Patent Publication Number: US-11048202-B2

Title: Sheet conveyance apparatus having paper dust removal and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet conveyance apparatus for conveying a sheet and an image forming apparatus including the same. 
     Description of the Related Art 
     In general, a printer of an electrophotographic system transfers a toner image formed on a photosensitive drum to a sheet fed from a cassette, fixes the toner image on the sheet, and then discharges the sheet outside the apparatus. Paper dust may be generated on the sheet due to rubbing between a conveyance roller, a separating pad, and the like, and paper dust adheres to the photosensitive drum or toner, which causes deterioration of image quality. 
     Hitherto, an image forming apparatus including a first paper dust removing roller coming into contact with a sheet to capture paper dust on the sheet and a first sponge member scraping paper dust adhering to the first paper dust removing roller has been proposed (see JP-A-2003-267579). In the image forming apparatus, in a case where the first paper dust removing roller rotates in a forward rotation direction, paper dust is scraped by the first sponge member, but when the first paper dust removing roller rotates in a reverse rotation direction, there is a concern that paper dust scraped by the first sponge member flows back to a conveyance path. Therefore, in the forward rotation direction of the first paper dust removing roller, a first reverse conveyance preventing member for scraping paper dust from the first paper dust removing roller is provided upstream of the first sponge member. In a case where the first paper dust removing roller rotates in the reverse rotation direction, paper dust is scraped by the first reverse conveyance preventing member. 
     A slight gap is provided between the first paper dust removing roller and the first reverse conveyance preventing member, so that scraping of paper dust by the first sponge member when the first paper dust removing roller rotates in the forward rotation direction is not inhibited. When the first paper dust removing roller rotates in the forward rotation direction, the gap allows conveyance of paper dust toward the first sponge member and when a second paper dust removing roller rotates in the reverse rotation direction, the gap limits the conveyance of paper dust to a conveyance path as a certain lump. 
     However, although the first reverse conveyance preventing member described in JP-A-2003-267579 can restrict the conveyance of paper dust which has become a large lump, for example, paper dust having a small particle size mainly composed of a filler of the sheet or the like may pass through the gap. Therefore, the paper dust passing through the gap adheres to the photosensitive drum or the toner and there is a concern that image defects occur. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a sheet conveyance apparatus includes a conveyance portion including a rotary member, and a counter member facing the rotary member so as to form a conveyance nip together with the rotary member, the conveyance portion being configured to convey a sheet at the conveyance nip by the rotary member rotating in a first direction, a first contact member configured to come into contact with a surface of the rotary member at a first position, a second contact member configured to come into contact with the surface of the rotary member at a second position located downstream of the conveyance nip and upstream of the first position in the first direction, and a contacting and separating mechanism configured to abut the second contact member against the surface of the rotary member and separate the second contact member from the surface of the rotary member. The contacting and separating mechanism causes the second contact member to separate from the surface of the rotary member when the rotary member rotates in the first direction, and causes the second contact member to abut against the surface of the rotary member when the rotary member rotates in a second direction opposite to the first direction. 
     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 overall schematic view illustrating a printer according to a first embodiment. 
         FIG. 2A  is a perspective view illustrating a sheet conveyance apparatus. 
         FIG. 2B  is a sectional view illustrating the sheet conveyance apparatus. 
         FIG. 3A  is a sectional view illustrating a state where a sheet is conveyed by a conveyance nip. 
         FIG. 3B  is a sectional view illustrating a state where the sheet is pulled out in an opposite direction to a sheet conveyance direction. 
         FIG. 3C  is a sectional view illustrating a state where a driving roller and a driven roller are stopped. 
         FIG. 4A  is a perspective view illustrating a sheet conveyance apparatus according to a second embodiment. 
         FIG. 4B  is a sectional view illustrating the sheet conveyance apparatus. 
         FIG. 5A  is a sectional view illustrating a state where a sheet is conveyed by a conveyance nip. 
         FIG. 5B  is a sectional view illustrating a state where the sheet is pulled out in an opposite direction to a sheet conveyance direction. 
         FIG. 5C  is a sectional view illustrating a state where a driving roller and a driven roller are stopped. 
         FIG. 6A  is a perspective view illustrating a modification example of the first embodiment. 
