JP2018180242A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of improving the detection accuracy of the rotation of a fixing belt and to provide an image forming apparatus.SOLUTION: A fixing device 40 includes a rotating endless fixing belt 41, a heater 43 which heats the fixing belt 41, a pad 42 which is provided inside the fixing belt 41, a pressure roller 44 which is provided in a position facing the pad 42 across the fixing belt 41 and presses the fixing belt 41 to the pad 42, to form a fixing nip NP between the pressure roller 44 and the fixing belt 41, a detection member 50 which detects the movement of the fixing belt 41, and a rotation detection part which detects the rotation of the fixing belt 41 on the basis of a detection result by the detection member 50. The detection member 50 detects the movement of the fixing belt 41 in a detection position SP which is a detection position SP outside the fixing belt 41 and faces the pad 42 across the fixing belt 41.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device and an image forming apparatus. More particularly, the present invention relates to a fixing device and an image forming apparatus for fixing a toner image on a transfer material by passing the transfer material through a fixing nip.

  The electrophotographic image forming apparatus includes an MFP (Multi Function Peripheral), a facsimile machine, a copier, a printer, etc. having a scanner function, a facsimile function, a copying function, a function as a printer, a data communication function, and a server function. is there.

  The image forming apparatus generally forms an image on a sheet by the following method. The image forming apparatus forms an electrostatic latent image on an image carrier and develops the electrostatic latent image using a developing device to form a toner image. Next, the image forming apparatus transfers the toner image to the sheet, and the fixing device fixes the toner image on the sheet. Further, in the image forming apparatus, a toner image is formed on the photosensitive member, and the toner image is transferred to the intermediate transfer belt using the primary transfer roller, and the toner image on the intermediate transfer belt using the secondary transfer roller There are also secondary transfer devices to paper.

  When the image forming apparatus performs printing, it is necessary to heat the fixing device to a predetermined temperature. Since it takes time to heat the fixing device, attempts have been made to shorten the heating time of the fixing device by adopting the DH (Direct Heating) method which directly heats the fixing belt with a heater.

  In the DH type fixing device, it is important to detect the rotation of the fixing belt from the viewpoint of securing safety. That is, the heat capacity of the fixing belt is set low for the purpose of enhancing the heating efficiency. In order to prevent ignition due to local heating of the fixing belt, it is necessary to detect the rotation of the fixing belt and to confirm that the fixing belt is rotating normally.

  On the other hand, the fixing belt is made of a thin film in order to secure the fixing function such as low heat capacity and good releasability. For this reason, the fixing belt is fragile and there is little room for additional processing. Furthermore, during operation of the fixing device, the fixing belt becomes high temperature, and the fixing belt is in a severe environment where flapping (irregular movement of the fixing belt due to rotation) is likely to occur. For these reasons, it has not been easy to detect the rotation of the fixing belt.

  Conventional techniques for detecting the rotation of the fixing belt are disclosed, for example, in the following Patent Documents 1 to 5 and the like. In Patent Document 1 listed below, a fixing roller having a fixing sleeve on the outermost periphery, a pressure member that presses the fixing roller to form a nip, a heating mechanism that heats the fixing sleeve, and a rotational speed of the fixing sleeve are described. There is disclosed a configuration provided with a rotation detection mechanism unit to detect. The rotation detection component includes a rubber roller in contact with the fixing sleeve, and the rotation of the fixing sleeve is detected by the rotation of the rubber roller.

  In Patent Document 2 below, a heating roller heated by electromagnetic induction of induction heating means, a fixing roller provided parallel to the heating roller, a heating roller and a fixing roller are stretched and heated by the heating roller Together with the endless fixing belt rotated by the heating roller and the fixing roller, at least one detection hole formed in the fixing belt, and movement of the detection hole in the rotation direction of the detection hole accompanying the rotation of the fixing belt And a transmissive sensor.

  In Patent Document 3 listed below, a fixing belt, a cylindrical rotation detection member covering the outer peripheral surface of the end portion of the fixing belt, and a driven rotation member that contacts the outer peripheral surface of the rotation detection member and follows the rotation of the rotation detection member And a light sensor for detecting the rotation of the driven rotary member.

  Patent Document 4 below discloses a configuration provided with an endless film and a photo interrupter that detects the circumferential speed of the endless film. A plurality of holes are formed at equal intervals at one side end of the endless film, and a masking process is performed around the entire edge of the same end to shield light of the photo interrupter.

  In the following Patent Document 5, an endless rotating film and a pressing member for pressing the film from its inner surface toward the rotating body to form a nip portion, which is a conductive contact layer in contact with the inner surface of the film There is disclosed a configuration provided with a pressing member provided, and a detection means for detecting conduction between the contact layer and the contact layer due to film breakage.

JP, 2011-191590, A JP 2002-40839 A Unexamined-Japanese-Patent No. 2014-109654 JP-A-8-190298 JP, 2015-132701, A

  However, in the techniques of Patent Documents 1 to 4, there is a problem that the detection position of the rotation changes when the fixing belt is flapped, and the detection accuracy of the rotation of the fixing belt is low. In particular, when the fixing belt does not rotate for a long time and continues to be pressed by the pressure roller, the pressing belt may cause irreversible deformation (fixing of the fixing belt) to the fixing belt. The location where such irreversible deformation has occurred has been a factor that reduces the detection accuracy of the rotation of the fixing belt.

  When the technology of Patent Document 5 is applied to detection of the rotation of the fixing belt, the rotation is detected based on conduction of the inner peripheral surface of the fixing belt. However, since the inner peripheral surface of the fixing belt to be the detection position is roughened by the attached grease or sliding, there is a problem that the detection accuracy of the rotation of the fixing belt is low.

  The present invention is for solving the above-mentioned problems, and an object thereof is to provide a fixing device and an image forming apparatus capable of improving the detection accuracy of the fixing belt rotation.

  A fixing device according to one aspect of the present invention is a fixing device that fixes a toner image to a transfer material by causing a transfer material to pass through a fixing nip, and heats a rotating endless fixing belt and the fixing belt. The fixing member is provided at a position facing the pressing member via the heating member, the pressing member provided inside the fixing belt, and the fixing belt, and the fixing nip is formed between the fixing belt by pressing the fixing belt against the pressing member. A pressure member to be formed, a detection member for detecting the movement of the fixing belt, and a rotation detection means for detecting the rotation of the fixing belt based on the detection result by the detection member, the detection member detecting the outside of the fixing belt The movement of the fixing belt is detected at a detection position facing the pressing member via the fixing belt.

  Preferably, in the fixing device, the length of the pressing member in the rotation shaft direction of the fixing belt is longer than the length of the fixing belt in the rotation shaft direction of the fixing belt, and the length of the fixing belt in the rotation shaft direction of the fixing belt is It is longer than the length of the pressure member in the direction of the rotation shaft of the fixing belt.

  Preferably, in the fixing device, the detection position is a position closer to the end portion of the fixing belt than the pressure member in the rotation shaft direction of the fixing belt.

  Preferably, in the fixing device, the detection position is a position where a fixing nip exists in the transfer material conveyance direction.

  Preferably, in the fixing device described above, the fixing nip and the detection position are on the same straight line when viewed in a cross section taken along a plane including the rotation axis direction of the fixing belt.

  In the above-described fixing device, preferably, the pressure member is rotationally driven, and the fixing belt is a free belt which is driven by the rotation of the pressure member.

  Preferably, in the fixing device, the detection member does not contact the fixing belt.

