JP2006276645A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in an electromagnetic induction heating system and capable of effectively preventing excess temperature rise of a non-paper passing area. <P>SOLUTION: The fixing device has a fixing member 1 which generates heat by electromagnetic induction and heats a sheet to be fed to predetermined fixing temperature. The fixing device has ferrite cores 32 provided along the fixing member 1 so as to guide magnetic fluxes generated by an excitation coil 31 to the fixing member 1. The fixing device has heating elements 33-1, 33-2 which heat a part We equivalent to a non-paper passing area equivalent to non-paper passing areas 1-1, 1-2 of the ferrite cores 32 when a sheet with small size of 5-2 among a plurality of kinds of size to be fed is fed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device, and more particularly to a fixing device that heats a conveyed sheet and fixes an image on the sheet. Such a fixing device is used in an electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile machine.

  In a general fixing device having a halogen lamp or a resistance heating element as a heating source, a plurality of halogen lamps or resistance heating elements corresponding to the sizes of various papers passing through the fixing roller are not provided. It prevents overheating in the paper area.

As a recent fixing device, an electromagnetic induction heating type that includes an exciting coil wound around a ferrite core and heats a fixing roller by electromagnetic induction is widely used. In such an electromagnetic induction heating type fixing device, it is difficult to provide a plurality of exciting coils according to various paper sizes because of the configuration in which magnetic flux is generated by the winding exciting coil. Therefore, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2001-23767) and Patent Document 2 (Japanese Patent Laid-Open No. 2001-318545), the heat of the fixing roller (heat roller, pressure roller) heated by electromagnetic induction, By setting the ferrite core around which the exciting coil is wound to the Curie temperature or higher, excessive temperature rise in the non-sheet passing region is prevented.
Japanese Patent Laid-Open No. 2001-23767 JP 2001-318545 A

  However, in the above conventional electromagnetic induction heating type fixing device, although the fixing roller itself heated by electromagnetic induction heats up relatively quickly, the ferrite core heats up more slowly than that, so the ferrite core is curie. It takes some time for the temperature to rise. For this reason, in actuality, the temperature of the non-sheet passing region is not lowered unless the excessive temperature rise is continued for a while. As a result, there are problems such as image defects and damage to the fixing device such as smoke and fire.

  This problem becomes prominent when a fixing belt having a smaller heat capacity is used instead of a general fixing roller for the purpose of completing warm-up in a short time and reducing power consumption.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic induction heating type fixing device that can effectively prevent an excessive temperature rise in a non-sheet passing region.

In order to solve the above problems, the fixing device of the present invention is:
A fixing member that generates heat by electromagnetic induction and heats the conveyed sheet to a predetermined fixing temperature;
A ferrite core provided along the fixing member so as to guide the magnetic flux generated by the exciting coil to the fixing member;
When a small-sized sheet among a plurality of sizes that can be conveyed is conveyed, a heating element is provided that heats a portion corresponding to a non-sheet-passing area corresponding to a non-sheet-passing area in the ferrite core.

  Here, the “small size” sheet means a sheet having a size smaller than the maximum size among a plurality of sizes that can be conveyed. “Size” refers to the size in a direction perpendicular to the conveyance direction of a sheet passing through the fixing member (this is referred to as “sheet width direction”).

  The “non-sheet passing region” refers to a region of the surface of the fixing member where the sheet does not pass in the sheet width direction.

  In the fixing device of the present invention, similarly to the conventional electromagnetic induction heating type fixing device, the ferrite core guides the magnetic flux generated by the exciting coil to the fixing member. Fixing temperature is reached. The sheet passing through the fixing member is heated to the fixing temperature, and the image is fixed on the sheet.

  Here, when a maximum size sheet is conveyed among a plurality of size sheets that can be conveyed, the entire sheet passing area of the fixing member is uniformly deprived of heat by the sheet in the width direction of the sheet. Only the end of the fixing member does not overheat. Therefore, the entire sheet passing area of the fixing member can be maintained at the fixing temperature. At this time, since the fixing temperature is lower than the Curie temperature of the ferrite core, the function of the ferrite core to guide the magnetic flux by the heat from the fixing member is not lost.

