JP2006163200A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an excessive temperature rise of the paper non-passing area of a heat generation body by a small structure. <P>SOLUTION: A fixing device includes a coil 230 for generating a magnetic flux; a heat generation roller 210 induced and heated by the magnetic flux; a core 240 to be disposed opposite the heat generation roller 210 via the coil 230 between them; a magnetic shield body 250 disposed between the coil 230 and the core 240 and used to open or close a magnetic path corresponding to the paper non-passaging area of the heat generation roller 210; and a displacing means for displacing the magnetic shield body 250 between a magnetic path shielding position that is the winding center of the coil 230 and a magnetic path uncovering position that is part of the winds of the coil 230. Thus, the magnetic shield body 250 is displaced from the part of the winds of the coil 230 to the winding center without sticking out from both ends of the coil 230 and shields the magnetic path corresponding to the paper non-passaging area of the heat generation roller 210. This makes it possible to prevent an excessive temperature rise of the paper non-passaging area of the heat generation roller 210 by the small structure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device that heats and fixes an unfixed image on a recording medium using electromagnetic induction heating type heating means, and more particularly to an image forming apparatus such as an electrophotographic type or electrostatic recording type copying machine, facsimile, and printer. The present invention relates to a fixing device that is useful for use.

  In an induction heating (IH) type fixing device, an eddy current is generated in a heating element by a magnetic field and formed on a recording medium such as transfer paper and an OHP sheet by Joule heat of the heating element by the eddy current. The fixed unfixed image is heat-fixed on the recording medium.

  This electromagnetic induction heating type fixing device has an advantage that heat generation efficiency is high and the rise time until heat is generated at a predetermined fixing temperature can be shortened as compared with a heat roller type fixing device using a halogen lamp as a heat source. Have.

  However, in a fixing device using a film-like fixing belt or sleeve having a small heat capacity as the heating element, even when the recording medium is passed, the heat of the heating element is taken away and the temperature of the sheet passing area is lowered. . Thus, in this type of fixing device, the heating element is heated in a timely manner so that the temperature of the sheet passing area is maintained at a predetermined fixing temperature. For this reason, in a fixing device using a heating element having a small heat capacity, when a recording medium having a small size is continuously fed, the heating element is continuously heated, and the temperature of the non-sheet passing area is changed. This causes a phenomenon that the temperature becomes abnormally higher than the temperature, that is, an excessive temperature rise phenomenon in a non-sheet passing region.

  In order to prevent the heating element from exceeding the heat resistance temperature due to this excessive temperature rise in the non-sheet passing area, the number of sheets of the recording medium can be limited and the interval between the sheets to be passed can be increased. However, all of these measures reduce the printing efficiency (number of prints per unit time).

  Conventionally, as a fixing device that solves such a problem, only the magnetic flux that acts on the non-sheet passing region of the heating element is moved in the heating width direction of the heating element among the magnetic flux of the magnetic flux generating means that electromagnetically heats the heating element. What prevents the excessive temperature rise of a non-paper passing area | region by shielding with a possible magnetic shielding body (magnetic-flux shielding board) is known (for example, refer patent document 1 and patent document 2 etc.).

Further, as another fixing device for solving the above problem, a second magnetic core corresponding to the non-sheet passing region is disposed behind the first magnetic core of the magnetic flux generating means for electromagnetically heating the heating element. It is known that the temperature distribution in the longitudinal direction of the heating element is changed by changing the gap between the first magnetic core and the second magnetic core (for example, see Patent Document 3).
Japanese Patent Laid-Open No. 10-74009 JP 2003-123957 A JP 2003-123961 A

  However, since the fixing devices described in Patent Document 1 and Patent Document 2 are configured to advance and retract the magnetic shield in the heat generation width direction with respect to the non-sheet passing region of the heat generator, the magnetic shield is configured to be at both end portions of the magnetic flux generating means. There is a problem that the fixing device main body is enlarged due to a large protrusion. Further, since the fixing devices described in Patent Document 1 and Patent Document 2 have a configuration in which the magnetic shield is disposed inside the heating element, the heat dissipation performance is poor and the magnetic shielding body itself is excessively heated.

  Further, in the fixing device described in Patent Document 3, the distance between the first magnetic core and the heating element does not change even when the second magnetic core is displaced with respect to the first magnetic core. The magnetic gap between the area and the non-sheet passing area is constant. For this reason, in this fixing device, the magnetic flux wraps around from the end of the sheet passing area corresponding to the first magnetic core to the end of the non-sheet passing area corresponding to the second magnetic core, and the heating element The effect of suppressing the magnetic flux in the non-sheet passing region is lowered. Therefore, in this fixing device, when a small-sized recording medium is continuously passed, heat accumulates in the non-sheet passing area of the heating element, and it is difficult to effectively suppress overheating.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device that can prevent an excessive temperature increase in a non-sheet passing region of a heating element with a small configuration.

  In order to solve such a problem, a fixing device of the present invention includes a coil that generates magnetic flux, a heating element that is induction-heated by the magnetic flux, a core that is disposed on the opposite side of the heating element across the coil, A magnetic shield disposed between the coil and the core to open and close a magnetic path corresponding to a non-sheet passing region of the heating element; a magnetic path blocking position which is a winding center of the coil; and a winding portion of the coil And a displacement means for displacing the magnetic shield at a magnetic path release position.

  According to the present invention, the magnetic shield is displaced from the winding portion of the coil to the winding center without protruding from both ends of the coil, and the magnetic path corresponding to the non-sheet passing region of the heating element is cut off. With this configuration, it is possible to prevent overheating of the non-sheet passing region of the heating element.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, components having the same configuration or function and corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

(Embodiment 1)
First, an image forming apparatus suitable for mounting the fixing device according to the first embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus equipped with a fixing device according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the image forming apparatus 100 includes an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 101, a charger 102, a laser beam scanner 103, a developing device 105, a paper feeding device 107, and a cleaning device 113. And a fixing device 200.

  In FIG. 1, the surface of the photosensitive drum 101 is uniformly charged to a predetermined negative dark potential by the charger 102 while being rotated at a predetermined peripheral speed in the direction of the arrow.

  The laser beam scanner 103 outputs a laser beam 104 modulated in accordance with a time-series electric digital pixel signal of image information input from a host device such as an image reading device or a computer (not shown), and is uniformly charged. The surface of the photosensitive drum 101 is scanned and exposed by a laser beam 104. As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 101 decreases to a bright potential, and an electrostatic latent image is formed on the surface of the photosensitive drum 101.

  The developing device 105 includes a developing roller 106 that is driven to rotate. The developing roller 106 is disposed to face the photosensitive drum 101, and a thin layer of toner is formed on the outer peripheral surface thereof. Further, a developing bias voltage whose absolute value is smaller than the dark potential of the photosensitive drum 101 and larger than the bright potential is applied to the developing roller 106.

  As a result, the negatively charged toner on the developing roller 106 adheres only to the light potential portion on the surface of the photosensitive drum 101, and the electrostatic latent image formed on the surface of the photosensitive drum 101 is reversely developed and developed. As a result, an unfixed toner image 111 is formed on the photosensitive drum 101.

