JP5308677B2 - Image forming apparatus - Google Patents

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 through a nip between a pair of heated rollers and a heating belt and a roller. 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). Envelope IH).

  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 shield disposed between an induction heating coil and a core is divided into a magnetic path cutoff position which is a winding center of the coil and a magnetic part which is a winding part of the coil. It has a function to be displaced to the road release position. According to this prior art, when the magnetic shield is displaced from the winding portion of the coil to the winding center, the magnetic path corresponding to the non-sheet passing region of the heat generating roller is interrupted. It is thought that excessive temperature rise in the paper passing area can be prevented.

The second prior art (Patent Document 3) shields magnetism using a magnetic shielding plate having high magnetic permeability and high electrical resistance. In particular, in this prior art, the magnetic flux shielding plate is normally located outside the gap portion between the fixing roller and the magnetic flux generation portion, and moves to the gap portion with the deformation of the thermal actuator at a high temperature. It has become.
JP-A-6-31801 JP 2006-163200 A (FIGS. 2 and 3) Japanese Patent Laying-Open No. 2006-267180 (FIGS. 6 and 7)

  However, the magnetic shield used in the first prior art (Patent Document 2) is an aluminum plate having a certain large area, and even if it is moved to the magnetic open position, the magnetic shield (aluminum) is placed on the coil. Plate), which causes a certain degree of magnetic shielding effect. For this reason, the first prior art has a problem that the heat conversion efficiency during heating deteriorates.

  On the other hand, since the second prior art (Patent Document 3) has a structure in which the magnetic shielding plate is retracted outside the gap portion, there is no problem of producing a magnetic shielding effect until retracting as described above. However, this time, when retracting the magnetic shielding plate to the outside of the gap portion, a storage space is required, which causes another problem that the installation space for the coil or the like is compressed. For this reason, in the second prior art, it is difficult to take a sufficient installation area of the coil with respect to the fixing roller, and there is a problem that the heating efficiency is lowered accordingly. To supplement this point, it is necessary to increase the size of the fixing roller itself. However, increasing the size of the fixing roller causes an increase in heat capacity, and is not suitable for shortening the warm-up time.

  Accordingly, the present invention provides a structure that does not inadvertently increase the installation space for the magnetic adjustment member, and is less likely to produce a magnetic shielding effect when the magnetic adjustment member is retracted during induction heating. It is.

  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. In particular, the fixing unit is disposed along the outer surface of the heating member, and a coil formed around a predetermined winding center to generate a magnetic field for induction heating of the heating member, and the heating member sandwiching the coil. A core made of a magnetic material to form a magnetic path passing through the center of the winding around the coil, and a nonmagnetic metal magnetic adjustment member formed in a ring shape around a predetermined ring center And the position of the magnetic adjustment member from the magnetic path, the shielding position where the magnetism is shielded by overlapping the ring center and the winding center substantially coaxially in the middle of the magnetic path through the winding center to the heating member And a magnetic adjustment means for displacing the ring center and the winding center to a retracted position where the passage of magnetism is allowed by being non-coaxial.

  The magnetic adjustment member employed in the present invention has a unique form in which a nonmagnetic metal is formed into a ring shape. That is, when a ring-shaped non-magnetic metal is placed in a magnetic field, an induced current is generated in the circumferential direction of the ring due to the penetration of a magnetic field (complex magnetic flux) perpendicular to the inner surface of the ring. A reverse demagnetizing field is generated. The magnetic adjustment member can exhibit a magnetic shielding effect by canceling the magnetic field (interlaced magnetic flux) penetrating the inner side of the ring in the vertical direction.

  Such a magnetic adjusting member has the highest shielding effect when a unidirectional magnetic field that vertically penetrates the inside of the ring is generated. Conversely, even if the inside of the ring is vertically penetrated, the magnetic field is bidirectional. When passing through and going through or making a U-turn, the shielding effect does not occur. The inventors of the present invention pay attention to this point, and in the shielded position as described above, the ring center is placed on the same axis as the coil winding center in the middle of the magnetic path so that a unidirectional penetrating magnetic field (complex magnetic flux) is generated. In the retracted position, the ring center and the coil winding center are made non-coaxial so that they can be bidirectional (or U-turned). The magnetic field is passed and no magnetic shielding effect is generated.

  Thereby, it is possible to obtain a sufficient temperature rise and shorten the warm-up time without reducing the heat generation efficiency during induction heating of the heating member. Further, since the magnetic adjustment member may overlap with the coil winding region at the retracted position, it is not necessary to secure a storage space outside the coil and the core, and space saving can be achieved accordingly. . Moreover, since the magnetic adjustment member has a ring shape and is hollow, the mass of the member can be kept small even if a sufficiently wide range (ring width) is secured. Therefore, the material cost can be reduced, and the power (for example, motor output) when displacing the magnetic adjustment member can be minimized.

