JP2014224853A - Fixing rotary member and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a fixing rotary member having an inverted crown shape, to obtain an output image of higher quality.SOLUTION: A fixing rotary member 30 fixes a toner image on a recording medium by allowing the recording medium with the toner image transferred thereto to pass through a pressure-contact nip. The fixing roller 30 includes a small-diameter part 33, and large-diameter parts 31 and 32 which are located outside of each end of the small-diameter part and in peripheral length of which in a rotation direction are longer than the small-diameter part 33. When the small-diameter part 33 and the large-diameter parts 31 and 32 are projected along a rotation axis direction and virtually superimposed on a projection plane PP orthogonal to the rotation axis direction, distances L1-L4 between a surface of the small-diameter part 33 and surfaces of the large-diameter parts 31 and 32 in normal direction are different in each of circumferential arbitrary spots S1-S4 on a surface of the small-diameter part 33 drawn in the projection plane.

Description

  The present invention relates to a fixing rotating member and an image forming apparatus, and more particularly to a fixing rotating member that fixes a toner image on a recording medium and an image forming apparatus including such a fixing rotating member.

  Image forming apparatuses such as printers, copiers, and multifunction machines form a toner image on a recording medium such as paper using an electrophotographic system. The toner image is heated and pressed by a fixing unit in the image forming apparatus and fixed on the recording medium. In a general fixing unit, two rollers (fixing rotating members) that are rotatably supported are used. A pressure nip is formed between these rollers. The recording medium that has entered the pressure nip is conveyed to the downstream side as these rollers rotate while being sandwiched between these rollers, and is heated and pressurized in the course of the conveyance. Is done.

  When the recording medium passes through the pressure nip, wrinkles are likely to occur on the recording medium due to the high pressure force acting on the pressure nip. When thin paper having low rigidity is used as the recording medium, wrinkles are more likely to occur. As disclosed in Japanese Patent Application Laid-Open No. 04-274473 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2005-195856 (Patent Document 2), a roller having an inverted crown shape is used to suppress the generation of wrinkles. May be. Such a roller has a shape in which the outer diameter (peripheral length) in the rotation direction gradually decreases from the end side in the rotation axis direction toward the center side.

  When the roller has an inverted crown shape, the rotation radius on the end side of the roller is larger than the rotation radius on the center side of the roller. The surface speed on the end side of the roller is faster than the surface speed on the center side of the roller. When the recording medium passes through the pressure nip, due to the difference in surface speed, the pressure nip has a tensile force to pull the recording medium from the center side of the recording medium toward the end side of the recording medium. Occur.

  When the recording medium enters the pressure nip, there may be a case where a bend or the like is formed in a part of the recording medium. This bending can cause wrinkles in the recording medium. When the roller has an inverted crown shape, even if a part of the recording medium is bent or the like, the recording medium is stretched from the center side to the end side by the tensile force, The bending can be reduced or eliminated, and the generation of wrinkles is suppressed.

Japanese Patent Laid-Open No. 04-274473 JP 2005-195856 A

  In consideration of obtaining an output image having higher quality using a roller having a reverse crown shape (rotating member for fixing), the reverse crown amount of the roller is important. The reverse crown amount is a value expressed by the difference between the outer diameter on the end side and the outer diameter on the center side in the rotation axis direction of the roller. Japanese Patent Laid-Open No. 04-274473 (Patent Document 1) and Japanese Patent Laid-Open No. 2005-195856 (Patent Document 2) describe a shape in which the reverse crown amount is always constant in the rotational direction (in other words, at each position in the circumferential direction). Is disclosed.

  When the reverse crown amount is always constant in the rotation direction, excessive distortion tends to accumulate in the recording medium in the process of passing the recording medium through the pressure nip. This is a phenomenon that is likely to occur when the reverse crown amount is larger than necessary and the surface speed on the end side of the roller is higher than necessary compared to the surface speed on the center side of the roller. The influence of excessive strain accumulation appears at the rear end in the recording medium conveyance direction. For example, when excessive strain accumulates, the rear end portion in the conveyance direction of the recording medium jumps up or flutters during the conveyance process.

  When the reverse crown amount is always constant in the rotation direction, it may be difficult to appropriately reduce the bending or the like formed on the recording medium. This is a phenomenon that is likely to occur when the reverse crown amount is smaller than necessary and the surface speed on the end side of the roller is slower than necessary compared to the surface speed on the center side of the roller. Even if a bend or the like is formed on a part of the recording medium, the bend cannot be reduced or eliminated, and the recording medium is wrinkled.

  When the trailing end of the recording medium bounces or flutters, the recording medium easily comes into contact with the conveyance guide, or the recording medium easily enters the pressure nip in an unintended posture. When the recording medium enters the pressure nip in an unintended posture, unevenness occurs in the amount of heat applied to the recording medium, and as a result, image defects such as uneven gloss may occur. Image defects also occur when wrinkles occur on the recording medium. When these phenomena occur, it becomes difficult to obtain an output image having higher quality.

  The present invention has been made in view of the above circumstances, and when using a fixing rotating member having an inverted crown shape, an output image having higher quality can be fixed on a recording medium. An object of the present invention is to provide a fixing rotation member that can be fixed, and an image forming apparatus including such a fixing rotation member.

  The fixing rotating member according to the present invention forms a pressure nip with a member disposed oppositely, and passes the recording medium onto which the toner image has been transferred through the pressure nip. A fixing rotating member to be fixed to a small-diameter portion, a large-diameter portion that is located on both outer sides of the small-diameter portion in the rotation axis direction, and has a circumferential length longer in the rotation direction than the small-diameter portion; An intermediate portion located between the small-diameter portion and the large-diameter portion and having a shape in which the circumference gradually increases from the small-diameter portion side toward the large-diameter portion. When the portion and the large diameter portion are projected along the rotation axis direction and viewed virtually superimposed on a projection plane orthogonal to the rotation axis direction, they are drawn within the projection plane. On the surface of the small diameter part A plurality of arbitrary positions direction, distance between the surface of the surface and the large diameter portion of the smaller-diameter portion in the normal direction of each said arbitrary position is different for each of the arbitrary point.

  Preferably, when a cross-sectional shape in a direction perpendicular to the rotation axis direction is viewed, both the outer edge of the small diameter portion and the outer edge of the large diameter portion have a circular shape, and are within the projection plane. The center of the small diameter portion and the center of the large diameter portion to be drawn are formed at positions shifted from each other.

  Preferably, when the cross-sectional shape in a direction orthogonal to the rotation axis direction is viewed, one of the outer edge of the small diameter portion and the outer edge of the large diameter portion has a non-circular shape.

  Preferably, a part of the outer edge of the small-diameter portion drawn in the projection plane overlaps the outer edge of the large-diameter portion drawn in the projection plane.

  An image forming apparatus according to the present invention includes an image forming unit that forms a toner image on a recording medium, and a fixing unit that includes the fixing rotation member according to the present invention and fixes the toner image on the recording medium. .

  Preferably, the circumference of the small diameter portion of the fixing rotation member is longer than the total length in the conveyance direction of the recording medium.

  Preferably, a detection unit that detects a rotation angle of the fixing rotation member, and a control unit that controls the timing at which the recording medium enters the press-contact nip based on the rotation angle detected by the detection unit, Prepare.

  Preferably, the control unit has a portion in which a distance between the surface of the small diameter portion and the surface of the large diameter portion in the normal direction in the circumferential direction of the fixing rotation member is maximized. The timing at which the pressure nip enters the pressure nip coincides with the timing at which the leading edge of the recording medium enters the pressure nip.

  Preferably, the control unit has a portion in which a distance between a surface of the small diameter portion and a surface of the large diameter portion in the normal direction in the circumferential direction of the fixing rotation member is minimized. The timing at which the pressure nip enters the pressure nip coincides with the timing at which the rear end of the recording medium in the conveyance direction enters the pressure nip.