  On the other hand, when a small-sized sheet is conveyed, the heating element heats a portion corresponding to the non-sheet passing region of the ferrite core. When the temperature of the portion corresponding to the non-sheet passing region of the ferrite core exceeds the Curie temperature, the portion corresponding to the non-sheet passing region loses the function of guiding the magnetic flux to the fixing member, and the non-sheet passing region of the fixing member is substantially reduced. No longer generates heat. Therefore, the temperature of the non-sheet passing region of the fixing member is rapidly lowered as compared with the conventional example. As described above, according to the present invention, excessive heating of the non-sheet passing region of the fixing member can be effectively prevented by positively heating the portion corresponding to the non-sheet passing region of the ferrite core with the heating element. As a result, image defects and damage to the fixing device such as smoke and fire can be prevented.

  The fixing device according to an embodiment includes a sheet passing size determining unit that determines the size of the conveyed sheet.

  In the fixing device according to this embodiment, the sheet passing size determining unit can determine whether a maximum size sheet or a small size sheet is conveyed among a plurality of size sheets that can be conveyed. it can. Therefore, an operation corresponding to the size of the conveyed sheet can be performed.

  In the fixing device according to one embodiment, the fixing member is a fixing belt.

  Generally speaking, the fixing belt has a smaller heat capacity than the fixing roller. Therefore, in the fixing device of this embodiment, it is possible to complete warm-up and reduce power consumption in a short time. Moreover, as described above, according to the present invention, it is possible to effectively prevent an excessive temperature rise in the non-sheet passing region of the fixing member. Therefore, there is no problem caused by using a fixing belt as the fixing member.

  In the fixing device according to an embodiment, the heating element is disposed on the opposite side of the ferrite core from the fixing member.

  Here, “the side opposite to the fixing member” with respect to the ferrite core means the side opposite to the portion of the fixing member that receives electromagnetic induction via the ferrite core.

  In the fixing device of this embodiment, the heating element is disposed on the opposite side of the ferrite core from the portion that receives electromagnetic induction of the fixing member. Therefore, the heat generated by the heating element does not directly heat the portion of the fixing member that receives electromagnetic induction. Accordingly, it is possible to reduce the influence of the heat generation of the heating element on the temperature of the fixing member.

In one embodiment, the fixing device includes:
A first power supply control unit for controlling power supply to the excitation coil;
Second power supply control for controlling power supply to the heating element so as to heat a portion corresponding to the non-sheet passing region of the ferrite core to a preset temperature when the small-sized sheet is conveyed. It has the part.

  In the fixing device according to this embodiment, when the small-sized sheet is conveyed, the second power supply control unit supplies power to the heating element, and the ferrite core corresponds to a non-sheet passing region. Can be heated to a preset temperature, for example, a temperature exceeding the Curie temperature of the ferrite core. Thereby, the non-sheet passing region of the fixing member can be prevented from substantially generating heat, and excessive temperature rise can be effectively prevented.

  In the fixing device according to the embodiment, the second power supply control unit may cause the temperature of the portion corresponding to the non-sheet passing region of the ferrite core to exceed the Curie temperature of the portion when the small size sheet is conveyed. It is characterized by controlling to.

  In the fixing device of this embodiment, when the small-sized sheet is conveyed, the non-sheet passing area of the fixing member can be prevented from substantially generating heat, and an excessive temperature rise can be effectively prevented. .

In one embodiment, the fixing device includes:
A temperature detection sensor that detects the temperature of the portion corresponding to the non-sheet passing region of the ferrite core,
The second power supply control unit controls power supply to the heating element based on an output of the temperature detection sensor.

  In the fixing device of this embodiment, the temperature of the portion corresponding to the non-sheet passing region of the ferrite core can be easily controlled.