  Preferably, the fixing device further includes a marking portion provided in an area passing the detection position when the fixing belt rotates, and having a reflectance that periodically changes along the rotation direction of the fixing belt, and the detection member And an optical sensor for emitting light to the marking portion present at the detection position and receiving the reflected light, and the rotation detection means detects the rotation of the fixing belt based on a periodic change in the amount of light received by the optical sensor. .

  Preferably, in the fixing device, the detection member further includes a guide portion which guides the light from the light sensor to the marking portion present at the detection position, and guides the light reflected by the marking portion present at the detection position to the light sensor.

  Preferably, the fixing device further includes a magnet provided in a region passing the detection position when the fixing belt rotates, and the detection member is provided at a distance from the magnet and a magnet resulting from the rotation of the fixing belt And the rotation detecting means detects the rotation of the fixing belt based on the rotation of the disk.

  Preferably, the fixing device further includes a magnet provided in a region passing the detection position when the fixing belt rotates, and the detection member is provided at a distance from the magnet and a magnet resulting from the rotation of the fixing belt The rotation detecting means detects the rotation of the fixing belt based on the information indicating the electromotive force generated in the coil.

  In the above-described fixing device, preferably, the detection member contacts the fixing belt.

  Preferably, in the fixing device, the detection member is in contact with a detection position provided on the outer surface of the fixing belt, is driven to rotate by rotation of the fixing belt, and has a rotational axis identical to that of the pressure member. And a sensor that detects the rotation of the driven member, wherein the rotation detection means detects the rotation of the fixing belt based on the detection result of the sensor.

  Preferably, the fixing device further includes a projecting member provided in an area passing the detection position when the fixing belt rotates, and convex with respect to the outer surface of the fixing belt along the rotation direction of the fixing belt, The detection member includes a contact member that moves when contacting the projection member, and the rotation detection means detects the rotation of the fixing belt based on the movement of the contact member.

  Preferably, in the fixing device, the fixing belt includes an endless base layer, and an endless release layer provided on the outer diameter side of the base layer and in contact with the pressing member, and the protruding member is lower than the lower layer. The projection member is provided between the formation and the release layer and viewed in a cross section perpendicular to the rotation axis of the fixing belt, the projecting member has a continuous shape from both ends in the rotation direction of the fixing belt to the apex.

  Preferably, in the fixing device, the projection member includes a hollow portion.

  Preferably, in the fixing device, one end of the protruding member in the rotational direction of the fixing belt is bonded to the outer surface of the fixing belt, and the other end of the protruding member in the rotating direction of the fixing belt is fixed It is not glued to the outer surface of the belt.

  Preferably, in the fixing device, the contact member rotates about a rotation axis extending in a first direction when contacting the projection member, and is movable in a second direction orthogonal to the first direction. A first member, a second member fixed to the first member, extending in a third direction orthogonal to each of the first and second directions, and oscillating with rotation of the first member; And a sensor for detecting the swing of the second member, wherein the rotation detection means detects the rotation of the fixing belt based on the detection result of the sensor.

  Preferably, the fixing device further includes a side plate provided at an end of the fixing belt in the rotation axis direction and supporting the second member in a swingable manner, and the sensor is a fixing belt by the side plate in the rotation axis direction of the fixing belt. It is separated from

  Preferably, in the fixing device, the pressing member includes a hollow portion at a position opposite to the detection position via the fixing belt.

  An image forming apparatus according to another aspect of the present invention includes a toner image forming unit that forms a toner image on a transfer material, and the fixing device described above.

  According to the present invention, it is possible to provide a fixing device and an image forming apparatus capable of improving the detection accuracy of the rotation of the fixing belt.

FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus 1 according to a first embodiment of the present invention. FIG. 3 is a top view showing the configuration of the fixing device 40 in the first embodiment of the present invention. FIG. 3 is a front view showing the configuration of the fixing device 40 in the first embodiment of the present invention. It is a top view which shows typically a mode that the pad 42 deform | transforms into concave shape. It is a top view which shows the structure of the pad 42 in the 2nd Embodiment of this invention. FIG. 14 is a top view showing a configuration in the vicinity of a detection member 50 of a fixing device 40 according to a third embodiment of the present invention. FIG. 18 is a top view showing a configuration in the vicinity of a detection member 50 of a fixing device 40 of a modified example of the third embodiment of the present invention. It is a front view which shows the structure of the fixing device 40 in the 4th Embodiment of this invention. FIG. 25 is a top view showing a configuration near a detection member 50 of a fixing device 40 according to a fifth embodiment of the present invention. It is a front view showing the composition of fixing device 40 in a 5th embodiment of the present invention. It is a top view which shows the structure of the fixing device 40 in the 6th Embodiment of this invention. It is a perspective view showing the composition of driven member 541 in a 6th embodiment of the present invention. It is a front view showing the composition of fixing device 40 in a 7th embodiment of the present invention. It is a figure which shows the structure of the optical sensor 553 in the 7th Embodiment of this invention, Comprising: It is a figure which shows the structure at the time of seeing from the rotating shaft 551a side. FIG. 33 is a cross-sectional view showing a configuration in the vicinity of the protruding member 63 of the fixing device 40 of the first modified example of the seventh embodiment of the present invention. FIG. 33 is a cross-sectional view showing a configuration in the vicinity of the protruding member 63 of the fixing device 40 of the second modified example of the seventh embodiment of the present invention. FIG. 25 is a top view showing a configuration in the vicinity of a detection member 50 of a fixing device 40 according to an eighth embodiment of the present invention. FIG. 25 is a perspective view showing a configuration in the vicinity of a detection member 50 of a fixing device 40 according to an eighth embodiment of the present invention. FIG. 21 is a front view showing a configuration in the vicinity of a detection member 50 of a fixing device 40 according to an eighth embodiment of the present invention. FIG. 25 is a side view showing a configuration in the vicinity of a detection member 50 of a fixing device 40 according to an eighth embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described based on the drawings.

  In the following embodiments, the case where the image forming apparatus on which the fixing device is mounted is an MFP will be described. The image forming apparatus on which the fixing device is mounted may be a facsimile machine, a copier, a printer, or the like in addition to the MFP.

  First Embodiment

  First, the configuration of the image forming apparatus in the present embodiment will be described.

  In the drawings, the width direction when the image forming apparatus 1 is viewed from the front is the x-axis direction, the depth direction is the y-axis direction, and the height direction is the z-axis. Each of the x-axis, y-axis and z-axis is orthogonal to one another.

  FIG. 1 is a cross-sectional view showing the configuration of an image forming apparatus 1 according to a first embodiment of the present invention.

  Referring to FIG. 1, image forming apparatus 1 in the present embodiment is an MFP, and mainly includes sheet conveyance unit 10, toner image formation unit 20, control unit 30, and fixing device 40. .

  The sheet conveyance unit 10 includes a sheet feed tray 11, a sheet feed roller 12, a plurality of conveyance rollers 13, a sheet discharge roller 14, and a sheet discharge tray 15. The sheet feeding tray 11 accommodates a sheet M (an example of a transfer material) for forming an image. The paper feed tray 11 may be plural. The paper feed roller 12 is provided between the paper feed tray 11 and the transport path TR. Each of the plurality of transport rollers 13 is provided along the transport path TR. The paper discharge roller 14 is provided at the most downstream part of the transport path TR. The discharge tray 15 is provided at the top of the image forming apparatus main body 1a.

  The toner image forming unit 20 combines four color images of Y (yellow), M (magenta), C (cyan), and K (black) in a so-called tandem system to form a toner image on a sheet. The toner image forming unit 20 includes an image forming unit 21 for each YMCK color, an intermediate transfer belt 22, a primary transfer roller 23 for each YMCK color, and a secondary transfer roller 24.

