Patent Publication Number: US-10766723-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an image forming apparatus that includes a belt conveyance device in a detachably attachable manner. 
     Description of the Related Art 
     There is a generally known issue that a belt member laid under tension on a plurality of tension rollers and conveyed rotationally may lean to either end of the rollers at the time of rotary driving, depending on the accuracy of outer diameters of the rollers and the accuracy of alignment between the rollers. To solve this issue, for example, Japanese Translation of PCT International Application No. 2001-520611 and Japanese Patent Laid-Open No. 2014-178505 suggest an alignment method by which, at the occurrence of belt leaning, a steering roller as a steering member is tilted by an unbalanced force of friction with the belt to cancel out autonomously the belt-leaning speed (hereinafter, called autonomous steering method). In the belt conveyance devices described in these publications, a steering roller support member is tiltably arranged on a frame member that rotatably supports the tension rollers including a driving roller, so that both ends of the steering roller are rotatably held by the steering roller support member. 
     In addition, for example, Japanese Patent Laid-Open No. 2013-171204 discloses a configuration that a belt conveyance device is detachably attached to an apparatus through an opening on the side of an apparatus body. In this configuration, the belt conveyance device can be inserted and removed by guiding the belt width-direction ends of the belt conveyance device along opposed guide rails in the apparatus body. 
     However, in such a configuration as described in Japanese Patent Laid-Open No. 2013-171204 that the belt conveyance device is detachably attachable by guiding the belt width-direction ends along the opposed guide rails in the apparatus body, the steering roller and the steering roller support member sag under their own weights during insertion and removal. To insert and remove the belt conveyance device without interference with a structure located under the insertion and removal path of the belt conveyance device, the belt conveyance device needs to follow a path lifted upward for the sag or more. This increases the space needed for insertion and removal. 
     In particular, in the autonomous-steering belt conveyance device, the steering roller is longitudinally tilted to further increase the space necessary for insertion and removal in combination with the sagging. 
     SUMMARY OF THE INVENTION 
     It is thus desirable to achieve the autonomous tilt of the steering roller in a state of being attached to the apparatus body and prevent the sagging of the steering roller when being inserted into or removed from the apparatus body even in the tilted state, thereby to suppress increase in the space necessary for insertion and removal without interference with a structure located under the insertion and removal path. 
     To solve the foregoing issues, an image forming apparatus of the present invention includes an apparatus body; and a belt conveyance device that is detachably attached to the apparatus body, wherein the belt conveyance device has a first roller configured to support an endless belt member; a frame member that supports rotatably said first roller; a second roller configured to support an endless belt member; a steering unit that supports rotatably said second roller, the steering unit being supported to be tiltable with respect to the frame member around an axial line vertical to an axial line of the second roller; and a sliding member provided in a state where rotation is restricted at both end portions of the second roller. When the belt member moves to one axial end side of the second roller, the steering unit tilts with respect to the frame member in a direction that the belt moves to the other axial end side of the second roller by a force generated by contacting the belt and the sliding member. The apparatus further includes a first guiding portion that is provided in the apparatus body to support a first guided portion provided in the frame member and guide the belt conveyance device attached to or detached from the apparatus body; and a second guiding portion that is provided in the apparatus body to support a second guided poprtion provided in the steering unit, release the second guided portion at an attachment position of the belt conveyance device to the apparatus body, and guide the belt conveyance device attached to or detached from the apparatus body. 
     According to the present invention, the steering unit is tiltable at the attached position, and is guided together with the frame member by the guiding portion in the process of attachment or removal. This makes it possible to achieve the tilt of the steering unit, regulate the sagging of the steering unit, and suppress increase in the space necessary for insertion and removal without interference with a structure located under the insertion and removal path. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustrative diagram of a configuration of an image forming apparatus. 
         FIGS. 2A, 2B, and 2C  are illustrative diagrams of an intermediate transfer unit. 
         FIG. 3  is a perspective view of an autonomous steering mechanism. 
         FIGS. 4A, 4B, and 4C  are illustrative diagrams describing operations of the autonomous steering mechanism. 
         FIG. 5  is a perspective view of an intermediate transfer belt cleaner in an attached state. 
         FIG. 6  is a cross-sectional view of the intermediate transfer belt cleaner in the attached state. 
         FIG. 7  is an illustrative diagram of the image forming apparatus from which an intermediate transfer unit is pulled out through an opening portion. 
         FIG. 8  is an illustrative diagram of a side plate configuration of the image forming apparatus. 
         FIG. 9  is a perspective view of the intermediate transfer unit attached to guide rails. 
         FIG. 10  is an illustrative diagram of the guide rail. 
         FIG. 11  is a perspective side view of the intermediate transfer unit. 
         FIGS. 12A and 12B  are illustrative diagrams of posture correction of a tilted steering portion. 
         FIG. 13  is an illustrative diagram of a configuration of an image forming apparatus in Example 2. 
         FIG. 14  is a perspective view of an intermediate transfer unit in an attached state in Example 2. 
         FIG. 15  is a cross-sectional view of a steering portion and its vicinity in Example 2. 
         FIG. 16  is an illustrative diagram of the image forming apparatus from which the intermediate transfer unit is pulled out through an opening portion in Example 2. 
         FIG. 17  is an illustrative diagram of guide positions in the process of attachment of the intermediate transfer unit in Example 2. 
         FIG. 18  is an illustrative diagram of guide positions in the process of detachment of the intermediate transfer unit in Example 2. 
         FIG. 19  is a perspective view of a collected toner conveyance portion in Example 3. 
         FIG. 20  is a perspective view of the collected toner conveyance portion without an intermediate transfer belt portion in Example 3. 
