Patent Publication Number: US-8116642-B2

Title: Developer stirring unit, developing device and image forming apparatus

Description:
FIELD OF THE INVENTION 
     The invention relates to a developer stirring unit for stirring developer, a developing device including the developer stirring unit, and an image forming apparatus comprising the developing device; especially, relates to a developer stirring unit, a developing device and an image forming apparatus that can detect remainder amount of developer. 
     BACKGROUND OF THE INVENTION 
     In recent years, many image forming apparatuses of electronic photography type are utilized such as printer, facsimile apparatus, copying apparatus, multiplex apparatus and the like. As such apparatus, it has an image formation composed of respective processes of charging, exposing, developing, transferring, fixing and cleaning. In these processes, developing process is to use a developing device to make developing roller serving as developer carrying body carry developer (i.e. toner) so as to perform a development of electrostatic latent image with respect to photosensitive drum serving as an electrostatic latent image carrying body. 
     In such developing device, besides the developing roller, a supplying roller for supply toner to the developing roller, and a toner stirring unit for stirring toner as developer stirring unit are furnished. 
       FIG. 16A  is a first explanatory diagram showing a conventional toner stirring unit; and  FIG. 16B  is a second explanatory diagram showing a conventional toner stirring unit. 
     A toner stirring unit  100 , as shown by  FIG. 16A , includes a toner hopper  102  for accommodating toner  101  as accommodating tank; a stirring bar  103  as stirring member; and a driving section  104 . The stirring bar  103  has a built-in magnet  105 ; and is supported to freely rotate by a supporting pivot  106  in the toner hopper  102 . On one end of the supporting pivot  106 , a projection portion  106   a  is formed, the driving section  104  presses the projection portion  106   a  to make the supporting pivot  106  and the stirring bar  103  rotate along a direction of arrow “A”. Further, under the toner hopper  102 , a magnetic sensor  107  is furnished which can detects strength of magnetic field coming from the magnet  105 . 
     When a rotation force is transferred from a driving unit (not shown) so that the driving section  104  rotates, the stirring bar  103  rotates together with the supporting pivot  106 , after its tip rotated to an uppermost position i.e. an upper dead point position, the stirring bar  103  rotates to drop quicker than the driving section  104  through its own weight. Then, as shown by  FIG. 16A , the stirring bar  103  stops on the toner  101  accommodated in the toner hopper  102 . At that time, a control circuit (not shown) judges a stop position of the stirring bar  103  so as to judge a remainder amount of the toner  101  in the toner hopper  102 , on the basis of the strength of magnetic field detected by the magnetic sensor  107 . It may refer to Patent Document 1. 
     Patent Document 1: Japan patent publication of No. Heisei 09-054488. 
     However, in such conventional toner stirring unit  100 , in the case that the remainder amount of the toner  101  in the toner hopper  102  becomes little, as shown by  FIG. 16B , the stirring bar  103  produces rebound or vibration when dropping to the toner  101 . Therefore, there is problem that the remainder amount of toner could not be correctly judged. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the invention to provide a developer stirring unit, a developing device and an image forming apparatus that can solve the above problem, so as to correctly judge a remainder amount of developer in accommodating tank. 
     A first aspect of the invention is to provide a developer stirring unit, the developer stirring unit comprises a accommodating tank that accommodates developer; a stirring member that has at least one shaft portion and is used to stir the developer accommodated in the accommodating tank; a bearing member that couples with the shaft portion, and supports the stirring member to possibly rotate around the shaft portion serving as rotation axis and to possibly move along a axis direction of the rotation axis; a driving section that drives the stirring member to rotate; and a judging section that judges a remainder amount of the developer in the accommodating tank, wherein the stirring member is controlled to move along an axis direction of the rotation axis together with rotating along a rotation direction of the rotation axis. 
     A second aspect of the invention is to provide a developing device, the developing device comprises a developer stirring unit that includes a accommodating tank that accommodates developer; a stirring member that has at least one shaft portion and is used to stir the developer accommodated in the accommodating tank; a bearing member that couples with the shaft portion, and supports the stirring member to possibly rotate around the shaft portion serving as rotation axis and to possibly move along a axis direction of the rotation axis; a driving section that drives the stirring member to rotate; and a judging section that judges a remainder amount of the developer in the accommodating tank, wherein the stirring member is controlled to move along an axis direction of the rotation axis together with rotating along a rotation direction of the rotation axis. 
     A third aspect of the invention is to provide an image forming apparatus, the image forming apparatus comprises a developing device, wherein the developing device has a developer stirring unit that includes a accommodating tank that accommodates developer; a stirring member that has at least one shaft portion and is used to stir the developer accommodated in the accommodating tank; a bearing member that couples with the shaft portion, and supports the stirring member to possibly rotate around the shaft portion serving as rotation axis and to possibly move along a axis direction of the rotation axis; a driving section that drives the stirring member to rotate; and a judging section that judges a remainder amount of the developer in the accommodating tank, wherein the stirring member is controlled to move along an axis direction of the rotation axis together with rotating along a rotation direction of the rotation axis. 
     The Effect of the Present Invention 
     According to the developer stirring unit, the developing device and the image forming apparatus of the invention, because the stirring member drops in accordance with bearing member while moving along a rotation axis direction, even if developer in accommodating tank becomes little, rebound or vibration can be prevented from occurring. Therefore, it is possible to correctly judge remainder amount of developer. 