  Preferably, the detection unit is a distance measuring sensor arranged to face the surface of the fixing rotation member.

  Preferably, the fixing rotation member is provided with a marking, and the detection unit detects a rotation angle of the fixing rotation member by detecting the marking.

  Preferably, information relating to the timing at which the image forming unit forms the toner image on the recording medium is input to the control unit, and the control unit causes the recording medium to enter the press-contact nip based on the information. Control the timing of entry.

  Preferably, the recording medium further includes a speed adjustment unit that adjusts the conveyance speed of the recording medium, and the control unit controls the speed adjustment unit to adjust the conveyance speed, so that the recording medium enters the pressure nip. Control timing.

  Preferably, the apparatus further includes a position adjusting unit that adjusts a pressure contact force acting on the pressure nip by changing a relative positional relationship between the member disposed opposite to the fixing rotation member. The control unit controls the position adjusting unit so that the pressing force is reduced when the recording medium is not positioned in the pressing nip.

  According to the present invention, when a fixing rotating member having an inverted crown shape is used, a fixing rotating member capable of fixing an output image having higher quality onto a recording medium, and such fixing rotation. An image forming apparatus including a member can be obtained.

1 is a diagram illustrating an image forming apparatus according to Embodiment 1. FIG. 2 is a perspective view showing a fixing roller used in the image forming apparatus in Embodiment 1. FIG. FIG. 3 is a diagram illustrating a state when a fixing roller used in the image forming apparatus according to Embodiment 1 is viewed from the direction of arrow III in FIG. 2. 3 is a diagram illustrating a relationship between a rotation angle θ (°) of a fixing roller used in the image forming apparatus according to Embodiment 1 and a rotation radius of a portion of the fixing roller facing a pressure nip. FIG. 6 is a first plan view schematically showing the action and effect of the fixing roller used in the image forming apparatus in Embodiment 1. FIG. FIG. 6 is a second plan view schematically showing the action and effect of the fixing roller used in the image forming apparatus in the first embodiment. It is a top view which shows typically the effect | action and effect of a fixing roller used for the image forming apparatus in a comparative example. 6 is a diagram illustrating an image forming apparatus according to Embodiment 2. FIG. FIG. 4 is a diagram illustrating a fixing roller used in the image forming apparatus according to the second embodiment, and corresponds to FIG. 3 according to the first embodiment. FIG. 10 is a diagram illustrating a relationship between a rotation angle θ (°) of a fixing roller used in the image forming apparatus according to Embodiment 2 and a rotation radius of a portion of the fixing roller facing a pressure nip. FIG. 10 is a perspective view showing a fixing roller and the like used in an image forming apparatus in a modification of the second embodiment. FIG. 6 is a diagram illustrating a fixing roller used in the image forming apparatus according to the third embodiment, and corresponds to FIG. 3 according to the first embodiment. 6 is a diagram illustrating a relationship between a rotation angle θ (°) of a fixing roller used in the image forming apparatus according to Embodiment 3 and a rotation radius of a portion of the fixing roller facing a pressure nip. FIG. FIG. 10 is a diagram illustrating a fixing unit, a cam mechanism, and the like used in an image forming apparatus according to a modification of the third embodiment. FIG. 10 is a diagram illustrating a fixing unit, a cam mechanism, and the like used in an image forming apparatus according to another modification of the third embodiment. It is a figure which shows the image forming apparatus in other embodiment. It is a figure which shows the result regarding an experiment example (A3 size paper). It is a figure which shows the result regarding an experiment example (A2 size paper).

  Embodiments based on the present invention will be described below with reference to the drawings. In the description of each embodiment, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, the amount, and the like unless otherwise specified. In the description of each embodiment, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Embodiment 1]
(Image forming apparatus 100)
FIG. 1 is a diagram showing an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 includes an image forming unit 10 and a fixing unit 20. The image forming unit 10 is supplied with a recording medium 90 from a device (not shown) (see arrow AR90). The recording medium 90 has a front end 91 and a rear end 92. The leading end 91 is a part of the recording medium 90 that is located on the most downstream side (front side) in the transport direction (arrow AR90 direction). The rear end 92 is a portion located on the most upstream side (rear side) in the transport direction (arrow AR 90 direction) of the recording medium 90.

  The image forming unit 10 forms a toner image 94 on the recording medium 90 (details will be described later). The recording medium 90 is conveyed from the image forming unit 10 toward the fixing unit 20 along the conveyance path 93 by a conveyance device (not shown). The fixing unit 20 has a pressure nip 50. The fixing unit 20 heats and presses the toner image 94 on the recording medium 90 when the recording medium 90 passes through the pressure nip 50, and fixes the toner image 94 on the recording medium 90. The recording medium 90 that has passed through the fixing unit 20 is sent to a paper discharge unit (not shown). As described above, the recording medium 90 on which an image is formed can be obtained. The details of each of these components will be described below.

(Image forming unit 10)
The image forming unit 10 includes a photosensitive drum 11, an intermediate transfer roller 12, a cleaning device 13, a charging device 14, an exposure device 15, a liquid developing device 16, a secondary transfer roller 17, and a cleaning device 18. The photosensitive drum 11 rotates in the direction of the arrow AR11. The intermediate transfer roller 12, the cleaning device 13, the charging device 14, the exposure device 15, and the liquid developing device 16 are arranged around the photosensitive drum 11 in this order along the rotation direction of the photosensitive drum 11.

  The charging device 14 charges the surface of the photosensitive drum 11 to a predetermined potential. The exposure device 15 irradiates the surface of the photosensitive drum 11 with light based on predetermined image information. The surface of the photosensitive drum 11 is exposed by light from the exposure device 15. An electrostatic latent image is formed on the surface of the photosensitive drum 11.

  The liquid developing device 16 includes a liquid developer (not shown). The liquid developer has a carrier liquid and toner particles. The liquid developer is conveyed onto the surface of the photosensitive drum 11. The carrier liquid and toner particles are electrostatically adsorbed on the surface of the photosensitive drum 11. By developing the electrostatic latent image carried on the photosensitive drum 11, a toner image (not shown) corresponding to the shape of the electrostatic latent image is formed on the surface of the photosensitive drum 11.

  The intermediate transfer roller 12 rotates in the direction of the arrow AR12 while being in contact with the photosensitive drum 11. The toner image on the photosensitive drum 11 is transferred from the photosensitive drum 11 onto the intermediate transfer roller 12 at the contact portion (nip portion) between the photosensitive drum 11 and the intermediate transfer roller 12. The carrier liquid and toner particles remaining on the photosensitive drum 11 without being transferred are removed from the surface of the photosensitive drum 11 by the cleaning device 13.

  The secondary transfer roller 17 is disposed so as to face the intermediate transfer roller 12, and rotates in the direction of the arrow AR17. The recording medium 90 passes between the secondary transfer roller 17 and the intermediate transfer roller 12 (see arrow AR90). The toner image is transferred from the intermediate transfer roller 12 onto the recording medium 90 at the nip portion between these rollers. A toner image 94 is formed on the recording medium 90. The carrier liquid and toner particles remaining on the intermediate transfer roller 12 without being transferred are removed from the surface of the intermediate transfer roller 12 by the cleaning device 18. The recording medium 90 on which the toner image 94 is formed is transported toward the fixing unit 20 by a transport device (not shown) along the transport path 93.

  The image forming unit 10 of the image forming apparatus 100 shown in FIG. 1 includes a single liquid developing device 16. The image forming apparatus 100 may include a plurality of liquid developing devices 16 in order to form a color image. The number of installed liquid developing devices 16 is determined according to the color developing method required for the image forming apparatus 100. The intermediate transfer roller 12 is not an essential component and is used as necessary. The image forming apparatus 100 of the present embodiment constitutes a so-called wet image forming apparatus, and a liquid developer is used as the developing means. The image forming apparatus 100 may use a dry one-component developer composed only of toner, or a dry two-component developer composed of toner and carrier particles, instead of the liquid developer.