         FIG. 21A  is a perspective overall view of a path portion in Example 3, and  FIG. 21B  is a perspective view of a first path member in the path portion in Example 3. 
         FIG. 22  is a perspective view of a second path member in the path portion in Example 3. 
         FIGS. 23A and 23B  are cross-sectional views of the intermediate transfer belt unit before being set to an apparatus body. 
         FIGS. 24A and 24B  are cross-sectional views of the intermediate transfer belt unit after being set to the apparatus body. 
         FIGS. 25A and 25B  are perspective views of the intermediate transfer belt unit in the process of being set to the apparatus body. 
         FIG. 26A  is an illustrative diagram of a guide rail on the rear side of the apparatus body in Example 3, and  FIG. 26B  is an illustrative diagram of a guide rail on the front side of the apparatus body in Example 3. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments of the present invention will be described below in detail with reference to the drawings. However, dimensions, materials, shapes, and relative arrangements of components described in relation to the embodiments are not intended to limit the scope of the invention to them unless otherwise specified. 
     EXAMPLE 1 
     (Image Forming Apparatus) 
       FIG. 1  is an illustrative diagram of an image forming apparatus. As illustrated in  FIG. 1 , an image forming apparatus  100  is an intermediate transfer-system tandem color digital printer including four image forming portions  109  along an intermediate transfer belt  101 . 
     Four photosensitive drums  103  as image bearing members have surfaces charged with even electric charge by charging rollers  104 . Laser scanners  105  accept the input of image signals of yellow, magenta, cyan, and black, and irradiate the drum surfaces with laser light according to the image signals to neutralize the electric charge and form latent images. The latent images on the drums are developed by development devices  106  with toners of yellow, magenta, cyan, and black. The developed toner images on the drums are primarily transferred by primary transfer rollers  107  in sequence onto the intermediate transfer belt  101 , thereby to forming a full-color toner image on the surface of the intermediate transfer belt  101 . The transfer residual toners on the photosensitive drums  103  are collected by drum cleaners  108 . 
     Meanwhile, a transfer material P such as a paper sheet is fed by a sheet feeding roller  121  from a cassette feeding portion  120  to a registration roller  122 , and further sent to a secondary transfer portion T 2  in synchronization with the toner image on the intermediate transfer belt. The toner image on the intermediate transfer belt is transferred to the transfer material P by a secondary transfer inner roller  110  and a secondary transfer outer roller  111  in the secondary transfer portion T 2 , and then sent to a fuser  130 . When the transfer material P is sent to the fuser  130 , the toner image is fused into the transfer material P by heat and pressure in the fuser  130 , and is ejected to the outside of the device. The transfer residual toner on the intermediate transfer belt  101  having not been transferred in the secondary transfer portion T 2  is collected by an intermediate transfer belt cleaner  102 . 
     (Intermediate Transfer Unit) 
       FIGS. 2A to 2C  are illustrative diagrams of an intermediate transfer unit. An intermediate transfer unit  200  is a belt conveyance device having the intermediate transfer belt  101  that is laid under tension on a plurality of tension rollers and rotationally conveyed. The intermediate transfer belt  101  is an endless belt member made of polyimide or the like. The intermediate transfer belt  101  is laid under tension on a driving roller  110 , a steering roller  112 , tension rollers  113  and  114 , and the primary transfer rollers  107  rotatably supported by part of the frame  201 . These components are integrally assembled into the intermediate transfer unit  200 . The driving roller  110  as a first roller also acts as secondary transfer inner roller constituting the secondary transfer portion T 2 . The steering roller  112  as a second roller also acts as a tension roller that is biased by a compression spring  213  to pressurize the intermediate transfer belt  101  from the inner side to apply tensile force to the intermediate transfer belt  101 . 
     As illustrated in  FIG. 2A , the primary transfer rollers  107  constitute primary transfer units T 1  together with the photosensitive drums  103  via the intermediate transfer belt  101 , and transfer toner images of yellow, magenta, cyan, and black in an overlapping manner on the intermediate transfer belt  101  to form a color image. Meanwhile, at the formation of a monochrome image, an up-and-down mechanism (not illustrated) separates the primary transfer rollers of yellow, magenta, and cyan, the intermediate transfer belt  101 , and the photosensitive drums as illustrated in  FIG. 2B  to stop the photosensitive drums of yellow, magenta, and cyan. Then, a monochrome toner image is formed on the intermediate transfer belt  101  by the primary transfer roller and the photosensitive drum of black constituting the primary transfer portion T 1  via the intermediate transfer belt  101 . When the image forming apparatus is in the standby state, the primary transfer roller of black and the tension roller  114  are also moved to separate completely the intermediate transfer belt  101  from the four photosensitive drums  103  as illustrated in  FIG. 2C . 
     (Autonomous Steering Mechanism) 
       FIG. 3  is a perspective view of an autonomous steering mechanism, and  FIGS. 4A to 4C  are illustrative diagrams of operations of the autonomous steering mechanism. 
     The steering roller  112  has both ends supported by a steering roller support member  211  constituting the steering unit so that the steering roller  112  is rotated along with the rotation of the intermediate transfer belt  101 . The steering roller  112  has slide ring portions  212  regulated in rotation at the both end portions. In Example 1, the slide ring portions  212  contain bearings  212   a  and also act as sliding members for the steering roller  112 . The slide ring portions (sliding members)  212  are supported to be slidable with respect to the steering roller support member  211  in the directions of arrow X such that the steering roller  112  is biased by the compression spring  213  toward the intermediate transfer belt  101 . The slide ring portions  212  are provided at the axial end portions of the steering roller  112 . The steering roller support member  211  is supported via a rotation shaft  214  in such a manner to be tiltable with respect to the frame  201 . The rotation shaft  214  is supported such that the steering roller support member  211  constituting the steering unit is tiltable with respect to the frame  201  as a frame member around an axial line  214   a  vertical to an axial line  112   a  of the steering roller  112 . 
