Patent Publication Number: US-8989646-B2

Title: Cleaning device, image carrier unit, and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application claims priority to Japanese Patent Application No. 2012-134554 filed on Jun. 14, 2012, the entire contents of which are incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to a cleaning device for use to clean an image carrier capable of carrying a toner image, an image carrier unit including the cleaning device, and an image forming apparatus including the cleaning device. 
     A known image forming apparatus for use to form an image on a sheet (recording medium) employs a technique in which the sheet passes up from below through a transfer nip formed between a photosensitive drum and a transfer roller. A toner image is formed on the photosensitive drum and the formed toner image is then transferred to the sheet at the transfer nip. The image forming apparatus further includes a fixing section. The sheet having the toner image transferred thereto undergoes a fixing process in the fixing section and is then output. 
     In this technique, in order to clean up residual toner on the photosensitive drum after the transfer of the toner image at the transfer nip, a cleaning device is disposed facing the photosensitive drum. In the case where, as above, the sheet passes up from below through the transfer nip, the cleaning device located downstream of the transfer nip in the direction of rotation of the photosensitive drum is mostly disposed above the photosensitive drum. 
     When like this the cleaning device is disposed above the photosensitive drum, residual toner removed from the photosensitive drum may fall from around the cleaning device. Therefore, a toner sealing member is provided around the cleaning device and held in contact with the photosensitive drum in order to prevent residual toner from falling. However, if a large amount of toner piles up on top of the toner sealing member, the toner presses the toner sealing member against the photosensitive drum. Thus, the contact pressure of the toner sealing member against the photosensitive drum is increased. If in this state paper powder of a sheet adheres to the cylindrical surface of the photosensitive drum at the transfer nip and moves to the distal end of the toner sealing member with the rotation of the photosensitive drum, the paper powder grows with time into a mass between the distal end of the toner sealing member and the cylindrical surface of the photosensitive drum. As a result, the mass of paper powder may lift up the distal end of the toner sealing member to cause troubles, such as toner leakage. 
     SUMMARY 
     A cleaning device according to the present disclosure includes a rotary member, a sheet member, and a toner conveying member. 
     The rotary member includes a peripheral surface held in contact with a cylindrical surface of an image carrier above a rotation axis of the image carrier. The rotary member is configured to be driven into rotation so that the peripheral surface thereof travels, at a contact position thereof with the image carrier, in the same direction as but with a linear speed difference from the image carrier and thereby allow toner deposited on the cylindrical surface of the image carrier to adhere to the peripheral surface of the rotary member. 
     The sheet member includes a distal end extending toward the cylindrical surface of the image carrier. The sheet member is in contact at the distal end with the cylindrical surface of the image carrier above the rotation axis thereof and upstream of the contact position of the rotary member in a direction of rotation of the image carrier. 
     The toner conveying member includes a rotation axis extending in a direction of length of the rotary member. The toner conveying member is disposed above the sheet member and facing the peripheral surface of the rotary member. The toner conveying member further includes a spiral member provided around the rotation axis thereof to extend in an axial direction of the rotation axis and is configured to be driven into rotation about the rotation axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the appearance of an image forming apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional view showing the internal structure of the image forming apparatus according to the above embodiment of the present disclosure. 
         FIG. 3  is a cross-sectional view showing the internal structure of an image carrier unit in the above embodiment of the present disclosure. 
         FIG. 4  is a cross-sectional view showing the internal structure of an image carrier unit for comparison with the present disclosure. 
         FIG. 5  is a schematic view for illustrating a state that toner piles up on a toner seal. 
         FIG. 6  is a schematic view for illustrating a state that the distal end of the toner seal is lifted up by a mass of paper powder. 
         FIG. 7  is an enlarged cross-sectional view of a second conveying screw and the surrounding area in an embodiment of the present disclosure. 
         FIG. 8  is an enlarged cross-sectional view of a second conveying screw and the surrounding area in another embodiment of the present disclosure. 
         FIG. 9  is an enlarged cross-sectional view of a second conveying screw and the surrounding area in still another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a description will be given of an embodiment as one aspect of the present disclosure.  FIG. 1  is a perspective view showing the appearance of an image forming apparatus  1  according to the embodiment of the present disclosure.  FIG. 2  is a sectional side view showing the internal structure of the image forming apparatus  1  according to the embodiment of the present disclosure. Here, a black and white printer is exemplified as the image forming apparatus  1 . However, the image forming apparatus may be a copier, a facsimile machine, a multifunction peripheral having these functions or an image forming apparatus capable of forming color images. 
     The image forming apparatus  1  includes a body housing  10  having an approximately cuboid housing structure and further includes a paper feed section  20 , an image forming section  30 , a fixing section  40 , and a toner container  50  all of which are housed in the body housing  10 . 