  The image forming apparatus according to the present invention includes the fixing device and a sheet passing size instruction section that sends a signal indicating the size of the conveyed sheet to the fixing device.

  In the image forming apparatus of the present invention, the sheet passing size instruction section sends a signal indicating the size of the sheet conveyed to the fixing member to the fixing device. Therefore, the fixing device can operate according to the size of the conveyed sheet. That is, when a sheet of the maximum size among a plurality of sizes that can be conveyed is conveyed, the entire sheet passing area of the fixing member is uniformly deprived of heat by the sheet in the width direction of the sheet. Only the end of the member will not overheat. Therefore, the entire sheet passing area of the fixing member can be maintained at the fixing temperature. At this time, since the fixing temperature is lower than the Curie temperature of the ferrite core, the function of the ferrite core to guide the magnetic flux by the heat from the fixing member is not lost.

  On the other hand, when a small-sized sheet is conveyed, the heating element heats a portion corresponding to the non-sheet passing region of the ferrite core. When the temperature of the portion corresponding to the non-sheet passing region of the ferrite core exceeds the Curie temperature, the portion corresponding to the non-sheet passing region loses the function of guiding the magnetic flux to the fixing member, and the non-sheet passing region of the fixing member is substantially reduced. No longer generates heat. Therefore, the temperature of the non-sheet passing region of the fixing member is rapidly lowered as compared with the conventional example. As described above, according to the present invention, excessive heating of the non-sheet passing region of the fixing member can be effectively prevented by positively heating the portion corresponding to the non-sheet passing region of the ferrite core with the heating element. As a result, image defects and damage to the fixing device such as smoke and fire can be prevented.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 shows a cross-sectional configuration of an electromagnetic induction heating type fixing device 90 as one embodiment. 2 shows a view of FIG. 1 viewed from the left side, and FIG. 3 shows a view of FIG. 1 viewed from above. For ease of understanding, a casing (described later) is omitted in FIGS. The fixing device 90 is mounted on an electrophotographic image forming apparatus and fixes a toner image on a sheet 5 as a sheet conveyed with toner attached thereto.

  As shown in FIG. 1, the fixing device 90 includes a casing 50 having a conveyance path 50 </ b> C for the paper 5. The casing 50 includes two portions 50A and 50B corresponding to the left and right sides of the conveyance path 50C in FIG. The conveyance path 50 </ b> C includes a pair of upper and lower guides 51 </ b> A, 51 </ b> B; 52 </ b> A, 52 </ b> B that guide the paper 5.

  The left portion 50A of the casing 50 has a cylindrical fixing belt 1 as a fixing member, a holder 15 made of a nonmagnetic material arranged along the left half of the outer periphery of the fixing belt 1, and held by the holder 5. The excitation coil 31, the ferrite core 32 arranged so as to cover the outer periphery of the excitation coil 31, and the heating element 33 are accommodated. The excitation coil 31 and the ferrite core 32 constitute an electromagnetic induction heating unit that heats the fixing belt 1 by electromagnetic induction. On the other hand, the cylindrical pressure roller 2 is accommodated in the right portion 50 </ b> B of the casing 50.

  The fixing belt 1 has a conductive layer (Ni in this example having a thickness of about 0.04 mm) that generates heat by electromagnetic induction so that the conveyed paper can be heated to a predetermined fixing temperature (described later), and a thickness surrounding the surface. And a release layer made of PFA (perfluoroalkoxy) of about 0.03 mm. Inside the fixing belt 1, a support member 11 extending in the axial direction and an elastic member 12 attached to the support member 11 and in contact with the inner peripheral surface of the fixing belt 1 are provided. A thermistor 41 is attached to the support member 11 via a flexible arm 13. The thermistor 41 is in contact with the inner peripheral surface of the fixing belt 1 and functions as a temperature detection sensor that detects the temperature of the fixing belt 1.