(Fixing unit 20)
The fixing unit 20 heats the toner image 94 transferred onto the recording medium 90 and fixes the toner image 94 on the recording medium 90. The fixing unit 20 of the present embodiment includes a fixing roller 30 and a pressure roller 40. The fixing roller 30 and the pressure roller 40 are arranged so that their rotation axes are parallel to each other. Bearing members (not shown) are provided at both axial ends of the fixing roller 30 and the pressure roller 40. The fixing roller 30 and the pressure roller 40 are rotatably supported by these bearing members. The fixing roller 30 and the pressure roller 40 are configured such that the recording medium 90 conveyed along the conveyance path 93 passes between the fixing roller 30 and the pressure roller 40.

  The fixing roller 30 and the pressure roller 40 each include a metal core, a silicon rubber layer provided on the outer periphery of the core, and a fluororesin release layer provided on the outer periphery of the silicon rubber layer. Including. The metal core is composed of a member having high thermal conductivity such as aluminum. The silicon rubber layer is provided as an elastic layer in order to ensure the pressure nip width. The release layer made of a fluororesin is provided in order to improve the release property on the roller surface. The thickness of the release layer made of fluororesin is, for example, 10 μm to 50 μm, and the material thereof is, for example, PTFE (polytetrafluoroethylene) or PFA (perfluoroalkoxy polymer).

  The pressure roller 40 is further provided with a pressure mechanism (not shown) having a spring or the like. The pressure roller 40 is urged in the direction in which the fixing roller 30 is provided so as to come into pressure contact with the fixing roller 30 with a predetermined force. By the urging, a pressure nip 50 is formed between the fixing roller 30 and the pressure roller 40. The pressure roller 40 is rotationally driven at a predetermined peripheral speed by a drive mechanism (not shown). The fixing roller 30 is driven to rotate by receiving the pressure friction force from the pressure roller 40. The fixing roller 30 may be rotated and the pressure roller 40 may be driven to rotate.

  The fixing roller 30 and the pressure roller 40 include a heater lamp 30H and a heater lamp 40H, respectively. The surface temperature of each of the fixing roller 30 and the pressure roller 40 is controlled to a desired temperature by a control unit (not shown). When the recording medium 90 passes through the pressure nip 50, the fixing roller 30 and the pressure roller 40 heat and press the toner image 94 on the recording medium 90 to fix the toner image 94 on the recording medium 90. The recording medium 90 that has passed through the fixing unit 20 is sent to a paper discharge unit (not shown). As described above, an image is formed on the recording medium 90.

(Fixing roller 30)
FIG. 2 is a perspective view showing the fixing roller 30. FIG. 3 is a view showing a state when the fixing roller 30 is viewed from the direction of arrow III in FIG. As described above, the fixing roller 30 according to the present embodiment forms the pressure nip 50 (see FIG. 1) between the fixing roller 30 and the pressure roller 40 (see FIG. 1) disposed to face the fixing roller 30. The fixing roller 30 fixes the toner image 94 on the recording medium 90 by passing the recording medium 90 onto which the toner image 94 has been transferred, through the pressure nip 50.

  The fixing roller 30 functions as a “fixing rotating member”, and the pressure roller 40 functions as a “member disposed oppositely”. Hereinafter, the configuration and functions of the fixing roller 30 having a so-called reverse crown shape will be described focusing on the fixing roller 30, but the present invention is not limited to this configuration. The pressure roller 40 can also function as a “fixing rotating member”. In this case, the pressure roller 40 has an inverted crown shape as will be described in detail below, and the fixing roller 30 functions as a “facing member”. Both the fixing roller 30 and the pressure roller 40 may have an inverted crown shape as described in detail below. In this case, one of the fixing roller 30 and the pressure roller 40 functions as a “rotating member for fixing”, and the other of the fixing roller 30 and the pressure roller 40 functions as a “member disposed oppositely”. To do. Regarding these matters, not only this embodiment but also the following embodiments can be said in common.

  With reference to FIGS. 2 and 3, the fixing roller 30 includes large diameter portions 31 and 32, a small diameter portion 33, intermediate portions 34 and 35, and a support shaft 36. The small-diameter portion 33 of the present embodiment is located at the center of the fixing roller 30 in the direction in which the rotating shaft 37 of the fixing roller 30 extends (hereinafter also referred to as the rotating shaft direction).

  The large diameter portions 31 and 32 and the intermediate portions 34 and 35 are respectively positioned on both outer sides of the small diameter portion 33 in the rotation axis direction. The large diameter portion 31 is located outside the intermediate portion 34 in the rotation axis direction, and the large diameter portion 32 is located outside the intermediate portion 35 in the same direction. The intermediate part 34 is located between the small diameter part 33 and the large diameter part 31 in the rotation axis direction, and the intermediate part 35 is located between the small diameter part 33 and the large diameter part 32 in the same direction.

  The large diameter portions 31 and 32 are portions constituting both end surfaces of the fixing roller 30 in the rotation axis direction. The large diameter portions 31 and 32 include both end surfaces of the fixing roller 30 in the rotation axis direction. The large diameter portions 31 and 32 have a shape in which the circumferential length in the rotation direction is longer than that of the small diameter portion 33.

  The intermediate portion 34 has a shape in which the circumferential length in the rotation direction gradually increases from the small diameter portion 33 side toward the large diameter portion 31 side, and the intermediate portion 35 also has the shape having the large diameter portion 32 from the small diameter portion 33 side. It has a shape in which the circumferential length in the rotational direction gradually increases as it goes to the side of the surface. The intermediate portions 34 and 35 have a so-called taper shape, and the fixing roller 30 as a whole has a so-called reverse crown shape.

  When the fixing unit 20 (see FIG. 1) performs the fixing operation, the fixing roller 30 rotates about the rotation shaft 37. When viewing the rotation radius with respect to the rotation shaft 37, the large diameter portion 31 has the rotation radius RE1, the large diameter portion 32 has the rotation radius RE2, and the small diameter portion 33 has the rotation radius RC. In the present embodiment, the turning radius RE1 and the turning radius RE2 are the same value, and the turning radius RC is smaller than these values.

  When the cross-sectional shape in a direction orthogonal to the rotation axis direction is seen, both the outer edge of the small diameter portion 33 and the outer edges of the large diameter portions 31 and 32 have a circular shape (see FIG. 3). When the small-diameter portion 33 and the large-diameter portions 31 and 32 are projected along the rotation axis direction, and these are viewed virtually superimposed on a projection plane PP (see FIG. 3) orthogonal to the rotation axis direction. The centers 39 of the large diameter portions 31 and 32 are located on the rotation shaft 37 of the fixing roller 30. The rotation radii RE1 and RE2 of the large diameter portions 31 and 32 are constant values and do not change even if the fixing roller 30 rotates (see the solid line LE in FIG. 4).

  On the other hand, the center 38 of the small diameter portion 33 and the centers 39 of the large diameter portions 31 and 32 drawn in the projection plane PP are formed at positions shifted from each other. The small diameter portion 33 is formed such that its center 38 is displaced from the rotation shaft 37. The rotation radius RC of the small diameter portion 33 changes as the fixing roller 30 rotates (see the dotted line LC in FIG. 4).

  Referring to FIG. 3, the small-diameter portion 33 and the large-diameter portions 31 and 32 are projected along the rotation axis direction, and these are virtually superimposed on the projection plane PP orthogonal to the rotation axis direction. Suppose. The surfaces of the large-diameter portions 31 and 32 drawn in the projection plane PP are shown using solid lines in FIG. As described above, this solid line has a circular shape. The surface of the small-diameter portion 33 drawn in the projection plane PP is shown using a dotted line in FIG. As described above, this dotted line also has a circular shape.