  On the other hand, the paper feeding device 107 feeds the recording paper 109 as a recording medium one sheet at a time by the paper feeding roller 108. The recording paper 109 fed from the paper feeding device 107 passes through a pair of registration rollers 110 and is fed to the nip portion between the photosensitive drum 101 and the transfer roller 112 at an appropriate timing synchronized with the rotation of the photosensitive drum 101. As a result, the unfixed toner image 111 on the photosensitive drum 101 is transferred onto the recording paper 109 by the transfer roller 112 to which a transfer bias is applied.

  The recording paper 109 to which the unfixed toner image 111 is transferred in this way is separated from the photosensitive drum 101 and then guided by the recording paper guide 114 and conveyed toward the fixing portion of the fixing device 200. The fixing device 200 heat-fixes the unfixed toner image 111 on the recording paper 109 conveyed to the fixing portion.

  The recording paper 109 on which the unfixed toner image 111 is heat-fixed passes through the fixing device 200 and then is discharged onto a paper discharge tray 115 provided outside the image forming apparatus 100.

  On the other hand, the photosensitive drum 101 from which the recording paper 109 has been separated is subjected to the subsequent image formation repeatedly by removing residuals such as transfer residual toner on the surface thereof by the cleaning device 113.

  Next, the fixing device 200 of the image forming apparatus 100 will be described. FIG. 2 is a schematic cross-sectional view showing the configuration of the main part of the fixing device according to Embodiment 1 of the present invention. FIG. 3 is a schematic cross-sectional view showing an operation mode of the magnetic shield in the fixing device according to Embodiment 1 of the present invention. FIG. 4 is a schematic plan view for explaining an operation mode of the fixing device according to the first embodiment of the present invention.

  As shown in FIG. 2, the fixing device 200 according to the first embodiment includes a heating roller 210 as a heating element, a pressure roller 220, a coil 230, a core 240, a magnetic shield 250, a temperature sensor 260, and the like. ing.

  In FIG. 2, the heat generating roller 210 is formed of a cylindrical roller member having a diameter of 34 (mm), for example, and is rotatably supported on a main body side plate (not shown) of the fixing device 200. As a material for the heat roller 210, for example, a magnetic material such as iron or nickel is preferably used. Since the heat generating roller 210 made of a magnetic material increases the magnetic flux, the heat generation efficiency can be improved.

  The pressure roller 220 is rotatably supported on the main body side plate of the fixing device 200 so as to form a fixing nip through which the recording paper 109 passes by being in pressure contact with the heat generating roller 210 across the sheet passing path of the recording paper 109. Yes.

  The pressure roller 220 is rotated in a direction (clockwise in the drawing) in which the recording paper 109 on which the toner image 111 is formed and carried is conveyed in the direction of the arrow by a driving unit (not shown). The heating roller 210 is driven to rotate by the rotation of the pressure roller 220. Here, although the heat roller 210 is configured to rotate following the pressure roller 220, the pressure roller 220 may be configured to rotate following the heat roller 210.

  The pressure roller 220 is preferably made of a material having low thermal conductivity such as silicon rubber having a hardness of JISA 30 degrees. As a material of the pressure roller 220, for example, heat-resistant resin such as fluoro rubber and fluoro resin, or other rubber may be used.

  Further, it is desirable that the pressure roller 220 is coated on the outer peripheral surface with a coating material in which resin or rubber such as PTFE, PFA, or FEP is used alone or mixed in order to improve wear resistance and releasability.

  The coil 230 is formed, for example, by rotating a litz wire, which is a bundle of thin copper wires, into a semi-cylindrical shape so as to face the outer peripheral surface of the upper half of the heat generating roller 210. The coil 230 generates a magnetic flux by generating a magnetic flux around it when a voltage is applied from a power source (not shown) and an alternating current flows.

  The core 240 includes an arch core 241 formed so as to cover the outer peripheral surface of the coil 230 and side cores 242 disposed on both side portions of the arch core 241. Of the magnetic flux generated by the coil 230, the heating roller 210. The magnetic path of the magnetic flux generated on the opposite side is formed.

  The core 240 is preferably formed of a magnetic material having a high magnetic permeability and specific resistance, such as ferrite and permalloy. That is, since ferrite is ferromagnetic, magnetic flux is strengthened and heat generation efficiency is improved. Further, since ferrite has high thermal conductivity and specific heat, it is possible to suppress the temperature rise of the magnetic shield 250 by absorbing heat generated in the magnetic shield 250.

  The magnetic shield 250 is rotatable between a coil 230 and a core 240 at a portion facing a non-sheet passing area of the heat generating roller 210 when a small size recording sheet 109 is passed through the fixing nip. Is arranged. Then, the magnetic shield 250 has a magnetic path cutoff position that is a winding center of the coil 230 shown in FIG. 2 and a magnetic path release position that is a winding part of the coil 230 shown in FIG. It is displaced to.

  A large eddy current flows through the magnetic shield 250 due to the action of the magnetic field between the coil 230 and the core 240, and a repulsive magnetic field is generated in the direction that cancels the magnetic flux generated from the coil 230.

  As a result, as shown in FIG. 2, in a state where the magnetic shield 250 is displaced to the magnetic path blocking position that is the winding center of the coil 230, the non-sheet passing region of the heat roller 210 with the small size paper width Lmin shown in FIG. 4. Is weakened by a repulsive magnetic field generated by the magnetic shield 250. Further, the magnetic flux acting on the non-sheet passing area having the small size paper width Lmin is weakened, thereby suppressing the heat generation in the non-sheet passing area of the heating roller 210 when the small size recording paper 109 is passed.

  On the other hand, as shown in FIG. 3, in a state where the magnetic shield 250 is displaced to a magnetic path opening position (a position indicated by a broken line in FIG. 4) that is a winding part of the coil 230, at least the heating roller 210 shown in FIG. The paper passing area having the maximum size paper width Lmax generates heat uniformly by the action of the magnetic field.

  As described above, in the fixing device 200, the heat generation width of the heat generation roller 210 can be switched by switching the position of the magnetic shield 250 according to the size of the recording paper 109 passed through the fixing nip.

  Here, the arrangement position of the magnetic shield 250 is determined in accordance with the sheet passing reference of the recording sheet 109 to the fixing nip. That is, when the sheet passing reference of the recording paper 109 is the center reference, as shown in FIG. 4, the pair of magnetic shields 250 are opposed to the two non-sheet passing regions generated at both ends of the small size sheet width Lmin. Respectively. Further, when the sheet passing reference of the recording paper 109 is the one-side reference, one magnetic shield 250 is disposed at a position facing one non-sheet passing region at one end of the small size sheet width Lmin.

  As a material of the magnetic shield 250, a conductive material such as aluminum or copper having a small specific resistance is suitable. In addition, the thickness of the magnetic shield 250 is preferably equal to or greater than the skin depth in order to reduce the resistance, and is preferably about 1 mm, for example. Thus, by making resistance low, heat_generation | fever of magnetic shielding body 250 itself can be suppressed.