     When the intermediate transfer belt  101  laid under tension in balance with respect to the axial center of the steering roller  112  as illustrated in  FIG. 4A  leans to the left side (one axial side) as illustrated in  FIG. 4B , a friction force occurs between the intermediate transfer belt  101  and the slide ring portions  212  at the both ends. In this case, the laying widths of the intermediate transfer belt  101  on the right and left slide ring portions  212  are different. When the friction force of the left side with the larger laying width (one axial side) is greater than the friction force of the right side (the other axial side), the steering roller  112  is tilted and lowered on the left side. As a result, the driving roller  110  and the steering roller  112  go out of alignment, and the intermediate transfer belt  101  leans to the right side in the winding portion of the steering roller  112  to correct the leaning of the belt position. Meanwhile, when the intermediate transfer belt  101  leans to the right side (the other axial side) as illustrated in  FIG. 4C , the friction force between the intermediate transfer belt  101  and the slide ring portion  212  on the right side (the other axial side) increases to tilt the steering roller  112  to be lowered on the right side. As a result, the intermediate transfer belt  101  leans to the left side (the one axial side) in the winding portion of the steering roller  112  to correct the leaning of the belt position. 
     In the intermediate transfer unit  200 , generally, when the intermediate transfer belt  101  is rotationally driven, the intermediate transfer belt  101  leans to one side under the influence of the misalignment of the tension rollers and the slight longitudinal distribution of the roller diameters. In response to this, the balance of friction force between the intermediate transfer belt  101  and the slide ring portions  212  at the both ends gradually changes to tilt the steering roller  112 . This gradually slows down the leaning speed of the intermediate transfer belt  101 , and then the intermediate transfer belt  101  converges on the steering tilt posture in which the belt leaning is balanced out. 
     (Intermediate Transfer Belt Cleaner) 
       FIG. 5  is an illustrative diagram of the intermediate transfer belt cleaner  102  in the attached state, and  FIG. 6  is a cross-sectional view of the same. The steering unit tiltably supported by the frame  201  includes the intermediate transfer belt cleaner  102  as a cleaning unit that abuts with the intermediate transfer belt  101  at a position opposed to the steering roller  112  to clean up the intermediate transfer belt  101 . 
     The intermediate transfer belt cleaner  102  brings the leading end of a cleaning blade  31  into abutment with the position opposed to the steering roller  112  via the intermediate transfer belt  101  to collect the transfer residual toner on the intermediate transfer belt  101 . As described above, the steering roller  112  has the both ends rotationally supported by the slide ring portions (bearing members)  212 . The steering roller  112  is supported via the compression spring  213  to be slidable on the steering roller support member  211 . The intermediate transfer belt cleaner  102  has the both ends fixed to the slide ring portions  212  to integrate with the steering roller  112  and tilt together with the steering roller support member  211 . That is, even when the intermediate transfer belt  101  leans to one side to tilt the steering roller  112 , the cleaning blade  31  can press the intermediate transfer belt  101  at a constant position in parallel to the intermediate transfer belt  101  to keep the state of friction with the intermediate transfer belt  101  in a stable manner. 
     Hereinafter, the steering roller  112  and the intermediate transfer belt cleaner  102  tilted together with the steering roller support member  211  by the rotation shaft  214  with respect to the frame  201  of the intermediate transfer unit  200  will be collectively called steering portion (steering unit)  210 . In the intermediate transfer unit  200 , the steering portion  210  is provided downstream of the frame  201  as seen from the attachment direction. 
     (Attachment and Detachment Configuration of the Intermediate Transfer Unit) 
     As illustrated in  FIG. 7 , the image forming apparatus  100  has an opening portion  140  on one side surface where the four image forming portions  109  are aligned. The intermediate transfer unit  200  can be attached to and detached from the interior of the housing of the image forming apparatus  100  through the opening portion  140 . The image forming apparatus  100  has the one side surface with an opening and closing member  115  that can be opened and closed with respect to the image forming apparatus  100 . The opening portion  140  can be opened by opening the opening and closing member  115  as illustrated in  FIG. 7 . In this case, attached to the opening and closing member  115  are the secondary transfer outer roller  111  opposed to the driving roller (the secondary transfer inner roller)  110  of the intermediate transfer unit  200  and one of the registration rollers  122 . Therefore, the conveyance path of the transfer material can also be opened by opening the opening and closing member  115 . 
       FIG. 8  is an illustrative diagram of the image forming apparatus  100  as seen from the opening portion  140  side. As illustrated in  FIG. 8 , the housing (apparatus body) of the image forming apparatus  100  has opposed side plates  151  and  152  coupled to each other by a plurality of stays  153 . The intermediate transfer unit  200  installed in the image forming apparatus  100  includes guide ribs (first guided portions)  202  and  203  on both side surfaces of the frame  201  as seen from the axial direction of the tension rollers. On the inner wall surfaces of the side plates  151  and  152  of the image forming apparatus  100 , guide rails (first guiding portions)  161  and  162  are opposed to the guide ribs  202  and  203  to hold the guide ribs  202  and  203 . In the image forming apparatus of the embodiment illustrated in  FIG. 7 , the four image forming portions  109  including the photosensitive drums  103  are arranged under the intermediate transfer unit  200 , and are rotationally driven via a cup ring  171  by a drive unit  170  provided on the one sideplate  152  as illustrated in  FIG. 8 . Therefore, the intermediate transfer unit  200  is inserted or removed while passing over the image forming portions  109  in the alignment direction as illustrated in  FIG. 7 . 
       FIG. 9  is a perspective view of the intermediate transfer unit  200  attached to the guide rail  162 . In fact, the guide rail  161  is also arranged at a position opposed to the guide rail  162 , but  FIG. 9  does not illustrate the guide rail  161  for the purpose of showing the side surface of the intermediate transfer unit  200 .  FIG. 10  is an illustrative diagram of the guide rail  162 , and  FIG. 11  is a perspective view of the side surface of the intermediate transfer unit opposed to the guide rail  162 . In the example of  FIG. 11 , the guide rail  162  is also arranged at a position opposed to the guide rail  161 , but  FIG. 11  does not illustrate the guide rail  162  for the purpose of showing the side surface of the intermediate transfer unit  200 . 
     As described above, when the image forming apparatus is in the standby state, the intermediate transfer belt  101  is separated from the four photosensitive drums  103  (see  FIG. 2C ). However, when the intermediate transfer unit  200  is inserted or removed, the posture of the intermediate transfer unit becomes unstable due to play between the guide ribs  202  and  203  of the intermediate transfer unit  200  and the guide rails  161  and  162  of the apparatus housing. To avoid a contact between the intermediate transfer unit  200  and the image forming portions  109  including the photosensitive drums  103 , it is desirable to leave a larger clearance between them than that in the standby state of the apparatus. 
     Accordingly, the guide rails  161  and  162  are provided with guide grooves (first guiding portions)  161   a  and  162   a  to support the guide ribs (first guided portions)  202  and  203  of the frame  201 . The guide grooves  161   a  and  162   a  in the guide rails  161  and  162  are not linear but are bent to lift the intermediate transfer unit  200  at a position B shifted by a predetermined amount from an attachment position A as illustrated in  FIG. 10 . However, this increases upwardly the space necessary for insertion and removal of the intermediate transfer unit for the height at which the intermediate transfer unit  200  is to be lifted. In the intermediate transfer unit made longer in the insertion and removal direction as in Example 1, the frame  201  is provided with the plurality of guide ribs  202  and  203  supported by the guide rails  161  and  162  in the insertion and removal direction. In this case, as illustrated in  FIGS. 9 and 11 , guide ribs  202   a  and  202   b  and guide ribs  203   a  and  203   b  as first guided portions are respectively arranged on upstream and downstream sides of the frame  201  in the insertion and removal direction. In the guide grooves  161   a  and  162   a  constituting the first guiding portions, the positions A and B refer to a first position including an attachment position where the intermediate transfer unit  200  as the belt conveyance device is located and attached to the apparatus body, and a second position higher than the first position by the height at which the intermediate transfer unit  200  is to be lifted. The attachment position here refers to the position where the intermediate transfer unit  200  is located and attached to the apparatus body (housing) of the image forming apparatus. 
     In this manner, the intermediate transfer unit  200  is regulated in posture during insertion or removal by supporting and guiding the guide ribs  202  and  203  on the both side surfaces of the frame  201  along the guide grooves  161   a  and  162   a  in the guide rails  161  and  162  of the image forming apparatus  100 . This makes it possible to avoid the intermediate transfer unit  200  from contacting surrounding components such as the image forming portions  109  under the intermediate transfer unit  200  and the stays  153  above the intermediate transfer unit  200 , thereby preventing scratches on the intermediate transfer belt  101 . 
     Meanwhile, in the intermediate transfer unit  200 , the posture of the steering portion  210  tiltable with respect to the frame  201  is not sufficiently regulated only by the guide ribs  202  and  203 . That is, when the steering roller  112  tilts depending on the leaning position of the intermediate transfer belt  101 , the steering portion  210  has the end lowered on the leaning side of the intermediate transfer belt  101  and may contact the image forming portions  109  under the intermediate transfer unit during insertion or removal. 
     Accordingly, in Example 1, the end of the steering portion  210  has a guide projection (second guided portion)  215  as illustrated in  FIG. 11 . Further, the opposed guide rail  162  of the image forming apparatus  100  has a second guide groove (second guiding portion)  162   b  to support the guide projection  215  as illustrated in  FIG. 10 . The second guide groove  162   b  supports the guide projection  215  to regulate the posture of the steering portion  210  while the steering portion  210  passes from an attachment start position F in the opening portion  140  of the image forming apparatus  100  over the image forming portions  109 . However, after the steering portion  210  passes over the image forming portions  109 , the second guide groove  162   b  releases the guide projection  215  at a position C in front of the attachment position (attachment completion position) A. In the process of attaching the intermediate transfer unit  200  to the apparatus body, the second guide groove  162   b  guides the intermediate transfer unit  200  from the second position to the first position, and then releases the guide projection  215 . Accordingly, the posture of the steering portion  210  becomes tiltable with respect to the frame  201  positioned by the first guide grooves  161   a  and  162   a  at the attachment position of the intermediate transfer unit  200 , which allows autonomous steering against the leaning of the intermediate transfer belt  101 . 
       FIG. 10  illustrates the second guide groove (second guiding portion)  162   b  in the guide rail  162 . In addition to this, a second guide groove (second guiding portion)  161   b  may be provided in the opposed guide rail  161  and the guide projection (second guided portion)  215  illustrated in  FIG. 9  may be provided at the end of the steering portion  210  opposed to the guide rail  161  to regulate the posture of the steering portion  210  on the both axial sides.  FIG. 11  illustrates the guide projection  215  arranged on the side surface of the intermediate transfer belt cleaner  102 . However, the guide projection  215  maybe provided at the end of the steering roller support member  211 , for example, as far as it can be tilted with respect to the frame  201 . In the guide grooves  161   b  and  162   b  constituting the second guiding portions, the positions A and C refer to a first position including the attachment position where the intermediate transfer unit  200  as the belt conveyance device is located and attached to the apparatus body, and a second position higher than the first position by the height at which the intermediate transfer unit  200  is to be lifted. 
     When the intermediate transfer unit  200  is detached, the steering portion  210  is tilted at the attachment position A depending on the leaning position of the intermediate transfer belt  101 , and the end of the steering portion  210  on the lean side of the intermediate transfer belt  101  is lowered as compared to the portion in vicinity of the rotation shaft  214 . Accordingly, as illustrated in  FIGS. 12A and 12B , the intermediate transfer unit  200  starts to be moved from the attachment position A to the opening portion  140  of the image forming apparatus  100 , and then the guide projection  215  at the end of the steering portion  210  is guided from a position D by the second guide groove  162   b.  That is, the second guide groove  162   b  has a regulation portion  162   b   1  that, in the process of detaching the intermediate transfer unit  200  from the apparatus body, supports the released guide projection  215  to regulate the position of the steering portion  210 . After supporting the guide projection  215  by the regulation portion  162   b   1  to regulate the position of the steering portion  210 , the second guide groove  162   b  guides the intermediate transfer unit  200  to the second position higher than the first position. This makes it possible to correct the tilted posture of the steering portion  210  such that the steering roller  112  becomes approximately parallel to the other tension rollers supported by the frame  201 . 
     The second guide groove  162   b  is arranged to press the guide projection  215  from above and under the guide projection  215  even when the steering portion  210  is tilted at the maximum.  FIG. 12A  illustrates a path on which the guide projection  215  displaced (moved) downward due to the tilt of the steering portion  210  is pressed upward by the regulation portion  162   b   1  of the guide groove  162   b  from the position D to the position C to correct the tilted posture of the steering portion  210 , and then the guide projection  215  is moved along the guide groove  162   b.    FIG. 12B  illustrates a path on which the guide projection  215  displaced (moved) upward due to the tilt of the steering portion  210  is pressed downward by the regulation portion  162   b   1  of the guide groove  162   b  from the position D to the position C to correct the tilted posture of the steering portion  210 , and then the guide projection  215  is moved along the guide groove  162   b.  In this manner, the regulation portion  162   b   1  of the guide groove  162   b  is formed to press the displaced guide projection  215  in both the upward and downward directions as illustrated in  FIGS. 12A and 12B .  
     When the second guide grooves  161   b  and  162   b  are provided in the opposed guide rails  161  and  162  on the both sides of the intermediate transfer unit  200  to correct the tilted posture of the steering portion  210  by the guide projections  215  at the both ends of the steering portion  210 , the second guide grooves  161   b  and  162   b  may press the guide projection  215  either upward or downward. In Example 1, the guide projection  215  is projected laterally from the steering portion  210 , and the second guide grooves  161   b  and  162   b  are made to be concave. However, these components are not limited to the foregoing shapes as long as they can support and regulate the ends of the steering portion  210 . 
     As described above, according to Example 1, the steering portion  210  can be freely tilted at the attachment position, and is guided together with the frame  201  by the guide rails  161  and  162  in the process of attachment and detachment. This makes it possible to achieve the tilt of the steering portion  210 , regulate the sagging of the steering portion  210 , and suppress increase in the space necessary for insertion and removal without interference with structures such as the image forming portions under the path of insertion and removal. 
     EXAMPLE 2 
       FIG. 13  is an illustrative diagram of an image forming apparatus in Example 2.  FIG. 14  is a perspective view of the intermediate transfer unit  200  in the attached state according to Example 2, and  FIG. 15  is a cross-sectional view of the steering portion  210  and its vicinity. The schematic configuration of the image forming apparatus in Example 2 is almost identical to that of Example 1 described above, and the members with identical functions will be given the identical reference signs, and descriptions of them will be omitted. 
     As described above, the steering portion  210  is supported via the rotation shaft  214  in such a manner as to be tiltable with respect to the frame  201  of the intermediate transfer unit  200 . The rotation shaft  214  bears the weight of the steering portion  210 . As illustrated in  FIG. 13 , a diagonally downward resultant force F 1  acts on the steering roller  112  due to a belt tension applied to the intermediate transfer belt  101 . At the time of rotation of the intermediate transfer belt, a downward force F 2  acts on the steering portion  210  due to friction force of the cleaning blade  31  in abutment with the outer peripheral surface of the belt. In this manner, when the downward force acts on the steering portion  210  to generate an excessive bending force on the frame  201  supporting the rotation shaft  214 , the frame  201  gets deformed to displace downward and sag the steering portion  210 . As a result, there occurs problems such as reduction in the ability of returning the leaning belt due to inhibition of the autonomous steering operation and image failure without application of desired belt tension. 
     Accordingly, as illustrated in  FIGS. 14 and 15 , the stay  153  constituting the housing of the image forming apparatus  100  includes a second support portion  180  supporting the steering portion  210  at a position approximately identical to the position of the rotation shaft  214  as seen from the axial direction of the steering roller. The second support portion  180  is a support portion that is provided in the apparatus body to support the steering portion  210  to be tiltable with respect to the frame  201  around the axial line vertical to the axial line of the steering roller. Accordingly, the second support portion  180  bears the downward force applied to the steering portion  210  to prevent the sagging of the steering portion  210 . In Example 2, the bottom of the housing of the intermediate transfer belt cleaner  102  has an abutment portion  102   b  to the second support portion  180 . 
     According to this configuration, as illustrated in  FIG. 15 , the steering portion  210  can be supported by the second support portion  180  at the attachment position of the intermediate transfer unit  200 . However, when the intermediate transfer unit  200  is inserted into or removed from the image forming apparatus  100 , the abutment portion  102   b  of the steering portion  210  separates from the second support portion  180  as illustrated in  FIG. 16 . Thus, the steering portion  210  is not supported by the second support portion  180  but sags under its own weight and by the action of the belt tension. 
