Abstract:
A rotary member includes a rotary shaft with a flange that projects radially out from a position near an end of the rotary shaft. A shaft end portion of the rotary shaft projects longitudinally beyond the flange and has a lubricant filling hole for receiving a lubricant. The rotary member also includes a bearing with a wall surface that has a recess. The recess has an opening and a closed depth end. The shaft end portion is accommodated in the recess so that the flange contacts the wall surface and closes off the recess to define a substantially closed space that can retain lubricant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a bearing structure applicable to a rotary member, such as a roller-like member, as well as to a toner storage device and an image forming apparatus provided with the bearing structure. 
     2. Description of the Related Art 
     In image forming apparatuses using electrophotographic technology, such as copying machines and printers, photosensitive drums are wide used as image carrying members. Generally, image forming operation performed by using a photosensitive drum is as follows. A charging device uniformly charges a surface of the photosensitive drum to a specific electric potential and an exposure unit projects a light beam emitted from a light emitting diode (LED) onto the surface of the photosensitive drum. The electric potential of the surface of the photosensitive drum is attenuated in areas exposed to the light beam, whereby an electrostatic latent image of an original image is formed on the drum surface. A developing unit develops the electrostatic latent image, thereby forming a toner image on the surface of the photosensitive drum. The toner image is transferred to a sheet of paper when the sheet is passed through an image transfer area where the photosensitive drum is held in contact with or in close proximity with a transfer roller. 
     An image forming apparatus includes a number of rotary members which rotate about longitudinal axes thereof, such as a photosensitive drum, a development roller, a cleaning roller, a fixing roller, a toner transporting screw and a sheet transport roller. Performance of these members as rotating elements, or rotational performance thereof, exerts a direct influence on various performance capabilities of the apparatus, such as image forming capability, toner image fixing capability, toner transporting capability and sheet transporting capability. It is therefore important to smoothly rotate the rotary members. For this purpose, each of the rotary members is provided with bearing structures at ends of a rotary shaft thereof for supporting the rotary shaft to permit the rotary member to smoothly rotate about the longitudinal axis. 
     Japanese Unexamined Patent Publication No. 2008-39865 describes a waste toner collection container provided with an example of the aforementioned kind of bearing structure. This waste toner collection container contains a transporting screw and has a bearing structure which includes a through hole formed in the container so that a rotary shaft of the transporting screw is fitted in the through hole. Generally, the bearing structure includes such functional elements as ball bearings to provide satisfactory rotational performance. Nevertheless, bearing structures with simplified arrangements, such as those employing through holes like the one mentioned above or recesses formed in walls of a housing for fitting ends of rotary shafts for the sake of compact design and cost reduction without using the functional elements, are used quite often in practice. 
     There are cases where a lubricant like grease is used in the bearing structure to improve the rotational performance thereof. The use of the lubricant serves to smoothen sliding motion of the rotary shafts, enhance wear resistance thereof and prevent generation of unpleasant noise. For example, there is a case where a lubricant is injected into or applied to a recess formed in a wall of a housing which supports an end of a rotary shaft of a rotary member during a process of assembling an apparatus. 
     On the other hand, however, there is a possibility that the lubricant leaks from the recess in the wall which supports the end of the rotary shaft, resulting in a shortage of the lubricant. The shortage of the lubricant can worsen the sliding motion of the rotary shaft and cause generation of unpleasant noise. Additionally, leakage of the lubricant to undesired areas can potentially smear a curved outer surface of a roller-like member or a sheet of paper or contaminate a large quantity of toner collected from the surface of the photosensitive drum prior to development. Particularly if the lubricant leaks to an area where a large quantity of toner is present, the toner will gather into a mass or stick to that area, potentially causing such problems as an increase in torque required for rotating the rotary member or lockup of rotation thereof. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a compact and low-cost bearing structure capable of providing stable lubricating performance. 
     In one aspect of the invention, a bearing structure for a rotary member intended to achieve the above object includes a rotary shaft provided in the rotary member, a flange formed at an end portion of the rotary shaft, the flange having a portion projecting radially outward from the rotary shaft, a shaft end portion projecting from the rotary shaft longitudinally outward beyond the flange, a lubricant filling hole formed in the shaft end portion, and a bearing supporting the rotary member rotatably about the rotary shaft, the bearing including a recess capable of accommodating the shaft end portion and a wall portion with which the flange is placed in contact. 
