Patent Publication Number: US-7917076-B2

Title: Toner conveying device and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent application No. 2009-018420, filed Jan. 29, 2009, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a toner conveying device used to feed toner in an image forming apparatus including, for example, an image bearing member that forms a toner image on the surface thereof. The present invention also relates to a cleaning device for cleaning the surface of the image bearing member, including the toner conveying device, and to an image forming apparatus using the toner conveying device or the cleaning device. 
     2. Description of the Related Art 
     Conventionally, a developing device of an image forming apparatus uses a toner conveying device for feeding toner. The toner conveying device includes, for example, a tubular conveying pipe having an inner diameter that gradually decreases from the upstream side toward the downstream side and a conveying screw that is concentrically arranged in the conveying pipe so as to be rotatable. 
     The inside and outside diameters of the conveying pipe gradually decrease toward the downstream side. In this structure, toner fed through the conveying pipe toward the downstream side is compressed, on the downstream side, due to the rotation of the conveying screw about the axis. Friction caused by the compression charges the carrier, which is made of synthetic resin and is located in the toner, increasing the charge level of the toner deposited on the carrier. This increase in the charge level creates a smooth toner image on the circumferential surface of the photosensitive drum. 
     Furthermore, conventionally, it is known to use as a toner conveying device in the developing device of the image forming apparatus, a toner conveying device that has a conveying screw for feeding toner in a housing, a portion of the conveying screw corresponding to a toner supply port in the housing having an outside diameter that is slightly larger than that of the other portions or a screw pitch that is slightly larger than that of the other portions. This structure increases the feeding speed of the toner near the toner supply port when the toner is supplied to the developing device through the toner supply port, thereby preventing the toner from staying. Thus, the supply of toner to the device is smoothly performed. 
     In this type of toner conveying device, both the inside diameter of the conveying pipe and the outside diameter of the conveying screw gradually decrease toward the downstream side. However, the purpose of such a structure is not to prevent toner from sticking to the inner wall surface of the pipe or to make the amount of toner fed uniform, but to compress the toner on the downstream side to increase the charging level. 
     In these toner conveying devices, the conveying screw has a large diameter only near the toner supply port of the housing of the developing device. Countermeasures against toner sticking to the bottom of the housing at other portions or to achieve a uniform conveyance of toner are not considered by these devices. Therefore, there is a problem in that toner may deposit on and stick to the bottom of the housing on the upstream side of the toner supply port, making a smooth conveyance of toner difficult. 
     SUMMARY 
     The present invention provides a toner conveying device capable of preventing the partial deposition and sticking of toner in the conveying pipe and of stably feeding toner and an image forming apparatus using the toner conveying device. 
     A toner conveying device according to an embodiment of the present invention includes: a conveying pipe for feeding toner, an inside diameter thereof changing in a pipe-axis direction; and a conveying screw coaxially arranged in the conveying pipe, the conveying screw feeds toner by rotating about its axis. The conveying screw includes a screw shaft that rotates about the axis, and a spiral fin that is formed spirally around the outer circumferential surface of the screw shaft. The distance between the outer circumferential surface of the spiral fin and the inner circumferential surface of the conveying pipe is substantially constant in the pipe-axis direction. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       In the accompanying drawings: 
         FIG. 1  is a sectional view illustrating the internal structure of an embodiment of the image forming apparatus, including a cleaning device having a toner conveying device of the present invention. 
         FIG. 2  illustrates an intermediate transfer unit having an intermediate transfer belt of the embodiment of  FIG. 1 . 
         FIGS. 3A and 3B  are schematic front perspective views illustrating the relative positional relationship between an intermediate frame and a belt cleaning device,  FIG. 3A  illustrates a state immediately before a waste-toner discharging pipe is connected to a waste-toner collecting pipe, and  FIG. 3B  illustrates a state in which the waste-toner discharging pipe is connected to the waste-toner collecting pipe. 
         FIGS. 4A and 4B  are schematic rear perspective views for illustrating the relative positional relationship between the intermediate frame and the belt cleaning device,  FIG. 4A  illustrates a state immediately before the waste-toner discharging pipe is connected to the waste-toner collecting pipe, and  FIG. 4B  illustrates a state in which the waste-toner discharging pipe is connected to the waste-toner collecting pipe. 
         FIG. 5  is a perspective view of the belt cleaning device according to an embodiment of the present invention. 
         FIG. 6  is a partial exploded perspective view of  FIG. 5 , illustrating the waste-toner discharging pipe and a shutter mechanism according to an embodiment of the present invention. 
         FIG. 7  is a partial perspective view of  FIG. 5 , illustrating, in an assembled state, a waste-toner discharging pipe and a shutter mechanism according to an embodiment of the present invention. 
         FIGS. 8A and 8B  are enlarged perspective views of a shutter tube according to an embodiment of the present invention,  FIG. 8A  illustrating the shutter tube viewed from the rear right, and  FIG. 8B  illustrating the shutter tube viewed from the front right. 
         FIGS. 9A and 9B  are perspective views illustrating a connecting operation for connecting the belt cleaning device to a toner collection unit,  FIG. 9A  illustrates a state immediately before the waste-toner discharging pipe of the belt cleaning device is connected to a waste-toner receiving member of the toner collection unit, and  FIG. 9B  illustrates a state in which the waste-toner discharging pipe of the belt cleaning device is connected to the waste-toner receiving member of the toner collection unit. 
         FIGS. 10A and 10B  are side sectional views illustrating the connection operation for connecting the belt cleaning device to the toner collection unit,  FIG. 10A  illustrates a state immediately before the waste-toner discharging pipe of the belt cleaning device is connected to the waste-toner receiving member of the toner collection unit, and  FIG. 10B  illustrates a state in which the waste-toner discharging pipe of the belt cleaning device is connected to the waste-toner receiving member of the toner collection unit. 
         FIGS. 11A to 11C  are side sectional views of toner conveying devices according to various embodiments of the present invention,  FIG. 11A  illustrates the toner conveying device according to one embodiment,  FIG. 11B  illustrates the toner conveying device according to another embodiment, and  FIG. 11C  illustrates the toner conveying device according to a still another embodiment. 
