JP2017026724A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in a configuration in which a first support roller for a belt is automatically moved to a second support roller, capable of improving position accuracy of the first support roller to the second support roller.SOLUTION: Provided is an image forming apparatus 100 having: a plurality of support rollers 71-74 including a first support roller 73 on a downstream side of a plurality of image carriers 1Y-1K and a support roller 74 on the downstream side of the first support roller 73; and a control part 50 capable of making switch between a first state in which a belt 7 is in contact with at least the most downstream image carrier 1K and a second state in which the belt 7 is separated from the image carrier 1K. The image forming apparatus is configured to have a support member 21 for rotatably supporting the first support roller 73 around the rotating shaft of the second support roller 74 while keeping a constant distance between the rotating shaft of the first support roller 73 and the rotating shaft of the second support roller 74, and a moving mechanism 20 for moving the first support roller 73 between a first position in the first state and a second position in the second state.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a fax machine using an electrophotographic system or an electrostatic recording system.

  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 (hereinafter, also simply referred to as “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 has an image forming section that forms an image with toner of each color of yellow, magenta, cyan, and black. As an example, a tandem-type electrophotographic image forming apparatus employing an intermediate transfer method has an intermediate transfer belt that is an endless belt stretched around a plurality of stretch rollers (support rollers) as an intermediate transfer member, A plurality of photoconductors are arranged side by side along the intermediate transfer belt. The primary transfer of the toner image from the photoreceptor to the intermediate transfer belt is performed, for example, by applying a voltage to a primary transfer member that contacts the photoreceptor via the intermediate transfer belt.

  In this type of image forming apparatus, the intermediate transfer belt is brought into contact with the photoconductor during image formation, while at the time of non-image formation or when the intermediate transfer belt or photoconductor is attached to or detached from the image forming apparatus main body. In some cases, the photoconductor is separated (Patent Document 1).

  Such a separation operation is automatically executed under the control of the control unit of the apparatus main body without user operation from the viewpoint of user convenience.

JP 2002-23515 A

  In order to ensure a sufficient amount of separation when the intermediate transfer belt is separated from the photosensitive member, in addition to the primary transfer member, intermediate transfer that forms a surface of the intermediate transfer belt stretched opposite to the plurality of photosensitive members. A configuration for moving a belt tension roller is known.

  For example, a primary transfer roller that is provided on the inner peripheral surface side of the intermediate transfer belt and serves as a primary transfer member that forms a primary transfer portion, and a secondary transfer inner roller that is a stretching roller that forms a secondary transfer portion. An auxiliary roller that is a tension roller may be provided between them. In this case, for example, when the intermediate transfer belt is separated from all the photosensitive members, the auxiliary roller may be moved in addition to the primary transfer roller.

  However, if there is a difference in the width direction between the secondary transfer inner roller and the auxiliary roller due to variations in the member that holds the auxiliary roller or backlash of the movable part, the intermediate transfer belt will wrinkle and image defects will occur. May occur. In particular, the above problem can be significant in a configuration in which the auxiliary roller is not moved while checking the distance between the secondary transfer inner roller and the auxiliary roller and the occurrence of wrinkles.

  Accordingly, an object of the present invention is to improve the positional accuracy of the first support roller with respect to the second support roller in a configuration in which the first support roller of the belt is automatically moved with respect to the second support roller. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a plurality of image carriers that are arranged in a substantially straight line and on which toner images are formed, and are arranged along the arrangement direction of the plurality of image carriers, A movable endless belt for carrying the transferred toner image, and a plurality of support rollers for stretching the belt, adjacent to the downstream side of the plurality of image carriers in the moving direction of the belt; A first support roller that is disposed, and a first transfer roller that is disposed adjacent to the downstream side of the first support roller in the moving direction of the belt, and that forms a transfer portion for transferring a toner image from the belt to a recording material. A plurality of support rollers, a first state in which the belt is in contact with at least the most downstream image carrier in the moving direction of the belt among the plurality of image carriers; Among multiple image carriers A control unit capable of switching to at least a second state in which the belt is separated from the most downstream image carrier, and a rotation shaft of the first support roller; A support member that rotatably supports the first support roller around the rotation axis of the second support roller while maintaining a constant distance from the rotation axis of the second support roller; An image forming apparatus comprising: a moving mechanism that moves the first support roller between a first position in the first state and a second position in the second state. It is.

  According to the present invention, in the configuration in which the first support roller of the belt is automatically moved with respect to the second support roller, the positional accuracy of the first support roller with respect to the second support roller can be improved. .