  The above configuration is a structure in which a coil and a core are arranged outside the heating member (so-called outer IH), but the present invention is a structure in which the coil and the core are arranged inside the heating member (so-called inclusion IH). Also good. In this case, the fixing unit is arranged along the inner surface of the heating region as viewed in the circumferential direction of the heating member, and around a predetermined winding center to generate a magnetic field for induction heating of the heating member in the heating region. A formed coil, a core disposed with the coil inside the heating member, a core made of a magnetic material to form a magnetic path passing through the coil winding center inside the heating member, and around a predetermined ring center Non-magnetic metal magnetic adjustment member formed in a ring shape, and the position of the magnetic adjustment member overlaps the center of the ring and the winding center in the middle of the magnetic path from the winding center to the heating member. And a magnetic adjustment means for displacing to a retreat position where the passage of magnetism is allowed by deviating from the magnetic path and making the ring center and the winding center non-coaxial. It becomes.

  Similarly, in the above-described configuration (including IH), the magnetic adjustment member can be displaced to the shielding position inside the heating member to obtain a sufficient magnetic shielding effect by the magnetic adjustment member, and at the retracted position. Since the magnetic adjustment member allows the magnetism to pass through satisfactorily, sufficient heating efficiency can be exhibited. In this case, since the coil and the core including the magnetic adjustment member can be arranged inside the heating member, sufficient space saving can be achieved.

  In addition to the above, the present invention has the following features.

(1) The magnetic adjustment means is configured to displace the magnetic adjustment member between the coil and the core.
(2) Alternatively, the magnetic adjustment means is configured to displace the magnetic adjustment member between the heating member and the coil.

  In any of the above configurations (1) and (2), the magnetic adjustment member can shield the magnetism in the middle of the magnetic path passing through the center of the coil at the shielding position, and reliably pass the magnetism at the retracted position. Can be tolerated. The features (1) and (2) can be applied to both the outer IH and the inner IH.

(3) It is preferable that the magnetic adjustment means sets the position where the current flowing in the circumferential direction of the magnetic adjustment member is substantially zero when the magnetic field is generated by the coil as the retracted position. In other words, if the current flowing through the magnetic adjustment member (in the ring) at the retracted position is zero, no demagnetizing field is generated from the magnetic field generated by the coil from that, so that the magnetic induction of the heating member is not hindered.

(4) The magnetic adjustment means can reciprocate the magnetic shielding member between the retracted position and the shielding position, and can adjust the amount of magnetic shielding according to the amount of displacement therebetween. In this case, when the magnetic adjustment means displaces the magnetic adjustment member, the magnetism is hardly shielded at all at the retracted position, but the magnetic shielding amount can be gradually increased from the retracted position toward the shield position. Therefore, the amount of magnetic shielding can be finely adjusted according to the temperature rise condition of the heating member.

(5) The magnetic adjustment member has a square ring shape divided into a plurality of parts when viewed in the longitudinal direction of the heating member, and has different ring widths as viewed in the circumferential direction of the heating member, and the fixing unit The ring width is set to the minimum in the vicinity of the minimum sheet passing area of the sheet conveyed by.

  That is, since the ring-shaped magnetic adjustment member exhibits a magnetic shielding effect within the inner range of the ring, among the plurality of magnetic adjustment members, those having a large ring width have the largest magnetic shielding amount. As the ring width decreases, the amount of magnetic shielding decreases accordingly. Therefore, normally, the ring width is set to the minimum in the vicinity of the minimum sheet passing region where overheating of the heating member is not likely to be a problem, and as the distance from the sheet increases in the direction of the sheet passing width (the width direction of the heating member). If the ring width is increased, the magnetism can be effectively shielded outside the minimum sheet passing area where excessive temperature rise is likely to be a problem, and it is possible to reliably cope with sheet size switching.

(6) Moreover, it is preferable that the magnetic adjustment member is comprised with the conductor whose width dimension is 1 mm-5 mm and whose thickness is 0.5 mm-3 mm. In other words, the magnetic adjusting member needs to reduce the specific resistance (electric resistance) of the member as much as possible in order to effectively suppress the Joule heat generation and shield the magnetism. With the above-mentioned member dimensions, it is possible to secure good conductivity by sufficiently reducing the specific resistance of the magnetic adjustment member, obtain a sufficient magnetic shielding effect, and reduce the weight of the magnetic adjustment member. Can do.

(7) The magnetic adjustment member is preferably made of a nonmagnetic metal made of copper. Thereby, the specific resistance of the member can be reduced, the Joule heat generation of the member itself can be suppressed, and a good magnetic shielding effect can be obtained.

  In the present invention, the heating member may be in the form of a metal roller or a metal belt. Any form is suitable for the induction heating method using a coil.

  The present invention achieves sufficient heat generation efficiency when the magnetic adjustment member is moved to the retracted position while saving space as the entire fixing unit, and shields the magnetism by the magnetic adjustment member when the paper size is switched, An excessive temperature rise of the heating member can be reliably prevented.

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 lower part of the apparatus main body 2, a paper feed cassette 5 for storing paper is disposed. A stack tray 6 for supplying manually fed sheets is disposed 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 disposed on the left side of the apparatus main body 2, from the right to the left. Is provided with a second transport path 10 for transporting paper fed from the stack tray 6 to the image forming section 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 arranged.

  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 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. 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 disposed so as to face the peripheral surface of the photosensitive drum 32, and a periphery of the photosensitive drum 32 on the downstream side of the charging unit 33. A laser scanning unit 34 for irradiating a laser beam to a specific position on the surface, and a developing unit disposed 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 35 and a cleaning unit 36 disposed 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 disposed near the image forming unit 26, a front roller (driven roller) 39 disposed near the image forming unit 29, and a rear roller. 38 and the intermediate transfer belt 40 disposed between the front roller 39 and the downstream side of the developing unit 35 in the photosensitive drum 32 of each of the image forming units 26 to 29 can be pressed through the intermediate transfer belt 40. The four 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 transfer rollers 41 of the image forming units 26 to 29. Become.

