JP2013174716A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a difference of thermal load inside and outside a second area at the start of pressurization.SOLUTION: A heating belt 51 is configured by an endless belt member, and rotates to carry paper contacting an outer peripheral surface thereof. An electromagnetic induction portion 53 has an exciting coil which generates a high-frequency magnetic field around the coil when an AC current is supplied, and causes the whole area in a width direction on the outer peripheral surface of the rotating heating belt 51 to generate heat. A resistance heating element 582 is disposed on an inner peripheral surface side of the heating belt 51, and heats an area included in the whole area in the width direction of the outer peripheral surface of the heating belt 51 and having narrower width than the width of the whole area through the heating belt 51, by Joule heat generated by energizing. A pressurizing roll 52 clips paper with the outer peripheral surface of the heating belt 51, and pressurizes the paper toward the outer peripheral surface. A control portion separates the pressurizing roll 52 from the outer peripheral surface to be heated by the electromagnetic induction portion 53, and then has the paper pressurized by the pressurizing roll 52 and heated by the resistance heating element 582.

Description

  The present invention relates to a fixing device and an image forming apparatus.

In Patent Document 1, a heater is energized so that a main thermistor maintains a constant temperature, and the size of a recording material (medium) to be passed is detected, and a sub-thermistor is detected in the passing region of the detected size of the recording material. The image forming apparatus determines whether or not to switch to the control of energizing the heater so as to maintain the temperature of the sub-thermistor depending on whether or not is included.
In Patent Document 2, a first temperature detection element that detects the temperature of a heating body and performs temperature control is disposed in an area through which a recording material having a minimum width that can be supplied to the image forming apparatus and used can pass. The second temperature detection element that controls the temperature by detecting the temperature of the heating body is at a position different from the first temperature detection element in the longitudinal direction of the heating body and can be used by supplying it to the image forming apparatus An image forming apparatus arranged outside a region through which a recording material having a minimum width passes is described.

JP 2009-186891 A JP 2008-185955 A

  The present invention includes a belt for conveying a medium, a first heating unit that heats a first region on the outer peripheral surface of the belt, a second heating unit that heats a second region that is narrower than the first region, An object of the present invention is to reduce a difference in heat load between the inside and outside of a second region at the start of pressurization in a fixing device including a pressurizing unit that sandwiches a medium together with an outer peripheral surface.

  According to a first aspect of the present invention, there is provided a fixing device that heats an endless belt that conveys a medium in contact with an outer peripheral surface, and a first region having a first width on the outer peripheral surface of the belt. A first heating unit that fixes an image formed on the passing medium; and a second region that is included in the first region and has a second width that is narrower than the first width. A second heating unit that fixes an image formed on a medium passing through the medium, a pressurizing unit that sandwiches the medium together with the outer peripheral surface and pressurizes the medium toward the outer peripheral surface, and the second of the mediums. When fixing an image formed on a medium having a width narrower than the width, the pressure unit is moved away from the outer peripheral surface, and the first region is heated by the first heating unit. To pressurize the medium to heat the second region to the second heating unit. Characterized in that it comprises a control unit for.

  According to a second aspect of the present invention, there is provided a fixing device according to the first aspect, further comprising a measurement unit that measures the temperature of the belt, and the control unit is narrower than the second width of the medium. When fixing an image formed on a medium having a width, the pressurizing unit is separated from the outer peripheral surface, the first heating unit is heated by the first heating unit, and a target temperature that is a target temperature is set. Then, after the temperature measured by the measuring unit reaches, the medium is pressurized by the pressurizing unit, and the second heating unit is heated by the second heating unit.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the measuring unit measures a temperature at a position that is included in the first area and not included in the second area. A first measurement unit; and a second measurement unit that measures a temperature of a position included in the second region, wherein the control unit is configured to control the temperature measured by the first measurement unit and the second measurement unit. A value serving as an index is calculated using the measured temperature, and after the calculated value satisfies a predetermined condition, the medium is pressurized by the pressure unit, and the second heating unit is The second region is heated.

  According to a fourth aspect of the present invention, there is provided the fixing device according to any one of the first to third aspects, wherein the first heating unit generates an alternating magnetic field and performs electromagnetic induction in the alternating magnetic field. One region is heated, and the second heating unit heats the second region by Joule heat generated by flowing electricity.

  A fixing device according to a fifth aspect of the present invention is the fixing device according to the fourth aspect, wherein the belt includes a member that generates heat by generating an eddy current when an AC magnetic field passes, and the first heating unit includes the first heating unit, The AC magnetic field is passed through the member to heat the first region, and the second heating unit is disposed on the inner peripheral surface side of the belt, and the Joule heat is transmitted to the outer peripheral surface through the belt. And the second region is heated.

  The fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the control unit applies a medium having a width narrower than the second width of the medium. When fixing the formed image, the pressurizing unit is separated from the outer peripheral surface, and only the first region is heated by the first heating unit or the first heating unit according to the state of the belt. The first region is selected by the second heating unit to heat the second region, and the medium is pressurized by the pressure unit after the first region or the second region is heated. The second heating part is heated by the second region.

  An image forming apparatus according to a seventh aspect of the present invention includes an image forming unit that forms an image on a medium, and a transport unit that transports the medium on which the image is formed by the image forming unit to the first region or the second region. And a fixing device according to any one of claims 1 to 6, wherein the image is fixed on the medium conveyed by the conveying means.

According to the first and seventh aspects of the invention, the belt that conveys the medium, the first heating unit that heats the first region on the outer peripheral surface of the belt, and the second region that is narrower than the first region are heated. In a fixing device including a second heating unit and a pressurizing unit that sandwiches the medium together with the outer peripheral surface of the belt, the first heating unit does not heat the first heating unit before the pressurization is started. It is possible to reduce the difference in heat load between the two regions.
According to the invention which concerns on Claim 2, compared with the case where the heating by a 1st heating part is not performed before a pressurization start, the temperature difference in the 2nd area | region at the time of a pressurization start can be reduced.
According to the invention which concerns on Claim 3, the conditions which the temperature difference in the 2nd area | region in the time of a pressurization start should satisfy | fill can be set.
According to the invention which concerns on Claim 4, a 1st heating part and a 2nd heating part can each heat without affecting each other.
According to the fifth aspect of the present invention, the space used for fixing can be reduced as compared with the case where the second heating unit is not disposed on the inner peripheral surface side of the belt.
According to the invention which concerns on Claim 6, the heating means of the belt at the time of a pressurization start can be changed according to the state of a belt.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a diagram illustrating an outline of a fixing unit. It is the figure which looked at the fixing | fixed part from arrow III-III in FIG. It is the figure which looked at the fixing | fixed part from arrow IV-IV in FIG. It is a figure which shows an example of the external appearance of a resistance heating element. It is a figure which expands and shows a part of heating belt. It is a figure for demonstrating the effect | action of the thermosensitive magnetic alloy in the temperature below a Curie point. It is a figure for demonstrating the effect | action of the thermosensitive magnetic alloy in the temperature more than a Curie point. It is a figure which shows the outline | summary of the fixing | fixed part when a pressure roll is moved to -y direction. FIG. 6 is a flowchart showing the operation of the image forming apparatus according to the present embodiment. It is a figure for demonstrating the temperature distribution of a heating belt. It is a figure for demonstrating the temperature distribution of the heating belt in a modification. It is a figure for demonstrating the temperature distribution of the heating belt in a modification.

1. Embodiment 1-1. Configuration FIG. 1 is a diagram showing an overall configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a control unit 11, a storage unit 12, developing units 13Y, 13M, 13C, and 13K, a transfer unit 14, a fixing unit 15, a transport unit 16, and an operation unit. Part 17. Note that the symbols Y, M, C, and K indicate configurations corresponding to yellow, magenta, cyan, and black toners, respectively. Each of the developing units 13Y, 13M, 13C, and 13K is different only in the toner used, and there is no significant difference in the configuration. Hereinafter, when it is not necessary to particularly distinguish each of the developing units 13Y, 13M, 13C, and 13K, the alphabet at the end of the code indicating the color of the toner is omitted and referred to as “developing unit 13”.