It is a schematic sectional drawing of an image forming apparatus (all contact state). It is a schematic sectional drawing of an image forming apparatus (black contact state). 1 is a schematic cross-sectional view of an image forming apparatus (fully separated state). FIG. 2 is a block diagram illustrating a schematic control mode of a main part of the image forming apparatus. It is typical sectional drawing which shows the movement locus | trajectory of each roller in the case of switching of a separated state. FIG. 2 is a perspective view of an intermediate transfer unit for explaining a moving mechanism in Embodiment 1 (all contact state). FIG. 2 is a perspective view of an intermediate transfer unit for explaining a moving mechanism in Embodiment 1 (fully separated state). It is a schematic sectional drawing of the other example of an image forming apparatus.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[Example 1]
1. FIG. 1 is a schematic 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 tandem type laser beam printer that employs an intermediate transfer method that can form a full-color image using an electrophotographic method. The image forming apparatus 100 forms an image on a recording material (recording medium, transfer material) P in accordance with an image signal sent from a computer or the like.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units SY, SM, SC, and SK as a plurality of image forming units (stations). The first, second, third, and fourth image forming units SY, SM, SC, and SK form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively.

  In this embodiment, the basic configuration and operation of the first, second, third, and fourth image forming units SY, SM, SC, and SK are different in the color of toner used in the developing process described later. Except for this, it is substantially the same. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of a symbol representing an element for any color will be omitted, and the element will be described generally.

  The image forming unit S includes a photosensitive drum 1 that is a rotatable drum type electrophotographic photosensitive member (photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure. In the image forming unit S, the following process devices are sequentially arranged around the photosensitive drum 1 in the rotation direction. First, a charging roller 2 that is a roller-type charging member as a charging unit is disposed. Next, an exposure device (laser scanner) 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 that is a roller-type primary transfer member as a primary transfer means is disposed. Next, a drum cleaner 6 as a photosensitive member cleaning means is disposed. The exposure apparatus 3 is configured as a single unit that can expose the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units SY, SM, SC, and SK.

  The surface of the rotating photosensitive drum 1 is charged almost uniformly by a charging roller 2 to a predetermined potential having a predetermined polarity (negative polarity in this embodiment). The surface of the charged photosensitive drum 1 is exposed by the exposure device 3 based on the input image information signal, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 4 using toner as a developer, and a toner image is formed on the photosensitive drum 1. In this embodiment, a toner image is formed by image part exposure and reversal development. That is, the exposed portion on the photosensitive drum 1 where the absolute value of the potential is 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.

  The image forming apparatus 100 includes an intermediate transfer unit 70 disposed to face the image forming units SY, SM, SC, and SK. The intermediate transfer unit 70 includes an intermediate transfer belt 7 constituted by a rotatable endless belt as an intermediate transfer member. The intermediate transfer belt 7 is stretched around a tension roller 71, an upstream auxiliary roller 72, a downstream auxiliary roller 73, and a driving roller 74 as a plurality of stretching rollers (support rollers). The intermediate transfer belt 7 rotates (circulates) in the direction of arrow R2 in the drawing when the driving roller 74 is driven to rotate. On the inner peripheral surface (back surface) side of the intermediate transfer belt 7, the primary transfer rollers 5Y, 5M, 5C, and 5K described above are disposed to face the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is urged toward the photosensitive drum 1 via the intermediate transfer belt 7 to form 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. On the outer peripheral surface (front surface) side of the intermediate transfer belt 7, a secondary transfer roller 8, which is a roller-type secondary transfer member serving as a secondary transfer unit, is disposed facing the drive roller 74. The secondary transfer roller 8 is urged toward the driving roller 74 via the intermediate transfer belt 7, and passes through a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 7 and the secondary transfer roller 8 are in contact with each other. Form. The drive roller 74 also has a function as a facing member (secondary transfer inner roller, secondary transfer facing roller) of the secondary transfer roller (secondary transfer outer roller) 8. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a belt cleaner 76 as an intermediate transfer member cleaning unit is disposed so as to face the tension roller 71. The intermediate transfer unit 70 will be described in detail later.

  The toner image formed on the photosensitive drum 1 as described above is rotated at the primary transfer portion N1 by the predetermined pressure and electrostatic load bias applied by the primary transfer roller 5 at the intermediate transfer belt 7 that is rotating. Transferred (primary transfer) on top. For example, when forming a full-color image, toner images of each color of yellow, magenta, cyan, and black formed on the photosensitive drums 1Y, 1M, 1C, and 1K are transferred so as to be sequentially superimposed on the intermediate transfer belt 7. . In this case, the image forming process of each color processed in parallel by each image forming unit S is performed at a timing of superimposing on the toner image transferred onto the intermediate transfer belt 7 by the upstream primary transfer unit N1. As a result, a multiple toner image for a full color image is formed on the intermediate transfer belt 7. The toner remaining on the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is removed from the photosensitive drum 1 by the drum cleaner 6 and collected.