  The image forming unit 21 for each color of Y, M, C, and K includes a photosensitive drum 25, a charging roller 26, an exposure device 27, a developing device 28, a cleaning device 29, and the like. The photosensitive drum 25 is rotationally driven in the direction indicated by the arrow α in FIG. Around the photosensitive drum 25, a charging roller 26, a developing device 28, and a cleaning device 29 are provided. The charging roller 26 is provided in proximity to the photosensitive drum 25. The exposure device 27 is provided below the photosensitive drum 25.

  The intermediate transfer belt 22 is provided on the upper part of the image forming unit 21 of each color of Y, M, C, and K. The intermediate transfer belt 22 is annular, and is wound around a rotating roller 22 a. The intermediate transfer belt 22 is rotationally driven in the direction indicated by the arrow β in FIG. Each of the primary transfer rollers 23 opposes each of the photosensitive drums 25 with the intermediate transfer belt 22 interposed therebetween. The secondary transfer roller 24 is in contact with the intermediate transfer belt 22 in the transport path TR.

  The fixing device 40 fixes the toner image on the sheet by conveying the sheet carrying the toner image along the conveyance path TR while gripping the sheet.

  The image forming apparatus 1 rotates the photosensitive drum 25 to charge the surface of the photosensitive drum 25 by the charging roller 26. The image forming apparatus 1 exposes the charged surface of the photosensitive drum 25 by the exposure device 27 in accordance with the image forming information, and forms an electrostatic latent image on the surface of the photosensitive drum 25.

  Next, the image forming apparatus 1 supplies toner from the developing device 28 to the photosensitive drum 25 on which the electrostatic latent image is formed to perform development, and forms a toner image on the surface of the photosensitive drum 25.

  Next, the image forming apparatus 1 sequentially transfers the toner image formed on the photosensitive drum 25 to the surface of the intermediate transfer belt 22 using the primary transfer roller 23 (primary transfer). In the case of a full color image, on the surface of the intermediate transfer belt 22, a toner image in which toner images of Y, M, C, and K colors are combined is formed.

  The image forming apparatus 1 removes the toner remaining on the photosensitive drum 25 without being transferred to the intermediate transfer belt 22 by the cleaning device 29.

  Subsequently, the image forming apparatus 1 conveys the toner image formed on the surface of the intermediate transfer belt 22 to a position facing the secondary transfer roller 24 by the rotation roller 22a.

  On the other hand, the image forming apparatus 1 feeds the sheet M stored in the sheet feeding tray 11 by the sheet feeding roller 12 and the intermediate transfer belt 22 and the secondary along the conveyance path TR by each of the plurality of conveyance rollers 13. It leads between the transfer roller 24. Then, the image forming apparatus 1 transfers the toner image formed on the surface of the intermediate transfer belt 22 to the sheet M by the secondary transfer roller 24.

  The image forming apparatus 1 guides the sheet M on which the toner image is transferred to the fixing device 40, and the toner image is fixed to the sheet M by the fixing device 40. Thereafter, the image forming apparatus 1 discharges the sheet M on which the toner image is fixed to the sheet discharge tray 15 by the sheet discharge roller 14.

  Control unit 30 includes a central processing unit (CPU) for controlling the entire image forming apparatus 1 according to the control program, a ROM for storing the control program, and a random access memory (RAM) for forming a work area of the CPU. There is. The control unit 30 includes a rotation detection unit 31 (an example of a rotation detection unit). The rotation detection unit 31 detects the rotation of the fixing belt 41 based on the detection result by the detection member 50 described later. The rotation detection unit 31 is realized by the CPU operating according to the control program.

  FIGS. 2 and 3 are diagrams showing the configuration of the fixing device 40 according to the first embodiment of the present invention. FIG. 2 is a top view, and FIG. 3 is a front view.

  Referring to FIGS. 2 and 3, fixing device 40 includes fixing belt 41, pad 42 (an example of a pressing member), heater 43 (an example of a heating member), and pressure roller 44 (an example of a pressing member). And a pad frame 45 and a detection member 50. The fixing device 40 causes the sheet to pass through the fixing nip NP of the fixing belt 41 and the pressure roller 44, thereby applying heat and pressure to the sheet from the fixing belt 41 to fix the toner image on the sheet.

  The fixing belt 41 is an endless belt. The fixing belt 41 is supported at a position where it is in pressure contact with the pressure roller 44 to form a fixing nip portion by being nipped by a guide member (side plate) (not shown) at both end portions in the axial direction.

  The pad 42 is provided inside the fixing belt 41. The pad 42 extends parallel to the extending direction of the rotation shaft of the fixing belt 41. The pad 42 presses the fixing belt 41 against the pressure roller 44 from the inside.

  Here, the portion PO corresponds to a portion on the outside of the fixing belt 41 facing the pad 42 via the fixing belt 41. In other words, the portion PO corresponds to a portion where the fixing belt 41 is pressed against the pad 42.

  The heater 43 is provided inside the fixing belt 41. The heater 43 extends in parallel with the extension direction of the rotation shaft of the fixing belt 41. The heater 43 heats the fixing belt 41 to a predetermined target temperature. As the heater 43, a halogen heater or the like is used.

  The pressure roller 44 is provided at a position facing the pad 42 via the fixing belt 41. The pressure roller 44 forms a fixing nip NP with the fixing belt 41 by pressing the fixing belt 41 against the pad 42. The pressure roller 44 is rotationally driven in the direction indicated by the arrow AR11. The fixing belt 41 is a free belt that follows the rotation of the pressure roller 44, and rotates in the direction indicated by the arrow AR12.

  The pad frame 45 is provided inside the fixing belt 41. The pad frame 45 extends parallel to the extending direction of the rotation shaft of the fixing belt 41. The pad frame 45 holds the pad 42.

  The rotational axis direction of the fixing belt 41, the longitudinal direction of the pad 42, and the rotational axis direction of the pressure roller 44 are all in the y-axis direction.

  The fixing belt 41 has a thickness of about 100 to 300 μm and is made very thin. This is for reducing the heat capacity of the fixing belt 41 and shortening the temperature rising time of the fixing device 40 from the viewpoint of user-friendliness. For this reason, if the fixing belt 41 is erroneously kept heated without being rotated, there is a risk of smoke and ignition in a few seconds. In order to avoid such a situation, a detection member 50 for detecting the movement of the fixing belt 41 is provided. Detection member 50 is provided, for example, near the outer surface of fixing belt 41.

  During the rotation of the fixing device 40, the fixing belt 41 is likely to flap. Here, the flapping of the fixing belt 41 means the fluctuation of the position of the fixing belt 41 in the radial direction as shown by the arrow AR13. The flapping of the fixing belt 41 is particularly likely to occur in the portion (other than the portion PO) of the fixing belt 41 which is not pressed by the pad 42. On the other hand, in the portion PO, since the fixing belt 41 is pressed by the pad 42, flapping of the fixing belt 41 hardly occurs.

  Therefore, the detection member 50 moves the fixing belt 41 in the rotational direction at the detection position SP facing the pad 42 via the fixing belt 41 on the outer side of the fixing belt 41 (that is, the detection position SP present in the portion PO). To detect

  The above-described detection position SP is in the vicinity of the fixing nip NP. Since the fixing belt 41 is nipped by the pad 42 and the pressure roller 44 at the fixing nip NP, even if the fixing belt 41 has an unnecessary deformation (a distortion of the fixing belt), it is caused by the unnecessary deformation. The fluctuation of the position of the fixing belt 41 at the detection position SP can be suppressed.