     In another aspect of the invention, a toner storage device includes a toner transporting screw having a rotary shaft and a screw portion which rotates about a longitudinal axis thereof as a result of rotation of the rotary shaft for transporting toner in a longitudinal direction, a flange formed at an end portion of the rotary shaft, the flange having a portion projecting radially outward from the rotary shaft, a shaft end portion projecting from the rotary shaft longitudinally outward beyond the flange, a lubricant filling hole formed in the shaft end portion, and a housing accommodating the toner transporting screw, the housing having an inside wall surface facing the shaft end portion and a recess formed by hollowing out part of the inside wall surface of the housing for accommodating the shaft end portion, wherein part of the flange is in contact with part of the inside wall surface surrounding the recess. 
     In still another aspect of the invention, an image forming apparatus includes an image carrying member on which a toner image is formed, and a toner storage device for storing toner, wherein the toner storage device is configured in the same way as the aforementioned toner storage device. 
     These and other objects, features and advantages of the invention will become more apparent upon a reading of the following detailed description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view generally showing the structure of a printer provided with a bearing structure according to a preferred embodiment of the invention; 
         FIG. 2  is an enlarged cross-sectional view showing a portion around an image-forming portion of the printer of  FIG. 1 ; 
         FIG. 3  is a fragmentary sectional side view showing a portion around a toner discharging screw of a cleaning unit shown in  FIG. 2 ; 
         FIG. 4  is a fragmentary enlarged cross-sectional view showing the bearing structure of the toner discharging screw shown in  FIG. 3 ; and 
         FIG. 5  is a fragmentary perspective view showing one end of a shaft of the toner discharging screw shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention is now described with reference to  FIGS. 1 to 5 . First, an image forming apparatus provided with a bearing structure of the embodiment of the invention is described along with image forming operation performed by the apparatus referring to  FIG. 1  which is a schematic cross-sectional view generally showing the structure of a printer  1 , an example of the image forming apparatus. As illustrated in  FIG. 1 , a right side corresponds to a front side of the printer  1  and a left side corresponds to a rear side of the same. 
     The printer  1  has an apparatus body  2  incorporating a paper cassette  3  at a bottom part thereof, the paper cassette  3  holding stacked printing sheets P. Provided above a downstream end in a sheet feeding direction of the paper cassette  3  is a sheet feeding mechanism  4  which picks up and feeds each successive printing sheet P from the paper cassette  3  in an upper-right direction (as illustrated in  FIG. 1 ). The paper cassette  3  can be removed by horizontally pulling the same out of the apparatus body  2  in a frontward direction thereof (rightward direction as illustrated in  FIG. 1 ) and reinstated in the apparatus body  2  by pushing the paper cassette  3  in the opposite direction. 
     A manual feed tray  5  is provided in a middle part of the front side of the apparatus body  2  of the printer  1 . The manual feed tray  5  is made swingable up and down about a pivot shaft provided at a lower end of the manual feed tray  5 , the pivot shaft extending generally horizontally in a lateral direction. The manual feed tray  5  can be opened by pulling an upper end thereof to swing the manual feed tray  5  outward (rightward as illustrated in  FIG. 1 ) about the pivot shaft and can be closed by swinging the manual feed tray  5  in the opposite direction. When the manual feed tray  5  is opened, a user can place a printing sheet P on top of the manual feed tray  5  for manually feeding the printing sheet P. 
     The manual feed tray  5  is used when printing an image on such recording media as sheets of paper of a different size which are not held in the paper cassette  3 , sheets of thick paper or transparent sheets of film for an overhead projector. Such non-standard printing sheets are placed one by one on the manual feed tray  5  and fed successively leftward by a feeding mechanism  6  which is provided to the left of the manual feed tray  5  as illustrated in  FIG. 1 . When not in use, the manual feed tray  5  is set at a closed position as shown in  FIG. 1 . 
     Provided downstream in the sheet feeding direction of the paper cassette  3  and the manual feed tray  5  are a sheet feeding path  7 , registration rollers  8 , an image-forming portion  20  and an image transfer portion  30 . The printing sheet P fed from the paper cassette  3  or the manual feed tray  5  passes through the sheet feeding path  7  and reaches the registration rollers  8  which align the printing sheet P to make up for any oblique feed thereof and feed the printing sheet P into the image transfer portion  30  such that a toner image formed by the image-forming portion  20  would be transferred to the printing sheet P with correct timing. 