  The control unit 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and a computer program (hereinafter simply referred to as a program) in which the CPU is stored in the ROM or the storage unit 12. Are read and executed to control each unit of the image forming apparatus 1.

The operation unit 17 includes operation elements such as operation buttons for inputting various instructions. The operation unit 17 receives an operation by a user and supplies a signal corresponding to the operation content to the control unit 11.
The storage unit 12 is a large-capacity storage unit such as a hard disk drive, and stores a program read by the CPU of the control unit 11.

  The conveyance part 16 has a container and a conveyance roll. The container accommodates a sheet P as a medium that has been cut into a predetermined size. Among the above-described sizes of the paper P, at least two different sizes are defined in the direction perpendicular to the transport direction, that is, in the width direction. Here, two types of paper P are used: a maximum width paper P1 and a narrow paper P2 that is narrower than the maximum width paper P1. The maximum width paper P1 is the paper having the maximum size in the width direction among the papers P handled by the image forming apparatus 1. These two types of paper P are distinguished by the control unit 11 depending on the container in which they are stored. The paper P accommodated in each container is taken out one by one by a transport roll according to an instruction from the control unit 11 and transported to the transfer unit 14 via a paper transport path. The medium is not limited to paper, and may be a resin sheet, for example. In short, the medium may be any medium that can record an image on the surface.

  Each developing unit 13 includes a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, a primary transfer roll 35, and a drum cleaner 36. The photosensitive drum 31 is an image carrier having a charge generation layer and a charge transport layer, and is rotated in the direction of an arrow D13 in the drawing by a driving unit (not shown). The charger 32 charges the surface of the photosensitive drum 31. The exposure device 33 includes a laser emission source, a polygon mirror, and the like (both not shown), and a photoconductor after the laser light corresponding to the image data is charged by the charger 32 under the control of the control unit 11. Irradiation toward the drum 31. Thereby, a latent image is held on each photosensitive drum 31. The image data may be acquired from an external device by the control unit 11 via a communication unit (not shown). The external device is, for example, a reading device that reads an original image or a storage device that stores data indicating an image.

  The developing device 34 contains a two-component developer containing toner of any one of Y, M, C, and K and a magnetic carrier such as ferrite powder. The tip of the magnetic brush formed on the developing unit 34 comes into contact with the surface of the photosensitive drum 31 so that the toner is exposed on the surface of the photosensitive drum 31 by the exposure device 33, that is, the image line of the electrostatic latent image. An image is formed (developed) on the photosensitive drum 31.

  The primary transfer roll 35 generates a predetermined potential difference at a position where the intermediate transfer belt 41 of the transfer unit 14 faces the photosensitive drum 31, and the image is transferred to the intermediate transfer belt 41 by this potential difference. The drum cleaner 36 removes untransferred toner remaining on the surface of the photosensitive drum 31 after image transfer, and removes the surface of the photosensitive drum 31. That is, the drum cleaner 36 removes unnecessary toner and charges from the photosensitive drum 31 in preparation for the next image formation.

  The transfer unit 14 includes an intermediate transfer belt 41, a secondary transfer roll 42, a belt conveyance roll 43, and a backup roll 44, and determines an image formed by the developing unit 13 according to a user operation. This is a transfer section that transfers the paper P to the paper P of the selected paper type. The intermediate transfer belt 41 is an endless belt member, and the belt conveyance roll 43 and the backup roll 44 stretch the intermediate transfer belt 41. At least one of the belt conveyance roll 43 and the backup roll 44 is provided with a drive unit (not shown), and moves the intermediate transfer belt 41 in the direction of arrow D14 in the drawing. Note that the belt conveyance roll 43 or the backup roll 44 that does not have a driving unit rotates following the movement of the intermediate transfer belt 41. As the intermediate transfer belt 41 moves and rotates in the direction of the arrow D14 in the drawing, the image on the intermediate transfer belt 41 is moved to a region sandwiched between the secondary transfer roll 42 and the backup roll 44.

  The secondary transfer roll 42 transfers the image on the intermediate transfer belt 41 onto the paper P conveyed from the conveyance unit 16 by a potential difference with the intermediate transfer belt 41. The belt cleaner 49 removes untransferred toner remaining on the surface of the intermediate transfer belt 41. Then, the transfer unit 14 or the conveyance unit 16 conveys the paper P on which the image is transferred to the fixing unit 15. The developing unit 13 and the transfer unit 14 are an example of an image forming unit that forms an image on a medium in the present invention.

  The fixing unit 15 fixes the image transferred onto the paper P by heating. FIG. 2 is a diagram showing an outline of the fixing unit 15. FIG. 3 is a view of the fixing unit 15 as viewed from the direction of arrows III-III in FIG. 4 is a view of the fixing unit 15 as viewed from the direction of arrows IV-IV in FIG. Hereinafter, in order to explain the arrangement of each component of the fixing unit 15, the space in which each component is arranged is represented as an xyz right-handed coordinate space. Also, among the coordinate symbols shown in the figure, a symbol in which a black circle is drawn in a circle with a white inside represents an arrow heading from the back side to the near side. A direction along the x-axis in space is referred to as an x-axis direction. Of the x-axis directions, the direction in which the x component increases is referred to as + x direction, and the direction in which the x component decreases is referred to as -x direction. For the y and z components, the y-axis direction, + y direction, -y direction, z-axis direction, + z direction, and -z direction are defined. The fixing unit 15 shown in FIG. 2 is the fixing unit 15 viewed from the direction of arrows II-II in FIG. Further, when passing through the fixing unit 15, the paper P is transported in the z-axis direction with the surface on which the image is formed facing the + y direction. That is, the z-axis direction is the conveyance direction of the paper P, and the x-axis direction is the width direction of the paper P.

  The fixing unit 15 includes a heating belt 51, a pressure roll 52, an electromagnetic induction unit 53, a magnetic core 54, a measuring unit 55, a pressing pad 56, a holder 57, an auxiliary unit 58, and a shielding member 59. I have. As shown in FIG. 2, the heating belt 51 rotates in the arrow D51 direction around an axis O1 parallel to the x-axis direction. As shown in FIG. 2, the pressure roll 52 includes a metal cylindrical core member 521 and an elastic layer 522 provided on the surface of the core member 521. The core material 521 rotates in the arrow D52 direction around an axis O2 that is an axis parallel to the axis O1, and accordingly, the elastic layer 522 rotates in the arrow D52 direction. The material of the elastic layer 522 is, for example, rubber such as a silicone rubber layer or a fluorine rubber layer. The elastic layer 522 may include a surface release layer (fluororesin layer) on the surface thereof.

  The pressure roll 52 is configured to move along the y-axis direction by a drive unit (moving mechanism) (not shown). The axis O2 of the core member 521 of the pressure roll 52 is located in the -y direction of the axis O1, but the distance from the axis O1 changes when the pressure roll 52 is moved by the drive unit (moving mechanism). The position of the axis O2 shown in FIG. 2 is a position when the distance from the axis O1 is shorter than the sum of the radius of the heating belt 51 and the radius of the pressure roll 52. In this case, the pressure roll 52 contacts the outer peripheral surface of the heating belt 51 directly or via the paper P, and pressurizes the outer peripheral surface or the paper P on the outer peripheral surface. Hereinafter, the position of the pressure roll 52 at this time is referred to as a “contact position”.

  The pressure roll 52 when in the contact position presses the sheet P conveyed by the conveying unit 16 against the heating belt 51 while rotating by a driving unit (rotating mechanism) (not shown), thereby heating the sheet P by the heating belt 51. To assist. The heating belt 51 is driven and rotated by the pressure roll 52 by the frictional force from the pressure roll 52. That is, the pressure roll 52 is an example of a pressure unit in the present invention, and sandwiches the paper P (medium) together with the outer peripheral surface of the heating belt 51 and presses the paper P toward the outer peripheral surface.