     The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a first cross-sectional diagram showing a main structure of toner stirring unit in embodiment 1 of the present invention; 
         FIG. 1B  is a second cross-sectional diagram showing a main structure of toner stirring unit in embodiment 1 of the present invention; 
         FIG. 2  is a cross-sectional side view showing a summary structure of printer of the present invention; 
         FIG. 3  is a cross-sectional side view showing a summary structure of print mechanism section; 
         FIG. 4  is a first cross-sectional side view showing a structure of image forming unit containing toner stirring unit of the present invention; 
         FIG. 5  is a summary cubic diagram showing a stirring bar; 
         FIG. 6A  is a first diagram for explaining structure and operation of a sensor section; 
         FIG. 6B  is a second diagram for explaining structure and operation of a sensor section; 
         FIG. 6C  is a third diagram for explaining structure and operation of a sensor section 
         FIG. 7  is a cubic diagram showing a structure of bearing member; 
         FIG. 8  is a cubic diagram showing a structure of bearing drive member in embodiment 1; 
         FIG. 9  is a second cross-sectional side view showing a structure of image forming unit containing toner stirring unit of the present invention; 
         FIG. 10A  is a first diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention; 
         FIG. 10B  is a second diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention; 
         FIG. 10C  is a third diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention; 
         FIG. 10D  is a fourth diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention; 
         FIG. 10E  is a fifth diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention; 
         FIG. 11A  is a first diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention; 
         FIG. 11B  is a second diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention; 
         FIG. 11C  is a third diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention; 
         FIG. 11D  is a fourth diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention; 
         FIG. 11E  is a fifth diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention; 
         FIG. 12A  is a first cross-sectional diagram showing a main structure of toner stirring unit in embodiment 2 of the present invention; 
         FIG. 12B  is a second cross-sectional diagram showing a main structure of toner stirring unit in embodiment 2 of the present invention; 
         FIG. 13  is a cross-sectional diagram showing a structure of bearing drive member in embodiment 3; 
         FIG. 14  is a cross-sectional diagram showing a main structure of toner stirring unit in embodiment 4 of the present invention; 
         FIG. 15  is a cross-sectional diagram showing a structure of bearing drive member in embodiment 5; 
         FIG. 16A  is a first explanatory diagram showing a conventional toner stirring unit; and 
         FIG. 16B  is a second explanatory diagram showing a conventional toner stirring unit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the invention will be described in detail hereinbelow with reference to the drawings. Here, it is to explain example when applying the present invention to a stirring unit, a developing device which has the toner stirring unit and an electronic photographic printer which includes the developing device. 
     Embodiment 1 
       FIG. 2  is a cross-sectional side view showing a summary structure of printer of the present invention. 
     A printer  10 , as an image forming apparatus of electronic photographic type, which includes a developing device containing toner stirring unit, as shown by  FIG. 2 , comprises a paper feeding mechanism section  11 , a printing mechanism section  12 , a fixing mechanism section  13  and a paper ejecting mechanism section  14 . 
     Further, the printer  10  comprises a printer controlling section (not shown) for controlling the respective sections  11 ˜ 14 . The printer controlling section includes a control substrate  15  to perform supply of voltage from a power source (not shown) to respective sections; perform drives of respective motors (not shown) for controlling respective rollers (described below) to rotate; perform print control and the like on the basis of information of respective sensors. Further, the printer controlling section, as a judging section, has a function to judge remainder amount of toner (i.e. developer). 
     With a start of print process, the printer controlling section starts to supply electric current to the fixing mechanism section  13 . 
     The fixing mechanism section  13 , as shown by  FIG. 2 , includes a heat roller  16  having a built-in heat source; and a backup roller  17 . 
     When the surface of the heat roller  16  comes to a predetermined fixation temperature, the printer controlling section controls respective rollers in the printing mechanism section  12  to rotate. Then, at a predetermined timing, the paper feeding mechanism section  11  starts to feed paper to the printing mechanism section  12 . 
     The paper feeding mechanism section  11 , as shown by  FIG. 2 , includes a cassette  19  which is furnished on the underside of the printer  10  and in which plural print medium  18  are accumulated; a hopping roller  20 ; an upper registration roller  21  and a lower registration roller  22 . 
     When the hopping roller  20  starts to rotate by a control of the printer controlling section, the print medium  18  accommodated in the cassette  19  is conveyed to medium conveyance route. Then, through rotation of the upper registration roller  21  and the lower registration roller  22 , the print medium  18  is conveyed to the printing mechanism section  12 . 
       FIG. 3  is a cross-sectional side view showing a summary structure of print mechanism section. 
     The printing mechanism section  12 , as shown by  FIGS. 2  and  3 , is composed of image forming unit  23  containing developing device; exposing unit  24  and transfer roller  25 . 
     The image forming unit  23  has a photosensitive drum  26  as an image carrying body. The photosensitive drum  26  is furnished to expose from the underside of the image forming unit  23  so that its surface contacts with the transfer roller  25 . 