         FIG. 12  is a partial enlarged side sectional view of a toner conveying device according to a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described below with reference to the attached drawings.  FIG. 1  is a sectional view illustrating the internal structure of an image forming apparatus according to an embodiment, which employs a cleaning device having a toner conveying device of the present invention. In  FIG. 1 , the X direction refers to a left-right direction, more specifically, “the −X” direction references the left and “the +X” direction references the right. In this embodiment, the image forming apparatus is a printer  10 . 
     As illustrated in  FIG. 1 , the printer  10  includes a printer body  11 , a sheet feeding section  12  that stores sheets P, an image forming section  13  for transferring toner images to the sheet P fed from the sheet feeding section  12 , a fixing section  14  for fixing the toner image that was transferred to the sheet P in the image forming section  13 , and a sheet-output section  15  that outputs the sheet P that have undergone the fixing process in the fixing section  14 . 
     The sheet feeding section  12  includes a sheet cassette  121 , that is removably attached to the lower part of the printer body  11 , and can store a plurality of sheets P, and pick-up rollers  122  that are located at the upper right of the sheet cassette  121  in  FIG. 1 . The sheets P that are stored in the sheet cassette  121  are picked up, one at a time, by the pick-up rollers  122  and are fed to the image forming section  13 . 
     The image forming section  13  forms toner images on the sheet P fed from the sheet feeding section  12 . In this embodiment, the image forming section  13  includes, from the upstream (left in  FIG. 1 ) side to the downstream side, a magenta unit  13 M that uses magenta toner, a cyan unit  13 C that uses cyan toner, a yellow unit  13 Y that uses yellow toner, and a black unit  13 K that uses black toner. 
     These units  13 M,  13 C,  13 Y, and  13 K, positioned above an intermediate transfer unit  20 , each include a photosensitive drum (image bearing member)  131 , a charger  132 , an exposure device  133 , a developing device  134 , and a toner container  135 . 
     The photosensitive drum  131  forms an electrostatic latent image and a toner image according to the electrostatic latent image on the circumferential surface thereof. The photosensitive drum  10  is coaxially supported with a drum shaft that extends in a front-rear direction (the direction perpendicular to the plane of the sheet of  FIG. 1 ) so as to be rotatable about the shaft. 
     In this embodiment, the chargers  132  have charging wires. The discharge from the charging wires charges the circumferential surfaces of the photosensitive drums  131 , forming a uniform charge thereon. 
     The exposure devices  133  irradiate the circumferential surfaces of the photosensitive drums  131 , which are uniformly charged by the chargers  132 , using laser beams according to image information to form electrostatic latent images. 
     The developing devices  134  supply toner to the circumferential surfaces of the photosensitive drums  131 , where the electrostatic latent images are formed, thereby forming toner images. 
     The toner containers  135  are removably attached to the developing devices  134  to supply toner to the developing devices  134 . 
     The drum cleaning devices  136  remove waste toner from the circumferential surfaces of the photosensitive drums  131 . 
     The intermediate transfer unit  20  is positioned below the photosensitive drums  131  of the units  13 M,  13 C,  13 Y, and  13 K and includes an intermediate transfer belt  21 , on which the toner images formed on the circumferential surfaces of the photosensitive drums  131  are superimposed to form a color image. The intermediate transfer unit  20  includes an intermediate frame  201 , illustrated by a two-dot broken line in  FIG. 1 , that moves in the front-rear direction (the direction perpendicular to the plane of the sheet of  FIG. 1 ) and is removably attached to the printer body  11 . 
     The intermediate transfer unit  20  has a belt cleaning device  30  that removes residual waste toner thereby cleaning the surface. 
     Primary transfer rollers  22  are located opposite the photosensitive drums  131  with the intermediate transfer belt  21  therebetween. Bias voltages applied to the primary transfer rollers  22  electrically transfer the toner images on the photosensitive drums  131  to the surface of the intermediate transfer belt  21 . 
     A secondary transfer roller  137  for electrically transferring the color toner image on the intermediate transfer belt  21  to the sheet P, fed from the sheet feeding section  12 , is positioned at the lower part of the intermediate transfer belt  21  in  FIG. 1 . 
     The photosensitive drums  131  rotate counterclockwise in  FIG. 1  and receive toner from the corresponding developing devices  134 . 
     The chargers  132  include charging wires through which a power source (not shown) supplies a high voltage. Corona discharge from the wires uniformly charges the circumferential surfaces of the photosensitive drums  131 . Instead of using the chargers  132 , the circumferential surfaces of the photosensitive drums  131  may be charged by being contacted by the charging rollers, to which a high voltage is applied. 
     The exposure devices  133  irradiate the circumferential surfaces of the photosensitive drums  131 , which are uniformly charged by the chargers  132 , with laser beams, according to the image data that was inputted from a computer or the like (not shown). The laser beams form electrostatic latent image on the circumferential surfaces of the photosensitive drums  131 . By applying toner from the developing devices  134  to the electrostatic latent images, toner images are formed on the circumferential surfaces of the photosensitive drums  131 . Then, these toner images are transferred to the running intermediate transfer belt  21 . 
     The developing devices  134  include stirring/conveying members and have developing rollers at the bottom thereof, whose circumferential surfaces are opposite to the circumferential surfaces of the photosensitive drums  131 . The rotation of the developing roller supplies toner to the circumferential surfaces of the photosensitive drums  131 . 
     The fixing section  14  fixes the image that was transferred to the sheet P at the image forming section  13 . The fixing section  14  includes a fixing roller  141  that is heated by an electric heater, such as a halogen lamp, and a pressure roller  142  that is opposite to the fixing roller  141 . The pressure roller  142  is positioned below the fixing roller  141  and the circumferential surface thereof is pressed against the fixing roller  141 . 
     The sheet P, to which the image is transferred by the intermediate transfer belt  21  in the image forming section  13 , is guided by the running intermediate transfer belt  21  and is fed into the fixing section  14 , while being held between the intermediate transfer belt  21  and the secondary transfer roller  137 . The sheet P is heated as it passes between the fixing roller  141  and the pressure roller  142 , whereby the toner image is fixed to the sheet P. 