     Accordingly, at the insertion or removal of the intermediate transfer unit  200 , the guide projection  215  at least at one end of the steering portion  210  is supported by the second guide groove  161   b  (or  162   b ) in the guide rail  161  (or  162 ) of the image forming apparatus  100 . This suppresses the sagging of the steering portion  210  at the insertion or removal of the intermediate transfer unit  200 . When the steering portion  210  sags significantly without being supported by the second support portion  180 , it is desirable to provide the guide projection  215  at the both ends of the steering portion  210  so that the posture of the steering portion  210  can be regulated by the second guide grooves  161   b  and  162   b  in the guide rails  161  and  162  on the both sides. 
     As described above, to achieve autonomous steering against the leaning of the intermediate transfer belt  101 , the second guide groove  161   b  (or  162   b ) releases the guide projection  215  at the position C in front of the attachment position (attachment completion position) A in the process of attaching the intermediate transfer unit  200  to the apparatus body. Meanwhile, the abutment portion  102   b  in proximity to the rotation shaft  214  of the steering portion  210  reaches the second support portion  180  of the image forming apparatus  100  from a position E in front of the attachment position (attachment completion position) A. In this case, the steering portion  210  is supported by not only the rotation shaft  214  but also the guide projection  215  at the axial end or the abutment portion  102   b  in the axial center to prevent the sagging of the steering portion  210 . From that viewpoint, as illustrated in  FIG. 17 , the release position C of the guide projection  215  from the second guide groove  162   b  is located on the downstream side of the supportable position E of the abutment portion  102   b  by the second support portion  180  as seen from the attachment direction (reaching the position C after the position E). The steering portion  210  supported by the guide projection  215  is lowered together with the frame  201  guided by the guide ribs  202  and  203  to the positioning height at the position B (first position). However, in the process of attaching the intermediate transfer unit  200  to the apparatus body, it is desirable to set the position B on the downstream side of the supportable position E of the abutment portion  102   b  by the second support portion  180  as seen from the attachment direction (reaching the position B after the position E) so that the abutment portion  102   b  of the steering portion  210  is lowered from above and placed on the second support portion  180 . 
     In the process of detaching the intermediate transfer unit  200  from the apparatus body, between the attachment position A and the position E where the second support portion  180  can support the abutment portion  102   b  of the steering portion  210  as illustrated in  FIG. 18 , the second guide grooves  161   b  and  162   b  guide the guide projections  215  from the position D to the position C to correct the tilted posture of the steering portion  210  and support the steering portion  210  to be approximately parallel to the frame  201 . After that, the steering portion  210  is lifted together with the frame  201  from the positioning height (first position) to the insertion and removal height (second position) by the bending of the first guide grooves  161   a  and  162   a  and the second guide grooves  161   b  and  162   b  at the position B. 
     That is, in Example 2, in the process of attaching or detaching the intermediate transfer unit  200 , there is an overlap between the section where the second support portion  180  supports tiltably the steering portion  210  and the section where the second guide grooves  161   b  and  162   b  support the guide projections  215 . More specifically, in the process of attaching the intermediate transfer unit  200  to the apparatus body, the second support portion  180  supports the steering portion  210  before the second guide grooves  161   b  and  162   b  release the guide projections  215 . In the process of detaching the intermediate transfer unit  200  from the apparatus body, the second support portion  180  supports the steering portion  210  until the second guide grooves  161   b  and  162   b  support the guide projections  215 . 
     Accordingly, regulating the tilted posture and sagging of the steering portion  210  allows the intermediate transfer unit  200  to be inserted or removed without contact with the image forming portions  109  under the intermediate transfer unit  200 . This eliminates the need to lift the intermediate transfer unit  200  excessively at the time of insertion or removal of the intermediate transfer unit  200 , thereby suppressing increase in the space necessary for insertion and removal of the intermediate transfer unit  200 . 
     EXAMPLE 3 
       FIGS. 19 to 26  are illustrative diagrams of an image forming apparatus in Example 3.  FIG. 19  is a perspective view of an intermediate transfer unit and a collected toner conveyance portion in Example 3.  FIG. 20  is a perspective view of the collected toner conveyance portion without the intermediate transfer belt portion in Example 3. The schematic configuration of the image forming apparatus in Example 3 is almost identical to those of Examples 1 and 2 described above, and the members with identical functions will be given the identical reference signs, and descriptions of them will be omitted. 
     As illustrated in  FIG. 19 , the transfer residual toner on the intermediate transfer belt  101  is scraped off by the cleaning blade  31  (see  FIG. 20 ) in the cleaning container  28  of the intermediate transfer belt cleaner  102  and dropped as collected toner into the cleaning container  28 . As illustrated in  FIG. 19 , the collected toner dropped into the cleaning container  28  is conveyed by a conveyance screw  36  (see  FIG. 20 ) arranged along the longitudinal side of the intermediate transfer belt cleaner  102  toward an apparatus body front side Fr illustrated in  FIG. 19  and is discharged through a toner outlet  28   b  (see  FIG. 24B ). 
     Then, as illustrated in  FIG. 20 , the collected toner discharged from the toner outlet  28   b  is contained in a collection container  37  (see  FIGS. 23A and 23B ) attached to the apparatus body through a path portion  33  formed from a first path member  34  and a second path member  35 . The collection container  37  has a cylindrical portion  35   d  (see  FIG. 24B ) into which a nozzle portion  34   c  is inserted through an opening  37   a  such that the nozzle portion  34   c  and the cylindrical portion  35   d  overlap in a non-contact state in the height direction. 