     The body housing  10  includes a front cover  11  on the front side and a rear cover  12  on the rear side. When the front cover  11  is opened, the toner container  50  is exposed on the front side. Thus, the user can take out the toner container  50  from the front side of the body housing  10  when the toner container  50  is out of toner. The rear cover  12  is a cover that can be opened in the event of a sheet jam and during maintenance. Each of the image forming section  30  and the fixing section  40  can be taken out as a unit from the rear side of the body housing  10  by opening the rear cover  12 . Furthermore, the body housing  10  is provided at both lateral sides with a left cover  12 L (see  FIG. 1 ) and a right cover  12 R (not seen in  FIG. 1 ) opposite to the left cover  12 L, each of which extends in the vertical direction. A front portion of the left cover  12 L is provided with an air inlet  12 La to take air into the body housing  10 . The top surface of the body housing  10  is provided with a paper output section  13  to which a sheet after image formation is to be output. Various devices for use in performing image formation are disposed in the interior space S (see  FIG. 2 ) defined by the front cover  11 , the rear cover  12 , the left cover  12 L, the right cover  12 R, and the paper output section  13 . 
     The paper feed section  20  includes a paper feed cassette  21  capable of containing sheets to be subjected to an image forming process (see  FIG. 2 ). The paper feed cassette  21  partly extends forwardly beyond the front surface of the body housing  10 . The top surface of a portion of the paper feed cassette  21  housed in the body housing  10  is covered with a paper feed cassette top plate  21 U. The paper feed cassette  21  includes a sheet containing space in which a bundle of sheets are contained, a lift plate configured to lift up the bundle of sheets for the purpose of paper feed, and so on. A sheet forwarding part  21 A is provided above the rear end of the paper feed cassette  21 . In the sheet forwarding part  21 A, a paper feed roller  21 B is disposed to forward the uppermost one of the bundle of sheets in the paper feed cassette  21  for each operation. 
     The image forming section  30  performs an image forming process for forming a toner image on a sheet forwarded from the paper feed section  20 . The image forming section  30  includes a photosensitive drum  31  (image carrier) and further includes a charging device  32 , an exposure device (not seen in  FIG. 2 ), a developing device  33 , a transfer roller  34 , and a cleaning device  35  all of which are disposed around the photosensitive drum  31 . The image forming section  30  is disposed between the left cover  12 L and the right cover  12 R. 
     The photosensitive drum  31  has a rotation axis  31 A and includes a cylindrical surface  31 B rotatable about the rotation axis  31 A (see  FIG. 3 ). An electrostatic latent image can be formed on the cylindrical surface  31 B and a toner image corresponding to the electrostatic latent image can be carried on the cylindrical surface  31 B. An example of the photosensitive drum  31  that can be used is a photosensitive drum in which an amorphous silicon (a-Si) based material is used as a photosensitive material. 
     The charging device  32  is configured to uniformly charge the surface of the photosensitive drum  31  and includes a charging roller held in contact with the photosensitive drum  31 . 
     The cleaning device  35  includes a cleaning blade and so on. The cleaning device  35  cleans toner left behind on the peripheral surface of the photosensitive drum  31  having undergone the transfer of a toner image and conveys the toner to an unshown recovery device. Furthermore, the photosensitive drum  31 , the charging device  32 , and the cleaning device  35  are configured in combination as a drum unit  31 H (an example of the image carrier unit, see  FIG. 3 ). The cleaning device  35  and the drum unit  31 H will be described in detail later. 
     The exposure device includes a laser light source and optical elements, including a mirror and a lens. The exposure device irradiates the peripheral surface of the photosensitive drum  31  with light modulated based on image data given by an external device, such as a personal computer, to form an electrostatic latent image. The developing device  33  supplies toner to the peripheral surface of the photosensitive drum  31  in order to develop the electrostatic latent image on the photosensitive drum  31  to form a toner image. The developing device  33  includes: a developing roller  331  capable of carrying toner to be supplied to the photosensitive drum  31 ; and first and second conveying screws  332 ,  333  configured to circulate and convey a developer while agitating the developer inside an unshown development housing. 
     The transfer roller  34  is a roller configured to transfer a toner image formed on the peripheral surface of the photosensitive drum  31  to a sheet. The transfer roller  34  is held in contact with the cylindrical surface  31 B of the photosensitive drum  31  to form a transfer nip TP (see  FIG. 3 ). The transfer roller  34  is configured to be given a transfer bias of reverse polarity to the toner. 
     The fixing section  40  performs a fixing process for fixing the transferred toner image on the sheet. The fixing section  40  includes: a fixing roller  41  internally provided with a heat source; and a pressure roller  42  pressed against the fixing roller  41  and forming a fixing nip with the fixing roller  41 . When the sheet having the toner image transferred thereto is passed through the fixing nip, the toner image is fixed on the sheet by heating from the fixing roller  41  and pressing from the pressure roller  42 . 
     The body housing  10  is internally provided with a main conveyance path  22 F and a reverse conveyance path  22 B in order to convey sheets. The main conveyance path  22 F extends from the sheet forwarding part  21 A of the paper feed section  20  via the image forming section  30  and the fixing section  40  to a paper output port  14  provided facing the paper output section  13  located at the top surface of the body housing  10 . The reverse conveyance path  22 B is a conveyance path for use to return the sheet one side of which has already been subjected to printing to a position of the main conveyance path  22 F upstream of the image forming section  30 . 
