JP2016224381A - Belt device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt device and an image formation device with which it is possible to reduce, by a simple structure, the vibration of the support member of a rubbing member caused by a friction force generated between an endless belt and the rubbing member.SOLUTION: A belt device 70 has an endless belt 7 and a plurality of rubbing members 51 that rub the belt 7 supported by a rotatable support member 53 and moving, the plurality of rubbing members 51 including a first rubbing member whose belt winding angle is a first angle and a second rubbing member whose belt winding angle is a second angle larger than the first angle. The belt device is configured so that a revolving center placement angle θy pertaining to the second rubbing member is different from revolving center placement angles θm, θc, θk pertaining to the first rubbing member, where the angle formed by a straight line linking the center point of a contact part between the belt 7 and the rubbing members 51 and the revolving center of the support member 53 is defined as a revolving center placement angle θ.SELECTED DRAWING: Figure 14

Description

  The present invention relates to a belt device having an endless belt used in an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus using an electrophotographic method or an electrostatic recording method, and an image forming device including the belt device. It relates to the device.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method or an electrostatic recording method, an appropriate image is formed on a drum-shaped or belt-shaped electrophotographic photosensitive member (photosensitive member) or an image carrier that is an electrostatic recording dielectric. A toner image is formed in the process. The toner image is directly transferred to a recording material conveyed by a recording material carrier (direct transfer method), or is first transferred to an intermediate transfer member and then secondarily transferred to a recording material (intermediate transfer method). . An endless belt is often used as a recording material carrier or an intermediate transfer member. As such an image forming apparatus, for example, there is a tandem type image forming apparatus that independently includes an image forming unit that forms an image with toners of yellow, magenta, cyan, and black.

  An image forming apparatus adopting an intermediate transfer method and a tandem method for forming an image using an electrophotographic method will be further described as an example. This image forming apparatus has, for example, a photosensitive drum, which is a drum-type photosensitive member, as an image carrier, and an intermediate transfer belt constituted by an endless belt as an intermediate transfer member. The toner image formed on the photosensitive drum is primarily transferred to the intermediate transfer belt by the action of a transfer member (primary transfer member) provided to face each photosensitive drum via the intermediate transfer belt.

  As the primary transfer member, a member that rubs an intermediate transfer belt that moves (endlessly moves) such as a pad-like, brush-like, or blade-like member may be used. Such a primary transfer member typically contacts the inner peripheral surface of the intermediate transfer belt at the surface. Such a primary transfer member has a relatively large frictional force with the intermediate transfer belt, and may cause a so-called stick-slip phenomenon in which deformation and restoration are repeated due to movement of the intermediate transfer belt. As a result, vibration of the primary transfer member may occur as noise.

  Therefore, there is a method in which a rotation fulcrum is provided on a support member that supports the primary transfer member so that the primary transfer member can stably come into contact with the intermediate transfer belt even during an image forming operation so that the support member can be rotated ( Patent Document 1).

  Further, in a tandem image forming apparatus, output of a color image is not always required, and for example, output of a black monochrome image is often required. For this reason, when outputting a black monochrome image, there is a type in which the rotation of the photosensitive drums of the image forming units other than black is stopped while all the photosensitive drums are in contact with the intermediate transfer belt. However, in this case, the intermediate transfer belt and the photosensitive drum easily deteriorate due to friction between the stopped photosensitive drum and the intermediate transfer belt.

  Therefore, when outputting a black monochrome image, there is a method in which the primary transfer member is separated from the photosensitive drum in the image forming unit other than black, and the intermediate transfer belt and the photosensitive drum are separated (Patent Document 2). In Patent Document 2, the contact position between the photosensitive drum for black and the intermediate transfer belt is arranged in the direction in which the intermediate transfer belt is pushed into a straight line connecting the contact positions between the photosensitive drums for other colors and the intermediate transfer belt. Is disclosed. Thus, when outputting a black monochrome image, the distance between the photosensitive drum of the image forming unit other than black and the intermediate transfer belt can be sufficiently increased.

JP 2007-187867 A JP 2014-163958 A

  However, for example, when an arrangement mode of the photosensitive drum as described in Patent Document 2 is employed, depending on the image forming unit, there is a case where a force is exerted by the intermediate transfer belt to push down the primary transfer member.

  In the case where the primary transfer member that rubs the intermediate transfer belt is supported by a rotatable support member, if the balance of the force applied to the support member is unstable when a stick-slip occurs, vibration is generated. And noise may occur. This is because the direction of the force applied to the rotation shaft of the support member is changed by the movement of the intermediate transfer belt in the image forming portion where the force to push down the primary transfer member is applied by the intermediate transfer belt as described above. The case becomes noticeable.

  In the above, the intermediate transfer type image forming apparatus has been described as an example, but the same problem may occur in the direct transfer type image forming apparatus. The same problem may occur in any belt device having an endless belt and a rubbing member supported by a rotatable support member that rubs the moving belt.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a belt device and an image forming device that can reduce vibrations of a supporting member of a rubbing member due to a frictional force generated between the endless belt and the rubbing member with a simple configuration. Is to provide a device.

  The above object is achieved by the belt device and the image forming apparatus according to the present invention. In summary, the present invention is provided with a plurality of stretching rollers, a movable endless belt stretched around the plurality of stretching rollers, and an inner peripheral surface of the belt so as to be in contact with the belt. A plurality of rubbing members that rub against the belt as the belt moves, and a plurality of rubbing members that respectively support the plurality of rubbing members and have a rotation shaft. The plurality of support members, a plurality of holding portions that respectively hold the rotation shafts of the plurality of support members, and the plurality of supports so as to press the plurality of rubbing members toward the inner peripheral surface of the belt. A plurality of rubbing members, wherein the wrapping angle of the belt on the upstream side of the contact portion in the moving direction of the belt is a first angle of a first angle. The first rubbing member and the first angle A second rubbing member having a larger second angle, and when viewed in a direction substantially perpendicular to the moving direction of the belt, each of the plurality of rubbing members in the moving direction of the belt The rotation about the second rubbing member when an angle formed by a straight line connecting the center point of the contact portion and the rotation center of the support member and an arbitrary reference line is a rotation center arrangement angle. The belt arrangement is characterized in that a center arrangement angle is different from the rotation center arrangement angle with respect to the first rubbing member.

  According to another aspect of the present invention, a plurality of image carriers, a plurality of stretching rollers, and an endless belt that is stretched by the plurality of stretching rollers and is movable in contact with the plurality of image carriers. And is provided so as to be able to come into contact with the inner peripheral surface of the belt so as to face each of the plurality of image carriers via the belt, and with the movement of the belt at a contact portion with the inner peripheral surface of the belt A plurality of rubbing members for rubbing the belt, a plurality of rotatable support members that respectively support the plurality of rubbing members and have a rotation shaft, and rotation shafts of the plurality of support members. An image forming apparatus comprising: a plurality of holding portions that respectively hold; and pressing means that respectively press the plurality of support members so as to press the plurality of rubbing members toward the inner peripheral surface of the belt. The plurality of rubbing members are configured to transfer the belt. A first rubbing member having a first winding angle of the belt on the upstream side of the contact portion in a direction and a second rubbing member having a second angle larger than the first angle. A center point of the contact portion in the moving direction of the belt and a rotation center of the support member with respect to each of the plurality of rubbing members when viewed in a direction substantially perpendicular to the moving direction of the belt. When the angle formed by the connected straight line and an arbitrary reference straight line is a rotation center arrangement angle, the rotation center arrangement angle related to the second rubbing member is the rotation related to the first rubbing member. An image forming apparatus is provided that is different from the central arrangement angle.