  The lengths of the fixing belt 41, the pad 42, and the pressure roller 44 in the rotational axis direction (y-axis direction) of the fixing belt 41 have a relationship of pressure roller 44 <fixing belt 41 <pad 42. Is preferred. Thus, the detection position SP can be provided at the position TP on the end side of the fixing belt 41 with respect to the pressure roller 44 in the rotational axis direction of the fixing belt 41, and the above-described detection position SP can be easily realized. . It is preferable that the detection position SP be within the nip width W. The nip width W is a position where the fixing nip NP is present in the sheet conveyance direction (vertical direction in FIG. 3). The area of the nip width W in the fixing belt 41 is an area in which the fixing belt 41 is sandwiched between the pad 42 and the pressure roller 44, and flapping of the fixing belt 41 is particularly hard to occur.

  The pad 42 preferably includes a hollow portion 42 a at a position facing the detection position SP via the fixing belt 41. The hollow portion 42a is a portion where the pad 42 is hollowed out. Since the temperature rising speed of the fixing belt 41 is fast, it is preferable that the detection cycle by the detection member 50 be short. Therefore, when the detection member 50 mechanically detects the movement of the fixing belt 41 or when the detection member 50 contacts the fixing belt 41, noise may be generated from the detection member 50. The noise can be reduced by providing the hollow portion 42a.

  Although the configuration described in the seventh embodiment (configuration shown in FIG. 13) is shown as a specific configuration of the detection member 50 in the present embodiment, the specific configuration of the detection member in the present embodiment is shown. The configuration may be arbitrary. The detection member 50 is not limited to mechanical as described later. The detection member 50 may be in contact with the fixing belt 41 or may be in non-contact with the fixing belt 41.

  According to the present embodiment, by setting the portion of the fixing belt 41 supported from the inside by the pad 42 as the detection position SP of the detection member 50, it is possible to suppress the flapping of the fixing belt 41 at the detection position SP. The detection accuracy of the rotation of the fixing belt can be improved.

  Second Embodiment

  FIG. 4 is a top view schematically showing how the pad 42 deforms into a concave shape.

  Referring to FIG. 4, generally, both ends in the longitudinal direction (y-axis direction) of pad 42 are supported by image forming apparatus body 1a, while the central portion in the longitudinal direction of pad 42 is not supported. For this reason, by the pressing force received from the pressing roller 44, the central portion in the longitudinal direction of the pad 42 is easily deformed into a concave shape. When the deformation of the central portion in the longitudinal direction of the pad 42 to a concave shape is significant, the pressure applied to the fixing belt 41 at the fixing nip NP is reduced, and the fixing belt 41 is easily flapped.

  FIG. 5 is a top view showing the configuration of the pad 42 in the second embodiment of the present invention.

  Referring to FIG. 5, the pad 42 in the present embodiment has a shape in which the central portion in the longitudinal direction of the pad 42 is convex toward the pressure roller 44 side. By forming the pad 42 as shown in FIG. 5, even when the pad 42 is deformed as described above, it is possible to prevent the central portion of the pad 42 in the longitudinal direction from being deformed into a concave shape. In the detection position SP, the surface 42 reliably comes into contact with the inner surface of the fixing belt 41. When the pad 42 has a shape as shown in FIG. 5, the longitudinal center of the pad 42 is deformed by the pressure from the pressure roller 44. As a result, the fixing nip NP and the detection position SP are on the same straight line (a straight line parallel to the y-axis) LN, as shown in FIG. Will be present.

  The configurations and the operations of the image forming apparatus and the fixing device other than the above are the same as the configurations and the operations of the image forming apparatus and the fixing device in the first embodiment. And their description will not be repeated.

  Third Embodiment

  In the following third to eighth embodiments, specific configurations for detecting the rotation of the fixing belt 41 will be described.

  FIG. 6 is a top view showing the configuration in the vicinity of the detection member 50 of the fixing device 40 according to the third embodiment of the present invention.

  Referring to FIG. 6, fixing device 40 in the present embodiment includes a marking unit 61. The marking unit 61 is provided in a region passing the detection position SP when the fixing belt 41 rotates. The marking unit 61 has a reflectance that changes periodically along the rotation direction of the fixing belt 41 (the direction indicated by the arrow AR12). Specifically, the marking portion 61 is formed of a plurality of films of the same shape made of a highly reflective material such as aluminum foil. The plurality of films are provided at equal intervals along the rotation direction of the fixing belt 41, and are adhered to the fixing belt 41.

  The detection member 50 in the present embodiment includes an optical sensor 511. The light sensor 511 is made of, for example, a reflection type photo interrupter. The light sensor 511 is provided near the outer surface of the fixing belt 41 and at a position facing the pad 42 via the fixing belt 41. The light sensor 511 is provided in non-contact with the fixing belt 41. The light sensor 511 emits light to the marking portion 61 present at the detection position SP, and receives the reflected light. The light sensor 511 performs an output corresponding to the amount of received light to the rotation detection unit 31.

  The amount of light received by the light sensor 511 increases when the light emitted from the light sensor 511 is reflected by the film, and decreases when it is reflected at a position other than the film. Do.

  The rotation detection unit 31 detects the rotation of the fixing belt 41 based on a periodic change in the amount of light received by the light sensor 511.

  The configurations and the operations of the image forming apparatus and the fixing device other than the above are the same as the configurations and the operations of the image forming apparatus and the fixing device in the first embodiment. And their description will not be repeated.

  Generally, the fixing belt 41 has a thickness of only about 100 to 300 μm and a low strength. Further, the surface of the fixing belt 41 is coated with a fluorocarbon resin (PFA) or the like, and the abrasion resistance is low. For this reason, when the detection member 50 contacts, the fixing belt 41 is likely to be broken or worn. The detection member 50 according to the present embodiment can detect the movement of the fixing belt 41 in a non-contact state with the fixing belt 41 by including the light sensor 511. It can prevent applying a load to rotation. As a result, breakage or wear of the fixing belt 41 can be suppressed.

  FIG. 7 is a top view showing the configuration in the vicinity of the detection member 50 of the fixing device 40 according to a modification of the third embodiment of the present invention.

  Referring to FIG. 7, detection member 50 in the present modification further includes a light guide 512 (an example of a guide portion). The light guide 512 is provided in non-contact with the fixing belt 41. One end of the light guide 512 is provided at a position facing the detection position SP, and the other end of the light guide 512 is provided at a position facing the light sensor 511. The light guide 512 guides the light from the light sensor 511 to the marking unit 61 present at the detection position SP, and guides the light reflected by the marking unit 61 present at the detection position SP to the light sensor 511.

  The fixing device 40 preferably further includes a side plate 46 for supporting the fixing belt 41. The light sensor 511 is separated from the fixing belt 41 by the side plate 46 in the rotational axis direction of the fixing belt 41.

  While the fixing belt 41 is in operation, the temperature in the vicinity of the fixing belt 41 is a high temperature of about 200.degree. Therefore, by providing the light guide 512 between the light sensor 511 and the fixing belt 41, the light sensor 511 can be kept away from the fixing belt 41, and erroneous detection of the light sensor 511 due to heat can be suppressed. Further, by providing the side plate 46, heat transfer from the fixing belt 41 to the light sensor 511 can be suppressed, and detection failure of the light sensor 511 due to heat can be prevented.

  The light sensor 511 may be a transmission sensor as well as a reflection sensor.