     The printer  1  includes an optical system  9  located above the image-forming portion  20 . The optical system  9  produces a laser beam L (shown by a dot-and-dash line in the Figure) based on an image data signal representative of text and/or graphic information externally fed from a computer (not shown) to the printer  1 . Then, the image-forming portion  20  produces an electrostatic latent image of an original image on a photosensitive drum  21  which serves an image carrying member. The electrostatic latent image is converted into the aforementioned toner image. Then, the toner image is transferred to the printing sheet P fed with proper timing by the registration rollers  8  at an image transfer nipping part where the photosensitive drum  21  is pressed against a transfer roller  31  of the image transfer portion  30 . 
     Provided downstream in the sheet feeding direction of the image-forming portion  20  and the image transfer portion  30  is a fixing unit  10 . The printing sheet P carrying the unfixed toner image is fed into the fixing unit  10  in which the toner image is fixed to the printing sheet P by application of heat and pressure between a heating roller and a pressure roller. 
     Provided further downstream of the fixing unit  10  are a sheet output path  11 , a sheet output port  12  and a sheet output tray  13 . The printing sheet P ejected from the fixing unit  10  is transported upward along the sheet output path  11  and delivered onto the sheet output tray  13  provided at the top of the apparatus body  2  through the sheet output port  12 . 
     Described next with reference to  FIGS. 1 and 2  are details of the structure of a portion around the image-forming portion  20  of the printer  1  and the operation thereof.  FIG. 2  is an enlarged cross-sectional view showing the portion around the image-forming portion  20 . The photosensitive drum  21  serving as the image carrying member is located approximately in the middle of the image-forming portion  20 . Provided close to the photosensitive drum  21  are a charging unit  40 , a developing unit  50 , a cleaning unit  60  and a static charge eliminating unit  70  which are disposed in this order along a rotating direction of the photosensitive drum  21 . The image transfer portion  30  is located between the developing unit  50  and the cleaning unit  60  as if along the rotating direction of the photosensitive drum  21 . 
     The photosensitive drum  21  has a longitudinal axis extending horizontally in a sheet width direction which is perpendicular to the sheet feeding direction in the printer  1 , or perpendicular to the plane of paper of  FIG. 2 . The photosensitive drum  21  is an inorganic photoreceptor drum having an electrically conductive roller core member made of aluminum, for instance, and a photosensitive layer of amorphous silicon which is an inorganic photoconductive material deposited on an outer surface of the roller core member by vacuum evaporation or the like. As an alternative, the photosensitive drum  21  may be a drum employing an organic photoconductor (OPC). The photosensitive drum  21  is driven by an unillustrated driver in such a manner that an outer peripheral surface of the photosensitive drum  21  turns at a speed equal to a sheet feeding speed. 
     The charging unit  40  is a scorotron charger which uses corona discharge. Alternatively, the charging unit  40  may be a corotron charger which also uses corona discharge or a contact-type charger using a charging roller or a brush, for instance. The charging unit  40  uniformly charges the outer peripheral surface of the photosensitive drum  21  to a specific electric potential of a particular polarity. 
     The developing unit  50  has a housing  51  incorporating a development roller  52 , a transporting screw  53  and an agitating screw  54 . The development roller  52  is of a contact or noncontact development type disposed in the proximity of the photosensitive drum  21 . A bias of the same polarity as the charging polarity of the photosensitive drum  21  is applied to the development roller  52 . The development roller  52  thus biased imparts an electric charge to toner used as a developer. The electrostatic latent image on the outer peripheral surface of the photosensitive drum  21  is developed as electrically charged toner particles move to the surface of the photosensitive drum  21 . The toner is initially stored in a toner feeding container  55  provided above the developing unit  50  as shown in  FIG. 1  and is supplied into the housing  51  from above the agitating screw  54  by means of an unillustrated toner feeder. The toner supplied to the housing  51  is transported up to the development roller  52  by the agitating screw  54  and the transporting screw  53  while being agitated. 
