagonally when viewed in the axial direction of the heat roller. .

As a result, the cooling air from the upstream side is not supplied along the axial direction of the heat roller, but is supplied to the coil from an oblique direction inclined with respect to the axial line, and the airflow that has deprived the heat of the coil is also inclined. To be discharged.
However, when cooling air is supplied in an oblique direction with respect to the axial direction of the heat roller, there is a problem that uneven cooling of the coil seen in this axial direction occurs.

  This is because a core portion that performs magnetic induction heating of the heat roller is provided around the coil, and the core portion, particularly the arch core, extends across the axial direction of the heat roller to cover the outside of the coil, and the arch core. The cooling air from the upstream side blows on the support member of the arch core and then flows in a spiral shape, and is disturbed between adjacent support members. This is because it becomes difficult to face the inner coil.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device capable of solving the above-described problems and preventing coil cooling unevenness in the axial direction of the heat roller, and an image forming apparatus equipped with the fixing device.

  A first invention for achieving the above object is a fixing device for fixing an image on a recording medium, which is disposed along an outer surface of a heating member, and extends in the axial direction of the heating member so that the heating member is arranged. A coil that generates a magnetic field for induction heating, and is arranged on the opposite side of the heating member across the coil, extends in a direction intersecting the axis of the heating member, covers the outside of the coil, and the axis of the heating member An arch core disposed at a plurality of positions at intervals in the direction, having a core part that forms a magnetic path around the coil, and an upstream side and a downstream side obliquely with respect to the arch core arrangement, Cooling means that cools the coil with cooling air from the upstream side and a plurality of support members that support each arch core are provided, eliminating turbulent flow that occurs downstream of this support member, via the coil from the upstream side Then downstream To produce a flow of cooling air towards the to and a laminar flow means.

  According to the first aspect of the invention, the heating member is induction-heated by a magnetic field of a coil disposed along the outer surface thereof, and a method (outer packaging IH) in which the toner image is heated and melted is adopted. Specifically, the core portion having a plurality of arch cores is also arranged along the outer surface of the heating member to form a magnetic path that guides the magnetic field generated by the coil, and this magnetic field is guided to the core portion to perform magnetic induction heating. .

Further, the cooling means cools the coil to prevent the temperature from rising, thereby protecting the fixing device.
Here, the cooling means has a diagonal line as viewed in the axial direction of the heating member, specifically, an upstream side and a downstream side obliquely with respect to the arrangement of each arch core, and cooling air from the upstream side. Is directed downstream via a coil by a plurality of support members that respectively support the arch cores.

  These support members are provided with laminarization means, which eliminates turbulent flow that occurs downstream of the support members and generates a flow of cooling air from the upstream side to the downstream side via the coil. Therefore, the cooling air from the upstream side quickly passes through each support member and reaches the coil to cool, and the airflow that has taken away the heat of the coil quickly passes through each support member and reaches the downstream side. Therefore, it is possible to prevent uneven cooling of the coil as viewed in the axial direction of the heating member, and to make the fixing performance at the center portion and both end portions as viewed in the width direction of the recording medium conveyed uniform.

According to a second aspect of the present invention, in the configuration of the first aspect of the present invention, a cooling air supply port and a discharge port constituted by adjacent support members are provided, and the laminarization means connects the supply port and the discharge port from the upstream side. It is characterized by inclining in the direction of shortcut to the downstream side.
According to the second aspect of the invention, in addition to the action of the first aspect of the invention, the adjacent support members constitute the cooling air supply port on the upstream side and the cooling air discharge port on the downstream side. However, since these supply ports and discharge ports are inclined in a direction that short-circuits the distance from the upstream side to the downstream side via the coil, the turbulence of the airflow can be reliably eliminated, and in the axial direction of the heating member. It is possible to reliably prevent uneven cooling of the seen coil. Further, since the cooling air flows efficiently, the driving cost of the cooling means can be reduced.

According to a third aspect of the present invention, in the configuration of the second aspect, each support member is configured in the same shape.
According to the third aspect of the invention, in addition to the operation of the second aspect of the invention, since only one type of support member is required, the manufacturing cost of the apparatus can be reduced.
According to a fourth aspect of the present invention, in the configuration of the first aspect of the invention, the cooling air supply port and the discharge port are constituted by adjacent support members, and the laminarization means is configured so that each supply port is far from the upstream side. Accordingly, it is separated from the axis of the heating member, and each discharge port is brought closer to the axis of the heating member as it approaches the downstream side.

  According to the fourth aspect of the invention, in addition to the action of the first aspect of the invention, the adjacent support members constitute the cooling air supply port on the upstream side and the cooling air discharge port on the downstream side. However, the supply ports are competing with increasing distance from the upstream side, and the same amount of airflow can be supplied from each supply port toward the coil. Moreover, since the discharge port is competing as it approaches the upstream side, the same amount of airflow can be discharged from the coil side from each discharge port. As a result, the turbulence of the airflow can be reliably eliminated, and the coil cooling unevenness seen in the axial direction of the heating member can be reliably prevented. Further, since the cooling air flows efficiently, the driving cost of the cooling means can be reduced.