     The main conveyance path  22 F (sheet conveyance path) is extended to allow a sheet to pass up from below through the transfer nip TP formed between the photosensitive drum  31  and the transfer roller  34 . Furthermore, a registration roller pair  23  is disposed in the main conveyance path  22 F upstream of the transfer nip TP. The sheet is once stopped between the registration roller pair  23  to correct any skew and then forwarded therefrom to the transfer nip with a predetermined timing for image transfer. A plurality of conveyance rollers configured to convey sheets are disposed at various points of the main conveyance path  22 F and reverse conveyance path  22 B. For example, a paper output roller pair  24  as the conveyance rollers is disposed near the paper output port  14 . 
     Next, a description will be given of the structure of the drum unit  31 H in this embodiment with reference to  FIGS. 3 to 6 .  FIG. 3  is an enlarged cross-sectional view of the drum unit  31 H in this embodiment. Note that  FIG. 3  is shown as a view in which the right-and-left direction of the plane of  FIG. 2  (the front-to-rear direction of the image forming apparatus  1  in  FIG. 2 ) is inverted. 
     Referring to  FIG. 3 , the drum unit  31 H includes the photosensitive drum  31 , the charging device  32 , and the cleaning device  35 . The drum unit  31 H further includes an unshown pair of side plates (not shown) at both ends in the right-and-left direction (the direction perpendicular to the plane of  FIG. 3 ). The photosensitive drum  31  is rotatably supported by the pair of side plates. Furthermore, the charging device  32  and the cleaning device  35  are supported at positions facing the photosensitive drum  31  by the pair of side plates. The photosensitive drum  31  is driven into rotation in the direction of the arrow DP in  FIG. 3 . The side plates of the drum unit  31 H are provided with their respective fixing parts (not shown). The fixing parts are designed to fix the drum unit  31  to the body housing  10  of the image forming apparatus  1  when the drum unit  31 H is fitted to the body housing  10  of the image forming apparatus  1 . Thus, the drum unit  31 H is positioned in place in the image forming apparatus  1 . Each of the fixing parts is formed of, for example, a fastening hole through which a screw can be fastened. 
     The charging device  32  is disposed forwardly of the photosensitive drum  31 . The charging device  32  includes a charging roller  321 , a cleaning roller  322 , and a charging housing  32 H. The charging housing  32 H has an opening facing the cylindrical surface (peripheral surface) of the photosensitive drum  31  in side view shown in  FIG. 3 . The charging roller  321  and the cleaning roller  322  are rotatably supported inside the charging housing  32 H. 
     The charging roller  321  is a roll member whose surface is made of rubber material. A charging voltage can be applied to the charging roller  321  by an unshown bias applying device. The charging roller  321  is held in contact with the peripheral surface of the photosensitive drum  31  and configured to be rotated by following the rotation of the photosensitive drum  31 . The charging roller  321  to which a charging voltage is applied uniformly charges the peripheral surface of the photosensitive drum  31 . 
     The cleaning roller  322  is held in contact with the charging roller  321  and configured to rotate with a linear speed difference from the charging roller  321 . The cleaning roller  322  is a brush roller made of electrically conductive nylon fibers. When the charging roller  321  is in contact with the surface of the photosensitive drum  31 , toner and foreign matters adhere to the surface of the charging roller  321 . Furthermore, when a charging voltage is applied to the charging roller  321  to generate a discharge at the contact position of the charging roller  321  with the photosensitive drum  31 , discharge products are deposited on the surface of the charging roller  321 . The cleaning roller  322  is rotated in contact with and with a linear speed difference from the charging roller  321 , so that toner, foreign matters, and discharge products deposited on the surface of the charging roller  321  can be appropriately removed. 
     The cleaning device  35  is disposed above the photosensitive drum  31 . The cleaning device  35  includes a cleaner housing  35 H, a cleaning blade  351 , a first conveying screw  352 , and an abrasive roller  353 . The cleaning device  35  further includes a scraper  354 , a scraper holder  355 , and an upper seal  356 . The cleaning device  35  still further includes a plate  358 , an anti-drag sheet  359 , a toner seal  360 , and a second conveying screw  361 . 
     The cleaner housing  35 H is a housing that supports various members inside the cleaning device  35 . Referring to  FIG. 3 , the cleaning device  35  is disposed to cover the photosensitive drum  31  and the charging device  32  from above. Particularly, a front portion of the cleaner housing  35 H as viewed in  FIG. 3  is placed above the charging roller  321 . A midportion of the cleaner housing  35 H in the front-to-rear direction in side view of  FIG. 3  has a shape raised in an arc. A rear portion of the cleaner housing  35 H is defined by a housing rear wall  35 H 1  (second standing wall). The housing rear wall  35 H 1  is a wall portion extended in the vertical direction. The housing rear wall  35 H 1  is disposed facing the abrasive roller  353  to be described later. Furthermore, an upper wall  35 H 2  and a sidewall  35 H 3  are provided at the lower end of the housing rear wall  35 H 1 . The upper wall  35 H 2  is a wall portion extended in the front-to-rear direction from the lower end of the housing rear wall  35 H 1 . The upper wall  35 H 2  (an example of the upper wall portion) is formed by bending a lower end portion of the housing rear wall  35 H 1  rearwardly. On the other hand, the sidewall  35 H 3  (an example of the first standing wall) is a wall portion extended vertically from the rear end of the upper wall  35 H 2 . The sidewall  35 H 3  is formed by bending a rear end portion of the upper wall  35 H 2  downwardly. The upper wall  35 H 2  and the sidewall  35 H 3  are disposed facing the second conveying screw  361  from above and behind, respectively. 
