JP2013182178A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a thermal load for a heating belt, when an image is fixed to a medium whose width is smaller than that of the heating belt by the heating belt.SOLUTION: When the control part of an image forming apparatus determines that a paper used for an instructed image formation is a maximum width paper, the control part stops the end sensor of a measurement part and the resistance heating element of an auxiliary part. Then, the control part reads temperature measured by a central sensor and controls high-frequency power supplied to the exciting coil of an electromagnetic induction part, according to the read temperature. On the other hand, when the control part determines that the paper used for the image formation is not the maximum width paper, the control part reads the temperature measured by the central sensor and controls power supplied to the resistance heating element of the auxiliary part, according to the read temperature. Then, the control part reads the temperature measured by the end sensor and controls the high-frequency power supplied to the exciting coil of the electromagnetic induction part, according to the read temperature.

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 controls the temperature by detecting the temperature of the heating element 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 can be used by supplying it to the image forming apparatus at a position different from the first temperature detection element in the longitudinal direction of the heating body. 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 relates to a fixing device including a first heating section that heats a first area and a second heating section that heats a second area that is narrower than the first area, and is generated due to a temperature difference between the inside and outside of the second area. The purpose is to reduce the heat load.

  According to a first aspect of the present invention, there is provided a fixing device that heats a first region having a first width to fix an image formed on a medium passing through the first region, and the first heating unit. A second heating unit that heats a second region that is included in the region and has a second width narrower than the first width to fix an image formed on a medium that passes through the second region; A control unit that controls the first heating unit and the second heating unit, wherein the control unit displays an image formed on a second medium having a width smaller than the second width of the medium. When fixing, the first heating unit is controlled to heat the first region, and the second heating unit is controlled to heat the second region.

  According to a second aspect of the present invention, there is provided the fixing device according to the first aspect, wherein the first measurement unit that measures the temperature of the position that is included in the first region and is not included in the second region; A second measuring unit that measures the temperature of a position included in the second region, and the control unit fixes the first measuring unit or the second measuring unit when fixing the image formed on the first medium. When fixing the image formed on the second medium by controlling the first heating unit so that the temperature measured by the measurement unit becomes a predetermined first temperature to heat the first medium. The first heating unit is controlled so that the temperature measured by the first measurement unit becomes a predetermined second temperature, and the temperature measured by the second measurement unit is the second temperature. The temperature is higher than the first temperature and reaches a predetermined third temperature. And it controls the second heating unit to, characterized in that to heat the second medium.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the first heating unit generates an alternating magnetic field and heats the first region by electromagnetic induction in the alternating magnetic field. The second heating unit heats the second region by Joule heat generated by flowing electricity.

  According to a fourth aspect of the present invention, in the fixing device according to the third aspect, the first heating unit rotates in contact with the medium and rotates the medium so as to pass through the first region. Passing the AC magnetic field to an endless belt having an outer peripheral surface to convey, causing eddy current due to electromagnetic induction to a member included in the belt, heating the first region, and the second heating unit Is arranged on the inner peripheral surface side of the belt, and transmits the Joule heat to the outer peripheral surface via the belt to heat the second region.

  An image forming apparatus according to a fifth 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 4, wherein the image is fixed on the medium conveyed by the conveying means.

According to the first and fifth aspects of the present invention, in the fixing device including the first heating unit that heats the first region and the second heating unit that heats the second region that is narrower than the first region, The heat load generated by the temperature difference between the inside and outside of the second region can be reduced as compared with the case where the heating by the first heating unit is not performed when the second region is heated by the two heating units.
According to the second aspect of the present invention, in the fixing device including the first heating unit that heats the first region and the second heating unit that heats the second region that is narrower than the first region, the second heating is performed. The temperature difference between the inside and outside of the second region can be reduced as compared with the case where the heating by the first heating unit is not performed when the second region is heated by the portion.
According to the invention which concerns on Claim 3, a 1st heating part and a 2nd heating part can each heat without affecting each other.
According to the invention which concerns on Claim 4, the space used for fixing can be made small compared with the case where a 2nd heating part is not arrange | positioned at the inner peripheral surface side of the endless belt used for the heating by a 1st heating part.