  The pressure roller 2 has an elastic layer made of Si foam rubber having a thickness of 5 mm and a PFA (tetrafluoroethylene and perfluoroalkyl vinyl ether) having a thickness of 30 μm surrounding the surface of the elastic layer made of Si foam rubber having a thickness of 5 mm in this example. And a release layer made of a copolymer) is provided. The pressure roller 2 is urged toward the fixing belt 1 by a spring (not shown) and forms a nip with the fixing belt 1. The pressure roller 2 is rotated clockwise in FIG. 1 by a motor (not shown) during the fixing operation. Accordingly, the fixing belt 1 is rotated counterclockwise in FIG. 1, and the sheet 5 subjected to the fixing process through the nip is conveyed from below to above.

  As shown in FIG. 2, the exciting coil 31 is formed by winding a conducting wire into an oval shape a plurality of times. Specifically, the exciting coil 31 includes an outward path conductor portion 31a and a return path conductor portion 31b extending in the longitudinal direction (left and right direction in FIG. 2), and arcuate curved conductor portions 31c and 31d that connect between them. In addition, in order to increase the current-carrying efficiency, one conducting wire is a bundle of several tens to several hundreds of strands (copper wires having a diameter of about 0.18 mm to 0.20 mm and insulated with enamel). Is a known stranded wire having a diameter of about several millimeters.

  As shown in FIG. 1, the forward conductive wire portion 31 a and the backward conductive wire portion 31 b of the exciting coil 31 are fitted and accommodated in the upper half 15 a and the lower half 15 b of the holder 15, respectively. The layer formed by the excitation coil 31 accommodated in the holder 15 has the same curvature as the outer periphery of the fixing roller 1 and is along the outer periphery of the fixing belt 1.

  In the cross section shown in FIG. 1, the ferrite core 32 has an arc portion 32p arranged along the outward path portion 31a and the return path portion 31b of the exciting coil 31 with the same curvature, and the upper and lower edges of the arc portion 32p. From the center of the arc portion 32p toward the outer peripheral surface of the fixing belt 1 through the gaps between the protrusions 32a and 32b extending from the edge toward the outer peripheral surface of the fixing belt 1 and the forward conductor portion 31a and the backward conductor portion 31b of the exciting coil 31. And extending protrusions 32c and 32d (see FIG. 5). As a result, the forward wire portion 31 a of the exciting coil 31 corresponds to the upper half of the arc portion 32 p of the ferrite core 32, the protrusions 32 a and 32 c, and the protrusions 32 a and 32 c on the outer peripheral surface of the fixing belt 1. It is in a state surrounded by parts. Further, the return wire portion 31 b of the exciting coil 31 is a portion corresponding to the lower half of the arc portion 32 p of the ferrite core 32, the protrusions 32 b and 32 d, and the protrusion 32 b and 32 d on the outer peripheral surface of the fixing belt 1. It is in a state surrounded by.

The ferrite core 32 is made of a uniform magnetic material. In this example, the composition of the ferrite core 32 is Fe ₂ O ₃ : 54% / MnO: 31% / Zn0: 15%. Thereby, the Curie temperature Tc of each part of the ferrite core 32 is the same, and is adjusted to about 250 ° C. As a material of the ferrite core 32, it is desirable to use a material having a high magnetic permeability. However, when a material in which magnetic powder is dispersed in a resin material is used as the material of the ferrite core 32, the magnetic permeability is relatively low, but the shape can be freely set.

  As shown in FIG. 2, the ferrite core 32 is set to have substantially the same dimension W <b> 1 as the forward conductor portion 31 a, the return conductor portion 31 b and the holder 15 of the exciting coil 31 in the longitudinal direction. The longitudinal dimension is the width of the maximum size paper supplied to the apparatus, in this example, the width W1 (= 297 mm) of the A3 size paper so that A3 size paper defined by Japanese Industrial Standards can be processed. Is substantially consistent. The longitudinal directions of the exciting coil 31, the ferrite core 32, and the holder 15 are parallel to the central axis of the fixing belt 1 and the pressure roller 2 in FIG. 1, in other words, with respect to the conveyance direction of the sheet 5 in the nip portion. This corresponds to the width direction of the paper 5 which is substantially vertical.