  Fourth Embodiment

  FIG. 8 is a front view showing the configuration of the fixing device 40 according to the fourth embodiment of the present invention. In FIG. 8, illustration of the pressure roller 44 is omitted.

  Referring to FIG. 8, fixing device 40 in the present embodiment includes a plurality of magnets 62. The plurality of magnets 62 are provided in a region that passes the detection position SP when the fixing belt 41 rotates. The plurality of magnets 62 are provided at equal intervals along the rotation direction of the fixing belt 41 (the direction indicated by the arrow AR12). The plurality of magnets 62 travel around the fixing belt 41 as the fixing belt 41 rotates. The number of magnets 62 is arbitrary.

  The detection member 50 in the present embodiment includes a disk 521. The disk 521 is provided near the outer surface of the fixing belt 41 and at a position facing the pad 42 via the fixing belt 41. The disk 521 is provided in non-contact with the fixing belt 41 at a distance from the plurality of magnets 62. The disk 521 has a cylindrical shape, and can rotate in a direction indicated by an arrow AR 21 around a rotation axis parallel to the rotation axis of the fixing belt 41. The outer peripheral surface of the disk 521 is alternately magnetized to the N pole and the S pole at equal intervals along the rotational direction of the disk (the direction indicated by the arrow AR21).

  The disk 521 rotates due to the fluctuation of the magnetic field from the plurality of magnets 62 caused by the rotation of the fixing belt 41. That is, every time each of the plurality of magnets 62 passes the detection position SP due to the rotation of the fixing belt 41, the disc acts by the interaction between the fluctuation of the magnetic field from the magnet 62 and the magnet magnetized on the outer peripheral surface of the disc 521. The 521 rotates little by little. The disk 521 performs an output on the rotation detection unit 31 according to the rotation of the disk 521 (the amount of rotation of the disk 521, the posture of the disk 521, etc.).

  The rotation detection unit 31 detects the rotation of the fixing belt 41 based on the output from the disk 521 (the rotation of the disk 521).

  The configurations and the operations of the image forming apparatus and the fixing device other than the above are the same as the configurations and the operations of the image forming apparatus and the fixing device in the first embodiment. And their description will not be repeated.

  The detection member 50 according to the present embodiment can detect the movement of the fixing belt 41 in a non-contact state with respect to the fixing belt 41 by including the disc 521, so that the detecting member 50 rotates the fixing belt 41. Can be prevented from being loaded. As a result, breakage or wear of the fixing belt 41 can be suppressed.

  Fifth Embodiment

  FIG. 9 is a top view showing the configuration in the vicinity of the detection member 50 of the fixing device 40 according to the fifth embodiment of the present invention. FIG. 10 is a front view showing the configuration of the fixing device 40 according to the fifth embodiment of the present invention.

  Referring to FIGS. 9 and 10, fixing device 40 in the present embodiment includes a magnet 62. The magnet 62 is provided in a region that passes the detection position SP when the fixing belt 41 rotates. The magnet 62 goes around the fixing belt 41 as the fixing belt 41 rotates. Here, although the number of magnets 62 is one, the number of magnets 62 is arbitrary.

  The detection member 50 in the present embodiment includes a coil 531. The coil 531 is provided near the outer surface of the fixing belt 41 and at a position facing the pad 42 with the fixing belt 41 interposed therebetween. The coil 531 is provided in non-contact with the fixing belt 41 at a distance from the magnet 62.

  When the magnet 62 passes the detection position SP due to the rotation of the fixing belt 41, the magnetic field of the magnet 62 fluctuates, and the number of magnetic lines of force passing through the inside of the coil 531 changes. Thereby, an induced electromotive force is generated in the coil 531. Both ends of the coil 531 are connected to the rotation detection unit 31, and information (induction current and power value) indicating the dielectric electromotive force of the coil 531 is output to the rotation detection unit 31. This output value shows periodic fluctuation.

  The rotation detection unit 31 detects the rotation of the fixing belt 41 based on the output value from the coil 531.

  The configurations and the operations of the image forming apparatus and the fixing device other than the above are the same as the configurations and the operations of the image forming apparatus and the fixing device in the first embodiment. And their description will not be repeated.

  The detection member 50 according to the present embodiment includes the coil 531 so that the movement of the fixing belt 41 can be detected in a non-contact state with respect to the fixing belt 41, so that the detection member 50 rotates the fixing belt 41. Can be prevented from being loaded. As a result, breakage or wear of the fixing belt 41 can be suppressed.

  Sixth Embodiment

  FIG. 11 is a top view showing the configuration of the fixing device 40 according to the sixth embodiment of the present invention. FIG. 12 is a perspective view showing the configuration of a driven member 541 in the sixth embodiment of the present invention.

  Referring to FIGS. 11 and 12, detection member 50 in the present embodiment includes driven member 541 and light sensor 542 (an example of a sensor). The driven member 541 has a disk shape, and is provided at the end of the pressure roller 44 in the rotation axis direction. The outer circumferential surface of the driven member 541 is in contact with a detection position SP provided on the outer surface of the fixing belt 41. Accordingly, the driven member 541 is driven to rotate in the direction indicated by the arrow AR11 in accordance with the rotation of the fixing belt 41 (rotation in the direction indicated by the arrow AR12). The driven member 541 has the same rotation axis as the rotation axis of the pressure roller 44, and rotates independently of the rotation of the pressure roller 44.

  The outer peripheral surface of the driven member 541 has a reflectance that changes periodically along the rotation direction of the driven member 541. Specifically, on the outer peripheral surface of the driven member 541, a plurality of films of the same shape made of a highly reflective material such as aluminum foil are provided at equal intervals along the rotational direction of the driven member 541. .

  The light sensor 542 detects the rotation of the driven member 541 and is made of, for example, a reflection type photo interrupter. The light sensor 542 is provided near the outer peripheral surface of the driven member 541 at a distance from the driven member 541. The light sensor 542 emits light to the outer peripheral surface of the driven member 541 as indicated by an arrow AR31, and receives the reflected light. The light sensor 542 outputs the rotation detection unit 31 according to the amount of received light.

  The amount of light received by the optical sensor 542 increases when the light emitted from the optical sensor 542 is reflected by the film, and decreases when reflected by a position other than the film. Do. The rotation detection unit 31 detects the rotation of the fixing belt 41 based on a periodic change in the amount of light received by the light sensor 542 (the detection result of the light sensor 542).

  The configurations and the operations of the image forming apparatus and the fixing device other than the above are the same as the configurations and the operations of the image forming apparatus and the fixing device in the first embodiment. And their description will not be repeated.

  According to the present embodiment, the movement of the fixing belt 41 can be detected in a state of being in contact with the fixing belt 41 by including the driven member 541 that is driven to rotate by the rotation of the fixing belt 41. As a result, the rotation of the fixing belt 41 can be detected with a simple configuration. Further, by making the driven member 541 and the pressure roller 44 coaxial with each other, the diameter of the driven member 541 can be increased. Thus, the frictional force between the driven member 541 and the fixing belt 41 can be increased, and a situation where the driven member 541 slips on the fixing belt 41 can be avoided.

  Seventh Embodiment

  FIG. 13 is a front view showing the configuration of the fixing device 40 according to the seventh embodiment of the present invention. FIG. 13A is a view showing a state in which the projection member 63 exists at the detection position SP. FIG. 13B is a view showing a state in which the projection member 63 is not present at the detection position SP. In FIG. 13, the pressure roller 44 is not shown. FIG. 14 is a view showing the configuration of the optical sensor 553 according to the seventh embodiment of the present invention, and showing the configuration when viewed from the side of the rotation shaft 551a.