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 explaining the effect | action of the thermosensitive magnetic alloy in the temperature below a Curie point. It is a figure explaining the effect | action of the thermosensitive magnetic alloy in the temperature more than a Curie point. FIG. 6 is a flowchart showing the operation of the image forming apparatus according to the present embodiment. It is a figure explaining the temperature distribution which arises in a heating belt by an electromagnetic induction part. It is a figure explaining the temperature distribution which arises in a heating belt with the resistance heating element of an auxiliary | assistant part. It is a figure explaining the temperature distribution which arises in a heating belt with an electromagnetic induction part and a resistance heating element.

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 buttons and the like for inputting various instructions, receives an operation by the 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 drive 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 unit 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 measurement unit 55, a pressing pad 56, a holder 57, and an auxiliary unit 58. 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 an arrow D52 direction around an axis O2 that is an axis parallel to the axis O1 and is arranged in the −y direction of the axis O1, and accordingly, the elastic layer 522 is rotated in the arrow D52 direction. Rotate to. The material of the elastic layer 522 is, for example, 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 assists the heating of the paper P by the heating belt 51 by pressing the paper P conveyed by the conveyance unit 16 against the heating belt 51 while being rotated by a driving unit (not shown). The heating belt 51 is driven and rotated by the pressure roll 52 by the frictional force from the pressure roll 52.

The measuring unit 55, the pressing pad 56, the holder 57, and the auxiliary unit 58 are disposed on the inner peripheral side of the heating belt 51.
The holder 57 is a rod-shaped member extending in the x-axis direction, and both ends (not shown) are fixed to the casing of the image forming apparatus 1. The holder 57 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 holder 57 is relatively less affected by the induced magnetic field and less susceptible to the induced magnetic field than when other materials are used. The holder 57 supports the pressing pad 56 toward the arrow D56 direction (−y direction) shown in FIG. 2, that is, the direction in which the pressing roll 52 is disposed.

  The pressing pad 56 is made of an elastic body such as silicone rubber or fluorine rubber, or a heat resistant resin such as PPS or LCP (Liquid Crystal Polymer), and is supported by the holder 57 at a position facing the pressure roll 52. The pressing pad 56 is arranged in a state of being pressed from the pressure roll 52 via the heating belt 51 and presses the heating belt 51 from the inside 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 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 auxiliary portion 58 includes a spring member 584 that supports the temperature-sensitive magnetic alloy 581.

  The spring member 584 is, for example, a curved metal plate spring, and fixes the temperature-sensitive magnetic alloy 581 to the holder 57 and supports it so as to press against the inner peripheral surface of the heating belt 51. Even if the heating belt 51 is eccentric and displaced in the radial direction by the spring member 584, the temperature-sensitive magnetic alloy 581 follows the displacement and maintains a contact state with the inner peripheral surface of the heating belt 51. .

  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. The 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 preferably 170 ° C to 250 ° C, more preferably 190 ° C. ~ 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 spring member 584. The temperature-sensitive magnetic alloy 581 is partly heated 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, desirably 0.3 to 0.6 mm. The shape of the temperature-sensitive magnetic alloy 581 is a shape obtained by cutting out a part corresponding to a predetermined central angle range (for example, 30 ° to 180 °) from the cylindrically-shaped alloy having the above thickness. There are no particular restrictions.

  The resistance heating element 582 is a resistor that generates Joule heat by flowing electricity and transmits the Joule heat to the outer peripheral side of the heating belt 51 through the heating belt 51 to heat the paper P. 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 electromagnetic induction part 53, the temperature-sensitive magnetic alloy 581 and the damping member 583 are all arranged 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, this first region 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 second medium having a narrower width 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 first 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), and is fixed to the holder 57 by a support member (not shown). When the AC magnetic field generated by the electromagnetic induction unit 53 and passed through the heating belt 51 and the temperature-sensitive magnetic alloy 581 passes through the attenuation member 583, electromagnetic induction occurs and eddy current flows inside the attenuation member 583. 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. In order to stop heating the heating belt 51 at a temperature equal to or higher than the Curie point, it is desirable to select a material that generates an eddy current that cancels the eddy current generated in the heating belt 51 for the damping member 583. .