  In the cross section shown in FIG. 1, the heating element 33 is provided along the outer peripheral surface of the arc portion 32 p of the ferrite core 32 for the purpose of heating the ferrite core 32. In this example, the heating element 33 is formed by sealing a resistance wire 33a that generates heat when energized on a base material 33b made of heat-resistant glass. The heating element 33 is disposed on the opposite side of the fixing belt 1 with respect to the ferrite core 32. Therefore, the heat generated by the heat generator 33 does not directly affect the fixing belt 1.

  As shown in FIG. 3, the heating element 33 has a ferrite core when a small-size paper 5-2 (the width is expressed as W2) among a plurality of sizes supplied to the apparatus is conveyed in the longitudinal direction. 32 is provided at a position covering the non-sheet-passing area corresponding portions We and We corresponding to the non-sheet-passing areas 1-1 and 1-2 on the fixing belt 1 (the two heating elements 33 are respectively denoted by reference numerals 33- 1, 33-2). Each sheet is supplied to the central portion 1-C (symmetric with respect to the center line C) of the fixing belt 1 and the pressure roller 2 with respect to the longitudinal direction. Accordingly, the non-sheet-passing area equivalent portions We and We are both end portions of the ferrite core 32.

  Further, as shown in FIG. 1, a thermistor 42 as a temperature detection sensor is attached to the non-sheet-passing area equivalent portion We of the ferrite core 32 in order to detect the temperature of the non-sheet-passing area equivalent portion We. .

  As can be clearly seen from FIG. 2, the exciting coil 31 is connected to an AC (alternating current) power supply 60 via wirings 63-1, 63-2. A first switch 61 is inserted in the wiring 63-1, and power supply to the exciting coil 31 is turned on and off by the first switch 61. On the other hand, the heating elements 33-1 and 33-2 are connected to the AC power supply 60 in series via separate wirings 64-1, 64-2 and 64-3. A second switch 62 is inserted in the wiring 64-1, and power supply to the heating element 33 is turned on and off by the second switch 62. Note that thermostats 65 and 66 (see FIG. 4) for interrupting the circuit when the temperature rises abnormally are inserted in the wiring 63-1 connected to the exciting coil 31 and the wiring 64-1 connected to the heating element 33, respectively. .

  FIG. 4 shows a circuit configuration of the power supply control unit of the fixing device 90. The power supply control unit includes a CPU (central processing unit) 67 that controls the first switch 61 and the second switch 62 to be turned on and off.

  A signal representing the temperature of the fixing belt 1 is input to the CPU 67 from a connection point between the voltage dividing resistor R1 and the thermistor 41, and a non-sheet passing region of the ferrite core 32 from a connection point between the voltage dividing resistor R2 and the thermistor 42. A signal indicating the temperature of the corresponding portion We is input. Further, the CPU 67 receives a sheet passing size signal SigW indicating the size of the sheet 5 to be conveyed from the operation panel 90 of the image forming apparatus provided with the fixing device 90 or an external computer. The operation panel 90 or an external computer functions as a sheet passing size instruction unit.

  At the time of image formation (that is, at the time of fixing operation), the CPU 67 outputs an exciting coil remote signal SigIH to the first switch 61 based on the temperature of the fixing belt 1 indicated by the output of the thermistor 41 and performs on / off control. Thereby, an alternating current of 10 kHz to 100 kHz is applied to the exciting coil 31.