The measuring unit 55, the pressing pad 56, the holder 57, the auxiliary unit 58, and the shielding member 59 are disposed on the inner peripheral surface side of the heating belt 51.
The holder 57 includes a frame 571, a support member 572, a fixing member 573, and an elastic member 574. The frame 571 is a member extending in the x-axis direction, and both end portions (not shown) of the x-axis direction are fixed to the casing of the image forming apparatus 1. The frame 571 is made of, for example, a heat-resistant resin such as glass mixed PPS (polyphenylene sulfide) or a nonmagnetic metal such as gold (Au), silver (Ag), aluminum (Al), or copper (Cu). Is formed. As a result, the frame 571 is relatively less affected by the induced magnetic field and less susceptible to the induced magnetic field than when other materials are used. The frame 571 supports the pressing pad 56 in the arrow D56 direction (−y direction) shown in FIG. 2, that is, in the direction in which the pressing roll 52 is disposed.

  The frame 571 that supports the pressing pad 56 is made of a material having high rigidity so that the amount of bending in a state where the pressing pad 56 receives the pressing force from the pressing roll 52 becomes a certain amount or less. Thereby, the uniformity of the pressure (nip pressure) in the x-axis direction in the nip region R1 is maintained. Both the support member 572 and the fixing member 573 are attached to the frame 571 by a connecting tool such as a screw.

  The shielding member 59 is disposed between the electromagnetic induction portion 53 and the frame 571 and makes it difficult for the magnetic path generated from the electromagnetic induction portion 53 to leak to the frame 571 side. As shown in FIG. 2, one end portion 591 of the shielding member 59 is fixed by a fixing member 573 attached to the frame 571. The fixing member 573 also fixes an upstream end portion in the rotation direction of the heating belt 51 among the end portions of the auxiliary portion 58. On the other hand, the other end portion 592 of the shielding member 59 is coupled to the downstream end portion in the rotational direction among the end portions of the auxiliary portion 58. The elastic member 574 is disposed between the end portion 592 of the shielding member 59 and the support member 572.

  In this configuration, since the shielding member 59 is made of aluminum or the like and has elasticity, the end portion 592 of the shielding member 59 moves in the + y direction and the −y direction with the end portion 591 as a fulcrum. The elastic member 574 generates a force in the right direction, that is, the + y direction as viewed in FIG. This force pushes the end 592 side of the shielding member 59 in the + y direction.

  The pressing pad 56 is made of a heat resistant resin such as LCP (Liquid Crystal Polymer) and is supported by the frame 571 of the holder 57 at a position facing the pressure roll 52. The pressing pad 56 is disposed in a state of being pressed from the pressure roll 52 via the heating belt 51, and presses the heating belt 51 from the inner peripheral surface side toward the direction of the pressure roll 52 (−y direction). Thereby, a nip region R <b> 1 is formed between the heating belt 51 and the pressure roll 52. The sheet P is conveyed so as to pass through the nip region R1. In the nip region R <b> 1, the pressing pad 56 is deformed so as to be recessed toward the axis O <b> 1 by the pressing of the pressing roll 52, and the heating belt 51 has a shape along the shape of the deformed pressing pad 56. The pressing pad 56 may be made of an elastic body such as silicone rubber or fluorine rubber.

  The auxiliary portion 58 includes a temperature-sensitive magnetic alloy 581, a resistance heating element 582, and a damping member 583 that are stacked in this order from the inner peripheral surface side of the heating belt 51 toward the axis O <b> 1.

  The temperature-sensitive magnetic alloy 581 is a metal material having a Curie point, and is, for example, a Ni-Fe-based or Ni-Cr-Fe-based magnetic shunt alloy. This Curie point is preferably in the range of not less than the set temperature of the heating belt 51 and not more than the heat resistant temperature of the heating belt 51. Specifically, for example, it is desirably 170 ° C. or more and 250 ° C. or less, more desirably 190. It is at least 230 ° C.

  The temperature-sensitive magnetic alloy 581 is configured in a shape along the inner peripheral surface of the heating belt 51, is in contact with the inner peripheral surface of the heating belt 51, and is disposed to face the electromagnetic induction portion 53 via the heating belt 51. . Further, the temperature-sensitive magnetic alloy 581 is disposed in contact with the inner peripheral surface of the heating belt 51 while maintaining the heating belt 51 in a cylindrical shape without contact with the holder 57 by the shielding member 59. The temperature-sensitive magnetic alloy 581 generates heat by being electromagnetically induced by the action of a magnetic field generated from the electromagnetic induction portion 53.

  The thickness of the temperature-sensitive magnetic alloy 581 is, for example, 0.05 to 1.0 mm, preferably 0.3 to 0.6 mm. The shape of the temperature-sensitive magnetic alloy 581 is a shape in which a portion corresponding to a predetermined central angle range (for example, 30 ° or more and 180 ° or less) is cut out from an alloy formed in a cylindrical shape having the above-described thickness. There are no particular restrictions.

  The temperature-sensitive magnetic alloy 581 is formed with three notches 5810 as openings at the end in the circumferential direction and upstream in the rotation direction of the heating belt 51 so as to be lined up in three locations in the x-axis direction. Each of the notches 5810 is formed at a position facing the electromagnetic induction portion 53 (see FIG. 2). Note that the cutout portion 5810 only needs to cut the end portion as compared with the case where the through hole is formed in the temperature-sensitive magnetic alloy 581, so that the measurement portion 55 described later is easily attached.

  The resistance heating element 582 generates Joule heat by flowing electricity, and transmits the Joule heat to the outer peripheral surface of the heating belt 51 via the temperature-sensitive magnetic alloy 581 and the heating belt 51 to heat the paper P. It is. As shown in FIGS. 3 and 4, the resistance heating element 582 has a shorter axial length (width) than the electromagnetic induction portion 53, the temperature-sensitive magnetic alloy 581, and the damping member 583. Specifically, as shown in FIG. 4, the resistance heating element 582 is disposed in a range from the position x3 to x6, and the width thereof is w2. On the other hand, the heating belt 51, the electromagnetic induction part 53, the temperature-sensitive magnetic alloy 581 and the damping member 583 are all disposed in the range from the position x1 to x8, and the width is w4 longer than w2.

A region heated by the electromagnetic induction unit 53 (hereinafter referred to as a first region) is a range from the above-described positions x1 to x8. Therefore, the first region corresponds to the entire region in the width direction of the heating belt 51 and is an example of the first region in the present invention.
A region heated by the resistance heating element 582 (hereinafter referred to as a second region) is a range from the position x3 to x6 described above. Therefore, this second region is a region included in the first region in the present invention, and has a width w2 (the first width in the present invention) that is narrower than the width w4 of the first region (corresponding to the first width in the present invention). 2 (corresponding to a width of 2).

  The width of the above-mentioned narrow paper P2 is w1 shorter than w2, and the narrow paper P2 is transported from the transfer section 14 by the transfer section 14 or the transport section 16, and is inside the range (second region) from the position x3 to x6. It passes through a range from a certain position x4 to x5. Accordingly, when the narrow paper P2 passes through the fixing unit 15, it is included in the range in the width direction of the resistance heating element 582, that is, the second region, and does not protrude. The narrow paper P2 is an example of a medium having a width narrower than the second width in the present invention.

  Further, the width of the maximum width paper P1 is w3 longer than w2 and shorter than w4, and the maximum width paper P1 is conveyed from the transfer unit 14 by the transfer unit 14 or the conveyance unit 16, and is in a range (first order) from the position x1 to x8. 1 range) and outside the range from position x3 to x6, it passes through the range from position x2 to x7. Therefore, when the maximum width sheet P1 passes through the fixing unit 15, the maximum width sheet P1 is included in the range in the width direction of the electromagnetic induction unit 53, the temperature-sensitive magnetic alloy 581, and the attenuation member 583, that is, the first region. The range of the resistance heating element 582 in the width direction (second region) always protrudes. The maximum width paper P1 is an example of a medium having a width narrower than the first width and wider than the second width in the present invention. The transfer unit 14 or the conveyance unit 16 is an example of a conveyance unit that conveys a medium on which an image is formed by the image forming unit to the first area or the second area in the present invention.

  FIG. 5 is a diagram illustrating an example of the appearance of the resistance heating element 582. As shown in FIG. 5, the resistance heating element 582 includes two electrodes 582a and 582c, a resistance member 582b connected so as to meander between the two electrodes, and two films sandwiching the resistance member 582b from both sides. 582d. For example, the resistance member 582b is stainless steel having a thickness of 30 μm, and the two films 582d are each made of polyimide having a thickness of 50 μm. By applying a voltage to the two electrodes 582a and 582c, the resistance member 582b generates heat.