     In the image forming unit  23 , around the photosensitive drum  26 , a charging roller  27  serving as charging unit, a developing roller  28  serving as developer carrying body, and a cleaning roller  29  serving as cleaning means are furnished to contact with the surface of the photosensitive drum  26 . 
     Further, in the image forming unit  23 , a sponge roller  30  serving as developer supply member, and a blade  31  serving as layer regulating member are furnished around the developing roller  28 . 
     Furthermore, on the upside of the image forming unit  23 , a toner cartridge  32  is removably attached for accommodating toner serving as developer. The toner cartridge  32  has a toner accommodating space  33  for accommodating toner, and has a shutter (not shown). After the toner cartridge  32  is installed in a predetermined position, when a lever (not shown) is rotated, the shutter of the toner cartridge  32  is opened, the toner accommodated in the toner accommodating space  33  is replenished to a toner keeping space  34  inside the image forming unit  23  and is kept in the toner keeping space  34 . The toner kept in the toner keeping space  34  is supplied by the developing roller  28 , and a toner layer with a predetermined thickness is formed on the surface of the developing roller  28  by the blade  31 . 
     Further, in the image forming unit  23 , a sensor section  35  is furnished for detecting toner remainder amount in the toner keeping space  34 . Regarding a detail explanation of the sensor section  35 , it will be stated below. 
     When the print medium  18  fed by the paper feeding mechanism section  11  reaches a predetermined position, the printer controlling section controls the charging roller  27  to uniformly charge the surface of the photosensitive drum  26 , and controls the exposing unit  24  to emit light. Thereby, on the surface of the photosensitive drum  26 , an electrostatic latent image is formed. Then, toner on the developing roller  28  adheres to the electrostatic latent image so that a toner image is formed on the surface of the photosensitive drum  26 . 
     When the print medium  18  is conveyed and reaches between the photosensitive drum  26  and the transfer roller  25 , the toner image on the photosensitive drum  26  is transferred onto the surface of the print medium  18  by the transfer roller  25 . Then, transfer remainder toner that is remaining on the surface of the photosensitive drum  26  is removed by the cleaning roller  29 . The print medium  18  on which the toner image is transferred, is further conveyed to the fixing mechanism section  13 . 
     In the fixing mechanism section  13 , the heat roller  16  is driven to rotate, with the rotation of the heat roller  16 , the backup roller  17  is also driven to rotate. When the print medium  18  is conveyed in between the heat roller  16  and the backup roller  17 , the print medium  18  is heated and pressed so that the toner image transferred in the printing mechanism section  12  is fixed. Later, the print medium  18  is conveyed from the fixing mechanism section  13  to the paper ejecting mechanism section  14 . 
     The paper ejecting mechanism section  14 , as shown by  FIG. 2 , includes ejecting rollers  36 ˜ 39 , and stacker  40  used for stacking the print medium  18 . 
     When the print medium  18  which is performed by a fixing process of toner image by the fixing mechanism section  13 , is conveyed to the paper ejecting mechanism section  14 , through a control of the printer controlling section, the respective ejecting rollers  36 ˜ 39  start to rotate. The print medium  18 , after conveyed by the ejecting rollers  36 ˜ 37 , is ejected to the stacker  40  furnished at the upside of the printer  10  by the ejecting rollers  38 ˜ 39 . 
     Next, it is to explain a detail structure of the image forming unit  23 . 
       FIG. 4  is a first cross-sectional side view showing a structure of image forming unit containing toner stirring unit of the present invention. 
     The image forming unit  23  includes a developing device. The developing device has a toner stirring unit as a developer stirring unit. Further, the image forming unit  23  includes a unit body section  41 , in the unit body section  41 , a toner hopper  43  is furnished as a accommodating tank in which toner  42  is accommodated. 
     On the upper of the unit body section  41  of the image forming unit  23 , the toner cartridge  32  is installed for replenishing the toner  42  to the toner keeping space  34  ( FIG. 3 ) formed by the toner hopper  43 . Further, in the unit body section  41 , as shown by  FIG. 3 , the photosensitive drum  26 , the developing roller  28  and the sponge roller  30  are furnished, the sponge roller  30  supplies the toner  42  accommodated in the toner hopper  43  to the developing roller  28 , the developing roller  28  further supplies the toner to the photosensitive drum  26 . 
     In the toner hopper  43 , a stirring bar  44  is furnished as stirring member. 
       FIG. 5  is a summary cubic diagram showing a stirring bar. 
     The stirring bar  44  is made from iron in the embodiment, and is rotatively supported by bearing drive member and bearing member that will be described below. The stirring bar  44 , as shown by  FIG. 5 , has a stirring portion  44   c  that is in parallel with rotation axis; orthogonal portions  44   b  and  44   b ′ that extend from two ends of the stirring portion  44   c  along an orthogonal direction being at right angles to the stirring portion  44   c ; and shaft portions  44   a  and  44   a ′ that are furnished on ends of the orthogonal portions  44   b  and  44   b ′ and serve as rotation shafts coinciding with rotation axis line. The stirring bar  44  regards the shaft portions  44   a  and  44   a ′ as center, rotates along a direction of an arrow A so as to use the stirring portion  44   c  to stir the toner  42  accommodated in the toner hopper  43 . 
     In the image forming unit  23 , the sensor section  35  is placed under the toner hopper  43  as position detection section. 