     The image transfer portion  30  includes the aforementioned transfer roller  31  which serves as an image transfer member. The transfer roller  31  is pressed against the photosensitive drum  21  to form the image transfer nipping part through which the printing sheet P is passed. The transfer roller  31  is rotated by an unillustrated driver in such a manner that an outer peripheral surface of the transfer roller  31  turns at the same turning speed as the outer peripheral surface of the photosensitive drum  21 . An image transfer bias of a polarity opposite to the charging polarity of the photosensitive drum  21  and the toner is applied to the transfer roller  31  if necessary. Shown by an alternate long and two short dashed line in  FIG. 2  is a path along which the printing sheet P is transported. 
     The cleaning unit  60  (toner storage device) is located downstream of the image transfer nipping part along the rotating direction of the photosensitive drum  21  as shown in  FIG. 2 . The cleaning unit  60  has a housing  61  incorporating a cleaning roller  62 , a cleaning blade  63  and a toner discharging screw  64  (toner transporting screw) which is a rotary member. The cleaning roller  62  and the cleaning blade  63  are pressed against the photosensitive drum  21  for cleaning the outer peripheral surface of the photosensitive drum  21  by removing any material adhering to the surface of the photosensitive drum  21  including residual toner left thereon after the toner image has been transferred to the printing sheet P. The toner removed from the surface of the photosensitive drum  21  is once held in the housing  61  and discharged into an unillustrated waste toner collection container provided outside the cleaning unit  60 . 
     The static charge eliminating unit  70  is provided with an LED  71 . It is to be noted that another type of light source, such as an electroluminescent (EL) lamp or a fluorescent lamp, may be used instead of the LED  71 . As the static charge eliminating unit  70  projects static charge eliminating light emitted from the LED  71  to the photosensitive drum  21 , a static charge imparted to the surface of the photosensitive drum  21  is eliminated in preparation of a charging process in succeeding image forming operation. 
     Configured as thus far described, the printer  1  operates in the aforementioned manner. The bearing structure of the printer  1  of the present embodiment is for the toner discharging screw  64  (rotary member) of the cleaning unit  60  for cleaning the surface of the photosensitive drum  21 . 
     The bearing structure of the embodiment is now described in great detail with reference to  FIGS. 3 to 5  in addition to  FIG. 2 .  FIG. 3  is a fragmentary sectional side view showing a portion around the toner discharging screw  64  of the cleaning unit  60 ,  FIG. 4  is a fragmentary enlarged cross-sectional view showing the bearing structure  80  of the toner discharging screw  64 , and  FIG. 5  is a fragmentary perspective view showing one end of a shaft  64   a  (rotary shaft) of the toner discharging screw  64 . 
     The toner discharging screw  64  provided in the cleaning unit  60  shown in  FIGS. 2 and 3  is supported at both ends by the housing  61  and is caused to rotate by a driving force transmitted from an unillustrated end of the toner discharging screw  64 . At the other end of the toner discharging screw  64  opposite to the aforementioned end from which the driving force is transmitted, the shaft  64   a  is rotatably supported by the housing  61  via the bearing structure  80 . 
     As shown in  FIGS. 3 to 5 , the bearing structure  80  includes a flange  81 , the shaft  64   a,  a shaft end portion  64   b  and lubricant filling holes  83  provided on the toner discharging screw  64 , as well as a recess  82  and a wall surface  61   a  (wall portion/inside wall surface) provided on the housing  61 . The flange  81  is formed on the end of the shaft  64   a  opposite to the end thereof from which the driving force is transmitted, projecting radially outward from the shaft  64   a . The shaft end portion  64   b  is a portion of the shaft  64   a  projecting longitudinally outward beyond the flange  81  on a common axis with the shaft  64   a . The lubricant filling holes  83  are holes formed in the shaft end portion  64   b  for retaining a lubricant. The recess  82  is a hollow portion formed in the housing  61  for accommodating the shaft end portion  64   b  of the toner discharging screw  64 . The wall surface  61   a  is a portion of the housing  61  with which the flange  81  is placed in contact. In the bearing structure of the present embodiment, the recess  82  and the wall surface  61   a  together constitute a bearing. 