  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. 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 side 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 side 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. 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 (registered trademark), etc.) Or a nonmagnetic metal such as a hard magnetic 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. (Desirably 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 unit 53 passes in the thickness direction of the conductive heat generating layer 512, electromagnetic induction is generated and eddy current flows inside the conductive heat generating layer 512. The conductive heat generating layer 512 generates heat when the eddy current flows. As described above, the conductive heat generating layer 512 is heated by the AC magnetic field generated by the electromagnetic induction unit 53. Hereinafter, heating of the heating belt 51 having the conductive heat generating layer 512 by electromagnetic induction in an alternating magnetic field in this way, that is, heating, 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 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 below 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 damping member 583, an eddy current is generated in the passing portion, so that the damping member 583 generates heat slightly. The damping member 583 cancels the original magnetic field by the demagnetizing field generated by the eddy current and suppresses the heat generation of the heating belt.

  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.

  The measurement unit 55 shown in FIG. 2 is disposed inside the heating belt 51 and measures the temperature of the heating belt 51. The measuring unit 55 includes, for example, a thermistor, and measures the temperature of the heating belt 51 by measuring the voltage of the thermoelectromotive force generated thereby. The measured temperature is transmitted to the control unit 11. 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.

  When fixing the image formed on the maximum width paper P1, the control unit 11 causes the temperature of the heating belt 51 measured by the center sensor 551 (second measurement unit) to approach the preset first temperature. The high frequency power supplied to the exciting coil of the electromagnetic induction unit 53 is controlled. On the other hand, when fixing the image formed on the narrow paper P2, the control unit 11 causes the temperature of the heating belt 51 measured by the end sensor 552 (first measurement unit) to approach the preset second temperature. In this way, the high-frequency power supplied to the exciting coil of the electromagnetic induction unit 53 is controlled, and the temperature of the heating belt 51 measured by the center sensor 551 (second measurement unit) is higher than the second temperature. The power supplied to the resistance heating element 582 of the auxiliary portion 58 is controlled so as to approach the preset third temperature.

  The heating belt 51 controlled so as to approach the preset temperature described above performs a fixing process for heating the paper P conveyed to the nip region R1 via the intermediate transfer belt 41. The sheet P 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 portion of the image forming apparatus 1.

1-2. Operation FIG. 9 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 image formation instruction has been received (step S1; YES), the control unit 11 controls each unit of the image forming apparatus 1 and starts an image formation process (step S2).

  Next, the control unit 11 determines whether or not the paper P used for the instructed image formation is the maximum width paper P1 (step S3). When determining that the paper P used for image formation is the maximum width paper P1 (step S3; YES), the control unit 11 stops the end sensor 552 of the measurement unit 55 and the resistance heating element 582 of the auxiliary unit 58 ( Step S4). And the control part 11 reads the temperature measured by the center part sensor 551 (step S5), and controls the high frequency electric power supplied to the exciting coil of the electromagnetic induction part 53 according to the read temperature (step S6). The control unit 11 determines whether or not the image formation has been completed (step S7). If it is determined that the image formation has not been completed (step S7; NO), the process returns to step S5. When it determines with image formation having been complete | finished (step S7; YES), the control part 11 complete | finishes a process.

  On the other hand, when it is determined in step S3 described above that the paper P used for image formation is not the maximum width paper P1 (step S3; NO), the control unit 11 reads the temperature measured by the center sensor 551 (step S8). The electric power supplied to the resistance heating element 582 of the auxiliary unit 58 is controlled according to the read temperature (step S9). Then, the temperature measured by the end sensor 552 is read (step S10), and the high frequency power supplied to the exciting coil of the electromagnetic induction unit 53 is controlled according to the read temperature (step S11). The control unit 11 determines whether or not the image formation has been completed (step S12). If it is determined that the image formation has not been completed (step S12; NO), the process returns to step S8. When it determines with image formation having been complete | finished (step S12; YES), the control part 11 complete | finishes a process.