     In this manner, the sidewall  35 H 3  is provided lateral to the second conveying screw  361  and to the opposite side thereof to the abrasive roller  353  to extend vertically and face the second conveying screw  361 . Thus, toner can be conveyed by the second conveying screw  361  while being squeezed in between the second conveying screw  361  and the sidewall  35 H 3 . Therefore, the toner can be stably conveyed in the axial direction of the photosensitive drum  31  by the second conveying screw  361 . 
     In addition, since the upper wall  35 H 2  is provided to cover the second conveying screw  361  from above, the space above the second conveying screw  361  is terminated by the upper wall  35 H 2 . Therefore, it can be prevented that the toner being conveyed by the second conveying screw  361  is driven away from the second conveying screw  361  by centrifugal force thereof. 
     The cleaning blade  351  is disposed horizontally along the bottom of the cleaner housing  35 H. The cleaning blade  351  is a plate-like member made of rubber material. The cleaning blade  351  is supported by a blade holder  351 H. The blade holder  351 H is a sheet metal member of L-shape in cross-sectional view of  FIG. 3 . The blade holder  351 H is secured to the cleaner housing  35 H by a blade mounting screw  351 B. The cleaning blade  351  and the blade holder  351 H are secured to each other by an adhesive. As a result, a fixed end of the cleaning blade  351  is formed. On the other hand, a distal end of the cleaning bade  351  is a free end and is held in contact with the peripheral surface of the photosensitive drum  31 . The distal end of the cleaning blade  351  is held in contact with the cylindrical surface  31 B of the photosensitive drum  31  downstream of the abrasive roller  353  to be described later in a direction of rotation of the photosensitive drum  31  (the direction of the arrow DP). As a result, residual (deposited) toner on the peripheral surface of the photosensitive drum  31  is removed by the distal end of the cleaning blade  351 . 
     The first conveying screw  352  is rotatably supported above the cleaning blade  351  by the cleaner housing  35 H. The first conveying screw  352  includes a shaft and a spiral fin member (spiral member) provided around the shaft. The first conveying screw  352  conveys collected toner PT, which has been scraped by and accumulates on the cleaning blade  351 , in the axial direction of the rotation axis  31 A of the photosensitive drum  31 . 
     The abrasive roller  353  (an example of the rotary member) is disposed behind the first conveying screw  352 . The abrasive roller  353  includes a peripheral surface held in contact with the cylindrical surface  31 B of the photosensitive drum  31  above the rotation axis  31 A thereof. For example, the abrasive roller  353  is held in contact with the cylindrical surface  31 B of the photosensitive drum  31  somewhere in between the transfer nip TP and a position right above the rotation axis  31 A of the photosensitive drum  31 . More specifically, the abrasive roller  353  is held in contact with the cylindrical surface  31 B at the position right above the rotation axis  31 A of the photosensitive drum  31  or slightly upstream of the position in the direction of rotation of the photosensitive drum  31 . The contact position of the abrasive roller  353  with the cylindrical surface  31 B is defined as a contact position CP. The abrasive roller  353  is a rubber roller whose surface is roughened. The abrasive roller  353  is rotated (in the direction of the arrow DC) with a linear speed difference from the photosensitive drum  31  while being held in contact with the surface of the photosensitive drum  31 . The surface of the abrasive roller  353  traps toner deposited on the cylindrical surface  31 B of the photosensitive drum  31 . Furthermore, the abrasive roller  353  grinds deposits, such as discharge products, deposited on the surface of the photosensitive drum  31 . During the grinding, a constant amount of toner adheres to the peripheral surface of the abrasive roller  353 , resulting in improved performance of removal (grinding) of the discharge products. 
     The scraper  354  is a vertically extended plate-like member. In this embodiment, the scraper  354  is formed of a 0.05 mm thick SUS sheet. The lower end of the scraper  354  is held in contact with the peripheral surface of the abrasive roller  353 . The lower end of the scraper  354  is held in contact with the peripheral surface of the abrasive roller  353  against the direction of rotation of the abrasive roller  353  (the direction of the arrow DC). The scraper  354  is held in contact with the peripheral surface of the abrasive roller  353  with a predetermined resilient force, so that the amount of toner having adhered to the peripheral surface of the abrasive roller  353  is regulated. As a result, the toner collected by the abrasive roller  353  falls on the cleaning blade  351 . Furthermore, the amount of toner adhering to the peripheral surface of the abrasive roller  353  is evenly distributed, which prevents the abrasive roller  353  from varying in performance of removal of discharge products. 