       FIG. 6A  is a first diagram for explaining structure and operation of a sensor section;  FIG. 6B  is a second diagram for explaining structure and operation of a sensor section; and  FIG. 6C  is a third diagram for explaining structure and operation of a sensor section. 
       FIGS. 6A and 6B  show rotation operation of sensor lever; and  FIG. 6C  is a plane view by observing the sensor lever from the upside (the side of the toner hopper  43 ). 
     The sensor section  35 , as shown by  FIGS. 6A˜6C , is formed to contain a sensor lever  46 . The sensor lever  46 , as shown by  FIGS. 6A and 6B , is formed like a shape of “&lt;” character. On the front edge of the sensor lever  46 , a magnet  47  is furnished. A center portion is supported by a support shaft  48  to be rotatable. 
     Further, near to the back edge of the sensor lever  46 , a sensor  49  is furnished for detecting position of the back edge of the sensor lever  46 . In the embodiment, the sensor  49  is a photo sensor having light emitting element and light receiving element, the sensor  49  detects shining state or shading state and outputs ON/OFF signal to the printer controlling section according to the detection. 
     For example, on the one hand, as shown by  FIG. 6A , the stirring portion  44   c  of the stirring bar  44  locates in a lowermost position of a bearing drive member  45  with which the shaft portion  44   a  is coupled, that is, locates in a position separating from a lower dead point position. In the case, the front edge of the sensor lever  46  locates in a drop position due to deadweight, the sensor  49  detects a shading state on the basis of the position of the back edge of the sensor lever  46 , and outputs an OFF signal. 
     On the other hand, as shown by  FIG. 6B , such case is shown that the stirring portion  44   c  of the stirring bar  44  locates in lower dead point position. In the case, because the magnet  47  is attracted by the stirring bar  44  made from iron, the front edge of the sensor lever  46  rotates to rise along a counterclockwise direction from the state of  FIG. 6A , and the back edge of the sensor lever  46  drops. Meanwhile, the sensor  49  detects a shining state and outputs an OFF signal. 
     The printer controlling section, as position detecting section and judging section, when ON/OFF signal is inputted from the sensor  49 , judges a remainder amount of the toner  42  in the toner hopper  43  on the basis of the signal. That is, when OFF signal is inputted, the printer controlling section judges that the toner remainder amount is not little; when ON signal is inputted, the printer controlling section judges that the toner remainder amount is little. 
     Moreover, as a position detecting section, instead of the sensor section  35 , magnetic sensor also can be applied. In the case, through furnishing a magnet to the inside of the stirring portion  44   c  of the stirring bar  44 , the magnetic sensor detects the strength of magnetic field produced by the magnet. Then, the printer controlling section can obtain position information of the stirring portion  44   c  on the basis of detection information. The printer controlling section performs a judgment of toner remainder amount on the basis of the obtained position information. 
     Next, it is to explain structure of toner stirring unit of the embodiment. 
       FIG. 1A  is a first cross-sectional diagram showing a main structure of toner stirring unit in embodiment 1 of the present invention; and  FIG. 1B  is a second cross-sectional diagram showing a main structure of toner stirring unit in embodiment 1 of the present invention. 
     In a toner stirring unit  50  of the embodiment, on the side wall portion of the toner hopper  43 , a bearing member  51  which supports the stirring bar  44  to possibly rotate, and a bearing drive member  45  are furnished respectively. 
     The bearing member  51  is fixed on the side wall portion of the toner hopper  43 , and couples with the shaft portion  44   a ′ of the stirring bar  44  as shown by  FIGS. 1A and 1B . 
       FIG. 7  is a cubic diagram showing a structure of bearing member. 
     As shown by  FIG. 7 , the bearing member  51  has an open end. As shown by  FIGS. 1A and 1B , the shaft portion  44   a ′ of the stirring bar  44  is inserted into the open end. An inner diameter of the open end of the bearing member  51  is set to be bigger than an outer diameter of the shaft portion  44   a ′ in order to possibly move the stirring bar  44  along a rotation axis direction i.e. a direction of an arrow B ( FIG. 1A ) or a direction of an arrow C ( FIG. 1 ). Further, on the open end, as shown by  FIG. 7 , a slant portion  51   a  is furnished as a bearing slant portion, the bearing member  51  is regulated a position of the stirring bar  44  in the rotation axis direction on the basis of the shape of the slant portion  51   a.    
     The bearing drive member  45 , as bearing member and drive member, is placed on the side wall portion of the toner hopper  43 ; and couples with the shaft portion  44   a  as shown by  FIGS. 1A and 1B . 
       FIG. 8  is a cubic diagram showing a structure of bearing drive member in embodiment 1. 
     The bearing drive member  45 , as shown by  FIG. 8 , has a cylindrical portion  52  and a stirring gear  53  coupled with the cylindrical portion  52 . 
     The cylindrical portion  52  of the bearing drive member  45 , as shown by  FIGS. 1A and 1B , is rotatively supported by the side wall portion of the toner hopper  43 , and the shaft portion  44   a  of the stirring bar  44  is inserted into the cylindrical portion  52 . The inner diameter of the cylindrical portion  52  is also set to be bigger than the outer diameter of the shaft portion  44   a  as well as the inner diameter of the open end of the bearing member  51 . 