  The temperature sensor 260 is provided so as to be in contact with the outer peripheral surface of the heat generating roller 210 in the rotational direction downstream of the coil 230 and detects the temperature of the heat generating roller 210. When the temperature sensor 260 detects that the temperature of the heat generating roller 210 has reached a temperature suitable for fixing the unfixed toner image 111, the control unit (not shown) starts the operation of the paper feed roller 108, that is, the start of the printing operation. It becomes possible.

  When the temperature sensor 260 detects that the temperature of the heat generating roller 210 has become higher than a predetermined threshold, the supply of alternating current from the power source (not shown) to the coil 230 is controlled.

  In addition, although the core 240 in this example has a semicircular cross-sectional shape, the core 240 does not necessarily have to have a shape that follows the shape of the coil 230. It may be a letter shape.

  Next, the displacement means 500 that switches the position of the magnetic shield 250 will be described.

  FIG. 5 is a schematic perspective view showing an example of the magnetic shield displacing means in the fixing device according to the first embodiment of the present invention.

  The displacement means 500 of this example attaches the magnetic shield 250 to the rotating shaft 502 of the stepping motor 501, and rotates the magnetic shield 250 between the magnetic path blocking position and the magnetic path opening position by forward and reverse rotation of the rotating shaft 502. It has a configuration.

  The stepping motor 501 is disposed in the hollow portion of the heat generating roller 210 so that the rotation shaft 502 is positioned at the rotation center of the magnetic shield 250. As a result, the stepping motor 501 does not protrude to the side of the heat generating roller 210, and an increase in the size of the apparatus is avoided.

  In FIG. 5, the rotation shaft 502 of the stepping motor 501 rotates forward and backward by a preset angle according to the size of the recording paper 109 to be passed. As a result, the magnetic shield 250 is displaced to the magnetic path blocking position that is the winding center of the coil 230 shown in FIG. 2 and the magnetic path release position that is the winding site of the coil 230 shown in FIG.

  FIG. 6 is a schematic perspective view showing another example of the displacement means of the magnetic shield in the fixing device according to Embodiment 1 of the present invention.

  The displacement means 600 of this example has a configuration in which the magnetic shield 250 is rotated in the forward and reverse directions by the stepping motor 601 via the timing belt 602 and the pulleys 603 and 604. The stepping motor 601 is disposed on the side of the heat generating roller 210 in order to avoid an increase in the size of the apparatus.

  In FIG. 6, the pulley 603 attached to the rotation shaft of the stepping motor 601 rotates forward and backward by a preset angle according to the size of the recording paper 109 to be passed. As a result, the magnetic shield 250 passes through the timing belt 602 and the pulley 604, and the magnetic path blocking position that is the winding center of the coil 230 shown in FIG. 2 and the magnetic part that is the winding portion of the coil 230 shown in FIG. Displaces to the road release position.

  The displacement means 600 in this example is an example in which the paper passing reference of the recording paper 109 is the center reference, and a pair of magnetic shields 250 are attached to both ends of the rotating shaft 605 of the pulley 604, respectively. ing.

  FIG. 7 is a schematic cross-sectional view showing still another example of the magnetic shield displacing means in the fixing device according to the first embodiment of the present invention. FIG. 8 is a schematic cross-sectional view showing a state in which the magnetic shield shown in FIG. 7 is displaced to the magnetic path opening position.

  As shown in FIG. 7, in the displacement means 700 of this example, the actuator 702 of the plunger 701 is attached to the free end of the support arm 251 of the magnetic shield 250, and the magnetic shield 250 is moved to the magnetic path by turning the plunger 701 on / off. It is configured to rotate between a blocking position and a magnetic path opening position. The plunger 701 is disposed below the side core 242 in order to avoid an increase in the size of the apparatus.

  In FIG. 7, when the plunger 701 is turned on / off, the support arm 251 of the magnetic shield 250 is moved in the forward / reverse direction by a predetermined angle according to the size of the recording paper 109 to be passed through the coil spring 703. Fluctuate. By the swing of the support arm 251, the magnetic shield 250 has a magnetic path blocking position that is the winding center of the coil 230 shown in FIG. 7 and a magnetic path release position that is the winding part of the coil 230 shown in FIG. 8. It is displaced to.

  FIG. 9 is a schematic cross-sectional view showing still another example of the magnetic shield displacing means in the fixing device according to Embodiment 1 of the present invention. FIG. 10 is a schematic cross-sectional view showing a state where the magnetic shield shown in FIG. 9 is displaced to the magnetic path opening position.

  The displacement means 900 of the present example has a configuration in which the planetary gear device 901 rotates the magnetic shield 250 between the magnetic path blocking position and the magnetic path opening position. The planetary gear device 901 in the displacement means 900 of this example has a planetary gear 902, a sun gear 903, and an internal gear 904, and the internal gear 904 is the inner peripheral surface of the heat generating roller 210 in order to avoid an increase in the size of the device. Is formed.

  As shown in FIGS. 9 and 10, the sun gear 903 is rotatably supported on the rotation shaft 211 of the heat generating roller 210. The planetary gear 902 is rotatably supported on the free end of the planetary arm 905 and meshes with the sun gear 903 and the internal gear 904. The planetary arm 905 is rotatably supported on the rotation shaft 211 of the heat generating roller 210 and is frictionally coupled to the sun gear 903.

  The magnetic shield 250 is pivotally supported by the support arm 251 on the rotating shaft 211 of the heat roller 210 so as to be freely slidable. The support arm 251 is friction-coupled with the sun gear 903. Further, the displacement means 900 is provided with an advancing / retracting member 907 that advances / retreats with respect to the rotation trajectory of the support shaft 906 of the planetary gear 902.

  As shown in FIG. 9, in a state where the advance / retreat member 907 has advanced into the rotation trajectory of the support shaft 906 of the planetary gear 902, the planetary arm 905 is prevented from rotating. In this state, when the heat generating roller 210 rotates in the arrow direction (counterclockwise), the sun gear 903 rotates clockwise via the internal gear 904 and the planetary gear 902.

  The rotation of the sun gear 903 causes the support arm 251 that is frictionally coupled to the sun gear 903 to swing in the same direction (clockwise). The swinging of the support arm 251 is prevented when the right side portion of the magnetic shield 250 abuts against the stopper 908. As a result, the magnetic shield 250 is displaced to the magnetic path blocking position, which is the winding center of the coil 230 shown in FIG.

  On the other hand, as shown in FIG. 10, when the advance / retreat member 907 is retracted from the rotation trajectory of the support shaft 906 of the planetary gear 902, the planetary gear 902 revolves around the sun gear 903 due to the rotation of the heating roller 210. Due to the revolution of the planetary gear 902, the planetary arm 905 rotates counterclockwise, and the sun gear 903 friction-coupled thereto rotates in the same direction.

  As the sun gear 903 rotates, the support arm 251 frictionally coupled to the sun gear 903 swings counterclockwise. The swinging of the support arm 251 is prevented when the left side portion of the magnetic shield 250 abuts against the stopper 909. As a result, the magnetic shield 250 is displaced to the magnetic path release position that is the winding portion of the coil 230 shown in FIG.