  The damping member 583 is made of a nonmagnetic material such as aluminum (Al). In particular, when the temperature of the temperature-sensitive magnetic alloy 581 becomes a temperature equal to or higher than the Curie point, the temperature-sensitive magnetic alloy 581 becomes a non-magnetic material, so that an alternating magnetic field easily passes through the damping member 583. Note that the magnetism of the thermosensitive magnetic alloy 581 is lost at a temperature equal to or higher than the Curie point, and the eddy current is canceled by the nonmagnetic damping member 583.

  Since the auxiliary portion 58 is coupled at the end portion 592 of the shielding member 59, the force generated by the elastic member 574 acts as a force that presses the auxiliary portion 58 against the heating belt 51. As a result, the temperature-sensitive magnetic alloy 581 is pressed against the heating belt 51. The temperature-sensitive magnetic alloy 581 remains pressed against the heating belt 51 even when the pressure roll 52 repeatedly contacts and separates from the heating belt 51 by the drive unit (moving mechanism). Therefore, the change of the shape of the heating belt 51 becomes slight and the substantially circular shape is maintained. That is, the elastic member 574 suppresses deformation of the heating belt 51. As a result, since the contact state between the heating belt 51 and the temperature-sensitive magnetic alloy 581 is unlikely to change, the possibility that the inner surface of the heating belt 51 is damaged by the end of the temperature-sensitive magnetic alloy 581 is suppressed.

  Furthermore, since the resistance heating element 582 and the damping member 583 also move in the direction pressed by the elastic member 574 together with the temperature sensitive magnetic alloy 581, the temperature sensitive magnetic alloy 581, the resistance heating element 582 and the damping member 583 are in contact with each other. Changes are unlikely to occur. Therefore, the state of magnetic path formation hardly changes, and the heat diffusion effect by the damping member 583 hardly changes. Therefore, whether the pressure roll 52 is away from the heating belt 51 or in contact with the heating belt 51, the heating belt 51, the temperature-sensitive magnetic alloy 581, the resistance heating element 582, and the damping member 583 are in contact with each other. Is preserved. As a result, even when the pressure roll 52 returns to the contact position to perform the fixing operation, the state of supply of the heat generated by the temperature-sensitive magnetic alloy 581 to the heating belt 51 hardly changes, and the fixing operation is quick. To begin.

  Further, the mutual contact state of the heating belt 51, the temperature-sensitive magnetic alloy 581, the resistance heating element 582, and the damping member 583 is maintained, so that heat hardly diffuses to the outside and heating is performed even when the fixing operation is not performed. It is difficult for the belt 51, the temperature-sensitive magnetic alloy 581, the resistance heating element 582, and the damping member 583 to change in temperature. Therefore, also in this respect, the fixing operation is started quickly and power is saved.

  The elastic member 574 is not particularly limited, and a leaf spring, a coil spring, or the like can be used. However, it is preferable to use a coil spring from the viewpoint of easy assembly and a high degree of freedom in design. Further, the attachment position of the elastic member 574 is not particularly limited as long as the temperature-sensitive magnetic alloy 581 and the damping member 583 can be pressed against the heating belt 51. However, it is on the downstream side in the rotation direction of the heating belt 51 that the shape of the heating belt 51 is likely to change when the pressure roll 52 is separated from the heating belt 51. Further, from the viewpoint of preventing the heating belt 51 from being damaged by the downstream end portion of the temperature-sensitive magnetic alloy 581 described above, the elastic member 574 is an end portion of the temperature-sensitive magnetic alloy 581 or a location adjacent to the end portion. It is preferable that the heating belt 51 is disposed on the downstream side with respect to the rotation direction.

  In the above-described example, the one end 591 of the shielding member 59 is fixed. However, in the present embodiment, it is not limited to the case where it is completely fixed by bonding, welding, screwing, etc. This includes the case of fixing with a degree of freedom by fitting. In this case, assembly is easy.

  The electromagnetic induction unit 53 includes an excitation coil to which an alternating current having a frequency determined from an excitation circuit (not shown) is supplied according to an instruction from the control unit 11. This frequency is, for example, a frequency of an alternating current generated by a general general-purpose power supply, for example, a frequency of 20 kHz to 100 kHz. The amount of the alternating current is controlled by the control unit 11. An exciting coil is a coil formed by winding litz wires, which are bundled copper wires insulated from each other, wound in a closed loop shape such as an elliptical shape or a rectangular shape. By supplying the alternating current from the exciting circuit to the exciting coil, an alternating magnetic field centering on the litz wire is generated around the electromagnetic induction portion 53. The greater the amount of current is, the greater the intensity of the generated alternating magnetic field.

  The heating belt 51 is composed of an endless belt member whose original shape is a cylindrical shape. The heating belt 51 conveys the paper P (medium) that contacts the outer peripheral surface by rotating. When an alternating current is supplied to the exciting coil of the electromagnetic induction unit 53, a high frequency magnetic field is generated around the exciting coil, and this acts on a member included in the rotating heating belt 51 to generate heat, thereby causing the heating belt 51 to generate heat. The sheet P that contacts and passes through the first region is heated. As a result, the electromagnetic induction unit 53 heats the medium via the heating belt 51 with the amount of heat corresponding to the supplied power, and fixes the image transferred to the medium to the medium. Therefore, the electromagnetic induction part 53 is an example of the 1st heating part in this invention.

  Further, the resistance heating element 582 is disposed on the inner peripheral surface side of the heating belt 51, and transmits Joule heat generated by flowing electricity to the outer peripheral surface of the heating belt 51 via the heating belt 51. Heat. Here, since the range in the width direction of the resistance heating element 582 is the second area described above, the area where Joule heat is transmitted from the resistance heating element 582 on the outer peripheral surface of the heating belt 51 is the same as the second area. is there. Therefore, the resistance heating element 582 is an example of the second heating unit in the present invention.

  FIG. 6 is an enlarged view showing a part of the heating belt 51. The heating belt 51 includes a base material layer 511, a conductive heat generation layer 512, an elastic layer 513, and a surface release layer 514 in this order from the inner peripheral surface side toward the outer peripheral surface side. The base material layer 511 is formed of a heat-resistant sheet-like member, supports the conductive heat generation layer 512, and forms the mechanical strength of the heating belt 51 as a whole. The base material layer 511 is formed of a material and a thickness having physical properties (relative magnetic permeability, specific resistance) that allow a magnetic field to pass therethrough. The base material layer 511 does not generate heat due to the action of a magnetic field or is less likely to generate heat than the conductive heat generation layer 512. The base material layer 511 is, for example, nonmagnetic stainless steel having a thickness of 30 μm or more and 200 μm or less (desirably 50 μm or more and 150 μm or less, more desirably 100 μm or more and 150 μm or less), soft magnetic material (for example, permalloy, sendust, etc.), or hard magnetic It is formed using a non-magnetic metal such as a material (Fe—Ni—Co or Fe—Cr—Co alloy) or a resin material such as a polyimide belt having a thickness of 50 μm to 200 μm.

  The conductive heat generating layer 512 is made of, for example, a nonmagnetic metal such as gold (Au), silver (Ag), aluminum (Al), copper (Cu), or a metal alloy thereof, and has a thickness of 2 μm to 20 μm. It is a member formed to be (preferably 5 μm or more and 10 μm or less). These materials are paramagnetic materials having a relative permeability of about 1 and a specific resistance of 2.7 × 10 −8 Ω · m or less. When the AC magnetic field generated by the electromagnetic induction portion 53 passes in the thickness direction of the conductive heat generating layer 512, electromagnetic induction is generated and eddy current is generated inside the conductive heat generating layer 512. The conductive heat generating layer 512 generates heat when this eddy current is generated. As described above, the conductive heat generating layer 512 is heated by the AC magnetic field generated by the electromagnetic induction unit 53. Hereinafter, the heating, ie, heating, of the heating belt 51 having the conductive heat generating layer 512 by electromagnetic induction in an alternating magnetic field is referred to as “electromagnetic induction heating”.