     After the fixing process, the sheet P is fed upward through a sheet-output conveying path  101  by a pair of output rollers  143 . The sheet P passes through a sheet-output port  152  and is fed to the sheet-output tray  151  provided at the top of the printer body  11 . 
       FIG. 2  illustrates the intermediate transfer unit  20  including the intermediate transfer belt  21  etc., illustrated in  FIG. 1 . Similar to  FIG. 1 , in  FIG. 2 , the −X direction refers to the left and the +X direction refers to the right. As shown in  FIG. 2 , the intermediate transfer unit  20  includes the primary transfer rollers  22 , the driving roller  23 , the following roller  24 , the pressing roller  25 , a bending roller  26 , upper tension rollers  27 , lower tension rollers  28 , and the intermediate transfer belt  21  looped around the aforementioned rollers. 
     In the front view, viewed from the direction perpendicular to the plane of the sheet of  FIG. 2 , the intermediate frame  201  is shaped such that it is elongated in the left-right direction and has an inverted triangular plate extending downwardly from the lower edge on substantially the right half thereof. From a plan view, as illustrated in  FIG. 3 , the intermediate frame  201  has a rectangular shape that is elongated in the left-right direction. 
     The primary transfer rollers  22  are positioned at equal intervals in the left-right direction along the upper edge of the intermediate frame  201  corresponding to the photosensitive drums  131  of the units  13 M,  13 C,  13 Y, and  13 K. 
     The driving roller  23  is located at the left end of the intermediate frame  201 . The driving roller  23  is driven by a belt-driving motor  230 . The belt-driving motor  230  is located behind the driving roller  23  (behind the sheet of  FIG. 2 ), coaxially with the driving roller  23 . The driving roller  23  is coaxially connected to a driving shaft  231  of the belt-driving motor  230  so as to be integrally rotatable. 
     The following roller  24  is located at the right end of the intermediate frame  201 . The intermediate transfer belt  21  loops around the driving roller  23  and the following roller  24 . The four primary transfer rollers  22  and the five upper tension rollers  27  are positioned along the lower surface of the upper belt of the intermediate transfer belt  21 . 
     The pressing roller  25 , that presses the intermediate transfer belt  21  against the secondary transfer roller  137 , is located at the lowest position of the inverted triangle provided on the right half of the intermediate frame  201 , so as to be oppose to the secondary transfer roller  137  with the intermediate transfer belt  21  being therebetween. Due to the pressing roller  25  pressing the intermediate transfer belt  21  against the secondary transfer roller  137 , the toner image on the intermediate transfer belt  21  is transferred to the sheet P conveyed to the position of the pressing roller  25 . 
     The bending roller  26  is located in the intermediate frame  201  substantially immediately below the primary transfer roller  22  of the cyan unit  13 C on the right side of the driving roller  23 . The bending roller  26  bends the intermediate transfer belt  21  upward at this position. 
     The secondary transfer roller  137  located immediately below the pressing roller  25  is pressed by the pressing roller  25  with the intermediate transfer belt  21  therebetween. A bias voltage from a power source (not shown) that electrostatically attracts the toner image off the intermediate transfer belt  21  is applied to the secondary transfer roller  137 . Thus, the toner image on the intermediate transfer belt  21  is transferred to the sheet P passing between the intermediate transfer belt  21  and the secondary transfer roller  137 . 
     Each upper tension roller  27  is located to the left of the corresponding primary transfer roller  22  and the left of the following roller  24 . One of the lower tension rollers  28  is located between the bending roller  26  and the pressing roller  25 , and the other lower tension rollers  28  is located between the following roller  24  and the pressing roller  25 . The upper and lower tension rollers  27  and  28  serve to maintain the tension of the intermediate transfer belt  21 . 
     In this embodiment, the belt cleaning device  30  is attached below the lower tension roller  28 , on the left side, with the intermediate transfer belt  21  therebetween, in the intermediate frame  201  of the thus-configured intermediate transfer unit  20 . 
       FIGS. 3A ,  3 B,  4 A, and  4 B are schematic perspective views illustrating the relative positional relationship between the intermediate frame  201  and the belt cleaning device  30 .  FIGS. 3A and 3B  are front perspective views, and  FIGS. 4A and 4B  are rear perspective views. Among them,  FIGS. 3A and 4A  illustrate the state immediately before the waste-toner discharging pipe  60  is connected to the waste-toner collecting pipe  82 , and  FIGS. 3B and 4B  illustrate the state in which the waste-toner discharging pipe  60  is connected to the waste-toner collecting pipe  82 . In  FIGS. 3A ,  3 B,  4 A, and  4 B, the X direction refers to the left-right direction and the Y direction refers to the front-rear direction. More specifically, the −X direction refers to the left, the +X direction refers to the right, the −Y direction refers to the front, and the +Y direction refers to the rear. 
     As illustrated in  FIGS. 3A ,  3 B,  4 A, and  4 B, the intermediate frame  201  has a rectangular shape that is elongated in the left-right direction, in plan view. The intermediate frame  201  includes a front frame plate  202  having a shape corresponding to the path along which the intermediate transfer belt  21  runs, in front view, viewed from the −Y direction, a rear frame plate  203  having substantially the same shape as the front frame plate  202  and positioned on the rear side opposite the front frame plate  202 . The intermediate frame  201  also includes a left frame plate  204  and a right frame plate  205  extending between the front frame plate  202  and the rear frame plate  203  at the left end and at the right end, respectively. 
     The primary transfer rollers  22 , the driving roller  23 , the following roller  24 , the pressing roller  25 , the bending roller  26 , the upper tension rollers  27 , and the lower tension rollers  28  are secured between the front frame plate  202  and the rear frame plate  203  so as to be rotatable about predetermined shafts. The intermediate transfer belt  21  is looped around rollers  22  to  28 . 
     The printer body  11  has a rear wall  111  located on the rear side, and a left side wall  112  and a right side wall  113  extending toward the front from the left and right edges of the rear wall  111 , respectively. The intermediate transfer unit  20  is positioned between the left side wall  112  and the right side wall  113 , so as to be movable in a front-rear direction. 