According to a fifth aspect, in the configuration of the fourth aspect, each support member is larger as the cross-sectional area of each supply port is farther from the upstream side, and as the cross-sectional area of each discharge port is closer to the downstream side. It is characterized by having a smaller shape.
According to the fifth aspect of the invention, in addition to the action of the fourth aspect of the invention, the cross-sectional area of the supply port that receives the cooling air increases as the distance from the upstream side increases, and the cross-sectional area of the discharge port that discharges the cooling air increases. It is enlarged as it approaches the side, and the same amount of airflow can be reliably supplied and discharged from each supply port and each discharge port toward the coil.

According to a sixth aspect of the present invention, there is provided an image forming apparatus in which the fixing device according to the first to fifth aspects of the present invention is mounted on an image forming apparatus, and a toner image formed by the image forming unit is fixed to a recording medium using the fixing apparatus. Features.
According to the sixth invention, in addition to the effects of the first to fifth inventions, the heating efficiency and the fixing performance of the heating member are ensured and a good toner image is formed. As a result, the reliability of the image forming apparatus is improved. Will improve.

  According to the present invention, the laminarization means of the support member generates a flow of cooling air from the upstream side to the downstream side via the coil, and can prevent uneven cooling of the coil as viewed in the axial direction of the heating member. A fixing device and an image forming apparatus equipped with the fixing device can be provided.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. 2 is a longitudinal sectional view of a fixing unit. FIG. It is a top view which shows the structure around an arch core in detail. It is a top view which shows the structural example of an arch core. FIG. 5 is an exploded plan view of the arch core of FIG. 4. It is a figure explaining the flow of the cooling air in the example of FIG. It is a top view which shows the other structural example of an arch core holder. It is a top view of the arch core of FIG. It is a figure explaining the flow of the cooling air in the example of FIG. It is a figure explaining the flow of the cooling air of a comparative example.

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, for example, a printer, a copier, and a facsimile apparatus that perform printing by transferring a toner image onto the surface of a sheet as an example of a recording medium based on image information input from the outside, and a composite having these functions. It can take the form of a machine or the like. In the following embodiments, the recording medium is not limited to a sheet, and can be implemented even if the recording medium is other than a sheet (such as an OHP sheet).

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. The discharge tray 3 is provided.
In the lower part of the apparatus main body 2, a paper feed cassette 5 for storing paper is disposed. In addition, a stack tray 6 is provided in the central portion of the apparatus main body 2 for supplying paper of a type not stored in the paper feed cassette 5 to the apparatus main body 2. An image forming unit 7 is provided on the upper part of the apparatus main body 2, and the image forming unit 7 transmits image data such as characters and patterns transmitted from a host device such as a PC connected to the image forming apparatus 1. The image is formed on the paper based on the above.

  As shown in FIG. 1, a first transport path 9 for transporting a sheet fed from the sheet feeding cassette 5 to a secondary transfer unit 23 described later is disposed on the left side of the apparatus body 2. From the right part to the left part, a second transport path 10 for transporting the sheet fed from the stack tray 6 to the secondary transfer unit 23 is provided. Further, a fixing unit (fixing device) 14 that performs a fixing process on a sheet on which an image has been transferred by the secondary transfer unit 23, and a sheet on which the fixing process has been performed are disposed on an upper left portion in the apparatus main body 2. A third conveyance path 11 that conveys the toner to the third conveyance path 11 is disposed.

  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 conveyance path 9 side by sheet by the paper feed roller 17 and the separating roller pair 18.

The stack tray 6 can be opened and closed on the outer surface of the apparatus main body 2, and sheets are placed one by one on the manual feed portion 19 or a plurality of sheets are stacked. Note that the sheets placed on the manual feed unit 19 are fed out one by one to the second conveyance path 10 side by the pick-up roller 20 and the separating roller pair 21.
The first conveyance path 9 and the second conveyance path 10 are joined before the registration roller pair 22, and the paper that has reached the registration roller pair 22 waits here for skew adjustment and timing adjustment. Thereafter, the image is sent to the secondary transfer unit 23.

  The full color toner image on the intermediate transfer belt 40 is secondarily transferred to the sheet by the secondary transfer unit 23 on the sent sheet. Thereafter, the sheet on which the toner image is fixed by the fixing 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. Then, after the toner image on the opposite surface is fixed by the fixing unit 14, it passes through the third conveyance path 11 and is discharged to the discharge tray 3 by the discharge roller pair 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. An intermediate transfer unit 30 is provided which holds the toner images of the respective colors formed in 29 in a superimposed manner.
Each of the image forming units 26 to 29 is on the downstream side in the rotation direction of the photosensitive drum 32, the charging unit 33 disposed to face the circumferential surface of the photosensitive drum 32, and the photosensitive drum 32 of the charging unit 33. A laser scanning unit 34 for irradiating a laser beam to a specific position on the peripheral surface of the photosensitive drum 32, and a downstream side in the rotational direction of the photosensitive drum 32 at the laser beam irradiation position from the laser scanning unit 34. A developing unit 35 disposed opposite to the circumferential surface of the photosensitive drum 32; and a cleaning unit disposed downstream of the developing unit 35 in the rotation direction of the photosensitive drum 32 and opposed to the circumferential surface of the photosensitive drum 32. 36.