  Referring to FIGS. 13 and 14, fixing device 40 in the present embodiment includes protruding member 63. The projecting member 63 is provided in a region which passes the detection position SP when the fixing belt 41 rotates. The projecting member 63 has a shape that is convex with respect to the outer surface of the fixing belt 41 along the rotation direction of the fixing belt 41. The projecting member 63 goes around the fixing belt 41 in accordance with the rotation of the fixing belt 41 (in the direction indicated by the arrow AR12). Here, although the number of the projecting members 63 is one, the number of the projecting members 63 is arbitrary.

  The detection member 50 in the present embodiment includes a contact portion 551, an arm portion 552, and a light sensor (photo sensor) 553. The contact portion 551 and the arm portion 552 (an example of the contact member) can swing around the rotation shaft 551a. The rotating shaft 551 a is provided at the upper end of the contact portion 551. The surface on the fixing belt 41 side in the contact portion 551 contacts a detection position SP provided on the outer surface of the fixing belt 41. The arm 552 has a rod-like shape with a sufficient length. An upper end portion of the arm portion 552 is fixed to a lower end portion of the contact portion 551.

  The light sensor 553 is provided at a position through which the lower end 552 a of the arm 552 passes. The light sensor 553 includes a light source 553a and a light receiving unit 553b. The light source 553a and the light receiving unit 553b face each other across a locus TC drawn by the lower end portion 552a of the arm portion 552 when the arm portion 552 moves. The light source 553a emits light to the light receiving unit 553b as indicated by an arrow AR43. The light receiving unit 553 b receives the light and outputs the rotation detection unit 31 according to the amount of received light.

  The contact portion 551 and the arm portion 552 periodically contact with the projecting member 63 when the fixing belt 41 rotates. When the protruding member 63 moves to reach the detection position SP due to the rotation of the fixing belt 41, the contact portion 551 contacts the protruding member 63 as shown in FIG. 13A. The contact portion 551 and the arm portion 552 move (rock) as indicated by the arrow AR41. The lower end 552a of the arm 552 moves between the light source 553a and the light receiving unit 553b. The light from the light source 553a is blocked by the lower end portion 552a, and the amount of light received by the light receiving portion 553b is reduced.

  When the projecting member 63 moves and leaves the detection position SP due to the rotation of the fixing belt 41, the contact portion 551 is released from the projecting member 63, as shown in FIG. 13B. The contact portion 551 and the arm portion 552 move (rock) as indicated by the arrow AR42. The lower end portion 552a of the arm portion 552 is disengaged from between the light source 553a and the light receiving portion 553b. The amount of light received by the light receiving unit 553b recovers to the original amount of light received.

  As described above, each time the protruding member 63 passes the detection position SP, the output of the light receiving unit 553b temporarily decreases. The rotation detection unit 31 detects the rotation of the fixing belt 41 based on the output value from the light receiving unit 553b (the movement of the contact unit 551 and the arm unit 552).

  The impact applied to the fixing belt 41 when the detecting member 50 contacts the projecting member 63 is reduced, and the detecting member 50 is assured of variation in the height of the surface of the fixing belt 41 when the projecting member 63 passes the detection position SP. Preferably, the projecting member 63 is small in order to follow. Further, it is preferable that the boundary between both end portions of the projection member 63 and the surface of the fixing belt 41 in the rotation direction of the fixing belt 41 (the direction indicated by the arrow AR12) be gentle. On the other hand, it is preferable that the arm portion 552 be long in order to amplify the change in position when the detection member 50 contacts the projection member 63.

  The configurations and the operations of the image forming apparatus and the fixing device other than the above are the same as the configurations and the operations of the image forming apparatus and the fixing device in the first embodiment. And their description will not be repeated.

  The detection member 50 in the present embodiment can amplify the fluctuation of the position of the detection member 50 due to the contact with the projection member 63 by including the arm portion 552. Thus, the detection accuracy of the movement of the fixing belt 41 can be improved.

  FIG. 15 is a cross-sectional view showing the configuration in the vicinity of the projecting member 63 of the fixing device 40 of the first modified example of the seventh embodiment of the present invention. FIG. 15 is a cross-sectional view of the fixing belt 41 as viewed in a cross section perpendicular to the rotation axis.

  Referring to FIG. 15, the fixing belt 41 of the present modification includes a base layer 411, a rubber layer 412 (an example of an underlayer), and a toner release layer 413 (an example of a release layer). The base layer 411 is endless and provided on the innermost side of the fixing belt 41. The base layer 411 is made of polyimide (PI) or the like. The rubber layer 412 is endless and is provided on the outer diameter side of the base layer 411. The toner release layer 413 is endless and is provided on the outer diameter side of the rubber layer 412. The toner release layer 413 is provided on the outermost surface of the fixing belt 41 and is in contact with the pressure roller 44. The toner release layer 413 is made of PFA or the like.

  The protruding member 63 is provided between the rubber layer 412 and the toner release layer 413. When viewed in the cross section shown in FIG. 15, the projecting member 63 has a continuous shape from both ends to the vertex in the rotation direction (direction indicated by the arrow AR12) of the fixing belt 41. The projecting member 63 also includes a hollow portion 63a. The hollow portion 63a is filled with air or the like. The toner releasing layer 413 present on the outer diameter side of the protruding member 63 locally protrudes on the outer diameter side of the fixing belt 41 together with the protruding member 63.

  According to this modification, since the projection member 63 is covered by the surface layer of the fixing belt 41, the contact portion 551 of the detection member 50 can smoothly trace the portion of the fixing belt 41 where the projection member 63 exists. . As a result, the protrusion member 63 is less likely to be peeled off, and the friction of the contact portion 551 is reduced, and damage to the fixing belt 41 can be reduced.

  Further, by providing the hollow portion 63a inside the projection member 63, the projection member 63 is deformed by the force received from the contact portion 551 when the projection member 63 contacts the contact portion 551 while securing the height of the projection member 63. It is possible to Thereby, the force received from the contact portion 551 can be relaxed while securing the height of the projection member 63. In addition, since heat can be transmitted to the inside of the hollow portion 63a, the heat shock of the projection member 63 due to a rapid temperature rise can be mitigated.

  FIG. 16 is a cross-sectional view showing the configuration in the vicinity of the projecting member 63 of the fixing device 40 of the second modified example of the seventh embodiment of the present invention. FIG. 16 is a cross-sectional view of the fixing belt 41 as viewed in a cross section orthogonal to the rotation axis.

  Referring to FIG. 16, the projecting member 63 of this modification is made of a heat-resistant elastic material such as silicone rubber. When viewed in the cross section shown in FIG. 16, the projecting member 63 has a continuous shape from both ends to the vertex in the rotation direction (direction indicated by the arrow AR12) of the fixing belt 41. The projecting member 63 is adhered to the outer surface of the fixing belt 41 by an adhesive 64 at the downstream end (the end on the left side in FIG. 16) of the fixing belt 41 in the rotational direction. The upstream end (the end on the right side in FIG. 16) of the protruding member 63 in the rotational direction of the fixing belt 41 is not adhered to the outer surface of the fixing belt 41.

  When the protruding member 63 is adhered to the fixing belt 41, the fixing belt 41 receives a force from the protruding member 63 due to the thermal expansion of the protruding member 63 or the deformation due to the rotational movement. According to this modification, since the projection member 63 is formed of a heat-resistant elastic body, the projection member 63 is deformed so as to conform to the shape of the fixing belt 41. Thereby, the force applied to the fixing belt 41 can be reduced.