  The elastic layer 513 is formed using a material such as silicone rubber, fluorine rubber, or fluorosilicone rubber that is deformed when a pressure is applied and returns to its original shape when the applied pressure is removed. For example, the elastic layer 513 is formed using a silicone rubber having a hardness of 10 ° to 30 ° (JIS-A) as a material so as to have a thickness of 100 μm to 600 μm. Since the image transferred onto the paper P by the secondary transfer roll 42 is formed by laminating each color toner as powder, there are fine protrusions and depressions. The elastic layer 513 is adapted to deform in accordance with the bulge or depression of this image. If the elastic layer 513 is not deformed in this way, the amount of heat supplied between the portion in contact with the heating belt 51 and the portion not in contact with the heating belt 51 will vary, resulting in unevenness in the degree to which the image is fixed. . This unevenness is reduced by the elastic layer 513 being deformed as described above.

  Since the surface release layer 514 is in direct contact with the image (toner) formed on the paper, it is desirable that the release property with respect to the toner is higher. The surface release layer 514 has a relatively high release property with respect to the toner, and examples thereof include PFA (Tetrafluoroethylene-Perfluoroalkylvinylether Copolymer), PTFE (polytetrafluoroethylene), A silicone copolymer or a composite layer thereof is used as a material. Further, the smaller the thickness of the surface release layer 514, the shorter the period required until the layer becomes thinner due to wear and cannot function as the release layer, that is, the life of the heating belt 51 is shortened. On the other hand, as the thickness increases, the heat capacity of the heating belt 51 increases, and the time required to heat the heating belt 51 to a predetermined temperature increases. The surface release layer 514 is formed to have a thickness of 1 μm or more and 50 μm or less, assuming that these lifetimes and times are within a predetermined range.

  The magnetic core 54 shown in FIG. 2 is an arc-shaped ferromagnetic body made of, for example, sintered ferrite, ferrite resin, permalloy or the like. These materials are oxides or alloy materials having a relatively high magnetic permeability. The magnetic core 54 induces a magnetic field line (magnetic flux) of an alternating magnetic field generated around the excitation coil, and forms a path (magnetic path) of the magnetic field line that passes through the heating belt 51 from the magnetic core 54 and returns to the magnetic core 54. When the magnetic core 54 forms a magnetic path, the magnetic field lines of the AC magnetic field are concentrated on a portion of the heating belt 51 facing the magnetic core 54. A shield (not shown) is provided outside the magnetic core 54 as viewed from the axis O1. This shield shields the magnetic field and suppresses leakage to the outside.

  FIG. 7 is a diagram for explaining the action of the temperature-sensitive magnetic alloy 581 at a temperature lower than the Curie point. Since the temperature-sensitive magnetic alloy 581 is a ferromagnetic material at a temperature below the Curie point, the AC magnetic field generated by the electromagnetic induction unit 53 and passed through the heating belt 51 is changed along the shape of the temperature-sensitive magnetic alloy 581. Pass through the interior. Therefore, as shown in FIG. 7, a magnetic path L <b> 0 that surrounds the electromagnetic induction portion 53 and the heating belt 51 and has a shape along the magnetic core 54 and the temperature-sensitive magnetic alloy 581 is formed. Since the temperature-sensitive magnetic alloy 581 forms the magnetic path L0 along its shape, the magnetic flux density passing through the heating belt 51 becomes relatively high, and the heat generation amount of the heating belt 51 also increases. In addition, since it is difficult for the AC magnetic field to escape from the temperature-sensitive magnetic alloy 581, the heat generation amount in the temperature-sensitive magnetic alloy 581 also becomes relatively large.

  On the other hand, FIG. 8 is a diagram for explaining the action of the temperature-sensitive magnetic alloy 581 at a temperature equal to or higher than the Curie point. At a temperature above the Curie point, the temperature-sensitive magnetic alloy 581 becomes a non-magnetic material. Therefore, the AC magnetic field generated by the electromagnetic induction unit 53 and passed through the heating belt 51 passes through the temperature-sensitive magnetic alloy 581 and reaches the resistance heating element 582 and the attenuation member 583. Since the attenuation member 583 is a non-magnetic material and allows the AC magnetic field to pass therethrough, as shown in FIG. 8, the electromagnetic induction unit 53, the heating belt 51, the temperature-sensitive magnetic alloy 581, the resistance heating element 582, and the attenuation member 583. A magnetic path L1 having a shape surrounding the periphery of the substrate is formed. When the magnetic path L1 passes through the attenuation member 583, an eddy current is generated in the passing portion, and thus the attenuation member 583 generates heat. However, since the resistance value of the attenuation member 583 is low, heat generation is small.

  Incidentally, the damping member 583 sandwiches the resistance heating element 582 together with the temperature-sensitive magnetic alloy 581, but is not in direct contact with the temperature-sensitive magnetic alloy 581. Therefore, the heat generated by the damping member 583 is difficult to be transmitted to the temperature-sensitive magnetic alloy 581 by heat conduction. The heat generated by the damping member 583 is further transmitted to the heating belt 51 disposed outside the temperature-sensitive magnetic alloy 581 compared to the heat generated by the temperature-sensitive magnetic alloy 581 itself being transmitted to the heating belt 51. Have difficulty. As described above, at the temperature equal to or higher than the Curie point, the heating rate of the heating belt 51 is reduced as compared with the temperature lower than the Curie point.

  FIG. 9 is a diagram showing an outline of the fixing unit 15 when the pressure roll 52 is moved in the arrow Dd direction (−y direction) in FIG. 2 by a driving unit (moving mechanism) (not shown). The position of the axis O2 shown in FIG. 9 is a position when the distance from the axis O1 is longer than the sum of the radius of the heating belt 51 and the radius of the pressure roll 52. In this case, the pressure roll 52 is separated from the outer peripheral surface of the heating belt 51. Hereinafter, the position of the pressure roll 52 at this time is referred to as a “separated position”. This “separation” means that a certain object is arranged at a distance from another reference object.

  The pressure roll 52 when in the separated position is not in contact with the heating belt 51. That is, an air layer exists between the pressure roll 52 and the heating belt 51. Therefore, due to the thermal resistance of the air layer, the heat flux from the heating belt 51 toward the pressure roll 52 is smaller than when they are in contact. That is, the heat of the heating belt 51 is less likely to flow through the pressure roll 52 when in the separated position than in the pressure roll 52 when in the contact position. When the pressure roll 52 is moved in the arrow Da direction (+ y direction) shown in FIG. 9, the pressure roll 52 reaches the contact position and enters the state shown in FIG. 2. The control part 11 controls the drive part (movement mechanism) mentioned above, and arrange | positions the pressurization roll 52 in the contact position shown in FIG. 2, and the separation position shown in FIG.

  2 and 9 is arranged on the inner peripheral surface side of the heating belt 51 and measures the temperature of the heating belt 51. The measurement part 55 has temperature sensors, such as a thermocouple, for example, measures the temperature of the heating belt 51 by measuring the voltage of the thermoelectromotive force which arises by this. The measured temperature is transmitted to the control unit 11.

  A notch 5810 of the temperature-sensitive magnetic alloy 581 is provided with a measuring unit 55 that contacts the inner peripheral surface of the heating belt 51 and detects the temperature of the surface of the heating belt 51. The measuring unit 55 measures the temperature of the surface of the heating belt 51 by changing the resistance value according to the amount of heat given from the surface of the heating belt 51.

  As shown in FIG. 4, the measurement unit 55 includes a center sensor 551 and an end sensor 552. The center sensor 551 measures the temperature of the heating belt 51 corresponding to the center in the width direction of the paper P. The end sensor 552 measures the temperature of a portion of the heating belt 51 that is outside in the width direction from the region through which the narrow paper P2 passes and is included in the region through which the maximum paper P1 passes. That is, the center sensor 551 measures the temperature of the portion (that is, the paper passing portion) through which each paper P passes, regardless of whether the maximum width paper P1 or the narrow paper P2 passes, and the end sensor 552 The temperature of the non-sheet passing portion for the small width paper P2 and the portion that is the paper passing portion for the maximum width paper P1 is measured.