     The flange  81  is formed on the shaft  64   a  of the toner discharging screw  64  at a position located longitudinally inward from the shaft end portion  64   b . The flange  81  is formed in a generally disk shape projecting radially outward from a cylindrical outer surface of the shaft  64   a  as depicted in  FIG. 5 . The flange  81  need not however have the disk shape. What is essential is that the flange  81  has a portion projecting radially outward from the shaft  64   a.    
     The recess  82  is formed in the wall surface  61   a  of the housing  61  which supports the toner discharging screw  64 . Formed by hollowing out part of the wall surface  61   a , the recess  82  is a cylindrical cavity capable of accommodating the shaft end portion  64   b , the recess  82  having an inside diameter smaller than the outside diameter of the flange  81 . When the toner discharging screw  64  is supported by the wall surface  61   a , an outer peripheral part of a side surface of the flange  81  is in close contact with the wall surface  61   a  as shown in  FIGS. 3 and 4 . In this condition, there is created a space S around the shaft end portion  64   b  of the shaft  64   a  between the shaft end portion  64   b  and inside surfaces of the recess  82  in areas located radially outward and longitudinally outward the shaft end portion  64   b.    
     The lubricant filling holes  83  are formed in the shaft end portion  64   b  of the shaft  64   a . Specifically, the lubricant filling holes  83  include a first hole  83   a  and a second hole  83   b  as depicted in  FIG. 4 . The first hole  83   a  is a cylindrical hole formed longitudinally inward from an end surface of the shaft end portion  64   b  on the common axis with the shaft  64   a  for a specific length. The second hole  83   b  is also a cylindrical hole formed from one point to an opposite point on a cylindrical outer surface of the shaft end portion  64   b  in a direction perpendicular to the longitudinal axis of the shaft  64   a . The second hole  83   b  thus formed has two openings directed radially outward in opposite directions in the cylindrical outer surface of the shaft  64   a . The first hole  83   a  and the second hole  83   b  intersects each other at a point on the longitudinal axis of the shaft  64   a  ( 64   b ) therewithin and are connected to each other. 
     The lubricant is filled into the lubricant filling holes  83  before the toner discharging screw  64  is mounted in the housing  61  during a process of assembling the cleaning unit  60 . Grease having a relatively high viscosity is a preferable example of the lubricant. Without filling the lubricant into the recess  82 , or into the space S shown in  FIG. 4 , the shaft end portion  64   b  of the shaft  64   a  is fitted into the recess  82  and the toner discharging screw  64  is mounted in the housing  61 . 
     As thus far described, the bearing structure  80  of the present embodiment is a bearing structure supporting the toner discharging screw  64  rotatably about a rotary axis thereof, the bearing structure  80  including the flange  81 , the lubricant filling holes  83  formed in the shaft end portion  64   b  of the shaft  64   a  and the cylindrically shaped recess  82  whose inside diameter is smaller than the outside diameter of the flange  81  for accommodating the shaft end portion  64   b.    
     In this bearing structure, it is possible to fill the lubricant in the lubricant filling holes  83 , and not in the recess  82 , during the process of assembling the cleaning unit  60 . As a result, the lubricant exhibits surface tension, and this makes it possible to prevent the lubricant from leaking out of the recess  82  before the cleaning unit  60  is used after the process of assembly. When the cleaning unit  60  is used during operation of the printer  1 , the lubricant filled in the lubricant filling holes  83  is caused to flow out slowly from the lubricant filling holes  83  due to a centrifugal force exerted on the shaft  64   a  by the rotating toner discharging screw  64 . 
     Since the bearing structure  80  of this embodiment does not employ any functional element like a ball bearing, it is possible to provide a compact and low-cost bearing structure. Also, since the lubricant is initially retained in the lubricant filling holes  83 , it is possible to prevent the bearing structure  80  from running short of the lubricant due to leakage thereof from the recess  82  accommodating the shaft end portion  64   b  of the shaft  64   a , so that satisfactory rotational performance of the toner discharging screw  64  (rotary member) is obtainable. 
     Furthermore, since the second hole  83   b  has the openings directed radially outward in the cylindrical outer surface of the shaft  64   a , it is possible to allow the lubricant to flow out easily from the lubricant filling holes  83 , so that the bearing structure  80  of the embodiment can quickly provide an improved lubricating effect at the beginning of use of the cleaning unit  60 . It will be appreciated from the foregoing discussion that the present invention can provide the bearing structure  80  by which excellent rotational performance of the rotary member can be obtained. 