  When it is intended to make the projecting member 63 a gentle shape, the length of the fixing belt 41 in the rotational direction (the direction indicated by the arrow AR12) increases. When the length in the rotational direction of the fixing belt 41 in the projecting member 63 increases, the area of the surface of the fixing belt 41 in contact with the projecting member 63 increases, and a large area of the surface of the fixing belt 41 receives force from the projecting member 63 It will be.

  According to this modification, since the downstream end of the fixing belt 41 in the rotational direction of the protruding member 63 is not adhered, part of the force that the fixing belt 41 receives from the protruding member 63 can be released. The force received by the fixing belt 41 from the projecting member 63 can be relaxed.

  Eighth Embodiment

  When unnecessary deformation occurs in the fixing belt 41 which can not be completely suppressed even by the fixing nip NP (for example, the fixing belt 41 is not used for a long time and the fixing belt 41 is in a state where unnecessary deformation (癖) is generated). If, for example, the temperature rises or flapping occurs, the detection member 50 may misidentify an unnecessary deformation generated in the fixing belt 41 as the projection member 63. In order to avoid such a situation, when detecting the movement of the fixing belt 41, the detecting member 50 in the present embodiment is configured to determine whether the movement of the fixing belt 41 is caused by the projection member 63 or the fixing belt 41. Distinguish whether it is due to unnecessary deformation.

  FIGS. 17 to 20 are views showing the configuration in the vicinity of the detecting member 50 of the fixing device 40 according to the eighth embodiment of the present invention. 17 is a top view, FIG. 18 is a perspective view, FIG. 19 is a front view, and FIG. 20 is a side view. In FIG. 18 to FIG. 20, the configuration of a part of the fixing device 40 and the detection member 50 is omitted.

  Referring to FIGS. 17 to 20, fixing device 40 in the present embodiment includes protruding member 63. Referring to FIG. The configuration of projecting member 63 is the same as that of the seventh embodiment, and therefore the description thereof will not be repeated.

  Detection member 50 in the present embodiment includes shaft member 561 (an example of a first member), fixing member 562, shaft member 563 (an example of a second member), and optical sensor 564 (an example of a sensor). Contains.

  The shaft member 561 includes two front end portions 561a and 561b, a rotating shaft 561c, and a rear end portion 561d. The end portions 561 a and 561 b are portions where the end of the rotation shaft 561 c on the fixing belt 41 side is branched into two. The leading end portion 561 a always contacts the outer surface of the fixing belt 41 when the fixing belt 41 rotates, and does not contact the projecting member 63. The leading end portion 561 b contacts the outer surface of the fixing belt 41 when the fixing belt 41 rotates, and periodically contacts the protruding member 63. The position of the outer surface of the fixing belt 41 in contact with the leading end portion 561b is the detection position SP. The shaft member 561 rotates in a direction indicated by an arrow AR51 about a rotation shaft 561c extending in the x-axis direction when the tip end portion 561b contacts the projection member 63.

  Hereinafter, the posture of the shaft member 561 when the tip portion 561b is not in contact with the projection member 63 is referred to as a basic posture, and the posture of the shaft member 561 when the tip portion 561b is in contact with the projection member 63 (arrow AR51 The posture rotated in the direction shown may be referred to as a detection posture.

  The shaft member 561 is movable in the z-axis direction. The rear end portion 561 d is an end portion of the rotation shaft 561 c opposite to the fixing belt 41. The rear end portion 561 d is fixed to the image forming apparatus main body 1 a so as to enable the above-described movement of the shaft member 561.

  The fixing member 562 fixes the vicinity of the tip end portion of the shaft member 563 to the rotating shaft 561 c. The shaft member 563 extends in the y-axis direction. When the shaft member 561 rotates in the direction indicated by the arrow AR51, the shaft member 563 swings (moves) in the direction indicated by the arrow AR52 with the shaft member 561 as a central axis.

  The light sensor 564 detects the swing of the shaft member 563. The optical sensor 564 is provided at a position where the rear end 563 a of the shaft member 563 exists when the shaft member 561 is in the basic posture. The light sensor 564 includes a light source 564a and a light receiving unit 564b. The light source 564a and the light receiving unit 564b face each other so as to sandwich the rear end portion 563a when the shaft member 561 is in the basic posture. The light source 564a emits light to the light receiving unit 564b as indicated by an arrow AR53. The light receiving unit 564 b receives the light and outputs an output according to the received light amount to the rotation detection unit 31. When the shaft member 561 is in the basic posture, the light from the light source 564a is blocked by the rear end portion 563a, so the amount of light received by the light receiving portion 564b is low.

  When the protruding member 63 reaches the detection position SP due to the rotation of the fixing belt 41, the leading end portion 561b contacts the protruding member 63. The shaft member 561 rotates in the direction indicated by the arrow AR51, and shifts from the basic posture to the detection posture. The shaft member 563 swings in the direction indicated by the arrow AR52. The light from the light source 564a is received by the light receiving unit 564b without being blocked by the rear end 563a. Thus, the amount of light received by the light receiving unit 564b is increased.

  Thereafter, when the projection member 63 passes the detection position SP by the rotation of the fixing belt 41, the shaft member 561 returns to the basic posture. Since the light from the light source 564a is blocked by the rear end 563a, the amount of light received by the light receiver 564b is reduced.

  As described above, each time the protruding member 63 passes the detection position SP, the output of the light receiving unit 564b temporarily increases. The rotation detection unit 31 detects the rotation of the fixing belt 41 based on the output value (the swing of the shaft member 563) from the light receiving unit 564b.

  By the way, the unnecessary deformation generated in the fixing belt 41 usually occurs along the rotation axis direction of the fixing belt 41. Therefore, when the fixing belt 41 generates unnecessary deformation and the deformed portion of the fixing belt 41 passes the detection position SP, both of the leading end portions 561a and 561b are shown by the arrow AR53. Ascends (moves) in the outer diameter direction. When both of the tip portions 561a and 561b rise, the shaft member 563 moves in the direction indicated by the arrow AR52, but the amount of movement is small. The light from the light source 564a remains blocked by the rear end portion 563a, and the amount of light received by the light receiving portion 564b remains reduced.

  As described above, when the fixing belt 41 undergoes unnecessary deformation and the deformed portion of the fixing belt 41 passes the detection position SP, the output of the light receiving unit 564b does not change. Therefore, the rotation detection unit 31 does not erroneously recognize the unnecessary deformation of the fixing belt 41 as the projection member 63, and does not erroneously detect the rotation of the fixing belt 41.

  Referring particularly to FIG. 17, fixing device 40 further includes a side plate 46 supporting fixing belt 41. The side plate 46 is provided at an end of the fixing belt 41 in the rotational axis direction. The side plate 46 further supports the shaft member 563 so as to be pivotable in the direction indicated by the arrow AR52. The light sensor 564 is separated from the fixing belt 41 by the side plate 46 in the rotational axis direction of the fixing belt 41.

  The configurations and the operations of the image forming apparatus and the fixing device other than the above are the same as the configurations and the operations of the image forming apparatus and the fixing device in the first embodiment. And their description will not be repeated.

  According to the present embodiment, the detection member 50 can distinguish whether the movement of the fixing belt 41 is due to the projection member 63 or the unnecessary deformation of the fixing belt 41. Therefore, the detection accuracy of the rotation of the fixing belt 41 can be improved. Further, when the fixing device 40 has a light pressure contact mode and a high pressure contact mode as the pressure contact state between the fixing belt 41 and the pressure roller 44, the difference in the bending of the fixing belt 41 due to the difference in the pressure contact state is also It can correspond. Further, by providing the side plate 46, heat transfer from the fixing belt 41 to the light sensor 564 can be suppressed, and detection failure of the light sensor 564 due to heat can be prevented.