  The first transport path 9 transports the paper fed from the paper feed cassette 5 to the intermediate transfer unit 30 side, and includes a plurality of transport rollers 43 disposed at predetermined positions in the apparatus main body 2. And a registration roller 22 disposed 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 a roller pair including, for example, a heating pressure roller 44 and a fixing roller 45. Of these, the pressure roller 44 is made of, for example, metal, and the fixing roller 45 is made of a metal core and an elastic body. It has a surface layer (for example, silicon sponge) and a release layer (for example, PFA). Further, a heating belt (not shown in FIG. 1) is wound around the outer periphery of the fixing roller 45 as a heating member. 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, a transport roller 49 is disposed at an appropriate position in the third transport path 11, and the discharge roller 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.

[First example]
FIG. 2 is a longitudinal sectional view showing a structural example (first 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.

  The fixing unit 14 includes a pressure roller 44, a fixing roller 45, and a heating belt 48 wound around the outer periphery thereof. While the pressure roller 44 is made of metal, the fixing roller 45 has an elastic layer of silicon sponge on the surface (inside the heating belt 48), so a flat nip is provided between the heating belt 48 and the fixing roller 45. Is formed. A halogen heater 44 a is provided inside the pressure roller 44. The base material of the heating belt 48 is 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.

  In addition, the fixing unit 14 includes an IH coil unit 50 outside the fixing roller 45 (heating belt 48) (not shown in FIG. 1). The IH coil unit 50 includes an arch core 54 and a pair of side cores 56 in addition to the induction heating coil 52. The arch core 54 and the side core 56 are, for example, magnetic bodies obtained by sintering ferrite powder. Here, the arch core 54 is divided into three pieces, but the arch core 54 may be integrally formed.

〔coil〕
In the example of FIG. 2, the induction heating coil 52 is disposed on a virtual arc surface along the arc-shaped outer surface in order to perform induction heating in the arc-shaped portion of the fixing roller 45 (heating belt 48). Actually, for example, a resin cover (not shown) is arranged outside the fixing roller 45 (heating belt 48), and the induction heating coil 52 is arranged in a winding shape on the resin cover.

[Winding center]
Although not shown here, the induction heating coil 52 is wound in an oval shape in a plan view (as viewed from above in FIG. 2). That is, the fixing roller 45 (heating belt 48) has a length sufficient to cover the maximum sheet passing width of the sheet, and generates a magnetic field in substantially the entire longitudinal direction thereof. Also, it extends to a range slightly longer than the entire length of the fixing roller 45 and the like. Therefore, the induction heating coil 52 can induction heat the substantially entire region in the longitudinal direction of the fixing roller 45 and the like. On the other hand, in the cross section shown in FIG. 2, a magnetic field can be generated by substantially the upper half of the fixing roller 45 and the like. Therefore, the induction heating coil 52 can induction-heat substantially half of the circumference of the fixing roller 45 and the like. Such an induction heating coil 52 is formed around the winding center (reference numeral C in the drawing) in the cross section of FIG. 2, and the winding center substantially coincides with the center line of the fixing roller 45 and the like. In the following description, “winding center” refers to a center line (symbol C) viewed in the cross section shown in FIG.

  In the first example, a thermistor 62 (which may be a thermostat) is installed facing the outside of the fixing roller 45. The thermistor 62 can be disposed, for example, at a location where the magnetic field intensity by the induction heating coil 52 is high and does not interfere with the induction heating coil 52.

[Magnetic adjustment member]
In addition, the IH coil unit 50 is provided with a magnetic adjustment member 60 positioned between the induction heating coil 52 and the arch core 54. The magnetic adjustment member 60 is a non-magnetic metal (for example, oxygen-free copper) having a rectangular ring shape in plan view. Since it is ring-shaped, the inside of the magnetic adjustment member 60 is hollow (hollow), and the cross-sectional shape is shown only at both ends in FIG. However, as shown in FIG. 2, the magnetic adjustment member 60 is formed to be curved in an arc shape as a whole. The center of curvature of the magnetic adjustment member 60 is substantially coincident with the center of rotation of the fixing roller 45, for example, and the radius of curvature is larger than the virtual arc surface on which the induction heating coil 52 is disposed, and the induction heating coil. The length does not interfere with 52.

  FIG. 3 is a perspective view showing a structural example (1) of the magnetic adjustment member 60. As described above, the magnetic adjustment member 60 has a rectangular ring shape as a whole, and its four sides are constituted by a pair of linear portions 60a opposed in the width direction and a pair of arc portions 60b opposed in the longitudinal direction.

[Magnetic adjustment means]
The magnetic adjustment member 60 is supported by a support member 64 at one end in the longitudinal direction, for example. The support member 64 includes, for example, a fan-shaped side plate 64a and an arc-shaped top plate 64b. The side plate 64a extends downward from the top plate 64b as seen in FIG. 3, and a drive shaft 66 is attached to the main part thereof. The drive shaft 66 is connected to, for example, a drive mechanism (stepping motor and speed reduction mechanism) (not shown). When the drive shaft 66 is rotated by the drive mechanism, the magnetic adjustment member 60 can be displaced in the rotation direction together with the support member 64. it can.