  As described above, the displacement means 900 displaces the magnetic shield 250 by utilizing the rotation of the heat generating roller 210, so that a driving source such as a motor or a plunger is not necessary, and the size of the recording paper 109 to be passed is passed. Accordingly, the heat generation width of the heat generation roller 210 can be switched by merely moving the advance / retreat member 907 forward and backward.

  In the fixing device 200 of this example, the width W1 in the displacement direction of the magnetic shield 250 is configured to be larger than the width W2 in the same direction of the winding center of the coil 230 as shown in FIG. As a result, the magnetic flux acting on the non-sheet passing area of the heat generating roller 210 can be shielded more effectively, and it is possible to reliably prevent overheating due to the accumulation of heat in the non-sheet passing area of the heat generating roller 210. become able to.

  Further, the width W1 in the displacement direction of the magnetic shield 250 in the fixing device 200 of the present example is configured to be narrower than the winding width W3 in the same direction of the winding portion of the coil 230 as shown in FIG. Yes. Thus, when the magnetic shield 250 is displaced to the magnetic path release position, the magnetic shield 250 faces a position that avoids the magnetic path, so that the magnetic shield 250 does not affect the magnetic flux. Therefore, in this fixing device 200, even if the magnetic shield 250 is displaced to the winding part of the coil 230, heat generation unevenness does not occur in the heat generating roller 210, and good fixing of large size paper can be obtained. .

  The width W1 of the magnetic shield 250 and the widths W2 and W3 of the coil 230 can also be defined by angles θ1, θ2, and θ3, as shown in FIGS.

  As described above, in the fixing device 200 of this example, since the magnetic shield 250 moves in the sheet passing direction, the size of the device can be reduced compared to the conventional fixing device configured to move the magnetic shield in the longitudinal direction. be able to.

  Further, in the conventional fixing device, the core is divided into four parts in order to avoid interference with the magnetic shield. However, in the fixing device 200 of this example, the core 240 is arranged so as to surround the coil 230 without being divided. Therefore, the ratio of the core 240 to the magnetic path is increased, the magnetic coupling between the coil 230 and the heat roller 210 is good, and the heat generation efficiency of the heat roller 210 is good.

  By the way, even if the thickness of the magnetic shield 250 is sufficient, the magnetic shield 250 has a resistance, and thus generates a little heat due to the magnetic flux generated by the coil 230. Therefore, in the fixing device 200, if the recording paper 109 is continuously passed, the heat of the magnetic shield 250 is gradually accumulated and excessively heated, so that heat dissipation is required.

  For this reason, in the conventional fixing device in which the magnetic shield is inside the heating element, the temperature of the magnetic shield is more likely to rise. On the other hand, in the fixing device 200 of this example, since the coil 230 is disposed outside the heat generating roller 210, the heat of the magnetic shield 250 can be diffused to the outside air, and the magnetic shield 250 is excessively heated. The temperature can be suppressed.

  Further, as shown in FIG. 4, the fixing device 200 of the present example includes a blower 270 for cooling the magnetic shield 250 by blowing air. Therefore, in this fixing device 200, the magnetic shield 250 can be cooled by the air flow of the blower 270 to further suppress the temperature rise of the magnetic shield 250.

  Since the coil 230 has a resistance, the coil 230 itself generates heat when a current is applied to the coil 230. When the temperature of the coil 230 rises, the impedance increases and the efficiency of induction heating decreases, or the coil 230 is damaged by heat. In the fixing device 200 of this example, the coil 230 can also be cooled by the blower 270.

  Here, when the coil and the magnetic shield are inside the heating element as in the conventional fixing device, it is difficult to cool the coil and the magnetic shielding body while heating the heating element. In the apparatus 200, since the coil 230 is disposed outside the heat generating roller 210, it is easy to cool the coil 230 and the magnetic shield 250.

  In addition, as shown in FIG. 4, the fixing device 200 of the present example has a large number of openings 241 a for heat dissipation in a region of the arch core 241 of the core 240 that faces the winding portion of the coil 230. Thereby, the heat of the coil 230 and the magnetic shield 250 can be dissipated to the outside air. It is also possible to insert an arm for displacing the magnetic shield 250 from the opening 241a. When the sheet passing reference of the recording paper 109 is the center reference, it is possible to connect the respective magnetic shields 250 disposed at positions facing the two non-sheet passing regions by this arm. The displacement means of the shield 250 can be simplified. Even if the opening 241 a is formed in the arch core 241 in this way, if the core 240 faces the winding center of the coil 230, the temperature unevenness in the longitudinal direction of the heating roller 210 does not occur.

  Here, the opening 241a of the arch core 241 may be formed larger as the distance from the installation position of the blower 270 increases. As a result, the coil 230 can be cooled substantially uniformly over the entire area by compensating for the decrease in cooling capacity due to the air blown from the position far from the position where the blower 270 is disposed by the heat radiation from the opening 241a.

  Further, in the fixing device 200 of this example, since the coil 230 and the core 240 are disposed outside the heat generating roller 210, it is possible to efficiently replace and maintain parts such as the heat generating roller 210 that are consumables. Can do.

(Embodiment 2)
Next, a fixing device according to Embodiment 2 of the present invention will be described. FIG. 13 is a schematic cross-sectional view showing the configuration of the main part of the fixing device according to Embodiment 2 of the present invention. FIG. 14 is a schematic cross-sectional view showing an operation mode of the magnetic shield in the fixing device according to Embodiment 2 of the present invention.

  As shown in FIG. 13, the fixing device 1300 according to the second embodiment includes two magnetic shields 250 </ b> A and 250 </ b> B between a coil 230 and a core 240 corresponding to a non-sheet passing region on one side of the heat roller 210. Are arranged so as to be freely displaceable.

  Each of the magnetic shields 250A and 250B has a magnetic path blocking position that is a winding center of the coil 230 shown in FIG. 13 and a magnetic path release position that is a winding part of the coil 230 shown in FIG. It is displaced to.

  A large eddy current flows in each of the magnetic shields 250A and 250B due to the action of the magnetic field between the coil 230 and the core 240, and a repulsive magnetic field is generated in a direction that cancels the magnetic flux generated from the coil 230 by the eddy current.

  As a result, as shown in FIG. 13, when the magnetic shields 250 </ b> A and 250 </ b> B are displaced to the magnetic path blocking position that is the winding center of the coil 230, the magnetic flux acting on the non-sheet passing region of the heat generating roller 210 is magnetically shielded. It is weakened by the repulsive magnetic field generated in the bodies 250A and 250B. Further, by weakening the magnetic flux acting on the non-sheet passing area, heat generation in the non-sheet passing area of the heat generating roller 210 when the small-size recording paper 109 is passed is suppressed.

  On the other hand, as shown in FIG. 14, when the magnetic shields 250 </ b> A and 250 </ b> B are displaced to the magnetic path opening position where the coil 230 is wound, the maximum sheet passing area of the heating roller 210 is reduced by the action of the magnetic field. Fever.