  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 sections 35 of the image forming units 26 to 29, two-component developers each containing black toner, yellow toner, cyan toner, and magenta toner are stored in each developing device 51, respectively.

  The intermediate transfer unit 30 straddles the rear roller 38 disposed near the image forming unit 26, the front roller 39 disposed near the image forming unit 29, and the rear roller 38 and the front roller 39. The intermediate transfer belt 40 can be press-contacted with the intermediate transfer belt 40 at a position downstream of the photosensitive drum 32 in the rotation direction of the developing unit 35 of the photosensitive drum 32 of each of the image forming units 26 to 29. Four primary transfer rollers 41 are provided.

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 primary transfer rollers 41 of the image forming units 26 to 29, and finally a full-color toner image. It becomes.
The first transport path 9 and the second transport path 10 are for transporting the paper fed from the paper feed cassette 5 and the stack tray 6 to the secondary transfer unit 23 side, and in the apparatus main body 2, a predetermined transport path is formed. A plurality of conveying roller pairs 43 disposed at the position and a registration roller pair 22 disposed in front of the secondary transfer unit 23 for timing the image forming operation and the sheet conveying operation in the image forming unit 7. And.

  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 a roller pair including, for example, a pressure roller 44 and a fixing roller 45, and the pressure roller 44 includes, for example, a metal core and an elastic surface layer (for example, silicon rubber) and a release layer (for example). For example, the fixing roller 45 has a metal core and an elastic surface layer (for example, silicon sponge). Further, a heat roller (heating member) 46 is provided adjacent to the fixing roller 45, and a heating belt (heating member) 48 is wound around the cylindrical 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 and 47 are respectively provided on the upstream side and the downstream side of the fixing unit 14, and the sheet conveyed through the secondary transfer unit 23 is upstream of the conveyance path 47. Through the pressure 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 discharge tray 3. For this reason, the transport roller pair 49 is disposed at an appropriate position in the third transport path 11, and the discharge roller pair 24 is disposed 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 the image forming apparatus 1 in a posture inclined left or right from the state shown in FIG.

  The fixing unit 14 of this embodiment includes the pressure roller 44, the fixing roller 45, the heat roller 46, and the heating belt 48 as described above. The pressure roller 44 is formed, for example, by forming a Si rubber layer having a thickness of about 2 to 5 mm on a metal (for example, SUS) cored bar, and further laminating a release layer (for example, PFA) on the surface layer to have a diameter of about 50 mm. It's a roller. The fixing roller 45 is a roller having a diameter of about 45 mm by laminating a silicon rubber sponge layer having a thickness of about 5 to 10 mm on a metal core (for example, SUS).

The heat roller 46 has a core metal made of a magnetic metal (eg, Fe) having a diameter of about 30 mm and a thickness of about 0.2 to 1.0 mm, and a release layer (eg, PFA) is formed on the surface thereof. Rotates with rotation of a shaft (not shown).
Further, the heating belt 48 is a ferromagnetic material (for example, Ni electroformed base material) having a base material thickness of, for example, 35 μm (1 μm = 1 × 10 ⁻⁶ m), and a thin film having a thickness of about 200 to 500 μm on its surface An elastic layer (for example, silicon rubber) is formed, and a release layer (for example, PFA) is formed on the outer surface, and the heat generation temperature is adjusted to a range of 150 to 200 ° C., for example. In the case where the heating belt 48 does not have a heat generation function, a resin belt such as PI may be used.

As described above, since the fixing roller 45 has a silicon sponge elastic layer as a surface layer, a flat nip is formed between the heating belt 48 and the pressure roller 44. A halogen heater 44 a is 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, induction heating is performed on the arc-shaped portions of the heat roller 46 and the heating belt 48, so the induction heating coil (coil) 52 is on a virtual arc surface along the arc-shaped outer surface of the heat roller 46. Is arranged. Actually, the coil bobbin 53 is arranged outside the heat roller 46 and the heating belt 48, and the induction heating coil 52 is arranged in a winding shape on the bobbin 53. The material of the bobbin 53 is preferably a heat resistant resin (for example, PPS, PET, LCP), and the coil 52 is fixed to the coil bobbin 53 using, for example, a silicon-based adhesive.

[Core part]
As shown in FIG. 2, the center core 58 is located at the center of the IH coil unit 50, and the arch core 54 and the side core 56 are arranged so as to form a pair on both sides thereof. Of these, the arch cores 54 on both sides are ferrite cores formed in a cross-sectional arch shape that is symmetrical to each other, and the overall length thereof is longer than the region where the induction heating coil 52 is disposed. The side cores 56 on both sides are ferrite 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 region where the induction heating coil 52 is disposed.