  It is assumed that normal lines L1 to L4 are drawn for each arbitrary portion of the plurality of arbitrary portions S1 to S4 in the circumferential direction on the surface of the small-diameter portion 33 (a line indicated by a dotted line in FIG. 3). In the present embodiment, the distances D1 to D4 between the surface of the small diameter portion 33 and the surfaces of the large diameter portions 31 and 32 in the direction in which these normal lines L1 to L4 extend (hereinafter also referred to as the normal direction). Is different for each arbitrary location. Such a roller shape may be realized by the shape of a metal core, or may be realized by the thickness of the elastic layer.

  FIG. 4 is a diagram showing the relationship between the rotation angle θ (°) of the fixing roller 30 and the rotation radius of the portion of the fixing roller 30 facing the pressure nip 50 (see FIG. 1). As shown in FIG. 4, when the rotation angle of the fixing roller 30 is θ, the large diameter portions 31 and 32 have the rotation radii RE1 and RE2, and the small diameter portion 33 has the rotation radius RC. The rotation radii RE1 and RE2 are constant values and do not change even when the fixing roller 30 rotates (see the solid line LE in FIG. 4). On the other hand, the rotation radius RC changes as the fixing roller 30 rotates (see the dotted line LC in FIG. 4).

  That is, when the fixing roller 30 is rotated, the center (center 39) of the cross-sectional circle of the large diameter portions 31 and 32 and the rotation shaft 37 are always constant, and the rotation radii RE1 and RE2 of the large diameter portions 31 and 32 are It does not change. On the other hand, the center (center 38) of the cross-sectional circle of the small diameter portion 33 and the rotation shaft 37 are deviated, and the rotation radius RC of the small diameter portion 33 changes with the rotation of the roller. The manner in which the fixing roller 30 contacts the surface of the recording medium 90 changes as the roller rotates.

  Since the fixing roller 30 has a so-called reverse crown shape, a tensile force is generated in the pressure nip 50 to pull the recording medium from the center side to the end side of the recording medium 90. In the present embodiment, the difference between the rotation radius RC of the small-diameter portion 33 located in the center of the fixing roller 30 and the rotation radii RE1 and RE2 of the large-diameter portions 31 and 32 located on the end side of the fixing roller 30 is described. The tensile force acting from the center side to the end side of the recording medium 90 can be periodically changed according to the change.

  Referring to FIG. 5, when the recording medium 90 passes through the pressure nip 50, the bending 71 formed on the recording medium 90 is crushed by a high pressing force in the pressure nip 50, thereby causing the recording medium 90 to be crushed. Wrinkles occur. The fixing roller 30 of the present embodiment has an inverted crown shape, and the surface speed on the end side of the roller is faster than the surface speed on the center side of the roller (the white arrow in FIG. reference).

  Even if the recording medium 90 has the bend 71, when the recording medium 90 passes through the press-contact nip 50, a tensile force (from black to black in FIG. By acting, the deflection 71 is removed from the recording medium 90 before the deflection 71 is crushed, and the generation of wrinkles can be suppressed. As the tensile force acting on the recording medium 90 increases, the generation of wrinkles can be further suppressed. In order to increase the tensile force acting on the recording medium 90, the difference in rotational radius between the roller end portions (large diameter portions 31, 32) and the central side (small diameter portion 33) (ie, the reverse crown amount). Should be increased.

  Referring to FIG. 6, on the other hand, strain gradually accumulates in the recording medium 90 along with the tensile force applied to the recording medium 90 when the recording medium 90 passes through the pressure nip 50. The influence of strain accumulation appears at the rear end portion (rear end 92) in the conveyance direction of the recording medium 90. When the distortion is excessively accumulated, the rear end portion in the transport direction of the recording medium 90 jumps up or flutters during the transport process. In order to suppress the jumping and fluttering of the rear end of the recording medium 90, it is effective to reduce the accumulation of strain caused by the tensile force, that is, to reduce the tensile force acting on the recording medium 90. It is.

  In order to reduce the tensile force acting on the recording medium 90, the difference in rotational radius between the roller end side (large diameter portions 31, 32) and the central side (small diameter portion 33) (that is, the reverse crown amount) is set. Just make it smaller. As described above with reference to FIGS. 3 and 4, in the present embodiment, the distances D <b> 1 to D <b> 4 between the surface of the small-diameter portion 33 and the surfaces of the large-diameter portions 31 and 32 are made different at arbitrary locations. ing. Therefore, according to the fixing roller 30 of the present embodiment, as the fixing roller 30 rotates, the amount of reverse crown in the region facing the pressure nip 50 varies, so that excessive strain accumulation is suppressed and recording is performed. It is possible to contemplate coexistence with effectively reducing the bending formed in the medium 90. For example, since the reverse crown amount in the region facing the pressure nip 50 varies with the rotation of the fixing roller 30, excessive strain accumulation is suppressed by the presence of a region having a small reverse crown amount (region having a small tensile force). Therefore, it is possible to effectively reduce the flexure formed on the recording medium 90 due to the presence of a region having a large reverse crown amount (a region having a large tensile force).

  Referring to FIG. 7, as described at the beginning, Japanese Patent Laying-Open No. 04-274473 (Patent Document 1) and Japanese Patent Laying-Open No. 2005-195856 (Patent Document 2) have a reverse crown amount in the rotational direction (in other words, Then, a roller having a shape that is always constant (at each position in the circumferential direction) is disclosed. In the case of such a configuration (the fixing roller 30Z in FIG. 7), it is possible to achieve both of suppressing the accumulation of excessive strain and effectively reducing the bending formed on the recording medium 90. Have difficulty. For example, even if the bending formed at the front end 91 of the recording medium 90 can be eliminated, the excessive accumulation of distortion causes a jump 72 to occur near the rear end 92 of the recording medium 90, A flutter 73 may occur. If the reverse crown amount is made small in order to suppress the occurrence of the jump 72 and the flutter 73, the tensile force becomes insufficient and it becomes difficult to remove the deflection appropriately.

  When the distances D1 to D4 between the surface of the small-diameter portion 33 and the surfaces of the large-diameter portions 31 and 32 are made different at arbitrary locations as in the present embodiment, for example, a region having a large reverse crown amount ( By effectively functioning the region having a large tensile force, it is possible to eliminate the bending of the recording medium 90 that causes wrinkles, and the region having a small reverse crown amount (the region having a small tensile force) functions effectively. By doing so, excessive accumulation of tensile force is suppressed, and phenomena such as jumping and fluttering are less likely to occur. Therefore, the fixing roller 30 according to the present embodiment can obtain an output image having higher quality than a roller having a shape in which the reverse crown amount is always constant in the rotation direction. More preferably, an output image having high quality can be obtained more easily by performing the control as in the second embodiment described below.

[Embodiment 2]
The image forming apparatus 101 according to the present embodiment will be described with reference to FIGS. As shown in FIG. 8, the image forming apparatus 101 includes an image forming unit 10, a fixing unit 20 </ b> A, a conveyance device 60, a control unit 80, a speed adjustment unit 81, and detection units 82 and 83. The image forming unit 10 of the image forming apparatus 101 is configured similarly to the image forming unit 10 in the first embodiment described above. The fixing unit 20A includes a fixing roller 30A (rotating member for fixing) and a pressure roller 40.

  FIG. 9 is a diagram illustrating the fixing roller 30A, and corresponds to FIG. 3 in the first embodiment. Also in the present embodiment, the large diameter portions 31 and 32 have a circular shape, and the rotation radii RE1 and RE2 of the large diameter portions 31 and 32 are constant values even when the fixing roller 30A rotates. It does not change (see solid line LE in FIG. 10). The small diameter portion 33 also has a circular shape, and the rotation radius RC of the small diameter portion 33 changes as the fixing roller 30A rotates (see the dotted line LC in FIG. 10).

