JP6512951B2 - Belt device and image forming apparatus - Google Patents

Description

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

  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 serving as an electrostatic recording dielectric. A toner image is formed in the process. The toner image is directly transferred to the recording material conveyed by the recording material carrier (direct transfer method), or temporarily transferred to the recording material after being primarily transferred to the intermediate transfer member (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, there is, for example, a tandem type image forming apparatus which independently has an image forming portion for forming an image with toners of respective colors 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 bearing member, and an intermediate transfer belt constituted by an endless belt as an intermediate transfer member. Then, the toner image formed on the photosensitive drum is primarily transferred to the intermediate transfer belt by the action of the transfer member (primary transfer member) provided opposite to each photosensitive drum via the intermediate transfer belt.

  As the above-mentioned primary transfer member, for example, a member such as a pad-like, brush-like or blade-like member which rubs a moving (endless moving) intermediate transfer belt 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 or the like in which deformation and recovery are repeated due to the movement of the intermediate transfer belt. As a result, vibration of the primary transfer member may be generated as noise.

  Therefore, there is a method of providing a pivot for supporting the primary transfer member so that the primary transfer member can stably contact the intermediate transfer belt even during the image forming operation, thereby making the support member pivotable. Patent Document 1).

  In addition, in the image forming apparatus of the tandem system, it is not always required to output a color image. For example, the output of a black single color image is often required. Therefore, when outputting a black monochromatic image, there is also a system which stops the rotational driving of the photosensitive drums of the image forming portion other than black in a state where all the photosensitive drums are in contact with the intermediate transfer belt. However, in this case, the friction between the stopped photosensitive drum and the intermediate transfer belt tends to deteriorate the intermediate transfer belt and the photosensitive drum.

  Therefore, when outputting a black single color image, there is a method of separating the primary transfer member from the photosensitive drum in an image forming section other than black and separating the intermediate transfer belt and the photosensitive drum (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 against the straight line connecting the contact positions between the photosensitive drum for the other colors and the intermediate transfer belt. Disclose what to do. Thus, when outputting a black monochrome image, the distance between the photosensitive drum of the image forming portion other than black and the intermediate transfer belt can be sufficiently separated.

JP 2007-187867 A JP, 2014-163956, A

  However, in the case of adopting the disposition mode of the photosensitive drums as described in, for example, Patent Document 2, depending on the image forming unit, a force may be exerted to cause the intermediate transfer belt to push down the primary transfer member.

  When the primary transfer member that slides on the intermediate transfer belt is supported by the rotatable support member, vibration may occur if the balance of forces applied to the support member is unstable when stick-slip or the like occurs. It may happen and noise may occur. This is because, as described above, in the image forming unit in which a force is exerted to push the primary transfer member downward by the intermediate transfer belt, the direction of the force applied to the pivot shaft of the support member changes as the intermediate transfer belt moves. It will be noticeable in the case.

  Although the intermediate transfer type image forming apparatus has been described above as an example, the same problem may occur in a direct transfer type image forming apparatus. Also, similar problems can arise in any belt device having an endless belt and a rubbing member supported on a pivotable support member that rubs a moving belt.

  Therefore, an object of the present invention is to provide a belt device and an image forming apparatus capable of reducing the vibration of the supporting member of the rubbing member due to the frictional force generated between the endless belt and the rubbing member with a simple configuration. It is providing a device.

  The above object is achieved by a belt device and an 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 for rubbing the belt along with the movement of the belt at a contact portion with the inner circumferential surface of the belt, and the plurality of rubbing members, each having a rotation shaft, which is rotatable The plurality of supports such that the plurality of support members, the plurality of holding portions that respectively hold the rotation axes of the plurality of support members, and the plurality of rubbing members are pressed toward the inner circumferential surface of the belt A belt device having pressing means for respectively pressing the members, wherein the plurality of rubbing members have a first winding angle of the belt on the upstream side of the contact portion in the moving direction of the belt; Sliding member and the first angle And a second rubbing member having a second angle which is larger than the second rubbing member, and when viewed in a direction substantially orthogonal to the moving direction of the belt, in the moving direction of the belt with respect to each of the plurality of rubbing members. When an angle formed by a straight line connecting the center point of the contact portion and the rotation center of the support member with an arbitrary reference straight line is a rotation center arrangement angle, the rotation related to the second rubbing member The center arrangement angle is a belt device characterized by being different from the rotation center arrangement angle with respect to the first rubbing member.

  According to another aspect of the present invention, an endless belt is stretched over a plurality of image carriers, a plurality of tension rollers, and the plurality of tension rollers, and is movable in contact with the plurality of image carriers. And is provided so as to be able to contact the inner peripheral surface of the belt so as to face each of the plurality of image carriers via the belt, and in accordance with the movement of the belt at the contact portion with the inner peripheral surface of the belt. A plurality of pivotable supporting members that respectively support the plurality of rubbing members slidingly rubbing the belt and the plurality of rubbing members and have a pivoting axis, and the pivoting axes of the plurality of supporting members In the image forming apparatus, the image forming apparatus has a plurality of holding portions that respectively hold the pressing member and a pressing unit that presses the plurality of support members so as to press the plurality of rubbing members toward the inner circumferential surface of the belt. The plurality of rubbing members transfer the belt. A first rubbing member with a first winding angle of the belt on the upstream side of the contact portion in the first direction and a second rubbing member with a second angle larger than the first angle The center point of the contact portion in the moving direction of the belt and the rotation center of the support member with respect to each of the plurality of rubbing members when viewed in a direction substantially orthogonal to the moving direction of the belt; The rotation center arrangement angle with respect to the second rubbing member is the rotation direction with respect to the first rubbing member, where the angle formed by the connected straight line and an arbitrary reference straight line is the rotation center arranging angle. An image forming apparatus is provided that is characterized by being different from the centering angle.