  The temperature distribution generated in the heating belt 51 by the above operation will be described. FIG. 10 is a diagram for explaining a temperature distribution generated in the heating belt 51 by the electromagnetic induction unit 53. The electromagnetic induction portion 53 has a length of w4 in the width direction. For this reason, the heating belt 51 that generates heat by the electromagnetic induction unit 53 heats the entire region in the width direction of each of the sheets P regardless of whether the maximum width sheet P1 or the small width sheet P2 passes through the fixing unit 15. . As shown in FIG. 10A, the control unit 11 controls the electromagnetic induction unit 53 to raise the temperature of the heating belt 51 located upstream of the nip region R1 to the temperature T1. Here, the temperature T1 is an example of a predetermined first temperature in the present invention, and is a temperature necessary for fixing the image on the paper P. Since the region R101 shown in FIG. 10A is a position corresponding to the end of the heating belt 51 at the position x1 or the position x8, even if ΔTa that is the temperature difference between the temperature T1 and the temperature T0 occurs in the width direction, the heating is performed. It is difficult for the belt 51 to be loaded. Further, even if a load is applied and a crack or the like occurs in the heating belt 51, the paper P does not pass through the region R101, so that the influence on image formation is suppressed.

  When the maximum width sheet P1 passes through the nip region R1, the maximum width sheet P1 passes through the range from the position x2 to x7, so that the portion of the heating belt 51 corresponding to the range is deprived of heat. As a result, the range from the position x2 to the position x7 through which the maximum width sheet P1 passes in the heating belt 51 is the temperature T2. That is, the temperature distribution of the heating belt 51 is as shown in FIG. 10B downstream of the nip region R1. A region R102 shown in FIG. 10B is a portion corresponding to the outside in the width direction of the maximum width paper P1 in the range of the electromagnetic induction portion 53. In this region R102, since the maximum width paper P1 does not directly take heat, the temperature is higher than the portion through which the maximum width paper P1 has passed, but the high temperature portion is a relatively narrow region in the width direction. Therefore, as shown by the arrow in FIG. 10B, the heat diffuses in the width direction, so that the temperature of the heating belt 51 becomes uniform.

  Here, assuming that the heating belt 51 is heated to the temperature T1 by the control of only the electromagnetic induction unit 53 and the narrow paper P2 is passed, the temperature distribution of the heating belt 51 is as shown in FIG. Become. A region R103 illustrated in FIG. 10C is wider in the width direction than the region R102 illustrated in FIG. Therefore, compared with the region R102 shown in FIG. 10B, the heat remaining in the region R103 shown in FIG. 10C is difficult to diffuse in the width direction. Therefore, when image formation on the narrow paper P2 continues, the heating belt 51 accumulates heat in the region R103, and the heating belt 51 is partially heated. The partially heated heating belt 51 has a temperature gradient in the axial direction, and there is a difference in thermal expansion at each position in the axial direction according to the temperature gradient, so that the heating belt 51 may be distorted or cracked. is there. Further, since the paper P is partially heated excessively, toner fixing failure may occur. Furthermore, since excess heat that is not used for fixing is generated in the region R103 of the heating belt 51, energy is wasted.

  FIG. 11 is a diagram for explaining a temperature distribution generated in the heating belt 51 by the resistance heating element 582 of the auxiliary portion 58. When electric power is supplied to the resistance heating element 582 of the auxiliary unit 58, Joule heat is generated in the resistance heating element 582. As a result, the heat generated in the resistance heating element 582 is transmitted to the heating belt 51 via the temperature-sensitive magnetic alloy 581 in contact with the resistance heating element 582, and the temperature of the portion of the heating belt 51 facing the resistance heating element 582 is measured. Rises. For example, as shown in FIG. 11A, the control unit 11 controls the power supplied to the resistance heating element 582 to raise the temperature of the heating belt 51 located upstream of the nip region R1 to the temperature T1. When the image formed on the narrow paper P2 is fixed by the heating belt 51 having the temperature distribution shown in FIG. 11A, the temperature distribution of the heating belt 51 in the downstream of the nip region R1 is as shown in FIG. ) As shown. In the region R112 shown in FIG. 11B, the temperature of the narrow paper P2 is higher than that of the portion through which the narrow paper P2 has passed because it does not directly take heat, but the high temperature portion is a relatively narrow region in the width direction. is there. Therefore, as shown by the arrow in FIG. 11B, the heat diffuses in the width direction, so that the temperature of the heating belt 51 becomes uniform.