  Assume that the small-diameter portion 33 and the large-diameter portions 31 and 32 are projected along the rotation axis direction and viewed virtually superimposed on the projection plane PP orthogonal to the rotation axis direction. The surfaces of the large-diameter portions 31 and 32 drawn in the projection plane PP are shown using solid lines in FIG. The surface of the small-diameter portion 33 drawn in the projection plane PP is shown using dotted lines in FIG. In the present embodiment, a part of the outer edge of the small-diameter portion 33 drawn in the projection plane PP overlaps with the outer edges of the large-diameter portions 31 and 32 drawn in the projection plane PP at the position indicated by the point P. ing. That is, the reverse crown amount at the position indicated by the point P is zero.

  The position indicated by the point P corresponds to a portion of the surface in the circumferential direction of the fixing roller 30A where the distance between the surface of the small diameter portion 33 and the surface of the large diameter portions 31, 32 in the normal direction is minimized. ing. On the other hand, the fixing roller 30 </ b> A has a position indicated by a point Q on the opposite side of the point P around the rotation shaft 37. The position indicated by the point Q corresponds to the portion of the surface in the circumferential direction of the fixing roller 30A where the distance between the surface of the small diameter portion 33 and the surface of the large diameter portions 31, 32 in the normal direction is maximized. ing. The reverse crown amount at the position indicated by the point Q is the largest among the fixing rollers 30A.

  FIG. 10 is a diagram illustrating the relationship between the rotation angle θ (°) of the fixing roller 30A and the rotation radius of the portion of the fixing roller 30A that faces the pressure nip 50 (see FIG. 8). As shown in FIG. 10, when the rotation angle of the fixing roller 30A is θ, the large diameter portions 31 and 32 have the rotation radii RE1 and RE2, and the small diameter portion 33 has the rotation radius RC. The rotation radii RE1 and RE2 are constant values and do not change even if the fixing roller 30A rotates (see the solid line LE in FIG. 10). On the other hand, the rotation radius RC changes as the fixing roller 30A rotates (see the dotted line LC in FIG. 10).

  Referring again to FIG. 8, the conveyance device 60 includes rollers 61 and 62 and a belt member 63. The belt member 63 is wound around the rollers 61 and 62. The recording medium 90 is conveyed from the image forming unit 10 to the fixing unit 20A by the belt member 63 of the conveying device 60. The rotation speed of the roller 61 is adjusted by the speed adjustment unit 81.

  The speed adjusting unit 81 is controlled by the control unit 80, and the speed at which the belt member 63 conveys the recording medium 90 (conveying speed) is adjusted by adjusting the rotational speed of the roller 61. The detection unit 82 detects the movement of the recording medium 90 conveyed by the belt member 63. Information regarding the movement (position) of the recording medium 90 detected by the detection unit 82 is sent to the control unit 80. The control unit 80 controls the speed adjustment unit 81 based on the information detected by the detection unit 82, thereby adjusting the timing at which the recording medium 90 enters the pressure nip 50 of the fixing unit 20A (delaying or speeding up). Can do.

  The detection unit 83 is disposed so as to face the surface of the fixing roller 30A. The detection unit 83 is, for example, a distance measuring sensor, and can directly detect the rotation angle of the fixing roller 30A by directly measuring the distance between the detection unit 83 and the surface of the roller central portion. Information regarding the rotation angle of the fixing roller 30 </ b> A detected by the detection unit 83 is sent to the control unit 80. The control unit 80 according to the present embodiment controls the timing at which the recording medium 90 enters the pressure nip 50 of the fixing unit 20A based on the information regarding the rotation angle of the fixing roller 30A detected by the detection unit 83.

  The control unit 80, for example, the timing at which the portion indicated by the point Q (see FIG. 9) of the fixing roller 30A (the portion where the tensile force with respect to the recording medium 90 is maximum) enters the pressure nip 50, and the conveyance of the recording medium 90. The timing when the tip 91 in the direction enters the pressure nip 50 is matched. The control unit 80 can adjust the timing at which the leading end 91 in the conveyance direction of the recording medium 90 enters the pressure nip 50 by controlling the speed adjustment unit 81 based on the information acquired from the detection unit 82.

  Deflection that may cause wrinkles may be formed at the leading edge 91 of the recording medium 90 in the paper feed process, the transfer process, and the transfer process from the transfer process to the fixing process upstream of the fixing process. According to the above control by the control unit 80, the tip 91 of the recording medium 90 enters the pressure nip 50 when the position of the point Q forms the pressure nip 50. The tensile force applied to the recording medium 90 by the position of the point Q is larger than the tensile force applied to the recording medium 90 by other portions. By utilizing the position of the point Q, which has a large suppression effect on the occurrence of wrinkles, for the actual wrinkle suppression, it is possible to effectively prevent wrinkles from being formed on the recording medium 90 after the recording medium 90 has passed through the pressure nip 50. It becomes possible to suppress.

  Further, according to the above control by the control unit 80, as the recording medium 90 passes through the pressure nip 50, the reverse crown amount of the portion of the fixing roller 30A that contacts the recording medium 90 gradually decreases. When the recording medium 90 enters the pressure nip 50, the function of sufficiently suppressing wrinkles is exhibited. Therefore, not only the generation of wrinkles is suppressed, but also the accumulation of distortion is suppressed, and it is also effective that the rear end 92 in the conveyance direction of the recording medium 90 jumps up or flutters during the conveyance process. It is suppressed.

  Since the wrinkle suppressing function is sufficiently exerted when the recording medium 90 enters the press nip 50, the fluctuation range of the reverse crown amount can be increased. For example, the reverse crown amount at the position of the point P can be set to zero as in the present embodiment, or the reverse crown amount at the position of the point P can be relatively small. In this case, the circumferential length of the small diameter portion 33 of the fixing roller 30 </ b> A is preferably longer than the total length in the conveyance direction of the recording medium 90. Since the fixing is performed by the region from the point Q to the point P on the surface of the fixing roller 30A, the reverse crown amount of the portion of the fixing roller 30A that contacts the recording medium 90 gradually increases throughout the fixing process. Will become smaller. It is possible to further expect both suppression of accumulation of excessive strain and effective reduction of the bending formed in the recording medium 90.

  The control unit 80, for example, the timing at which the portion indicated by the point P (see FIG. 9) of the fixing roller 30A (the portion where the tensile force on the recording medium 90 is minimum or zero) enters the pressure nip 50, and the recording medium 90. The timing when the rear end 92 in the conveyance direction enters the pressure nip 50 may be made coincident. According to this control, the rear end 92 of the recording medium 90 enters the pressure nip 50 when the position of the point P forms the pressure nip 50. The tensile force applied to the recording medium 90 by the position of the point P is smaller than the tensile force applied to the recording medium 90 by other portions. A position other than the point P, which has a large suppression effect on the occurrence of wrinkles, is used for wrinkle suppression, and the timing at which the position of the point P where the accumulation of distortion can be most suppressed enters the press nip 50 and the rear end 92 of the recording medium 90 are The timing of entering the pressure nip 50 coincides. Even with this control, it is possible to further expect a coexistence of suppressing the accumulation of excessive strain and effectively reducing the flexure formed on the recording medium 90.

  In the present embodiment, the control unit 80 controls the speed adjusting unit 81 based on the information detected by the detecting unit 82, thereby adjusting the timing at which the recording medium 90 enters the pressure nip 50 of the fixing unit 20A. The control unit 80 is not limited to this configuration, and information regarding the timing at which the image forming unit 10 forms the toner image 94 on the recording medium 90 is input to the control unit 80, and the control unit 80 presses the recording medium 90 on the basis of the information. The timing of entering the nip 50 may be controlled. Even with this control, the timing at which the portion indicated by the point Q enters the pressure nip 50 is matched with the timing at which the leading end 91 of the recording medium 90 enters the pressure nip 50, or the timing at which the portion indicated by the point P enters the pressure nip 50. The timing at which the rear end 92 of the recording medium 90 enters the pressure nip 50 can be matched. These controls can be performed without using the speed adjusting unit 81. When the speed adjusting unit 81 is used, the timing at which the recording medium 90 enters the press nip 50 can be controlled with higher accuracy.