  ADVANTAGE OF THE INVENTION According to this invention, the vibration of the supporting member of a rubbing member resulting from the frictional force which generate | occur | produces between an endless belt and a rubbing member can be reduced with a simple structure.

1 is a schematic sectional view of an image forming apparatus. It is a schematic perspective view of an intermediate transfer unit. It is a top view of a primary transfer unit. FIG. 6 is a cross-sectional view in the short-side direction of the primary transfer unit. It is the side view and perspective view of a primary transfer member. FIG. 6 is a perspective view and a longitudinal sectional view of a periphery of a support member of a primary transfer unit. It is a side view of a primary transfer unit. FIG. 6 is a cross-sectional view illustrating a contact state of the primary transfer unit in the color mode and (b) the monochrome mode. FIG. 6 is a cross-sectional view for explaining the force applied to the primary transfer unit of the first image forming unit (comparative example). FIG. 6 is a cross-sectional view for explaining a force applied to a primary transfer unit of a second image forming unit (comparative example and example). FIG. 6 is a cross-sectional view for explaining a force applied to a primary transfer unit of a third image forming unit (comparative example and example). FIG. 10 is a cross-sectional view for explaining a force applied to a primary transfer unit of a fourth image forming unit (comparative example and example). FIG. 6 is a cross-sectional view for explaining the force applied to the primary transfer unit of the first image forming unit (Example). FIG. 6 is a cross-sectional view showing the arrangement relationship of each primary transfer unit.

  Hereinafter, the belt device and the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[Example 1]
1. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a laser beam printer that employs an intermediate transfer method or a tandem method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes, as a plurality of image forming units (stations), first, second, third, and third images that form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. A fourth image forming unit SY, SM, SC, SK is included. Note that elements having the same functions and configurations provided in the image forming units SY, SM, SC, and SK are not particularly distinguished, and are suffixed with “ Y, “M”, “C”, and “K” are omitted, and the elements will be described collectively.

  In the image forming unit S, a photosensitive drum 1 that is a rotatable drum type electrophotographic photosensitive member (photosensitive member) as an image carrier is disposed. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 which is a roller-type charging member as a charging unit. The surface of the charged photosensitive drum 1 is exposed according to image information by an exposure device (laser scanner) 3 as an exposure means (image writing means), and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. Is done. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) using a toner as a developer by a developing device 4 as a developing unit, and a toner image is formed on the photosensitive drum 1. In this embodiment, a toner image is formed by image portion exposure and reversal development. That is, the exposed portion on the photosensitive drum 1 whose absolute value of potential has been lowered by being exposed after being uniformly charged is charged to the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1. Adhered toner adheres.

  Opposite to each photosensitive drum 1 of each image forming section S, an intermediate transfer belt 7 constituted by an endless belt as an intermediate transfer member is disposed. The intermediate transfer belt 7 is an example of an endless belt (endless moving member) that is stretched by a plurality of stretching rollers and is movable in contact with a plurality of image carriers. The intermediate transfer belt 7 is rotationally driven in the direction of arrow R2 in the figure. The toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt by the action of the primary transfer unit 5 as a primary transfer unit in a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other. 7 is electrostatically transferred (primary transfer). At this time, a primary transfer bias (primary transfer voltage) having a polarity opposite to the charging polarity (normal charging polarity) of the toner at the time of development is applied to a primary transfer member 51 described later of the primary transfer unit 5. For example, when forming a full-color image, the toner images of the respective colors formed on the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially transferred so as to be superimposed on the intermediate transfer belt 7. The toner remaining on the photosensitive drum 1 after the primary transfer is removed from the photosensitive drum 1 and collected by a drum cleaner 6 as a photosensitive member cleaning means.

  On the other hand, a recording material (recording medium, transfer material, sheet) P such as recording paper stored in the cassette 10 is transferred to a secondary transfer portion (secondary transfer) by a feeding roller 11, a conveyance roller 12, a separation roller 13, and a registration roller 14. (Next transfer nip) conveyed to N2. The secondary transfer portion N2 is a contact portion between the intermediate transfer belt 7 and the secondary transfer roller 8 that is a roller-type secondary transfer member serving as a secondary transfer unit. The toner image formed on the intermediate transfer belt 7 is electrostatically transferred onto the recording material P that is nipped and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8 in the secondary transfer portion N2. (Secondary transfer). At this time, a secondary transfer bias (secondary transfer voltage) having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 8. The toner remaining on the intermediate transfer belt 7 after the secondary transfer (secondary transfer residual toner) is removed from the intermediate transfer belt 7 and collected by an intermediate transfer body cleaning unit (not shown).

  The recording material P onto which the toner image has been transferred is heated and pressed by a fixing device 15 as a fixing unit, and the toner image is fixed thereon. The recording material P on which the toner image is fixed is discharged (output) to a discharge tray 18 by a discharge roller 16 and a discharge roller 17.

  The image forming apparatus 100 according to the present exemplary embodiment can execute a color mode (color print) capable of forming a full-color image and a monochrome mode (monochrome print) capable of forming a black single-color image. In the color mode, a full color image can be formed by the process as described above using all of the first, second, third, and fourth image forming units SY, SM, SC, and SK. On the other hand, in the monochrome mode, a black single-color image can be formed by using the same process as described above using only the fourth image forming unit SK. As will be described in detail later, the contact / separation state between the photosensitive drums 1Y, 1M, 1C, and 1K and the intermediate transfer belt 7 is changed between the color mode and the monochrome mode.

  Each image forming section S is constituted by the photosensitive drum 1, the charging roller 2, the exposure device 3 for writing an image of each color component, the developing device 4, the primary transfer unit 5, and the drum cleaner 6. Further, the photosensitive drum 1 of each image forming unit S, the charging roller 2, the developing device 4 and the drum cleaner 6 as process means acting on the photosensitive drum 1 are integrated with the apparatus main body 110 of the image forming apparatus 100. The removable process cartridge 9 is configured.

2. Intermediate Transfer Unit Next, the intermediate transfer unit 70 as a belt device in this embodiment will be described.

  Here, regarding the image forming apparatus 100, the right side of FIG. 1 is “front (front)”, the left side of FIG. 1 is “back (rear)”, the front side of FIG. 1 is “left”, and the back side of FIG. Is “right”. Further, regarding the image forming apparatus 100, the upper side in FIG. 1 is “upper” and the lower side in FIG. 1 is “lower”. A line connecting the left side and the right side of the image forming apparatus 100 (a line substantially perpendicular to the paper surface of FIG. 1) is substantially parallel to the rotational axis direction of the photosensitive drum 1 and is substantially orthogonal to the moving direction of the intermediate transfer belt 7. A door 120 that opens the inside of the apparatus main body 110 is provided on the front surface of the image forming apparatus 100. By opening the door 120, each process cartridge 9 and the intermediate transfer unit 70 can be attached to and detached from the apparatus main body 110.

  FIG. 2 is a schematic perspective view of the intermediate transfer unit 70. In FIG. 2, the intermediate transfer belt 7 is not shown. The intermediate transfer unit 70 includes an intermediate transfer belt 7, a driving roller 71, a tension roller 72, an auxiliary roller 73, a frame 74, a left side plate 75, a right side plate 76, primary transfer units 5Y, 5M, 5C, and 5K, and a separation member 77. .