     The cylindrical portion  52 , as shown by  FIG. 8 , has a broken part which is formed on the open end. On the broken part, a drive portion  52   a , a slant portion  52   b  and a contact portion  52   c  are formed. 
     The drive portion  52   a  is a part to press the shaft portion  44   a  of the stirring bar  44  and drive the stirring bar  44  to rotate. 
     The slant portion  52   b  regulates the position of the stirring bar  44  in the rotation axis direction on the basis of the shape of itself, as bearing slant portion. 
     The contact portion  52   c  is a part to contact the stirring bar  44  when the stirring bar  44  drops toward the lower dead point position ( FIG. 1B ). 
     The bearing drive member  45  makes one end of the cylindrical portion  52  project toward the outside of the side wall portion of the toner hopper  43 . Then, the stirring gear  53  is coupled with the projecting part. The stirring gear  53  rotates with the rotation of the photosensitive drum  26  ( FIG. 4 ), so as to drive the cylindrical portion  52  to rotate. Regarding these rotations, they are explained by using  FIG. 9 . 
       FIG. 9  is a second cross-sectional side view showing a structure of image forming unit containing toner stirring unit of the present invention. 
     In the image forming unit  23 , as shown by  FIG. 9 , a gear member  54  engaging with the photosensitive drum  26 ; a gear member  55  engaging with the gear member  54 ; and a gear member  56  engaging with the gear member  55  are furnished respectively as a rotation drive mechanism section. 
     Through rotations in the rotation drive mechanism section, the bearing drive member  45  rotates together with the stirring gear  53  and the cylindrical portion  52 . When the drive portion  52   a  of the cylindrical portion  52  contacts with the shaft portion  44   a  of the stirring bar  44 , the stirring bar  44  is pressed through the drive portion  52   a  drives the shaft portion  44   a  so as to rotate together with the bearing drive member  45 . 
     Next, it is to explain rotation operation of the stirring bar  44  in the toner stirring unit  50  in detail. 
     First is to explain stirring operation to stir the toner  42  in the toner stirring unit  50  and remainder amount judging operation of the toner  42  in the printer  10  on which the toner stirring unit  50  is installed by using drawing, in the case that a lot of toner  42  is accommodated in the toner hopper  43 . 
       FIG. 10A  is a first diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention;  FIG. 10B  is a second diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention;  FIG. 10C  is a third diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention;  FIG. 10D  is a fourth diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention; and  FIG. 10E  is a fifth diagram for explaining stirring operation of toner stirring unit when a lot of toner is accommodated in embodiment 1 of the present invention. 
     In the toner stirring unit  50 , the bearing drive member  45  ( FIG. 1 ) rotates at a predetermined speed, synchronously with the rotation of the photosensitive drum  26 , through the rotation drive mechanism section shown by  FIG. 9 . Then, when the drive portion  52   a  of the cylindrical portion  52  contacts the shaft portion  44   a  of the stirring bar  44 , with the rotation of the bearing drive member  45 , the shaft portion  44   a  is pressed by the drive portion  52   a . Thereby, the stirring bar  44  is driven to rotate, and rotates along a direction of an arrow A as shown by  FIGS. 10A and 10B . 
     The bearing drive member  45  and the stirring bar  44  rotate together, as shown by  FIGS. 1A and 10C , when the stirring portion  44   c  of the stirring bar  44  reaches the upper dead point position and slightly passes through the upper dead point position, the stirring bar  44  rotates to drop quicker than the drive portion  52   a  due to deadweight. Then, as shown by  FIG. 10D , the stirring portion  44   c  of the stirring bar  44  reaches the upper surface of the toner  42  accumulated in the toner hopper  43  and stops on the upper surface. That is, it is possible to a remainder amount of the toner  42  in the toner hopper  43  on the basis of a stop position of the stirring portion  44   c.    
     In the printer  10  on which the toner stirring unit  50  is installed, the printer controlling section judges the remainder amount of the toner  42  on the basis of an input signal outputted just after the drive portion  52   a  of the bearing drive member  45  reaches an uppermost position ( FIG. 10C ), from the sensor section  35 . As shown by  FIG. 10D , in the case that the stirring portion  44   c  stops in a position separating from a lower dead point position, the front edge of the sensor lever  46  of the sensor section  35  drops due to deadweight as shown by  FIG. 6A . At that time, the sensor  49  detects a shading state on the basis of a position of the back edge of the sensor lever  46 , and outputs OFF signal. The printer controlling section judges that the stop position of the stirring portion  44   c  is not the lower dead point position, that is, judges that the remainder amount of the toner  42  in the toner hopper  43  is not little, on the basis of the input of the OFF signal outputted from the sensor  49 . 
     The bearing drive member  45  continues to rotate at a predetermined speed after the stirring bar  44  dropped. Then, when the drive portion  52   a  catches up with the stirring bar  44  to contacts with the shaft portion  44   a , the drive portion  52   a  rotates while pressing the shaft portion  44   a . Thereby, the stirring portion  44   c  of the stirring bar  44  is pressed into the toner  42  accumulated in the toner hopper  43 , and rotates while stirring the toner  42  ( FIG. 10E ). Then, the toner stirring unit  50  repeats these operations shown by the  FIGS. 10A˜10E . 