     The scraper  354  is mounted to the scraper holder  355 . The scraper holder  355  is disposed to cover the abrasive roller  353  from above. The scraper holder  355  is formed of a bent sheet metal material. A midportion of the scraper holder  355  extends horizontally. A front portion of the scraper holder  355  is bent downward and supports the scraper  354 . A rear portion of the scraper holder  355  is bent rearward and downward. 
     The upper seal  356  is secured on the scraper holder  355 . One end of the upper seal  356  is supported on the midportion of the scraper holder  355  and the other end thereof is placed to project forwardly beyond the scraper holder  355 . The upper seal  356  has the function, when the toner having adhered to the peripheral surface of the abrasive roller  353  is scraped by the scraper  354 , of blocking upwardly scattered toner particles. 
     The plate  358  is disposed behind and facing the housing rear wall  35 H 1 . The plate  358  is a vertically extended sheet metal member. A plate upper portion  358 T which is an upper end portion of the plate  358  is bent rearward and then curved upward. Furthermore, the plate  358  is secured to the cleaner housing  35 H by a fastening screw located out of a paper passage area. A plate lower portion  358 S (an example of the support member) which is a lower end portion of the plate  358  is disposed to bend forward. The plate lower portion  358 S is disposed next to a lateral portion of the cleaner housing  35 H. The plate lower portion  358 S extends from the lateral portion of the cleaner housing  35 H toward the cylindrical surface  31 B of the photosensitive drum  31 . One end of the toner seal  360  is attached to an end of the plate lower portion  358 S located toward the cylindrical surface  31 B. The plate lower portion  358 S supports the toner seal  360 . 
     The anti-drag sheet  359  is extended vertically along the plate  358 . An upper portion of the anti-drag sheet  359  is secured to the plate  358  by adhesion to form a fixed end portion of the anti-drag sheet  359 . On the other hand, a lower portion of the anti-drag sheet  359  is placed to project downward beyond the plate  358  and thus form a free end portion of the anti-drag sheet  359 . A lower and distal end of the anti-drag sheet  359  is placed close to the peripheral surface of the photosensitive drum  31 . 
     The toner seal  360  (an example of the sheet member) is extended horizontally along the plate lower portion  358 S of the plate  358 . The toner seal  360  is a 100 μm thick urethane sheet. A basal end portion (rear portion) of the toner seal  360  is secured to the plate lower portion  358 S by adhesion. The basal end portion of the toner seal  360  forms a fixed end  360 F of the toner seal  360 . The fixed end  360 F is a part of an adhering region of the toner seal  360  adhering to the plate lower portion  358 S and is nearest to a distal end  360 S of the toner seal  360  in the adhering region. In other words, the fixed end  360 F refers to a part of the toner seal  360  located at the same position as an end  3581  of the plate lower portion  358 S in a direction from these ends toward the cylindrical surface  31 B of the photosensitive drum  31 . 
     In the toner seal  360 , its distal end  360 S on the side opposite to its basal end extends toward the cylindrical surface  31 B of the photosensitive drum  31 . The distal end  360 S forms a free end of the toner seal  360  and is in contact with the peripheral surface of the photosensitive drum  31 . To sum up, the toner seal  360  is interposed between the plate lower portion  358 S and the cylindrical surface  31 B of the photosensitive drum  31  and, with its basal end attached to the plate lower portion  358 S, its distal end  360 S as the other end is in contact with the cylindrical surface  31 B. 
     The distal end  360 S of the toner seal  360  is located above the rotation axis  31 A in side view shown in  FIG. 3 . The distal end  360 S is in contact with the cylindrical surface  31 B of the photosensitive drum  31  upstream of the abrasive roller  353  in the direction of rotation of the photosensitive drum  31 . In this relation, the toner seal  360  extends in a direction of approach to a reference line RL connecting between the rotation axis  31 A of the photosensitive drum  31  and the contact point CP thereof with the abrasive roller  353  in cross-sectional view orthogonal to the rotation axis  31 A and then reaches the cylindrical surface  31 B. The toner seal  360  has the function of preventing the toner from leaking from the interior of the cleaner housing  35 H. 
     The second conveying screw  361  (an example of the toner conveying member) is disposed in a space defined by the upper wall  35 H 2 , the sidewall  35 H 3 , and the plate lower portion  358 S. The shaft (rotation axis) of the second conveying screw  361  extends in the direction of length of the abrasive roller  353 . The second conveying screw  361  is disposed above the toner seal  360  and facing the peripheral surface of the abrasive roller  353 . The second conveying screw  361  is rotatably supported at both ends in the direction orthogonal to the plane of  FIG. 3  by the cleaner housing  35 H. The second conveying screw  361  includes the shaft and a fin member (an example of the spiral member). The fin member is provided around the shaft and has a spiral shape extending in the axial direction of the shaft. The second conveying screw  361  is driven into rotation about the axis of the shaft to convey the toner piled up on the toner seal  360  in the axial direction of the rotation axis  31 A of the photosensitive drum  31 . 