  The center sensor 551 is an example of the second measurement unit in the present invention, and the end sensor 552 is an example of the first measurement unit in the present invention. Further, as shown in FIG. 4, one end sensor 552 is disposed in each of the + x direction and the −x direction of the center sensor 551, but the number of end sensors 552 is not limited to two. . For example, the end sensor 552 may be disposed only in one of these two locations.

  When there is an instruction for image formation, the control unit 11 moves the pressure roll 52 to the separation position. And the control part 11 supplies to the exciting coil of the electromagnetic induction part 53 so that the temperature of the heating belt 51 measured by the center part sensor 551 (2nd measurement part) may approach the temperature (target temperature) set as a target. To control the high-frequency power. Since the pressure roll 52 is not in contact with the heating belt 51, the heat generated in the heating belt 51 is not easily taken away by the pressure roll 52. Therefore, the electromagnetic induction heating of the heating belt 51 by the electromagnetic induction unit 53 is performed more rapidly than when the pressure roll 52 is disposed at the contact position.

  For example, the control unit 11 determines whether or not the difference between the temperature of the heating belt 51 measured by the center sensor 551 (second measurement unit) and the set target temperature is equal to or less than a threshold value. When it is determined that the difference is equal to or less than the threshold value, the control unit 11 switches the control on the assumption that the temperature of the heating belt 51 has approached the target temperature.

  When fixing the image formed on the maximum width paper P <b> 1 after the temperature of the heating belt 51 approaches the target temperature, the control unit 11 moves the pressure roll 52 to the contact position, and the electromagnetic induction unit 53 performs electromagnetic Continue induction heating. As a result, the heating belt 51 heated in the first area performs a fixing process for heating the maximum width sheet P1 conveyed to the nip area R1 via the intermediate transfer belt 41. The maximum width sheet P1 that has undergone the fixing process by the fixing unit 15 is discharged by the transport unit 16 to a sheet storage area provided in the upper part of the image forming apparatus 1.

  On the other hand, when fixing the image formed on the narrow paper P2, the control unit 11 moves the pressure roll 52 to the contact position, and heats the heating belt 51 from the electromagnetic induction heating by the electromagnetic induction unit 53 to the resistance heating element. Switch to conduction heat transfer by 582. That is, for example, when the difference between the temperature of the heating belt 51 measured by the center sensor 551 (second measurement unit) and a preset target temperature is equal to or less than a threshold value, the control unit 11 The power supply to the exciting coil 53 is stopped and power is supplied to the resistance heating element 582.

  The heating belt 51 that heats the second region by the conduction heat transfer of the resistance heating element 582 performs a fixing process for heating the narrow paper P2 conveyed to the nip region R1 through the intermediate transfer belt 41. The narrow paper P <b> 2 that has undergone the fixing process by the fixing unit 15 is discharged by the transport unit 16 to a paper storage provided in the upper part of the image forming apparatus 1.

1-2. Operation FIG. 10 is a flowchart showing the operation of the image forming apparatus 1 according to this embodiment. The control unit 11 of the image forming apparatus 1 determines whether an image forming instruction is received from the user via the operation unit 17 (step S1). Then, the control unit 11 continues this determination while determining that an instruction for image formation has not been received (step S1; NO). When it is determined that an instruction for image formation has been received (step S <b>1; YES), the control unit 11 sets a target temperature T <b> 1 for the heating belt 51. (Step S2). The target temperature T1 is a temperature that the heating belt 51 should reach, and is determined based on, for example, the content of the image formation instruction such as the type, material, and thickness of the paper P to be used. Moreover, the control part 11 may determine target temperature T1 using various measuring devices. For example, the control unit 11 may measure the internal humidity of the image forming apparatus 1 with a hygrometer and reflect the measurement result on the target temperature T1.

  Next, the control part 11 controls the high frequency electric power supplied to the exciting coil of the electromagnetic induction part 53, and heats the 1st area | region which is the whole area | region of the width direction in the heating belt 51 (step S3). And the control part 11 reads the value of the temperature of the heating belt 51 measured by the center part sensor 551 (2nd measurement part) (step S4), and determines whether this temperature reached | attained target temperature T1. (Step S5). When it determines with the read temperature not having reached target temperature T1 (step S5; NO), the control part 11 returns a process to step S3. When it is determined that the read temperature has reached the target temperature T1 (step S5; YES), the controller 11 moves the pressure roll 52 in the direction of the arrow Da shown in FIG. The outer circumferential surface of the belt 51 is brought into contact with the outer circumferential surface to pressurize it (step S6).

  The control unit 11 determines whether or not the sheet P used for the image formation is the maximum width sheet P1 based on the content of the image formation instruction determined to have been received in step S1 (step S7). When it is determined that the paper P used for image formation is not the maximum width paper P1 (step S7; NO), the control unit 11 stops the electromagnetic induction heating by the electromagnetic induction unit 53 and starts control of the resistance heating element 582. (Step S8), image formation is started (Step S9). On the other hand, when it is determined that the paper P used for image formation is the maximum width paper P1 (step S7; YES), the control unit 11 starts image formation while continuing the electromagnetic induction heating by the electromagnetic induction unit 53 ( Step S9). When image formation is performed, the transport unit 16 transports the paper P before the fixing process to the fixing unit 15 and passes the outer peripheral surface of the heating belt 51 pressed by the pressure roll 52. As a result, the paper P is pressurized by the pressure roll 52, and the image formed on the paper P is fixed.

  The controller 11 determines whether or not the image formation has been completed (step S10), and continues this determination while determining that the image formation has not been completed (step S10; NO). When it is determined that the image formation is completed (step S10; YES), the control unit 11 ends the process.

  The temperature distribution generated in the heating belt 51 by the above operation will be described. FIG. 11 is a diagram for explaining the temperature distribution of the heating belt 51. If the control unit 11 controls the resistance heating element and heats the heating belt 51 by conduction heat transfer without performing electromagnetic induction heating by the electromagnetic induction unit 53 in step S3 described above, the temperature distribution of the heating belt 51 is assumed. Is as shown in FIG. That is, in the heating belt 51, the region R111 in the −x direction is not heated at the boundary B111 and is maintained at a low temperature (here, T0), and is the region in the + x direction up to the boundary B112. A certain region R112 is heated to a target temperature T1. In addition, the heating belt 51 is kept at a low temperature without heating the region R113 in the + x direction from the boundary B112.

  The outer peripheral surface of the heating belt 51 having this temperature distribution has a temperature difference ΔTa in the region R111, the region R112, and the region R113 with the boundary B111 and the boundary B112 as the boundaries, so that the thermal load in each region is Differently, the brittleness to impact is different. When the pressure roller 52 pressurizes the outer peripheral surface in step S6, the region R112 has a higher target temperature T1 than the regions R111 and R113 and is softer than these, so that it is deformed into a different shape and is heated. May be damaged.

  On the other hand, the control unit 11 of the image forming apparatus 1 described above performs electromagnetic induction heating by the electromagnetic induction unit 53 regardless of the type of the paper P in step S3. Therefore, when the pressure roll 52 presses the outer peripheral surface of the heating belt 51 in step S6, the temperature distribution of the heating belt 51 is as shown in FIG. That is, when the pressure roll 52 presses the outer peripheral surface of the heating belt 51, the outer peripheral surface of the heating belt 51 is at the target temperature T1 over the entire region in the width direction. There is no. Therefore, even if the control unit 11 moves the pressure roll 52 and pressurizes the outer peripheral surface of the heating belt 51, compared with the case where the temperature distribution shown in FIG. Since the ease of deformation of the outer peripheral surface is substantially uniform, the resistance of the heating belt 51 to the impact is increased.

  After this, since the temperature distribution on the outer peripheral surface of the heating belt 51 is only the resistance heating element 582 where the heating source heats the second region, the temperature in the region other than the second region decreases, and FIG. It approaches the shape shown in (a). However, while the change in temperature distribution occurs, the pressure roll 52 is in contact with the outer peripheral surface of the heating belt 51 and continues to pressurize the outer peripheral surface. Therefore, there is a difference in brittleness to impact in the width direction of the outer peripheral surface. Even if it occurs, there is little possibility that the heating belt 51 is damaged.