  The toner image on the intermediate transfer belt 7 is transferred between the intermediate transfer belt 7 and the secondary transfer roller 8 by the predetermined pressure and electrostatic load bias applied by the secondary transfer roller 8 in the secondary transfer portion N2. Is transferred (secondary transfer) onto the recording material P that is nipped and conveyed. The recording material P is supplied to the secondary transfer portion N2 by the feeding device 9 in accordance with the timing at which the toner image on the intermediate transfer belt 7 is conveyed to the secondary transfer portion N2. The toner remaining on the intermediate transfer belt 7 after the secondary transfer process (secondary transfer residual toner) is removed from the intermediate transfer belt 7 by the belt cleaner 76 and collected.

  The recording material P onto which the toner image has been transferred is conveyed to a fixing device 10 as a fixing unit. The fixing device 10 melts and fixes the toner image on the recording material P by applying a predetermined pressure and heat to the recording material P in a fixing nip formed by the opposing fixing roller 10a and pressure roller 10b. The recording material P on which the toner image is fixed is then discharged (output) to the outside of the apparatus main body 110 of the image forming apparatus 100.

  In this embodiment, in each image forming unit S, the photosensitive drum 1 and the charging roller 2, the developing device 4, and the drum cleaner 6 as process means acting on the photosensitive drum 1 can be integrally attached to and detached from the apparatus main body 110. A simple process cartridge.

2. Intermediate Transfer Unit Next, the basic configuration and operation of the intermediate transfer unit 70 in this embodiment will be described in more detail. In this embodiment, the intermediate transfer belt unit 70 includes an intermediate transfer belt 7, stretching rollers 71 to 74 of the intermediate transfer belt 7, primary transfer rollers 5Y, 5M, 5C, and 5K, a belt cleaner 76, and the like. Has been. The intermediate transfer unit 70 can be attached to and detached from the apparatus main body 110.

  Here, a direction substantially orthogonal to the moving direction of the surface of the intermediate transfer belt 7 is also referred to as a “thrust direction”. This thrust direction is substantially parallel to the rotation axis direction of the photosensitive drum 1 and the stretching rollers 71 to 74. Further, with respect to the image forming apparatus 100, the vertical direction refers to the vertical direction in the vertical direction, but does not mean just above or directly below, but above the horizontal with respect to a reference position or element, It also includes being below. Note that the positional relationship of the positions or elements in the image forming apparatus 100 refers to the positional relationship when the image forming apparatus 100 is disposed in a normally used posture.

  The four photosensitive drums 1Y, 1M, 1C, and 1K are arranged side by side along the moving direction of the surface of the intermediate transfer belt 7. In this embodiment, the arrangement direction of the four photosensitive drums 1Y, 1M, 1C, and 1K is a substantially horizontal direction. More specifically, in the present embodiment, the four photosensitive drums 1Y, 1M, 1C, and 1K are arranged in a substantially straight line so that the common tangent line on all the intermediate transfer units 70 side is substantially horizontal. ing. Here, the arrangement direction of the four photosensitive drums 1Y, 1M, 1C, and 1K is also referred to as “drum arrangement direction”.

  The intermediate transfer unit 70 is configured to be long in one direction along the drum arrangement direction as a whole. The intermediate transfer unit 70 includes an intermediate transfer belt 7. The intermediate transfer belt 7 is stretched around a tension roller 71, an upstream auxiliary roller 72, a downstream auxiliary roller 73, and a driving roller 74 as a plurality of stretching rollers (support rollers). The intermediate transfer belt 7 is disposed along the drum arrangement direction, and is long in one direction along the drum arrangement direction in a state of being stretched by a plurality of stretching rollers 71 to 74 (the horizontal dimension is vertical). Rotate on the transport trajectory (longer than the outer dimension in the direction). The tension roller 71 is urged from the inner peripheral surface side to the outer peripheral surface side of the intermediate transfer belt 7 by a tension spring 75 as an urging unit (tension applying unit), and applies tension to the intermediate transfer belt 7. The upstream auxiliary roller 72 and the downstream auxiliary roller 73 support the intermediate transfer belt 7 on the upstream side and the downstream side of the four photosensitive drums 1Y to 1K in the rotation direction of the intermediate transfer belt 7, respectively, and support the four photosensitive drums 1Y. A surface (image transfer surface) stretched opposite to 1K is formed. The driving roller 75 transmits a rotational driving force from a driving motor (not shown) as a driving means to the intermediate transfer belt 7 to rotate (move, convey) the intermediate transfer belt 7 in the direction of the arrow R2 in the drawing. In this embodiment, the drive roller 74 also functions as a secondary transfer inner roller that forms the secondary transfer portion N2.