     More specifically, rail members  29  are each located between the left frame plate  204  and the left side wall  112 , and between the right frame plate  205  and the right side wall  113 . The rail members  29  include fixed rails  291  that are secured to the left and right side walls  112  and  113  so as to face each other and extend in a front-rear direction. Movable rails  292  are provided on the left and right frame plates  204  and  205  so as to be slidably supported by the fixed rails  291 . 
     Thus, the intermediate transfer unit  20  can be moved between a stored position and a pulled-out position by gripping grips  202   a  provided at appropriate positions on the front frame plate  202  and moving the intermediate transfer unit  20  in a front-rear direction. 
     A positioning pin  114 , which projects forward, is provided at substantially the center, in a left-right direction, of the rear wall  111 . A positioning hole  206  is provided in the rear frame plate  203 , of the intermediate transfer unit  20 , at a position corresponding to the positioning pin  114 —slightly below the upper edge of the intermediate transfer unit  20 . Wherein the intermediate transfer unit  20  is inserted into the printer body  11 , the positioning pin  114  is received in the positioning hole  206 . Thus, the intermediate transfer unit  20  is positioned in the printer body  11 . 
     In the intermediate frame  201  of the thus-configured intermediate transfer unit  20 , the belt cleaning device  30  is attached at a position immediately to the left to the pressing roller  25  and immediately below the lower tension roller  28  on the left side, with the intermediate transfer belt  21  therebetween. Thus, the belt cleaning device  30  moves with the intermediate frame  201 . 
       FIG. 5  is a perspective view illustrating the belt cleaning device  30  according to an embodiment. Similar to  FIGS. 4A and 4B , in  FIG. 5 , the −X direction refers to the left, the +X direction refers to the right, the −Y direction refers to the front, and the +Y direction refers to the rear. 
     As illustrated in  FIG. 5 , the belt cleaning device  30  includes a box-shaped casing  31 , indicated by a two-dot broken line. The box-shaped casing  31  includes a brush roller  40  whose circumferential surface is in contact with the surface of the intermediate transfer belt  21 , a charging roller  45  that electrostatically removes the waste toner, scraped off the intermediate transfer belt  21  by the brush roller  40 , by suction, and a blade  43  that scrapes off the waste toner deposited on the circumferential surface of the charging roller  45 . The casing  31  also includes a screw member (conveying screw)  50  that feeds the waste toner scraped off by the blade  43  toward the waste-toner collecting pipe  82  (described below), the waste-toner discharging pipe  60  that extends through the rear plate  311  projecting toward the waste-toner collecting pipe  82  on the rear side, and a shutter structure  70  fitted to the outer circumference of the waste-toner discharging pipe  60 . 
     The waste-toner discharging pipe  60  and a portion of the screw member  50  located in the waste-toner discharging pipe  60  form an embodiment of the toner conveying device  1  of the present invention. The toner conveying device  1  will be described below. 
     The brush roller  40  includes a brush shaft  41  positioned between the rear plate  311  and a front plate  312  of the casing  31 , at an upper position. Bristles  42  are attached to the brush shaft  41  in a column shape coaxially with the brush shaft  41 . A brush-driving motor  39  with a driving shaft extends in a front-rear direction and is secured to the front side of the front plate  312 . The driving shaft of the brush-driving motor  39  is coaxially connected to the brush shaft  41  so as to be rotatable together with the brush shaft  41 . Thus, the driving rotation of the brush-driving motor  39  is directly transmitted to the brush roller  40 . 
     The waste toner, that is scraped off from the intermediate transfer belt  21  by the rotation of the brush roller  40  and deposited on the circumferential surface of the charging roller  45 , is removed by the blade  43  and falls on the screw member  50  located therebetween. 
     The screw member  50  includes a screw shaft  51  extending between the rear plate  311  and the front plate  312  in the casing  31 , at a lower position, and a spiral fin  52  that is coaxially formed around the screw shaft  51 . The screw member  50  extends through the inside of the waste-toner discharging pipe  60 . Therefore, rotation of the spiral fin  52 , about the screw shaft  51 , forces the waste toner that has accumulated on the bottom of the casing  31  toward the toner collection unit  80  through the waste-toner discharging pipe  60 . 
     A gear mechanism  38  for transmitting the driving force of the brush-driving motor  39  to the screw member  50  is located in the casing  31 , on the rear plate  311  side. Thus, the driving rotation of the brush-driving motor  39  is transmitted to the screw member  50  via the brush shaft  41  and the gear mechanism  38 . 
     In this belt cleaning device  30 , a predetermined number of column-shaped front engaging projections  32  are provided on the front plate  312  of the casing  31  so as to project forward, and a predetermined number of column-shaped rear engaging projections  33  are provided on the rear plate  311  of the casing  31 . 
     The front frame plate  202  of the intermediate frame  201  ( FIGS. 4A and 4B ) includes engaging holes  202   b  at positions that correspond to the front engaging projections  32 . The front engaging projections  32  are slidably inserted into the engaging holes  202   b . The rear frame plate  203  has elongated holes  203   a  extending in a top-bottom direction, at positions that correspond to the rear engaging projections  33 , into which the rear engaging projections  33  are inserted. By inserting the front engaging projections  32  into the engaging holes  202   b , and the rear engaging projections  33  into the elongated holes  203   a , the belt cleaning device  30  is coupled to the intermediate frame  201 . 
     The elongated holes  203   a  that receive the rear engaging projections  33  are elongated so that there is clearance to compensate for any dimensional error or assembly error when the waste-toner discharging pipe  60  is connected to the waste-toner collecting pipe  82  (described below). To provide this compensation, the waste-toner discharging pipe  60  can move vertically. 
     When the intermediate transfer unit  20  is in a pulled-out state and then pushed into the printer body  11 , the tip of the waste-toner discharging pipe  60  is connected to the toner collection unit  80  located behind the rear wall  111  of the printer body  11 . Thus, the waste toner scraped off from the intermediate transfer belt  21  by the belt cleaning device  30  is collected by the toner collection unit  80 . 