     As stated above, the remainder amount of the toner  42  in the toner hopper  43  is judged on the basis of signal outputted from the sensor section  35 . 
     Next, it is to explain stirring operation to stir the toner  42  in the toner stirring unit  50  and remainder amount judging operation of the toner  42  in the printer  10 , in the case that a little of toner  42  is accommodated in the toner hopper  43 . 
       FIG. 11A  is a first diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention;  FIG. 11B  is a second diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention;  FIG. 11C  is a third diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention;  FIG. 11D  is a fourth diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention; and  FIG. 11E  is a fifth diagram for explaining stirring operation of toner stirring unit when a little toner is accommodated in embodiment 1 of the present invention. 
     When the drive portion  52   a  of the bearing drive member  45  contacts with the shaft portion  44   a  of the stirring bar  44  ( FIG. 11A ), and the drive portion  52   a  rotates while pressing the shaft portion  44   a , the stirring bar  44  rotates along a direction of an arrow A together with the bearing drive member  45  as shown by  FIGS. 11A and 11B . 
     Then, as shown by  FIGS. 1A and 11C , when the stirring portion  44   c  of the stirring bar  44  reaches the upper dead point position and slightly passes through the upper dead point position, the stirring bar  44  rotates to drop quicker than the drive portion  52   a  due to deadweight. At that time, because only a little of the toner  42  is accommodated in the toner hopper  43 , the stirring bar  44  drops to the lower dead point position as shown by  FIG. 11D , and the shaft portion  44   a  collides with the contact portion  52   c  of the bearing drive member  45  and stop operating as shown by  FIG. 1B . At that time, the toner  42  ( FIG. 11C ) which is in the toner hopper  43  and is coagulating and mal-distributing, is stirred by the stirring portion  44   c  so as to spread ( FIG. 11D ). 
     In the printer  10 , the printer controlling section judges the remainder amount of the toner  42  in the toner hopper  43  on the basis of an input signal outputted just after the drive portion  52   a  of the bearing drive member  45  reaches an uppermost position ( FIG. 11C ), from the sensor section  35 . When the stirring portion  44   c  stops in the lower dead point position, the front edge of the sensor lever  46  of the sensor section  35  rises because the magnet  47  is attracted by the stirring bar  44  made from iron, the back edge of the sensor lever  46  drops as shown by  FIG. 6B . Therefore, the sensor  49  detects a shining state and outputs ON signal. The printer controlling section judges that the stop position of the stirring portion  44   c  is the lower dead point position, that is, judges that the remainder amount of the toner  42  in the toner hopper  43  is little, on the basis of the input of the ON signal. 
     The bearing drive member  45  continues to rotate at a predetermined speed, when the drive portion  52   a  contacts with the shaft portion  44   a  of the stirring bar  44 , the drive portion  52   a  rotates together with the stirring bar  44  while pressing the shaft portion  44   a  ( FIG. 11E ). Then, the toner stirring unit  50  repeats these operations shown by the  FIGS. 11A˜11E . 
     As stated above, it is judged that the stirring bar  44  drops to the lower dead point position, and the remainder amount of the toner  42  is little. 
     However, in conventional toner stirring unit, in the case that the remainder amount of toner in toner hopper becomes little, as shown by  FIG. 16B , the stirring bar produces rebound or vibration when dropping to the lower dead point position. Therefore, there is problem that error detection occurs because of chattering phenomenon, and that the remainder amount of toner could not be correctly judged. 
     However, in the toner stirring unit  50  of the embodiment, the stirring bar  44  is supported to possibly rotate along a rotation axis direction through the bearing drive member  45  and the bearing member  51 , when the stirring bar  44  drops toward the lower dead point position due to deadweight, once the orthogonal portion  44   b  contacts with the slant portion  52   b  of the bearing drive member  45 , the orthogonal portion  44   b  smoothly drops along the slant portion  52   b  in the contact state. In the case, the stirring bar  44  moves along a direction of an arrow C shown in  FIG. 1B , as a rotation axis direction, on the basis of the shape of the slant portion  52   b . Through such smooth drop, even if the shaft portion  44   a  of the stirring bar  44  collides with the contact portion  52   c  of the bearing drive member  45 , because such occurrence of rebound or vibration is inhibited, so the chattering phenomenon is prevented from happening. Therefore, the printer  10  can correctly judge the remainder amount of the toner  42  in the toner hopper  43 . 
     Moreover, when the drive portion  52   a  catches up with the stirring bar  44  to contact with the shaft portion  44   a  ( FIG. 11E ), the stirring bar  44  is driven to rotate to upper dead point position by the drive portion  52   a  so as to rise ( FIGS. 11A˜11C ). During the stirring bar  44  rises, once the orthogonal portion  44   b ′ contacts with the slant portion  51   a  of the bearing member  51 , the stirring bar  44  rises while moving along a direction of an arrow B ( FIG. 1A ) i.e. rotation axis direction in the contact state, on the basis of the shape of the slant portion  51   a.    
     As stated above, in the toner stirring unit and the printer of the embodiment, slant portions are furnished on bearing member and bearing drive member, through the bearing member and the bearing drive member, stirring bar is supported to possibly rotate and possibly move along rotation axis direction. Therefore, it is possible to inhibit rebound or vibration when stirring bar drops. As a result, it is possible to correctly judge remainder amount of toner. 