     The path portion  33  is detachably attachable to the cleaning container  28  of the intermediate transfer belt cleaner  102  to collect the toner from the cleaning container  28 . The first path member  34  as a path member is supported by the apparatus body when the intermediate transfer unit  200  is not attached to the apparatus body. The first path member  34  is coupled to the cleaning container  28  when the intermediate transfer unit  200  is attached to the apparatus body. The coupled first path member  34  becomes swingable together with the steering portion  210  including the cleaning container  28 , and allows the toner outlet  28   b  to communicate with the opening  37   a  to guide the toner from the cleaning container  28  to the collection container  37  through the second path member  35  (see  FIGS. 24A and 24B ). 
     Next, a configuration of the path portion  33  will be described in detail with reference to  FIGS. 21 to 24 .  FIG. 21A  is a perspective view of the entire path portion  33  in Example 3, and  FIG. 21B  is a perspective view of the first path member  34  in the path portion  33  in Example 3.  FIG. 22  is a perspective view of the second path member  35  in the path portion  33  in Example 3.  FIG. 23A  is a cross-sectional view of the intermediate transfer unit  200  that is being inserted into the apparatus body  100  as seen from the Fr side of  FIG. 19 , and  FIG. 23B  is a cross-sectional view of  FIG. 23A  as seen from the opposite Rr side.  FIG. 24A  is a cross-sectional view of the intermediate transfer unit  200  completely set to the apparatus body  100 , and  FIG. 24B  is a cross-sectional view of  FIG. 24A  as seen from the opposite side. 
     As illustrated in  FIG. 21A , the path portion  33  includes the first path member  34  and the second path member  35  that is fixed to the apparatus body to couple to and communicate with the collection container  37 . The path portion  33  further has a toggle coil spring  88  (see  FIG. 24A ) that switches the rotation direction depending on the positional relationship with a rotation center  87  (see  FIG. 23A ) of the shutter member  32  to shift the shutter member  32  to the open position or the closed position. The toggle coil spring  88  has one end locked with a projection  86  on the intermediate transfer unit  200  and the other end locked with a projection  32   d  on the shutter member  32  as illustrated in  FIG. 24A . 
     As illustrated in  FIGS. 23A and 23B , the shutter member  32  has a lever portion  32   a  as an abutment portion and a shutter engagement portion  32   b.  When the intermediate transfer belt cleaner  102  is coupled to the path portion  33 , the lever portion  32   a  is slid on a lever abutment portion  35   b  and a shutter abutment portion  35   f  (also see  FIG. 21A ) of the second path member  35  and rotated. The lever abutment portion  35   b  constitutes an abutted portion that moves the shutter member  32  while the lever portion (abutting portion)  32   a  abuts with the lever abutment portion  35   b  in cooperation with the attachment of the intermediate transfer unit  200  to the image forming apparatus  100 . The second path member  35  has an engagement portion  35   e  (also see  FIG. 22 ) that engages with the rotated lever portion  32   a  as illustrated in  FIG. 24A  to regulate further rotation. When the intermediate transfer belt cleaner  102  is separated from the path portion  33 , the engagement portion  35   e  engages with the leading end of the lever portion (abutting portion)  32   a  and rotates the lever portion  32   a  in the counterclockwise direction in  FIG. 25A  (the direction of closing the shutter member  32 ).  FIGS. 25A and 25B  are perspective views of the intermediate transfer belt unit that is being set to the apparatus body.  FIG. 25A  illustrates the state with the closed shutter member  32 , and  FIG. 25B  illustrates the state with the opened shutter member  32 . 
     As illustrated in  FIGS. 21A and 21B , the first path member  34  has an engagement portion  34   a  for engagement with the intermediate transfer belt cleaner  102 , a fixed hook portion  34   b,  and a nozzle portion  34   c  that communicates with the toner outlet  28   b  (see  FIG. 24B ). The first path member  34  is fixed and supported on the intermediate transfer belt cleaner  102  side by sandwiching the corresponding portions ( 31   a  and  32   b ) of the intermediate transfer belt cleaner  102  between the engagement portion  34   a  and the fixed hook portion  34   b.  Accordingly, the first path member  34  operates following the steering operation of the steering portion  210 . 
     When being not engaged with the intermediate transfer belt cleaner  102 , the first path member  34  has an engagement hook portion  34   e  that protrudes in a hook form toward the rear side of the curved shape portion and enters an opening portion  35   g  on the top of a posture holding convex portion  35   a  (see  FIG. 22 ) of the second path member  35  for temporary engagement. Then, the engagement hook portion  34   e  abuts with a posture holding convex portion (predetermined portion)  35   a  of the apparatus body and is tentatively held. After the attachment of the intermediate transfer unit  200  to the image forming apparatus  100 , the first path member  34  is coupled to the cleaning container  28  and is separated from the posture holding convex portion  35   a,  and becomes movable together with the steering portion  210 . 
     As illustrated in  FIG. 22 , the second path member  35  has the cylindrical portion  35   d  as well as the posture holding convex portion  35   a,  the lever abutment portion  35   b,  the engagement portion  35   e,  the shutter abutment portion  35   f,  and the opening portion  35   g  described above. The cylindrical portion  35   d  has a flexible sheet material  38  as a sealing member that prevents the dispersion of the collected toner from the toner outlet  28   b  between a toner inlet  35   c  and the nozzle portion  34   c  inserted into the toner inlet  35   c.  The sheet material  38  is rectangular in shape and has two diagonal slashes  38   a.  When the sheet material  38  is placed as illustrated in  FIG. 22 , the toner outlet  28   b  can be inserted into the toner inlet  35   c  via the slashes  38   a.  Due to the presence of the sheet material  38 , it is possible to prevent the dispersion of the toner discharged from the toner outlet  28   b  to the opening  37   a  between the opening  37   a  and the toner outlet  28   b.    