         FIG. 6B  is a perspective view illustrating a modification example of the second embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     Overall Configuration 
     First, a first embodiment of the invention will be described. A printer  1  as an image forming apparatus is a laser beam printer of an electrophotographic system for forming a monochrome toner image. As illustrated in  FIG. 1 , the printer  1  includes a sheet feeding apparatus  30  feeding a stacked sheet, and a sheet conveyance apparatus  50  conveying the sheet fed by the sheet feeding apparatus  30 . In addition, the printer  1  includes an image forming unit  20  forming an image on the sheet conveyed by the sheet conveyance apparatus  50 , a fixing unit  40  fixing the image transferred to the sheet, and a sheet discharge roller pair  11  capable of discharging the sheet to a sheet discharge tray  12 . 
     When an image forming command is output to the printer  1 , an image forming process is started by the image forming unit  20  based on image information input from an external computer or the like connected to the printer  1 . The image forming unit  20  includes a process cartridge  25 , a laser scanner  24 , and a transfer roller  7 . The process cartridge  25  includes a photosensitive drum  6  rotating in an arrow direction, and a charge roller  21 , a developing roller  22 , and a cleaning blade  23  which are disposed along the photosensitive drum  6 . The photosensitive drum  6  and the transfer roller  7  form a transfer nip T 1 . The process cartridge  25  is detachable from an apparatus body of the printer  1 . 
     The laser scanner  24  radiates a laser beam toward the photosensitive drum  6  based on the input image information. In this case, the photosensitive drum  6  is precharged by the charge roller  21  and is irradiated with the laser beam, so that an electrostatic latent image is formed on the photosensitive drum  6 . Thereafter, the electrostatic latent image is developed by the developing roller  22  and the monochrome toner image is formed on the photosensitive drum  6 . 
     In parallel to the image forming process, a sheet P is fed from the sheet feeding apparatus  30 . The sheet feeding apparatus  30  has a stacking portion  2  capable of stacking a sheet and a downstream side in a feeding direction of the sheets stacked on the stacking portion  2  is supported by a sheet supporting portion  31 . The sheet supporting portion  31  is pivotably supported around a pivot shaft  31   a  and is urged upward by a spring  32 . The sheet supporting portion  31  is pressed downward against an urging force of the spring  32  by a cam (not illustrated) every time one sheet is fed. The sheets P supported by the sheet supporting portion  31  are fed by a feed roller  3  and are separated one by one by a separating pad  33  urged toward the feed roller  3  by a spring  34 . 
     The sheet conveyance apparatus  50  includes a driving roller  4  as a counter member and a driven roller  5  as a rotary member for forming a conveyance nip N 1 , and the sheets P which are separated one by one are conveyed toward the transfer nip T 1  by the conveyance nip N 1 . The driving roller  4  and the driven roller  5  may constitute a registration roller pair for correcting a skew of the sheet P by causing a distal end of sheet P to abut against the conveyance nip N 1 . 
     The toner image on the photosensitive drum  6  is transferred to the sheet P conveyed by the conveyance nip N 1  by an electrostatic load bias applied to the transfer roller  7  at the transfer nip T 1 . Residual toner remaining on the photosensitive drum  6  is recovered by the cleaning blade  23 . A predetermined heat and pressure are applied to the sheet P to which the toner image is transferred by the fixing unit  40 , and the toner is melted and fixed. The fixing unit  40  includes a heating roller  9  having a heater  8  and a pressure roller  10 . The sheet P passed through the fixing unit  40  is discharged to the sheet discharge tray  12  by the sheet discharge roller pair  11 . 
     The printer  1  of the embodiment has a configuration capable of only single-side printing, but may have a configuration in which a duplex conveyance path is provided downstream of the fixing unit  40  in the sheet conveyance direction and the sheet P where an image is formed on a first surface is guided again to the transfer nip T 1  by the duplex conveyance path. 
     Sheet Conveyance Apparatus 
     Next, the sheet conveyance apparatus  50  will be described in detail with reference to  FIG. 2 . In the embodiment, as illustrated in  FIG. 2A , two sheet conveyance apparatuses  50  are juxtaposed in a width direction (arrow Y direction in the drawing) of the sheet on a drive shaft  4   a  driven by a motor M as a drive source, and the two sheet conveyance apparatuses  50  have the same configuration. 
     The sheet conveyance apparatus  50  includes a conveyance portion  45  conveying the sheet in the conveyance nip N 1 , a sponge  13  as a first contact member, a backflow preventing member  14  as a second contact member, and a contacting and separating mechanism  60 . The conveyance portion  45  includes the driving roller  4  driven by the drive shaft  4   a  and the driven roller  5  driven to rotate by the driving roller  4 . The driving roller  4  faces the driven roller  5 . The driven roller  5  includes a sheet conveyance surface  5   b  as a surface abutting against a peripheral surface of the driving roller  4  to form the conveyance nip N 1  and a pair of sliding surfaces  5   a  disposed on both sides of the sheet conveyance surface  5   b  in the axial direction. The driven roller  5  is urged toward the driving roller  4  by a spring (not illustrated). That is, the sheet conveyance surface  5   b  serves as a roller portion that comes into contact with the sheet to convey the sheet. 
     The sponge  13  is held by a sponge holding member (not illustrated) and contacts with the sheet conveyance surface  5   b  of the driven roller  5  with a predetermined abutting pressure. The backflow preventing member  14  is made of a material such as MYLAR (registered trademark) which is a polyester resin and is urged toward the sheet conveyance surface  5   b  of the driven roller  5  by its own weight and a spring  104 . The backflow preventing member  14  is capable of abutting against the sheet conveyance surface  5   b  at a second position downstream of the conveyance nip N 1  and upstream of the first position where the sponge  13  contacts with the sheet conveyance surface  5   b  in an arrow B 1  direction illustrated in  FIG. 3A . The sponge  13  and the backflow preventing member  14  are formed to be longer than the sheet conveyance surface  5   b  in the width direction, and come into contact with the sheet conveyance surface  5   b , so that paper dust adhering to the sheet conveyance surface  5   b  can be scraped through an overall region in the width direction to be removed. 
     As illustrated in  FIGS. 2A and 2B , the contacting and separating mechanism  60  includes a transmitting portion  70  transmitting the driving force to the backflow preventing member  14  and an abutment portion  105  against which the rotating backflow preventing member  14  abuts. The transmitting portion  70  includes a driven roller  101  as a supporting portion driven to rotate by the driven roller  5  by sliding on the sliding surface  5   a  of the driven roller  5 , a driven roller holder  102 , and a spring  103 . The driven roller  101  includes a rotation shaft  101   a  and a pair of disc members  101   b  fixed to the rotation shaft  101   a  and abutting against the sliding surfaces  5   a  on both sides of the sheet conveyance surface  5   b . That is, the disc member  101   b  as a second engagement portion is in engagement with the sliding surface  5   a  as the first engagement portion and is driven to rotate. 
     The backflow preventing member  14  is rotatably supported by the rotation shaft  101   a  with a slight gap. The driven roller holder  102  supports the rotation shaft  101   a  of the driven roller  101  rotatably and slidably in an upward and downward direction (arrow Z direction in the drawing) and restricts an upward movement of the rotation shaft  101   a  at a predetermined position. 
     The spring  103  urges the driven roller holder  102  downward, that is, toward the driven roller  5 , and the disc member  101   b  of the driven roller  101  contacts with the sliding surface  5   a  of the driven roller  5  with a predetermined pressure. The driving force of the motor M is transmitted to the backflow preventing member  14  via the drive shaft  4   a , the driving roller  4 , the driven roller  5 , and the driven roller  101 . More specifically, the driven roller  101  is rotated by being in engagement with the sliding surface  5   a  of the driven roller  5 , and the backflow preventing member  14  integrally rotates with the rotation shaft  101   a  by a frictional force between the rotation shaft  101   a  of the driven roller  101  and the backflow preventing member  14 . As described above, the rotation shaft  101   a  of the driven roller  101  supporting the backflow preventing member  14  is driven to rotate by the driven roller  5 . 
     Operation of Backflow Preventing Member 
     Next, an operation of the backflow preventing member  14  will be described in detail with reference to  FIG. 3 .  FIG. 3A  illustrates a state where the sheet P is conveyed by an image forming job or the like. As illustrated in  FIG. 3A , in a case where the driving roller  4  rotates in an arrow A 1  direction, the driven roller  5  driven by the driving roller  4  rotates in the arrow B 1  direction as the first direction and the sheet P is conveyed in an arrow S 1  direction by the conveyance nip N 1 . Therefore, the sheet P is conveyed toward the transfer nip T 1  (see  FIG. 1 ) and an image is formed at the transfer nip T 1  which is an image forming position. 
     The driven roller  101  is rotated in an arrow C 1  direction by coming into contact with the sliding surface  5   a  of the driven roller  5  rotating in the arrow B 1  direction. When the driven roller  101  rotates in the arrow C 1  direction, the backflow preventing member  14  also rotates in an arrow D 1  direction against the urging force of the spring  104  by the frictional force with the rotation shaft  101   a  of the driven roller  101 . When abutting against the abutment portion  105  provided in the casing of the printer  1 , the backflow preventing member  14  is kept separate from the sheet conveyance surface  5   b  of the driven roller  5 . In this case, the rotation shaft  101   a  of the driven roller  101  rotates in the arrow C 1  direction, but the backflow preventing member  14  is in sliding contact with the rotation shaft  101   a  and a posture is maintained in a state of abutting against the abutment portion  105 . 
       FIG. 3B  illustrates a state where the sheet P is pulled out in an arrow S 2  direction opposite to the arrow S 1  direction, that is, toward the feed roller  3  (see  FIG. 1 ) by a jam processing operation or the like. As illustrated in  FIG. 3B , when the sheet P is pulled out in the arrow S 2  direction, the driving roller  4 , the driven roller  5 , the driven roller  101 , and the backflow preventing member  14  rotate in a direction opposite to the rotation direction described in  FIG. 3A , that is, the arrow A 2 , B 2 , C 2 , and D 2  directions respectively. 
     As described above, when the driven roller  5  rotates in the arrow B 2  direction as the second direction opposite to the arrow B 1  direction, the backflow preventing member  14  rotates in the arrow D 2  direction by the frictional force with the rotation shaft  101   a  of the driven roller  101 , its own weight, and the urging force of the spring  104 . Therefore, the backflow preventing member  14  reliably contacts with the sheet conveyance surface  5   b  of the driven roller  5 . In this case, the rotation shaft  101   a  of the driven roller  101  rotates in the arrow C 2  direction, but the backflow preventing member  14  is in sliding contact with the rotation shaft  101   a  and a posture is maintained in a state of abutting against the sheet conveyance surface  5   b  of the driven roller  5 . 
       FIG. 3C  illustrates a state where the motor M (see  FIG. 2A ) is stopped and the driving roller  4 , the driven roller  5 , and the driven roller  101  are stopped. In this case, as illustrated in  FIG. 3C , the backflow preventing member  14  is urged in the arrow D 2  direction by its own weight and the urging force of the spring  104 , and a posture is maintained in a state of abutting against the sheet conveyance surface  5   b  of the driven roller  5 . 
     As described above, as illustrated in  FIG. 3A , the backflow preventing member  14  is separated from the sheet conveyance surface  5   b  of the driven roller  5  when the driven roller  5  rotates in the arrow B 1  direction in which the sheet P is normally conveyed. Therefore, the backflow preventing member  14  does not hinder a scraping operation of the paper dust by the sponge  13 . 
     In addition, as illustrated in  FIG. 3B , when the driven roller  5  rotates in the arrow B 2  direction, the paper dust scraped by the sponge  13  rides on the sheet conveyance surface  5   b  of the driven roller  5  and sometimes moves toward the conveyance nip N 1 . However, the backflow preventing member  14  contacts with the sheet conveyance surface  5   b , so that the paper dust on the sheet conveyance surface  5   b  can be reliably removed. Moreover, since the backflow preventing member  14  contacts with the sheet conveyance surface  5   b  without any gap, paper dust having a small particle size such as a filler (for example, calcium carbonate or talc) contained in the sheet P can also be scraped. Therefore, image defects due to the paper dust can be prevented. In addition, the paper dust on the sheet conveyance surface  5   b  is scraped, so that slipping of the sheet P at the conveyance nip N 1  can be reduced and image defects such as image displacement at the transfer nip T 1  can be prevented. 
     In addition, the contacting and separating mechanism  60  that causes the backflow preventing member  14  to abut against and separate from the sheet conveyance surface  5   b  has a simple mechanical configuration and the backflow preventing member  14  is rotated using the driving force transmitted from the driven roller  5 , so that it is possible to provide the sheet conveyance apparatus  50  having high reliability with low cost. 
     Second Embodiment 
     Next, a second embodiment of the invention will be described, and the second embodiment is a modification of the configuration of the contacting and separating mechanism  60  of the first embodiment. Therefore, configurations similar to those of the first embodiment will be omitted or described by attaching the same reference numerals to the drawings. 
     Sheet Conveyance Apparatus 
     As illustrated in  FIGS. 4A and 4B , a sheet conveyance apparatus  150  includes a driving roller  4 , a driven roller  5  driven to rotate by the driving roller  4 , a sponge  13 , a backflow preventing member  14 , and a contacting and separating mechanism  160 . The contacting and separating mechanism  160  includes a transmitting portion  170  transmitting a driving force of a motor M to the backflow preventing member  14 , and an abutment portion  105 . 
     The transmitting portion  170  includes a driving gear  201  as a first gear fixed to an end portion of a drive shaft  4   a  of the driving roller  4 , an idler gear  204  as a second gear in engagement with the driving gear  201 , an output gear  203  as a third gear in engagement with the idler gear  204 , and a rotation shaft  202  fixed to the output gear  203 . The backflow preventing member  14  is rotatably supported by the rotation shaft  202  as a supporting portion with a slight gap and is rotatable together with the rotation shaft  202  by a frictional force with the rotation shaft  202 . In addition, the idler gear  204  is in engagement between the driving gear  201  and the output gear  203 , so that a rotation direction of the backflow preventing member  14  is the same as a rotation direction of the driving roller  4 , and is opposite to a rotation direction of the driven roller  5 . 
     Operation of Backflow Preventing Member 
     Next, an operation of the backflow preventing member  14  will be described in detail with reference to  FIGS. 5A to 5C .  FIG. 5A  illustrates a state where a sheet P is conveyed by an image forming job or the like. As illustrated in  FIG. 5A , in a case where the driving roller  4  rotates in an arrow A 1  direction, the driven roller  5  driven by the driving roller  4  rotates in an arrow B 1  direction and the sheet P is conveyed by a conveyance nip N 1  in an arrow S 1  direction. 
     A driving force of a motor M driving the drive shaft  4   a  is transmitted to the rotation shaft  202  via the driving gear  201 , the idler gear  204 , and the output gear  203  (see  FIG. 4A ), and the rotation shaft  202  rotates in an arrow E 1  direction. When the rotation shaft  202  rotates in the arrow E 1  direction, the backflow preventing member  14  also rotates in the arrow D 1  direction against an urging force of a spring  104  by a frictional force with the rotation shaft  202 . When abutting against an abutment portion  105  provided in the casing of the printer  1 , the backflow preventing member  14  is kept separate from a sheet conveyance surface  5   b  of the driven roller  5 . In this case, the rotation shaft  202  rotates in the arrow E 1  direction, but the backflow preventing member  14  is in sliding contact with the rotation shaft  202  and maintained in the posture in which it abuts against the abutment portion  105 . 
       FIG. 5B  illustrates a state where the sheet P is pulled out by the jam processing operation or the like in an arrow S 2  direction opposite to the arrow S 1  direction, that is, toward the feed roller  3  (see  FIG. 1 ). As illustrated in  FIG. 5B , when the sheet P is pulled out in the arrow S 2  direction, the driving roller  4 , the driven roller  5 , the rotation shaft  202 , and the backflow preventing member  14  rotate in a direction opposite to the rotation direction described in  FIG. 5A , that is, the arrow A 2 , B 2 , E 2 , and D 2  directions, respectively. 
     As described above, when the driven roller  5  rotates in the arrow B 2  direction opposite to the arrow B 1  direction, the backflow preventing member  14  rotates in the arrow D 2  direction by a frictional force with the rotation shaft  202 , its own weight, and an urging force of the spring  104 . Therefore, the backflow preventing member  14  reliably contacts with the sheet conveyance surface  5   b  of the driven roller  5 . In this case, the rotation shaft  202  rotates in the arrow E 2  direction, but the backflow preventing member  14  is in sliding contact with the rotation shaft  202  and maintained in the posture in which it contacts with the sheet conveyance surface  5   b  of the driven roller  5 . 
       FIG. 5C  illustrates a state where the motor M (see  FIG. 4A ) is stopped and the driving roller  4 , the driven roller  5 , and the rotation shaft  202  are stopped. In this case, as illustrated in  FIG. 5C , the backflow preventing member  14  is urged in the arrow D 2  direction by its own weight and the urging force of the spring  104 , and maintained in the posture in which it contacts with the sheet conveyance surface  5   b  of the driven roller  5 . 