As the material of the intermediate transfer belt 7, a highly rigid resin such as PVDF (polyvinylidene fluoride), polyamide, polyimide, PET (polyethylene terephthalate), and polycarbonate is used in order to suppress the generation of wrinkles during rotational driving. Is desirable. Further, if the thickness of the intermediate transfer belt 7 is too thin, there is a concern that sufficient durability due to wear may not be obtained, and if it is too thick, the intermediate transfer belt 7 is appropriately used at the portion that is wound around the stretching rollers 71 to 74. There is a concern that dents and folds may occur without bending. Therefore, the thickness of the intermediate transfer belt 7 is desirably in the range of 0.02 mm to 0.50 mm. In this embodiment, a resin belt having a polyimide base layer is used as the intermediate transfer belt 7. This intermediate transfer belt 7 has a tensile elastic modulus E = 18000 N / cm ² and a film thickness of 0.08 mm.

  In this embodiment, the belt cleaner 76 has a cleaning blade 76 a made of urethane rubber and disposed so as to contact the intermediate transfer belt 7 at a position facing the tension roller 71. The cleaning blade 76 a is arranged in the counter direction with respect to the movement of the surface of the intermediate transfer belt 7. The cleaning blade 76a is set at a set angle (angle formed with the tangent to the intermediate transfer belt 7 at the contact portion) of 25 °, a contact pressure of 30 gf / cm, and the hardness of the urethane rubber is 75 ° in terms of JIS-A hardness. The thickness of the urethane rubber is 2 mm.

3. Next, the contact / separation state (separation state) between the photosensitive drum 1 and the intermediate transfer belt 7 will be described.

  The image forming apparatus 100 according to the present exemplary embodiment can execute an image forming operation in a full color mode in which all the image forming units SY, SM, SC, and SK can form images and form full color images. In addition, the image forming apparatus 100 according to the present exemplary embodiment can execute an image forming operation in a monochrome mode in which an image is formed only in the black image forming unit SK to form a black monochrome image. When the monochrome mode is executed, the intermediate transfer belt 7 is separated from the photosensitive drum 1 in the image forming portions SY, SM, and SC for yellow, magenta, and cyan that are not used for image formation. This is because the wear of the photosensitive drums 1Y, 1M, and 1C for the respective colors of yellow, magenta, and cyan and the intermediate transfer belt 7 is reduced, thereby extending their life. In this embodiment, the intermediate transfer belt 7 can be separated from the photosensitive drum 1 in all the image forming units SY, SM, SC, and SK. This is for preventing the rubbing trace of the contact portion between the intermediate transfer belt 7 and the photosensitive drum 1 due to vibration when the image forming apparatus 100 is transported or moved during non-image formation.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment can switch the contact / separation state between the photosensitive drum 1 and the intermediate transfer belt 7 to the following states. First, the intermediate transfer belt 7 is in contact with all the photosensitive drums 1Y, 1M, 1C, and 1K (hereinafter referred to as “all contact state”). Second, the intermediate transfer belt 7 is in contact with only the black photosensitive drum 1K (hereinafter also referred to as “black contact state”). Third, the intermediate transfer belt 7 is separated from all the photosensitive drums 1Y, 1M, 1C, and 1K (hereinafter, also referred to as “totally separated state”). In this embodiment, as described below, the disengagement state is switched by changing the arrangement of the primary transfer rollers 5Y, 5M, 5C, and 5K, the upstream auxiliary roller 72, and the downstream auxiliary roller 73. .

  1, 2, and 3 are schematic cross-sectional views of the image forming apparatus 100 in the full contact state, the black contact state, and the full separation state, respectively. FIG. 4 is a schematic diagram showing a schematic control mode of the operation for switching the contact state between the photosensitive drum 1 and the intermediate transfer belt 7.

  In the full contact state shown in FIG. 1, all the primary transfer rollers 5Y, 5M, 5C, and 5K are in positions (contact positions) that contact the corresponding photosensitive drums 1Y, 1M, 1C, and 1K via the intermediate transfer belt 7. Be placed. In the full contact state, the upstream auxiliary roller 72 and the downstream auxiliary roller 73 are arranged on a common tangent line of all the photosensitive drums 1Y, 1M, 1C, and 1K. As a result, the intermediate transfer belt 7 is brought into contact with all the photosensitive drums 1Y, 1M, 1C, and 1K.