  According to the present invention, it is possible to reduce the vibration of the support member of the rubbing member due to the frictional force generated between the endless belt and the rubbing member with a simple configuration.

1 is a schematic cross-sectional view of an image forming apparatus. FIG. 2 is a schematic perspective view of an intermediate transfer unit. It is a top view of a primary transfer unit. FIG. 2 is a cross-sectional view of a primary transfer unit in the lateral direction. FIG. 6A is a side view and a perspective view of a primary transfer member. FIG. 6A is a perspective view and a longitudinal cross-sectional view of the periphery of a support member of a primary transfer unit. It is a side view of a primary transfer unit. FIG. 5 is a cross-sectional view showing the contact and separation states of the primary transfer unit in (a) color mode and (b) monochrome mode. FIG. 13 is a cross-sectional view for describing a force applied to a primary transfer unit of a first image forming unit (comparative example). FIG. 14 is a cross-sectional view for explaining the force applied to the primary transfer unit of the second image forming unit (comparative example and example). FIG. 14 is a cross-sectional view for explaining the force applied to the primary transfer unit of the third image forming unit (comparative example and example). FIG. 14 is a cross-sectional view for explaining the force applied to the primary transfer unit of the fourth image forming unit (comparative example and example). FIG. 7 is a cross-sectional view for explaining the force applied to the primary transfer unit of the first image forming unit (embodiment). FIG. 5 is a cross-sectional view showing the arrangement of the primary transfer units.

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

Example 1
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 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 of the present embodiment is a laser beam printer adopting an intermediate transfer method and a tandem method capable of forming a full color image using an electrophotographic method.

  The image forming apparatus 100, as a plurality of image forming units (stations), forms first, second, third, and so on images for yellow (Y), magenta (M), cyan (C), and black (K), respectively. The fourth image forming units SY, SM, SC, and SK are included. In the case where an element having a common function and configuration provided in each of the image forming units SY, SM, SC, and SK does not need to be particularly distinguished, a symbol at the end of the code indicating that it is an element for any color Y "," M "," C ", and" K "are abbreviated and the said element is explained in a comprehensive manner.

  In the image forming portion S, a photosensitive drum 1 which is a rotatable drum type electrophotographic photosensitive member (photosensitive member) as an image bearing member is disposed. The photosensitive drum 1 is rotationally driven in the direction of the arrow R1 in the drawing. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by the charging roller 2 which is a roller type charging member as charging means. The charged surface of the 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 Be 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 means, and a toner image is formed on the photosensitive drum 1. In the present embodiment, a toner image is formed by image area exposure and reversal development. That is, in the exposed portion on the photosensitive drum 1 where the absolute value of the potential is lowered by being exposed after being uniformly charged, the charged polarity of the charging polarity of the photosensitive drum 1 (negative in this embodiment) is charged. Toner adheres.

  An intermediate transfer belt 7 formed of an endless belt as an intermediate transfer member is disposed to face each photosensitive drum 1 of each image forming unit S. The intermediate transfer belt 7 is an example of an endless belt (endless moving member) stretched by a plurality of stretching rollers and capable of moving in contact with a plurality of image carriers. The intermediate transfer belt 7 is rotationally driven in the direction of arrow R2 in the drawing. 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 at a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 1 and the intermediate transfer belt 7 contact. 7 electrostatically transferred (primary transfer). At this time, a primary transfer bias (primary transfer voltage) having a polarity reverse 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, toner images of the respective colors formed on the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially transferred onto the intermediate transfer belt 7 in a superimposed manner. The toner remaining on the photosensitive drum 1 after the primary transfer is removed from the photosensitive drum 1 by a drum cleaner 6 as a photosensitive member cleaning unit and collected.

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

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

  The image forming apparatus 100 of the present 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, all of the first, second, third and fourth image forming portions SY, SM, SC and SK can be used to form a full color image by the process as described above. On the other hand, in the monochrome mode, only the fourth image forming unit SK can be used to form a black monochromatic image in the same process as described above. Then, as described later in detail, the contact / separation state between each of the photosensitive drums 1Y, 1M, 1C, 1K and the intermediate transfer belt 7 is changed between the color mode and the monochrome mode.

  Each image forming unit S is configured 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 and the charging roller 2 as a process means acting on the photosensitive drum 1, the developing device 4 and the drum cleaner 6 are integrated with the main body 110 of the image forming apparatus 100. Thus, the removable process cartridge 9 is configured.

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

  Here, with regard to 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 rear side of FIG. As "right". Further, regarding the image forming apparatus 100, the upper side of FIG. 1 is referred to as “upper”, and the lower side of FIG. 1 is referred to as “lower”. A line connecting the left and right sides 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 substantially orthogonal to the movement direction of the intermediate transfer belt 7. At the front of the image forming apparatus 100, a door 120 for opening the inside of the apparatus main body 110 is provided. 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. As shown in FIG. In FIG. 2, the intermediate transfer belt 7 is not shown. The intermediate transfer unit 70 includes an intermediate transfer belt 7, a drive 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, 5K, and a separation member 77. .

  The intermediate transfer belt 7 is composed of a flexible endless belt (film) made of a resin material or a rubber material. The intermediate transfer belt 7 is stretched around a driving roller 71 as a stretching roller (supporting roller), a tension roller 72 and an auxiliary roller 73. 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 a driving unit (not shown) provided in the apparatus main body 110, and moves the intermediate transfer belt 7 (endless movement). 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 an urging means, and tension (belt tension) Give).

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

  Further, the above-described secondary transfer roller 8 is disposed at a position facing the driving roller 71 via the intermediate transfer belt 7. Then, the secondary transfer roller 8 is pressed toward the driving roller (secondary transfer opposing roller) 71 via the intermediate transfer belt 7, and the secondary transfer portion where the intermediate transfer belt 7 and the secondary transfer roller 8 contact with each other. N2 is formed.

  The separating member 77 separates the primary transfer members 51Y, 51M, 51C from the photosensitive drums 1Y, 1M, 1C of the first, second, third image forming portions SY, SM, SC in order to separate the intermediate transfer belt 7 from the photosensitive drums 1Y, 1M, 1C. The photosensitive drums 1Y, 1M, and 1C are separated. The separating member 77 will be further described later. The separating member 77 moves between a position where the rubbing members other than the specific rubbing member among the plurality of sliding members are in contact with the inner peripheral surface of the belt and a position where the sliding members are separated from the inner peripheral surface of the belt. It is an example of the moving means to make it.

3. Primary Transfer Unit Next, the primary transfer unit 5 in this embodiment will be described. In the present 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, configurations and operations common to the respective image forming units S will be described in a general manner, and different configurations and operations in some of the image forming units S will be appropriately pointed out.

  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 cross-sectional view of a portion of the primary transfer unit 5 as viewed along a direction substantially orthogonal to the movement 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 extending in one direction, which is disposed along the rotational axis direction of the photosensitive drum 1 (the direction substantially orthogonal to the movement direction of the intermediate transfer belt 7). The primary transfer member 51 is an example of a rubbing member provided so as to be in contact with the inner circumferential surface of the belt, and rubbing the belt as the belt moves at a contact portion with the inner circumferential surface of the belt. FIG. 5A is a side view of the primary transfer member 51 in the longitudinal direction. 5B is a perspective view of the primary transfer member 51. FIG. In the present embodiment, the dimension L of the primary transfer member 51 in the longitudinal direction (direction substantially orthogonal to the moving direction of the intermediate transfer belt 7) is L = 238 mm. In the present embodiment, the dimension W of the primary transfer member 51 in the lateral direction (direction substantially parallel to the moving direction of the intermediate transfer belt 7) is W = 4 mm. In the present embodiment, a velvet-like (brush-like) fabric formed of conductive nylon fibers is used as the material of the primary transfer member 51.

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

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

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

  The primary transfer member 51 is supported by the support member 53 by supporting the holding member 52 holding the primary transfer member 51 by the support member 53. The support members 53 are respectively disposed at both ends of the primary transfer member 51 in the longitudinal direction, and each support member 53 is substantially at the center in a direction (width direction) substantially orthogonal to the movement direction of the intermediate transfer belt 7. It is constructed in line symmetry. The primary transfer member 51 has a pressing member (biasing member) 54 as a pressing unit (biasing unit) at each end in the longitudinal direction, thereby pressing (biasing) the support member 53, thereby the photosensitive drum It is pressed in the direction towards 1. In the present embodiment, the pressing member 54 is constituted by 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 (rear surface) of the intermediate transfer belt 7 and the primary transfer member 51 can be brought into close contact with each other. There is.

  FIG. 6A is a perspective view of the left end portion of the primary transfer member 51 and its vicinity. 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. As shown in FIG. 6A, both ends of the holding member 52 in the longitudinal direction are fixed to the support member 53 by being lightly press-fitted into the fitting portions 53b formed in the support member 53. . In the present embodiment, the support member 53 is formed of a resin material. Further, as shown in FIG. 6 (b), the contact member 55 has a bottom 55a and two side portions 55b, 55b extending in the same direction substantially parallel to each other in the direction substantially orthogonal to the bottom 55a. It has a spring shape. The contact member 55 is disposed between the two side portions 55 b and 55 b so as to sandwich the end weld portion 51 b of the primary transfer member 51 and the inner surface of the fitting portion 53 b of the support member 53. The upper side portion 55 b of the contact member 55 is in contact with the end welding 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. The primary transfer bias can be supplied to the primary transfer member 51 from an electric substrate (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 FIG. As shown in FIGS. 6 (a) and 7, the support member 53 is provided at one end in the longitudinal direction, which is disposed along the movement direction of the intermediate transfer belt 7, with a rotation shaft (rotational fulcrum) 53a. Have. The rotation axis (swing axis) of the rotation shaft 53a is disposed substantially parallel to the rotation axis direction of the photosensitive drum 1 (the direction substantially orthogonal to the movement direction of the intermediate transfer belt 7). The support member 53 is held by a holding portion 74 a whose pivot shaft 53 a is formed on the frame 74. As a result, the primary transfer unit 5 is rotatable (pivotable) about the rotational shaft 53a, that is, with the engagement portion between the rotational shaft 53a and the holding portion 74a as a fulcrum. Further, by the rotation shaft 53a being held by the holding portion 74a, positioning in the movement direction of the intermediate transfer belt 7 of the primary transfer unit 5 is performed.

4. Separation of Primary Transfer Unit As described above, the image forming apparatus 100 according to this embodiment can form an image in the color mode and the monochrome mode. In the color mode, the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other in all of the first, second, third and fourth image forming portions 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, and the fourth image forming unit SK Only the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other.

  In the following description, elements provided for each of the image forming units SY, SM, SC, and SK may be distinguished by adding “Y”, “M”, “C”, and “K” at 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 separating member 77 switches the contact / separation state of the YMCK photosensitive drums 1Y, 1M, 1C, 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, 53C are disposed at one end in the longitudinal direction (opposite to the pivot shaft 53a) disposed along the movement direction of the intermediate transfer belt 7. It has an engaging portion 53c. On the other hand, as shown in FIG. 2, the spacing member 77 has a spacing action portion 77 a that engages with the engagement portion 53 c of the YMC support members 53 Y, 53 M, 53 C. In the present embodiment, the separating member 77 receives a driving force from a driving source (not shown) for driving the driving roller 71, and linearly moves (reciprocates, translates) substantially parallel to the moving direction of the intermediate transfer belt 7. ).

  When the separating member 77 is moved in the direction in which the separating acting portion 77a approaches the pivot shaft 53a of the YMC supporting members 53Y, 53M, 53C, the separating acting portion 77a becomes the engaging portion 53c of the YMC supporting members 53Y, 53M, 53C. It engages and slides on the engaging portion 53c. Thus, the separation member 77 rotates the YMC support members 53Y, 53M, and 53C 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, and 51C from the intermediate transfer belt 7, and separates the intermediate transfer belt 7 from the YMC photosensitive drums 1Y, 1M, and 1C. The position of the separation member 77 at this time is referred to as a collar separation position.

  On the other hand, when the separating member 77 is moved from the collar separating position in a direction away from the pivoting shaft 53a of the YMC support members 53Y, 53M, 53C from the separating member 77, the separating agent 77a engages. It slides on the part 53, and the engagement is finally released. As a result, the YMC support members 53Y, 53M, and 53C rotate 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 move to the intermediate transfer belt 7. It abuts on the YMC photosensitive drums 1Y, 1M and 1C via the above. The position of the separation member 77 at this time is referred to as a collar contact position. In the present embodiment, the engagement portion 53c is not provided in the K support member 53K, and the separation action portion 77a corresponding to the K image forming portion SK is not provided in the separation member 77.

  FIG. 8A shows the contact and 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, and 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 of coming into contact with the lower surfaces of the photosensitive drums 1Y, 1M, 1C, 1K respectively corresponding to them, and pressed with a predetermined pressing force. It will be in the state. As a result, the YMCK primary transfer units 5Y, 5M, 5C, 5K form a nip between the YMCK photosensitive drums 1Y, 1M, 1C, 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 And contact.

  Here, in the present embodiment, the K photosensitive drums 1K are 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 a straight line connecting the contact positions of the YMC photosensitive drums 1Y, 1M, and 1C with the intermediate transfer belt 7. Thus, the intermediate transfer belt 7 is disposed in the direction of pushing 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 portion between the YMC primary transfer members 51Y, 51M, 51C and the inner peripheral surface of the intermediate transfer belt 7. Are disposed 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 the contact and separation states of 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 collar separation position. In this state, the YMC primary transfer members 51Y, 51M, and 51C are moved about 4 mm in the direction away from the intermediate transfer belt 7, and are separated from the inner circumferential surface of the intermediate transfer belt 7. Further, as described above, the YMC photosensitive drums 1Y, 1M, and 1C and the K photosensitive drum 1K have different heights. Therefore, when the YMC primary transfer members 51Y, 51M, and 51C separate from the intermediate transfer belt 7, the intermediate transfer belt 7 also moves away from the YMC photosensitive drums 1Y, 1M, and 1C by about 2 mm. As a result, the YMC photosensitive drums 1Y, 1M, 1C and the intermediate transfer belt 7, and the intermediate transfer belt 7 and the YMC primary transfer members 51Y, 51M, 51C are separated by about 2 mm.

  In this embodiment, when viewed in the 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 in tension with the drive roller 71. It is disposed on a common tangent with the roller 72.

5. Arrangement of Support Member of Primary Transfer Unit 5-1. Overview 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. The rotational shaft 53a of the support member 53 constituting the rotational 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 rotating shaft 53a becomes unstable, vertical vibration may occur, which may result in generation of noise. Therefore, it is desirable that forces in the same direction act on the pivot 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 It is arranged above the common tangent line of 71 and the tension roller 72. Therefore, in the contact / separation state in the color mode shown in FIG. 8A, a force pulling downward may act on the YC primary transfer units 5Y and 5C. In addition, the force applied to the primary transfer unit 5 changes in the stop state and the movement state of the intermediate transfer belt 7. Then, in the primary transfer unit 5 in which the pulling force acts downward as described above, the direction of the force applied to the rotating shaft 53a may change as the intermediate transfer belt 7 moves. In particular, when the rotation shaft 53a of the support member 53 is disposed on the upstream side 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 portion SY. Vibration of the pivot shaft 53a of the support member 53 is likely to occur. This will be described in more detail below.

5-2. Force acting on the primary transfer unit and generation mechanism of vibration Next, in order to facilitate understanding of the configuration of the present 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. Do. 9, 10, 11 and 12 are sectional views taken in a direction substantially orthogonal to the moving direction of the intermediate transfer belt 7 for explaining the forces applied to the YMCK primary transfer units 5Y, 5M, 5C, 5K, respectively. FIG.

  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 other configuration is substantially the same.

The following static forces are always generated.
F1: upward force F2 received from the pressing member 54: downward force received from the intermediate transfer belt 7

  The force F1 received from the pressing member 54 works toward the rotational center of the photosensitive drum 1 in any of the Y, M, C, and K image forming units SY, SM, SC, and SK. Further, the YMC primary transfer members 51Y, 51M, 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 Y receives a downward force F 2 due to the bending of the intermediate transfer belt 7. Similarly, the downstream end of the C primary transfer member 51 C receives a downward force F 2 due to the bending of the intermediate transfer belt 7. By this force F2, in the YC image forming units SY and SC, a central 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 A moment is generated on the pivot shaft 53a with O as a fulcrum. In the MK image forming units SM and SK, no force is generated that the intermediate transfer belt 7 applies to the MK primary transfer units 5M and 5K. The pressing force of each of the image forming units SY, SM, SC, and SK is adjusted such that F1−F2 = 2.8N.

Next, there are the following dynamic forces generated when the intermediate transfer belt 7 moves.
F3: Frictional force between the primary transfer member 51 and the intermediate transfer belt 7 and adsorption force generated when the primary transfer bias is supplied (hereinafter, also referred to as "tangential force")
F4: Force to push the pivot shaft 53a upward F5: Frictional force between the pivot 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 of F3 acts between the rotation axis 53a and the transfer unit central point O, and “F3 × sin θ × cos θ” which is a cos θ component of this component It acts on the pivot shaft 53a as an upward force F4. Further, with the occurrence of F4, on the positioning surface of the rotating shaft 53a in the movement direction of the intermediate transfer belt 7, a frictional force acts as a downward force F5 with the holding portion 74a.

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

  Next, the generation mechanism of the 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. In addition, since F3 is zero, F4 and F5 generated by F3 are also zero, and only a static force (force when the intermediate transfer belt 7 is not moving) is temporarily applied to the primary transfer unit 5 Will work.

  The primary transfer unit 5 repeats the above operation, and the vertical direction of the force applied to the rotary shaft 53a in the static state is opposite to the vertical direction of the force applied to the rotary shaft 53a in the dynamic state. In the case, the vertical vibration occurs. This is a generation mechanism of the primary transfer unit 5 vibration.

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

・ Y image formation unit (Fig. 9)
L1y (the distance from the transfer unit center point Oy to the rotation center of the rotation shaft 53aY) = 30 mm
L2y (the distance from the transfer unit center point Oy to the positioning surface in the moving direction of the intermediate transfer belt 7 of the rotating shaft 53aY) = 27 mm
L3y (the distance from the transfer unit center point Oy to the upstream end of the primary transfer member 51Y) = 2 mm
θy1 (an angle formed by a tangent of the intermediate transfer belt 7 from the drive roller 71 to the Y primary transfer portion N1Y and a straight line connecting the transfer portion central point Oy and the rotation center of the rotation shaft 53aY) = 9.5 °
θy2 (the angle between 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 (friction coefficient of sliding portion between pivot shaft 53aY and frame 74) = 0.2
T (tension pressure of intermediate transfer belt 7) = 42.5 N
F1y (push-up force of pressing member 54) = 4.6 N
F2y (depressing force that T applies to the upstream end of the primary transfer member 51Y) = − (T × sin θy2) = − 1.8N
F3y (assumed maximum tangent force) = 5 N
F4y (push-up force to the rotating shaft 53aY generated by F3) = F3y × sin (θy1 + θy2) × cos (θy1 + θy2) = 1.02N
F5y (frictional force between the rotation shaft 53aY and the frame 74) = - {F3y × cos 2 (θy1 + θy2) × μ} = - 0.96N
Msy (static moment around transfer center point Oy)
= F 2 y × L 3 y = -3.6 N · mm
Mdy (dynamic moment around the transfer center point Oy)
= Msy + F4y x L1y + F5y x L2y = 1.08 N mm

M image forming unit (FIG. 10)
L1 m = 30 mm
L2m = 27mm
θm (an angle formed by a tangent 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 central 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 transfer center Om)
= 0 N · mm
Mdm (dynamic moment around transfer center point Om)
= Msm + F 4 m × L 1 m + F 5 m × L 2 m = 4.68 N · mm

・ C image forming unit (FIG. 11)
L1c = 30 mm
L2c = 27 mm
L3 c (the distance from the transfer unit center point Oc to the downstream end of the primary transfer member 51 C) = 2 mm
θc1 (an angle formed by a 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 central point Oc and the rotation center of the rotation shaft 53aC) = 12 °
θc2 (an angle formed by a tangent of the intermediate transfer belt 7 from the M primary transfer portion N1M to the C primary transfer portion N1C and a 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 intermediate transfer belt 7) = 42.5 N
F1c = 3.9N
F2c (the pressing force that T applies 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 transfer center point Oc)
= F 2 c ×-L 3 c = 2.2 N · mm
Mdc (dynamic moment around transfer center point Oc)
= Msc + F4c x L1c + F5c x L2c = 10.45 N mm

・ K image formation unit (Fig. 12)
L1k = 30 mm
L2k = 27 mm
θk1 (an angle formed by a tangent of the intermediate transfer belt 7 from the C primary transfer portion N1C to the K primary transfer portion N1K and a straight line connecting the transfer portion central point Oc and the rotation center of the rotation shaft 53aK) = 13.5 °
θk2 (an 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
F5 k = − {F 3 k × cos ² (θ k 1 −θ k ² ) × μ} = − 0.96 N
Msk (static moment around transfer center Ok)
= 0 N · mm
Mdk (dynamic moment around the transcription center point Ok)
= Msk + F 4 k × L 1 k + F 5 k × L 2 k = 4.68 N · mm

  As described above, in the comparative example, the vertical direction of the static moment Msy and the dynamic moment Mdy around the transfer unit center point Oy is switched only in the Y image forming unit SY. Therefore, in the comparative example, in the Y image forming unit SY, vibration of the rotation shaft 53a is likely to occur at the time of occurrence of stick-slip, for example.

  This is because the winding angle (θy2) of the intermediate transfer belt 7 with the primary transfer member 51Y at the upstream end of the primary transfer member 51Y is relatively large in the Y image forming unit SY. That is, in the Y image forming unit SY, since the winding angle is relatively large, a downward force acts on the upstream end of the primary transfer member 51Y, and as a result, the rotation shaft 53aY of the support member 53Y is downward. The lower 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. This can be represented by the angle between the tangent of and 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 at the upstream end of the primary transfer portion N1K.

5-3. Next, the force applied to the primary transfer unit 5 in the contact / separation state in the color mode in the present embodiment will be described. FIG. 13 is a cross-sectional view seen in the 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 the present embodiment.

  In the present embodiment, the height of the pivot shaft 53aY of the support member 53Y is lowered by the amount of θy2 in the Y image forming unit SY based on the examination result in the above-described comparative example. Accordingly, an angle θy1 between the tangent 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 central point Oy and the rotation center of the rotation shaft 53aY is 12 ° = Θ y 1 ').

  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 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, since the upstream end of the primary transfer member 51Y is substantially parallel to the surface of the intermediate transfer belt 7, the upstream end of the primary transfer member 51Y is directed downward. 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 acts on the downstream end. Therefore, an upward force acts on the pivot shaft 53aY of the support member 53Y with the downstream end 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 in the comparative example.
L1y = 30 mm
L2y = 27 mm
L3 y = 2 mm
θy1 ′ = 12 °
θy2 = 2.5 °
μ = 0.2
T = 42.5N
F1y = 4.6N
F2y (the pressing force that T applies 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 transfer center point Oy)
= F 2 y ×-L 3 y = 3.6 N · mm
Mdy (dynamic moment around the transfer center point Oy)
= Mys + F4y x L1y + F5y x L2y = 14.52 N mm

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

FIG. 14 schematically shows the arrangement relationship of the primary transfer unit 5 in each image forming unit S of this embodiment. Here, when viewed in a direction substantially orthogonal to the movement direction of the intermediate transfer belt 7, an angle between 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 Is a rotation center arrangement angle θ. At this time, in the present 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 each of 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 of at least two of the plurality of primary transfer members 51 with the primary transfer member 51 and the intermediate transfer belt 7 And approximately parallel). At this time, in the present embodiment, the rotation center arrangement angles θy, θm, θc, θk for the YMCK primary transfer members 5Y, 5M, 5C, 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 at the YMC primary transfer portions N1Y, N1M, N1C (common tangent of the YMC photosensitive drum 1), θy, θm, θc,. θ k is as follows.
θy = θy1 + θy2 = 14.5 °
θm = 12 °
θc = θc1 = 12 °
θk = θk1-θk2 = 12 °
(Since the tangent line of the intermediate transfer belt 7 at the YMC primary transfer portions N1Y, N1M, N1C and the tangent line 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 at 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 for a part of the primary transfer member 51 is made different from the rotation center arrangement angle θ for the other primary transfer members 51. More specifically, the rotation center arrangement angle θ for a part of the primary transfer member 51 is made larger than the rotation center arrangement angle θ for the other primary transfer members 51. As a result, even when stick-slip occurs, it is possible to suppress the generation of vertical vibration of the pivot shaft 53a of the support member 53 with respect to the primary transfer member 51 in part.

  The M image forming unit SM and the K image forming unit SK whose static moment is 0 N · mm are also rotated by lowering the height of the rotating shaft 53 a of the support member 53 as in the Y image forming unit SY. The center arrangement angle θ may be increased. As a result, even 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 is further enhanced. It can be enhanced.

  As described above, according to the present embodiment, the vibration of the support member 53 of the primary transfer member 51 caused by 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 described based on the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiment, the intermediate transfer type image forming apparatus in which the endless belt is an intermediate transfer member has been described, but the present invention is not limited to this. The present invention can also be applied to a direct transfer type image forming apparatus. The image forming apparatus of the direct transfer type has a conveyance belt (recording material holding belt) composed of an endless belt as a recording material holding member in place of the intermediate transfer belt in the image forming apparatus of FIG. In this image forming apparatus, the toner images formed on the photosensitive drums in the respective image forming units are transferred to the recording material carried and conveyed on the conveying belt in the respective transfer units by the action of the transfer member. In this case, the configuration of the image forming unit is the same as that of the image forming apparatus shown in FIG. 1, and the transfer member (transfer unit) is the same as the primary transfer member (primary transfer unit) of the image forming apparatus shown in FIG. Is used. Also in such a direct transfer type image forming apparatus, the same problem of noise due to the vibration of the transfer unit as in the case of the intermediate transfer type image forming apparatus may occur. Therefore, by applying the present invention to such a direct transfer type image forming apparatus, the same effect as that of the above-described embodiment can be obtained.

  Further, in the above-described embodiment, the transfer members of the image forming portion other than the specific image forming portion among the plurality of image forming portions can be separated from the belt, but the transfer members of all the image forming portions are separated from the belt It may be possible.

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

  Further, in the above-described embodiment, an example in which the image forming apparatus is a laser beam printer has been described, but the present invention is not limited to this. The present invention can be applied to an image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction machine having a plurality of functions of these, or an original conveying apparatus used by connecting to a light printer. That is, the present invention is applicable to any belt device having an endless belt and a rubbing member supported by a rotatable support member for rubbing a moving belt.

  In the above-described embodiment, the contact position between the transfer member and the belt of one of the plurality of transfer members is disposed in the direction of pushing the belt inwardly 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 if the contact positions between all the transfer members and the belt are arranged on the same straight line. That is, in the moving direction of the belt, a region between the most upstream transfer portion and the most downstream transfer portion is defined as a transfer region. At this time, for example, a straight line connecting the contact positions of each transfer member and the belt is common to a tension roller disposed adjacent to the upstream side of the transfer region and a tension roller disposed adjacent to the downstream side. It may be disposed on the outer peripheral side (upper side) of the belt than the tangent line of the belt. Also in this case, in the most upstream transfer portion, a force is applied to the transfer member toward the inner peripheral side of the belt by the belt. Then, 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 pivot axis of the support member of the most upstream transfer portion. Therefore, even in such a configuration, by applying the present invention, it is possible to suppress the vibration of the pivot shaft of the support member and to suppress the generation of noise as in the case of the above-described embodiment.

  That is, according to the present invention, the winding angle of the belt to the transfer member on the upstream side of the contact portion between the inner circumferential surface of the belt and the transfer member is higher than the first rubbing member of the first angle and the first angle. It is applicable if it is the composition which has a plurality of transfer members containing the 2nd rubbing member of a large 2nd angle. In such a configuration, the rotation center arrangement angle θ for the second rubbing member may be different from the rotation center arrangement angle θ for the first rubbing member. More specifically, as described above, the rotation center arrangement angle θ for the second rubbing member may be set larger than the rotation center arrangement angle θ for the first rubbing member. At this time, the transfer member having a large wrap angle is not limited to one. For example, the contact position between the transfer member and the belt may be alternately repeated along the moving direction of the belt. In this configuration, the tension surface of the belt between the transfer member and the tension roller and transfer member disposed on the upstream side of the transfer member is inclined more than the other transfer members in two or more transfer members (wound It is conceivable that the angle is large). In this case, the rotation center arrangement angle θ with respect to at least one of the two or more transfer members having a relatively large wrap angle is the rotation center arrangement of at least one transfer member having a wrap angle smaller than that of the transfer member. If different from the angle θ, a corresponding effect is obtained.

Reference Signs List 1 photosensitive drum 5 primary transfer unit 7 intermediate transfer belt 51 primary transfer member 53 support member 53 a rotational shaft 54 pressing member 70 intermediate transfer unit (belt device)
74 frame 74 a holding unit 100 image forming apparatus N 1 primary transfer unit S image forming unit

Claims (14)

With multiple tension rollers,
A movable endless belt stretched over the plurality of stretching rollers;
A plurality of rubbing members provided on the inner circumferential surface of the belt so as to be contactable, and rubbing the belt along with the movement of the belt at a contact portion with the inner circumferential surface of the belt;
A plurality of pivotable support members each supporting the plurality of rubbing members and having a pivot shaft;
A plurality of holding portions that respectively hold pivot shafts of the plurality of support members;
Pressing means for respectively pressing the plurality of support members so as to press the plurality of rubbing members toward the inner circumferential surface of the belt;
In a belt device having
The plurality of rubbing members are configured such that a winding angle of the belt on the upstream side of the contact portion in the moving direction of the belt is greater than a first rubbing member having a first angle and a first angle. Including a second rubbing member at an angle of 2,
The center point of the contact portion in the moving direction of the belt and the rotation center of the support member are connected to each of the plurality of rubbing members when viewed in a direction substantially orthogonal to the moving direction of the belt The rotation center arrangement angle with respect to the second rubbing member is the rotation center arrangement with respect to the first rubbing member, where the angle between the straight line and an arbitrary reference straight line is the rotation center arranging angle. Belt device characterized in that it is different from the 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 a contact portion between at least two rubbing members of the plurality of rubbing members and the belt. The belt device according to claim 1, wherein the angle is larger than the rotation center arrangement angle with respect to the first rubbing member.   The belt device according to claim 1, wherein a pivot shaft of the support member is disposed upstream of the contact portion in the moving direction of the belt.   Among the plurality of rubbing members, the rubbing members other than the specific rubbing member including the second rubbing member are respectively separated from the inner circumferential surface of the belt and the position where the rubbing member is in contact with the inner circumferential surface of the belt The belt device according to any one of claims 1 to 3, further comprising moving means for moving between the two positions.   When viewed in a direction substantially orthogonal to the moving direction of the belt, the contact portion relating to the specific rubbing member is relative to a straight line connecting the contact portions relating to the rubbing member other than the specific rubbing member. The belt device according to claim 4, wherein the belt device is disposed on the inner peripheral side of the belt.   Among the plurality of rubbing members, the specific rubbing member is disposed most downstream in the moving direction of the belt, and the second rubbing member is disposed most upstream in the moving direction of the belt The belt device according to claim 4 or 5, characterized in that   The belt according to any one of claims 1 to 6, wherein the rotation center arrangement angle of the rubbing members other than the second rubbing member among the plurality of rubbing members is the same. apparatus. With multiple image carriers,
With multiple tension rollers,
An endless belt stretched on the plurality of stretching rollers and movable in contact with the plurality of image carriers;
The belt is provided to face each of the plurality of image carriers via the belt so as to be in contact with the inner circumferential surface of the belt, and the belt is moved along with the movement of the belt at the contact portion with the inner circumferential surface of the belt. A plurality of rubbing members for rubbing
A plurality of pivotable support members each supporting the plurality of rubbing members and having a pivot shaft;
A plurality of holding portions that respectively hold pivot shafts of the plurality of support members;
Pressing means for respectively pressing the plurality of support members so as to press the plurality of rubbing members toward the inner circumferential surface of the belt;
In an image forming apparatus having
The plurality of rubbing members are configured such that a winding angle of the belt on the upstream side of the contact portion in the moving direction of the belt is greater than a first rubbing member having a first angle and a first angle. Including a second rubbing member at an angle of 2,
The center point of the contact portion in the moving direction of the belt and the rotation center of the support member are connected to each of the plurality of rubbing members when viewed in a direction substantially orthogonal to the moving direction of the belt The rotation center arrangement angle with respect to the second rubbing member is the rotation center arrangement with respect to the first rubbing member, where the angle between the straight line and an arbitrary reference straight line is the rotation center arranging angle. 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 a contact portion between at least two rubbing members of the plurality of rubbing members and the belt. The image forming apparatus according to claim 8, wherein the rotation center arrangement angle with respect to the first rubbing member is larger than the rotation center arrangement angle.   The image forming apparatus according to claim 8, wherein a pivot shaft of the support member is disposed upstream of the contact portion in the moving direction of the belt.   Among the plurality of rubbing members, the rubbing members other than the specific rubbing member including the second rubbing member are respectively separated from the inner circumferential surface of the belt and the position where the rubbing member is in contact with the inner circumferential surface of the belt The image forming apparatus according to any one of claims 8 to 10, further comprising moving means for moving between the position where it is moved.   When viewed in a direction substantially orthogonal to the moving direction of the belt, the contact position between the image carrier corresponding to the specific rubbing member and the belt is the contact between the rubbing members other than the specific rubbing member. In a direction in which the belt is pushed inward relative to a straight line connecting the contact position between the image carrier and the belt corresponding to the rubbing members other than the specific rubbing member in the state of being moved to the The image forming apparatus according to claim 11, wherein the image forming apparatus is disposed.   Among the plurality of rubbing members, the specific rubbing member is disposed most downstream in the moving direction of the belt, and the second rubbing member is disposed most upstream in the moving direction of the belt An image forming apparatus according to claim 11 or 12, characterized in that   The image according to any one of claims 8 to 13, wherein the rotation center arrangement angle of the rubbing members other than the second rubbing member among the plurality of rubbing members is the same. Forming device.