     While the invention has far been described with reference to the preferred embodiment thereof, the aforementioned arrangement of the embodiment is simply illustrative and may be modified in various ways without departing from the scope of the invention. Cited under (1) to (5) below are some examples of such modifications of the embodiment. 
     (1) The printer  1  of the foregoing embodiment is a monochrome printer using only black toner. The image forming apparatus of the invention is not limited to the monochrome printer but may be an image forming apparatus employing an intermediate transfer belt and a tandem engine or a rotary rack system for multicolor printing. 
     (2) Described thus far with reference to the preferred embodiment is an example in which the bearing structure of the invention is applied to the toner discharging screw  64  of the cleaning unit  60 . The bearing structure of the invention is also applicable to other kinds of rotary members. The bearing structure of the invention is applicable to various other kinds of rotary members than the toner discharging screw  64  shown in  FIG. 2 , such as the cleaning roller  62  of the cleaning unit  60 , the development roller  52 , the transporting screw  53  and the agitating screw  54  of the developing unit  50  (which is an example of a toner storage device), a transporting screw or an agitating paddle provided in the toner feeding container  55  (which is another example of a toner storage device), as well as the photosensitive drum  21 , the transfer roller  31  and the registration rollers  8  ( FIG. 1 ). The bearing structure of the invention, if applied to such rotary members provided at various locations in the printer  1 , will serve to smoothen sliding motion of shafts of these rotary members, enhance wear resistance thereof and prevent generation of unpleasant noise. Additionally, the bearing structure will serve also to prevent an increase in torque required for rotating the rotary members and lockup of rotation thereof caused by agglomeration or sticking of the toner. 
     (3) The invention is applicable not only to an image forming apparatus like a printer or to screws or roller-like members but also to a variety of bearing structures for supporting rotary members used in various apparatuses rotatably about respective rotary axes. 
     (4) The foregoing embodiment has illustrated an arrangement in which the lubricant filling holes  83  include the first hole  83   a  extending along the longitudinal axis of the shaft  64   a  and the second hole  83   b  extending perpendicular to the longitudinal axis of the shaft  64   a . This is just one example of the arrangement of the invention. In one variation, the arrangement may not include the first hole  83   a , for example. Also, while the second hole  83   b  extends perpendicular to the longitudinal axis of the shaft  64   a , the second hole  83   b  may be a hole extending at an oblique angle to the longitudinal axis of the shaft  64   a . Furthermore, there may be formed a plurality of holes arranged along a circumferential direction of the shaft end portion  64   b  instead of the second hole  83   b . Alternatively, a ringlike groove formed in the cylindrical outer surface of the shaft end portion  64   b  along the circumferential direction thereof may be used as a lubricant filling hole. 
     (5) While the shaft end portion  64   b  of the shaft  64   a  of the toner discharging screw  64  is a cylindrical part as illustrated in the foregoing embodiment, the shaft end portion  64   b  may have a rectangular or D-shaped cross section. Also, while the recess  82  formed in the wall surface  61   a  of the housing  61  is a cylindrical cavity, the recess  82  need not necessarily be cylindrically shaped but may be a cavity of any shape if it is possible to accommodate the shaft end portion  64   b  therein. Even in this case, however, it is desirable that an opening of the recess  82  be sealed off by the flange  81 , creating the generally closed space S in the recess  82 . 
     While the invention has thus far been described with reference to the illustrative embodiment thereof, principal arrangements and features of the invention can be summarized as follows. 
     In one aspect of the invention, a bearing structure for a rotary member includes a rotary shaft provided in the rotary member, a flange formed at an end portion of the rotary shaft, the flange having a portion projecting radially outward from the rotary shaft, a shaft end portion projecting from the rotary shaft longitudinally outward beyond the flange, a lubricant filling hole formed in the shaft end portion, and a bearing supporting the rotary member rotatably about the rotary shaft, the bearing including a recess capable of accommodating the shaft end portion and a wall portion with which the flange is placed in contact. 