  As described above, the image forming apparatus 1 stops the electromagnetic induction heating by the electromagnetic induction unit 53 and performs conduction heat transfer by the resistance heating element 582 of the auxiliary unit 58 when fixing the image on the narrow paper P2. Therefore, the image forming apparatus 1 heats the second region through which the narrow paper P2 passes, and does not heat other regions through which the narrow paper P2 does not pass, thus saving energy. On the other hand, the image forming apparatus 1 performs electromagnetic induction heating by the electromagnetic induction unit 53 before the pressure roll 52 presses the outer peripheral surface of the heating belt 51 even when fixing the image on the narrow paper P2. The entire area of the heating belt 51 is heated. Therefore, compared with the case where only the second region is heated by conduction heat transfer by the resistance heating element 582 without performing electromagnetic induction heating by the electromagnetic induction unit 53, the pressure roll 52 pressurizes the outer peripheral surface of the heating belt 51. When starting, the possibility that the heating belt 51 is damaged is suppressed.

2. Modification The above is the description of the embodiment, but the contents of this embodiment can be modified as follows. Further, the following modifications may be combined.

2-1. First Heating Unit In the embodiment described above, the electromagnetic induction unit 53 generates a high-frequency magnetic field (alternating magnetic field), and causes the member to be heated by causing it to act on a member included in the heating belt 51 that rotates. Although the paper P that passes through the first region in contact with the heating belt 51 is heated, the first heating unit that heats the paper P that passes through the first region is not limited to the electromagnetic induction unit 53. For example, a halogen heater or a resistance heating element may be used as the first heating unit to heat the first area and fix the image formed on the paper P passing through the first area. In short, the first heating unit only needs to heat the first region having the first width and fix the image formed on the medium passing through the first region.

2-2. Second Heating Unit In the embodiment described above, the resistance heating element 582 is disposed on the inner peripheral surface side of the heating belt 51, generates Joule heat by flowing electricity, and heats the Joule heat via the heating belt 51. Although the paper P is heated by being transmitted to the second region on the outer peripheral surface of the belt 51, the second heating unit that heats the paper P passing through the second region is not limited to the resistance heating element 582. For example, a resistance heating element disposed on the outer peripheral surface side of the heating belt 51 may be used as the second heating unit, or the paper P that passes through the second region by a halogen heater or an electromagnetic induction heater heating the second region. The image formed in the above may be fixed. In short, the second heating unit is formed in a medium that passes through the second region by heating the second region that is included in the first region and has a second width that is narrower than the first width. Any device that fixes the image may be used. It is desirable that the heating by the first heating unit and the heating by the second heating unit are based on different principles such as electromagnetic induction heating and conduction heat transfer. Since the heating principle by each heating unit is different, each heating unit heats each region without affecting each other.

2-3. Control According to Measurement In the above-described embodiment, the control unit 11 is configured so that the temperature of the heating belt 51 measured by the center sensor 551 (second measurement unit) of the measurement unit 55 approaches the target temperature T1. The high frequency power supplied to the 53 exciting coils was controlled. However, the control unit 11 does not use the center sensor 551 (second measurement unit) but the electromagnetic induction unit so that the temperature of the heating belt 51 measured by the end sensor 552 (first measurement unit) approaches the target temperature T1. 53 may be controlled.

  Moreover, the control part 11 may control the electromagnetic induction part 53 so that the value used as the parameter | index calculated using these two measured values may satisfy predetermined conditions. For example, the control unit 11 calculates an average value (for example, an arithmetic average) of the two measured values as an index value, and the electromagnetic induction unit so that the calculated average value approaches the target temperature T1. 53 may be controlled. In this case, a difference between the temperature of the heating belt 51 measured by the end sensor 552 (first measurement unit) and the temperature of the heating belt 51 measured by the center sensor 551 (second measurement unit) and a threshold value are obtained. In comparison, the control unit 11 may warn the user when the difference exceeds a threshold value.

  Further, the control unit 11 may not perform control according to the measurement by the measurement unit 55. For example, the control unit 11 may control the high frequency power supplied to the excitation coil of the electromagnetic induction unit 53 so as to heat a predetermined amount of heat.

2-4. Pressing Timing In the above-described embodiment, when the control unit 11 determines that the temperature of the heating belt 51 has reached the target temperature T <b> 1, the pressing roll 52 is disposed at the contact position, and the heating belt 51 is placed on the outer circumferential surface of the heating belt 51. The outer peripheral surface was pressed by contact, but after the electromagnetic induction heating by the electromagnetic induction unit 53 was stopped and the control of the resistance heating element 582 was started, the pressure roll 52 was arranged at the contact position and the heating belt The outer peripheral surface of 51 may be pressurized. FIG. 12 is a view for explaining the temperature distribution of the heating belt 51 in this modification. By the time the pressure roll 52 presses the outer peripheral surface of the heating belt 51, the heating means of the heating belt 51 is switched from electromagnetic induction heating by the electromagnetic induction portion 53 to conduction heat transfer by the resistance heating element 582. The temperature distribution of the heating belt 51 immediately before the roll 52 comes into contact is as shown in FIG.

  That is, in the heating belt 51, the region R121 in the −x direction is not heated at the boundary B121, and the temperature is lowered. For example, the temperature T0 is lower than the target temperature T1 and is the ambient temperature or the initial temperature. Becomes a higher temperature T3. Further, the region R122 that is the region in the + x direction of the boundary B121 and is the region up to the boundary B122 is heated and maintains the target temperature T1. Then, the region R123 in the + x direction from the boundary B122 is not heated, and the temperature decreases to T3. Thus, there may be a temperature difference ΔTb between the region R122 and the region R121 and between the region R122 and the region R123. However, even if a difference in brittleness to impact occurs in each region of the heating belt 51 due to the temperature difference ΔTb, the possibility that the heating belt 51 is damaged is suppressed unless the difference is large enough to cause damage. The That is, the control unit 11 may start pressurization by the pressure roll 52 when the temperature difference ΔTb is within an allowable range that does not cause the heating belt 51 to be damaged.

2-5. Medium In the above-described embodiment, the paper P as the medium uses two types of the maximum width paper P1 and the small width paper P2 narrower than the maximum width paper P1, but the medium handled by the image forming apparatus 1 Is not limited to two types, and may be three or more types. When there are three or more types of media, the image forming apparatus 1 may include a number of heating units according to the width of the media. And the area | region which a certain heating part heats should just be a thing which the medium matched with the heating part can pass. When the paper P other than the maximum width paper P1 is heated, the control unit 11 first heats the first region, which is the entire region in the width direction of the heating belt 51, by the first heating unit, and then pressurizes. What is necessary is just to pressurize the outer peripheral surface of the heating belt 51 by the roll 52 and to control the heating unit associated with the paper P. This saves energy and reduces the possibility of damage to the heating belt 51 at the start of pressurization.

2-6. Heating Control According to Belt State In the above-described embodiment, when the control unit 11 receives an image formation instruction, the control unit 11 controls the high-frequency power supplied to the excitation coil of the electromagnetic induction unit 53, and the width direction of the heating belt 51. The first region, which is the entire region, was heated until the temperature reached the target temperature T1. However, the control unit 11 may select a heating unit according to the state of the heating belt 51 when receiving an image formation instruction. FIG. 13 is a diagram for explaining the temperature distribution of the heating belt 51 in this modification. When an image is formed on the narrow paper P2, the temperature distribution on the outer peripheral surface of the heating belt 51 downstream of the nip region R1 shown in FIG. 2 is the temperature from the position x4 to x5 as shown in FIG. For example, the temperature T2 is lower than the temperature T0. This is because the heat from the positions x4 to x5 on the heating belt 51 is taken away by the narrow paper P2. In this case, since the resistance heating element 582 heats a range (second region) from the position x3 to x6 wider than the narrow paper P2, heat is generated by the narrow paper P2 in the vicinity of the positions x3 and x6. A boundary B131 and a boundary B132 that are hard to be taken are generated. The boundary B131 and the boundary B132 are higher than the temperature T2 by ΔTc. Although the width of the narrow paper P2 is narrower than that of the second region, the difference is relatively small. Therefore, the heat at the boundary B131 and the boundary B132 is diffused in the arrow direction (width direction) while the heating belt 51 rotates once.