     At that time, the first path member  34  abuts with the posture holding convex portion  35   a  and is supported in the state in which its tilt toward the rear side is regulated. Accordingly, it is possible to prevent the first path member  34  from being tilted in the direction of separating from the intermediate transfer unit  200  (the direction of arrow W) to cause a failure of connection with the intermediate transfer belt cleaner  102 . 
     However, in the foregoing configuration, when the intermediate transfer belt unit is not attached, the first path member  34  should not regulate the alignment operation of the steering unit. Thus, when the intermediate transfer belt unit is not attached, the position of the first path member  34  held by the posture holding convex portion  35   a  falls in the lower end of the alignment range of the steering portion  210 . Therefore, as described above, while the guide projection  215  of the steering portion  210  is released from the second guide groove  162   b  at the position C of the second guide groove  162   b  and then the second support portion  180  (see  FIG. 14 ) supports tiltably the steering portion  210 , if the front side Fr (see  FIG. 19 ) of the apparatus body with the shutter member  32  of the intermediate transfer belt cleaner  102  is substantially tilted upward, the shutter engagement portion  32   b  retracts above the fixed hook portion  34   b  and cannot lift the fixed hook portion  34   b.  Consequently, the opening  37   a  and the toner outlet  28   b  cannot communicate with each other, which leads to the dispersion of the collected toner and the breakage of the apparatus. 
     Accordingly, in Example 3, the guide groove (second guiding portion)  162   b  of the guide rail  162  on the rear side of the apparatus body and the guide groove (second guiding portion)  161   b  of the guide rail  161  on the front side of the apparatus body are respectively configured as illustrated in  FIGS. 26A and 26B .  FIG. 26A  is an illustrative diagram of the guide rail on the rear side of the apparatus body in Example 3, which illustrates schematically the guide rail  162  with the guide groove  162   b.    FIG. 26B  is an illustrative diagram of the guide rail on the front side of the apparatus body, which illustrates schematically the guide rail  161  with the guide groove  161   b.    
     The guide rail  161  illustrated in  FIG. 26B  is provided on one side of the apparatus body  100  illustrated in  FIG. 8 , as seen from the axial line direction of the steering roller  112  (the direction of the axial line  112   a  illustrated in  FIG. 3 ). The guide rail  162  illustrated in  FIG. 26A  is opposed to the guide rail  161  and provided on the side of the apparatus body  100  opposite to the one side illustrated in  FIG. 8  as seen from the axial line direction of the steering roller  112 . The other side of the apparatus body  100  with the guide rail  162  refers to the rear side Rr of the apparatus body with the drive unit  170  as illustrated in  FIG. 8 . The one side of the apparatus body  100  with the guide rail  161  refers to the side with the path portion  33  including the first path member  34  and the front side Fr of the apparatus body opposite to the rear side Rr of the apparatus body with the drive unit  170 . 
     The guide groove  161   b  on the one side (the front side Fr of the apparatus body) illustrated in  FIG. 26B  has a range in which the steering portion  210  is tilted and lowered as compared with the guide groove  162   b  on the other side illustrated in  FIG. 26A , in the process of attaching the intermediate transfer unit  200  to the apparatus body  100 . In this case, the range in which the guide groove  161   b  tilts the steering portion  210  is set from a position G where the steering portion  210  passes over the image forming portions  109  to the position C where the guide projection  215  is released in front of the attachment position (attachment completion position) A. 
     As illustrated in  FIG. 26B , the guide groove  161   b  of the guide rail  161  on the front side Fr of the apparatus body changes the position of the guide projection  215  with respect to the guide groove  162   b  on the rear side Rr of the apparatus body downward in the height direction from the position G where the steering portion  210  has passed over the image forming portions  109 . At that time, as illustrated in  FIG. 26A , the guide groove  162   b  of the guide rail  162  on the rear side Rr of the apparatus body does not change the position of the guide projection  215  in the height direction even when the steering portion  210  has passed the position G over the image forming portions  109 . This causes the guide projection  215  on the front side Fr of the apparatus body to be lowered in the height direction as compared with the guide projection  215  on the rear side Rr of the apparatus body. As illustrated in  FIG. 26B , the guide groove  161   b  of the guide rail  161  on the front side Fr of the apparatus body regulates the position of the guide projection  215  such that the tilt of the steering portion  210  falls in the lower end of the alignment range at the position C. Since the tilted posture of the steering portion  210  is maintained due to its own weight, the steering portion  210  can engage reliably with the first path member  34  even when the steering portion  210  is in a freely tiltable position. Accordingly, when the second support portion  180  (see  FIG. 14 ) supports tiltably the steering portion  210 , it is possible to prevent non-communication between the opening  37   a  and the toner outlet  28   b  that would lead to the dispersion of the collected toner and the breakage of the apparatus. 
     OTHER EXAMPLES 
     In the foregoing examples, the four image forming portions of different colors are used. However, the colors and the number of image forming portions are not limited but can be set as appropriate. 
     In the foregoing examples, a printer is taken as image forming apparatus. However, the present invention is not limited to this. For example, the present invention may be another image forming apparatus such as a facsimile machine or a copying machine, or a complex machine with a combination of these functions. In addition, the intermediate transfer unit having the intermediate transfer belt is taken as an example of a belt conveyance device detachably attachable to the image forming apparatus. However, the present invention is not limited to this but may be a conveyance unit including a conveyance belt that conveys a transfer material. The same advantageous effects can be achieved by applying the present invention to image forming apparatuses including these belt conveyance devices in a detachably attachable manner. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2017-064227, filed Mar. 29, 2017, and No. 2018-026932, filed Feb. 19, 2018, which are hereby incorporated by reference herein in their entirety.