  The intermediate transfer belt 7 is composed of a flexible endless belt (film) formed of a resin material or a rubber material. The intermediate transfer belt 7 is stretched around a driving roller 71, a tension roller 72, and an auxiliary roller 73 as a stretching roller (supporting roller). These three tension rollers are rotatably supported by the left side plate 75 and the right side plate 76. The left side plate 75 and the right side plate 76 are attached to the frame 74. The driving roller 71 is rotationally driven by driving means (not shown) provided in the apparatus main body 110 to move (endlessly move) the intermediate transfer belt 7. The tension roller 72 is urged from the inner peripheral surface side to the outer peripheral surface side of the intermediate transfer belt 7 by a tension spring (not shown) as urging means, and tension (belt tension) is applied to the intermediate transfer belt 7. ).

  On the inner peripheral surface side of the intermediate transfer belt 7, primary transfer units 5Y, 5M, 5C, and 5K are arranged corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K. Each primary transfer unit 5Y, 5M, 5C, 5K is supported by a frame 74. Then, a primary transfer member 51 (to be described later) of each primary transfer unit 5 is pressed against each photosensitive drum 1 via the intermediate transfer belt 7, and the primary transfer portion N1 in which each photosensitive drum 1 and the intermediate transfer belt 7 come into contact with each other. Is formed. The primary transfer unit 5 will be further described later.

  The secondary transfer roller 8 described above is disposed at a position facing the drive roller 71 with the intermediate transfer belt 7 interposed therebetween. Then, the secondary transfer roller 8 is pressed toward the driving roller (secondary transfer counter roller) 71 via the intermediate transfer belt 7 so that the intermediate transfer belt 7 and the secondary transfer roller 8 are in contact with each other. N2 is formed.

  The separation member 77 is used to move the primary transfer members 51Y, 51M, and 51C to separate the intermediate transfer belt 7 from the photosensitive drums 1Y, 1M, and 1C of the first, second, and third image forming units SY, SM, and SC. Separated from the photosensitive drums 1Y, 1M, and 1C. The spacing member 77 will be further described later. The separation member 77 moves between a position where a rubbing member other than a specific rubbing member among a plurality of sliding members is in contact with the inner circumferential surface of the belt and a position separated from the inner circumferential surface of the belt. It is an example of the moving means to be made.

3. Primary Transfer Unit Next, the primary transfer unit 5 in this embodiment will be described. In this embodiment, the basic configuration and operation of the primary transfer unit 5 are the same in the first, second, third, and fourth image forming units SY, SM, SC, and SK. Therefore, the configurations and operations common to the image forming units S will be described generally, and the configurations and operations different in some of the image forming units S will be pointed out as appropriate.

  FIG. 3 is a top view of the primary transfer unit 5 as viewed from the photosensitive drum 1 side. FIG. 4 is a schematic sectional view of a part of the primary transfer unit 5 as viewed along a direction substantially orthogonal to the moving direction of the intermediate transfer belt 7. The primary transfer unit 5 includes a primary transfer member 51, a holding member 52, a support member 53, a pressing member 54, and a contact member 55.

  The primary transfer member 51 is a member that is long in one direction and is disposed along the rotational axis direction of the photosensitive drum 1 (direction substantially orthogonal to the moving direction of the intermediate transfer belt 7). The primary transfer member 51 is an example of a rubbing member that is provided so as to be able to contact the inner peripheral surface of the belt and rubs the belt as the belt moves at a contact portion with the inner peripheral surface of the belt. FIG. 5A is a side view of the primary transfer member 51 in the longitudinal direction. FIG. 5B is a perspective view of the primary transfer member 51. In this embodiment, the dimension L in the longitudinal direction of the primary transfer member 51 (the direction substantially perpendicular to the moving direction of the intermediate transfer belt 7) is L = 238 mm. In this embodiment, the dimension W of the primary transfer member 51 in the short side direction (direction substantially parallel to the moving direction of the intermediate transfer belt 7) is W = 4 mm. In this embodiment, the material of the primary transfer member 51 is a velvet-like (brush-like) woven fabric formed using conductive nylon fibers.

  The primary transfer member 51 has a raised portion 51a and an end welded portion 51b which are different regions in the longitudinal direction. A region having a length L1 = 216 mm in the central portion in the longitudinal direction of the primary transfer member 51 is a raised portion 51a, and regions having a length L2 = 11 mm at both ends of the raised portion 51a are respectively end welded portions 51b. ing. The thickness of the fiber is H1 = about 1.5 mm at the raised portion 51a and H2 = about 0.5 mm at the end welded portion 51b. The raised portions 51 a have elasticity, and the primary transfer member 51 is disposed so that the raised portions 51 a can come into contact with the inner peripheral surface of the intermediate transfer belt 7.

  The primary transfer member 51 is not limited to a velvet-like (brush-like) member as in this embodiment. For example, as the primary transfer member 51, a pad-shaped member formed of a conductive urethane foam or the like as a conductive elastic member, a sheet-shaped member formed of an ultra high-molecular polyethylene sheet or the like as a conductive sheet, or these Combinations may be used. Alternatively, as the primary transfer member 51, a blade-like member formed of conductive rubber or the like as a conductive elastic member may be used.

  The primary transfer member 51 is fixed and held on the holding member 52 by a double-sided tape (not shown) as a fixing means. In the present embodiment, the holding member 52 includes a steel plate having a thickness of 0.8 mm, a top portion 52a, and two side portions 52b and 52b extending in the same direction in a direction substantially orthogonal to the top portion 52a. It is formed by bending into the shape it has. The primary transfer member 51 is held on the upper surface of the top portion 52 a of the holding member 52.

  Since the holding member 52 holding the primary transfer member 51 is supported by the support member 53, the primary transfer member 51 is supported by the support member 53. The support members 53 are arranged at both ends in the longitudinal direction of the primary transfer member 51, and each support member 53 is located at a substantial center in a direction (width direction) substantially perpendicular to the moving direction of the intermediate transfer belt 7. The line is symmetrical. The primary transfer member 51 is configured such that a pressing member (biasing member) 54 as a pressing unit (biasing unit) presses (biases) the support member 53 at both ends in the longitudinal direction, thereby the photosensitive drum. Is pushed in the direction toward 1. In this embodiment, the pressing member 54 is composed of a compression spring. As a result, the outer peripheral surface (front surface) of the photosensitive drum 1 and the outer peripheral surface (front surface) of the intermediate transfer belt 7 and the inner peripheral surface (back surface) of the intermediate transfer belt 7 and the primary transfer member 51 can be brought into close contact with each other. Yes.

  FIG. 6A is a perspective view of the vicinity of the left end portion of the primary transfer member 51. FIG. 6B is a longitudinal sectional view of the primary transfer member 51 in the vicinity of the left end portion of the primary transfer member 51. As shown in FIG. 6A, the holding member 52 is fixed to the support member 53 by lightly press-fitting both end portions in the longitudinal direction into fitting portions 53 b formed on the support member 53. . In the present embodiment, the support member 53 is formed of a resin material. As shown in FIG. 6B, the contact member 55 includes a bottom portion 55a and two side portions 55b and 55b extending in the same direction in a direction substantially orthogonal to the bottom portion 55a. It has a spring shape. The contact member 55 is disposed so as to sandwich the end welded portion 51b of the primary transfer member 51 and the inner surface of the fitting portion 53b of the support member 53 between the two side portions 55b and 55b. The upper side portion 55 b of the contact member 55 is in contact with the end welded portion 51 b of the primary transfer member 51, and the lower side portion 55 b is in contact with the pressing member 54. As a result, the pressing member 54 and the primary transfer member 51 are electrically connected. A primary transfer bias can be supplied to the primary transfer member 51 from an electric board (not shown) provided in the apparatus main body 110 via the pressing member 54 and the contact member 55.

  In the present embodiment, the holding member 52 and the support member 53 are separated, but they may be integrated.

  FIG. 7 is a side view of the primary transfer unit 5 held by the frame 74. As shown in FIGS. 6A and 7, the support member 53 has a rotation shaft (rotation fulcrum) 53 a at one end in the longitudinal direction arranged along the moving direction of the intermediate transfer belt 7. Have The rotation axis (oscillation axis) of the rotation shaft 53a is disposed substantially parallel to the rotation axis direction of the photosensitive drum 1 (direction approximately orthogonal to the moving direction of the intermediate transfer belt 7). The support member 53 is held by a holding portion 74 a having a rotation shaft 53 a formed on the frame 74. As a result, the primary transfer unit 5 is rotatable (swingable) around the rotation shaft 53a, that is, with the engaging portion between the rotation shaft 53a and the holding portion 74a as a fulcrum. Further, the rotation shaft 53a is held by the holding portion 74a, whereby the primary transfer unit 5 is positioned in the moving direction of the intermediate transfer belt 7.

4). Separation of Primary Transfer Unit The image forming apparatus 100 according to the present exemplary embodiment can form images in the color mode and the monochrome mode as described above. In the color mode, the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other in the first, second, third, and fourth image forming units SY, SM, SC, and SK. On the other hand, in the monochrome mode, in the first, second, and third image forming units SY, SM, and SC, the photosensitive drum 1 and the intermediate transfer belt 7 are separated from each other, and in the fourth image forming unit SK. Only the photosensitive drum 1 and the intermediate transfer belt 7 are brought into contact with each other.

  In the following description, elements provided for the image forming units SY, SM, SC, and SK may be distinguished by adding “Y”, “M”, “C”, and “K” to the beginning of the word. In the following description, “upstream side” and “downstream side” refer to the moving direction of the intermediate transfer belt 7.

  In this embodiment, the arrangement of the separation member 77 switches the contact / separation state between the YMCK photosensitive drums 1Y, 1M, 1C, and 1K and the intermediate transfer belt 7 in the color mode and the monochrome mode. That is, as shown in FIG. 7, the YMC support members 53Y, 53M, and 53C are disposed at one end in the longitudinal direction (on the side opposite to the rotation shaft 53a) arranged along the moving direction of the intermediate transfer belt 7. It has an engaging part 53c. On the other hand, as shown in FIG. 2, the separation member 77 has a separation action portion 77a that engages with the engagement portions 53c of the YMC support members 53Y, 53M, and 53C. In this embodiment, the separation member 77 receives a driving force from a driving source (not shown) that drives the driving roller 71, and moves linearly (reciprocating or linearly moving) substantially parallel to the moving direction of the intermediate transfer belt 7. )

  When the separation member 77 is moved in a direction in which the separation action portion 77a approaches the rotation shaft 53a of the YMC support members 53Y, 53M, and 53C, the separation action portion 77a and the engagement portion 53c of the YMC support members 53Y, 53M, and 53C Engage and slide on the engaging portion 53c. Accordingly, the separation member 77 rotates the YMC support members 53Y, 53M, and 53C in a direction away from the intermediate transfer belt 7 against the pressing force of the pressing member 54. As a result, the separation member 77 separates the YMC primary transfer members 51Y, 51M, 51C from the intermediate transfer belt 7 and separates the intermediate transfer belt 7 from the YMC photosensitive drums 1Y, 1M, 1C. The position of the separation member 77 at this time is defined as a color separation position.

  On the other hand, when the separation member 77 is moved from the collar separation position in a direction in which the separation member 77a separates from the rotation shaft 53a of the YMC support members 53Y, 53M, and 53C, the separation member 77a is engaged, contrary to the above. It slides on the part 53 and is finally disengaged. As a result, the YMC support members 53Y, 53M, and 53C are rotated in the direction approaching the intermediate transfer belt 7 by the pressing force of the pressing member 54, and finally the YMC primary transfer members 51Y, 51M, and 51C push the intermediate transfer belt 7. Through the YMC photosensitive drums 1Y, 1M, and 1C. The position of the separating member 77 at this time is defined as a collar contact position. In this embodiment, the K support member 53K is not provided with the engagement portion 53c, and the separation member 77 is not provided with the separation action portion 77a corresponding to the K image forming portion SK.

  FIG. 8A shows a contact / separation state between the YMCK photosensitive drums 1Y, 1M, 1C, and 1K and the intermediate transfer belt 7 in the color mode. At this time, the separation member 77 is located at the collar contact position. In this state, the YMCK primary transfer members 51Y, 51M, 51C, 51K lift the intermediate transfer belt 7 against the belt tension by the pressing force of the pressing member 54. Then, the YMCK primary transfer members 51Y, 51M, 51C, 51K are moved in the direction in which they contact the lower surfaces of the corresponding photosensitive drums 1Y, 1M, 1C, 1K, and are pressed with a predetermined pressing force. State. Thus, the YMCK primary transfer units 5Y, 5M, 5C, and 5K form nips between the YMCK photosensitive drums 1Y, 1M, 1C, and 1K and the intermediate transfer belt 7, respectively. That is, the intermediate transfer belt 7 is sandwiched between the YMCK primary transfer members 51Y, 51M, 51C, 51K and the YMCK photosensitive drums 1Y, 1M, 1C, 1K, and the YMCK photosensitive drums 1Y, 1M, 1C, 1K and the intermediate transfer belt 7 are sandwiched. And contact.

  Here, in this embodiment, the K photosensitive drum 1K is arranged so as to be shifted by 2 mm in the direction approaching the intermediate transfer belt 7 with respect to the YMC photosensitive drums 1Y, 1M, and 1C. That is, in the contact and separation state in the color mode, the contact position between the K photosensitive drum 1K and the intermediate transfer belt 7 is relative to the straight line connecting the contact positions between the YMC photosensitive drums 1Y, 1M, and 1C and the intermediate transfer belt 7. Thus, the intermediate transfer belt 7 is arranged in a direction to push it inward. In other words, the contact portion between the K primary transfer member 51K and the inner peripheral surface of the intermediate transfer belt 7 is a straight line connecting the contact portions between the YMC primary transfer members 51Y, 51M, 51C and the inner peripheral surface of the intermediate transfer belt 7. On the other hand, it is arranged on the inner peripheral side of the intermediate transfer belt 7. This is an arrangement for securing a gap between the YMC photosensitive drums 1Y, 1M, and 1C and the intermediate transfer belt 7 in the monochrome mode.