     The unshown exposure device, which is located downstream of the charging device  32  in the direction of rotation of the photosensitive drum  31 , forms an electrostatic latent image on the photosensitive drum  31  whose peripheral surface has been uniformly charged by the charging roller  321  of the charging device  32 . Then, the electrostatic latent image is made visible as a toner image by the developing device  33  (see  FIG. 2 ) disposed below the photosensitive drum  31 . The photosensitive drum  31  is rotated to travel from below upward at the transfer nip TP. Then, the toner image formed on the photosensitive drum  31  is transferred to a sheet being conveyed through the transfer nip TP from below upward. 
     Part of the toner image transferred to the sheet at the transfer nip TP remains as residual toner on the photosensitive drum  31 . With the rotation of the photosensitive drum  31 , the residual toner on the photosensitive drum  31  is conveyed from below upward to an area where the cleaning device  35  and the photosensitive drum  31  face each other. 
     Part of the residual toner conveyed to the area where the cleaning device  35  and the photosensitive drum  31  face each other adheres to the peripheral surface of the abrasive roller  353 . Furthermore, the remaining residual toner having not adhered to the peripheral surface of the abrasive roller  353  is scraped by the cleaning blade  351 . 
     Next, a description will be given of problems of the toner sealing member (sheet member) disposed in the cleaning device  35 . Part of the toner having adhered to the peripheral surface of the abrasive roller  353  is scraped by the scraper  354 . The residual toner passing over the distal end of the scraper  354  and still remaining on the peripheral surface of the abrasive roller  353  is traveled with the rotation of the abrasive roller  353  while passing through an area facing the scraper holder  355  and an area facing the housing rear wall  35 H 1 . During the travel, the toner adhering to the peripheral surface of the abrasive roller  353  is removed away from the abrasive roller  353  by the centrifugal force of the abrasive roller  353 . The toner removed away from the abrasive roller  353  is scattered in an area surrounded by the scraper holder  355 , the housing rear wall  35 H 1 , and the peripheral surface of the photosensitive drum  31 . 
       FIG. 4  is used for comparison with the cleaning device  35  according to the embodiment of the present disclosure and is a cross-sectional view of a drum unit  31 HW equipped with a cleaning device  35 W. The cleaning device  35 W includes a toner seal  380 . The toner seal  380 , like the toner seal  360 , is formed of a horizontally disposed urethane sheet. A basal end portion of the toner seal  380  is fixed and supported to a plate lower portion  357 S. A distal end of the toner seal  380  forms a free end and is held in contact with the peripheral surface of the photosensitive drum  31 . 
     Toner particles scattered from the peripheral surface of the abrasive roller  353  pile up on the toner seal  380  to form a toner accumulation TN.  FIGS. 5 and 6  are views showing states of the toner seal  380  and the surrounding area during the formation of the toner accumulation TN. Referring to  FIG. 5 , the toner accumulation TN formed of toner particles scattered on the toner seal  380  is gradually raised mountain-high. As a result, the self-weight of the toner accumulation TN gives the toner seal  380  a pressing force as shown by the arrow H. If the toner particles scattered on the toner seal  380  further pile up, the slope of the toner accumulation TN comes into contact with the peripheral surface of the abrasive roller  353 . Thus, as shown by the arrow G, a downward pressing force is applied to the toner accumulation TN with the rotation of the abrasive roller  353 . As a result, the contact pressure to be applied to the peripheral surface of the photosensitive drum  31  by the toner seal  380  will be increased. 
     Furthermore, while the toner image is transferred to the sheet P at the transfer nip TP, paper powder having adhered to the surface of the sheet P may be transferred to the peripheral surface of the photosensitive drum  31 . The paper powder having adhered to the peripheral surface of the photosensitive drum  31  is conveyed toward the distal end of the toner seal  380  with the rotation of the photosensitive drum  31 . If the toner accumulation TN is not formed on the toner seal  380 , the distal end of the toner seal  380  is in contact with the peripheral surface of the photosensitive drum  31  with a small contact pressure. In this case, the paper powder conveyed on the photosensitive drum  31  passes through between the distal end of the toner seal  380  and the peripheral surface of the photosensitive drum  31  and is then collected by the cleaning blade  351 . 
     However, if the distal end of the toner seal  380  is pushed hard against the peripheral surface of the photosensitive drum  31  by the toner accumulation TN piled up on the toner seal  380 , the paper powder cannot pass through between the distal end of the toner seal  380  and the peripheral surface of the photosensitive drum  31 . As a result, as shown in  FIG. 5 , a mass PD of paper powder is formed between the distal end of the toner seal  380  and the peripheral surface of the photosensitive drum  31 . 
     When the mass PD of paper powder grows with time, a portion of the toner seal  380  corresponding to a portion of the photosensitive drum  31  on which the mass PD exists is lifted up from the peripheral surface of the photosensitive drum  31  along the axial direction of the rotation axis  31 A of the photosensitive drum  31  (see  FIG. 6 ). As a result, the toner TN 1  starts to leak from the toner accumulation TN. The toner TN 1  falls along the peripheral surface of the photosensitive drum  31  with the force of the gravity (as shown by the arrow DT in  FIG. 6 ). Then, the toner TN 1  having reached the transfer nip TP adheres to the sheet P conveyed to the transfer nip TP. As a result, the sheet P will be contaminated with the toner. 