(Modification)
Referring to FIG. 11, in the above-described embodiment, detection unit 83 (see FIG. 8) is used as means for detecting the rotation angle of fixing roller 30A (see FIG. 8). As described above, the detection unit 83 is, for example, a distance measuring sensor.

  Like the fixing roller 30 </ b> B (rotating member for fixing) shown in FIG. 11, a marking 85 is provided in a region not used for fixing in the large-diameter portion 31, and the detection unit 84 reads the position of the marking 85. The rotation angle of the fixing roller 30B may be detected. The marking 85 may be provided on the outer end surface of the roller, or may be provided on the support shaft 36 of the roller. Also with this configuration, the same operations and effects as described above can be obtained.

  The marking 85 is a portion where the distance between the surface of the small-diameter portion 33 and the surface of the large-diameter portions 31 and 32 in the normal direction is maximized among the surfaces in the circumferential direction of the fixing roller 30B (points shown in FIG. 9). Q position), or a portion where the distance between the surface of the small-diameter portion 33 and the surface of the large-diameter portions 31 and 32 in the normal direction is minimized (the position of the point P shown in FIG. 9). It may be provided to correspond to).

[Embodiment 3]
With reference to FIGS. 12 and 13, an image forming apparatus according to the present embodiment will be described. Referring to FIG. 12, in the present embodiment, fixing roller 30C is used as a fixing rotating member. FIG. 12 is a diagram illustrating the fixing roller 30C, and corresponds to FIG. 3 in the first embodiment.

  In the present embodiment, the outer edges of the cross-sectional shapes of the large-diameter portions 31 and 32 have a circular shape, and the rotation radii RE1 and RE2 of the large-diameter portions 31 and 32 are even if the fixing roller 30A rotates. This is a constant value and does not change (see the solid line LE in FIG. 13). On the other hand, the outer edge of the cross-sectional shape of the small-diameter portion 33 has a non-circular shape (does not have a circular shape), and the rotation radius RC of the small-diameter portion 33 changes as the fixing roller 30A rotates. (Refer to the dotted line LC in FIG. 13).

  Assume that the small-diameter portion 33 and the large-diameter portions 31 and 32 are projected along the rotation axis direction and viewed virtually superimposed on the projection plane PP orthogonal to the rotation axis direction. The surfaces of the large-diameter portions 31 and 32 drawn in the projection plane PP are shown using solid lines in FIG. The surface of the small-diameter portion 33 drawn in the projection plane PP is shown using dotted lines in FIG. A part of the outer edge of the small-diameter portion 33 drawn in the projection plane PP overlaps with the outer edges of the large-diameter portions 31 and 32 drawn in the projection plane PP at the position indicated by the point P. That is, the reverse crown amount at the position indicated by the point P is zero.

  The position indicated by the point P corresponds to a portion of the surface in the circumferential direction of the fixing roller 30C where the distance between the surface of the small diameter portion 33 and the surface of the large diameter portions 31 and 32 in the normal direction is minimized. ing. The position indicated by the point Q corresponds to the portion of the surface in the circumferential direction of the fixing roller 30C where the distance between the surface of the small diameter portion 33 and the surface of the large diameter portions 31, 32 in the normal direction is maximized. ing. The reverse crown amount at the position indicated by the point Q is the largest among the fixing rollers 30C.

  FIG. 13 is a diagram illustrating the relationship between the rotation angle θ (°) of the fixing roller 30C and the rotation radius of the portion of the fixing roller 30C that faces the pressure nip 50 (not shown). As shown in FIG. 13, when the rotation angle of the fixing roller 30C is θ, the large diameter portions 31 and 32 have the rotation radii RE1 and RE2, and the small diameter portion 33 has the rotation radius RC. The rotation radii RE1 and RE2 are constant values and do not change even when the fixing roller 30C rotates (see the solid line LE in FIG. 13). On the other hand, the rotation radius RC changes as the fixing roller 30C rotates (see the dotted line LC in FIG. 13).

  As shown in FIG. 13, the fixing roller 30C of the present embodiment has a first region R1 and a second region R2. In the first region R1, the difference (reverse crown amount) between the rotation radii RE1, RE2 of the roller end portions (large diameter portions 31, 32) and the rotation radius RC of the central portion (small diameter portion 33) of the roller is Slowly decreases with rotation. In the second region R2, the difference (reverse crown amount) between the rotation radii RE1, RE2 of the roller end portions (large diameter portions 31, 32) and the rotation radius RC of the central portion (small diameter portion 33) of the roller is It grows sharply with rotation.

  Here, the circumferential length of the small-diameter portion 33 of the fixing roller 30C is made longer than the total length in the transport direction of the recording medium 90 to be used, and the total length in the transport direction of the recording medium 90 corresponds to the first region R1. To do. As in the case of the second embodiment described above, the control unit enters the portion indicated by the point Q (see FIG. 12) of the fixing roller 30C (the portion where the tensile force with respect to the recording medium 90 is maximized) into the pressure nip. The timing coincides with the timing at which the leading end 91 in the conveyance direction of the recording medium 90 enters the pressure nip.

  Since the fixing is performed by the region from the point Q to the point P on the surface of the fixing roller 30C, the reverse crown amount of the portion of the fixing roller 30C that contacts the recording medium 90 gradually increases throughout the fixing process. Will become smaller. By increasing the reverse crown amount at the portion corresponding to the tip 91 of the recording medium 90, the tensile force acting on that portion increases. By utilizing the position of the point Q, which has a large suppression effect on the occurrence of wrinkles, for the actual wrinkle suppression, it is possible to effectively prevent wrinkles from being formed on the recording medium 90 after the recording medium 90 has passed through the pressure nip 50. It becomes possible to suppress.

  On the other hand, by reducing the reverse crown amount in the portion corresponding to the rear end 92 of the recording medium 90, the tensile force acting on that portion is reduced. When the recording medium 90 enters the press nip 50, the function of sufficiently suppressing wrinkles is exhibited, and the accumulation of strain can be suppressed by reducing the tensile force, and the rear end 92 in the conveyance direction of the recording medium 90 is Jumping up and fluttering during the conveyance process are also effectively suppressed. According to this configuration, in the process in which one recording medium 90 (recording paper) is transported in the press-contact nip, the reverse crown amount can be designed according to the transport position of the recording medium 90, and wrinkles can be generated and It is possible to further suppress the jumping and fluttering.

  In the present embodiment, the range in which the region from the point Q to the point P on the surface of the fixing roller 30C is provided is greater than 180 ° when expressed as an angle in the circumferential direction. On the other hand, in the above-described second embodiment, the range where the region from the point Q to the point P on the surface of the fixing roller 30A (see FIG. 9) is provided is 180 ° when expressed in the circumferential direction. It has become. According to the fixing roller 30C of the present embodiment, it is possible to perform a fixing operation with a smaller roller size while suppressing the occurrence of wrinkles and flickering on one recording medium 90 (recording paper). Yes.

  In the present embodiment, the outer edge of the cross-sectional shape of the large-diameter portions 31 and 32 has a circular shape, and the outer edge of the cross-sectional shape of the small-diameter portion 33 has a non-circular shape. If any one of the outer edge of the small diameter part 33 and the outer edge of the large diameter parts 31 and 32 has a non-circular shape, it is not restricted to this structure, The effect similar to the above can be acquired. Also in this case, for example, the outer edge of the small-diameter portion 33 is configured to overlap the outer edges of the large-diameter portions 31 and 32 at the position indicated by the point P (configured so that the reverse crown amount is minimized), and the position indicated by the point Q In this case, the reverse crown amount may be maximized, and the timing at which the leading end 91 in the conveyance direction of the recording medium 90 enters the pressure nip 50 may be adjusted. The timing at which the rear end 92 in the conveyance direction of the recording medium 90 enters the pressure nip 50 may be adjusted.