     As described above, as illustrated in  FIG. 5A , when the driven roller  5  rotates in the arrow B 1  direction in which the sheet P is normally conveyed, the backflow preventing member  14  is separated from the sheet conveyance surface  5   b  of the driven roller  5 . Therefore, the backflow preventing member  14  does not hinder a scraping operation of paper dust by the sponge  13 . In addition, as illustrated in  FIG. 5B , when the driven roller  5  rotates in the arrow B 2  direction, the backflow preventing member  14  contacts with the sheet conveyance surface  5   b , so that the paper dust on the sheet conveyance surface  5   b  can be reliably removed. 
     In addition, in the backflow preventing member  14 , since the driving force from the driving gear  201  driven by the motor M is transmitted, a rotation load applied to the driven roller  5  driven to rotate by the driving roller  4  is smaller than that of the first embodiment. Therefore, the driven roller  5  can be more smoothly rotated and load fluctuation when a trailing edge of the sheet P passes through the conveyance nip N 1  is suppressed. As a result, conveyance shake of the sheet P at the transfer nip T 1  can be reduced and image defects can be reduced. 
     Moreover, in the first and second embodiments, a slight gap is provided between the rotation shafts  101   a  and  202 , and the backflow preventing member  14 , and the backflow preventing member  14  is rotatable relative to the rotation shafts  101   a  and  202 , but the invention is not limited thereto. For example, as illustrated in  FIG. 6A , a torque limiter  90  may be provided between the rotation shaft  101   a  and the disc member  101   b  of the driven roller  101 , and the backflow preventing member  14  may be fixed to the rotation shaft  101   a . In addition, as illustrated in  FIG. 6B , the torque limiter  90  may be provided between the output gear  203  and the rotation shaft  202 , and the backflow preventing member  14  may be fixed to the rotation shaft  202 . 
     In a state where the backflow preventing member  14  is separated from the abutment portion  105 , or the backflow preventing member  14  is separated from the sheet conveyance surface  5   b , the torque limiter  90  transmits a driving force to the rotation shafts  101   a  and  202 . In addition, in a state where the backflow preventing member  14  abuts against the abutment portion  105  or the sheet conveyance surface  5   b , the torque limiter  90  does not transmit the driving force to the rotation shafts  101   a  and  202 . Therefore, it is possible to realize the operation of the backflow preventing member  14  similar to those of the first and second embodiments. Moreover, the torque limiter  90  is not limited to the configuration described above but may be provided anywhere as long as it is provided in a driving path for transmitting the driving force to the rotation shafts  101   a  and  202 . 
     In addition, in the first and second embodiments, the backflow preventing member  14  is rotated by using the driving force of the motor M for driving the conveyance portion  45 , but the invention is not limited thereto and the backflow preventing member  14  may be rotated by a drive source other than the motor M. 
     In addition, the spring  103  is provided in the driven roller holder  102  and the casing of the printer  1 , and the spring  104  is provided between the backflow preventing member  14  and the casing of the printer  1 , but the invention is not limited thereto. For example, the springs  103  and  104  may be provided between the backflow preventing member  14  and a driven roller holder  102  which is described later. In addition, the abutment portion  105  may not be provided in the casing but be provided in the driven roller holder  102  or the like. In addition, the backflow preventing member  14  is urged toward the sheet conveyance surface  5   b  of the driven roller  5  by the spring  104  and its own weight but may be urged only by its own weight without the spring  104 . 
     In addition, materials of the sponge  13  and the backflow preventing member  14  are not limited, and the sponge  13  may be made by a rubber-like elastic body or a member using MYLAR, and the backflow preventing member  14  may be made by a sponge-like or rubber-like elastic body. 
     In addition, the sponge  13 , the backflow preventing member  14 , and the contacting and separating mechanisms  60  and  160  may be provided to remove paper dust of the rotary member other than the driven roller  5 . For example, the sponge  13 , the backflow preventing member  14 , and the contacting and separating mechanisms  60  and  160  may be provided to remove paper dust of the feed roller  3 , the driving roller  4 , and the sheet discharge roller pair  11 . In addition, a member forming the conveyance nip together with the rotary members is not limited to the rotary member such as a roller or a belt, but for example, may be a member which does not rotate like the separating pad  33 . 
     In addition, in any of the embodiments described above, the printer  1  of the electrophotographic system is described, but the invention is not limited thereto. For example, the invention can be applied to an image forming apparatus of an ink jet system for forming an image on a sheet by discharging an ink liquid from a nozzle. 
     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. 2018-082573, filed Apr. 23, 2018, which is hereby incorporated by reference herein in its entirety.