  For example, the arch core 54 is arranged at a plurality of locations at intervals in the longitudinal direction of the heat roller 46 (FIG. 3). In the present embodiment, the interval between adjacent arch cores 54 is about 10 mm. Also, the higher the arrangement density of the arch cores 54, the better the magnetic flux induction performance. However, even if the density is reduced to some extent, the performance degradation is small, so that high cost performance can be obtained within a range where sufficient performance can be exhibited. It is preferable to set the arrangement density. Further, when adjusting the temperature distribution of the heating belt 48 in the axial direction, it is possible to cope with the problem by adjusting the arrangement density of the arch cores 54. In the present embodiment, for example, the arrangement density of the arch core 54 is about 1/2 to 1/3 as a whole, and the arrangement density at both ends in the longitudinal direction of the induction heating coil 52 is set higher than the vicinity of the center, The temperature drop in the end region in the longitudinal direction of the heat roller 46 is also improved.

  Further, one side core 56 has a length of about 30 to 60 mm, and a plurality of side cores 56 are continuously arranged in the longitudinal direction of the heat roller 46 without any interval. The total length of the range in which the side core 56 is disposed corresponds to the length of the region in which the induction heating coil 52 is disposed. By arranging a plurality of side cores 56 in this way, there is an effect of leveling the fluctuation width of the temperature distribution due to the arrangement of the arch core 54. The arrangement of the cores 54 and 56 is determined, for example, according to the magnetic flux density (magnetic field strength) distribution of the induction heating coil 52, and the arch core 54 has been removed by a certain distance. The side core 56 compensates for the effect of converging the magnetic flux at the location, and the magnetic flux density distribution (temperature distribution) in the longitudinal direction is leveled.

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 and a thermostat 62 are installed inside the heat roller 46. The thermistor or the like 62 is disposed inside a portion of the heat roller 46 that generates a large amount of heat, particularly due to induction heating. More practically, a non-contact type sensor can be arranged below the coil unit 50 to detect the outer surface temperature of the heating belt 48.

  The center core 58 shown in FIGS. 2 and 3 is, for example, a ferrite core having a cylindrical cross section (outer diameter is about 18 mm). In the center of the center core 58, for example, a shaft 59 of nonmagnetic metal (SUS, etc.) or heat-resistant resin (PPS, PET, LCP, etc.) is inserted in the axial direction. It has a length corresponding to a paper width of 13 inches (about 340 mm).

(Shielding member)
Further, a shielding member 60 is attached to the center core 58 along its outer surface. The shielding member 60 has a thin plate shape and is formed to be curved in an arc shape as a whole. For example, the shielding member 60 may be installed in a state where it is embedded in the thick portion of the center core 58 as shown in the figure, or may be installed in a state of being attached to the outer surface of the center core 58. The shielding member 60 can be attached to the center core 58 using, for example, a silicon-based adhesive.

  The shielding member 60 is preferably a non-magnetic and highly conductive member, and for example, oxygen-free copper is used. The shielding member 60 shields the magnetic flux from the induction heating coil 52 by generating a reverse magnetic flux by an induced current caused by the penetration of a magnetic flux perpendicular to the surface, and canceling the complex magnetic flux (perpendicular magnetic flux). Further, by using a highly conductive member, Joule heat generation due to an induced current can be suppressed, and the magnetic flux can be shielded efficiently. 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.

  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 and the magnetic field strength decreases. On the other hand, when the center core 58 rotates 180 ° (the direction is not particularly limited) from the state shown in FIG. 2 and the shielding member 60 moves to a position (retracted position) farthest from the heating belt 48, the periphery of the induction heating coil 52 As a result, the magnetic resistance decreases, a magnetic path is formed through the arch core 54 and the side core 56 on both sides centering on the center core 58, and the magnetic flux acts on the heating belt 48 and the heat roller 46.

FIG. 3 is a plan view of the periphery of the center core 58. The center core 58 extends in the width direction of the sheet perpendicular to the sheet passing direction (the arrow direction in FIG. 3), and its total length is slightly larger than the maximum sheet passing width (for example, A3 length, A4 width).
The IH coil unit 50 is provided with, for example, a stepping motor 66, and the shaft 59 is rotated by power from the motor 66. Therefore, a driven gear 59a is attached to one end portion of the shaft 59, and an output gear 66a of the stepping motor 66 is engaged with the driven gear 59a. When the stepping motor 66 is driven, the shaft 59 is rotated by the power, and the center core 58 can be rotated around the longitudinal axis.

  At this time, in order to detect the rotation angle (rotational displacement amount from the reference position) of the center core 58, an index 98 is provided at one end of the shaft 59, and a photo interrupter 99 is combined therewith. The position of the index 98 is set to a reference position regarding the rotation angle of the center core 58, and the index 98 reacts (for example, shields light) from the photo interrupter 99 at the reference position.

The rotation angle of the center core 58 can be controlled by, for example, the number of drive pulses applied to the stepping motor 66. The stepping motor 66 is provided with a control unit (not shown). This control unit can be constituted by, for example, a control IC, an input / output driver, a semiconductor memory, and the like.
The detection signal from the photo interrupter 99 is input to the control IC through the input driver, and based on this, the control IC can detect the reference position of the center core 58. 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 information on the rotation angle suitable for the paper size (angle when the reference position is 0 degree) from the semiconductor memory (ROM), and reaches the target rotation angle. Drive pulses are output at regular intervals. The drive pulse is applied to the stepping motor 66 through the output driver, and the stepping motor 66 operates in response to the drive pulse.

  In the example shown in FIG. 3, three types of the first shielding member 60 a, the second shielding member 60 b, and the third shielding member 60 c are used as the shielding member (reference numeral 60 in FIG. 2) in the axial direction (longitudinal direction) of the center core 58. ) Are divided and arranged. These first to third shielding members 60a, 60b, and 60c are different in arrangement and length in the axial direction of the center core 58, and also in length in the circumferential direction of the center core 58 (width covering the center core 58). ing. Note that the first to third shielding members 60a, 60b, and 60c are not provided separately as described above, but may be provided integrally.

(Support member)
By the way, the arch core 54 of the present embodiment is integrally formed with the resin arch core holder (supporting member) 72 shown in FIG. 4 by insert molding. In the example of FIG. A total of 14 arch core holders 72 a to 72 g are arranged on the coil bobbin 53. Specifically, the arch core holders 72a to 72g are formed in a cross-sectional arch shape that is symmetrical to each other in the same manner as the arch cores 54 extending in the paper transport direction (vertical direction in FIG. 4). And one end (the lower end in FIG. 2) abuts the upper surface of the side core 56 and covers the outside of the coil 52.

In this embodiment, the arch core 54 is composed of seven types of arch core holders 72 a to 72 g, and two arch core holders 72 a to 72 g are prepared (a total of 14), and symmetrical positions with respect to the center position of the center core 58. Is arranged.
More specifically, each of the arch core holders 72a to 72g is formed in a substantially T shape in a plan view as shown in FIG. 5 and extends in the paper transport direction (vertical direction in FIG. 5) to straddle the coil 52. In FIG. 5, the arch portion has a convex top portion extending in the right direction and positioned above the center core 58 and the like. In these arch core holders 72a to 72g, the lengths of the arch portions are equal, and the lengths of the convex top portions extending in the axial direction of the center core 58 are also formed to be equal.

  First, the arch core holder 72a is disposed on the outermost side of the coil 52, for example, the folded portion. The arch core holder 72a is provided with a pair of arch cores 54 facing each other in the sheet conveyance direction, as compared with the arch core holders 72b to 72g, on the most front side as viewed in FIG. The convex top portion is also arranged closest to the front as viewed in FIG. 5, and extends from between the pair of arch cores 54 to the right in FIG.

  Next, the arch core holder 72b is disposed inside the arch core holder 72a, and is disposed, for example, in the innermost vicinity of the folded portion of the coil 52, for example. The arch core holder 72b is provided with a pair of arch cores 54 to be held on the back side as viewed in FIG. 5 from the arch core holder 72a. In addition, the top part is arrange | positioned in the back | inner side a little rather than the arch core holder 72a in FIG. 5, and it extends in the right direction of FIG.

  The arch core holder 72c is disposed inside the arch core holder 72b, for example, in the vicinity of the end of the center core 58. The arch core holder 72c includes the pair of arch cores 54 slightly behind the arch core holder 72b as viewed in FIG. The top portion is also arranged slightly behind the arch core holder 72b in FIG. 5, and extends from between the pair of arch cores 54 to the right in FIG.

  Subsequently, the arch core holder 72d is disposed on the inner side of the arch core holder 72c, for example, slightly on the inner side of the end portion of the center core 58. The arch core holder 72d is provided with the pair of arch cores 54 on the slightly back side as viewed in FIG. 5 from the arch core holder 72c, and the top portion is also disposed slightly on the back side in FIG. 5 from the arch core holder 72c. It extends in the right direction of FIG. 5 from between the pair of arch cores 54.

  Further, the arch core holder 72e is disposed on the inner side than the arch core holder 72d, and is disposed, for example, slightly on the inner side of the end portion of the center core 58. The arch core holder 72e is provided with the pair of arch cores 54 on the slightly back side as viewed in FIG. 5 from the arch core holder 72d, and the top portion is also disposed slightly on the back side in FIG. 5 from the arch core holder 72d. It extends in the right direction of FIG. 5 from between the pair of arch cores 54.

  The arch core holder 72f is disposed on the inner side than the arch core holder 72e, and is disposed slightly outside the central portion of the center core 58, for example. The arch core holder 72f is provided with the pair of arch cores 54 on the slightly back side as viewed in FIG. 5 from the arch core holder 72e, and the top portion is also disposed slightly on the back side in FIG. 5 from the arch core holder 72e. It extends in the right direction of FIG. 5 from between the pair of arch cores 54.

  Furthermore, the arch core holder 72g is disposed on the inner side of the arch core holder 72f, for example, in the vicinity of the center portion of the center core 58. The arch core holder 72g is provided with the pair of arch cores 54 slightly behind the arch core holder 72f as viewed in FIG. 5, in other words, slightly in front of the axis of the center core 58 (indicated by a one-dot chain line in FIG. 6). On the side. The top portion is also arranged slightly on the near side of the axis of the center core 58 and extends rightward in FIG. 5 from between the pair of arch cores 54.

As shown in FIG. 5, when the ends of the arch portions of the arch core holders 72a to 72g are aligned, it can be seen that the positions of the pair of arch cores 54 and the top portions are shifted.
Then, two arch core holders 72a to 72g are prepared, and the top portions of the arch core holders 72g and 72g are brought into contact with each other and arranged in the center portion of the center core 58 (FIG. 6).

  At this time, when the arch cores 54 of each arch core holder 72g are arranged symmetrically with respect to the axis of the center core 58 (shown by a one-dot chain line in FIG. 6), the arch portion of the arch core holder 72g located on the left side of the center of the center core 58 The both ends of the arch are arranged so as to be shifted with respect to both ends of the arch portion of the arch core holder 72g located on the right side (FIGS. 4 and 6). That is, the left arch core holder 72g seen in FIGS. 4 and 6 is disposed slightly behind the right arch core holder 72g.

  Next, the top portion of the arch core holder 72f is brought into contact with the surface opposite to the top portion of the arch core holder 72g. Also in this case, when the arch core 54 of the arch core holder 72f is arranged symmetrically with respect to the axis of the center core 58, both ends of the arch portion of the arch core holder 72f are shifted from both ends of the arch portion of the arch core holder 72g. (FIGS. 4 and 6). In other words, the arch core holder 72f located on the left side of the center of the center core 58 is arranged slightly behind the adjacent arch core holder 72g, whereas the arch core holder 72f located on the right side of the center of the center core 58 Is arranged slightly on the near side of the adjacent arch core holder 72g.

  Subsequently, an arch core holder 72e, an arch core holder 72d, an arch core holder 72c, an arch core holder 72b, and an arch core holder 72a are arranged in this order toward the outer side in the axial direction of the center core 58. As for each of these arch core holders 72a to 72e, when the pair of arch cores 54 are arranged symmetrically with respect to the axis of the center core 58, the adjacent arch core holders 72f and 72e, the adjacent arch core holders 72e and 72d, and the adjacent arch cores are arranged. The holders 72d and 72c, the adjacent arch core holders 72c and 72b, and the adjacent arch core holders 72b and 72a are all displaced from each other (FIGS. 4 and 6).

[Cooling means]
Here, in this embodiment, a duct is not used, and cooling air is supplied diagonally to the arrangement of the arch core holders 72 a to 72 g having the arch core 54.
Specifically, the cooling fan (upstream cooling means) 80 and the exhaust fan (downstream cooling means) 82 are arranged so that the left end side and the right end side of the axis of the center core 58 indicated by the one-dot chain line in FIG. In the intersecting direction, for example, the cooling fan 80 is disposed on the left front side in FIG. 6, and the exhaust fan 82 is disposed on the right back side in FIG.

Thereby, the cooling air from the cooling fan 80 is supplied to the coil 52 in a direction that obliquely intersects the center core 58 from the right front side of FIG. 6 when the axis of the center core 58 is arranged in the vertical direction. The cooled airflow is discharged to the outside via the exhaust fan 82 from the left back side in FIG.
[Laminarization means]
Among the arch core holders 72a to 72g described above, the lower half corresponds to the cooling air supply port 76 with respect to the axis of the center core 58 shown by the one-dot chain line in FIG. Corresponds to the cooling air discharge port 77, and laminarization means for eliminating the turbulent flow downstream of the arch core holder 72 is applied to the supply port 76 and the discharge port 77.

  That is, in the present embodiment, the adjacent arch core holders 72 a to 72 g are arranged so as to be shifted with respect to the axis of the center core 58, so that each supply port 76 is far from the cooling fan 80 as shown in FIG. 6. Accordingly, the exhaust ports 77 are separated from the axis of the center core 58 as the distance from the exhaust fan 82 increases.

  In this regard, in other words, in the arch shape of the arch core holders 72a to 72g, the arch-shaped cross-sectional area of each supply port 76 corresponding to the lower half with respect to the axis of the center core 58 shown by the one-dot chain line in FIG. On the other hand, the arched cross-sectional area of each discharge port 77 corresponding to the upper half with respect to the axis of the center core 58 gradually decreases as the distance from the cooling fan 80 increases. (FIG. 6).

  As a result, the distance from the cooling fan 80 is closer to the supply port 76 of the arch core holders 72b and 72c adjacent to the cooling fan 80, for example, than the supply port 76 of the arch core holders 72a and 72b. Since the arch-shaped cross-sectional area in contact with the cooling air is formed large, it becomes easy to take in the cooling air from the cooling fan 80 from the space generated by the difference in these cross-sectional areas.

Also, as each exhaust port 77 becomes closer to the exhaust fan 82, the arch-shaped cross-sectional area that comes into contact with the airflow becomes smaller, so that the airflow is exhausted from the space generated by the difference in these cross-sectional areas. It becomes easy to discharge toward the fan 82.
[Other structural examples of arch core holder]
By the way, in the said Example, although seven types of arch core holders 72a-72g are prepared 2 pieces each, as FIG. 7-9 shows, it is also possible to comprise with one type of arch core holders 72. It is.

Specifically, in this embodiment as well, the arch core 54 is insert-molded into the arch core holder 72 and is composed of a total of 14 arch core holders 72, while each arch core holder 72 is composed of the same shape, A pair of arch cores 54 facing each other in the sheet conveyance direction are also provided at the same position.
More specifically, each arch core holder 72 is formed in a substantially cross shape in plan view as shown in FIG. 8 and extends in the paper transport direction (vertical direction in FIG. 8) and straddles the coil 52. The arch portion is slightly inclined to the right side with respect to the sheet conveyance direction.

Each arch core holder 72 has a convex top portion that extends in the center of the center core 58 in the axial direction (left-right direction in FIG. 8) and is located above the center core 58 and the like. The pair of arch cores 54 are provided at symmetrical positions with respect to the axis of the center core 58 (indicated by a one-dot chain line in FIG. 9).
Then, 14 pieces of the one kind of arch core holders 72 are prepared, the top portions of the arch core holders 72 are brought into contact with each other, and the arch cores 54 are arranged symmetrically with respect to the axis of the center core 58. It is arranged slightly tilted to the right (FIGS. 7 and 9).

  Here, the cooling means of this embodiment is the same as that of the above embodiment, the cooling fan 80 is disposed on the left front side in FIG. 9 and the exhaust fan 82 is disposed on the right back side in FIG. 9 is supplied to the coil 52 in a direction that obliquely intersects the center core 58 from the left front side in FIG. 9, and the airflow that has cooled the coil 52 passes through the exhaust fan 82 from the right back side in FIG. It is discharged outside.

On the other hand, the laminarization means of this embodiment includes a supply port 76 in the lower half of the axis of the center core 58 indicated by a one-dot chain line in FIG. On the other hand, it is applied to the discharge port 77 in the upper half to eliminate the turbulent flow that occurs downstream of the arch core holder 72.
In other words, in this embodiment, each arch core holder 72 is disposed slightly inclined to the right side with respect to the sheet conveyance direction, and each supply port 76 faces the cooling fan 80, whereas each discharge port 77. Faces the exhaust fan 82.

  In this way, if the cooling fan 80 to the exhaust fan 82 are short-cut, the cooling fan 80 to the exhaust fan 82 are cooled as compared with the case where they are simply connected in the axial direction of the center core 58 and the sheet conveyance direction. Cooling air from the fan 80 easily flows into the coil 52, and airflow that has cooled the coil 52 is easily discharged to the exhaust fan 82.

  As described above, according to the present embodiment, the heat roller 46 and the heating belt 48 are induction-heated by the magnetic flux of the coil 52 disposed along the outer surface thereof, and a method (outer packaging IH) is performed that heats and melts the toner image. adopt. Specifically, the core portion including the plurality of arch cores 54 is also arranged along the outer surface of the heat roller 46 and the like to form a magnetic path for guiding the magnetic flux generated by the coil 52, and this magnetic flux is guided to the core portion to be magnetic. Induction heating is performed.

Further, the cooling means cools the coil 52 to prevent its temperature rise, and protects the fixing unit 14.
Here, the cooling means has a cooling fan 80 and an exhaust fan 82 diagonally as viewed in the axial direction of the heat roller 46 and the like, specifically, obliquely with respect to the arrangement of the arch cores 54. Cooling air from the fan 80 is directed to the exhaust fan 82 via the coil 52 by a plurality of arch core holders 72 that respectively support the arch cores 54.

  These arch core holders 72 are provided with laminarization means, which eliminates turbulent flow that occurs downstream of the arch core holder 72, and generates cooling air from the cooling fan 80 to the exhaust fan 82 via the coil 52. Generating flow. Therefore, the cooling air from the cooling fan 80 quickly passes between the arch core holders 72 and reaches the coils 52 to be cooled, and the airflow that has taken the heat of the coils 52 quickly passes between the arch core holders 72. To reach the exhaust fan 82.

  This point will be described in detail. The arch core holder 92 of the comparative example shown in FIG. 10 has the same shape, and is arranged along the paper transport direction (vertical direction in FIG. 10). In addition to the pair of arch cores 54, each arch core holder 92 is also provided at a symmetrical position with respect to the axis of the center core 58 (indicated by a one-dot chain line in FIG. 10), and the cooling air from the cooling fan 80 is shown in FIG. 10 is supplied to the coil 52 in a direction that crosses the center core 58 obliquely from the left front side of the air, and the airflow that has cooled the coil 52 is discharged to the outside via the exhaust fan 82 from the right back side in FIG.

  In this case, the lower half corresponds to the supply port 96 and the upper half corresponds to the discharge port 97 with respect to the axis of the center core 58 indicated by the one-dot chain line in FIG. The end portions thereof are arranged in the same straight line parallel to the axis of the center core 58, there is no difference in the cross-sectional area of the arch portion, and it is not directed to the fans 80 and 82 side, so that it is in the paper transport direction. It is suitable.

As shown in FIG. 10, the cooling air from the cooling fan 80 stays in a vortex at the downstream of the arch core holder 92, more specifically, at each supply port 96 and each discharge port 97. A turbulent flow that hinders the flow of cooling air occurs between the core holders 92.
However, in the arch core holder 72 of each of the embodiments described above, the turbulent flow that occurs downstream of the arch core holder 72 is eliminated (FIGS. 6 and 9), and the cooling air from the cooling fan 80 is sent to each arch core holder 72. The airflow that has quickly passed through the coil 52 reaches the coil 52 to be cooled, and the airflow that has deprived the heat of the coil 52 quickly passes through the arch core holders 72 and reaches the exhaust fan 82. The cooling unevenness of the coil 52 seen in the axial direction is prevented, and the fixing performance of the central portion and both end portions seen in the width direction of the conveyed paper can be made uniform.

  Further, the adjacent arch core holder 72 constitutes the supply port 76 on the cooling fan 80 side and the discharge port 77 on the exhaust fan 82 side, respectively, but as shown in the example of FIG. Are competing as they become farther from the cooling fan 80, and the same amount of airflow can be supplied from the supply ports 76 arranged in the axial direction of the center core 58 toward the coil 52. Further, since the discharge ports 77 are competing as they approach the cooling fan 80, the same amount of airflow can be discharged from the coils 52 from the discharge ports 77 arranged in the axial direction of the center core 58.

As a result, the turbulence of the airflow can be reliably eliminated, and the cooling unevenness of the coil 52 seen in the axial direction of the heat roller 46 and the like can be reliably prevented. Further, since the cooling air flows efficiently, the driving cost of the cooling means can be reduced.
Further, as shown in the example of FIG. 6, the arch-shaped cross-sectional area of the supply port 76 that receives the cooling air is increased as the distance from the cooling fan 80 increases, and the same amount of airflow is generated along the axial direction of the center core 58. The coil 52 can be reliably supplied to the coil 52, and the arch-shaped cross-sectional area of the discharge port 77 for discharging the cooling air is increased as the cooling fan 80 is approached, and the same in the axial direction of the center core 58. An amount of airflow can be reliably discharged from the coil 52.

  Furthermore, according to the example shown in FIG. 9, the angle formed by the formation surface of the supply port 76 and the discharge port 77 with respect to the axis of the center core 58 is not 90 °, but an acute angle. Since the distance from the cooling fan 80 to the exhaust fan 82 via the coil 52 is inclined, the turbulence of the airflow can be surely eliminated. In this case, the axial direction of the heat roller 46 and the like is also seen. Uneven cooling of the coil 52 can be reliably prevented. Further, since the cooling air flows efficiently, the driving cost of the cooling means can be reduced.

If only one type of arch core holder 72 by insert molding is used as in the example of FIG. 9, the manufacturing cost of the fixing unit 14 can be reduced, the coil bobbin 53 can be reduced, and the IH coil unit 50 can be reduced in size. it can.
Furthermore, as a result of forming a good toner image while ensuring the heating efficiency and fixing performance of the heat roller 46 and the like, the reliability of the image forming apparatus 1 is improved.

The present invention can be implemented with various modifications without being limited to the above-described embodiments. For example, although the present embodiment shows an example in which a printer is embodied as an image forming apparatus, the image forming apparatus of the present invention is naturally applicable to a multifunction machine, a copier, a facsimile machine, and the like.
And in any of these cases, similarly to the above, there is an effect that it is possible to prevent uneven cooling of the coil as seen in the axial direction of the heating member.

1 Printer (image forming device)
7 Image forming unit 14 Fixing unit (fixing device)
46 Heat roller (heating member)
48 Heating belt (heating member)
50 IH coil unit 52 Induction heating coil (coil)
54 Arch core 72, 72a-72g Arch core holder (supporting member)
76 Supply port 77 Discharge port 80 Cooling fan (upstream side cooling means)
82 Exhaust fan (downstream cooling means)

Claims (6)

A fixing device for fixing an image on a recording medium,
A coil disposed along the outer surface of the heating member and extending in the axial direction of the heating member to generate a magnetic field for induction heating the heating member;
It is arranged on the opposite side of the heating member across the coil, extends in a direction intersecting the axis of the heating member, covers the outside of the coil, and is spaced at intervals in the axial direction of the heating member. A core part comprising an arch core to be arranged and forming a magnetic path around the coil;
A cooling means having an upstream side and a downstream side obliquely with respect to the arrangement of the arch core, and cooling the coil with cooling air from the upstream side;
It is provided in a plurality of support members that respectively support the arch cores, eliminates the turbulent flow that occurs downstream of the support members, and flows the cooling air from the upstream side to the downstream side via the coil. And a laminarizing means for generating the fixing device. The fixing device according to claim 1,
The cooling air supply port and the discharge port constituted by the adjacent support members,
The laminarization unit inclines the supply port and the discharge port in a direction that shortcuts from the upstream side to the downstream side. The fixing device according to claim 2,
Each of the support members is configured in the same shape. The fixing device according to claim 1,
The cooling air supply port and the discharge port constituted by the adjacent support members,
The laminarization means separates the supply ports from the axis of the heating member as the distance from the upstream side increases, and approaches the axis of the heating member as the discharge ports approach the downstream side. A fixing device. The fixing device according to claim 4,
Each of the support members is configured to have a shape in which the cross-sectional area of each of the supply ports increases as the distance from the upstream side increases, and the cross-sectional area of each of the discharge ports decreases as it approaches the downstream side. A fixing device characterized by the above.   An image forming apparatus comprising: the fixing device according to claim 1 mounted in an image forming apparatus, and fixing the toner image formed by the image forming unit on the recording medium using the fixing device. apparatus.

Images