  Normally (when the temperature of the ferrite core 32 is equal to or lower than the Curie temperature Tc), as shown in FIG. 5, the magnetic flux F <b> 1 induced by the current flowing through the forward conductor portion 31 a of the exciting coil 31 is the arc portion of the ferrite core 32. It passes through a closed circuit formed by the upper half of 32p, the protrusions 32a and 32c, and the portion corresponding to the area between the protrusions 32a and 32c on the outer peripheral surface of the fixing belt 1. Similarly, the magnetic flux F2 induced by the current flowing through the return wire portion 31b of the exciting coil 31 is equivalent to the lower half of the arc portion 32p of the ferrite core 32, the portion corresponding to between the protrusions 32b and 32d, and the fixing belt 1. Passes through a closed circuit formed by the protrusions 32b and 32d. When the magnetic fluxes F1 and F2 passing through these closed circuits change according to the alternating current, an eddy current flows through the conductive layer of the fixing bell 1 and the conductive layer generates Joule heat. Since the ferrite core 32 guides the magnetic flux generated by the exciting coil 31 to the fixing belt 1 without leaking outside, the temperature of the fixing belt 1 is increased efficiently.

  In this way, the CPU 67 controls the fixing belt 1 to a predetermined fixing temperature Tfx = 180 ° C. Accordingly, the sheet 5 passing through the nip between the fixing belt 1 and the pressure roller 2 shown in FIG. 1 is heated to the fixing temperature, and the image is fixed on the sheet 5.

  Here, as shown in FIG. 9, when the maximum size paper 5-1 (width W1) among a plurality of sizes that can be transported is transported, the entire sheet passing area of the fixing belt 1 in the width direction of the paper is Since the heat is uniformly taken away by the paper, only the end portion of the fixing belt 1 does not overheat. Therefore, the temperature Tbt of the fixing belt 1 can be maintained at a predetermined fixing temperature Tfx = 180 ° C. over substantially the entire sheet passing region. At this time, since the fixing temperature Tfx is lower than the Curie temperature Tc = 250 ° C. of the ferrite core 32, the ferrite core 32 does not lose its function of guiding the magnetic flux by the heat from the fixing belt 1.

  On the other hand, as shown in FIG. 10, when the small-size paper 5-2 (width W2) is conveyed, the heat of the non-sheet passing area of the fixing belt 1 is not taken away by the paper, so that area (FIG. 10). The temperature of the region indicated by NG in the inside tends to exceed a predetermined fixing temperature Tfx = 180 ° C. Therefore, the CPU 67 functions as a sheet passing size determining unit, and determines whether or not the conveyed sheet is a small size sheet 5-2 based on the sheet passing size signal SigW as shown in FIG. (S1). When the conveyed paper is the small size paper 5-2, the temperature of the heating element 33 is adjusted (S2). That is, the CPU 67 outputs the heating element remote signal SigRH to the second switch 62 based on the temperature of the non-sheet passing region equivalent portion We of the ferrite core 32 indicated by the output of the thermistor 42 shown in FIG. To do. As a result, an alternating current is applied to the heating element 33, and as shown in the lower part of FIG. 11, the respective parts 33-1 and 33-2 of the heating element 33 replace the portions We and We corresponding to the non-sheet passing regions of the ferrite core 32. Heat. In this example, the CPU 67 controls the temperature of the heating element 33, and hence the temperature Tfc of the portion corresponding to the non-sheet passing region of the ferrite core 32, to a temperature 270 ° C. exceeding the Curie temperature Tc (= 250 ° C.) of the ferrite core 32. . When the temperature of the portion We corresponding to the non-sheet passing region of the ferrite core 32 exceeds the Curie temperature Tc, the portion We corresponding to the non-sheet passing region becomes nonmagnetic as shown in FIG. Therefore, the non-sheet passing area of the fixing belt 1 is not substantially heated. Therefore, as shown in the upper part of FIG. 11, the temperature Tbt of the fixing belt 1 is rapidly decreased with respect to the non-sheet passing region as compared with the conventional example.

  As described above, in the fixing device 90, the non-sheet-passing area corresponding portion We of the ferrite core 32 is actively heated by the heating element 33, thereby effectively increasing the temperature rise in the non-sheet-passing area of the fixing belt 1. Can be prevented. As a result, image defects and damage to the fixing device such as smoke and fire can be prevented.