  FIG. 4 is a perspective view showing a structural example (2) of the magnetic adjustment member 60. In this structural example (2), a flange portion 60c is formed on the pair of arc portions 60b. Thereby, the cross section of the magnetic adjustment member 60 can be enlarged in the circumferential direction, and the rigidity can be improved as a whole. In addition, the flange part may be formed on a pair of linear part 60a. Although not shown here, the magnetic adjustment member 60 can be supported by a support member similar to the structural example (1), and the magnetic adjustment member 60 can be displaced by a drive mechanism.

[Principle of magnetic shielding effect]
FIG. 5 is a conceptual diagram for explaining the principle of the magnetic shielding effect by the magnetic adjustment member 60. In FIG. 5, the magnetic adjustment member 60 is simplified as a simple wire model.

  5A: When a penetrating magnetic field (complex magnetic flux) is generated in the ring surface (virtual plane) in the vertical direction (one direction) with respect to the ring-shaped magnetic adjustment member 60, the magnetic adjustment member is thereby generated. An induced current is generated in 60 circumferential directions. Then, since a magnetic field (demagnetizing field) opposite to the penetrating magnetic field is generated by electromagnetic induction, they cancel each other and cancel the magnetic field. In this embodiment, this magnetic field canceling effect is used to shield magnetism.

  In FIG. 5, (B): As shown in the upper stage, a penetrating magnetic field is generated bidirectionally on the ring surface of the ring-shaped magnetic adjustment member 60. The case of (± 0) is assumed. In this case, almost no induced current is generated in the magnetic adjustment member 60. Therefore, the magnetic adjustment member 60 hardly exhibits the magnetic field canceling effect, and the bidirectional magnetic field passes through the magnetic adjustment member 60. The same applies to the case where the magnetic field passes in the U-turn direction inside the magnetic adjustment member 60 as shown in the lower part. In the present embodiment, the induction heating efficiency is increased by retracting the magnetic adjustment member 60 to a position where the magnetic field canceling effect cannot be obtained.

  FIG. 5C shows a case where a magnetic field (complex magnetic flux) is generated substantially in parallel with the ring surface of the ring-shaped magnetic adjustment member 60. In this case as well, almost no induced current is generated in the magnetic adjustment member 60, and therefore no magnetic field canceling effect is generated. Although not employed in the present embodiment, the evacuation technique is mainly used in the prior art. However, in order to obtain such a magnetic field environment around the induction heating coil 52, it is necessary to greatly displace the magnetic adjustment member 60, and the movable space increases accordingly.

  The inventors of the present invention pay attention to the fact that both the magnetic shielding effect and the magnetic shielding effect can be obtained by switching between (A) and (B) in FIG. 5, and the magnetic adjustment member 60 is retracted from the shielding position. The optimum magnetic adjustment method has been found by displacing to the position. Hereinafter, an example of the magnetic adjustment method will be described.

[Example of magnetic adjustment method]
FIG. 6 is a diagram illustrating a magnetic adjustment method using the magnetic adjustment member 60. 6A shows a state in which the magnetic adjustment member 60 is displaced to the shielding position, and FIG. 6B shows a state in which the magnetic adjustment member 60 has been displaced to the retracted position.

[Shielding position]
6A: Normally, when the induction heating coil 52 is energized, it passes through the side core 56 and the arch core 54 around it, passes through the air gap in the longitudinal direction at the position of the winding center C, and is heated. A magnetic path reaching 48 is formed. At this time, if the magnetic adjustment member 60 is placed in the middle of the magnetic path passing through the winding center C, the magnetic field is canceled according to the principle shown in FIG. Can be shielded. In such a shielding position, it is desirable that the ring center (center line of the ring surface) of the magnetic adjustment member 60 and the winding center (symbol C) as viewed in the cross section shown in FIG. .

[Evacuation position]
In FIG. 6, (B): On the other hand, when the position of the magnetic adjustment member 60 is shifted from the winding center C, for example, when it is displaced to a position overlapping the winding region of the induction heating coil 52 on one side, it passes through the winding center C. The shielding of the magnetic path is released and the magnetic field is generated satisfactorily. At this time, due to the principle shown in the lower part of FIG. 5B, the magnetic adjustment member 60 has almost no magnetic field canceling effect. Therefore, the magnetic field strength of the induction heating coil 52 is not hindered with the magnetic adjustment member 60 displaced to the retracted position. Thereby, the heating belt 48 can be induction-heated with high efficiency, and the warm-up time can be shortened. In such a retracted position, the ring center (symbol L in the drawing) of the magnetic adjustment member 60 is not coaxially overlapped with the winding center C (non-coaxial).

〔Condition setting〕
Next, the condition setting found by the inventors of the present invention will be described with an example. First, the magnetic adjustment member 60 is preferably a non-magnetic and well-conductive member in order to suppress Joule heat generation due to an induced current and efficiently shield the magnetism, and oxygen-free copper or the like is used as the material as described above. In addition, in order to improve the conductivity of the magnetic adjustment member 60, it is necessary to select a material having as small a specific resistance as possible and to increase the thickness of the material. Under the conditions found by the inventors of the present invention, the thickness of the magnetic adjustment member 60 is preferably 0.5 mm or more, and in this example, a thickness of 1 mm is used.