     As described above, the toner piled up on the toner seal  380  may create a mass PD of paper powder and finally contaminate the sheet P. To solve the above problems, in the cleaning device  35  according to this embodiment, the second conveying screw  361  is appropriately disposed above the toner seal  360 . 
     In this embodiment, as shown in  FIG. 3 , the above-mentioned second conveying screw  361  is disposed above the toner seal  360 . Particularly in this embodiment, the second conveying screw  361  is disposed above the toner seal  360  and in a space surrounded by the upper wall  35 H 2 , the sidewall  35 H 3 , and the plate lower portion  358 S. In addition, even if the toner piles up on the toner seal  360  as shown in  FIG. 4 , the second conveying screw  361  collects toner particles of the piled-up toner accumulation TN in the axial direction of the photosensitive drum  31 . This prevents that excess toner piles up on the toner seal  360 . As a result, it can be prevented that the toner piled up on the toner seal  360  increases the contact pressure of the toner seal  360  against the photosensitive drum  31 . Therefore, a mass PD of paper powder is less likely to be formed between the distal end of the toner seal  360  and the peripheral surface of the photosensitive drum  31 . This prevents that the distal end of the toner seal  360  is lifted up from the peripheral surface of the photosensitive drum  31  to cause toner leakage. Hence, it can be effectively prevented that the sheet P conveyed to the transfer nip TP is contaminated with the toner falling down from the distal end of the toner seal  360 . 
     Next, a preferred embodiment of the second conveying screw  361  will be described in further detail.  FIGS. 7 and 8  are enlarged cross-sectional views for illustrating different embodiments of the second conveying screw  361 . As shown in FIG.  3 , the peripheral edge of the rotating second conveying screw  361  is preferably disposed farther away from the distal end  360 S of the toner seal  360  than the fixed end  360 F of the toner seal  360  in the direction of extension of the toner seal  360 . In other words, the second conveying screw  361  is preferably disposed to avoid that the peripheral edge of the fin member located above the plate lower portion  358 S is located in an area nearer to the distal end  360 S of the toner seal  360  with respect to the end  3581  of the plate lower portion  358 S. 
     As shown in  FIG. 7 , if the peripheral edge of the second conveying screw  361 A is located nearer to the distal end  360 S (on the arrow D 71  side) than the fixed end  360 F, the toner conveyed by the rotation (in the direction of the arrow D 72 ) of the second conveying screw  361 A may press against the toner accumulation TN from above (in the direction of the arrow D 73 ). Thus, the toner seal  360  may be partly pushed toward the photosensitive drum  31 . For this reason, the peripheral edge of the rotating second conveying screw  361  is preferably disposed farther away from the distal end  360 S of the toner seal  360  than the fixed end  360 F of the toner seal  360 . Thus, the above phenomenon can also be prevented. Since, even in the embodiment shown in  FIG. 7 , the toner particles of the toner accumulation TN are conveyed in the axial direction of the photosensitive drum  31 , the lift-up of the distal end  361 S of the toner seal  360  as shown in  FIGS. 5 and 6  can be effectively prevented. 
     Furthermore, as shown by the arrow D 32  of  FIG. 3 , the second conveying screw  361  is preferably driven into rotation so that the peripheral surface thereof travels, at the position thereof facing the abrasive roller  353 , in the same direction as the peripheral surface of the abrasive roller  353 . In other words, the second conveying screw  361  is preferably driven into rotation so that a portion of the peripheral edge of the fin member facing the peripheral surface of the abrasive roller  353  travels downward. In the above embodiment shown in  FIG. 3 , the abrasive roller  353  and the second conveying screw  361  are rotated so that their portions facing each other travel from above downward. Unlike this, in a second conveying screw  361 B shown in  FIG. 8 , the peripheral edge of the rotating second conveying screw  361 B is disposed farther away from the distal end  360 S of the toner seal  360  (on the arrow D 81  side) than the fixed end  360 F of the toner seal  360  and the second conveying screw  361 B is rotated so that its portion facing the abrasive roller  353  travels from below upward (in the direction of the arrow D 82 ). In this case, as shown by the arrow D 83 , part of the toner may be sent toward the distal end  360 S of the toner seal  360  with the rotation of the second conveying screw  361 B. For this reason, as shown in  FIG. 3 , the second conveying screw  361  is preferably driven into rotation so that the peripheral surface thereof travels, at the position thereof facing the abrasive roller  353 , in the same direction as the peripheral surface of the abrasive roller  353 . Since, even in the embodiment shown in  FIG. 8 , the toner particles of the toner accumulation TN are conveyed in the axial direction of the photosensitive drum  31 , the lift-up of the distal end  361 S of the toner seal  360  as shown in  FIGS. 5 and 6  can be effectively prevented. 