  In the above-described control example (FIG. 7) by the CPU 67, the temperature of the heating element 33 is controlled only when the conveyed paper is the small size paper 5-2, and the maximum size paper 5-1 (width) When W1) is transported, power is not supplied to the heating element 33. However, the present invention is not limited to this, and when the maximum size paper 5-1 (width W <b> 1) is conveyed, the temperature of the heating element 33, and hence the temperature Tfc of the portion corresponding to the non-paper passing area of the ferrite core 32, is set. Further, it may be controlled to 180 ° C. which is the same as the normal fixing temperature Tfx.

  Further, instead of controlling the temperature of the heating element 33 based on the output of the thermistor 42 provided in the non-sheet-passing area equivalent portion We of the ferrite core 32, the heating element 33 is always energized to some extent (not to ignite). You may make it perform.

  In FIG. 12, the size of the conveyed paper is not two types, but various types (in this example, four types) of papers 5-1, 5-2, 5-3, and 5-4 (in this order, the smaller size) 2 shows an example of the configuration of the fixing device in the case of being conveyed. Each of the papers 5-1, 5-2, 5-3, and 5-4 is supplied to the central portion 1-C (symmetric with respect to the center line C) of the fixing belt 1 and the pressure roller 2 with respect to the longitudinal direction. The

  In this example, heat is generated so that the portion corresponding to the non-sheet passing region of the ferrite core 32 can be heated for each of the small-sized papers 5-2, 5-3, and 5-4 as compared with the maximum-size paper 5-1. Divide the body. That is, when the small-size paper 5-2 is conveyed, the heating element 33 provided at a position corresponding to the non-sheet passing regions 1-1 and 1-2 on the fixing belt 1 with respect to the longitudinal direction of the ferrite core 32. -1,33-2 is heated. When the next smallest sheet 5-3 is conveyed, it corresponds to the non-sheet passing areas 1-1, 1-3; 1-2, 1-4 on the fixing belt 1 in the longitudinal direction of the ferrite core 32. The heating elements 33-1 and 33-3; 33-2 and 33-4 provided at the positions are heated. When the smallest sheet 5-4 is conveyed, the non-sheet passing areas 1-1, 1-3, 1-5 on the fixing belt 1 with respect to the longitudinal direction of the ferrite core 32; 1-2, 1-4, Heating elements 33-1, 33-3, 33-5; 33-2, 33-4, 33-6 provided at positions corresponding to 1-6 are heated.

  In this case, even if there are many types of paper to be conveyed, excessive temperature rise in the non-sheet passing area of the fixing belt 1 can be effectively prevented. As a result, image defects and damage to the fixing device such as smoke and fire can be prevented.

  FIG. 13 shows a fixing device 190 obtained by modifying the fixing device 90 shown in FIG. For easy understanding, components corresponding to those in FIG. 1 are denoted by reference numerals increased by 100.

  In the fixing device of FIG. 1, an excitation coil 31, a ferrite core 32, and a heating element 33 are provided on the outer side of the cylindrical fixing belt 1 in order from the outer peripheral surface of the fixing belt 1. On the other hand, in the fixing device 190, an excitation coil 131, a ferrite core 132, and a heating element 133 are provided inside the cylindrical fixing belt 101 in order from the inner peripheral surface of the fixing belt 101. The thermistor 141 for detecting the temperature of the fixing belt 101 is provided in contact with the outer peripheral surface of the fixing belt 101 due to the restriction that there are many components inside the fixing belt 101. The thermistor 41 is attached to the inner surface of the casing 150 via an attachment member 114 and a flexible arm 113.

  In the fixing device 190 as well, as in the fixing device 90 in FIG. The heating element 133 is disposed on the opposite side of the ferrite core 132 from the part that receives the electromagnetic induction of the fixing belt 101, so that the heat generation of the heating element 133 directly heats the part that receives the electromagnetic induction of the fixing belt 101. There is nothing. Therefore, the influence of heat generated by the heat generating member 133 on the temperature of the fixing belt 101 is small.