  Moreover, about the angle which displaces the magnetic adjustment member 60, the inventors of this invention have shown the following conditions. For example, as shown in FIG. 6B, a horizontal line (this is a horizontal line in FIG. 6 and different from the mounted state) passing through the center of the shaft center of the fixing roller 45 is a reference angle. (= 0 °). When the angle (deg) of the ring center L of the magnetic adjustment member 60 is taken in the counterclockwise direction from the center, the above-described shielding position is optimally 90 °. On the other hand, the optimum condition can be set for the angle α of the retracted position based on the following concept.

  FIG. 7 is a distribution curve representing the intensity distribution of the radial magnetic field viewed around the fixing roller 45 (360 °). In FIG. 7, the horizontal axis represents the angle (deg) in the counterclockwise direction from the reference angle (= 0 °), and the vertical axis represents, for example, the radial magnetic field (A / m). Here, assuming that the magnetic adjustment member 60 is displaced to the retracted position and the magnetic field canceling effect is not working, the radial magnetic field has intensity peaks in the vicinity of 0 °, 90 °, and 180 °. It can be seen that almost no magnetic field is generated near 270 ° (directly below) where the induction heating coil 52 is not disposed.

  In such a magnetic field distribution, first, a point P at which the radial magnetic field becomes 0 on the distribution curve is taken, and values obtained by integrating the distribution curves in the 0 ° direction and 90 ° direction from this point P are the same (area S1 in the figure). = [Alpha] 1, [alpha] 2 is obtained as S2). It can be seen that if the magnetic adjustment member 60 is arranged within the range of the angles α1 to α2 thus obtained, the balance of the magnetic field becomes 0 at the retracted position, and as a result, the magnetic field is not inhibited.

Then, an angle (= (α1 + α2) / 2) that is the midpoint between the angles α1 and α2 on the horizontal axis is obtained, and this is set as the angle of the ring center L at the retracted position. When the distance from the center of the fixing roller 45 to the magnetic adjustment member 60 is a radius r, the length of a virtual arc located within the range of the angles α1 to α2 at the radius r is the optimum of the magnetic adjustment member 60. Ring width. In this example, the ring width W can be obtained by the following equation.
W = r × {(α2−α1) / 180} × π

  As described above, the optimum condition is obtained by setting the ring width of the magnetic adjustment member 60 to W (formula), the angle of the ring center at the retracted position to (α1 + α2) / 2, and the angle of the ring center at the shield position to 90 °. Can be set. In particular, since the balance of the magnetic field (areas S1, S2) is exactly 0 inside the ring at the retracted position, the generation of the magnetic field by the induction heating coil 52 is not hindered.

[Configuration example of magnetic adjustment member]
Next, FIG. 8 is a diagram illustrating a plurality of arrangement examples related to the magnetic adjustment member in a plan view. The vertical direction in FIG. 8 corresponds to the longitudinal direction of the fixing roller 45 (not shown in FIG. 8).

  8A: In this arrangement example, the magnetic adjustment member 60 has a single rectangular ring shape as described above, and is divided into two in the longitudinal direction. The magnetic adjustment member 60 is provided on both outer sides of the minimum sheet passing width W1 orthogonal to the sheet passing direction, and the magnetic adjusting member 60 is provided only slightly within the range of the minimum sheet passing width W1. The magnetic adjustment member 60 reaches slightly outside the maximum sheet passing width W2 at both ends of the fixing roller 45. The minimum sheet passing width W1 and the maximum sheet passing width W2 are determined by the minimum or maximum size sheet that can be printed by the image forming apparatus 1.

  FIG. 8B: In this arrangement example, three magnetic adjustment members 70, 72, 74 are arranged on both sides. Each of the magnetic adjustment members 70, 72, and 74 has a rectangular ring shape, but their ring widths are different in the longitudinal direction. That is, the magnetic adjustment member 74 closest to the minimum sheet passing region has the smallest ring width, and the ring widths are set larger in the order of the magnetic adjustment members 72 and 70 located on the outer side.

  8C: In this arrangement example, two magnetic adjustment members 80 are arranged on both sides, and the number of magnetic adjustment members 80 is the same as that in FIG. 8A, but each magnetic adjustment member 80 is a trapezoidal ring. The difference is that two bridge portions 80a are provided on the inner side. That is, each magnetic adjustment member 80 has the shortest ring width at a position close to the center in the longitudinal direction, and the ring width is gradually expanded from there toward both side ends. The bridge portions 80a are arranged at intervals in the longitudinal direction, and three rings are formed in one magnetic adjustment member 80 by the bridge portions 80a.

[Corresponding to size switching]
Correspondence to the paper size (paper passing width) is realized by switching the positions of the magnetic adjustment members 60 to 80 and partially shielding the magnetic field. At this time, the positions of the magnetic adjustment members 60 to 80 are slightly changed in accordance with the paper size (paper passing width), and the magnetic shielding amount is reduced as the paper size becomes larger, and conversely, the shielding amount is increased as the paper size becomes smaller. By doing so, it is possible to prevent the both end portions of the heating belt 48 from overheating. In the following description, in order to prevent complication, the notation of “magnetic adjustment member 60” is unified, but in that case, the magnetic adjustment members 70, 72, 74, 80, etc. of the arrangement example shown in FIG. Shall be.