  FIG. 8B shows a contact / separation state between the YMCK photosensitive drums 1Y, 1M, 1C, and 1K and the intermediate transfer belt 7 in the monochrome mode. At this time, the separation member 77 is located at the color separation position. In this state, the YMC primary transfer members 51 </ b> Y, 51 </ b> M, and 51 </ b> C are moved about 4 mm away from the intermediate transfer belt 7 and are separated from the inner peripheral surface of the intermediate transfer belt 7. Further, as described above, the YMC photosensitive drums 1Y, 1M, 1C and the K photosensitive drum 1K have different heights. Therefore, when the YMC primary transfer members 51Y, 51M, and 51C are separated from the intermediate transfer belt 7, the intermediate transfer belt 7 is also moved in the direction of about 2 mm away from the YMC photosensitive drums 1Y, 1M, and 1C. As a result, the YMC photosensitive drums 1Y, 1M, and 1C and the intermediate transfer belt 7, and the intermediate transfer belt 7 and the YMC primary transfer members 51Y, 51M, and 51C are separated from each other by about 2 mm.

  In this embodiment, when viewed in a direction substantially orthogonal to the moving direction of the intermediate transfer belt 7, the contact portion between the K primary transfer member 51K and the inner peripheral surface of the intermediate transfer belt 7 is substantially the same as the driving roller 71 and the tension. It is arranged on a common tangent line with the roller 72.

5. 5. Arrangement of support member of primary transfer unit 5-1. Outline of Vibration As described above, the primary transfer unit 5 forms a nip between the intermediate transfer belt 7 and the photosensitive drum 1 by the pressing force of the pressing member 54. Further, the rotation shaft 53a of the support member 53 constituting the rotation fulcrum (swinging fulcrum) of the primary transfer unit 5 is provided with a gap corresponding to the fitting dimension in the vertical direction with respect to the holding portion 74a of the frame 74. It is held by the holding portion 74a.

  In the dynamic state in which the intermediate transfer belt 7 is moving, if the vertical force applied to the rotation shaft 53a becomes unstable, vertical vibrations may occur, resulting in the generation of noise. Therefore, it is desired that the force in the same direction acts on the rotation shaft 53a in the static state and the dynamic state.

  Here, as described above, the YMC photosensitive drums 1Y, 1M, and 1C are disposed above the K photosensitive drum 1K. In particular, in this embodiment, when viewed in a direction substantially orthogonal to the moving direction of the intermediate transfer belt 7, the contact portion between the YMC primary transfer members 51Y, 51M, 51C and the inner peripheral surface of the intermediate transfer belt 7 is a driving roller. 71 and the tension roller 72 are disposed above the common tangent line. Therefore, in the contact / separation state in the color mode shown in FIG. 8A, a pulling force may be applied to the YC primary transfer units 5Y and 5C. Further, the force applied to the primary transfer unit 5 varies between the stopped state and the moved state of the intermediate transfer belt 7. As described above, in the primary transfer unit 5 in which a pulling force is applied, the direction of the force applied to the rotation shaft 53a may change due to the movement of the intermediate transfer belt 7. In particular, when the rotation shaft 53a of the support member 53 is disposed upstream of the contact portion between the intermediate transfer belt 7 and the primary transfer member 51 in the moving direction of the intermediate transfer belt 7, in the Y image forming unit SY. Vibration of the rotation shaft 53a of the support member 53 is likely to occur. This will be described in more detail below.

5-2. Next, in order to facilitate understanding of the configuration of this embodiment, the force applied to the primary transfer unit 5 in the contact and separation state in the color mode in the comparative example will be described. To do. 9, FIG. 10, FIG. 11 and FIG. 12 are cross sections viewed in a direction substantially perpendicular to the moving direction of the intermediate transfer belt 7 for explaining the forces applied to the YMCK primary transfer units 5Y, 5M, 5C and 5K, respectively. FIG.

  Note that the arrangement of the support member 53Y in the Y primary transfer unit 5Y is different between the comparative example and the present embodiment, and the rest is substantially the same.

There are the following static forces that occur constantly.
F1: Upward force received from the pressing member 54 F2: Downward force received from the intermediate transfer belt 7

  The force F1 received from the pressing member 54 works toward the rotation center of the photosensitive drum 1 in any of the YMCK image forming units SY, SM, SC, and SK. The YMC primary transfer members 51Y, 51M, and 51C push up the intermediate transfer belt 7 by 2 mm. Therefore, due to the tension pressure T of the intermediate transfer belt 7, the upstream end of the Y primary transfer member 51 </ b> Y receives a downward force F <b> 2 due to the bending of the intermediate transfer belt 7. Similarly, the downstream end portion of the C primary transfer member 51 </ b> C receives a downward force F <b> 2 due to the bending of the intermediate transfer belt 7. With this force F2, in the YC image forming units SY and SC, the center point in the moving direction of the intermediate transfer belt 7 at the contact portion between the inner peripheral surface of the intermediate transfer belt 7 and the primary transfer member 51 (hereinafter referred to as “transfer unit center point”). Also, a moment is generated on the rotation shaft 53a with O as a fulcrum. In the MK image forming units SM and SK, the force that the intermediate transfer belt 7 gives to the MK primary transfer units 5M and 5K is not generated. Further, the pressing force of each image forming unit SY, SM, SC, SK is adjusted so that F1−F2 = 2.8N.

Next, the following dynamic force is generated when the intermediate transfer belt 7 moves.
F3: Friction force between the primary transfer member 51 and the intermediate transfer belt 7 and an attractive force generated when a primary transfer bias is supplied (hereinafter also referred to as “tangential force”).
F4: Force that pushes up the rotating shaft 53a F5: Frictional force between the rotating shaft 53a and the holding portion 74a

  F4 and F5 are forces generated with the generation of F3. When F3 occurs, “F3 × sin θ”, which is a component force of F3, acts between the rotation shaft 53a and the transfer portion center point O, and “F3 × sin θ × cos θ” that is a cos θ component of this component force is generated. It acts on the rotating shaft 53a as an upward force F4. Further, as F4 is generated, the frictional force acts as a downward force F5 with the holding portion 74a on the positioning surface in the moving direction of the intermediate transfer belt 7 of the rotation shaft 53a.

  The above is the force acting on the primary transfer unit 5, and the resultant force determines the moment around the transfer portion center point O, that is, the vertical force applied to the rotation shaft 53a.

  Next, a mechanism for generating vibration of the primary transfer unit 5 will be described.

  As described above, when the intermediate transfer belt 7 moves, the primary transfer unit 5 receives a force in the moving direction of the intermediate transfer belt 7 by the tangential force F3. Thereafter, when the primary transfer unit 5 exerts a restoring force by its own rigidity, a slip occurs between the primary transfer member 51 and the intermediate transfer belt 7 at the moment when the restoring force exceeds the tangential force F3. At that moment, the tangential force F3 between the primary transfer member 51 and the intermediate transfer belt 7 becomes zero. Further, when F3 becomes zero, F4 and F5 generated by F3 also become zero, and only a temporary static force (force when the intermediate transfer belt 7 is not moving) is applied to the primary transfer unit 5 only. Come to work.

  The primary transfer unit 5 repeats the above operation, and the vertical direction of the force applied to the rotary shaft 53a in a static state is opposite to the vertical direction of the force applied to the rotary shaft 53a in a dynamic state. When this happens, vertical vibrations are generated. This is the generation mechanism of the vibration of the primary transfer unit 5.

  Here, with reference to FIG. 9, FIG. 10, FIG. 11 and FIG. 12, the force applied to each of the YMCK primary transfer units 5Y, 5M, 5C and 5K in the comparative example is calculated.

Y image forming unit (FIG. 9)
L1y (distance from the transfer portion center point Oy to the rotation center of the rotation shaft 53aY) = 30 mm
L2y (distance from the transfer portion center point Oy to the positioning surface in the moving direction of the intermediate transfer belt 7 of the rotation shaft 53aY) = 27 mm
L3y (distance from the transfer portion center point Oy to the upstream end of the primary transfer member 51Y) = 2 mm
θy1 (angle formed by the tangent line of the intermediate transfer belt 7 from the drive roller 71 to the Y primary transfer portion N1Y and the straight line connecting the transfer portion center point Oy and the rotation center of the rotation shaft 53aY) = 9.5 °
θy2 (angle formed by the tangent of the intermediate transfer belt 7 from the drive roller 71 to the Y primary transfer portion N1Y and the tangent of the intermediate transfer belt 7 from the Y primary transfer portion N1Y to the M primary transfer portion N1M) = 2.5 °
μ (coefficient of friction of sliding portion between rotating shaft 53aY and frame 74) = 0.2
T (tension pressure of the intermediate transfer belt 7) = 42.5N
F1y (pushing force of the pressing member 54) = 4.6N
F2y (pressing force applied by T to the upstream end of the primary transfer member 51Y) = − (T × sin θy2) = − 1.8N
F3y (assumed maximum tangential force) = 5N
F4y (pushing force generated by F3 with respect to the rotating shaft 53aY) = F3y × sin (θy1 + θy2) × cos (θy1 + θy2) = 1.02N
F5y (friction force between the rotating shaft 53aY and the frame 74) = − {F3y × cos ² (θy1 + θy2) × μ} = − 0.96N
Msy (static moment around the transfer center point Oy)
= F2y × L3y = -3.6N · mm
Mdy (dynamic moment around the transcription center point Oy)
= Msy + F4y × L1y + F5y × L2y = 1.08N · mm

M image forming unit (FIG. 10)
L1m = 30mm
L2m = 27mm
θm (angle formed by a tangent line of the intermediate transfer belt 7 from the Y primary transfer portion N1Y to the M primary transfer portion N1M and a straight line connecting the transfer portion center point Om and the rotation center of the rotation shaft 53aM) = 12 °
μ = 0.2
F1m = 2.8N
F3m = 5N
F4m = F3m × sin θm × cos θm = 1.02N
F5m = − (F3m × cos ² θm × μ) = − 0.96N
Msm (Static moment around the transcription center point Om)
= 0 N · mm
Mdm (dynamic moment around the transcription center point Om)
= Msm + F4m × L1m + F5m × L2m = 4.68N · mm

C image forming unit (FIG. 11)
L1c = 30mm
L2c = 27mm
L3c (distance from the transfer portion center point Oc to the downstream end of the primary transfer member 51C) = 2 mm
θc1 (angle formed by the tangent of the intermediate transfer belt 7 from the M primary transfer portion N1M to the C primary transfer portion N1C and a straight line connecting the transfer portion center point Oc and the rotation center of the rotation shaft 53aC) = 12 °
θc2 (angle formed by the tangent of the intermediate transfer belt 7 from the M primary transfer portion N1M to the C primary transfer portion N1C and the tangent of the intermediate transfer belt 7 from the C primary transfer portion N1C to the K primary transfer portion N1K) = 1. 5 °
μ = 0.2
T (tension pressure of the intermediate transfer belt 7) = 42.5N
F1c = 3.9N
F2c (pressing force applied by T to the downstream end of the primary transfer member 51C) = − (T × sin θc2) = − 1.1N
F3c = 5N
F4c = F3 × sin (θc1 + θc2) × cos (θc1 + θc2) = 1.13N
F5c = − {F3 × cos ² (θc1 + θc2) × μ} = − 0.95N
Msc (static moment around the transcription center point Oc)
= F2c × -L3c = 2.2N · mm
Mdc (dynamic moment around the transfer portion center point Oc)
= Msc + F4c × L1c + F5c × L2c = 10.45 N · mm

-K image forming unit (FIG. 12)
L1k = 30mm
L2k = 27mm
θk1 (angle formed by the tangent of the intermediate transfer belt 7 from the C primary transfer portion N1C to the K primary transfer portion N1K and the straight line connecting the transfer portion center point Oc and the rotation center of the rotation shaft 53aK) = 13.5 °
θk2 (angle formed by the tangent of the intermediate transfer belt 7 from the C primary transfer portion N1C to the K primary transfer portion N1K and the tangent of the intermediate transfer belt 7 from the K primary transfer portion N1K to the tension roller 72) = 1.5 °
μ = 0.2
F1k = 2.8N
F3k = 5N
F4k = F3k × sin (θk1−θk2) × cos (θk1−θk2) = 1.02N
F5k = − {F3k × cos ² (θk1−θk2) × μ} = − 0.96N
Msk (static moment around the transfer part center point Ok)
= 0 N · mm
Mdk (dynamic moment around the transfer part center point Ok)
= Msk + F4k × L1k + F5k × L2k = 4.68 N · mm

  As described above, in the comparative example, the vertical direction between the static moment Msy and the dynamic moment Mdy around the transfer portion center point Oy is switched only in the Y image forming portion SY. Therefore, in the comparative example, in the Y image forming unit SY, the rotation shaft 53a is likely to vibrate when stick slip occurs.

  This is because in the Y image forming unit SY, the winding angle (θy2) of the intermediate transfer belt 7 with respect to the primary transfer member 51Y at the upstream end of the primary transfer member 51Y is relatively large. That is, in the Y image forming unit SY, since the wrapping angle is relatively large, a downward force acts on the upstream end portion of the primary transfer member 51Y, and as a result, a downward force is applied to the rotation shaft 53aY of the support member 53Y. This is because the downward force is dominant in the static state.

  Here, when the winding angle is viewed in a direction substantially orthogonal to the moving direction of the intermediate transfer belt 7, the intermediate transfer belt 7 immediately downstream of the contact portion between the inner peripheral surface of the intermediate transfer belt 7 and the primary transfer member 51. And the angle formed by the tangent of the intermediate transfer belt 7 immediately downstream.

  In the MCK image forming units SM, SC, and SK, the winding angle is substantially zero. In the K image forming unit SK, the intermediate transfer belt 7 is wound around the photosensitive drum 1K side at the upstream end of the primary transfer unit N1K.

5-3. Next, the force applied to the primary transfer unit 5 in the contact / separation state in the color mode in this embodiment will be described. FIG. 13 is a cross-sectional view viewed in a direction substantially orthogonal to the moving direction of the intermediate transfer belt 7 for explaining the force applied to the Y primary transfer unit 5Y in this embodiment.

  In the present embodiment, the height of the rotation shaft 53aY of the support member 53Y is lowered by the amount of [theta] y2 in the Y image forming unit SY based on the examination result in the comparative example described above. As a result, the angle θy1 formed by the tangent line of the intermediate transfer belt 7 from the drive roller 71 to the Y primary transfer portion N1Y and the straight line connecting the transfer portion center point Oy and the rotation center of the rotation shaft 53aY is 12 ° ( = Θy1 ′).