     As illustrated in  FIGS. 4A and 4B , the toner collection unit  80  includes a waste toner reservoir  81  located on the bottom plate on the rear side of the printer body  11 . The waste-toner collecting pipe  82  extends upright from the top plate of the waste toner reservoir  81 . As illustrated in  FIGS. 9A and 9B , a waste-toner receiving member  83  having a connection opening (waste toner receiving port)  831  that opens forward, to which a pipe body  61  (described below) is connected, is positioned on the waste-toner collecting pipe  82 . 
       FIGS. 6 and 7  are partial views of  FIG. 5  illustrating the waste-toner discharging pipe  60  and the shutter structure  70  according to an embodiment.  FIG. 6  is a partial exploded perspective view of  FIG. 5 , and  FIG. 7  is a perspective view of the same in an assembled state. Similarly to  FIG. 3 , in  FIGS. 6 and 7 , the −X direction refers to the left, the +X direction refers to the right, the −Y direction refers to the front, and the +Y direction refers to the rear. 
     As illustrated in  FIG. 6 , the waste-toner discharging pipe  60  includes a pipe body (conveying pipe)  61  and a fixing base  62  for securing the pipe body  61  to the rear plate  311  of the casing  31 . The pipe body  61  has a conical portion  611  has a tapered shape that is coaxial with the pipe body  61  at a tip portion (rear end) thereof. The inclined circular surface of this tapered conical portion  611  allows the pipe body  61  to be easily coupled to the connection opening  831  in the waste-toner receiving member  83 . The conical portion  611  has, at the position of the shaft center, a center hole  611   a  that receive the tip of the screw shaft  51  to support the screw shaft  51 . 
     The pipe body  61  has a guide rail  612  extending in a front-rear direction on the top of the circumferential surface. This guide rail  612  serves to maintain a predetermined phase, when a shutter tube  71  of the shutter structure  70 , coupled to the outer circumference of the pipe body  61 , is moved in a front-rear direction. 
     The pipe body  61  has, on both the left and right sides thereof, a pair of slide-guide grooves  613  that are recessed toward each other and extend in a front-rear direction. These slide-guide grooves  613  determine the range in which the shutter structure  70 , coupled to the outer circumference of the pipe body  61 , can move. 
     The fixing base  62  includes a pipe holding tube  621  that is coaxial with the base end portion (front end) of the pipe body  61  and has a larger diameter than the pipe body  61 , and a rectangular flange  622  secured to the base end of the pipe holding tube  621  so as to be coupled to the outer circumference thereof. The waste-toner discharging pipe  60  is secured to the rear plate  311  of the casing  31  via the flange  622  which is screwed at four corners. 
     A waste-toner conveying path V for feeding waste toner toward the toner collection unit  80  by the rotation of the screw member  50 , about the axis, is formed in the pipe body  61  of the waste-toner discharging pipe  60 . 
     As illustrated in  FIG. 6 , the shutter structure  70  includes the shutter tube  71  coupled to the outer circumference of the pipe body  61 , so as to be in slidable contact therewith, and a coil spring  72  that urges the shutter tube  71 , that is coupled to the outer circumference of the pipe body  61 , toward the tip side. 
     The shutter structure  70 , in particular, the shutter tube  71 , will be described below with reference to  FIGS. 8A and 8B  (and the other drawings).  FIGS. 8A and 8B  are enlarged perspective views of the shutter tube  71  according to an embodiment, viewed from the rear right and from the front right, respectively. Similarly to  FIG. 3 , in  FIG. 8 , the −X direction refers to the left, the +X direction refers to the right, the −Y direction refers to the front, and the +Y direction refers to the rear. 
     As illustrated in  FIGS. 8A and 8B , the shutter tube  71  includes a tube body  711  having an inside diameter that is slightly larger than the outside diameter of the pipe body  61 , and an arcuate shutter plate  712  projecting rearwardly from substantially the lower half part of the rear edge of the tube body  711 . A plurality of spring-receiving projections  713  are located at equal intervals in the circumferential direction and project radially outwardly from the front edge of the tube body  711 . A plurality of stopper projections  714  are located at equal intervals in the circumferential direction and project radially outwardly from the rear edge of the tube body  711 . A pair of snap-fit members  715 , that function as elastic arms, extend in a front-rear direction and are formed at the rear edge of the tube body  711 , immediately above the left and right edges of the arcuate shutter plate  712 . A reinforcing rib  716  extends in a front-rear direction and projects radially outwardly from the top surface of the tube body  711 . 
     While the curvature of the inside diameter of the arcuate shutter plate  712  is the same as the inside diameter of the tube body  711 , the curvature of the outside diameter of the arcuate shutter plate  712  is slightly smaller than the outside diameter of the tube body  711 . This provides a margin on the shutter tube  71  for the sealing member (not shown) that is attached to the periphery of a waste toner discharge port  614  of the pipe body  61 . This structure enables the arcuate shutter plate  712  to be smoothly moved between an open position and a closed position while sliding on the sealing member. 
     In this embodiment, three spring-receiving projections  713  are located at equal intervals in the circumferential direction. Each spring-receiving projection  713  is shaped such that the edges, in the circumferential direction, extend along lines extending in the radial direction (diameter lines). The central angle formed between a pair of diameter lines is 60°. Thus, the length of the arc, in the circumferential direction, of the spring-receiving projections  713  on the circumferential surface of the tube body  711  equals the spaces between the adjacent spring-receiving projections  713 . 
     The spring-receiving projections  713  each include a fan-shaped projection  713   a , having a fan shape in front view and a roof-shaped projection  713   b  having an arcuate shape in front view, that project forward from the radially outer edge of the fan-shaped projection  713   a . The rear end of the coil spring  72 , coupled to the outer circumference of the pipe body  61 , is fitted to the gaps between the outer circumferential surface of the tube body  711  and the roof-shaped projections  713   b.    
     In this embodiment, one of the three spring-receiving projections  713  is positioned opposite the arcuate shutter plate  712  on the circumferential surface of the tube body  711 . 
     Similar to the above-described spring-receiving projections  713 , three stopper projections  714  are positioned at equal intervals in the circumferential direction. The stopper projections  714  are provided at locations that correspond to the spaces between the adjacent spring-receiving projections  713  in the front-rear direction. Similar to the above-described spring-receiving projections  713 , the central angles of these stopper projections  714  are 60°. This allows easy removal of the shutter tube  71  from the mold in which the shutter tube  71  is made; the shutter tube is made of a thermoplastic synthetic resin by injection molding. 