[Second example]
Next, FIG. 9 is a longitudinal sectional view showing a structural example (second example) of the fixing unit 14. Further, FIG. 9 shows a magnetic adjustment method using the magnetic adjustment member 60 together. 9A shows a state where the magnetic adjustment member 60 is displaced to the shielding position, and FIG. 9B shows a state where the magnetic adjustment member 60 is displaced to the retracted position.

  The second example is different from the first example in that the magnetic adjustment member 60 is displaced between the induction heating coil 52 and the fixing roller 45 (heating belt 48). The other configurations are the same as those in the first example, and here, the same reference numerals are given to items that are the same as those already described, and redundant descriptions thereof will be omitted.

[Shielding position]
9 (A): Also in the second example, when the induction heating coil 52 is energized, it passes through the side core 56 and the arch core 54 around it and passes through the air gap in the longitudinal direction at the position of the winding center C. Thus, a magnetic path reaching the heating belt 48 is formed. At this time, if the magnetic adjustment member 60 is placed in the middle of the magnetic path passing through the winding center C at a position between the induction heating coil 52 and the fixing roller 45, the magnetic field is generated according to the principle shown in FIG. Canceled. Therefore, also in the second example, the magnetism can be shielded within the range of the magnetic adjustment member 60. Also in the second example, at the shielding position, the ring center (center line of the ring surface) of the magnetic adjustment member 60 and the above-described winding center (symbol C) as seen in the cross section shown in FIG. desirable.

[Evacuation position]
In FIG. 9, (B): On the other hand, the position of the magnetic adjustment member 60 is shifted from the winding center C and overlaps, for example, the winding region of the induction heating coil 52 on one side between the induction heating coil 52 and the fixing roller 45. When displaced to the position, the shielding of the magnetic path passing through the winding center C is released, and a magnetic field is generated satisfactorily. Similarly, in the second example, the magnetic adjustment member 60 almost has a magnetic field canceling effect according to the principle shown in the lower part of FIG. 5B. Therefore, the magnetic field strength of the induction heating coil 52 is inhibited at the retracted position. There is no. Also in the second example, the ring center of the magnetic adjustment member 60 (symbol L in the figure) does not overlap with the winding center C on the retracted position (non-coaxial).

  As for other condition settings, those shown in the first example can be applied. In the second example, since the distance (radius r) from the center of the fixing roller 45 to the magnetic adjustment member 60 is smaller than in the first example, the ring width is reduced accordingly.

[Third example]
FIG. 10 is a longitudinal sectional view showing a structural example (third example) of the fixing unit 14. The fixing unit 14 of the third example has a structure in which a heat roller 46 is provided in the vicinity of the fixing roller 45, and a heating belt 48 is wound around the heat roller 46 and the fixing roller 45. The core of the heat roller 46 is, for example, iron, and a release layer (for example, PFA) is formed on the surface thereof.

  In the third example, induction heating is performed at the arc-shaped portions of the heating belt 48 and the heat roller 46. That is, the magnetic field generated by the induction heating coil 52 passes through the air gap at the positions of the side core 56, the arch core 54 and the winding center, passes through the heating belt 48 and the heat roller 46, and induction-heats them.

  In the third example, similarly to the first example, the magnetism can be shielded within the range of the magnetism adjusting member 60 by moving the magnetism adjusting member 60 to the shielding position. Thereby, it is possible to reliably prevent an excessive temperature rise at both ends of the heating belt 48 and the heat roller 46 during size switching. In the case of a large size paper, the magnetic shielding member 60 is moved to the retracted position to cancel the magnetic shielding effect, and the heating belt 48 and the heat roller 46 can be warmed up early.

  10 shows an example in which the magnetic adjustment member 60 is disposed between the induction heating coil 52 and the heating belt 48 (heat roller 46), the induction heating coil 52 and the arch core 54 are arranged as in the first example. The magnetic adjustment member 60 may be disposed between the magnetic adjustment member 60 and the magnetic adjustment member 60 may be displaced between them.

[Fourth example]
Next, FIG. 11 is a longitudinal sectional view showing a structural example (fourth example) of the fixing unit 14. The fixing unit 14 of the fourth example is different from the first to third examples in that it includes an inclusion type IH coil unit 50. The configuration of the magnetic adjustment member 60 may be the same as in the first to third examples.

  That is, the fixing unit 14 of the fourth example includes a pressure roller 44 and a heat roller 46, and fixes a toner image while conveying a sheet between these nips. Since the heat roller 46 is made of metal, this structure is suitable for fixing monochrome images. However, a structure in which a flat nip is formed between the heat roller 46 and the pressure roller 44 by providing an elastic layer on the surface layer may be employed. In this case, as in the first to third examples, it is suitable for fixing a full-color image.

  The internal type IH coil unit 50 includes an induction heating coil 52 and a ferrite core 55 provided inside the heat roller 46. That is, the induction heating coil 52 is disposed along the inner peripheral surface of the heat roller 46, and the center of the winding extends in the horizontal direction from, for example, the axis of the heat roller 46 as viewed in FIG.

  The ferrite core 55 is configured by combining two pieces in a T-shaped cross section. Of these, one piece extends along the winding center of the induction heating coil 52, and the other piece extends in the radial direction across the winding center.