  [Others]

  The embodiments and examples described above should be considered as illustrative in all points and not restrictive. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all the modifications within the meaning and scope equivalent to the claims.

DESCRIPTION OF SYMBOLS 1 image forming apparatus 1 a image forming apparatus main body 10 sheet conveying unit 11 sheet feeding tray 12 sheet feeding roller 13 conveying roller 14 sheet discharging roller 15 sheet discharging tray 20 toner image forming unit 21 image forming unit 22 intermediate transfer belt 22 a rotating roller 23 primary Transfer roller 24 Secondary transfer roller 25 Photosensitive drum 26 Charge roller 27 Exposure device 28 Development device 29 Cleaning device 30 Control unit 31 Rotation detection unit (an example of rotation detection means)
40 fixing device 41 fixing belt 42 pad (example of pressing member)
42a Pad hollow portion 43 heater (example of heating member)
44 Pressure roller (example of pressure member)
45 pad frame 46 side plate 50 detection member 61 marking portion 62 magnet 63 protrusion member 63 a hollow portion of protrusion member 64 adhesive 411 base layer 412 rubber layer (example of base layer)
413 Toner Release Layer (Example of Release Layer)
511, 542, 553, 564 Optical sensor (an example of a sensor)
512 light guide 521 disk 531 coil 541 driven member 551 contact portion (an example of the contact member)
551a Rotating shaft of contact portion and arm portion 552 Arm portion (an example of contact member)
552a lower end portion of arm portion 553a, 564a light source of light sensor 553b, 564b light receiving portion of light sensor 561, 563 shaft member (example of first and second members)
561a, 561b shaft member end portion 561c shaft member rotation shaft 561d, 563a shaft member rear end portion 562 fixing member M sheet NP fixing nip PO portion where pressing roller faces the pad through the fixing belt SP detection position TC TP A locus drawn by the lower end of the arm when moving the arm TP Position of the fixing belt at the end of the fixing belt relative to the pressure roller in the rotational axis direction of the fixing belt TR Transport path W Nip width

Claims (21)

A fixing device for fixing a toner image to the transfer material by passing the transfer material through a fixing nip,
A rotating endless fixing belt,
A heating member for heating the fixing belt;
A pressing member provided inside the fixing belt;
A pressure member provided at a position facing the pressing member via the fixing belt and forming the fixing nip with the fixing belt by pressing the fixing belt against the pressing member;
A detection member that detects the movement of the fixing belt;
A rotation detection unit that detects the rotation of the fixing belt based on the detection result of the detection member;
The fixing device detects a movement of the fixing belt at a detection position outside the fixing belt and at a detection position facing the pressing member via the fixing belt. The length of the pressing member in the rotation axis direction of the fixing belt is longer than the length of the fixing belt in the rotation axis direction of the fixing belt,
The fixing device according to claim 1, wherein a length of the fixing belt in a rotation shaft direction of the fixing belt is longer than a length of the pressing member in a rotation shaft direction of the fixing belt.   The fixing device according to claim 1, wherein the detection position is a position closer to an end portion of the fixing belt than the pressure member in the rotation shaft direction of the fixing belt.   The fixing device according to any one of claims 1 to 3, wherein the detection position is a position where the fixing nip is present in the transport direction of the transfer material.   The fixing device according to any one of claims 1 to 4, wherein the fixing nip and the detection position are on the same straight line when viewed in a cross section taken along a plane including the rotation axis direction of the fixing belt.   The fixing device according to any one of claims 1 to 5, wherein the pressure member is rotationally driven, and the fixing belt is a free belt that follows the rotation of the pressure member.   The fixing device according to claim 1, wherein the detection member does not contact the fixing belt. The image forming apparatus further includes a marking unit provided in an area passing through the detection position when the fixing belt rotates, and having a reflectance that periodically changes along the rotation direction of the fixing belt.
The detection member includes an optical sensor that emits light to the marking portion present at the detection position and receives the reflected light.
The fixing device according to claim 7, wherein the rotation detection unit detects the rotation of the fixing belt based on a periodic change in the amount of light received by the light sensor.   The detection member further includes a guide portion which guides the light from the light sensor to the marking portion present at the detection position, and guides the light reflected by the marking portion present at the detection position to the light sensor. The fixing device according to claim 8. It further comprises a magnet provided in an area passing through the detection position when the fixing belt rotates.
The detection member includes a disk which is provided at a distance from the magnet and which is rotated by the fluctuation of the magnetic field from the magnet due to the rotation of the fixing belt.
The fixing device according to claim 7, wherein the rotation detection unit detects the rotation of the fixing belt based on the rotation of the disk. It further comprises a magnet provided in an area passing through the detection position when the fixing belt rotates.
The detection member is provided at a distance from the magnet, and includes a coil that generates an electromotive force due to a change in the magnetic field of the magnet caused by the rotation of the fixing belt.
The fixing device according to claim 7, wherein the rotation detecting unit detects the rotation of the fixing belt based on information indicating an electromotive force generated in the coil.   The fixing device according to claim 1, wherein the detection member contacts the fixing belt. The detection member is
A driven member that contacts the detection position provided on the outer surface of the fixing belt, is driven to rotate by rotation of the fixing belt, and has the same rotation axis as the rotation axis of the pressure member;
A sensor for detecting the rotation of the driven member;
The fixing device according to claim 12, wherein the rotation detection unit detects the rotation of the fixing belt based on a detection result of the sensor. The fixing belt further includes a projecting member provided in a region passing through the detection position when the fixing belt rotates, and convex with respect to the outer surface of the fixing belt along the rotation direction of the fixing belt.
The detection member includes a contact member that moves when in contact with the projection member,
The fixing device according to claim 12, wherein the rotation detecting unit detects the rotation of the fixing belt based on the movement of the contact member. The fixing belt is
Endless base layer,
And an endless release layer provided on the outer diameter side of the base layer and in contact with the pressure member,
The protrusion member is provided between the base layer and the release layer,
The fixing device according to claim 14, wherein when viewed in a cross section orthogonal to the rotation axis of the fixing belt, the protruding members have a continuous shape from both end portions in the rotation direction of the fixing belt to a vertex.   The fixing device according to claim 14, wherein the protrusion member includes a hollow portion.   One end of the projecting member in the rotational direction of the fixing belt is bonded to the outer surface of the fixing belt, and the other end of the projecting member in the rotational direction of the fixing belt is the fixing belt The fuser device of claim 14, wherein the fuser device is not adhered to the outer surface of the belt. The contact member is
A first member that rotates around a rotation axis extending in a first direction when in contact with the projection member, and is movable in a second direction orthogonal to the first direction;
A second member fixed to the first member, extending in a third direction orthogonal to each of the first and second directions, and swinging with rotation of the first member;
And a sensor that detects the swing of the second member,
The fixing device according to claim 14, wherein the rotation detection unit detects the rotation of the fixing belt based on a detection result of the sensor. The fixing belt further includes a side plate provided at an end in the rotational axis direction of the fixing belt and swingably supporting the second member.
The fixing device according to claim 18, wherein the sensor is separated from the fixing belt by the side plate in a rotation shaft direction of the fixing belt.   The fixing device according to any one of claims 1 to 19, wherein the pressing member includes a hollow portion at a position facing the detection position via the fixing belt. A toner image forming unit for forming the toner image on the transfer material;
An image forming apparatus comprising the fixing device according to any one of claims 1 to 21.

Images