(Modification)
Referring to FIG. 14, as described above, fixing roller 30 </ b> C of the third embodiment has first region R <b> 1 and second region R <b> 2. In the second region R2, since the reverse crown amount increases steeply with the rotation of the roller, the pressure contact force variation between the rollers is also large in this region, and the shearing force acting in the rotation axis direction (longitudinal direction) of the roller. The fluctuation of becomes large. Therefore, when no special measures are taken, when the second region R2 forms the press-contact nip 50, a relatively large stress acts on the adhesive interface between the surface layer and the elastic layer of the roller, thereby reducing the durability of the roller. In some cases, the adhesive surface may peel off.

  As shown in FIG. 14, in order to relieve such stress, it is preferable to provide means for reducing the pressure contact force between the rollers. In the fixing unit 20 </ b> D of this modification, the drive unit 87 controls the cam mechanism 86. When the cam of the cam mechanism 86 rotates with respect to the spring 88 that generates a pressing force in the pressure nip 50, the fixing roller 30 and the pressure roller 40 are moved away from each other. When the second region R2 forms the pressure nip 50, the drive unit 87 changes the relative positional relationship between the fixing roller 30 and the pressure roller 40 and moves them away. Since the stress acting on the surface of the roller and the adhesive interface of the elastic layer can be reduced when the second region R2 forms the pressure nip 50, the durability of the roller is lowered and the adhesive surface is peeled off. Can be suppressed. Therefore, the cam mechanism 86 and the drive unit 87 can function as a position adjusting unit that adjusts the pressing force acting on the pressing nip.

  When the circumferential length of the small-diameter portion 33 of the fixing roller 30 is longer than the total length in the transport direction of the recording medium 90 to be used, the total length in the transport direction of the recording medium 90 corresponds to the first region R1. The recording medium 90 may be configured not to be positioned in the pressure nip 50 when the region R2 forms the pressure nip 50. In this case, even if the cam mechanism 86 and the drive unit 87 reduce the pressure contact force between the fixing roller 30 and the pressure roller 40, the occurrence of wrinkles and flickering with respect to the recording medium 90 (recording paper) is effectively suppressed. However, it is possible to perform a good fixing operation.

  Like the fixing unit 20 </ b> E illustrated in FIG. 15, the control unit 80 may control the driving unit 87 based on information regarding the rotation angle of the fixing roller 30 detected by the detection unit 83. According to the conveyance operation of the recording medium 90 and the rotational position of the second region R2, the relative positional relationship between the fixing roller 30 and the pressure roller 40 can be changed and moved away from each other with higher accuracy. It becomes possible. In this case, the control unit 80, the detection unit 83, the cam mechanism 86, and the drive unit 87 can function as a position adjusting unit that adjusts the pressing force acting on the pressing nip.

[Other embodiments]
Referring to FIG. 16, the fixing unit of each of the embodiments described above includes a fixing roller (fixing rotating member) and a pressure roller. Like the fixing unit 20F shown in FIG. 16, one fixing rotating member or both fixing rotating members constituting the fixing unit include a plurality of rollers and a fixing belt member 42 stretched by these rollers. You may have.

  In the fixing unit 20F, a fixing belt member 42 is stretched by a fixing roller 43 and a heating roller 41, and a heater lamp 41H is built in the heating roller 41. The fixing belt member 42 has a configuration in which a nickel electroforming belt, a heat-resistant polyimide belt or the like is used as a base, and an elastic layer or a release layer can be provided on the surface thereof. Also with this configuration, the same operational effects as described above can be obtained.

  The fixing roller in each of the above-described embodiments has a configuration in which the center (center 39) of the cross-sectional circle of the end portion (large diameter portion 31, 32) of the fixing roller coincides with the rotation shaft 37 of the roller. The center (center 38) of the cross-sectional circle of the center portion (small diameter portion 33) of the fixing roller may be configured to coincide with the rotation shaft 37 of the roller. As described above, the outer edge of the cross-sectional shape of the large-diameter portions 31 and 32 has a circular shape, and the outer edge of the cross-sectional shape of the small-diameter portion 33 is not limited to a configuration having a non-circular shape. Any one of the outer edge and the outer edges of the large diameter portions 31 and 32 may have a non-circular shape.

[Experimental example]
With reference to FIGS. 17 and 18, an example of an experiment conducted for verifying the effects of the above-described embodiments will be described. This experimental example includes Examples 1A to 2A and 1B to 3B and Comparative Examples 1A to 3A and 1B to 3B. In each of Examples 1A to 2A, 1B to 3B and Comparative Examples 1A to 3A and 1B to 3B, the image forming apparatus shown in FIG. 16 was used. The differences are as follows.

(Examples 1A and 1B)
As the fixing roller 30, a roller having the configuration shown in FIGS. 2 to 4 was used as in the first embodiment. The maximum value of the reverse crown amount of the fixing roller 30 was 1.0 mm, the minimum value was 0.2 mm, and the width of the roller surface in the rotation axis direction was 540 mm.

(Examples 2A and 2B)
As the fixing roller 30, a roller having the configuration shown in FIGS. 9 and 10 was used as in the second embodiment. The maximum value of the reverse crown amount of the fixing roller 30 was 1.0 mm, the minimum value was 0 mm, and the width of the roller surface in the rotation axis direction was 540 mm. Further, as shown in FIG. 8, a detection unit 83 that detects the rotation angle of the fixing roller 30 and a control unit 80 that controls the timing at which the recording medium 90 enters the pressure nip 50 are used. Under the control of the control unit 80, the timing at which the leading end 91 of the recording medium 90 enters the pressure nip 50 and the portion indicated by the point Q (see FIG. 12) of the fixing roller 30 (the portion where the tensile force on the recording medium 90 is maximized). ) Matched with the timing of entering the pressure nip 50.

(Example 3B)
As the fixing roller 30, a roller having the configuration shown in FIGS. 12 and 13 is used as in the third embodiment. The maximum value of the reverse crown amount of the fixing roller 30 was 1.0 mm, the minimum value was 0 mm, and the width of the roller surface in the rotation axis direction was 540 mm. Further, as shown in FIG. 8, a detection unit 83 that detects the rotation angle of the fixing roller 30 and a control unit 80 that controls the timing at which the recording medium 90 enters the pressure nip 50 are used. Under the control of the control unit 80, the timing at which the leading end 91 of the recording medium 90 enters the pressure nip 50 and the portion indicated by the point Q (see FIG. 12) of the fixing roller 30 (the portion where the tensile force on the recording medium 90 is maximized). ) Matched with the timing of entering the pressure nip 50. The peripheral length of the small diameter portion 33 of the fixing roller 30 was 200 mm. This value is longer than the total length in the transport direction of the recording medium 90 to be used, and the total length in the transport direction of the recording medium 90 substantially corresponds to the first region R1.

(Comparative Examples 1A and 1B)
As the fixing roller 30, a roller whose reverse crown amount is always constant in the rotation direction is used. The reverse crown amount was 1.0 mm.

(Comparative Examples 2A and 2B)
As the fixing roller 30, a roller whose reverse crown amount is always constant in the rotation direction is used. The reverse crown amount was 0.6 mm.

(Comparative Examples 3A and 3B)
As the fixing roller 30, a roller whose reverse crown amount is always constant in the rotation direction is used. The reverse crown amount was 0.2 mm.

(experimental method)
A3 size and A2 size recording media 90 were prepared. Using the image forming apparatus having the configuration of each example and each comparative example, 50 sheets of each were continuously printed on these recording media 90. Specifically, the image forming apparatus based on Example 1A is used to continuously print on 50 recording media 90 having A3 size, and the image forming apparatus based on Example 1B is used to have A3 size. Printing was continuously performed on 50 recording media 90.

Similarly, in Comparative Examples 1A to 3A, printing was continuously performed on 50 recording media 90 each having an A3 size. In Examples 1B to 3B, printing was continuously performed on 50 recording media 90 each having an A2 size. In Comparative Examples 1B to 3B, printing was continuously performed on 50 recording media 90 each having an A2 size. The recording medium 90 used was OK Coat L (manufactured by Oji Paper Co., Ltd.), and its basis weight was 64 g / m ² . At the time of fixing, the recording medium 90 was subjected to center paper passing through the center of the fixing roller in the rotational axis direction.