  In the fixing device 1300 of this example, since the two magnetic shields 250A and 250B are used, the magnetic flux passing through the winding center of the coil 230 can be blocked over a wide area. Therefore, according to the fixing device 1300, it is possible to more reliably prevent an excessive temperature rise in the non-sheet passing region of the heat roller 210.

(Embodiment 3)
Next, a fixing device according to Embodiment 3 of the present invention will be described. FIG. 15 is a schematic plan view showing the configuration of the main part of the fixing device according to Embodiment 3 of the present invention.

  As shown in FIG. 15, the fixing device 1500 according to the third embodiment has a medium size paper width Lmid non-passage between the coil 230 and the core 240 corresponding to the non-paper pass regions at both ends of the heat generating roller 210. A magnetic shield 250C having a width corresponding to the paper region and a magnetic shield 250D having a width corresponding to the non-sheet passing region having the small-size paper width Lmin are disposed so as to be displaceable.

  In FIG. 15, when the medium size recording paper 109 is passed through the fixing nip, only the magnetic shield 250C is the winding center of the coil 230 indicated by the broken line in FIG. Displaces to the magnetic path blocking position.

  When a small-size recording paper 109 is passed through the fixing nip, the magnetic shield 250C and the magnetic shield 250D are wound around the winding center of the coil 230 indicated by a broken line in FIG. The magnetic path is displaced to the magnetic path cutoff position.

  Further, when the maximum size recording paper 109 is passed through the fixing nip, the magnetic shield 250C and the magnetic shield 250D are wound around the coil 230 shown by a solid line in FIG. Are displaced to the magnetic path release position.

  A large eddy current flows in each magnetic shield 250C and magnetic shield 250D due to the action of the magnetic field between the coil 230 and the core 240, and a repulsive magnetic field is generated in a direction to cancel the magnetic flux generated from the coil 230 by the eddy current. To do.

  As a result, as shown by a broken line in FIG. 15, when the magnetic shield 250 </ b> C is displaced to the magnetic path blocking position that is the winding center of the coil 230, it acts on the non-sheet passing region of the medium size paper width Lmid of the heating roller 210. The magnetic flux that is generated is weakened by the repulsive magnetic field generated by the magnetic shield 250C. Further, the magnetic flux acting on the non-sheet passing area having the medium size sheet width Lmid is weakened, so that heat generation in the non-sheet passing area of the heat generating roller 210 when the medium size recording sheet 109 is passed is suppressed.

  Further, as indicated by broken lines in FIG. 15, when the magnetic shield 250 </ b> C and the magnetic shield 250 </ b> D are respectively displaced to the magnetic path blocking position that is the winding center of the coil 230, the small size paper width Lmin of the heating roller 210 is not increased. The magnetic flux acting on the paper passing area is weakened by the repulsive magnetic field generated by the magnetic shield 250C and the magnetic shield 250D. Further, the magnetic flux acting on the non-sheet passing area having the small size paper width Lmin is weakened, thereby suppressing the heat generation in the non-sheet passing area of the heating roller 210 when the small size recording paper 109 is passed.

  Further, as indicated by solid lines in FIG. 15, in the state where the magnetic shield 250C and the magnetic shield 250D are respectively displaced to the magnetic path opening position where the coil 230 is wound, the passage of the maximum size paper width Lmax of the heating roller 210 is achieved. The paper area generates heat uniformly by the action of the magnetic field.

  As described above, in the fixing device 1500, the heat generation width of the heat roller 210 is changed by switching the positions of the magnetic shield 250C and the magnetic shield 250D in accordance with the size of the recording paper 109 passed through the fixing nip. Can be switched in three ways.

  Here, the positions of the magnetic shield 250C and the magnetic shield 250D are determined in accordance with the sheet passing reference of the recording paper 109 to the fixing nip. That is, when the paper passing reference of the recording paper 109 is the center reference, as shown in FIG. 15, each pair of magnetic shields 250C and 250D is provided at both ends of the medium size paper width Lmid and the small size paper width Lmin. They are respectively arranged at positions facing the two non-sheet passing areas. Further, when the sheet passing reference of the recording paper 109 is the one-side reference, each one of the magnetic shield 250C and the magnetic shield 250D is one non-sheet passing region at one end of the medium size paper width Lmid and the small size paper width Lmin. It is arrange | positioned in the position facing.

  As described above, the fixing device 1500 of this example includes the two magnetic shields 250C and 250D respectively corresponding to the two non-sheet passing boundaries, and selectively displaces the magnetic shields 250C and 250D. It is possible to suppress an excessive temperature rise in the non-sheet passing area of the heat generation roller 210 when three types of recording sheets 109 of small size, medium size, and large size are passed.

(Embodiment 4)
Next, a fixing device according to Embodiment 4 of the present invention will be described. FIG. 16 is a schematic cross-sectional view showing a configuration of a main part of a fixing device according to Embodiment 4 of the present invention. FIG. 17 is a schematic cross-sectional view showing an operation mode of the magnetic shield in the fixing device according to Embodiment 4 of the present invention.

  As shown in FIG. 16, a fixing device 1600 according to the fourth embodiment includes a heat roller 210, a pressure roller 220, a coil 1630, a core 1640, a magnetic shield 1650, and the like.

  In FIG. 16, the heat generating roller 210 and the pressure roller 220 are configured in the same manner as that of the fixing device 200 according to the first embodiment.

  The coil 1630 is formed by, for example, rotating a litz wire, which is a bundle of thin copper wires, into a semi-cylindrical shape so as to face the inner peripheral surface of the upper half of the heat generating roller 210. The coil 1630 generates a magnetic flux by generating a magnetic flux around it when a voltage is applied from a power source (not shown) and an alternating current flows.

  The core 1640 is rotatably disposed in a portion facing the inner peripheral surface of the coil 1630, that is, in a hollow portion (inside) of the heat roller 210 so as to be coaxial with the rotation center of the heat roller 210. The core 1640 forms a magnetic path of the magnetic flux generated on the side opposite to the heat generating roller 210 among the magnetic flux generated by the coil 1630.

  The core 1640 is preferably formed of a magnetic material having high magnetic permeability and specific resistance, such as ferrite and permalloy. That is, since ferrite is ferromagnetic, magnetic flux is strengthened and heat generation efficiency is improved. In addition, since ferrite has high thermal conductivity and specific heat, it is possible to suppress the temperature rise of the magnetic shield 1650 by absorbing heat generated in the magnetic shield 1650.

  The magnetic shield 1650 is rotatable between a coil 1630 and a core 1640 at a position facing a non-sheet passing area of the heat generating roller 210 when a small size recording sheet 109 is passed through the fixing nip. Has been placed.

  The magnetic shield 1650 in the fixing device 1600 of this example is embedded in the outer periphery of the core 1640 as shown in FIG. The magnetic shield 1650 is displaced by a displacement means 1900, which will be described later, into a magnetic path cutoff position that is a winding center of the coil 1630 shown in FIG. 16 and a magnetic path release position that is a winding part of the coil 1630 shown in FIG. To do.

  A large eddy current flows through the magnetic shield 1650 due to the action of the magnetic field between the coil 1630 and the core 1640, and a repulsive magnetic field is generated in a direction that cancels the magnetic flux generated from the coil 1630.