     Embodiment 2 
       FIG. 12A  is a first cross-sectional diagram showing a main structure of toner stirring unit in embodiment 2 of the present invention; and  FIG. 12B  is a second cross-sectional diagram showing a main structure of toner stirring unit in embodiment 2 of the present invention. 
       FIG. 12A  shows that a stirring portion  44   c  of a stirring bar  44  locates in an upper dead point position in a toner stirring unit  60 ; and  FIG. 12B  shows that a stirring portion  44   c  of a stirring bar  44  locates in a lower dead point position in a toner stirring unit  60 . 
     A toner stirring unit  60  of the embodiment is different from embodiment 1 to furnish a slant portion  61   a  on a toner hopper  61 . 
     Moreover, in the embodiment, regarding the same component as that in embodiment 1, it is set to have the same symbol, and its detail explanation is omitted. 
     In the toner stirring unit  60 , on side wall portion of the toner hopper  61 , bearing member  62  and bearing drive member  45  to support the stirring bar  44  to possibly rotate, are furnished respectively. 
     The bearing member  62  is fixed on the side wall portion of the toner hopper  61 , and shaft portion  44   a ′ of the stirring bar  44  is inserted into an open end of the bearing member  62  as shown by  FIGS. 12A and 12B . An inner diameter of the open end of the bearing member  62  is set to be bigger than an outer diameter of the shaft portion  44   a ′ in order to possibly move the stirring bar  44  along a rotation axis direction. 
     Further, on the open end, as shown by  FIGS. 12A and 12B , a slant portion  61   a  is furnished as a bearing slant portion. On the basis of the shape of the slant portion  61   a , the stirring bar  44  is regulated about a position in the rotation axis direction. 
     Regarding stirring operation of the toner stirring unit  60  in the embodiment, it is similar to embodiment 1. 
     In the case that remainder amount of toner in the toner hopper  61  is little, the stirring bar  44 , after being driven to rotate to an upper dead point position by a bearing drive member  45 , drops toward the lower dead point position due to deadweight. Then, once the orthogonal portion  44   b  contacts with the bearing drive member  45 , the stirring bar  44  smoothly drops along the slant portion  61   a  while moving along a direction of an arrow C in  FIG. 12B ; and the shaft portion  44   a  collides with the contact portion  52   c  of the bearing drive member  45  and stops operating. In the case, because such occurrence of rebound or vibration is inhibited, so it is possible to correctly judge the remainder amount of toner. 
     Moreover, when the stirring bar  44  is driven to rotate to an upper dead point position by the bearing drive member  45 , once the orthogonal portion  44   b ′ contacts with the slant portion  61   a  of the toner hopper  61 , the stirring bar  44  rises while moving along a direction of an arrow D ( FIG. 12A ) in the contact state, on the basis of the shape of the slant portion  61   a.    
     As stated above, in the toner stirring unit of the embodiment, by comparison with embodiment 1, instead of the slant portion furnished on the bearing member, through furnishing such slant portion on the toner hopper, it is possible to obtain the same effect as that in the embodiment 1. Therefore, it is possible to inhibit chattering phenomenon from happening. As a result, it is possible to correctly judge remainder amount of toner. 
     Embodiment 3 
       FIG. 13  is a cross-sectional diagram showing a structure of bearing drive member in embodiment 3. 
     In the toner stirring unit of the embodiment, the shape of a slant portion  72   b  furnished on cylindrical portion  72  of bearing drive member  71  is different from that in embodiment 1. 
     Moreover, in the embodiment, regarding the same component as that in embodiment 1, it is set to have the same symbol, and its detail explanation is omitted. 
     In the toner stirring unit of the embodiment, the bearing drive member  71 , as bearing member and driving section, has a cylindrical portion  72 , and a stirring gear  53  coupled with the cylindrical portion  72 . 
     The cylindrical portion  72  of the bearing drive member  71 , as shown by  FIG. 13 , has a broken part formed on its open end. On the broken part, a drive portion  72   a , a slant portion  72   b  and a contact portion  72   c  are formed. 
     In the bearing drive member  45  of embodiment 1, the slant portion  52   b  is formed by cutting the cylindrical portion  52  in straight line shape. However, in the embodiment, in the bearing drive member  71  of the embodiment, as shown by  FIG. 13 , the slant portion  72   b  is formed by cutting the cylindrical portion  72  in an arc shape. 
     Regarding stirring operation of the toner stirring unit in the embodiment, it is similar to embodiment 1. 
     In the case that remainder amount of toner  42  in the toner hopper  43  is little, the stirring bar  44 , after being driven to rotate to an upper dead point position by a bearing drive member  71 , drops toward the lower dead point position due to deadweight. Then, in a state that the orthogonal portion  44   b  contacts with the bearing drive member  71 , the stirring bar  44  smoothly drops along the slant portion  61   a  while moving along a rotation axis direction; and the shaft portion  44   a  collides with the contact portion  72   c  of the bearing drive member  71  and stops operating. During dropping, because the stirring bar  44  can further smoothly drop on the basis of the shape of the slant portion  72   b , so it is possible to further inhibit rebound or vibration of the stirring bar  44  from occurring. 