     The curvature of the outside diameter of these stopper projections  714  is larger than the inside diameter of the connection opening  831  in the waste-toner receiving member  83 . Therefore, when the tip (rear end) of the pipe body  61  is inserted into the connection opening  831  in the waste-toner receiving member  83 , the pipe body  61  can enter the connection opening  831 , but the shutter tube  71  cannot due to the stopper projections  714 . 
     Accordingly, when the pipe body  61  is inserted into the connection opening  831 , the arcuate shutter plate  712  moves forward, thereby opening the waste toner discharge port  614  of the pipe body  61  which had been closed by the arcuate shutter plate  712 . 
     The pair of snap-fit members  715  are located immediately above the arcuate shutter plate  712 , at positions that are point-symmetrical to each other in the left-right direction with respect to the axis of the shutter tube  71 . These snap-fit members  715  extend rearwardly from the rear edge of the tube body  711  by the same distance which the arcuate shutter plate  712  extends. First slits  715   a , extending in a front-rear direction, are formed between the arcuate shutter plate  712  and the snap-fit members  715 . Second slits  715   b , extending forward, are formed at portions corresponding to the upper edges of the snap-fit members  715  of the tube body  711 . 
     The front ends of the first and second slits  715   a  and  715   b  are at the same position. The first and second slits  715   a  and  715   b  substantially increases the length of the snap-fit members  715 , allowing for radial elastic deformation. 
     The snap-fit members  715  each have a guided projection  715   c  projecting toward the other snap-fit member  715  at the tip (rear end) on the surface facing the other snap-fit member  715 . The guided projections  715   c  are shaped so that they can be fitted to the slide-guide grooves  613  provided in the pipe body  61 . This structure prevents the tube body  711  from slipping off from the pipe body  61  and can move in a front-rear direction a distance in which the guided projections  715   c  that allows the tube body  711  to move in a front-rear direction in the slide-guide grooves  613 . 
     The spring-receiving projections  713  are located at arbitrary positions between the front edge of the tube body  711  and the front ends of the first and second slits  715   a  and  715   b  (hereinafter referred to as a “projection placeable area S”). By providing the spring-receiving projections  713  at arbitrary positions in the projection placeable area S, the force of the coil spring  72  can be set to a desired value. That is, the spring-receiving projections  713  can be provided at positions where a preset force of the coil spring  72  can be obtained. This increases design flexibility. 
     In this embodiment, the reinforcing rib  716  is located at a position that is point-symmetrical to the arcuate shutter plate  712  with respect to the axis of the tube body  711  (that is, at the top of the tube body  711 ). A guided groove  716   a  is provided in the inner circumferential surface of the tube body  711  and extends in a front-rear direction over the entire length of the tube body  711  at a position corresponding to the reinforcing rib  716 . The guided groove  716   a  is dimensioned such that it slidably fits the outer circumference of the guide rail  612  that projects from the pipe body  61 . Accordingly, by fitting the shutter tube  71  to the pipe body  61  with the guided groove  716   a  being fitted to the outer circumference of the guide rail  612 , the shutter tube  71  can move in a front-rear direction along the pipe body  61  without rotating. 
     The coil spring  72  urges the shutter tube  71 , that is coupled to the outer circumference of the pipe body  61  toward the tip (rearward). The length of the coil spring  72  is set so that it extends at least between the front end surfaces of the fan-shaped projections  713   a  of the spring-receiving projections  713  and the rear surface of the flange  622  of the waste-toner discharging pipe  60 , when the shutter tube  71  is located at the front most side. 
     The inside diameter of the coil spring  72  is slightly larger than the outside diameters of the pipe holding tube  621  and shutter tube  71 . The outside diameter of the coil spring  72  is slightly smaller than the curvature of the inside diameter of the roof-shaped projection  713   b  of the spring-receiving projections  713 . Thus, by coupling the shutter tube  71  to the outer circumference of the pipe body  61  with the coil spring  72  being coupled to the outer circumference of the pipe body  61  and by coupling the guided projections  715   c  to the slide-guide grooves  613  in the pipe body  61 , the coil spring  72  is coupled to the waste-toner discharging pipe  60 , as illustrated in  FIG. 7 , and can urge the shutter tube  71  rearwardly. 
       FIGS. 9A ,  9 B,  10 A, and  10 B are diagrams illustrating an operation to connect the belt cleaning device  30  to the toner collection unit  80 .  FIGS. 9A and 9B  are perspective views, and  FIGS. 10A and 10B  are side sectional views corresponding to  FIGS. 9A and 9B . In these diagrams,  FIGS. 9A and 10A  illustrate the state immediately before the waste-toner discharging pipe  60  of the belt cleaning device  30  is connected to the waste-toner receiving member  83  of the toner collection unit  80 , and  FIGS. 9B and 10B  illustrate the state in which the waste-toner discharging pipe  60  of the belt cleaning device  30  is connected to the waste-toner receiving member  83  of the toner collection unit  80 . Similarly to  FIG. 5 , in  FIGS. 9A ,  9 B,  10 A, and  10 B, the −X direction refers to the left, the +X direction refers to the right, the −Y direction refers to the front, and the +Y direction refers to the rear. 
     The connection of the belt cleaning device  30  to the toner collection unit  80  will be described below with reference to  FIGS. 9A ,  9 B,  10 A, and  10 B (and other drawings if necessary). First, when the intermediate transfer unit  20  is inserted into the printer body  11 , as illustrated by open arrows in  FIGS. 3A and 4A , the belt cleaning device  30  supported by the intermediate frame  201  of the intermediate transfer unit  20  approaches the toner collection unit  80 . As a result, the waste-toner discharging pipe  60  extends through a through-window  111   a  located in the rear wall  111  of the printer body  11 , and the tip of the pipe body  61  of the waste-toner discharging pipe  60  faces the connection opening  831  in the waste-toner receiving member  83  of the toner collection unit  80 , as illustrated in  FIGS. 9A and 10A . 