  In the black contact state shown in FIG. 2, the primary transfer rollers 5Y, 5M, and 5C for yellow, magenta, and cyan colors are moved upward and are separated from the corresponding photosensitive drums 1Y, 1M, and 1C ( (Spaced position). At this time, in this embodiment, the primary transfer rollers 5Y, 5M, and 5C for yellow, magenta, and cyan are separated from the intermediate transfer belt 7. Further, in the black contact state, the upstream auxiliary roller 72 is moved upward and disposed at a position away from the common tangent line of all the photosensitive drums 1Y, 1M, 1C, and 1K. On the other hand, in the black contact state, the primary transfer roller 5K for black is disposed at a position (contact position) that contacts the corresponding photosensitive drum 1K via the intermediate transfer belt 7. Further, the downstream auxiliary roller 73 is disposed on a common tangent line of all the photosensitive drums 1Y, 1M, 1C, and 1K. Accordingly, the intermediate transfer belt 7 is separated from the photosensitive drums 1Y, 1M, and 1C for yellow, magenta, and cyan. The extra length of the intermediate transfer belt 7 generated by the movement of each roller is absorbed by the tension roller 71 moving in the arrow W direction (tension direction) in FIG.

  In the fully separated state shown in FIG. 3, all the primary transfer rollers 5Y, 5M, 5C, and 5K are moved upward and separated from the corresponding photosensitive drums 1Y, 1M, 1C, and 1K (separated positions). Placed in. At this time, in this embodiment, all the primary transfer rollers 5Y, 5M, 5C, and 5K are separated from the intermediate transfer belt 7. In the fully separated state, the upstream auxiliary roller 72 and the downstream auxiliary roller 73 are moved upward and are arranged at positions away from the common tangent line of all the photosensitive drums 1Y, 1M, 1C, and 1K. As a result, the intermediate transfer belt 7 is separated from all the photosensitive drums 1Y, 1M, 1C, and 1K.

  As shown in FIG. 4, in this embodiment, the primary transfer rollers 5Y, 5M, 5C, and 5K are moved by a separation / contact mechanism 30 as a separation / contact means. In the present embodiment, the upstream auxiliary roller 72 is moved by the upstream auxiliary roller moving mechanism 40 as the upstream auxiliary roller moving means. In this embodiment, the downstream auxiliary roller 73 is moved by the downstream auxiliary roller moving mechanism 20 as the downstream auxiliary roller moving means. The operations of the separation / contact mechanism 30, the upstream auxiliary roller moving mechanism 40, and the downstream auxiliary roller moving mechanism 20 are controlled by a CPU 50 as a control unit provided in the apparatus main body 110.

  In this embodiment, the primary transfer roller 5 separated from the photosensitive drum 1 is also separated from the intermediate transfer belt 7 in the black contact state or the completely separated state. As a result, it is easy to ensure the amount of separation of the intermediate transfer belt 7 from the photosensitive drum 1. However, the present invention is not limited to such a configuration, and the primary transfer roller 5 separated from the photosensitive drum 1 may be in contact with the intermediate transfer belt 7.

4). Next, the movement trajectory of each roller when the separation state between the photosensitive drum 1 and the intermediate transfer belt 7 is switched will be described.

  FIG. 5 shows an intermediate transfer showing movement trajectories of the primary transfer rollers 5Y, 5M, 5C, and 5K, the upstream auxiliary roller 72, and the downstream auxiliary roller 73 when the contact state between the photosensitive drum 1 and the intermediate transfer belt 7 is switched. 4 is a schematic cross-sectional view of a unit 70. FIG. The solid line in FIG. 5 shows the full contact state, and the broken line shows the full separation state. Moreover, the arrow on each roller shows the moving direction of each roller.

  In this embodiment, the primary transfer rollers 5Y, 5M, 5C, and 5K move in a direction substantially orthogonal to the drum arrangement direction, that is, in the up-down direction. Similarly, in the present embodiment, the upstream auxiliary roller 72 moves in a direction substantially orthogonal to the drum arrangement direction, that is, in the vertical direction.

  On the other hand, the movement locus of the downstream auxiliary roller 73 is as follows. The position of the downstream auxiliary roller 73 in the full contact state and the black contact state is referred to as a “first position”, and the position of the downstream auxiliary roller 73 in the fully separated state is referred to as a “second position”. At this time, the downstream auxiliary roller 73 arranged at the first position approaches the black photosensitive drum 1K along the drum arrangement direction and moves away from the photosensitive drum 1K along a direction substantially perpendicular to the drum arrangement direction. Moved to the second position. Further, the downstream auxiliary roller 73 disposed at the second position is moved in the opposite direction to the above and disposed at the first position. In particular, in this embodiment, the downstream auxiliary roller 73 moves in the direction of rotation about the rotation axis of the drive roller 74.