  Accordingly, as shown in FIG. 16, in a state where the magnetic shield 1650 is displaced to the magnetic path blocking position that is the winding center of the coil 1630, the magnetic flux acting on the non-sheet passing region of the heat generation roller 210 is magnetic shield 1650. It is weakened by the repulsive magnetic field generated in Further, by weakening the magnetic flux acting on the non-sheet passing area, heat generation in the non-sheet passing area of the heat generating roller 210 when the small-size recording paper 109 is passed is suppressed.

  On the other hand, as shown in FIG. 17, in the state where the magnetic shield 1650 is displaced to the magnetic path opening position where the coil 1630 is wound, the sheet passing area of the maximum size recording paper 109 of the heating roller 210 is affected by the magnetic field. Heats evenly.

  As described above, in the fixing device 1600, the heat generation width of the heat generating roller 210 can be switched by switching the position of the magnetic shield 1650 in accordance with the size of the recording paper 109 passed through the fixing nip.

  Here, the arrangement position of the magnetic shield 1650 is determined in accordance with the sheet passing standard of the recording sheet 109 to the fixing nip. That is, when the paper passing reference of the recording paper 109 is the center reference, as shown in FIG. 18, the pair of magnetic shields 1650 are arranged at positions facing the two non-passing areas at both ends of the core 1640, respectively. Established. When the sheet passing reference of the recording paper 109 is the one-side reference, one magnetic shield 1650 is disposed at a position facing one non-sheet passing region at one end of the core 1640.

  As a material of the magnetic shield 1650, a conductive material such as aluminum or copper having a small specific resistance is suitable. Further, the thickness of the magnetic shield 1650 is preferably equal to or greater than the skin depth in order to reduce the resistance, and is preferably about 1 mm, for example. Thus, by making resistance low, heat_generation | fever of magnetic shielding body 1650 itself can be suppressed.

  Next, the displacement means 1900 for switching the position of the magnetic shield 1650 will be described. FIG. 19 is a schematic perspective view showing the magnetic shield displacing means in the fixing device according to Embodiment 4 of the present invention.

  As shown in FIG. 19, the displacement means 1900 includes a small gear 1901 provided on the support shaft of the core 1640, a large gear 1902 that meshes with the small gear 1901, an arm 1903 and an arm 1903 integrated with the support shaft of the large gear 1902. It is composed of a solenoid 1904 that swings.

  In FIG. 19, when the solenoid 1904 is turned on (energized), the actuator of the solenoid 1904 moves and the arm 1903 swings. As the arm 1903 swings, the large gear 1902 rotates and the small gear 1901 rotates in a driven manner. With the driven rotation of the small gear 1901, the support shaft of the core 1640 rotates, and the magnetic shield 1650 is displaced from the magnetic path release position shown in FIG. 17 to the magnetic path cutoff position shown in FIG. Accordingly, the magnetic shield 1650 blocks the magnetic path between the coil 1630 and the core 1640 corresponding to the non-sheet passing region of the heat roller 210.

  On the other hand, when the solenoid 1904 in the on state is turned off (non-energized), the arm 1903 returns to the initial position shown in FIG. 19, and the spindles of the large gear 1902, the small gear 1901 and the core 1640 rotate in reverse. Then, the magnetic shield 1650 returns from the magnetic path blocking position shown in FIG. 16 to the magnetic path releasing position shown in FIG.

  As described above, the fixing device 1600 according to the fourth embodiment turns on / off the solenoid 1904 of the displacement unit 1900 to thereby turn the magnetic path between the coil 1630 and the core 1640 corresponding to the non-sheet passing region of the heat roller 210. Is blocked or released by the magnetic shield 1650 to control the magnetic coupling between the heat generating roller 210 and the coil 1630.

  That is, when the size of the recording paper 109 to be passed is the maximum size, the solenoid 1904 is kept in the OFF state in FIG. 19 and the magnetic shield 1650 is put on standby at the magnetic path release position shown in FIG. As a result, the magnetic flux generated by the coil 1630 flows throughout the longitudinal direction of the core 1640 and acts on the entire maximum size paper width Lmax of the heat generating roller 210, and the heat generation distribution in the longitudinal direction of the heat generating roller 210 is equal to the maximum size paper width Lmax. It is kept uniform throughout.

  On the other hand, when the size of the recording paper 109 to be passed is small, the solenoid 1904 is turned on in FIG. 19, and the magnetic shield 1650 is displaced to the magnetic path blocking position shown in FIG. As a result, the magnetic coupling with the coil 1630 in the non-sheet passing region of the heat generating roller 210 is reduced, and the magnetic flux generated by the coil 1630 passes only through the portion of the heat generating roller 210 having the small size paper width Lmin. Heat generation in the non-sheet-passing area 210 is suppressed, and overheating of the non-sheet-passing area can be prevented.

(Embodiment 5)
Next, a fixing device according to Embodiment 5 of the present invention will be described. FIG. 20 is a schematic cross-sectional view showing the configuration of the main part of the fixing device according to Embodiment 5 of the present invention. FIG. 21 is a schematic cross-sectional view showing an operation mode of the magnetic shield in the fixing device according to Embodiment 5 of the present invention.

  As shown in FIGS. 20 and 21, fixing device 2000 according to the fifth embodiment has the same configuration as fixing device 1600 according to the fourth embodiment except for core 2040.

  That is, as shown in FIG. 22, the fixing device 2000 according to the fifth embodiment includes a magnetic shield 2050A having a width corresponding to a non-sheet-passing area having an A4 size paper width and a B4 size paper width at the outer periphery of the core 2040. The magnetic shield 2050B having a width corresponding to the non-sheet passing region is embedded.

  FIG. 23 is a schematic perspective view showing the displacement means of each magnetic shield in the fixing device according to Embodiment 5 of the present invention.

  As shown in FIG. 23, the displacement means 2300 in the fixing device 2000 of this example rotates by supporting the small gear 2301 provided on the support shaft of the core 2040, the large gear 2302 meshing with the small gear 2301, and the large gear 2302. A stepping motor 2303 and the like are included.

  In FIG. 23, when the stepping motor 2303 is turned on (energized), the large gear 2302 is rotated by the rotation of the support shaft, and the small gear 2301 is driven to rotate. Due to the driven rotation of the small gear 2301, the support shaft of the core 2040 is rotated, and the magnetic shield having a length corresponding to the width of the non-sheet passing area of the recording paper size of the magnetic shields 2050A and 2050B. (Here, the magnetic shield 2050A) is displaced from the magnetic path release position shown in FIG. 21 to the magnetic path cutoff position shown in FIG.

  As a result, the magnetic path between the coil 1630 and the core 2040 corresponding to the non-sheet passing region of the heat roller 210 is blocked by the magnetic shield 2050A.

  On the other hand, when the A3 size width of the sheet passing area of the heat roller 210 is heated, as shown in FIG. 21, the magnetic shields 2050A and 2050B are moved to the magnetic path release position to the stepping motor 2303. Turn off the power.