     At this time, the belt cleaning device  30  is slightly inclined rearwardly due to the weight of the waste-toner discharging pipe  60  projecting rearwardly. Thus, the axis of the waste-toner discharging pipe  60  is not always aligned with the center line of the waste-toner receiving member  83  extending in a front-rear direction, and may be misaligned. However, because the diameter of the connection opening  831  is considerably larger than that of the pipe body  61 , and the tapered conical portion  611  is provided at the tip of the pipe body  61 , the tip of the pipe body  61  can pass through the connection opening  831  and enter the waste-toner receiving member  83 . 
     When the waste-toner discharging pipe  60  is inserted into the waste-toner receiving member  83  by a predetermined length, the stopper projections  714  of the shutter tube  71  interfere with the peripheral portion of the connection opening  831 . When, in this state, the intermediate transfer unit  20  is inserted further into the printer body  11 , the shutter tube  71  is urged relatively forward, opening the waste toner discharge port  614  of the pipe body  61  while the waste-toner discharging pipe  60 , resists the urging force of the coil spring  72 , and therefore is compressed relatively forward. 
     Accordingly, as illustrated in  FIG. 4B , when the intermediate transfer unit  20  is inserted until it stops into the printer body  11  and is in a stored position, the tip of the waste-toner discharging pipe  60  is inserted into the waste-toner receiving member  83 , as illustrated in  FIGS. 9B and 10B . As a result, the shutter tube  71  moves relatively forward, opening the waste toner discharge port  614  in the waste-toner receiving member  83 . 
     In this state, when the screw member  50  rotates about the screw shaft  51 , waste toner in the casing  31  of the belt cleaning device  30  is fed through the pipe body  61  toward the waste-toner receiving member  83 . The waste toner then passes through the waste toner discharge port  614 , the waste-toner receiving member  83 , and the waste-toner collecting pipe  82 , and is collected by the waste toner reservoir  81 . 
     In this embodiment, the toner conveying device  1  of the present invention is applied to the pipe body  61  of the waste-toner discharging pipe  60 . The toner conveying device  1  will be described below with reference to  FIG. 11  (and other drawings).  FIGS. 11A to 11C  are side sectional views of the toner conveying device  1  according to various embodiments, applied to the waste-toner discharging pipe  60 ,  FIG. 11A  illustrating a toner conveying device  1   a  according to an embodiment,  FIG. 11B  illustrating a toner conveying device  1   b  according to another embodiment, and  FIG. 11C  illustrating a toner conveying device  1   c  according to a still further embodiment. Similarly to  FIG. 5 , in  FIGS. 11A to 11C , the −Y direction refers to the front and the +Y direction refers to the rear. 
     The toner conveying devices  1   a ,  1   b , and  1   c  according to the embodiments have the same basic configuration, that is, they comprise the waste-toner discharging pipe  60  and the screw member  50 . 
     As described above, the screw member  50  includes the screw shaft  51  and the spiral fin  52  that is coaxially and spirally formed around the screw shaft  51 . As described above, the waste-toner discharging pipe  60  includes the pipe body  61 . The pipe body  61  has, inside thereof, the waste-toner conveying path V for feeding toner, and the screw member  50  is coaxially located therein. 
     In addition, the inside diameter of the pipe body  61  is changed in the pipe-axis direction. In the toner conveying devices  1   a ,  1   b , and  1   c  according to the embodiments, the inside diameter of the pipe body  61  gradually decreases from the base end side (front end side) toward the tip side (rear end side). 
     In the toner conveying devices  1   a ,  1   b , and  1   c  according to the embodiments, the distance between the outer circumferential surface of the spiral fin  52  and the inner circumferential surface of the pipe body  61  (gap distance d) is constant. 
     This structure allows toner to uniformly deposit on the bottom of the toner conveying path V formed in the pipe body  61  in a longitudinal direction. Thus, the problem of a large amount of toner being locally deposited can be effectively prevented. 
     Also, the problem of a large amount of toner being locally deposited and released and fed in a non-uniform manner, thereby clogging the toner conveying path V, can be effectively prevented. 
     Furthermore, in the toner conveying devices  1   a ,  1   b , and  1   c  according to the embodiments, the inside diameter of the pipe body  61  gradually and linearly decreases from one end (the base end portion) toward the other end (the tip portion). Therefore, for example, when the pipe body  61  is made by injection molding, the pipe body can be easily removed due to the gap formed between the core and the outer mold from the large diameter side. This is advantageous in that it allows the pipe body  61  to be easily produced. 
     The pipe body  61  of the toner conveying devices  1   a ,  1   b , and  1   c  according to the embodiments has an effective length L of 170 mm, an inside diameter (diameter) D 1  at the base end portion of 12 mm, and an inside diameter (diameter) D 2  at the tip portion of 10 mm. In the toner conveying devices  1   a ,  1   b , and  1   c , the gap distance d between the inner circumferential surface of the pipe body  61  and the outer circumferential surface of the spiral fin  52  is 0.6 mm. 
     The toner conveying device  1   a  according to an embodiment, shown in  FIG. 11A , is a basic configuration of the toner conveying device  1 . The pipe body  61 , has an inside diameter that decreases toward the tip, and the spiral fin  52  has an outside diameter that decreases toward the tip, as described above. The spiral pitch F of the spiral fin  52  is constant (in this embodiment, 10 mm) in the longitudinal direction. The diameter of the screw shaft  51  (shaft diameter D 3 ) is constant (in this embodiment, substantially 5 mm) in the longitudinal direction. 
     With the toner conveying device  1   a  according to this embodiment, because the outside diameter of the spiral fin  52  gradually decreases toward the tip while the shaft diameter D 3  of the screw shaft  51  is constant, the conveyance capacity of the spiral fin  52  gradually decreases as the toner moves toward the downstream side (rear side) along the toner conveying path V. 
     Thus, the toner is compressed as it moves toward the downstream side and the powder density thereof increases. However, this does not present an issue as the pipe body  61  has a waste toner discharge port  614  at the downstream end, through which the toner having a high powder density, due to the compression, is discharged at a high rate to the waste-toner receiving member  83  of the toner collection unit  80 . 