  By using such a movement locus of the downstream auxiliary roller 73, the separation between the photosensitive drums 1 Y, 1 M, 1 C, and 1 K and the intermediate transfer belt 7 without reducing the diameter of the drive roller 74 or the downstream auxiliary roller 73. The amount can be secured.

5. Next, the downstream auxiliary roller moving mechanism (hereinafter also simply referred to as “moving mechanism”) 20 that moves the downstream auxiliary roller (hereinafter also simply referred to as “auxiliary roller”) 73 in the present embodiment will be described. 6 and 7 are perspective views showing the configuration around the auxiliary roller 73 in the all contact state and the total separation state, respectively. Here, the configuration of one end portion in the thrust direction will be described, but in the present embodiment, the other end portion has the same configuration (axisymmetric with respect to the substantial center of the intermediate transfer belt 7 in the thrust direction). Yes. Further, here, the full contact state is illustrated as the first state of the auxiliary roller 73, but the black contact state is the same.

  As shown in FIG. 6, a support portion 21 a provided at one end portion of the support member 21 rotatably supports the end portion of the rotation shaft of the auxiliary roller 73. Further, the engaging portion 21 b provided at the other end portion of the support member 21 is engaged with the end portion of the rotation shaft of the drive roller 74. The rotation shaft of the drive roller 74 is rotatably supported by a frame (not shown) of the intermediate transfer unit 70. The drive roller 74 rotates at a fixed position with respect to the frame of the intermediate transfer unit 70.

  A contact portion 21 c provided on the support member 21 is in contact with a pressing portion 22 a provided on the slider 22. Accordingly, the auxiliary roller 73 is held at a height at which the photosensitive drums 1Y, 1M, 1C, and 1K are in contact with the intermediate transfer belt 7 (first position). The slider 22 is held by the intermediate transfer unit 70 so as to be slidable along the drum arrangement direction.

  A drive shaft 23 connected to a drive gear (not shown) provided on the apparatus main body 110 side is provided in the intermediate transfer unit 70. A driving force is input to the driving shaft 23 from a driving input source (not shown) on the apparatus main body 110 side via the driving gear. The drive shaft 23 is rotatably supported on the frame of the intermediate transfer unit 70. When the drive gear rotates about 120 °, the eccentric cam-shaped coupling 24 connected to the drive shaft 23 rotates, and the slider 22 moves in the direction of arrow H in FIG. 6 (from the black photosensitive drum 1K side to the cyan photosensitive drum). In the direction toward the drum 1C).

  As a result of the movement of the slider 22, the pressing portion 22 a of the slider 22 is retracted from the contact portion 21 c of the support member 21 as shown in FIG. 7. Then, the auxiliary roller 73 and the support member 21 are retracted from the height at which the photosensitive drums 1Y, 1M, 1C, and 1K are in contact with the intermediate transfer belt 7 by the tension of the intermediate transfer belt 7. At the time of retraction, the auxiliary roller 73 moves on the rotation locus around the rotation axis of the drive roller 73 because the engaging portion 21b of the support member 21 is engaged with the end of the rotation shaft of the drive roller 74. Moving. In other words, the auxiliary roller 73 and the drive roller 74 in the first position in the all contact state (or the black contact state), the second position in the all separation state, and the path from the first position to the second position. The distance between is approximately equal.

  Accordingly, since the distance between the auxiliary roller 73 and the driving roller 74 is kept substantially equal by the support member 21, even in the configuration in which the auxiliary roller 73 is automatically moved, the positional accuracy of the auxiliary roller 73 with respect to the driving roller 74. Can be improved. Further, the photosensitive drums 1Y, 1M, 1C, and 1K can be separated from the intermediate transfer belt 7 even in a configuration in which the auxiliary roller 73 and the driving roller 74 are close to each other in the full contact state (or the black contact state). .

  In this embodiment, the slider 22, the drive shaft 23, the coupling 24, the drive gear connected to the drive shaft 23, and a drive input source (drive source) for inputting a drive force to the drive shaft 23 through the drive gear. Thus, the moving mechanism 20 is configured.