[Shielding position]
In FIG. 11, (A): In the encapsulated IH coil unit 50, when the induction heating coil 52 is energized, it passes through a part of the heat roller 46 from the ferrite core 55 to the periphery of the induction heating coil 52 at the position of the winding center. A magnetic path for converging the magnetic field is formed in the ferrite core 55. Even in such an internal type IH coil unit 50, if the magnetic adjustment member 60 is placed in the middle of the magnetic path passing through the center of the winding, the magnetic field is canceled based on the principle shown in FIG. Magnetism can be shielded within the range of the adjusting member 60. In the shielding position, it is assumed that the ring center (center line of the ring surface) of the magnetic adjustment member 60 and the above-described winding center as viewed in the cross section shown in FIG.

[Evacuation position]
In FIG. 11 (B): On the other hand, when the position of the magnetic adjustment member 60 is shifted from the winding center, for example, when it is displaced to a position overlapping the winding region of the induction heating coil 52 on one side (upper side in FIG. 11), The shielding of the magnetic path passing through the center of the winding is released and a magnetic field is generated satisfactorily. At this time, according to the principle shown in the lower part of FIG. 5B, the magnetic adjustment member 60 has almost no magnetic field canceling effect, so that the magnetic field strength of the induction heating coil 52 is not hindered. Thereby, the heat roller 46 can be induction-heated with high efficiency and the warm-up time can be shortened. Also in the fourth example, the ring center of the magnetic adjustment member 60 is not coaxially overlapped with the winding center at the retracted position (non-coaxial).

  In the fourth example, similarly to the first example, the magnetism can be shielded within the range of the magnetism adjusting member 60 by moving the magnetism adjusting member 60 to the shielding position. Thereby, it is possible to reliably prevent an excessive temperature increase at both end portions of the heat roller 46 during size switching. In the case of a large size paper, the magnetic shielding member 60 is moved to the retracted position to cancel the magnetic shielding effect, and the heat roller 46 can be warmed up early.

  11 shows an example in which the magnetic adjustment member 60 is arranged between the induction heating coil 52 and the heat roller 46, the ferrite core 55 arranged along the center of the winding is shortened. The magnetic adjustment member 60 may be arranged inside the induction heating coil 52 using the space of minutes.

  The present invention can be implemented with various modifications without being limited to the above-described embodiments. The shape and arrangement of the magnetic adjustment member 60 are not limited to those shown in FIG. 8, and other shapes and arrangements may be employed.

  In the third example of the fixing unit 14, the IH coil unit 50 may be disposed at a planar position in addition to the arc-shaped position of the heating belt 48. In this case, the magnetic adjustment member 60 has a planar shape as a whole and is displaced by sliding in a linear direction between the induction heating coil 52 and the arch core 54 or between the induction heating coil 52 and the heating belt 48. May be.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. FIG. 3 is a longitudinal sectional view showing a structural example (first example) of the fixing unit. It is a perspective view which shows the structural example (1) of a magnetic adjustment member. It is a perspective view which shows the structural example (2) of a magnetic adjustment member. It is a conceptual diagram for demonstrating the principle of the magnetic shielding effect by a magnetic adjustment member. It is a figure which shows the adjustment method of the magnetism using a magnetic adjustment member. 6 is a distribution curve representing the intensity distribution of the radial magnetic field viewed around the fixing roller. It is the figure which showed the some example of arrangement | positioning regarding a magnetic adjustment member by planar view. FIG. 6 is a longitudinal sectional view showing a structural example (second example) of the fixing unit. FIG. 6 is a longitudinal sectional view showing a structural example (third example) of the fixing unit. FIG. 10 is a longitudinal sectional view showing a structural example (fourth example) of the 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 60 Magnetic adjustment member 62 Thermistor

Claims (13)