     The toner conveying device  1   b  according to an embodiment, shown in  FIG. 11B , is configured such that the spiral pitch F of the spiral fin  52  is substantially inversely proportional to the inside diameter of the pipe body  61  (that is, the spiral pitch F increases as the inside diameter of the pipe body  61  decreases). Thus, the spiral pitch F gradually increases toward the downstream side. In this embodiment, the spiral pitch F of the spiral fin  52  at the upstream-most position (upstream-most spiral pitch F 1 ) is 10 mm, and at the downstream-most position (downstream-most spiral pitch F 2 ) is 15.9 mm. 
     In the configuration of the toner conveying device  1   b  according to this embodiment, where the pipe body  61  has a large inside diameter, although the speed at which the rotation of the spiral fin  52  feeds toner is lower than that where it has a smaller inside diameter, the amount of toner feed by the spiral fin  52  per unit rotation angle is greater. In contrast, where the pipe body  61  has a smaller inside diameter, although the speed at which the rotation of the spiral fin  52  feeds toner is greater than that at the portion having a larger inside diameter, the amount of toner feed by the spiral fin  52  per unit rotation angle is smaller. 
     That is, by making the spiral pitch F of the spiral fin  52  substantially inversely proportional to the inside diameter of the pipe body  61 , increase/decrease of the feeding speed of the spiral fin  52  and increase/decrease of the amount of toner feed per unit rotation angle compensate for each other. As a result, the amount of toner feed by the pipe body  61  can be easily made uniform in the longitudinal direction of the pipe body  61 . 
     The toner conveying device  1   c  according to another embodiment, illustrated in  FIG. 11C , is configured such that the shaft diameter D 3  of the screw shaft increases or decreases with an increase or decrease in the inside diameter of the pipe body  61 . In this embodiment, the shaft diameter D 3  of the screw shaft  51 , in the pipe body  61 , on the upstream-most side (upstream-most side shaft diameter D 31 ) is 5 mm, and that on the downstream-most side (downstream-most side shaft diameter D 32 ) is 4 mm. The upstream-most spiral pitch F 1  is 10 mm, and the downstream-most spiral pitch F 2  is set to 14.2 mm. The other configurations are the same as those of the toner conveying device  1   b  according to the previous embodiment. 
     With the toner conveying device  1   c  having the above-described configuration, because variations in the amount of toner feed by the spiral fin  52  per unit rotation angle of the screw shaft  51  in the longitudinal direction of the pipe body  61  can be more precisely reduced, a more uniform feed of waste toner in the toner conveying path V can be achieved. 
     As the diameter of the screw shaft  51  decreases, the pitch of the spiral fin  52  also naturally decreases. Although too great a pitch makes the spiral fin  52  more likely to become flat due to elastic deformation or plastic deformation, there is an advantage in that a smaller pitch makes the spiral fin  52  less likely to lay flat. 
     The present invention is not limited to the above-described embodiments. 
     Although the image forming apparatus has been described with respect to printer  10  as an example in the above-described embodiments, the image forming apparatus is not limited to a printer  10 , and may, for example, be a copier, a facsimile machine, etc. 
     Although the shutter tube  71  includes three spring-receiving projections  713  and three stopper projections  714  in the above-described embodiments, the number of the spring-receiving projections  713  and stopper projections  714  is not limited to three, but may be two or more than three. 
     The specific values, mentioned in the above-described embodiments, of the inside diameters D 1  and D 2  of the base end portion and the tip portion, respectively, of the pipe body  61 , the shaft diameter D 3  of the screw shaft  51  including the upstream-most side shaft diameter D 31  and downstream-most side shaft diameter D 32 , the gap distance d between the outer circumferential surface of the screw shaft  51  and the inner circumferential surface of the pipe body  61 , and the upstream-most spiral pitch F 1  and downstream-most spiral pitch F 2  of the pipe body  61  are exemplary. Other values can be employed based on calculated results or test results according to equipment specifications and the properties of the toner. 
       FIG. 12  is a partial enlarged side sectional view of a toner conveying device  1   d  according to another embodiment. Similarly to  FIG. 10 , in  FIG. 12 , the −Y direction refers to the front and the +Y direction refers to the rear. 
     The toner conveying device  1   d  according to this embodiment includes a small-diameter pipe  61   a  having a constant diameter in the longitudinal direction and serving as a pipe body  61 ′, a large-diameter pipe  61   b  having a constant diameter in the longitudinal direction and located midway of the small-diameter pipe  61   a  coaxially therewith, a small-diameter screw member  50   a  located in the small-diameter pipe  61   a  coaxially therewith, and a large-diameter screw member  50   b  located in the large-diameter pipe  61   b  coaxially therewith. 
     The small-diameter screw member  50   a  and the large-diameter screw member  50   b  form the screw member  50 ′ according to this embodiment. 
     In the toner conveying device  1   d  according to this embodiment, the dimensions of the small-diameter spiral fin  52   a  and large-diameter spiral fin  52   b  are such that the distance between the inner circumferential surface of the small-diameter pipe  61   a  and the outer circumferential surface of the spiral fin of the small-diameter screw member  50   a  (small-diameter spiral fin  52   a ) (i.e., the gap distance d 1 ) equals the distance between the inner circumferential surface of the large-diameter pipe  61   b  and the outer circumferential surface of the spiral fin of the large-diameter screw member  50   b  (large-diameter spiral fin  52   b ) (i.e., the gap distance d 2 ) (d 1 =d 2 ). 
     With the toner conveying device  1   d  according to this embodiment, even if the large-diameter pipe  61   b  is located midway of the pipe body  61 ′ that is mainly formed of the small-diameter pipe  61   a , because the distance between the outer circumferential surface of the spiral fin of the screw member  50 ′ and the inner circumferential surface of the pipe body  61 ′ is constant, toner does not deposit locally in the pipe body  61 ′. 
     The toner conveying devices  1   a ,  1   b ,  1   c , and  1   d  according to the embodiments are used in the belt cleaning device  30  of the printer  10 . However, the toner conveying devices  1   a ,  1   b ,  1   c , and  1   d  of the present invention are not limited to use with the belt cleaning device  30 , but may be used with, for example, a toner conveying path for conveying toner from the toner containers  135  to the developing devices  134 . 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.