  However, a region R111 shown in FIG. 11A is a region close to the position x3 or the position x6, and is a sheet passing portion for the maximum width sheet P1 even though it is outside the sheet passing section for the small width sheet P2. If the temperature difference of ΔTa exceeds a certain threshold at that portion, the heating belt 51 may be distorted or cracks may be generated, thereby disturbing the formed image.

  FIG. 12 is a diagram illustrating the temperature distribution generated in the heating belt 51 by the resistance heating element 582 of the electromagnetic induction unit 53 and the auxiliary unit 58. When the narrow paper P2 is used for image formation, the control unit 11 of the image forming apparatus 1 controls the heating belt 51 of the fixing unit 15 so as to have a temperature distribution shown in FIG. That is, under the control of the control unit 11, the electromagnetic induction unit 53 generates heat by generating an eddy current in the heating belt 51 in the range from the position x1 to x8, and heats the resistance heating element 582 of the auxiliary unit 58 to generate heat. The range from position x3 to x6 of the belt 51 is heated by conduction heat transfer. Here, the two ranges from the position x1 to x3 and the position x6 to x8 of the heating belt 51 are both heated only by the alternating magnetic field generated by the electromagnetic induction unit 53, and the target temperature is The temperature is set to T3. Further, the range from the position x3 to x6 of the heating belt 51 is a range heated by conduction heat transfer by the resistance heating element 582 in addition to the AC magnetic field, and the target temperature is set to the temperature T1. ing. The temperature T3 is higher than the temperature T0 and lower than the temperature T1. Therefore, the temperature T3 is an example of the second temperature in the present invention, and the temperature T1 in this case is an example of the third temperature in the present invention.

  Thereby, in the region R121 shown in FIG. 12A, ΔTc which is a temperature difference between the temperature T1 and the temperature T3 is generated. This is a temperature difference smaller than the above-described temperature difference ΔTa, so that the heating belt 51 is distorted. The possibility of cracks is low compared to the case shown in FIG. In the region R122 shown in FIG. 12A, ΔTd, which is a temperature difference between the temperature T3 and the temperature T0, is generated, which is also a temperature difference smaller than the above-described temperature difference ΔTa. Further, since the region R122 is a position that hits the end of the heating belt 51, it is difficult to apply a load to the heating belt 51, and even if a crack occurs due to the load being applied, the paper P does not pass through. The effect is suppressed.

  When the image formed on the narrow paper P2 is fixed by the heating belt 51 having the temperature distribution shown in FIG. 12A, the temperature distribution of the heating belt 51 in the downstream of the nip region R1 is as shown in FIG. ) As shown. In the region R123 shown in FIG. 12B, the temperature of the narrow paper P2 is higher than that of the portion through which the narrow paper P2 has passed because it does not directly take heat, but the high temperature portion is a relatively narrow region in the width direction. is there. For this reason, the temperature of the heating belt 51 is made uniform as the heat diffuses in the width direction as indicated by arrows in FIG.

  As described above, the image forming apparatus 1 uses both the electromagnetic induction heating by the electromagnetic induction unit 53 and the conduction heat transfer by the resistance heating element 582 of the auxiliary unit 58 when fixing the image on the narrow paper P2. Since the temperature distribution generated in the axial direction of the belt 51 (that is, the width direction of the paper P) is adjusted stepwise, the thermal load on the heating belt 51 is reduced.

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 side 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.