     From the above viewpoints, the most preferred embodiment of the second conveying screw  361  is shown in  FIG. 9 . The portion of the peripheral edge of the rotating second conveying screw  361  nearest to the abrasive roller  353  is disposed farther away from the distal end  360 S of the toner seal  360  (on the arrow D 91  side) than the fixed end  360 F of the toner seal  360  and the second conveying screw  361  is rotated so that its portion (see  FIG. 3 ) facing the abrasive roller  353  travels from above downward (in the direction of the arrow D 92 ). In other words, the second conveying screw  361  is disposed to avoid that the peripheral edge of the fin member located above the plate lower portion  358 S is located in an area nearer to the distal end  360 S of the toner seal  360  with respect to the end  3581  of the plate lower portion  358 S. Furthermore, the second conveying screw  361  is driven into rotation so that the portion of the peripheral edge of the fin member facing the peripheral surface of the abrasive roller  353  travels downward. 
     In this case, the toner piled up on the toner seal  360  is drawn in toward the sidewall  35 H 3  (as shown by the arrow D 93 ) with the rotation of the second conveying screw  361 . Furthermore, the toner is conveyed in the axial direction of the photosensitive drum  31  by the spiral fin member of the second conveying screw  361 . Then, the toner is discharged into an unshown recovery tonner bottle disposed at an axial end of the drum unit  31 H. In this structure, the toner drawn in toward the sidewall  35 H 3  is axially conveyed while being squeezed in between the second conveying screw  361  and the sidewall  35 H 3 . During this conveyance, the toner is axially transported while moving up and down beside the sidewall  35 H 3  by gravity and the rotational force of the second conveying screw  361 . Furthermore, since the upper wall  35 H 2  is disposed above and facing the second conveying screw  361 , the toner is less likely to flow away from the upper edge of the second conveying screw  361  toward the distal end  360 S as shown by the arrow D 94 . 
     Moreover, the housing rear wall  35 H 1  extends upward from the upper wall  35 H 2 . The housing rear wall  35 H 1  is located farther away from the distal end  360 S (on the arrow D 91  side in  FIG. 9 ) of the toner seal  360  than the fixed end  360 F of the toner seal  360 . In other words, the housing rear wall  35 H 1  is disposed opposite the distal end  360 S of the toner seal  360  held in contact with the cylindrical surface  31 B of the photosensitive drum  31  with respect to the end  3581  of the plate lower portion  358 S along a direction of extension of the housing rear wall  35 H 1  toward the cylindrical surface  31 B. Therefore, toner particles scattered from the abrasive roller  353  and hitting the housing rear wall  35 H 1  fall in an area nearer to the second conveying screw  361  than the fixed end  360 F of the toner seal  360 . Thus, the fallen toner is appropriately collected by the second conveying screw  361 . 
     Furthermore, preferably, the second conveying screw  361  has a smaller diameter than the abrasive roller  353  and the housing rear wall  35 H 1  is disposed above the second conveying screw  361  and facing the abrasive roller  353 . In this case, even if toner particles scattered from the abrasive roller  353  hit the housing rear wall  35 H 1 , the hit toner particles fall along the housing rear wall  35 H 1  and are then conveyed by the second conveying screw  361 . 
     Although the drum units  31 H and image forming apparatuses  1  including their respective cleaning devices  35  according to the above embodiments of the present disclosure have thus far been described, the present disclosure is not limited to them and can take, for example, the following modified embodiments. 
     (1) Although the above embodiments have described a structure in which the second conveying screw  361  includes a shaft and a spiral fin member provided around the shaft, the present disclosure is not limited to this structure. In place of the second conveying screw  361 , a spiral coil spring may be rotatably disposed to extend in the axial direction of the photosensitive drum  31  or a spirally wound brush may be rotatably disposed. 
     (2) Although the above embodiments have described a structure in which the abrasive roller  353  and the cleaning blade  351  are disposed downstream of the toner seal  360  in the direction of rotation of the photosensitive drum  31 , the present disclosure is not limited to this structure. The abrasive roller  353  may be a cleaning roller configured to clean the surface of the photosensitive drum  31 . In this case, the cleaning blade  351  may be disposed downstream of the cleaning roller in the direction of rotation of the photosensitive drum  31  or no cleaning blade may be disposed. 
     (3) Although the above embodiments have described a structure in which the upper wall  35 H 2  and the sidewall  35 H 3  are disposed above and laterally (rearwardly in  FIG. 3 ) of, respectively, the second conveying screw  361 , the present disclosure is not limited to this structure. The plate  358  may be disposed laterally (rearwardly in  FIG. 3 ) of and directly facing the second conveying screw  361  or another wall portion may be disposed laterally of the second conveying screw  361 . 
     (4) Although the above embodiments have described a structure in which the cleaning device  35  including the toner seal  360  is disposed in the drum unit  31 H, the present disclosure is not limited to this structure. The cleaning device  35  including the toner seal  360  may be installed separately to the image forming apparatus  1 . 
     Various modifications and alterations of this disclosure will be apparent to those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein.