JP4805059B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus and an electrophotographic image forming apparatus using the same.

  Generally, a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer is composed of a fixing roller and a pressure roller that are pressed against each other. The fixing roller or both the fixing roller and the pressure roller After the roller is heated to a predetermined temperature (fixing temperature) by heating means including a halogen lamp (halogen heater) disposed inside the recording paper, the recording paper on which the unfixed toner image is formed is fixed to a fixing roller and a pressure roller. In many cases, the toner image is fixed by heat and pressure (heat roller fixing method) through a pressure contact portion (fixing nip portion).

  In particular, in a color fixing device, an elastic roller in which an elastic layer made of silicon rubber or the like is provided on the surface layer of the fixing roller is generally used.

  By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed according to the unevenness of the unfixed toner image and comes into contact so as to cover the toner image surface. This makes it possible to perform heat-fixing well on unfixed toner images, and at the same time, improves the releasability of color toners that are more likely to be offset than monochrome due to the effect of strain relief of the elastic layer at the fixing nip. can do. Furthermore, since the nip shape of the fixing nip is convex upward (on the fixing roller side) (so-called reverse nip shape), the paper peeling performance is improved and the paper can be peeled off without using a peeling means such as a peeling claw. (Self-strip) and image defects caused by the peeling means can be eliminated.

  Note that an image forming apparatus using monochromatic toner also employs a configuration in which an elastic layer is not provided on the fixing roller but an elastic layer is provided only on the pressure roller to ensure a fixing nip.

  By the way, the fixing roller or the pressure roller provided with the elastic layer has a very low heat conductivity of the elastic layer. There is a problem that the temperature of the fixing roller decreases during continuous paper feeding.

  In order to solve such a problem, there is known a configuration in which an external heating means is brought into contact with the surface of the fixing roller and the fixing roller is heated from the outside (external heating fixing method).

For example, Patent Document 1 discloses a technique (external belt heating and fixing method) that uses an external heating belt (endless belt) stretched around a belt suspension roller (support roller) as external heating means. In this technique, an external heating belt is used as the external heating unit, so that the contact area between the external heating unit and the fixing roller is increased to promote heat supply from the external heating unit to the fixing roller.
JP 2004-198559 A (published July 15, 2004)

  However, in the conventional fixing device of the external belt heat fixing system, a temperature difference is generated between the center portion and the end portion in the axial direction of the support roller, and as a result, a difference in glossiness is generated between the center portion and the end portion of the fixed image. For example, the uniformity of the image is impaired.

  As a first factor that causes such a temperature difference, first, when left after a fixing operation or after a temperature rise, the belt end comes into contact with another member (for example, a bearing or an end portion of the belt). The temperature of the roller end is lowered by heat conduction to a belt regulating member or the like that defines the position of the roller.

  Further, as a second factor, the sheet is taken in the sheet passing area of the supporting roller (the area of the supporting roller contacting the area of the belt contacting the portion of the fixing roller contacting the recording sheet; the sheet passing area of the recording sheet; the image forming range). If heat is supplied to the entire area in the axial direction of the support roller so as to compensate for the heat taken away in the paper passing area, the temperature of the non-paper passing area (recording paper non-passing area) at the end of the roller is increased. May be higher than the paper passing area.

  The present invention has been made in view of these problems, and an object thereof is to suppress a temperature difference between a central portion and an end portion of a support roller in an external heating belt fixing type fixing device.

  In order to solve the above problems, the fixing device of the present invention heats a fixing member, a pressure member, and a belt rotatably stretched between a plurality of support rollers, Including at least one external heating device that heats the member to be heated by contacting the peripheral surface of the pressure member, and the fixing member and the pressure member are conveyed while sandwiching the recording material, In the fixing device for fixing an unfixed image on the recording material to the recording material by heat and pressure, at least one of the plurality of support rollers is a cylindrical member having a heating source therein, The average cross-sectional area of the cross section perpendicular to the axial direction in the axially opposite end portions of the region of the support roller having the source in contact with the belt is the cross-sectional area of the cross section perpendicular to the axial direction in the axial central portion. of It is characterized in that less than average value.

  According to the above configuration, the average value of the cross-sectional area of the cross section perpendicular to the axial direction in the axially opposite end portions in the region of the support roller having the heating source that contacts the belt is the axial value in the axially central portion. It is smaller than the average value of the cross sectional area of the vertical cross section. Thereby, the amount of heat lost from the both end portions due to heat conduction to the outside can be suppressed, and the temperature of both end portions can be suppressed from decreasing. Therefore, a uniform and high-quality fixed image can be obtained by preventing a temperature difference between the both end portions and the central portion. Further, since the central portion has a larger cross-sectional area than both end portions, heat conduction in the axial direction is promoted more than both end portions. For this reason, it is possible to make the temperature distribution in the center portion during the fixing process uniform.

  The support roller having a heat source may have a structure in which the thickness at the both end portions is thinner than the thickness at the center portion.

  According to said structure, the cross-sectional area of the cross section perpendicular | vertical to the axial direction in a both-ends side part can be made smaller than the cross-sectional area of the cross section perpendicular | vertical to the axial direction in a center part.

  Further, the support roller having the heating source may have a constant outer diameter in a region in contact with the belt.

  When the outer diameter of the region in contact with the belt is not constant, a force in the axial direction of the support roller acts on the belt, which causes meandering and cracking. On the other hand, according to the above configuration, since the outer diameter of the region in contact with the belt is constant, it is possible to suppress meandering and cracking of the belt by suppressing the axial force of the support roller acting on the belt.

  Further, the support roller having the heating source may have a constant inner diameter in a region in contact with the belt.

  If the inner diameter of the region in contact with the belt is not constant, the clearance between the heating source and the inner peripheral surface of the support roller is not constant, and the amount of heat transferred from the heating source to the support roller varies depending on the position, so the temperature distribution is made uniform. It can be difficult. On the other hand, according to the above configuration, since the inner diameter of the region in contact with the belt is constant, the heat transfer amount to the heating source and the support roller can be made uniform, and the temperature distribution of the support roller can be made uniform.

  Moreover, the structure which has a hole in the outer peripheral surface of the said both end side part may be sufficient as the said support roller which has a heat source.

  According to said structure, the average value of the cross-sectional area of a cross section perpendicular | vertical to the axial direction in the said both end side part of the support roller can be made small by providing a hole in the outer peripheral surface of the said both end side part. Further, the heat capacity of the support roller is reduced, and the temperature of the support roller can be increased in a short time.

  Further, in the configuration having the hole portion, the support roller having the heating source may have a configuration in which an outer diameter and an inner diameter of a region in contact with the belt are constant.

  According to the above configuration, by providing holes in both end portions of the support roller, a cross section perpendicular to the axial direction in both end portions while keeping the outer diameter and inner diameter of the region in contact with the belt in the support roller constant. Can be made smaller than the cross-sectional area of the cross section perpendicular to the axial direction in the central portion. Therefore, meandering and cracking of the belt can be prevented, and the heat transfer amount to the heating source and the support roller can be made uniform, so that the temperature distribution of the support roller can be made uniform.

  In addition, the hole may be a spiral groove in each of the both end portions along the rotation direction of the support roller from the both ends of the support roller toward the center.

  According to the above configuration, when the belt approaches the one end side, the contact width between the belt on the opposite side to the side of the deviation and the region where the hole of the support roller is provided is the belt on the side of the deviation. And the contact width of the support roller with the region where the hole is provided. For this reason, the belt is biased to the side opposite to the shifting direction. Thereby, the meandering of the belt can be prevented. In addition, since the end of the belt can be prevented from coming into contact with other members, or the contact force against the other members can be reduced, the mechanical durability of the belt can be improved.

  The hole may penetrate the support roller.

  According to the above configuration, the radiant heat and infrared rays from the heating source provided inside the support roller can be directly applied to the belt through the hole, so that the temperature of the belt can be raised in a short time. Can do.

  Further, the support roller having a heating source has a plurality of holes of the same shape in the both end portions and the central portion, and the number of holes per unit surface area in the both end portions is the center. It is good also as a structure larger than the number of the holes per unit surface area in a part.

  According to the above configuration, since the number of holes per unit surface area in both end portions is larger than the number of holes per unit surface area in the central portion, the cross-sectional area of the cross section perpendicular to the axial direction in both end portions. Can be made smaller than the average value of the cross-sectional areas of the cross section perpendicular to the axial direction in the central portion. Moreover, since the hole part of the same shape is provided in the both end side part and the center part, since a hole part can be formed with the same specification and tool, processing is easy and manufacturing cost can be reduced.

In order to solve the above problems, the fixing device of the present invention heats a fixing member, a pressure member, and a belt rotatably stretched between a plurality of support rollers, Including at least one external heating device that heats the member to be heated by contacting the peripheral surface of the pressure member, and the fixing member and the pressure member are conveyed while sandwiching the recording material, In the fixing device for fixing an unfixed image on the recording material to the recording material by heat and pressure, at least one of the plurality of support rollers is a cylindrical member having a heating source therein, and the heating source The product of the thermal conductivity and the cross-sectional area of the cross section perpendicular to the axial direction in the support roller having the above is 60 × 10 ⁻⁶ (W · m / K) or less.

When the product of the thermal conductivity and the cross-sectional area in the support roller having the heating source is larger than 60 × 10 ⁻⁶ (W · m / K), the heat conduction in the axial direction becomes excessive at both axial ends. . For this reason, even if the heating source is controlled so that the region in contact with the belt at the time of standby heat retention is a uniform temperature, the temperature at both ends decreases due to heat conduction from both ends of the support roller, Inadequate fixing results in a non-uniform and low quality image.

On the other hand, according to the above configuration, the product of the thermal conductivity and the cross-sectional area of the support roller is 60 × 10 ⁻⁶ (W · m / K) or less. The temperature in the belt contact area can be made uniform.

  In order to solve the above problems, the fixing device of the present invention heats a fixing member, a pressure member, and a belt rotatably stretched between a plurality of support rollers, Including at least one external heating device that heats the member to be heated by contacting the peripheral surface of the pressure member, and the fixing member and the pressure member are conveyed while sandwiching the recording material, In the fixing device for fixing an unfixed image on the recording material to the recording material by heat and pressure, the plurality of support rollers are cylindrical members, and a support roller provided with a heating source therein, and Within the image forming range, the support roller with the heating source has a cross section perpendicular to the thermal conductivity and the axial direction than the support roller without the heating source. That the product of the area is large. It is a symptom.

  If the product of the thermal conductivity and the cross-sectional area of the support roller having a heating source is too small, the thermal conductivity in the axial direction is insufficient, and the image formation range (the portion that contacts the recording paper in the fixing member or pressure member) The temperature distribution of the area of the support roller that abuts the area of the belt that is in contact (image area) may increase. On the other hand, if the product of the thermal conductivity and the cross-sectional area of the support roller without a heating source is too large, the temperature at the end of the support roller decreases due to heat conduction from the end of the support roller to other members. As a result, the temperature at the belt end is lowered.

  On the other hand, according to the above configuration, the support roller with the heating source has a larger product of the thermal conductivity and the cross-sectional area than the support roller without the heating source. It is possible to make the temperature distribution in the image area uniform by promoting axial heat conduction in the roller. Further, heat conduction from the end portion of the support roller not provided with a heat source to other members can be suppressed, and a temperature drop at the belt end portion can be suppressed.

  In any one of the above-described configurations, the external heating device may be configured to rotate the belt during temperature rising heating and stop the rotation of the belt during standby temperature keeping.

  According to said structure, a belt can be uniformly heated along the circumferential direction by rotating a belt at the time of temperature rising heating. Further, by stopping the rotation of the belt during the standby temperature keeping, the power for rotating the belt can be reduced to save power, and the noise accompanying the rotation driving of the belt can be prevented. Furthermore, since the belt is not rotated, heat dissipation from the belt end can be suppressed. Thereby, the heat conduction from the support roller to the belt can be suppressed, and the temperature drop at the end of the support roller can be prevented.

  In any one of the configurations described above, the external heating device may have a configuration in which the surface temperature of the support roller having the heating source during standby warming is lower than that during the image forming operation.

  When the surface temperature of the support roller having the heating source is set to the same temperature as that during the image forming operation when the standby temperature is maintained, there is no heat loss due to paper passing during the standby temperature, so the heating energy supplied to the heating source is the image. It becomes smaller than the time of forming operation. For this reason, the temperature of the end tends to decrease due to heat conduction and heat dissipation from the end of the support roller. Therefore, if the surface temperature of the support roller is kept at the temperature at the time of image forming operation, the image formation is started while the temperature at the end of the support roller is lowered, and the fixed image has an image quality with uneven fixing. It becomes a low image.

  On the other hand, according to the above configuration, the surface temperature of the support roller at the time of standby heat retention is lower than the surface temperature at the time of image forming operation. By raising the temperature, the temperature distribution in the axial direction of the support roller can be made uniform, and the amount of heat can be supplied uniformly in the width direction of the belt. Moreover, the energy for heat insulation heating can be reduced by lowering the temperature at the time of standby heat insulation.

  In any of the above-described configurations, an external heating device that heats the fixing device by bringing the belt into contact with the peripheral surface of the fixing member, and a pressure member that contacts the belt with the peripheral surface of the pressure member. It is good also as a structure provided with the external heating apparatus heated.

  According to the above configuration, since the surface temperatures of both the fixing member and the pressure member can be controlled with high accuracy, a high-quality image can be stably obtained and high throughput can be continuously obtained.

  The image forming apparatus of the present invention includes any one of the fixing devices described above. Since uniform fixability can be realized along the axial direction of the support roller, a uniform and high-quality image can be obtained.

  As described above, in the fixing device according to the present invention, at least one of the plurality of support rollers is a cylindrical member having a heat source therein, and is in contact with the belt in the support roller having the heat source. Of the regions in contact with each other, the average value of the cross-sectional areas of the cross sections perpendicular to the axial direction in the axial both ends is smaller than the average value of the cross-sectional areas of the cross sections perpendicular to the axial direction in the central portion in the axial direction.

  Therefore, the amount of heat lost from both end portions due to heat conduction to the outside can be suppressed, so that the temperature of both end portions can be suppressed from decreasing, and a temperature difference between the end portions and the center portion can occur. Can be prevented, and a uniform and high-quality fixed image can be obtained.

In the fixing device of the present invention, at least one of the plurality of support rollers is a cylindrical member having a heating source therein, and a cross section perpendicular to the thermal conductivity and the axial direction of the support roller having the heating source. The product with the cross-sectional area is 60 × 10 ⁻⁶ (W · m / K) or less.

  Therefore, it is possible to make the temperature in the belt contact region uniform by suppressing the temperature drop at both ends.

  In the fixing device of the present invention, the plurality of support rollers are cylindrical members, and include a support roller having a heat source therein and a support roller having no heat source therein, and includes a heat source. The support roller has a larger product of the thermal conductivity and the cross-sectional area of the cross section perpendicular to the axial direction than the support roller without the heating source.

  Therefore, the heat distribution in the axial direction of the support roller having the heating source can be promoted, and the temperature distribution in the image area can be made uniform. Further, heat conduction from the support roller end portion to other members can be suppressed, and a temperature drop at the belt end portion can be suppressed.

[Embodiment 1]
(Configuration of image forming apparatus 1)
An embodiment of the present invention will be described. First, the image forming apparatus 1 provided with the fixing device of the present embodiment will be described with reference to FIG. FIG. 2 is a schematic diagram showing the internal structure of the image forming apparatus 1. This image forming apparatus 1 is a dry electrophotographic color image forming apparatus, and is based on image data transmitted from each terminal device connected via a network or image data read by a scanner (recording). Material) A printer that forms a color image or a monochrome image on P.

  The image forming apparatus 1 is a dry electrophotographic and quadruple tandem color printer, and includes a visible image forming unit 50, a paper transport unit 30, a fixing device 40, and a supply tray 20.

  The visible image forming unit 50 includes a yellow image forming unit 50Y, a magenta image forming unit 50M, a cyan image forming unit 50C, and a black image forming unit 50B. Specifically, the yellow image forming unit 50Y, the magenta image forming unit 50M, the cyan image forming unit 50C, and the black image forming unit 50B are arranged between the supply tray 20 and the fixing device 40 from the supply tray 20 side. They are attached in order.

  Each of these image forming units 50Y, 50M, 50C, 50B has substantially the same configuration, and based on the image data, a yellow image, a magenta image, a cyan image, and a black image are respectively applied to the paper P. Is to be transferred.

  Each of the image forming units 50Y, 50M, 50C, and 50B includes a photosensitive drum 51. Further, a charging roller 52, an LSU 53, a developing unit 54, a transfer roller 55, and a cleaning device 56 are provided around the photosensitive drum 51. The photosensitive drum 51 is disposed along the rotation direction (the F direction in FIG. 2).

  The photosensitive drum 51 of each of the image forming units 50Y, 50M, 50C, and 50B is a drum-shaped transfer roller having a photosensitive material on the surface, and is driven to rotate in the direction of arrow F. The charging roller 52 is for charging the surface of the photosensitive drum 51 uniformly (uniformly).

  The LSU (laser beam scanner unit) 53 of the image forming units 50Y, 50M, 50C, and 50B receives pixel signals corresponding to the yellow component, magenta component, cyan component, and black component in the image data, respectively. Yes. Each LSU 53 exposes the charged photosensitive drum 51 based on these image signals to generate an electrostatic latent image.

  The developing units 54 of the image forming units 50Y, 50M, 50C, and 50B have yellow, magenta, cyan, and black toner (developer), respectively. The toner has a function of developing the electrostatic latent image generated on the photosensitive drum 51 with these toners to generate a toner image (visualized image). As the developer, for example, a developer such as a non-magnetic one-component developer (non-magnetic toner), a non-magnetic two-component developer (non-magnetic toner and carrier), and a magnetic developer (magnetic toner) is used. be able to.

  The transfer roller 55 of the image forming units 50Y, 50M, 50C, and 50B is applied with a bias voltage having a polarity opposite to that of the toner. By applying this bias voltage to the paper P, the toner image on the photosensitive drum 51 is transferred to the paper. It is for transferring to P. The cleaning device 56 of the image forming units 50Y, 50M, 50C, and 50B removes the toner remaining on the photosensitive drum 51 after the image transfer onto the paper P. The transfer of the toner image onto the paper P as described above is repeated four times for four colors.

  The paper transport unit 30 includes a driving roller 31, a driven roller 32, and a transport belt 33, and transports the paper P so that a toner image is formed on the paper P in order by the image forming units 50Y, 50M, 50C, and 50B. Is.

  The driving roller 31 and the driven roller 32 stretch the conveyor belt 33, and the driving roller 31 has a predetermined peripheral speed (in this embodiment, monochrome image formation (monochrome mode) 355 mm / s, color image formation ( The color belt is controlled to rotate at 175 mm / s), so that the conveyor belt 33 rotates.

  The conveyance belt 33 is a belt that is placed between the driving roller 31 and the driven roller 32 so as to come into contact with the photosensitive drums 51 of the image forming units 50Y, 50M, 50C, and 50B. It is friction driven in the Z direction. The transport belt 33 electrostatically attracts the paper P sent from the supply tray 20 and transports the paper P sequentially to the image forming units 50Y, 50M, 50C, and 50B.

  Further, the sheet P on which the toner image is transferred by each of the image forming units 50Y, 50M, 50C, and 50B is peeled off from the conveying belt 33 by the curvature of the driving roller 31 and is conveyed to the fixing device 40 (the one-dot chain line in FIG. 2). Indicates the transport route). Note that the toner images after being transferred onto the paper P by the image forming units 50Y, 50M, 50C, and 50B are in an unfixed state on the paper P.

  The fixing device 40 heat-compresses the unfixed toner image transferred onto the paper P to the paper P. Specifically, the fixing device 40 includes a fixing roller 60 and a pressure roller 70. Then, a predetermined fixing speed (process speed; monochrome mode 355 mm / s, color mode 175 mm / s) and copying speed (number of copies per minute; for example, 70 sheets / monochrome mode with A4 landscape feed) from the visible image forming unit 50 Sheet P conveyed in color mode 40 sheets / minute) is fed to a fixing nip N formed between the fixing roller 60 and the pressure roller 70. Further, the fixing roller 60 and the pressure roller 70 convey the paper P while sandwiching it. At this time, the toner image (unfixed image) on the paper P is melted by the heat of the peripheral surface of the fixing roller 60 and is pressed by the fixing roller 60 and the pressure roller 70 to be fixed on the paper P. Fix as an image.

  Then, the sheet P after the toner image is fixed by the fixing device 40 is discharged to a discharge tray (not shown) outside the image forming apparatus 1. Thereby, the image forming process ends. A specific configuration of the fixing device 40 will be described later in detail.

  The image forming apparatus 1 also includes a color mode (multicolor mode) in which each image forming unit 50Y, 50M, 50C, and 50B performs image transfer on the paper P to form a color image (multicolor image), and the paper. Only the black image forming unit 50B can perform image transfer with respect to P, and a monochrome mode (monochrome mode) in which a monochrome image (monochrome image) is formed can be executed. More specifically, the control unit (control integrated circuit board or computer, not shown) provided in the image forming apparatus 1 is in either the color mode or the monochrome mode according to an input instruction from the user. Each of the image forming units 50Y, 50M, 50C, and 50B is controlled so as to execute the image formation corresponding to the selected mode.

  Further, the controller forms an image so as to convey the sheet P at a conveyance speed of 355 mm / S (also referred to as a process speed) in the color mode and convey the sheet P at a conveyance speed of 175 mm / S in the monochrome mode. It controls the sheet conveying means (the sheet conveying unit 30, the fixing roller 60, the pressure roller 70, etc.) of the apparatus 1.

(Configuration of Fixing Device 40)
Next, the fixing device 40 will be specifically described. FIG. 3 is a schematic diagram illustrating a schematic configuration of the fixing device 40. In addition to the fixing roller (fixing member) 60 and the pressure roller (fixing member) 70 described above, the fixing device 40 includes an external heating device 80, a control device 90, a rotation drive device 91, a belt moving device 110, and a heating power supply unit 99. It is the structure containing. If necessary, a web cleaning device for cleaning the surface of the fixing roller 60 may be further provided.

  The rotation driving device 91 rotates the fixing roller 60 and includes, for example, a motor and a gear. The operation of the rotation drive device 91 is controlled by the control device 90.

  The fixing roller 60 is a roller that rotates in the G direction shown in FIG. 3, and is formed by covering a metal hollow cylindrical cored bar 61, an elastic layer 62 that covers the outer peripheral surface of the cored bar 61, and the elastic layer 62. The release layer 63 is formed.

  The cored bar 61 is made of aluminum having an outer diameter of 46 mm and has a cylindrical shape. However, the material of the cored bar 61 is not limited to aluminum, and may be made of, for example, iron or stainless steel. The elastic layer 62 has a thickness of 3 mm and is made of heat-resistant silicon rubber (JIS-A hardness 20 degrees). The release layer 63 is made of a PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) tube having a thickness of about 30 μm. The material of the release layer 63 may be any material as long as it has excellent heat resistance and durability and has excellent release properties with respect to the toner. In addition to PFA, fluorine-based materials such as PTFE (polytetrafluoroethylene) can be used. Materials may be used. The fixing roller 60 thus configured has an outer diameter of 50 mm, and the surface hardness of the fixing roller 60 is 68 degrees (Asker C hardness). The width of the surface of the fixing roller 60 in the rotation axis direction is 320 mm.

  A thermistor 65 for detecting the temperature of the peripheral surface is in contact with the peripheral surface of the fixing roller 60, and a halogen lamp (heater lamp) 64 that emits heat when power is supplied to the inside of the cored bar 61. Is installed. The halogen lamp 64 is a heat source for the fixing roller 60. When power is supplied to the halogen lamp 64, the inside of the fixing roller 60 is heated to a predetermined temperature (180 ° C. in this embodiment) by the halogen lamp 64, and the fixing nip portion N The recording paper on which the unfixed toner image that passes through is formed is heated.

  In the present embodiment, one halogen lamp is incorporated. However, the present invention is not limited to this. For example, a plurality of heat generation distributions divided in the axial direction so as to form an optimum temperature distribution according to the paper size. A halogen lamp may be used. In this embodiment, the thermistor 65 is arranged so as to contact the longitudinal center of the fixing roller 60. However, the present invention is not limited to this, and is installed at the longitudinal end (non-sheet passing area) of the fixing roller 60. May be. Further, when the amount of heat generation differs between the central portion and the end portion by installing two halogen lamps or the like, a thermistor may be disposed at both the central portion and the end portion.

  The pressure roller 70 is a roller that rotates in the H direction shown in FIG. 3, and is formed by covering a metal hollow cylindrical cored bar 71, an elastic layer 72 that covers the outer peripheral surface of the cored bar 71, and the elastic layer 72. The release layer 73 is formed.

  The cored bar 71 has an outer diameter of 46 mm and is made of aluminum. However, the material of the cored bar 71 is not limited to aluminum, and may be made of iron or stainless steel. The elastic layer 72 is made of silicon rubber having a thickness of 2 mm and having heat resistance. The release layer 73 is made of a PFA tube having a thickness of about 30 μm. The material of the release layer 73 may be any material as long as it has excellent heat resistance and durability and has excellent release properties with respect to the toner. In addition to PFA, a fluorine-based material such as PTFE may be used. The outer diameter of the pressure roller 70 thus configured is 50 mm, and the surface hardness of the pressure roller 70 is 75 degrees (Asker C hardness).

  The pressure roller 70 is pressed against the fixing roller 60 with a predetermined load (600 N in this case) by an elastic member (spring) (not shown). As a result, a fixing nip portion N (a portion where the fixing roller 60 and the pressure roller 70 are in contact with each other, here a width of 9 mm in the recording paper conveyance direction) is formed between the peripheral surface of the fixing roller 60 and the peripheral surface of the pressure roller 70. Is done. Further, the pressure roller 70 is rotated in the direction opposite to the fixing roller 60 (the movement direction of both roller surfaces in the fixing nip portion is the same) following the rotation of the fixing roller 60. In the present exemplary embodiment, the pressure roller 70 is configured to be driven to rotate by the fixing roller 60, but is not limited thereto, and may be configured to be rotationally driven by a rotational driving unit different from the fixing roller 60.

  A thermistor 75 that detects the temperature of the peripheral surface is in contact with the peripheral surface of the pressure roller 70, and a halogen lamp (heater lamp) 74 that performs heat radiation by supplying power is provided inside the cored bar 71. is set up. The halogen lamp 74 is a heat source for the pressure roller 70. When power is supplied to the halogen lamp 74, the surface of the pressure roller 70 is heated to a predetermined temperature (150 ° C. in this embodiment).

  In this embodiment, the rubber hardness (75 degrees) of the pressure roller 70 is set higher than the rubber hardness (68 degrees) of the fixing roller 60, but this is between the pressure roller 70 and the fixing roller 60. This is because the fixing nip portion N formed in the above is formed in a reverse nip shape (the shape of the pressure roller 70 is almost unchanged and the fixing roller 60 is slightly recessed). The fixing nip portion N thus obtained had a nip width of 8.5 mm.

  Here, the reason why the fixing nip portion N between the pressure roller 70 and the fixing roller 60 has a reverse nip shape will be described. When the fixing nip portion N has a reverse nip shape, the paper P that has passed through the fixing nip portion N is discharged in a direction along the circumferential surface of the pressure roller 70, and thus the paper P is discharged from the fixing nip portion N. This is because self-peeling (peeling with a paper scraper without the need for forced peeling assisting means such as a peeling nail) becomes easier.

  When the surface hardness of the pressure roller 70 is lower than the surface hardness of the fixing roller 60, the shape of the fixing roller 60 remains almost unchanged in the fixing nip portion N between the fixing roller 60 and the pressure roller 70. Since the sheet P passes through the fixing nip portion N and is discharged in a direction along the peripheral surface of the fixing roller 60, self-peeling hardly occurs.

(Configuration of external heating device 80)
The external heating device 80 includes a support roller 81, a support roller 82, an endless belt (external heating belt) 83, a belt moving device 110, and belt regulating members 121 and 122 (not shown in FIG. 3). The endless belt 83 is stretched around the support rollers 81 and 82 so that the back surface (inner peripheral surface) side is in contact with the peripheral surfaces of the support rollers 81 and 82. The endless belt 83 is pressed against the fixing roller 60 with a predetermined pressing force (40N in this embodiment) when the support rollers 81 and 82 are in a first position to be described later. Thus, a heating nip (a contact portion between the endless belt 83 and the fixing roller 60; a width 20 mm in the circumferential direction of the fixing roller 60) is formed between the fixing roller 60 and the heating roller.

  Further, the endless belt 83 is driven to rotate by the fixing roller 60 by contacting the circumferential surface of the rotating fixing roller 60. As a result, the support rollers 81 and 82 rotate in the direction opposite to the rotation direction of the fixing roller 60 (K direction in FIG. 3). That is, when the control device 90 controls the rotation driving device 91 of the fixing roller 60 to rotationally drive the fixing roller 60, the endless belt 83 is fixed by the frictional force at the portion where the endless belt 83 and the fixing roller 60 are in contact with each other. The support rollers 81 and 82 and the endless belt 83 are rotated by being driven by the roller 60.

  The endless belt 83 is a belt member in which a fluororesin blended with PTFE and PFA as a release layer is coated with a thickness of 20 μm on the surface of a base material made of 90 μm-thick polyimide (product name: Upilex S). It is. However, the configuration of the endless belt 83 is not limited to this, and a belt member made of metal such as nickel, stainless steel, or iron may be used. Further, the inner diameter of the endless belt 83 is not limited to 30 mm. The material of the release layer of the endless belt 83 may be any material as long as it has excellent heat resistance and durability and excellent release properties from the toner. For example, PTFE or PFA may be used alone. The inner diameter of the endless belt 83 at room temperature (20 ° C.) is 30 mm (inner peripheral length 94 mm).

The width of the endless belt 83 (the axial width of the support rollers 81 and 82) is 320 mm at room temperature. However, since the thermal expansion coefficient of polyimide is 5.6 × 10 ⁻⁵ / deg, the endless belt 83 is about 3.6 mm (320 mm × 5.6 × 10 ⁻⁵ / deg × 200 deg) in the axial direction when the temperature rises by 200 deg. ≒ 3.6) Thermal expansion. Therefore, the belt width at 220 ° C., which is the set temperature during the fixing operation of the endless belt 83, is 323.6 mm.

  FIG. 1 is a cross-sectional view of a cross section parallel to the axial direction of the support rollers 81 and 82. Each of the support rollers 81 and 82 is a roller in which a fluororesin blended with PTFE and PFA as a release layer is coated on the surface of an aluminum cored bar with a thickness of 20 μm. In addition, as a material of the release layer, it is only necessary to have excellent heat resistance and durability and excellent release property with the toner. For example, a fluorine-based material such as PFA or PTFE (polytetrafluoroethylene) is used. can do. The inter-axis distance between the support rollers 81 and 82 is set to 23.0 mm.

  As shown in FIG. 1, the central portion A in the axial direction of the support rollers 81 and 82 has an outer diameter of 15 mm and an inner diameter of 9 mm (thickness of 3 mm), and has an outer diameter of 15 mm and an inner diameter of 11 mm (thickness of 2 mm) at both ends. A portion (end portion B of the belt contact portion) is provided, and further, a portion (roller end portion C) having an outer diameter of 13 mm and an inner diameter of 11 mm (thickness 1 mm) is provided on both ends thereof. Thereby, in the support rollers 81 and 82, the cross-sectional area of the cross section perpendicular to the axial direction is smaller at the end B of the belt contact portion and the roller end C than at the center A. The belt contact portion is a region where the endless belt 83 abuts, that is, the belt regulating members 121 and 122 disposed on one end side in the axial direction of the support rollers 81 and 82 and the belt regulating member 121 and disposed on the other end side. 122 is an area between.

  Further, the width (the length in the axial direction) of the central portion A is the maximum sheet passing area (when the recording sheet having the maximum width capable of performing the fixing process in this fixing device is passed, the sheet contacts the recording sheet in the fixing roller 60. The width of the support rollers 81 and 82 contacting the region of the endless belt 83 contacting the portion; the maximum recording paper passing region) is substantially the same as the width of the endless belt 83.

  Further, belt regulating members 121 and 122 and bearings 117 and 118 are provided at both end portions C in the axial direction of the support rollers 81 and 82 so as to come into contact with the outer peripheral surfaces of the support rollers 81 and 82. Details of the belt regulating members 121 and 122 and the bearings 117 and 118 will be described later.

  The support rollers 81 and 82 are pressed with a predetermined load against the peripheral surface of the fixing roller 60 via the endless belt 83 by a belt moving device 110 described later. As a result, the surface of the endless belt 83 comes into contact with the circumferential surface of the fixing roller 60, and a nip portion is formed between the surface of the endless belt 83 and the circumferential surface of the fixing roller 60. The nip width between the surface of the endless belt 83 and the circumferential surface of the fixing roller 60 is 20 mm (width along the circumferential direction of the fixing roller 60).

  A thermistor 85a for detecting the surface temperature of the endless belt 83 is in contact with the outer surface of the endless belt 83 in contact with the support roller 81. In addition, a halogen lamp (heater lamp) 86 a that generates heat when power is supplied is provided inside the support roller 81. Further, a thermistor 85b for detecting the surface temperature of the endless belt 83 is in contact with the outer surface of the endless belt 83 in contact with the support roller 82, and the inside of the support roller 82 is a halogen that generates heat due to power supply. A lamp (heater lamp) 86b is provided. The halogen lamps 86a and 86b are heat sources for the endless belt 83. When power is supplied to the halogen lamps 86a and 86b, heat is radiated from the halogen lamps 86a and 86b, and the endless belt 83 passes through the support rollers 81 and 82. It is heated to a predetermined temperature (220 ° C. in this embodiment). Since the endless belt 83 is in contact with the peripheral surface of the fixing roller 60 from the outside of the fixing roller 60, the peripheral surface of the fixing roller 60 can be heated through the contact portion. In the present embodiment, since the two thin-walled small-diameter support rollers 81 and 82 and the thin endless belt 83 are used as described above, the temperature of the endless belt 83 can be raised quickly.

  Next, the belt moving device 110 and the belt regulating members 121 and 122 provided in the fixing device 40 will be described. 4A shows a state in which the support rollers 81 and 82 are arranged by the belt moving device 110 at positions where the support rollers 81 and 82 are in contact with the fixing roller 60 via the endless belt 83 (first position). FIG. 4B is a cross-sectional view illustrating a state in which the support rollers 81 and 82 are disposed at positions separated from the fixing roller 60 (second position) by the belt moving device 110. 5A is a top view illustrating the configuration of the belt moving device 110, and FIG. 5B is a cross-sectional view illustrating the configurations of the support roller 82, the endless belt 83, and the belt regulating member 122.

  4A and 4B, the belt moving device 110 includes a side frame 111, an arm 112, an eccentric cam 113, a fulcrum (fulcrum member) 114, a fulcrum (fulcrum member) 115, and a coil spring 116. I have.

  The side frames 111 are provided at both ends of the support rollers 81 and 82, respectively, and rotatably support the support rollers 81 and 82 via bearings 117 and 118 as shown in FIG. is there. The bearings 117 and 118 are fixed to the side frame 111 at a predetermined inter-axis distance, thereby ensuring the parallelism between the support roller 81 and the support roller 82 (in this embodiment, the support is supported). The tolerance of parallelism between the roller 81 and the support roller 82 is 100 μm or less).

  The side frame 111 is pivotally supported by the arm 112 at a fulcrum 114 so as to be rotatable in a direction substantially perpendicular to the axial direction of the support rollers 81 and 82.

  The arm 112 is rotatably supported by a fulcrum 115 fixed to the frame of the fixing device 40 (not shown), and is urged by the coil spring 116 in a direction in contact with the fixing roller 60 with the fulcrum 115 as an axis.

  The eccentric cam 113 is provided in contact with the vicinity of the end of the arm 112. The eccentric cam 113 is rotationally driven by the control device 90 controlling driving means such as a motor (not shown).

  As a result, the control device 90 (movement control unit 90c) controls the driving means to rotate the eccentric cam 113 and move the support rollers 81 and 82 to the first position as shown in FIG. The eccentric cam 113 is rotated 180 degrees therefrom, and the support rollers 81 and 82 can be moved to the second position as shown in FIG. 4B.

  The distance between the fulcrum 114 at the first position and the peripheral surface of the fixing roller 60 is 28 mm, and the distance between the fulcrum 114 at the second position and the peripheral surface of the fixing roller 60 is 29.5 mm. That is, when moving from the first position to the second position, the movement amount (separation length) of the fulcrum 114 is 1.5 mm. The distance between the fulcrum 114 and the fulcrum 115 is 15 mm, and the distance between the contact point between the arm 112 and the eccentric cam 113 and the fulcrum 115 is 15 mm (therefore, the lever ratio is 1: 1). Therefore, the moving amount of the contact portion of the arm 112 with the eccentric cam 113 is also 1.5 mm.

  Further, when the rotation of the fixing roller 60 is stopped at the second position, the contact width (heating nip width) between the endless belt 83 and the fixing roller 60 in the rotation direction is about 10 mm. However, this contact width is a value that can change depending on the bending wrinkles and temperature of the endless belt 83. In general, when the belt is heated, the circumference of the belt is extended, so that the contact width increases. In this embodiment, the separation length is set to 1.5 mm. However, when the separation length is set to 4 mm, the endless belt 83 and the fixing roller 60 are brought into contact with each other by moving to the second position. Without being completely separated.

  As shown in FIGS. 5A and 5B, belt regulating members 121 and 122 are provided between the support rollers 81 and 82 and the bearings 117 and 118, respectively. When the endless belt 83 meanders, the belt regulating members 121 and 122 abut on the belt end portion and rotate to regulate the axial displacement of the support rollers 81 and 82 of the endless belt 83, This is for preventing the end of the endless belt 83 from sliding or sliding with the bearings 117 and 118.

  The belt regulating members 121 and 122 are rotatable with respect to the support rollers 81 and 82 (can be rotated independently of the rotation of the support rollers 81 and 82 around the rotation axis of the support rollers 81 and 82) and are supported. The rollers 81 and 82 are also installed so as to be movable independently of the support rollers 81 and 82 in the axial direction. Further, as shown in FIG. 5B, the belt restricting members 121 and 122 have a cross-sectional shape viewed from the axial direction of the support rollers 81 and 82 concentrically with a circle formed by the cross-section of the support rollers 81 and 82. The height H (mm) from the peripheral surface (belt suspension surface) of the support rollers 81 and 82 is set to 2.5 mm.

(Configuration of control device 90)
The control device 90 includes a temperature control unit 90a, a rotation control unit 90b, and a movement control unit 90c. The surface temperature of the endless belt 83, the surface temperature of the fixing roller 60, the surface temperature of the pressure roller 70, and the rotational driving of the fixing roller 60. The control integrated circuit board controls the movement of the belt position by the belt moving device 110.

  The temperature control unit 90 a is connected to the thermistors 65, 75, 85 a, and 85 b and the heating power supply unit 99. The heating power supply unit 99 is connected to the halogen lamps 64, 74, 86a, and 86b and supplies power for heating to these halogen lamps. The temperature control unit 90a switches the supply power from the heating power supply unit 99 to each halogen lamp based on the temperature detection results of the thermistors 65, 75, 85a, and 85b, the image forming mode, etc. The temperature of the endless belt 83, the fixing roller 60, and the pressure roller 70 is controlled to be a predetermined temperature.

  The rotation control unit 90b is connected to a rotation driving device 91 for driving the fixing roller 60 to rotate. The rotation control unit 90 b controls the rotation speed of the fixing roller 60 by controlling the operation of the rotation driving device 91.

  The movement control unit 90c is connected to the belt moving device 110. By controlling the operation of the eccentric cam 113 provided in the belt moving device 110, the supporting rollers 81 and 82 and the fixing roller provided in the external heating device 80 are controlled. The amount of heat supplied from the external heating device 80 to the fixing roller 60 is controlled by changing the contact width (heating nip width) between the endless belt 83 and the fixing roller 60 by controlling the relative position to the fixing roller 60. Yes. For example, the movement controller 90c continuously detects the temperature state of each member, the type of transfer medium (recording paper), the image forming mode (monochrome image forming mode and color image forming mode, or one sheet of paper passing through). The relative position of the support rollers 81 and 82 with respect to the fixing roller 60 is controlled between the first position and the second position in accordance with the sheet passing state, etc., and the contact area of the endless belt 83 (heating nip width) The amount of heat supplied from the external heating device 80 to the fixing roller 60 is controlled.

  When the copying speed is decreased, the movement control unit 90c moves the support rollers 81 and 82 from the first position to the second position. For example, the sheet conveyance speed in the monochrome mode is 355 mm / s, the color mode is set to 175 mm / s, and the fixing roller setting temperature in the monochrome mode and the fixing roller setting temperature in the color mode are the same at 180 ° C. When the heating nip width between the endless belt 83 and the fixing roller 60 is the same at 20 mm, if the set temperature of the endless belt 83 is 220 ° C. for the monochrome mode and 205 ° C. for the color mode, The amount of heat supplied from the external heating device 80 to the fixing roller 60 is substantially balanced.

  For this reason, when changing from the monochrome mode to the color mode, the temperature of the endless belt 83 is too higher than the set temperature. If the color image is fixed in a state where the temperature of the endless belt 83 is too high, the temperature of the fixing roller 60 becomes too high and the gloss of the color image becomes excessive or uneven gloss occurs, resulting in a reduction in image quality. To do. In order to avoid such a problem, it is conceivable to wait until the temperature of the endless belt 83 drops to a predetermined temperature when shifting from the monochrome mode to the color mode. However, it takes 30 seconds or more for the temperature of the endless belt 83 to decrease from 220 ° C. to 205 ° C., and the transition from the monochrome mode to the color mode cannot be performed smoothly, resulting in a waiting time. End up.

  Therefore, in this embodiment, the movement control unit 90c controls the relative positions of the support rollers 81 and 82 with respect to the fixing roller 60 (for example, by mechanically moving the support rollers 81 and 82 from the first position to the second position). The contact area between the belt 83 and the fixing roller 60 is reduced to suppress the heat supply from the external heating device 80 to the fixing roller 60.

  In addition, the movement control unit 90c makes contact between the endless belt 83 and the fixing roller 60 in order to increase the amount of heat supplied from the external heating device 80 to the fixing roller 60 to compensate for the amount of heat lost to the paper during continuous sheet passing. Increase the area.

  Immediately after the start of the image forming operation, the fixing roller 60 is heated and rotated in order to make the temperature distribution in the circumferential direction of the fixing roller 60 uniform. However, since the recording paper does not pass through the fixing nip, the fixing roller 60 No heat is taken away by the recording paper. If the support rollers 81 and 82 are in the first position in this state, the heat supply from the endless belt 83 to the fixing roller 60 becomes excessive, and the temperature of the fixing roller 60 becomes higher than the set temperature. Therefore, the movement control unit 90c controls the belt moving device 110 in order to change the amount of heat supplied from the external heating device 80 to the fixing roller 60 in a short time in order to avoid excessive supply of heat to the fixing roller 60. Thus, the contact area between the endless belt 83 and the fixing roller 60 is reduced.

  The movement control unit 90c determines the relative positions of the support rollers 81 and 82 relative to the fixing roller 60 according to the temperature state of each member, the type of transfer medium (recording paper), the image forming mode, and the like. You may make it control to the arbitrary positions between 2 positions.

  Further, in the fixing device 40, at the time of standby temperature keeping, the rotation control unit 90b stops the rotation of the fixing roller 60, and the temperature control unit 90a controls the power supplied from the heating power supply unit 99 to each halogen lamp, and the fixing roller The surface temperature of 60 is maintained at 170 ° C., and the surface temperatures of the support rollers 81 and 82 (the surface temperature of the endless belt 83 at the position in contact with the support rollers 81 and 82) are maintained at a constant temperature of 190 ° C.

  At the time of transition from the heat insulation standby state to the image forming operation state (fixing operation state), the rotation control unit 90b starts the rotation of the fixing roller 60, and the temperature control unit 90a transfers from the heating power supply unit 99 to each halogen lamp. The surface temperature of the fixing roller 60 is set to 185 ° C., and the surface temperature of the support rollers 81 and 82 (the surface temperature of the endless belt 83 at the position in contact with the support rollers 81 and 82) is set to 220 ° C. That is, in the present embodiment, the temperature of the fixing roller 60 and the support rollers 81 and 82 during the standby temperature is set lower than the temperature of the fixing roller 60 and the support rollers 81 and 82 during the fixing operation.

  As described above, in the fixing device 40 according to this embodiment, the cross-sectional area of the cross section perpendicular to the axial direction at the end B of the belt contact portion of the support rollers 81 and 82 provided in the external heating device 80 is the belt contact portion. It is smaller than the cross-sectional area of the cross section perpendicular to the axial direction of the central portion A.

  Thereby, heat conduction from the central portion A to the end portions B and C in the support rollers 81 and 82 is suppressed, and other members (bearings 117 and 118, belt regulating members 121 and 122) from the end portions B and C, Alternatively, the amount of heat lost from the support rollers 81 and 82 due to heat conduction into the air can be suppressed. Therefore, the temperature difference between the central portion A and the end portion B can be suppressed, and a uniform and high-quality fixed image can be obtained.

  Further, since the cross-sectional area of the cross section perpendicular to the axial direction at the central portion A is larger than the cross-sectional areas at the end portions B and C, the heat conduction in the axial direction at the central portion A can be promoted. The temperature distribution in the region can be made uniform.

  Since the support rollers 81 and 82 have a configuration in which the cross-sectional areas of the end portions B and C are smaller than the central portion A, if only the support rollers 81 and 82 are heated, the end portion B immediately after the temperature rise is considered. , C is higher than the central part A. However, in the configuration of the present embodiment, since the endless belt 83 is stretched around the support rollers 81 and 82, the heat of the support rollers 81 and 82 is conducted to the endless belt 83. And since the heat from the belt end to the air is promoted by the rotation of the endless belt 83, the temperature rise of the belt end and the ends B and C of the support rollers 81 and 82 is suppressed. Thereby, the temperature of the surface of the support rollers 81 and 82 can be made uniform.

  In the present embodiment, the outer diameters of the belt contact portions (central portion A and end portion B) of the support rollers 81 and 82 are made substantially uniform. Thereby, the tension acting on the endless belt 83 can be made uniform along the axial direction of the support rollers 81 and 82, and meandering and cracking of the endless belt 83 can be prevented. That is, if the outer diameter of the belt contact portion is not uniform or has a step, the endless belt 83 may meander or crack, and the outer diameter of the belt contact portion is substantially uniform. It is preferable that

  Further, in the present embodiment, the rotation of the fixing roller 60 is stopped at the time of standby temperature keeping, and the fixing roller 60 is rotated at the time of fixing operation (at the time of heating and heating). Since the endless belt 83 is configured to be driven and rotated by the fixing roller 60, the endless belt 83 stops rotating during the standby temperature keeping and rotates during the fixing operation.

  In this manner, by stopping the rotation of the fixing roller 60 during the standby heat retention, power saving and noise reduction can be achieved. Further, by stopping the rotation of the endless belt 83 during the standby heat retention, heat dissipation from the end of the endless belt 83 can be suppressed, and the temperature of the ends B and C of the support rollers 81 and 82 can be suppressed from decreasing. .

  Since the endless belt 83 does not rotate during the standby heat retention, the temperature of the portion of the endless belt 83 that is not in contact with the support rollers 81 and 82 is lowered. However, the endless belt 83 is thin and has the support rollers 81 and 82 and the fixing roller 60. Therefore, the temperature in the circumferential direction (the rotational direction of the endless belt 83) can be raised uniformly in a short time by starting the rotation at the time of transition from the heat insulation standby state to the fixing operation state.

  In the present embodiment, the temperature of the support rollers 81 and 82 during the standby heat retention is set lower than that during the fixing operation.

  Since there is no heat loss due to paper passing during standby, the heating power (heat retaining heating power) for maintaining the support rollers 81 and 82 at a constant temperature is small. For this reason, the temperatures of the end portions B and C are more likely to be lower than the central portion A due to heat conduction and heat dissipation from the end portions B and C. Accordingly, if the temperature of the support rollers 81 and 82 is set in the same manner as the temperature at the time of the fixing operation at the time of the standby temperature keeping, the fixing operation is started with the temperatures of the ends B and C being lowered. As a result, the first image becomes a low-quality image with uneven fixing after the heat retention standby.

  On the other hand, in the present embodiment, the temperature of the support rollers 81 and 82 at the time of standby heat retention is set lower than that at the time of the fixing operation, so by raising the temperature to a predetermined operating temperature at the start of the fixing operation, A uniform and large amount of heat can be supplied in the width direction (axial direction) of the support rollers 81 and 82. Therefore, the temperature of the central portion A and the end portions B and C can be quickly raised to the operating temperature, and the temperature drop in the end portions B and C can be eliminated to make the temperature distribution in the axial direction of the support rollers 81 and 82 uniform. it can. Moreover, the heating power at the time of standby heat retention can be suppressed by setting the temperature at the time of standby heat retention low.

(Modification of support rollers 81 and 82)
In this embodiment, by reducing the inner diameter of the end portion B of the belt contact portion, the cross-sectional area of the end portion B is made smaller than the cross-sectional area of the central portion A. The shape is not limited to this, and any shape may be used as long as the average value of the cross-sectional areas of the cross section perpendicular to the axial direction is smaller at the end B than at the center A.

  FIG. 6A is a plan view showing a modification of the support rollers 81 and 82, and FIG. 6B is a cross section of the support rollers 81 and 82 shown in FIG. FIG.

  The support rollers 81 and 82 according to this modification are provided with a semispherical hole 87a having a radius of 1 mm, which is shallower than the thickness of the support rollers 81 and 82, at the end B of the belt contact portion. The belt contact portions (central portion A and end portion B) of the support rollers 81 and 82 have a uniform thickness (outer diameter 15 mm, inner diameter 11 mm) except for the portion including the hole 87a.

  The pitch in the axial direction of the holes 87a is 3 mm, and the pitch in the circumferential direction is 24 degrees (fifteen are arranged at equal intervals along the circumferential direction). With this configuration, the average cross-sectional area at the end B of the belt contact portion provided with the hole 87a can be made smaller than the average cross-sectional area at the center A where the hole 87a is not provided.

  According to the configuration shown in FIGS. 6A and 6B, the hole 87a is provided in the peripheral surface of the support rollers 81 and 82, so that a step is formed on the inner peripheral surface and the outer peripheral surface of the support rollers 81 and 82. (Without changing the inner diameter and the outer diameter), the average value of the cross-sectional area of the end B can be changed. Therefore, it is possible to prevent meandering and cracking of endless belt 83 that occur when there is a step on the outer peripheral surface (when the outer diameter is not constant). Further, since there is no step on the inner peripheral surface (because the inner diameter is constant), the clearance between the halogen lamps 86a and 86b and the core metal of the support rollers 81 and 82 can be kept constant, and the temperature distribution can be made uniform. it can.

  Since the support rollers 81 and 82 and the endless belt 83 are not in contact with each other in the hole 87a, the amount of heat transferred from the support rollers 81 and 82 to the endless belt 83 at the end B is smaller than that at the center A. However, since the end B is out of the sheet passing area, the recording paper is not deprived of heat. For this reason, the temperature distribution in the axial direction of the support rollers 81 and 82 can be kept uniform, and a high-quality fixed image can be obtained.

  Moreover, the shape of a hole part, the pitch of an axial direction and the circumferential direction are not restricted to the example shown to Fig.6 (a) and FIG.6 (b), You may change suitably. Further, in the configuration shown in FIGS. 6A and 6B, the hole 87a is provided only at the end B of the belt contact portion. Good. In this case, for example, the number per unit surface area of the hole 87a provided in the central portion A (axial direction and / or circumferential pitch; number density) may be made larger than that of the end portion B.

  FIG. 7A is a plan view showing another modification of the support rollers 81 and 82, and FIG. 7B is a cross-sectional view parallel to the axial direction of the support rollers 81 and 82 shown in FIG. It is sectional drawing.

  The support rollers 81 and 82 according to this modification include a groove-shaped hole (groove) 87b at the end B of the belt contact portion. The belt contact portions (central portion A and end portion B) of the support rollers 81 and 82 have a uniform thickness (outer diameter 15 mm, inner diameter 11 mm) except for the hole 87b.

  The hole 87b has a semicircular cross section with a radius of 1 mm, which is shallower than the thickness of the support rollers 81 and 82, and the pitch in the axial direction of the hole 87b is 4 mm. Further, the hole 87b is formed in a spiral shape on the outer peripheral surface of the support rollers 81 and 82 so as to go toward the axial center side of the support rollers 81 and 82 along the rotation direction of the support rollers 81 and 82. (A hole 87b is formed so as to incline in the axial direction along the rotational direction). Therefore, the winding direction of the spiral of the hole 87b is opposite to each other at both end sides in the axial direction. 7A and 7B, the inclination angle with respect to the cross section perpendicular to the axial direction of the hole 87b is 30 degrees.

  Thus, by providing the hole 87b in the end portion B of the belt contact portion, the average value of the cross-sectional area of the end portion B perpendicular to the axial direction is set to be larger than the average value of the cross-sectional area in the central portion A. Can be small.

  Further, since the hole 87b is provided so as to incline toward the axially central side along the rotation direction, when the endless belt 83 approaches one end side of the support rollers 81 and 82, the side opposite to this shifting direction is provided. At the end B, the contact width with the endless belt 83 is smaller than the contact width with the endless belt 83 at the end B on the shift direction side. As a result, the endless belt 83 is urged toward the center in the axial direction. That is, since the contact width between the endless belt 83 and the end portion B (the portion where the hole portion 87b is formed) is increased on the side in the shift direction, the force acting on the endless belt 83 is increased, and the endless belt 83 is It is urged to the opposite side to this direction of deviation. Thereby, since the contact pressure of the endless belt 83 to the belt regulating members 121 and 122 can be lowered, the mechanical durability of the endless belt 83 can be improved.

  The shape and pitch of the hole 87b are not limited to the examples shown in FIGS. 7A and 7B, and may be changed as appropriate.

  FIG. 8A is a plan view showing still another modified example of the support rollers 81 and 82, and FIG. 8B is a sectional view of a cross section parallel to the axial direction.

  The support rollers 81 and 82 according to this modification include circular hole portions 87c having a radius of 1 mm that penetrate the support rollers 81 and 82 at the end B of the belt contact portion. The support rollers 81 and 82 have the same configuration as that shown in FIGS. 6A and 6B except that the hole 87 c penetrates the support rollers 81 and 82.

  With this configuration, the average cross-sectional area at the end B of the belt contact portion provided with the hole 87c can be made smaller than the average cross-sectional area at the center A where the hole 87c is not provided. The heat conduction in the axial direction of the rollers 81 and 82 can be suppressed. Further, since the heat capacity of the support rollers 81 and 82 is reduced, the temperature of the support rollers 81 and 82 can be increased in a short time. Further, since the hole 87c penetrates the support rollers 81 and 82, the radiant heat and infrared rays from the halogen lamps 86a and 86b provided inside the support rollers 81 and 82 can be directly applied to the endless belt 83. The temperature of the endless belt 83 can be increased in a short time. The shape and pitch of the holes 87c are not limited to the configurations shown in FIGS. 8A and 8B, and may be changed as appropriate.

  FIG. 9A is a plan view showing still another modified example of the support rollers 81 and 82, and FIG. 9B is a sectional view of a cross section parallel to the axial direction.

  The support rollers 81 and 82 according to this modification include a hole 87d penetrating the support rollers 81 and 82 in the central portion A in addition to the configuration shown in FIGS. 8A and 8B. Yes. The shape of the hole 87d is a circular shape having a radius of 1 mm, similar to the hole 87c provided at the end B of the belt contact portion.

  However, in the end portion B, the hole portion 87c is provided with an axial pitch of 3 mm and a circumferential pitch of 24 degrees (equal to 15 circumferential directions), whereas in the central portion A, the hole portion 87d. Are provided with an axial pitch of 6 mm and a circumferential pitch of 45 degrees (equal to the circumferential direction of 8). Therefore, although the hole 87d provided in the central portion A and the hole 87c provided in the end B have the same shape, the number (number density) of the holes 87c per unit area in the end B is greater. However, the number of holes 87d per unit area in the central portion A is larger.

  Thereby, the average value of the cross-sectional area at the end portion B of the belt contact portion can be made smaller than the average value of the cross-sectional area at the central portion A, and the heat conduction in the axial direction in the support rollers 81 and 82 is suppressed. Can do.

  Also, since the hole 87c and the hole 87d have the same shape, each hole can be machined with the same specifications and tools (since there is no need to change the machining conditions), the machining is easy, and the hole diameter Compared with the case where the hole depth is changed in the axial direction, the processing cost of the support rollers 81 and 82 can be reduced. The shape and number of the hole 87c and the hole 87d are not limited to the configuration shown in FIGS. 9A and 9B, and may be changed as appropriate. Further, the hole 87c and the hole 87d may have different shapes.

  In the present embodiment, two support rollers 81 and 82 are provided, the outer diameters of the support rollers 81 and 82 are the same, and a halogen lamp (heating source) is provided inside each of the support rollers 81 and 82. Although the configuration provided with 86a and 86b has been described, the present invention is not limited to this, and the present invention can be applied to any type of external belt heating type fixing device. For example, three or more support rollers may be provided. Moreover, the outer diameter of each support roller may be different. Furthermore, it is sufficient that at least one support roller provided with a heat source is provided, and a support roller not provided with a heat source may be included. Moreover, the heat source may be provided at a position different from the inside of each support roller. Further, it may be configured that any support roller (belt suspension roller) is not pressed against the fixing roller 60 during the fixing operation, and only the endless belt 83 is in contact with the fixing roller 60.

  In this embodiment, the configuration in which the fixing roller 60 is heated by the external heating device 80 has been described. However, the configuration is not limited to this. For example, the external heating device 80 may heat the pressure roller 70. Alternatively, an external heating device 80 for heating the fixing roller 60 and an external heating device 80 for heating the pressure roller 70 may be provided.

[Embodiment 2]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted.

  FIG. 10 is a cross-sectional view of a cross section parallel to the axial direction of the support rollers 81b and 82b according to the present embodiment. The support rollers 81b and 82b are provided in the external heating device 80 of the fixing device 40 in place of the support rollers 81 and 82 in the first embodiment.

The support rollers 81b and 82b are made of stainless steel having an outer diameter of 15 mm, a thickness of 40 μm, and a cross-sectional area of about 1.88 mm ² perpendicular to the central axis, and the thermal conductivity is about 15 W / m · K. Therefore, the product S of the cross-sectional area and the thermal conductivity is 28.20 × 10 ⁻⁶ (W · m / K).

In this embodiment, as the endless belt 83, a belt member in which a surface of a base material made of polyimide having an inner diameter of 30 mm and a thickness of 100 μm is coated with a fluororesin having a thickness of 20 μm as a release layer is used. Thereby, the cross-sectional area of the polyimide part is 9.46 mm ² , and the cross-sectional area of the fluororesin part is 1.90 mm ² . The polyimide has a thermal conductivity of 0.29 W / m · K, and the fluororesin has a thermal conductivity of 0.29 W / m · K. Therefore, the product S of the thermal conductivity and the cross-sectional area of the entire endless belt 83 is 3.29 × 10 ⁻⁶ (W · m / K).

  When the product S of the heat conductivity and the cross-sectional area of the support rollers 81b and 82b is large, the heat transfer in the axial direction is excessive on the outer side in the axial direction than the portion of the support rollers 81b and 82b in contact with the endless belt 83. . For this reason, even if the belt contact portion is heated so as to have a uniform temperature at the time of standby heat retention, due to heat conduction from the end portions in the axial direction of the support rollers 81b and 82b to the bearings 117 and 118 and the belt regulating members 121 and 122, The temperature at the end will decrease. As a result, the temperature for fixing the edge of the image is insufficient, resulting in a non-uniform and low-quality image, or poor fixing.

Therefore, in order to suppress the temperature drop at the end portion of the support roller and make the temperature in the belt contact area uniform, it is necessary to reduce the product S of the heat conductivity and the cross-sectional area of the support roller. Specifically, the product S of the thermal conductivity and the cross-sectional area of the support roller is set to 0 or more and 60 × 10 ⁻⁶ (W · m / K) or less, thereby suppressing the temperature drop at the end portion to contact the belt. The temperature of the area can be made uniform. In addition, the lower limit of thickness should just be able to endure mechanical stress.

In the support rollers 81b and 82b according to the present embodiment, the product S of the thermal conductivity (W / m · K) and the cross-sectional area (mm ² ) of the support roller is 3.29 × 10 ⁻⁶ (W · m / K). ), And smaller than 60 × 10 ⁻⁶ (W · m / K), it is possible to suppress the temperature drop at the end portions of the support rollers 81b and 82b and make the temperature in the belt contact area uniform.

In the present embodiment, the support rollers 81b and 82b having a constant cross-sectional area perpendicular to the axial direction are used. However, the present invention is not limited to this. The product of the cross-sectional area and the thermal conductivity in each part of the support roller may be 0 or more and 60 × 10 ⁻⁶ (W · m / K) or less, for example, similar to the support rollers 81 and 82 shown in the first embodiment. You may have the shape of.

[Embodiment 3]
Still another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those described in the first and second embodiments are denoted by the same reference numerals as those in the first and second embodiments, and the description thereof is omitted.

  This embodiment is different from the first embodiment in that an external heating device that heats the peripheral surface of the pressure roller 70 is provided. That is, the fixing device 40 according to the present embodiment is in contact with the peripheral surface of the pressure roller 70 that contacts the back surface of the recording paper (the surface on which the unfixed image is not formed) in the fixing nip portion. An external heating device for heating the peripheral surface of 70 is provided.

  FIG. 11A and FIG. 11B are explanatory diagrams showing the configuration of the pressure roller 70 and the external heating device 130 that heats the peripheral surface of the pressure roller 70. 11A shows a case where the support roller 132 provided in the external heating device 130 is in a first position described later, and FIG. 11B shows a case where the support roller 132 is in a second position described later. Is shown.

  As shown in these drawings, the external heating device 130 includes a support roller 131, a support roller (heating roller) 132, an endless belt 133, and a belt moving device 140.

  The endless belt 133 is stretched around the support rollers 131 and 132 so that the back side of the endless belt 133 is in contact with the peripheral surfaces of the support rollers 131 and 132. The endless belt 133 is provided on the upstream side in the rotation direction of the pressure roller 70 with respect to the fixing nip portion. When the support roller 132 is in a first position to be described later, a predetermined pressing force (40N in this embodiment) Is pressed against the pressure roller 70. As a result, a heating nip (a contact portion between the endless belt 133 and the pressure roller 70; a width 20 mm in the circumferential direction of the pressure roller 70) is formed between the pressure roller 70 and the heating roller.

  Further, the endless belt 133 is driven to rotate by the pressure roller 70 by contacting the circumferential surface of the pressure roller 70 that rotates. As a result, the support rollers 131 and 132 rotate in the direction opposite to the rotation direction of the pressure roller 70 (K direction in FIG. 11). That is, when the control device 90 controls the rotation driving device 91 of the fixing roller 60 to rotationally drive the fixing roller 60, the pressure roller 70 is driven to rotate by the fixing roller 60, and the endless belt 133 and the pressure roller 70 are moved. The endless belt 133 is moved following the pressure roller 70 by the frictional force at the contact portion, and the support rollers 131 and 132 and the endless belt 133 are rotated.

  The endless belt 133 is the same as the endless belt 83 provided in the external heating device 80 of the first embodiment.

The support roller 131 has the same configuration as the support rollers 81b and 82b in the second embodiment. That is, the support roller 131 is made of stainless steel having an outer diameter of 15 mm, a thickness of 40 μm, and a cross-sectional area of about 1.88 mm ² perpendicular to the central axis, a thermal conductivity of about 15 W / m · K, and a cross-sectional area of The product S of thermal conductivity is 28.20 × 10 ⁻⁶ (W · m / K). Note that a halogen lamp (heating source) is not provided inside the support roller 131.

Support roller 132 has an outer diameter of 15 mm, wall thickness 2 mm, the cross-sectional area perpendicular to the central axis is the aluminum roller 81.68Mm ^2, the thermal conductivity is 236 W / m · K, the cross-sectional area and thermal conductivity The product S is 19276 × 10 ⁻⁶ (W · m / K). Further, a halogen lamp is provided inside the support roller 132.

  As described above, the support roller 132 having a halogen lamp therein has a thermal conductivity and a cross-sectional area perpendicular to the axial direction (diameter-direction cross section) of the support roller 131 having no halogen lamp. The product is getting bigger.

  Note that a temperature detecting means (not shown) is provided on the outer peripheral surface of the contact portion of the endless belt 133 with the support roller 132, and the control device 90 controls the support roller 132 based on the detection result of the temperature detecting means. The amount of electric power supplied to the halogen lamp provided in the interior of the motor, the movement position of the support rollers 131 and 132 by the belt moving device 140, and the like are controlled.

  The support rollers 131 and 132 are pressed by the belt moving device 140 to the peripheral surface of the pressure roller 70 with a predetermined load via the endless belt 133. As a result, the surface of the endless belt 133 contacts the circumferential surface of the pressure roller 70, and a nip portion (heating nip portion) is formed between the surface of the endless belt 133 and the circumferential surface of the pressure roller 70. The heating nip width between the endless belt 133 surface and the circumferential surface of the pressure roller 70 is 20 mm (width along the circumferential direction of the pressure roller 70).

  The belt moving device 140 includes a side frame 141, an arm 142, an eccentric cam 143, a coil spring 144, and a fulcrum (fulcrum member) 145.

  The side frames 141 are provided on both ends of the support rollers 131 and 132, respectively, and support the support rollers 131 and 132 rotatably via bearings (not shown). In addition, this bearing may be fixed in the distance between shafts similarly to the bearings 117 and 118 provided in the external heating device 80 of the first embodiment, and the distance between the shafts may be variable.

  Further, the side frame 141 is fixed to the arm 142. Further, the arm 142 is pivotally supported at a fulcrum 145 with respect to a frame (not shown) of the fixing device 40 so as to be rotatable in a direction substantially perpendicular to the axial direction of the support rollers 131 and 132. The fulcrum 145 is provided at a position that coincides with the rotation axis of the support roller 131. Therefore, even if the arm 142 is rotated about the fulcrum 145, the position of the support roller 131 (the distance between the axes of the support roller 131 and the pressure roller 70) does not change. Here, the inter-axis distance between the support roller 131 and the pressure roller 70 is set such that the two rollers are pressed against each other with a predetermined pressure via the endless belt 133. A coil spring 144 is attached to a position of the arm 142 on the opposite side of the fulcrum 145 across the support roller 132, and the side frame 141 attached to the arm 142 by the coil spring 144 is directed toward the pressure roller 70. It is energized.

  The eccentric cam 143 is provided in contact with the vicinity of the end of the arm 142. The eccentric cam 143 is rotationally driven by the control device 90 controlling driving means such as a motor (not shown). As a result, the control device 90 controls the drive means to rotate the eccentric cam 143 and moves the support roller 132 to the first position as shown in FIG. 11A to pressurize the support rollers 131 and 132. The roller 70 is brought into pressure contact, or the eccentric cam 143 is rotated 180 degrees therefrom, and the support roller 132 is moved to the second position to separate the support roller 132 from the pressure roller 70 as shown in FIG. It can be done. Even in the second position, the support roller 131 is in pressure contact with the pressure roller 70.

  A belt between the support rollers 131 and 132 and the bearings provided at both ends of the support rollers 131 and 132 is the same as the belt regulating members 121 and 122 provided in the external heating device 80 in the first embodiment. A regulating member (not shown) is provided. That is, the height from the peripheral surface of the support rollers 131 and 132 is higher at both ends in the axial direction of the support rollers 131 and 132 than the distance between the support rollers 131 and 132 and the pressure roller 70 in the second position. A belt regulating member is provided.

  As described above, in this embodiment, the support roller 132 having a halogen lamp therein has a cross section perpendicular to the thermal conductivity and the axial direction in the image forming range, compared to the support roller 131 having no halogen lamp. The product with the cross-sectional area is larger.

  Thermal conductivity in a sheet passing area of the support roller 132 having a heating source (area of the support roller 132 in contact with the area of the endless belt 133 in contact with the portion of the pressure roller 70 in contact with the recording paper; image forming range) If the product S with the cross-sectional area of the cross section perpendicular to the axial direction is too small, the thermal distribution in the axial direction may be insufficient, and the temperature distribution in the paper passing area may become large. Further, in the case of continuously outputting paper having a width smaller than the width of the endless belt 133, only the portion through which the recording paper comes into contact is deprived of heat, and the shaft of the support roller 132 is made up to compensate for the deprived heat. If heat is supplied to the entire direction, the temperatures of the end portions of the support roller 132 and the endless belt 133 outside the sheet passing area are increased. In this state, if a recording paper having a width wider than that of the above recording paper is passed, the end portions of the support roller 132 and the endless belt 133 are at a high temperature, so that the uniformity of the fixed image is lost and non-uniform. Will result in a low quality image.

  Further, when the product S of the thermal conductivity and the cross-sectional area of the cross section perpendicular to the axial direction in the support roller 131 that does not have a heating source therein is too large, the bearing and the support metal plate from the end of the support roller 131 Due to heat conduction to the belt regulating members 121, 122, etc., the temperature at the end of the support roller 131 is lowered, and the temperature at the end of the endless belt 133 is lowered.

  On the other hand, in the present embodiment, the support roller 132 with a built-in heat source has a larger product S of the thermal conductivity and the cross-sectional area than the support roller 131 without a built-in heat source. While suppressing heat loss from the end of the roller 131, the heat transfer in the axial direction of the support roller 132 can be promoted to average the temperature distribution in the axial direction, and the temperature distribution in the axial direction of the endless belt 133 can be made uniform. can do.

In order to make the temperature distribution of the support roller having the heating source uniform, the larger the product of the thermal conductivity and the cross-sectional area, the better. However, the thinner the support roller, the shorter the heat conduction delay from the internal heat source to the belt, and the belt temperature can be controlled with high accuracy. Moreover, the one where the heat capacity of the support roller having the heating source is small can be raised to a predetermined temperature in a short time. For this reason, the product of the thermal conductivity in the image forming range of the support roller having a heating source and the cross-sectional area of the cross section perpendicular to the axial direction is larger than 5000 × 10 ⁻⁶ (W · m / K), and 25000. It is preferably smaller than × 10 ⁻⁶ (W · m / K).

  Further, the product of the thermal conductivity in the image forming range of the support roller having no heating source and the cross-sectional area of the cross section perpendicular to the axial direction is preferably less than half of that of the support roller having the heating source. Thereby, the temperature raising time can be shortened without greatly impairing the uniformity of the temperature distribution.

  In each of the above-described embodiments, the configuration in which the external heating device that heats the fixing roller 60 or the external heating device that heats the pressure roller 70 has been described. However, the configuration is not limited thereto, and external heating that heats the fixing roller 60 is described. An apparatus and an external heating device for heating the pressure roller 70 may be provided. When an external heating device is provided for each of the fixing roller 60 and the pressure roller 70, the surface temperatures of both the fixing roller 60 and the pressure roller 70 can be accurately controlled during continuous paper feeding and standby. As a result, high-quality images can be stably obtained, and at the same time, high throughput can be obtained continuously.

  Further, the external heating device 80 of the first and second embodiments may be used in place of the external heating device 130 of the third embodiment, and the external heating device 130 of the third embodiment is replaced with the external heating device 80 of the first and second embodiments. May be used.

  In this embodiment, the image forming apparatus that transports paper using the transport belt has been described. However, the configuration of the image forming apparatus is not limited to this. The present invention can be applied to any electrophotographic image forming apparatus. For example, an intermediate transfer belt may be used, or a structure in which a photosensitive member is transferred to a recording sheet may be used. Further, it may be a single color image or a multicolor image.

  In each of the above embodiments, the control device 90 is configured from the control integrated circuit board. However, the present invention is not limited to this, and the function of each control unit provided in the control device 90 using a processor such as a CPU. May be realized by software. In this case, for example, the control device 90 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, and a RAM (random access) that expands the program. memory), a storage device (recording medium) such as a memory for storing the program and various data. An object of the present invention is to provide a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program of the control device 90, which is software that realizes the functions described above, is recorded in a computer-readable manner The program is supplied to the control device 90, and the computer (or CPU or MPU) reads and executes the program code recorded on the recording medium.

  Examples of the recording medium include a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The control device may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. This communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, A satellite communication network or the like can be used. Further, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE1394, USB, power line carrier, cable TV line, telephone line, ADSL line, infrared rays such as IrDA and remote control, It is also possible to use wireless such as Bluetooth (registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network. The present invention can also be realized in the form of a computer data signal (data signal sequence) embedded in a carrier wave in which the program code is embodied by electronic transmission.

  In each of the above embodiments, a roller-shaped fixing member (fixing roller) and a pressure member (pressure roller) are used. However, the present invention is not limited to this. For example, a belt-shaped member may be used. .

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the embodiments can be obtained by appropriately combining the respective technical means disclosed in the above-described embodiments. The form is also included in the technical scope of the present invention.

  The present invention can be applied to a fixing device provided in an electrophotographic image forming apparatus such as a printer, a copier, a facsimile machine, or an MFP (Multi Function Printer).

It is sectional drawing of the support roller with which the fixing device concerning one Embodiment of this invention is equipped. 1 is a schematic diagram illustrating an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. 4A and 4B are explanatory views showing a fixing device according to an embodiment of the present invention, in which FIG. 5A shows a state in which the support roller is arranged at the first position, and FIG. 5B shows a state in which the support roller is arranged at the second position. . (A) is a top view showing a configuration of a belt moving device provided in a fixing device according to an embodiment of the present invention, and (b) is a sectional view thereof. (A) is a top view which shows the other example of the support roller with which the fixing device concerning one Embodiment of this invention is equipped, (b) is the sectional drawing. (A) is a top view which shows the further another example of the support roller with which the fixing device concerning one Embodiment of this invention is equipped, (b) is the sectional drawing. (A) is a top view which shows the further another example of the support roller with which the fixing device concerning one Embodiment of this invention is equipped, (b) is the sectional drawing. (A) is a top view which shows the further another example of the support roller with which the fixing device concerning one Embodiment of this invention is equipped, (b) is the sectional drawing. It is sectional drawing of the support roller with which the fixing device concerning other embodiment of this invention is equipped. FIG. 9 is an explanatory diagram illustrating a configuration of a fixing device according to still another embodiment of the present invention, where (a) illustrates a case where the support roller is disposed at the first position, and (b) illustrates a case where the support roller is disposed at the second position. Is shown.

Explanation of symbols

1 Image forming apparatus 40 Fixing apparatus 60 Fixing roller (fixing member)
64, 74, 86a, 86b Halogen lamp (heating source)
65, 75, 85a, 85b thermistor 70 pressure roller (pressure member)
80, 130 External heating devices 81, 81b, 82, 82b Support rollers 83, 133 Endless belts 87a, 87b, 87c, 87d Hole 117, 118 Bearing 121, 122 Belt regulating member 131 Support roller (support roller without a heating source) )
132 Support roller (support roller with heating source)
A Center part of belt contact part (center part)
B End of belt contact part (both ends)
C Roller end

Claims (7)

The member to be heated by heating a fixing member, a pressure member, and a belt that is rotatably stretched between a plurality of support rollers and bringing the belt into contact with the peripheral surface of the fixing member or the pressure member that is the member to be heated At least one external heating device that heats the recording material, and the fixing member and the pressure member convey the recording material while sandwiching the recording material, whereby an unfixed image on the recording material is heated and pressed by the recording material. In the fixing device for fixing to
At least one of the plurality of support rollers is a cylindrical member having a heat source inside the cylindrical cored bar,
In the region of the support roller having the heating source that is in contact with the belt, the average value of the cross-sectional area of the cross section perpendicular to the axial direction at the axially opposite end portions is the cross section of the cross section perpendicular to the axial direction at the central portion in the axial direction. Smaller than the average area,
The support roller having a heat source, recess the outer peripheral surface of the core metal so that the outer diameter of a plane perpendicular to the axial direction than other areas in a part of the region definitive outer peripheral surface of the both end side portions is reduced And the central portion is not provided with a hole , and the outer diameter of the central portion is constant,
The hole portions of the both end portions are spiral grooves inclined from the both end sides of the support roller toward the center side along the rotation direction of the support roller in each of the both end portions. A fixing device characterized. The support roller having a heating source is
The fixing device according to claim 1, wherein a thickness of the both end portions is thinner than a thickness of the central portion. The support roller having a heat source, a fixing device according to claim 1 or 2, characterized in that the inner diameter of the abutting region the belt is constant. The external heating device, rotate the belt during heating the heating fixing device according to any one of claims 1-3 which is in the standby state kept, characterized in that stopping the rotation of the belt. The external heating device, a fixing device according to the support roller of any one of claims 1 to 4, characterized by lower than when the surface temperature image forming operation in standby incubation with a heat source. An external heating device that heats the fixing device by contacting the belt with the peripheral surface of the fixing member; and an external heating device that heats the pressure member by contacting the belt with the peripheral surface of the pressing member. the fixing device according to claim 1, any one of 5, characterized in that there. An image forming apparatus characterized in that it comprises a fixing device according to any one of claims 1 to 6.

Images