     In this bearing structure, it is possible to fill the lubricant in the lubricant filling hole, and not in the recess, during a process of installing the rotary member. As a result, the lubricant exhibits surface tension, and this makes it possible to prevent the lubricant from leaking out of the recess before the rotary member is used after the process of installation thereof. When the rotary member is actually used, the lubricant filled in the lubricant filling hole is caused to flow out slowly from the lubricant filling hole due to a centrifugal force exerted on the rotary shaft by rotation of the rotary shaft. It is therefore possible to achieve a reduction in size and cost of the bearing structure. It is also possible to prevent leakage or shortage of the lubricant, so that the invention can provide a bearing structure capable of providing satisfactory rotational performance. 
     The aforementioned bearing structure of the invention should preferably be such that the flange has a disk shape and the recess is a cylindrical cavity whose inside diameter is smaller than the outside diameter of the flange. This makes it possible to reduce the flange and the recess in size. 
     Also, the bearing structure should preferably be such that the lubricant filling hole has an opening directed radially outward. This structure allows the lubricant to flow out easily from the lubricant filling hole due to the centrifugal force so that the bearing structure can quickly provide an improved lubricating effect at the beginning of operation of an apparatus. The invention can therefore provide a bearing structure capable of providing even satisfactory rotational performance. 
     Also, the bearing structure should preferably be such that the lubricant filling hole is a hole passing through the shaft end portion in a direction perpendicular to a longitudinal direction of the rotary shaft. This structure makes it possible to form the lubricant filling hole having two openings directed radially outward. 
     Also, the bearing structure should preferably be such that the lubricant filling hole includes a first hole formed in an end of the shaft end portion to a specific depth along the longitudinal direction of the rotary shaft and a second hole formed to pass through the shaft end portion in a direction perpendicular to a longitudinal direction of the rotary shaft, intersecting the first hole. This structure makes it possible to provide enhanced ease of filling the lubricant and improved retainability thereof. 
     Preferably, the aforementioned bearing structure of the invention further comprises a housing accommodating the rotary member, wherein the bearing is formed in an inside wall surface of the housing, the recess is formed by hollowing out part of the inside wall surface of the housing and the wall portion is part of the inside wall surface surrounding the recess. This structure makes it possible to form the bearing by using the inside wall surface of the housing. 
     In another aspect of the invention, a toner storage device includes a toner transporting screw having a rotary shaft and a screw portion which rotates about a longitudinal axis thereof as a result of rotation of the rotary shaft for transporting toner in a longitudinal direction, and a housing accommodating the toner transporting screw, wherein the rotary shaft has a flange having a portion projecting radially outward from the rotary shaft, a shaft end portion projecting longitudinally outward beyond the flange, and a lubricant filling hole formed in the shaft end portion, the housing having an inside wall surface facing the shaft end portion and a recess formed by hollowing out part of the inside wall surface of the housing for accommodating the shaft end portion, and wherein part of the flange is in contact with part of the inside wall surface surrounding the recess. 
     According to this structure of the toner storage device having the housing accommodating the toner transporting screw, it is possible to achieve a reduction in size and cost of the bearing structure capable of providing stable lubricating performance. 
     In one preferable mode of the invention, the toner storage device is a cleaning unit for cleaning an image carrying member, and the toner transporting screw is a toner discharging screw for discharging the toner from inside the housing. This makes it possible to configure a bearing structure of the toner discharging screw of the cleaning unit for cleaning the image carrying member in compact size and at low cost, still providing stable lubricating performance. 
     In still another aspect of the invention, an image forming apparatus includes an image carrying member on which a toner image is formed, and a toner storage device for storing toner. The toner storage device includes a toner transporting screw having a rotary shaft and a screw portion which rotates about a longitudinal axis thereof as a result of rotation of the rotary shaft for transporting the toner in a longitudinal direction, a flange formed at an end portion of the rotary shaft, the flange having a portion projecting radially outward from the rotary shaft, a shaft end portion projecting from the rotary shaft longitudinally outward beyond the flange, a lubricant filling hole formed in the shaft end portion, and a housing accommodating the toner transporting screw, the housing having an inside wall surface facing the shaft end portion and a recess formed by hollowing out part of the inside wall surface of the housing for accommodating the shaft end portion, wherein part of the flange is in contact with part of the inside wall surface surrounding the recess. 
     This application is based on Japanese patent application serial No. 2008-160339, filed in Japan Patent Office on Jun. 19, 2008, the contents of which is hereby incorporated by reference. 
     Although the present invention has been fully described by way of example with reference to the accompanied drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.