  In this embodiment, the slider 22, the drive shaft 23, the coupling 24, the drive gear, and the drive input source are shared with the separation / connection mechanism 30. In other words, in this embodiment, the separation / contact mechanism 30 moves the holder that holds the bearing member of each of the primary transfer rollers 5Y to 5K via the spring as the urging means by the movement of the slider 22 to thereby move the primary transfer roller. It is configured to move 5Y, 5M, 5C, and 5K. However, the present invention is not limited to such a configuration, and the moving mechanism 20 and the separating / connecting mechanism 30 may not be configured such that some components are shared. Further, the upstream auxiliary roller moving mechanism 40 and the downstream auxiliary roller moving mechanism 20 may have a configuration in which some components are made common. That is, the upstream auxiliary roller moving mechanism 40 may be configured to move the upstream auxiliary roller 72 by moving the bearing member of the upstream auxiliary roller 72 by moving the slider 22, for example.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment includes a plurality of image carriers 1Y to 1K that are arranged substantially linearly and on which toner images are formed. Further, the image forming apparatus 100 is arranged along the arrangement direction of the plurality of image carriers 1Y to 1K, and is a movable endless belt 7 that carries the toner images transferred from the plurality of image carriers 1Y to 1K. Have The image forming apparatus 100 includes a plurality of support rollers that stretch the belt 7, and includes a next first support roller (downstream auxiliary roller) 73 and a second support roller (drive roller) 74. Support rollers. The first support roller 73 is disposed adjacent to the downstream side of the plurality of image carriers 1Y to 1K in the moving direction of the belt 7. The second support roller 74 is disposed adjacent to the downstream side of the first support roller 73 in the moving direction of the belt 7, and forms a transfer portion N <b> 2 where the toner image is transferred from the belt 7 to the recording material P. In addition, the image forming apparatus 100 includes a control unit (CPU 50) that can be switched between the first state and the second state. The first state is a state in which the belt 7 is in contact with the image carrier 1 </ b> K at the most downstream side in the moving direction of the belt 7 among the plurality of image carriers 1 </ b> Y to 1 </ b> K. The second state is a state in which the belt 7 is separated from at least the most downstream image carrier 1K among the plurality of image carriers 1Y to 1K. Further, the image forming apparatus 100 is centered on the rotation axis of the second support roller 74 while maintaining a constant distance between the rotation axis of the first support roller 73 and the rotation axis of the second support roller 74. The support member 21 that rotatably supports the first support roller 73 is provided. Further, the image forming apparatus 100 includes a moving mechanism 20 that moves the first support roller 73 between the first position in the first state and the second position in the second state.

  In the present embodiment, the image forming apparatus 100 is disposed on the inner peripheral surface side of the belt 7, and a plurality of transfer members 5 </ b> Y to 5 </ b> K that transfer toner images from the plurality of image carriers 1 </ b> Y to 1 </ b> K to the belt 7. Have In this embodiment, among the plurality of transfer members 5Y to 5K, at least the most downstream transfer member 5K corresponding to the most downstream image carrier 1K is moved between the next contact position and the separated position. A contact mechanism 30 is provided. The contact position is a position in the first state, and the separation position is a position in the second state farther from the most downstream image carrier 1K than the contact position. In particular, in this embodiment, the separation / contact mechanism 30 moves each of the plurality of transfer members 5Y to 5K between the next contact position and the separation position. The contact position is a position when the belt is in contact with the corresponding image carrier 1, and the separation position is farther from the corresponding image carrier 1 than the contact position, and the belt 7 from the corresponding image carrier 1. Is the position when is separated. In the present embodiment, the image forming apparatus 100 is configured such that the belt 7 is in contact with all of the plurality of image carriers 1Y to 1K and the plurality of image carriers 1Y to 1K as the first state. Of these, the state where the belt 7 is in contact with only the most downstream image carrier 1K can be taken. In this embodiment, the image forming apparatus 100 can take the state where the belt 7 is separated from all of the plurality of image carriers 1Y to 1K as the second state.

  As described above, according to this embodiment, in the configuration in which the auxiliary roller 73 provided between the primary transfer roller 5 and the drive roller 74 is automatically moved, the positional accuracy of the auxiliary roller 73 with respect to the drive roller 74 is improved. Can do.

[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, the number of image forming units is four. However, the number of image forming units is not limited to this, and may be more or less. Further, the arrangement order of the image forming units for each color is not limited to that in the above-described embodiment.

  In the above-described embodiment, the driving roller among the plurality of stretching rollers also serves as the secondary transfer inner roller. However, the present invention is not limited to this. Further, the number of stretching rollers is not limited to four in the above-described embodiment, and may be more or less.

  In the above-described embodiment, the belt is arranged above the plurality of image carriers in the vertical direction. However, the arrangement relationship between the plurality of image carriers and the belt is not limited to this, for example, a plurality of image carriers. A belt may be disposed below the vertical direction of the image carrier.