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 disposed along an outer surface of the heating member and formed around a predetermined winding center to generate a magnetic field for inductively heating the heating member;
A core that is disposed on the opposite side of the heating member across the coil, and is made of a magnetic material to form a magnetic path that passes through the winding center around the coil;
A nonmagnetic metal magnetic adjustment member formed in a ring shape around a predetermined ring center;
The position of the magnetic adjustment member is a shielding position where the magnetism is shielded by overlapping the ring center and the winding center substantially coaxially in the middle of the magnetic path reaching the heating member through the winding center, Magnetic adjustment means for displacing the ring center and the winding center out of the magnetic path to a retracted position where the passage of magnetism is allowed by being non-coaxial ,
The magnetic adjustment member is
When a magnetic field penetrates inside the ring shape at the shielding position, a magnetic field is shielded by generating a demagnetizing field opposite to the penetrating magnetic field from an induced current generated in a circumferential direction, while the retracted position Then, the image forming apparatus is characterized in that the passage of magnetism is allowed by passing a magnetic field bidirectionally inside the ring shape . A fixing unit that fixes the toner image onto the sheet by at least heat from the heating member is conveyed by sandwiching the sheet on which the toner image is transferred in the image forming unit between the heating member and the pressure member. An image forming apparatus comprising:
The fixing unit includes:
A coil that is disposed along the inner surface of the heating region as viewed in the circumferential direction of the heating member, and that is formed around a predetermined winding center to generate a magnetic field for induction heating the heating member in the heating region; ,
A core that is disposed inside the heating member together with the coil, and is made of a magnetic material so as to form a magnetic path passing through the winding center of the coil inside the heating member;
A nonmagnetic metal magnetic adjustment member formed in a ring shape around a predetermined ring center;
The position of the magnetic adjustment member is a shielding position where the magnetism is shielded by overlapping the ring center and the winding center substantially coaxially in the middle of the magnetic path reaching the heating member through the winding center, Magnetic adjustment means for displacing the ring center and the winding center out of the magnetic path to a retracted position where the passage of magnetism is allowed by being non-coaxial ,
The magnetic adjustment member is
When a magnetic field penetrates inside the ring shape at the shielding position, a magnetic field is shielded by generating a demagnetizing field opposite to the penetrating magnetic field from an induced current generated in a circumferential direction, while the retracted position Then, the image forming apparatus is characterized in that the passage of magnetism is allowed by passing a magnetic field bidirectionally inside the ring shape . The image forming apparatus according to claim 1, wherein
The magnetic adjustment member is
A rectangular ring shape that is divided into a plurality of parts when viewed in the longitudinal direction of the heating member, and the individual ring widths as viewed in the circumferential direction of the heating member are different, and is the smallest sheet of paper conveyed by the fixing unit An image forming apparatus, wherein the ring width is set to a minimum in the vicinity of a sheet passing area . 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 disposed along an outer surface of the heating member and formed around a predetermined winding center to generate a magnetic field for inductively heating the heating member;
A core that is disposed on the opposite side of the heating member across the coil, and is made of a magnetic material to form a magnetic path that passes through the winding center around the coil;
A nonmagnetic metal magnetic adjustment member formed in a ring shape around a predetermined ring center;
The position of the magnetic adjustment member is a shielding position where the magnetism is shielded by overlapping the ring center and the winding center substantially coaxially in the middle of the magnetic path reaching the heating member through the winding center, Magnetic adjustment means for displacing the ring center and the winding center out of the magnetic path to a retracted position where the passage of magnetism is allowed by being non-coaxial,
The magnetic adjustment member is
A rectangular ring shape that is divided into a plurality of parts when viewed in the longitudinal direction of the heating member, and the individual ring widths as viewed in the circumferential direction of the heating member are different, and is the smallest sheet of paper conveyed by the fixing unit An image forming apparatus, wherein the ring width is set to a minimum in the vicinity of a sheet passing area .   A fixing unit that fixes the toner image onto the sheet by at least heat from the heating member is conveyed by sandwiching the sheet on which the toner image is transferred in the image forming unit between the heating member and the pressure member. An image forming apparatus comprising:
  The fixing unit includes:
  A coil that is disposed along the inner surface of the heating region as viewed in the circumferential direction of the heating member, and that is formed around a predetermined winding center to generate a magnetic field for induction heating the heating member in the heating region; ,
  A core that is disposed inside the heating member together with the coil, and is made of a magnetic material so as to form a magnetic path passing through the winding center of the coil inside the heating member;
  A nonmagnetic metal magnetic adjustment member formed in a ring shape around a predetermined ring center;
  The position of the magnetic adjustment member is a shielding position where the magnetism is shielded by overlapping the ring center and the winding center substantially coaxially in the middle of the magnetic path reaching the heating member through the winding center, Magnetic adjustment means for displacing the ring center and the winding center out of the magnetic path to a retracted position where the passage of magnetism is allowed by being non-coaxial,
  The magnetic adjustment member is
  A rectangular ring shape that is divided into a plurality of parts when viewed in the longitudinal direction of the heating member, and the individual ring widths as viewed in the circumferential direction of the heating member are different, and is the smallest sheet of paper conveyed by the fixing unit An image forming apparatus, wherein the ring width is set to a minimum in the vicinity of a sheet passing area. The image forming apparatus according to claim 1,
The magnetic adjustment means includes
An image forming apparatus, wherein the magnetic adjustment member is displaced between the coil and the core. The image forming apparatus according to claim 1,
The magnetic adjustment means includes
An image forming apparatus, wherein the magnetic adjustment member is displaced between the heating member and the coil. An image forming apparatus according to any one of claims 1 to 7,
The magnetic adjustment means includes
2. An image forming apparatus according to claim 1, wherein a position where a current flowing in a circumferential direction of the magnetic adjustment member is substantially zero when the magnetic field is generated by the coil is set as the retracted position. The image forming apparatus according to any one of claims 1 to 8 ,
The magnetic adjustment means includes
An image forming apparatus, wherein the magnetic shielding member is reciprocated between the retracted position and the shielding position, and a magnetic shielding amount can be adjusted according to a displacement amount between the reciprocating position and the shielding position. An image forming apparatus according to any one of claims 1 to 9,
The magnetic adjustment member is
An image forming apparatus comprising a conductor having a width dimension of 1 mm to 5 mm and a thickness of 0.5 mm to 3 mm. An image forming apparatus according to any one of claims 1 to 10,
The image forming apparatus, wherein the magnetic adjustment member is made of a nonmagnetic metal made of copper. An image forming apparatus according to any one of claims 1 to 11,
An image forming apparatus, wherein the heating member is a metal roller. The image forming apparatus according to any one of claims 1 to 12 ,
An image forming apparatus, wherein the heating member is a metal belt.

Images