2-3. Control According to Measurement In the above-described embodiment, when fixing the image formed on the maximum width paper P1, the control unit 11 is the first in which the temperature of the heating belt 51 measured by the center sensor 551 is set in advance. The high-frequency power supplied to the exciting coil of the electromagnetic induction unit 53 is controlled so as to approach the temperature of. When fixing the image formed on the narrow paper P2, the control unit 11 causes the electromagnetic induction unit 53 so that the temperature of the heating belt 51 measured by the end sensor 552 approaches the preset second temperature. The high-frequency power supplied to the exciting coil of the heater is controlled, and the temperature of the heating belt 51 measured by the center sensor 551 is higher than the second temperature and approaches a preset third temperature. The electric power supplied to the resistance heating element 582 of the auxiliary unit 58 was controlled. However, the control unit 11 may not perform control according to the measurement by the measurement unit 55. For example, the control unit 11 performs electromagnetic induction so as to heat a predetermined amount of heat when fixing an image formed on the maximum width paper P1 and when fixing an image formed on the small width paper P2. The high frequency power supplied to the exciting coil of the unit 53 and the power supplied to the resistance heating element 582 may be controlled. In short, the control unit 11 controls the first heating unit when fixing an image formed on the first medium having a width smaller than the first width and wider than the second width of the medium. When the first region is heated to fix an image formed on the second medium having a width smaller than the second width of the medium, the first region is heated by controlling the first heating unit. What is necessary is just to control a 2nd heating part and to heat a 2nd area | region.

  Further, when fixing the image formed on the width sheet P1, the control unit 11 does not use the center sensor 551 (second measurement unit) but the heating belt 51 measured by the end sensor 552 (first measurement unit). The high frequency power supplied to the exciting coil of the electromagnetic induction unit 53 may be controlled so that the temperature of the electromagnetic induction unit 53 approaches a first temperature set in advance. That is, when fixing the image formed on the first medium, the control unit 11 performs the first measurement so that the temperature measured by the first measurement unit or the second measurement unit becomes a predetermined first temperature. What is necessary is just to control a heating part and to heat a 1st medium.

2-4. 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 heating a sheet P other than the maximum width sheet P1, the control unit 11 controls the other heating unit in addition to the heating unit associated with the sheet P, so that the first region It is only necessary to adjust the temperature difference generated in the temperature and reduce the heat load generated by the temperature difference.

2-5. Program A 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. The 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, 52 ... pressure roll, 521 ... core material, 522 ... elastic layer, 53 ... electromagnetic induction part, 54 ... magnetic core, 55 ... measuring part, 551 ... center part sensor, 552 ... end part sensor, 56 ... Pressing pad, 57 ... Holder, 58 ... Auxiliary part, 581 ... Temperature sensitive magnetic alloy, 582 ... Resistance heating element, 582a, 582c ... Electrode, 582b ... Resistance member, 582d ... Film, 583 ... Attenuating member, 5 4 ... spring member, P ... paper, P1 ... maximum width sheet, P2 ... narrow paper, R1 ... nip area

Claims (5)

A first heating unit that heats a first region having a first width and fixes an image formed on a medium passing through the first region;
A second region that is included in the first region and has a second width narrower than the first width is heated to fix the image formed on the medium passing through the second region. A heating unit;
A control unit for controlling the first heating unit and the second heating unit,
The control unit controls the first heating unit to heat the first region when fixing an image formed on a second medium having a width smaller than the second width of the medium. And fixing the second region by controlling the second heating unit. 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 controller is
When fixing the image formed on the first medium, the first heating unit is set so that the temperature measured by the first measurement unit or the second measurement unit becomes a predetermined first temperature. To control the heating of the first medium,
When fixing the image formed on the second medium, the first heating unit is controlled so that the temperature measured by the first measurement unit becomes a predetermined second temperature. The second medium is heated by controlling the second heating unit so that the temperature measured by the second measuring unit is higher than the second temperature and becomes a predetermined third temperature. The fixing device according to claim 1. The first heating unit generates an alternating magnetic field and heats the first region by electromagnetic induction in the alternating magnetic field,
The fixing device according to claim 1, wherein the second heating unit heats the second region by Joule heat generated by flowing electricity. The first heating unit passes the AC magnetic field through an endless belt having an outer peripheral surface that rotates and conveys the medium so as to rotate in contact with the medium and pass through the first region. Generating an eddy current due to the electromagnetic induction in the member included in the first area, heating the first region,
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. 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, wherein an image is fixed on a medium conveyed by the conveying unit.

Images