  As described above, the fixing device 200 turns on / off the stepping motor 2303 of the displacement unit 2300 to thereby change the magnetic path between the coil 1630 and the core 2040 corresponding to the non-sheet passing region of the heat generating roller 210 to each magnetic shield. The magnetic coupling between the heat generating roller 210 and the coil 1630 is controlled by being blocked or released by 2050A and 2050B.

  Therefore, in the fixing device 2000, the magnetic shields 2050A and 2050B are selectively moved from the magnetic path release position shown in FIG. 21 to the magnetic path cutoff position shown in FIG. 20 according to the size of the recording paper 109 to be passed. The heat generation in the non-sheet passing area of the heat generating roller 210 according to the size of the recording paper 109 to be passed can be suppressed, and the excessive temperature rise in the non-sheet passing area of the heat generating roller 210 can be prevented. Become. As described above, in the fixing device 2000 of this example, it is possible to satisfactorily heat and fix the recording paper 109 having a plurality of sizes by the single heat roller 210.

  In the fixing device 2000, the opposite side of the coil 1630 is also a magnetic path release position, such as the position of the magnetic shield 2050B shown in FIG.

  In the fixing device according to each embodiment, the coil has an inductance of 10 μH or more and 50 μH or less and an electrical resistance of 0.5Ω or more and 5Ω or less at a frequency of 30 kHz in a state where the coil faces the heat generating roller 210. preferable. Thereby, a versatile and inexpensive excitation circuit can be used.

  Further, it is preferable that a current having a frequency of 20 kHz to 100 kHz is applied to the coil. Thereby, the loss of the power supply of an excitation circuit can be suppressed small, and the temperature increase of the heat generating roller 210 can be accelerated.

  A fixing device according to a first aspect of the present invention includes a coil that generates magnetic flux, a heating element that is induction-heated by the magnetic flux, a core that is disposed on the opposite side of the heating element across the coil, A magnetic shield disposed between a coil and the core and opening and closing a magnetic path corresponding to a non-sheet passing region of the heating element; a magnetic path blocking position which is a winding center of the coil; and a winding portion of the coil Displacement means for displacing the magnetic shield to a certain magnetic path release position is adopted.

  According to this configuration, the magnetic shield is displaced by the displacement means to a magnetic path blocking position that is a winding center of the coil and a magnetic path release position that is a winding portion of the coil. Here, since the magnetic path corresponding to the non-sheet passing region of the heating element is blocked in a state where the magnetic shield is displaced to the magnetic path blocking position which is the winding center of the coil, It is possible to prevent an excessive increase in temperature in the non-sheet passing region of the heating element due to regular sheet passing. On the other hand, when large-size paper is passed, the magnetic shield is not affected by the magnetic path by displacing the magnetic shield to the magnetic path release position. The paper passing area is uniformly heated. Thus, according to this configuration, the magnetic shield is displaced to the winding center and the winding part of the coil, that is, moves in the paper passing direction of the heating element, so that the apparatus can be configured in a small size. it can.

  A fixing device according to a second aspect of the present invention employs a configuration in which, in the first aspect, the coil is disposed outside the heating element.

  According to this configuration, since the coil is arranged outside the heating element, the heat of the magnetic shield can be diffused to the outside, and the temperature rise of the magnetic shield can be suppressed.

  A fixing device according to a third aspect of the present invention employs a configuration including a cooling means for cooling the magnetic shield in the first aspect or the second aspect.

  According to this configuration, the temperature of the magnetic shield can be suppressed by cooling the magnetic shield by the cooling means. According to this configuration, there is an effect that the coil is simultaneously cooled by the cooling means. Further, by adopting a configuration in which the coil is disposed outside the heating element, the coil can be easily cooled by the cooling means.

  In the fixing device according to a fourth aspect of the present invention, in the first aspect, the heating element is formed in an annular shape, the coil and the core are disposed in a hollow portion of the heating element, and the magnetic shield is provided. The structure which arrange | positioned to the said core is taken.

  According to this configuration, since the magnetic shield is disposed on the core, the magnetic shield can be easily displaced between the magnetic path cutoff position and the magnetic path release position by the rotation of the core. Can do. In addition, according to this configuration, since the magnetic shield is disposed in the core, heat generated in the magnetic shield can be conducted to the core and dissipated, and the magnetic shield Temperature rise can be prevented.

  The fixing device according to a fifth aspect of the present invention is the fixing device according to the first aspect or the fourth aspect, wherein a width of the magnetic shield in the paper passing direction is larger than an inner diameter of the coil in the paper passing direction. Take.

  In this configuration, since the magnetic path is blocked by the magnetic shield having a larger area than the magnetic path of the non-sheet passing region of the heating element, the magnetic flux acting on the non-sheet passing region of the heating element. Can be suppressed more effectively, and an excessive temperature rise in the non-sheet passing region can be prevented.

  The fixing device according to a sixth aspect of the present invention is the fixing device according to the first aspect or the fourth aspect, wherein the width of the magnetic shield in the paper passing direction is greater than the width of the coil winding portion in the paper passing direction. Also adopt a smaller configuration.

  In this configuration, when the magnetic shield is displaced to the magnetic path release position, the magnetic shield is in a state avoiding the magnetic path, and the magnetic shield affects the magnetic flux acting on the heating element. Since no heat is generated, unevenness of heat generation does not occur in the heating element, and good fixing of large size paper can be obtained.

  The fixing device according to a seventh aspect of the present invention employs a configuration including a plurality of magnetic shields respectively corresponding to a plurality of non-sheet-passing areas having different sizes in the first aspect or the fourth aspect. .

  According to this configuration, it is possible to suppress excessive temperature rise in the non-sheet passing area of the heating element when a plurality of recording sheets having different sizes are passed by selectively displacing each magnetic shield.

  The fixing device according to an eighth aspect of the present invention employs a configuration in which, in the first aspect, an opening is provided in a region of the core that faces the winding portion of the coil.

  According to this configuration, the heat of the coil and the magnetic shield can be dissipated to the surroundings through the opening provided in the core. Further, an arm for displacing the magnetic shield can be inserted from the opening.

  A fixing device according to a ninth aspect of the present invention employs a configuration having the core in at least a region facing the winding center of the coil in the first aspect.

  According to this configuration, the heat generating element does not have temperature unevenness in the longitudinal direction, and good fixing can be obtained.

  In the fixing device according to a tenth aspect of the present invention, in the first aspect or the fourth aspect, the magnetic shield is configured of a conductive material having a thickness equal to or greater than a skin depth.

  According to this configuration, since the resistance of the magnetic shield is lowered, heat generation of the magnetic shield itself can be suppressed.

  According to an eleventh aspect of the present invention, in the fixing device according to the first aspect or the fourth aspect, the magnetic shield is made of aluminum.

  According to this configuration, since the magnetic shield is made of aluminum having a low specific resistance, heat generation of the magnetic shield itself can be suppressed.

  A fixing device according to a twelfth aspect of the present invention employs a configuration in which the magnetic shield is made of copper in the first aspect or the fourth aspect.

  According to this configuration, since the magnetic shield is made of copper or the like having a low specific resistance, heat generation of the magnetic shield itself can be suppressed.