  Under the above conditions, it was verified whether or not wrinkles occurred in the recording medium 90 and whether or not image disturbance occurred in the image due to the jumping and fluttering that occurred at the rear end of the recording medium 90. FIG. 17 shows the evaluation results for A3 size paper, and FIG. 18 shows the evaluation results for A2 size paper. As an evaluation standard, when the number of the recording media 90 in which wrinkles or image disturbance occurred was 0, the evaluation was A. When the number of the recording media 90 in which wrinkles or image disturbance occurred was 1 or more and less than 5, the evaluation was B. When the number of recording media 90 in which wrinkles or image disturbance occurred was 5 or more, the evaluation was C.

  Referring to FIG. 17, when A3 size paper is used, it can be seen that in Examples 1A and 2A, image disturbance can be suppressed while suppressing generation of wrinkles. On the other hand, in Comparative Examples 1A, 2A, and 3A using a roller having a constant reverse crown amount, it can be understood that it is difficult to achieve both suppression of wrinkles and suppression of image distortion.

  Referring to FIG. 18, it can be seen that even when A2 size paper is used, in Examples 1B, 2B, and 3B, image disturbance can be suppressed while suppressing the generation of wrinkles. On the other hand, it can be seen that in Comparative Examples 1B, 2B, and 3B using a roller having a constant reverse crown amount, it is difficult to achieve both suppression of wrinkles and suppression of image distortion. Note that A2 size paper is larger than A3 size paper, and the condition for achieving both suppression of wrinkles and suppression of image distortion is greater when A2 size paper is used than when A3 size paper is used. And tough. In Comparative Examples 1B, 2B, and 3B, any of the evaluations for suppressing wrinkles and suppressing image disturbance is evaluation C, whereas in Examples 1B, 2B, and 3B, evaluation B is obtained at least. . In other words, according to Examples 1B, 2B, and 3B, evaluation B or higher is obtained in all cases.

  Also from the results of the above experimental examples, the fixing roller of the above-described embodiment can obtain an output image having higher quality than a roller having a shape in which the reverse crown amount is always constant in the rotation direction. It turns out that it becomes. Further, the timing at which the leading end 91 of the recording medium 90 enters the pressure nip 50 and the portion indicated by the point Q (see FIGS. 9 and 12) of the fixing roller 30 (the portion where the tensile force with respect to the recording medium 90 is maximized) are pressed. It can be seen that an output image having higher quality can be obtained by performing control so as to match the timing of entering the nip 50.

  As mentioned above, although each embodiment and experiment example based on this invention were described, each embodiment and experiment example disclosed this time are illustrations in all points, and are not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Image forming part, 11 Photosensitive drum, 12 Intermediate transfer roller, 13, 18 Cleaning device, 14 Charging device, 15 Exposure device, 16 Liquid developing device, 17th transfer roller, 20, 20A, 20D, 20E, 20F Fixing unit , 30, 30A, 30B, 30C, 30Z, 43 Fixing roller (fixing rotating member), 30H, 40H Heater lamp, 31, 32 Large diameter portion, 33 Small diameter portion, 34, 35 Intermediate portion, 36 Support shaft, 37 rotation Axis, 38, 39 center, 40 pressure roller, 41 heating roller, 41H heater lamp, 42 fixing belt member, 50 pressure nip, 60 transport device, 61, 62 roller, 63 belt member, 73 flutter, 80 control unit, 81 Speed adjuster, 82, 83, 84 detector, 85 marking, 86 cam mechanism, 7 Driving unit, 88 spring, 90 recording medium (recording paper), 91 leading edge, 92 trailing edge, 93 conveying path, 94 toner image, 100, 101 image forming apparatus, AR90 arrow (conveying direction), D1-D4 interval, L1 ~ L4 Normal, P, Q point, PP projection plane, R1 first region, R2 second region, RC, RE1, RE2 turning radius, S1-S4 arbitrary locations.

Claims (14)

A fixing rotating member for fixing a toner image on the recording medium by forming a pressing nip with a member disposed oppositely and passing the recording medium onto which the toner image has been transferred through the pressing nip; ,
A small diameter part,
A large-diameter portion that is located on both outer sides of the small-diameter portion in the rotational axis direction, and has a circumference in the rotational direction that is longer than the small-diameter portion;
An intermediate portion located between the small diameter portion and the large diameter portion in the rotation axis direction and having a shape in which the circumference gradually increases from the small diameter portion side toward the large diameter portion side. ,
When projecting the small diameter portion and the large diameter portion along the rotation axis direction and virtually seeing them on a projection plane orthogonal to the rotation axis direction, For a plurality of arbitrary locations in the circumferential direction on the surface of the drawn small-diameter portion, the interval between the surface of the small-diameter portion and the surface of the large-diameter portion in the normal direction for each arbitrary location is the arbitrary Different from place to place,
Rotating member for fixing. When looking at the cross-sectional shape in the direction orthogonal to the rotation axis direction, the outer edge of the small diameter portion and the outer edge of the large diameter portion both have a circular shape,
The center of the small diameter portion and the center of the large diameter portion drawn in the projection plane are formed at positions shifted from each other.
The fixing rotation member according to claim 1. When looking at the cross-sectional shape in the direction orthogonal to the rotation axis direction, either the outer edge of the small diameter portion and the outer edge of the large diameter portion have a non-circular shape,
The fixing rotation member according to claim 1. A part of the outer edge of the small diameter portion drawn in the projection plane overlaps the outer edge of the large diameter portion drawn in the projection plane,
The fixing rotation member according to any one of claims 1 to 3. An image forming unit for forming a toner image on a recording medium;
A fixing unit that includes the fixing rotation member according to claim 1 and fixes the toner image on the recording medium.
Image forming apparatus. The circumference of the small diameter portion of the fixing rotation member is longer than the total length in the conveyance direction of the recording medium,
The image forming apparatus according to claim 5. A detection unit for detecting a rotation angle of the fixing rotation member;
A control unit that controls the timing at which the recording medium enters the press-contact nip based on the rotation angle detected by the detection unit;
The image forming apparatus according to claim 5. The control unit is configured such that a portion where the distance between the surface of the small diameter portion and the surface of the large diameter portion in the normal direction is the largest among the surfaces in the circumferential direction of the fixing rotation member is the pressure nip. The timing of entering and the timing at which the leading end of the recording medium in the conveying direction enters the pressure nip,
The image forming apparatus according to claim 7. The control unit is configured such that a portion where the distance between the surface of the small diameter portion and the surface of the large diameter portion in the normal direction among the surfaces in the circumferential direction of the fixing rotation member is minimum is the pressure nip. The timing of entering and the timing at which the rear end of the recording medium in the conveying direction enters the pressure nip,
The image forming apparatus according to claim 7 or 8. The detection unit is a distance measuring sensor disposed to face the surface of the fixing rotation member.
The image forming apparatus according to claim 7. The fixing rotating member is provided with a marking,
The detection unit detects a rotation angle of the fixing rotation member by detecting the marking;
The image forming apparatus according to claim 7. Information relating to the timing at which the image forming unit forms the toner image on the recording medium is input to the control unit,
The control unit controls the timing at which the recording medium enters the pressure nip based on the information.
The image forming apparatus according to claim 7. A speed adjusting unit for adjusting the conveyance speed of the recording medium;
The control unit controls the timing at which the recording medium enters the pressure nip by controlling the speed adjusting unit to adjust the conveyance speed.
The image forming apparatus according to claim 7. A position adjusting unit that adjusts a pressure contact force acting on the pressure nip by changing a relative positional relationship between the member disposed opposite to the fixing rotation member;
The control unit controls the position adjusting unit so that the pressing force is reduced when the recording medium is not located in the pressing nip.
The image forming apparatus according to claim 7.

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