  That is, in the above-described comparative example, in the Y image forming unit SY, the winding angle (θy2) of the intermediate transfer belt 7 with respect to the primary transfer member 51Y at the upstream end of the primary transfer member 51Y is relatively large. Therefore, a downward force is applied to the upstream end of the primary transfer member 51Y in a static state. On the other hand, in the present embodiment, the upstream end of the primary transfer member 51Y is substantially parallel to the surface of the intermediate transfer belt 7, so that the upstream end of the primary transfer member 51Y has a downward direction. Power does not work. Instead, the downstream end of the primary transfer member 51Y becomes the bending point of the intermediate transfer belt 7, and a downward force is applied to the downstream end. Therefore, an upward force acts on the rotation shaft 53aY of the support member 53Y with the downstream end portion as a fulcrum.

Here, the force applied to the Y primary transfer unit 5Y in this embodiment is calculated. The force applied to the MCK primary transfer units 5M, 5C, and 5K is the same as that in the comparative example.
L1y = 30mm
L2y = 27mm
L3y = 2mm
θy1 ′ = 12 °
θy2 = 2.5 °
μ = 0.2
T = 42.5N
F1y = 4.6N
F2y (pressing force applied by T to the downstream end of the primary transfer member 51Y) = − (T × sin θy2) = − 1.8N
F3y = 5N
F4y = F3y × sin (θy1 ′ + θy2) × cos (θy1 ′ + θy2) = 1.21N
F5y = − {F3y × cos ² (θy1 + θy2) × μ} = − 0.94N
Msy (static moment around the transfer center point Oy)
= F2y × −L3y = 3.6 N · mm
Mdy (dynamic moment around the transcription center point Oy)
= Mys + F4y × L1y + F5y × L2y = 14.52N · mm

  As described above, in this embodiment, a force acts in the same direction (upward) on the rotation shaft 53aY of the support member 53Y in both the static state and the dynamic state.

FIG. 14 shows a simplified arrangement relationship of the primary transfer units 5 in each image forming unit S of the present embodiment. Here, an angle formed by a straight line connecting the transfer portion center point O and the rotation center of the support member 53 and an arbitrary reference straight line X when viewed in a direction substantially orthogonal to the moving direction of the intermediate transfer belt 7. Is the rotation center arrangement angle θ. At this time, in this embodiment, the rotation center arrangement angle θy for the Y primary transfer member 5Y is different from the rotation center arrangement angles θm, θc, and θk for the MCK primary transfer portions 5M, 5C, and 5K. For example, the reference straight line X is substantially parallel to the moving direction of the intermediate transfer belt 7 (more specifically, a straight line connecting contact portions between at least two primary transfer members 51 and the intermediate transfer belt 7 among the plurality of primary transfer members 51. And substantially parallel). At this time, in this embodiment, the rotation center arrangement angles θy, θm, θc, and θk for each of the YMCK primary transfer members 5Y, 5M, 5C, and 5K have the following relationship.
θy> θm = θc = θk

More specifically, when the reference straight line X is a tangent of the intermediate transfer belt 7 in the YMC primary transfer portions N1Y, N1M, and N1C (a common tangent of the YMC photosensitive drum 1), in this embodiment, θy, θm, θc, θk is as follows.
θy = θy1 + θy2 = 14.5 °
θm = 12 °
θc = θc1 = 12 °
θk = θk1-θk2 = 12 °
(Because the tangent of the intermediate transfer belt 7 at the YMC primary transfer portions N1Y, N1M, and N1C and the tangent of the intermediate transfer belt 7 from the K primary transfer portion N1K to the tension roller 72 are substantially parallel.)

  As described above, the winding angle of the intermediate transfer belt 7 with respect to the primary transfer member 51 on the upstream side of the contact portion between the inner peripheral surface of the intermediate transfer belt 7 and the primary transfer member 51 is at least partially in the primary transfer member 51. It may be larger than other primary transfer members 51. In this case, the rotation center arrangement angle θ related to a part of the primary transfer members 51 is made different from the rotation center arrangement angle θ related to other primary transfer members 51. More specifically, the rotation center arrangement angle θ related to a part of the primary transfer members 51 is made larger than the rotation center arrangement angle θ related to other primary transfer members 51. Thereby, even when stick-slip occurs, it is possible to suppress the occurrence of vertical vibration of the rotation shaft 53a of the support member 53 with respect to a part of the primary transfer member 51.

  Note that the M image forming unit SM and the K image forming unit SK having the static moment of 0 N · mm are also rotated by lowering the height of the rotation shaft 53a of the support member 53, similarly to the Y image forming unit SY. The center arrangement angle θ may be increased. Thereby, also in the M image forming unit SM and the K image forming unit SK, it is possible to generate a larger upward static moment with respect to the rotation shaft 53a, and the vibration suppressing effect in the entire intermediate transfer unit 70 can be further increased. Can be increased.

  As described above, according to this embodiment, the vibration of the support member 53 of the primary transfer member 51 due to the frictional force generated between the intermediate transfer belt 7 and the primary transfer member 51 is reduced with a simple configuration. be able to.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiment, an intermediate transfer type image forming apparatus in which an endless belt is an intermediate transfer member has been described. However, the present invention is not limited to this. The present invention can also be applied to a direct transfer type image forming apparatus. The direct transfer type image forming apparatus has a conveyance belt (recording material carrying belt) constituted by an endless belt as a recording material carrying body, instead of the intermediate transfer belt in the image forming apparatus of FIG. In this image forming apparatus, the toner image formed on the photosensitive drum in each image forming unit is transferred to the recording material carried and conveyed on the conveyance belt by the action of the transfer member in each transfer unit. In this case, the configuration of the image forming unit is the same as that of the image forming apparatus of FIG. 1, and the transfer member (transfer unit) is the same as the primary transfer member (primary transfer unit) of the image forming apparatus of FIG. Is used. Also in such a direct transfer type image forming apparatus, the problem of noise due to the vibration of the transfer unit similar to the case of the intermediate transfer type image forming apparatus may occur. Therefore, even in such a direct transfer type image forming apparatus, by applying the present invention, it is possible to obtain the same effect as in the above-described embodiments.

  In the above-described embodiment, the transfer members of the image forming units other than the specific image forming unit among the plurality of image forming units can be separated from the belt. However, the transfer members of all the image forming units are separated from the belt. You may be able to.

  Further, the image forming apparatus is not limited to one having four image forming units of yellow, magenta, cyan, and black as the plurality of image forming units, and may be more or less. The monochrome mode is not limited to the case of forming a black single color image, and may be any color.

  In the above-described embodiment, the example in which the image forming apparatus is a laser beam printer has been described. However, the present invention is not limited to this. The present invention can be applied to an image forming apparatus such as a printer, a copying machine, a facsimile, or a multifunction machine having a plurality of these functions, or a document conveying apparatus used in connection with a light printing machine. That is, the present invention can be applied to any belt device having an endless belt and a rubbing member supported by a rotatable support member that rubs the moving belt.

  In the above-described embodiment, the contact position between one transfer member and the belt among the plurality of transfer members is arranged in a direction to push the belt toward the inner peripheral side with respect to the contact position between the other transfer member and the belt. However, the present invention is not limited to this. For example, the present invention can be applied even when the contact positions of all the transfer members and the belt are arranged on the same straight line. That is, a transfer region is defined between the most upstream transfer portion and the most downstream transfer portion in the belt moving direction. At this time, for example, a straight line connecting the contact positions of the transfer members and the belt is common to the stretching roller disposed adjacent to the upstream side of the transfer region and the stretching roller disposed adjacent to the downstream side. May be disposed on the outer peripheral side (upward) of the belt with respect to the tangent line. Also in this case, at the most upstream transfer portion, a force is applied to the transfer member by the belt toward the inner peripheral side of the belt. As in the case of the above-described embodiment, a static moment may be generated toward the inner peripheral side of the belt with respect to the rotation shaft of the support member of the most upstream transfer unit. Therefore, even in such a configuration, by applying the present invention, it is possible to suppress the generation of noise by suppressing the vibration of the rotation shaft of the support member, as in the above-described embodiment.

  That is, according to the present invention, the winding angle of the belt with respect to the transfer member on the upstream side of the contact portion between the inner peripheral surface of the belt and the transfer member is greater than the first angle and the first rubbing member having the first angle. Any structure having a plurality of transfer members including a second rubbing member having a large second angle can be applied. In such a configuration, the rotation center arrangement angle θ related to the second rubbing member may be different from the rotation center arrangement angle θ related to the first rubbing member. More specifically, as described above, the rotation center arrangement angle θ related to the second rubbing member may be made larger than the rotation center arrangement angle θ related to the first rubbing member. At this time, the number of transfer members having a large winding angle is not limited to one. For example, there may be a configuration in which the contact position between the transfer member and the belt alternately alternates along the belt movement direction. In this configuration, the tension surface of the belt between the transfer member and the stretching roller or transfer member arranged on the upstream side of the transfer member is more inclined than the other transfer members at two or more transfer members (winding) (An angle is large). In this case, the rotation center arrangement angle θ related to at least one of the two or more transfer members having a relatively large winding angle is set as the rotation center arrangement of at least one transfer member having a smaller winding angle than the transfer member. If the angle θ is different, a corresponding effect can be obtained.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Primary transfer unit 7 Intermediate transfer belt 51 Primary transfer member 53 Support member 53a Rotating shaft 54 Press member 70 Intermediate transfer unit (belt apparatus)
74 Frame 74a Holding unit 100 Image forming apparatus N1 Primary transfer unit S Image forming unit

Claims (14)

A plurality of tension rollers,
A movable endless belt stretched between the plurality of stretch rollers;
A plurality of rubbing members which are provided so as to be able to contact the inner peripheral surface of the belt and rub the belt as the belt moves at a contact portion with the inner peripheral surface of the belt;
A plurality of pivotable support members that respectively support the plurality of rubbing members and have a pivot shaft;
A plurality of holding portions that respectively hold the rotation shafts of the plurality of support members;
Pressing means for pressing each of the plurality of support members so as to press the plurality of rubbing members toward the inner peripheral surface of the belt;
In a belt device having
The plurality of rubbing members include a first rubbing member having a first winding angle of the belt on the upstream side of the contact portion in the moving direction of the belt and a first rubbing member having a larger angle than the first angle. A second rubbing member at an angle of 2;
When viewed in a direction substantially perpendicular to the moving direction of the belt, the center point of the contact portion in the moving direction of the belt and the rotation center of the supporting member are connected to each of the plurality of rubbing members. When the angle formed by the straight line and an arbitrary reference straight line is the rotation center arrangement angle, the rotation center arrangement angle related to the second rubbing member is the rotation center arrangement related to the first rubbing member. A belt device characterized by being different from an angle.   The rotation center arrangement angle with respect to the second rubbing member when the reference straight line is substantially parallel to a straight line connecting the contact portions of at least two of the rubbing members and the belt. The belt device according to claim 1, wherein is larger than the rotation center arrangement angle with respect to the first rubbing member.   3. The belt device according to claim 1, wherein the rotation shaft of the support member is disposed upstream of the contact portion in the moving direction of the belt.   Of the plurality of rubbing members, the rubbing members other than the specific rubbing member including the second rubbing member are separated from the inner circumferential surface of the belt and the position where the rubbing members are in contact with the inner circumferential surface of the belt, respectively. The belt device according to any one of claims 1 to 3, further comprising moving means for moving between the moved positions.   When viewed in a direction substantially perpendicular to the moving direction of the belt, the contact portion related to the specific rubbing member is a straight line connecting the contact portions related to the rubbing member other than the specific rubbing member. The belt device according to claim 4, wherein the belt device is disposed on an inner peripheral side of the belt.   Among the plurality of rubbing members, the specific rubbing member is arranged on the most downstream side in the moving direction of the belt, and the second rubbing member is arranged on the most upstream side in the moving direction of the belt. The belt device according to claim 4 or 5, characterized by the above-mentioned.   The belt according to any one of claims 1 to 6, wherein the rotation center arrangement angles of the plurality of rubbing members other than the second rubbing member are the same. apparatus. A plurality of image carriers;
A plurality of tension rollers,
An endless belt which is stretched by the plurality of stretching rollers and is movable in contact with the plurality of image carriers;
The belt is provided so as to be in contact with the inner peripheral surface of the belt so as to face each of the plurality of image carriers via the belt, and the belt as the belt moves at a contact portion with the inner peripheral surface of the belt. A plurality of rubbing members for rubbing,
A plurality of pivotable support members that respectively support the plurality of rubbing members and have a pivot shaft;
A plurality of holding portions that respectively hold the rotation shafts of the plurality of support members;
Pressing means for pressing each of the plurality of support members so as to press the plurality of rubbing members toward the inner peripheral surface of the belt;
In an image forming apparatus having
The plurality of rubbing members include a first rubbing member having a first winding angle of the belt on the upstream side of the contact portion in the moving direction of the belt and a first rubbing member having a larger angle than the first angle. A second rubbing member at an angle of 2;
When viewed in a direction substantially perpendicular to the moving direction of the belt, the center point of the contact portion in the moving direction of the belt and the rotation center of the supporting member are connected to each of the plurality of rubbing members. When the angle formed by the straight line and an arbitrary reference straight line is the rotation center arrangement angle, the rotation center arrangement angle related to the second rubbing member is the rotation center arrangement related to the first rubbing member. An image forming apparatus characterized by being different from an angle.   The rotation center arrangement angle with respect to the second rubbing member when the reference straight line is substantially parallel to a straight line connecting the contact portions of at least two of the rubbing members and the belt. The image forming apparatus according to claim 8, wherein the angle is larger than the rotation center arrangement angle with respect to the first rubbing member.   The image forming apparatus according to claim 8, wherein the rotation shaft of the support member is disposed upstream of the contact portion in the moving direction of the belt.   Of the plurality of rubbing members, the rubbing members other than the specific rubbing member including the second rubbing member are separated from the inner circumferential surface of the belt and the position where the rubbing members are in contact with the inner circumferential surface of the belt, respectively. The image forming apparatus according to claim 8, further comprising a moving unit that moves the position between the moved positions.   When viewed in a direction substantially perpendicular to the moving direction of the belt, the contact position between the image carrier corresponding to the specific rubbing member and the belt is determined by the rubbing member other than the specific rubbing member. In a direction in which the belt is pushed inward with respect to a straight line connecting the contact positions of the image carrier and the belt corresponding to the rubbing member other than the specific rubbing member in the state where the belt is moved to the position The image forming apparatus according to claim 11, wherein the image forming apparatus is arranged.   Among the plurality of rubbing members, the specific rubbing member is arranged on the most downstream side in the moving direction of the belt, and the second rubbing member is arranged on the most upstream side in the moving direction of the belt. The image forming apparatus according to claim 11, wherein the image forming apparatus is an image forming apparatus.   The image according to any one of claims 8 to 13, wherein the rotation center arrangement angle with respect to a rubbing member other than the second rubbing member among the plurality of rubbing members is the same. Forming equipment.