  Further, the first support roller and the second support roller are not limited to the configuration in which the first support roller and the second support roller are disposed downstream of the most downstream image carrier in the belt rotation direction. For example, the first support roller and the second support roller may be arranged upstream of the most upstream image carrier in the belt rotation direction. In this configuration, for example, when the image carrier on the most downstream side in the rotation direction of the belt is an image carrier for black, the first support roller is disposed at the first position in the entire contact state, and the black contact It can be placed in the second position in the state and in the fully separated state.

  In the above-described embodiments, the intermediate transfer type image forming apparatus has been described as an example, but the present invention can also be applied to a direct transfer type image forming apparatus. FIG. 10 is a schematic cross-sectional view of a main part of a direct transfer type image forming apparatus. In FIG. 10, elements having the same or corresponding functions and configurations as those of the image forming apparatus of FIG. An image forming apparatus 100 in FIG. 10 has a recording material carrying belt 107 constituted by an endless belt as a recording material carrying body, instead of the intermediate transfer belt 7 in the image forming apparatus 100 in FIG. In the image forming apparatus 100 of FIG. 10, the toner image formed on the photosensitive drum 1 in each image forming unit S is transferred to the recording material P carried and conveyed on the recording material carrying belt 107 in each transfer unit N. Is done. Also in such a direct transfer type image forming apparatus 100, the contact state of the photosensitive drum 1 and the recording material carrying belt 107 can be set to a plurality of states such as an all contact state, a black contact state, and a total separation state similar to the above-described embodiment. May be configured to be switched to this state. In this case, the same problem as in the case of the intermediate transfer type image forming apparatus may occur. Therefore, the present invention can be applied to a direct transfer type image forming apparatus, and the same effects as those of the above-described embodiments can be obtained.

  In the above-described embodiments, the transfer member is a roller. However, the transfer member is not limited to this, and may be a block (pad) shape, a brush shape, a sheet shape, or a blade shape.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Primary transfer roller 7 Intermediate transfer belt 8 Secondary transfer roller 20 Downstream auxiliary roller moving mechanism (moving means)
21 Support member 30 Separation / detachment mechanism (detachment means)
70 Secondary transfer unit 73 Downstream auxiliary roller (first support roller)
74 Drive roller (second support roller)

Claims (9)

A plurality of image carriers on which toner images are formed, arranged in a substantially straight line;
A movable endless belt disposed along an arrangement direction of the plurality of image carriers and carrying a toner image transferred from the plurality of image carriers;
A plurality of support rollers for stretching the belt; a first support roller disposed adjacent to a downstream side of the plurality of image carriers in the moving direction of the belt; and the supporting roller in the moving direction of the belt A plurality of support rollers including a second support roller disposed adjacent to the downstream side of the first support roller and forming a transfer portion for transferring a toner image from the belt to a recording material;
A first state in which the belt is in contact with at least the most downstream image carrier in the moving direction of the belt among the plurality of image carriers; and at least the most downstream image carrier among the plurality of image carriers. A control unit capable of switching to a second state in which the belt is separated from the body;
In an image forming apparatus having
The first support roller is moved around the rotation shaft of the second support roller while maintaining a constant distance between the rotation shaft of the first support roller and the rotation shaft of the second support roller. A support member that rotatably supports,
A moving mechanism for moving the first support roller between a first position in the first state and a second position in the second state;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, further comprising: a plurality of transfer members that are arranged on an inner peripheral surface side of the belt and transfer a toner image from each of the plurality of image carriers to the belt.   Of the plurality of transfer members, at least a most downstream transfer member corresponding to the most downstream image carrier, a contact position in the first state, and farther from the most downstream image carrier than the contact position, The image forming apparatus according to claim 2, further comprising a separation mechanism that moves between the separation position and the separation position in the second state.   Each of the plurality of transfer members is moved from the corresponding image carrier, the contact position when the belt is in contact with the corresponding image carrier, and the farther from the corresponding image carrier than the contact position. The image forming apparatus according to claim 2, further comprising a separation mechanism that moves between the belt and a separation position when the belt is separated.   In the first state, the belt is in contact with all of the plurality of image carriers, and the belt is in contact with only the most downstream image carrier among the plurality of image carriers. 5. The image formation according to claim 4, wherein the belt is separated from all of the plurality of image carriers as the second state. 6. apparatus.   The image forming apparatus according to claim 3, wherein the separation / contact mechanism moves the transfer member in a direction substantially orthogonal to the arrangement direction.   The image forming apparatus according to claim 2, wherein the transfer member is a roller.   The image forming apparatus according to claim 1, wherein the second support roller is a drive roller that rotationally drives the belt.   The belt is an intermediate transfer body on which toner images are primarily transferred from the plurality of image carriers, and the second support roller forms a secondary transfer portion that transfers toner images from the belt to a recording material. The image forming apparatus according to claim 8.

Images