  According to a thirteenth aspect of the present invention, in the fixing device according to the first aspect or the fourth aspect, the core is made of ferrite.

  According to this configuration, since the core is made of ferromagnetic ferrite, the magnetic flux is strengthened and the heat generation efficiency of the heating element is improved. In addition, since the core made of ferrite has high thermal conductivity and specific heat, it is possible to suppress the temperature rise of the magnetic shield by absorbing heat generated in the magnetic shield.

  A fixing device according to a fourteenth aspect of the present invention employs a configuration in which the heating element is made of a magnetic material in the first aspect or the fourth aspect.

  According to this structure, since the said heat generating body consists of magnetic bodies, such as iron and nickel, for example, magnetic flux becomes strong and the heat generation efficiency of the said heat generating body improves.

  The fixing device according to a fifteenth aspect of the present invention is the fixing device according to the first aspect or the fourth aspect, wherein the coil has an inductance of 10 μH or more and 50 μH or less at a frequency of 30 kHz with the coil facing the heating element. The electric resistance is 0.5Ω or more and 5Ω or less.

  According to this configuration, a versatile and inexpensive excitation circuit can be used.

  A fixing device according to a sixteenth aspect of the present invention employs a configuration in which the frequency of the current applied to the coil is 20 kHz to 100 kHz in the first aspect or the fourth aspect.

  According to this configuration, it is possible to suppress the loss of the power source of the excitation circuit and to increase the temperature of the heating element faster.

  Since the fixing device according to the present invention can prevent an excessive temperature rise in the non-sheet passing area of the heating element with a small configuration, it can form an image in an electrophotographic or electrostatic recording type copying machine, facsimile, printer, or the like. It is useful as a fixing device for the apparatus.

1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus equipped with a fixing device according to Embodiment 1 of the present invention. 1 is a schematic cross-sectional view showing a configuration of a main part of a fixing device according to Embodiment 1 of the present invention. 1 is a schematic cross-sectional view showing an operation mode of a magnetic shield in a fixing device according to Embodiment 1 of the present invention. Schematic plan view for explaining the operation mode of the fixing device according to the first embodiment of the present invention. 1 is a schematic perspective view showing an example of a magnetic shield displacement means in the fixing device according to Embodiment 1 of the present invention. FIG. FIG. 7 is a schematic perspective view showing another example of the magnetic shield displacing means in the fixing device according to the first embodiment of the present invention. FIG. 7 is a schematic cross-sectional view showing still another example of the magnetic shield displacing means in the fixing device according to the first embodiment of the present invention. FIG. 7 is a schematic cross-sectional view showing a state where the magnetic shield shown in FIG. 7 is displaced to the magnetic path open position. FIG. 7 is a schematic cross-sectional view showing still another example of the magnetic shield displacing means in the fixing device according to the first embodiment of the present invention. FIG. 9 is a schematic cross-sectional view showing a state where the magnetic shield shown in FIG. 9 is displaced to the magnetic path open position. Schematic sectional view for explaining the relationship between the winding center of the coil and the width of the magnetic shield in the fixing device according to the first embodiment of the present invention. Schematic cross-sectional view for explaining the relationship between the coil winding portion and the width of the magnetic shield in the fixing device according to the first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a configuration of a main part of a fixing device according to Embodiment 2 of the present invention. Schematic sectional view showing an operation mode of the magnetic shield in the fixing device according to the second embodiment of the present invention. Schematic plan view showing a configuration of a main part of a fixing device according to Embodiment 3 of the present invention. Schematic cross-sectional view showing the configuration of the main part of a fixing device according to Embodiment 4 of the present invention. Schematic sectional view showing an operation mode of the magnetic shield in the fixing device according to Embodiment 4 of the present invention. Schematic perspective view showing the configuration of the core in the fixing device according to Embodiment 4 of the present invention. FIG. 7 is a schematic perspective view showing a magnetic shield displacing means in the fixing device according to Embodiment 4 of the present invention. Schematic cross-sectional view showing the configuration of the main part of the fixing device according to Embodiment 5 of the present invention. Schematic sectional view showing an operation mode of the magnetic shield in the fixing device according to the fifth embodiment of the present invention. Schematic perspective view showing the configuration of the core in the fixing device according to Embodiment 5 of the present invention. Schematic perspective view showing the displacement means of each magnetic shield in the fixing device according to Embodiment 5 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Photosensitive drum 102 Charging device 103 Laser beam scanner 105 Developing device 107 Paper feeding device 109 Recording paper 110 Registration roller 112 Transfer roller 113 Cleaning device 200, 1300, 1500, 1600, 2000 Fixing device 210 Heating roller 220 Pressure Roller 230 Coil 240 Core 250, 250A, 250B, 250C, 250D, 1650, 2050A, 2050B Magnetic shield 500, 600, 700, 900, 1900, 2300 Displacement means

Claims (17)

A coil for generating magnetic flux;
A heating element induction-heated by the magnetic flux;
A core disposed on the opposite side of the heating element across the coil;
A magnetic shield disposed between the coil and the core and opening and closing a magnetic path corresponding to a non-sheet passing region of the heating element;
A fixing device comprising: a displacement means for displacing the magnetic shield at a magnetic path blocking position that is a winding center of the coil and a magnetic path release position that is a winding portion of the coil.   The fixing device according to claim 1, wherein the coil is disposed outside the heating element.   The fixing device according to claim 1, further comprising a cooling unit that cools the magnetic shield.   The fixing device according to claim 1, wherein the heating element is formed in an annular shape, the coil and the core are disposed in a hollow portion of the heating element, and the magnetic shield is disposed in the core.   The fixing device according to claim 1, wherein a width of the magnetic shield in a paper passing direction is larger than an inner diameter of the coil in a paper passing direction.   The fixing device according to claim 1, wherein a width of the magnetic shield in a paper passing direction is smaller than a width of the coil winding portion in the paper passing direction.   The fixing device according to claim 1, further comprising a plurality of magnetic shields respectively corresponding to a plurality of non-sheet passing regions having different sizes.   The fixing device according to claim 1, wherein an opening is provided in a region of the core that faces the winding portion of the coil.   The fixing device according to claim 1, wherein the core is provided at least in a region facing a winding center of the coil.   The fixing device according to claim 1, wherein the magnetic shield is made of a conductive material having a thickness equal to or greater than a skin depth.   The fixing device according to claim 1, wherein the magnetic shield is made of aluminum.   The fixing device according to claim 1, wherein the magnetic shield is made of copper.   The fixing device according to claim 1, wherein the core is made of ferrite.   The fixing device according to claim 1, wherein the heating element is made of a magnetic material.   5. The fixing device according to claim 1, wherein the coil has an inductance of 10 μH to 50 μH and an electrical resistance of 0.5Ω to 5Ω at a frequency of 30 kHz with the coil facing the heating element.   The fixing device according to claim 1, wherein a frequency of a current applied to the coil is 20 kHz to 100 kHz. An image forming apparatus including a fixing unit that fixes an unfixed image formed on a recording medium,
An image forming apparatus using the fixing device according to claim 1 as the fixing unit.

Images