  However, when image formation is continuously performed on the narrow paper P2 or when image formation is performed on the paper P that is narrower than the narrow paper P2, heat at the boundary B131 and the boundary B132 is diffused in the width direction. It is possible that it will accumulate. The temperature distribution shown in FIG. 13B represents the temperature distribution when the heat at the boundary B131 and the boundary B132 is accumulated without being diffused in the width direction. As the heat accumulates, the high temperature portion of the boundary B131 spreads in the width direction and grows in the region R131, and the high temperature portion of the boundary B132 spreads in the width direction and grows in the region R132. A temperature difference ΔTd occurs during This temperature difference ΔTd is larger than the above-described temperature difference ΔTc, and is such that it cannot be diffused in the width direction while the heating belt 51 rotates once. In this case, if the electromagnetic induction part 53 is controlled and the 1st area | region of the heating belt 51 is heated, area | region R131 and area | region R132 may be heated excessively.

  Therefore, for example, when the image formation on the narrow paper P2 is continuously performed by the number of times equal to or greater than the threshold value, the control unit 11 performs the conduction heat transfer by the resistance heating element in addition to the electromagnetic induction heating by the electromagnetic induction unit 53. The heating belt 51 may be heated by use. At this time, the amount of heat generated by electromagnetic induction heating by the electromagnetic induction unit 53 may be reduced. Thereby, compared with the case where the heating belt 51 is heated only by the electromagnetic induction heating by the electromagnetic induction portion 53, the temperature difference between the high temperature portion and the low temperature portion on the outer peripheral surface of the heating belt 51 may be reduced. In this case, the number of continuous image formations on the narrow paper P2 is used as an indicator of the state of the heating belt 51.

  Further, the control unit 11 may select a heating means according to the temperature distribution of the heating belt 51 after passing through the paper P, instead of the continuous number of image formations on the narrow paper P2. In this case, an auxiliary measuring unit 55a for assisting the measurement of the temperature of the heating belt 51 is provided at the position indicated by the broken line in FIG. 2 or FIG. 9, and heating is performed based on the temperature measured by the auxiliary measuring unit 55a. What is necessary is just to select a means. The auxiliary measuring unit 55a is disposed on the inner peripheral surface side of the heating belt 51 and downstream of the nip region R1 in the direction of the arrow D51, and measures the temperature of the heating belt 51. Because of this arrangement, the auxiliary measuring unit 55a measures the temperature of the heating belt 51 after passing the paper P through the nip region R1. The auxiliary measuring unit 55a has a plurality of temperature sensors in the width direction, and the control unit 11 obtains a difference between the highest temperature and the lowest temperature among the temperatures measured by each temperature sensor. And when the calculated | required difference exceeds a threshold value, the control part 11 should just heat the heating belt 51 using the conductive heat transfer by a resistance heating element in addition to the electromagnetic induction heating by the electromagnetic induction part 53. FIG. In this case, the temperature distribution measured by each temperature sensor of the auxiliary measuring unit 55a is used as an index of the state of the heating belt 51. Each temperature sensor of the auxiliary measuring unit 55a is disposed at a position corresponding to the center sensor 551 and the end sensor 552 in order to detect a temperature difference in the width direction, and also at positions x3, x4, x5. It is desirable to arrange at a position corresponding to x6.

2-7. Program The program executed by the control unit 11 of the image forming apparatus 1 is readable by a computer device such as a magnetic recording medium such as a magnetic tape or a magnetic disk, an optical recording medium such as an optical disk, a magneto-optical recording medium, or a semiconductor memory. It can be provided in a state stored in a recording medium. In addition, this program may be downloaded to the control unit 11 via a communication line such as the Internet. Note that various devices other than the CPU may be applied as the control unit exemplified by the control unit 11. For example, a dedicated processor or the like is used.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Control part, 12 ... Memory | storage part, 13 ... Developing part, 14 ... Transfer part, 15 ... Fixing part, 16 ... Conveyance part, 17 ... Operation part, 31 ... Photosensitive drum, 32 ... Charging 33 ... Exposure device 34 ... Developer 35 ... Primary transfer roll 36 ... Drum cleaner 41 ... Intermediate transfer belt 42 ... Secondary transfer roll 43 ... Belt transport roll 44 ... Backup roll 49 ... Belt Cleaner 51 ... heating belt 511 ... base material layer 512 ... conductive heating layer 513 ... elastic layer 514 ... surface release layer 52 ... pressure roll 521 ... core material 522 ... elastic layer 53 ... electromagnetic Guide part, 54 ... Magnetic core, 55 ... Measuring part, 55a ... Auxiliary measuring part, 551 ... Center sensor, 552 ... End sensor, 56 ... Press pad, 57 ... Holder, 571 ... Frame, 572 ... Support member, 573 ... Fixed part 574 ... elastic member, 58 ... auxiliary part, 581 ... temperature-sensitive magnetic alloy, 582 ... resistance heating element, 582a, 582c ... electrode, 582b ... resistance member, 582d ... film, 583 ... damping member, 59 ... shielding member, 591 ... end, 592 ... end, P ... paper, P1 ... maximum width paper, P2 ... narrow paper, R1 ... nip region.

Claims (7)

An endless belt for conveying a medium in contact with the outer peripheral surface;
A first heating unit that heats a first region having a first width on the outer peripheral surface of the belt and fixes an image formed on a medium passing through the first region;
A second heating unit that heats a second region that is included in the first region and has a second width narrower than the first width, and fixes an image formed on a medium that passes through the second region; ,
A pressurizing unit that sandwiches the medium together with the outer peripheral surface and pressurizes the medium toward the outer peripheral surface;
When fixing an image formed on a medium having a width narrower than the second width of the medium, the first area is heated by the first heating section by separating the pressure section from the outer peripheral surface. And a controller that pressurizes the medium by the pressurizing unit and causes the second heating unit to heat the second region. A measuring unit for measuring the temperature of the belt;
When the controller fixes an image formed on a medium having a width smaller than the second width of the medium, the controller separates the pressurizing unit from the outer peripheral surface and causes the first heating unit to move to the first heating unit. The first region is heated, and after the temperature measured by the measurement unit reaches the target temperature, which is a temperature determined as a target, the medium is pressurized by the pressurizing unit, and the second heating unit is The fixing device according to claim 1, wherein the second region is heated. The measuring unit is
A first measurement unit that measures the temperature of a position that is included in the first region and not included in the second region;
A second measuring unit that measures the temperature of the position included in the second region,
The control unit calculates an index value using the temperature measured by the first measurement unit and the temperature measured by the second measurement unit, and the calculated value satisfies a predetermined condition. 3. The fixing device according to claim 1, wherein after the filling, the medium is pressurized by the pressure unit and the second region is heated by the second heating unit. 4. The first heating unit generates an alternating magnetic field and heats the first region by electromagnetic induction in the alternating magnetic field,
4. The fixing device according to claim 1, wherein the second heating unit heats the second region by Joule heat generated by flowing electricity. 5. The belt includes a member that generates heat by generating an eddy current when an alternating magnetic field passes through the belt,
The first heating unit heats the first region by passing the alternating magnetic field through the member,
The said 2nd heating part is arrange | positioned at the inner peripheral surface side of the said belt, transmits the said Joule heat to the said outer peripheral surface via the said belt, and heats the said 2nd area | region. The fixing device according to 1. When fixing an image formed on a medium having a width smaller than the second width of the medium, the control unit separates the pressurizing unit from the outer peripheral surface, and according to the state of the belt The first heating unit selects only the first region, or the first heating unit selects the first region and the second heating unit heats the second region, respectively. 6. The heating device according to claim 1, wherein after the region or the second region is heated, the medium is pressurized by the pressure unit, and the second region is heated by the second heating unit. The fixing device according to Item. Image forming means for forming an image on a medium;
Conveying means for conveying the medium on which the image is formed by the image forming means to the first area or the second area;
An image forming apparatus comprising: the fixing device according to claim 1, which fixes an image on a medium conveyed by the conveying unit.

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