  In the above-described embodiment, the case where paper is used as the sheet has been described. However, the material of the sheet may be paper or plastic. Further, the shape of the sheet may be a rectangle (for example, A4 or B5 defined by Japanese Industrial Standards) or a long object such as a roll.

  In the above-described embodiment, the sheet passing size signal SigW indicating the size of the sheet 5 to be conveyed is received from the operation panel 90 or an external computer. However, the present invention is not limited to this. A fixing device or an image forming apparatus may be provided with a paper passing size detection sensor for detecting the size of the conveyed paper so as to determine the size of the conveyed paper.

1 is a diagram illustrating a cross-sectional configuration of a fixing device according to an embodiment of the present invention. It is a figure which shows the place which looked at the thing of FIG. 1 from the left side. It is a figure which shows the place which looked at the thing of FIG. 1 from upper direction. FIG. 2 is a diagram illustrating a power supply system for the fixing device. It is a figure which shows typically the mode of the magnetic flux in case the temperature of a ferrite core is below Curie temperature. It is a figure which shows typically the mode of the magnetic flux in case the temperature of a ferrite core is more than Curie temperature. It is a figure which shows the control flow by CPU of the electric power supply system for the said fixing devices. It is a figure which shows the relationship between a ferrite core temperature and fixing belt heating efficiency. FIG. 6 is a diagram illustrating a temperature distribution in a longitudinal direction of a fixing belt when a maximum size sheet is supplied in the fixing device. FIG. FIG. 10 is a diagram illustrating a problem of excessive temperature rise at the end of the fixing belt when a small-size sheet is supplied. FIG. 6 is a diagram illustrating a temperature distribution in a longitudinal direction of a fixing belt and a ferrite core when a small-size sheet is supplied in the fixing device. FIG. 4 is a diagram illustrating a configuration example of a fixing device according to an embodiment in the case where various types of sizes of paper are conveyed. FIG. 2 is a diagram illustrating a configuration example of a fixing device according to an embodiment in which the fixing device of FIG. 1 is modified.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Fixing belt 2,102 Pressure roller 31,131 Excitation coil 32,132 Ferrite core 33,133 Heating element

Claims (8)

A fixing member that generates heat by electromagnetic induction and heats the conveyed sheet to a predetermined fixing temperature;
A ferrite core provided along the fixing member so as to guide the magnetic flux generated by the exciting coil to the fixing member;
A fixing device comprising a heating element that heats a portion corresponding to a non-sheet-passing region corresponding to a non-sheet-passing region in the ferrite core when a small-sized sheet among a plurality of sizes that can be transported is transported apparatus. The fixing device according to claim 1,
A fixing device comprising a sheet passing size determining unit for determining the size of the conveyed sheet. The fixing device according to claim 1,
The fixing device, wherein the fixing member is a fixing belt. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the heating element is disposed on the opposite side of the ferrite core from the fixing member. The fixing device according to claim 1,
A first power supply control unit for controlling power supply to the excitation coil;
Second power supply control for controlling power supply to the heating element so as to heat a portion corresponding to the non-sheet passing region of the ferrite core to a preset temperature when the small-sized sheet is conveyed. A fixing device comprising a section. The fixing device according to claim 5.
The second power supply control unit controls the temperature of a portion corresponding to the non-sheet passing region of the ferrite core to exceed the Curie temperature of the portion when the small-sized sheet is conveyed. Fixing device. The fixing device according to claim 5.
A temperature detection sensor that detects the temperature of the portion corresponding to the non-sheet passing region of the ferrite core,
The fixing device according to claim 2, wherein the second power supply control unit controls power supply to the heating element based on an output of the temperature detection sensor. A fixing device according to claim 1;
An image forming apparatus comprising: a sheet passing size instruction section that sends a signal representing the size of the conveyed sheet to the fixing device.

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