     As stated above, in the toner stirring unit of the embodiment, through forming the slant portion of bearing drive member into arc shape, it is possible to further inhibit chattering phenomenon from happening. As a result, it is possible to further correctly judge remainder amount of toner. 
     Embodiment 4 
       FIG. 14  is a cross-sectional diagram showing a main structure of toner stirring unit in embodiment 4 of the present invention. 
     In a toner stirring unit  80  of the embodiment, a structure is different from embodiment 1 to form a spring  82  supplying elastic force to bearing member  81 . 
     Moreover, in the embodiment, regarding the same component as that in embodiment 1, it is set to have the same symbol, and its detail explanation is omitted. 
     In the toner stirring unit  80  of the embodiment, on side wall portion of a toner hopper  83 , bearing member  81  and bearing drive member  45  to support the stirring bar  44  to possibly rotate, are furnished respectively. 
     The bearing member  81  is placed on the side wall portion of the toner hopper  83 , and shaft portion  44   a ′ of the stirring bar  44  is supported to rotate possibly. 
     In the bearing member  81 , as shown by  FIG. 14 , the spring  82 , as force supplying member, is placed on the back side of a support plane to support the stirring bar  44 . The spring  82  is furnished in a shrinking state in comparison with nature length, so that its one end is fixed on the bearing member  81 , and its other end is fixed on inner plane of the toner hopper  83 . Then, the spring  82  always supplies elastic force to the bearing member  81  and the stirring bar  44  supported by the bearing member  81  along a direction of an arrow F i.e. rotation axis direction. 
     Regarding stirring operation of the toner stirring unit  80  in the embodiment, it is similar to embodiment 1. 
     The stirring bar  44  rotates while its position is regulated in the rotation axis direction on the basis of the elastic force supplied by the bearing member  81  via the bearing member  81  and on the basis of the shape of the bearing drive member  45 . Then, because the stirring bar  44  smoothly drops due to deadweight along the slant portion  52   b  of the bearing drive member  45 , when the stirring bar  44  collides with the contact portion  52   c , such occurrence of rebound or vibration is inhibited. 
     As stated above, in the toner stirring unit of the embodiment, through furnishing bearing member to move possibly along rotation axis direction and furnishing a spring to supply elastic force to the stirring bar via the bearing member, it is possible to inhibit chattering phenomenon from happening. As a result, it is possible to correctly judge remainder amount of toner. 
     Embodiment 5 
       FIG. 15  is a cross-sectional diagram showing a structure of bearing drive member in embodiment 5. 
     The toner stirring unit of the embodiment has a similar structure to the toner stirring unit  80  of embodiment 4, but the shape of a slant portion  92   b  of a cylindrical portion  92  of bearing drive member  91  is different from that in embodiment 4. 
     Moreover, in the embodiment, regarding the same component as that in embodiment 4, it is set to have the same symbol, and its detail explanation is omitted. 
     In the toner stirring unit of the embodiment, the bearing drive member  91 , as bearing member and driving section, has a cylindrical portion  92 , and a stirring gear  53  coupled with the cylindrical portion  92 . 
     The cylindrical portion  92  of the bearing drive member  91 , as shown by  FIG. 15 , has a drive portion  92   a , a slant portion  92   b  and a contact portion  92   c.    
     In the bearing drive member  45  of embodiments 1 and 4, the slant portion  52   b  is formed by cutting the cylindrical portion  52  from an approximate center portion toward open end. However, in the embodiment, in the bearing drive member  91  of the embodiment, as shown by  FIG. 15 , the slant portion  92   b  is formed by cutting the cylindrical portion  92  from an approximate center portion toward a coupling part with the stirring gear  53 . 
     Regarding stirring operation of the toner stirring unit in the embodiment, it is similar to embodiment 4. 
     The stirring bar  44  rotates while its position is regulated in the rotation axis direction, after passed through the upper dead point position, then, smoothly drops due to deadweight along the slant portion  92   b  of the bearing drive member  91 . Therefore, when the stirring bar  44  collides with the contact portion  92   c , such occurrence of rebound or vibration is inhibited. 
     As stated above, in the toner stirring unit of the embodiment, through changing the shape of the slant portion of the bearing drive member together with supplying elastic force to the stirring bar, it is possible to obtain the same effect as the embodiment 4. As a result, it is possible to correctly judge remainder amount of toner. 
     The Utilization Possibility in Industry 
     In respective embodiments of the present invention, the bearing drive member, as bearing member, includes a slant portion that, as bearing slant portion, has a slant with respect to a direction of rotation axis, on a contact portion with stirring bar serving as stirring member; and the stirring bar moves along an axis direction of rotation axis together with rotating along rotation direction of rotation axis. However, the present invention is not limited in these embodiments. 
     Further, in the above stated explanation, only such case is explained that the present invention is applied to a printer as an image forming apparatus on which a developing device having a toner stirring unit is installed. However, the present invention is not limited in this case. The present invention also can be applied to various devices such as monochrome printer, copying apparatus, facsimile apparatus, multiplex apparatus having two functions or over and the like. 
     The present invention is not limited to the foregoing embodiments but many modifications and variations are possible within the spirit and scope of the appended claims of the invention.