Patent Publication Number: US-10331059-B2

Title: Developing device and image forming apparatus having a toner concentration detector and a retaining member that retains the developer in the toner concentration detecting region

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2016-020015 filed Feb. 4, 2016. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a developing device and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, a developing device includes a developer holding member that holds a developer, a supplying member that supplies the developer to the developer holding member, a transport member that transports the developer while passing the developer onto the supplying member through a passing member, the transport member including a discharge unit that discharges excess developer and that is provided downstream of the passing member in a transport direction, a detecting unit that is provided upstream of the discharge unit in the transport direction and that detects a toner concentration, and a retaining member that includes a non-application portion that prevents action of a force for transporting the developer radially outward and that retains the developer in a region corresponding to the detecting unit of the transport member, 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is an overall configuration diagram illustrating an image forming apparatus to which a developing device according to a first exemplary embodiment of the invention is applied; 
         FIG. 2  is a configuration diagram illustrating an image forming unit of the image forming apparatus according to the first exemplary embodiment of the invention; 
         FIG. 3A  is a front view illustrating a configuration of the developing device according to the first exemplary embodiment of the invention; 
         FIG. 3B  is a plan view illustrating a configuration of the developing device excluding an upper housing; 
         FIG. 4  is a plan view illustrating configurations of main parts of the developing device according to the first exemplary embodiment of the invention; 
         FIG. 5  is a front view illustrating a configuration of an agitation transporting member; 
         FIG. 6  is a perspective view illustrating the configuration of the agitation transporting member; 
         FIG. 7  is a configuration diagram illustrating an effect of an agitation transporting member in the related art; 
         FIG. 8  is a configuration diagram illustrating an effect of the agitation transporting member according to the first exemplary embodiment; 
         FIG. 9  is a graph illustrating an experiment example; 
         FIG. 10  is a graph illustrating a reference example; 
         FIG. 11  is a graph illustrating a comparative example; and 
         FIGS. 12A to 12G  are configuration diagrams each illustrating main parts of a developing device according to a second exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the exemplary embodiments of the invention will be described with reference to the drawings. 
     First Exemplary Embodiment 
       FIG. 1 . illustrates an overall configuration of an image forming apparatus to which a developing device according to a first exemplary embodiment of the invention is applied.  FIG. 2  an enlarged view illustrating main parts (including an image forming device) of the image forming apparatus. 
     Entire Configuration of Image Forming Apparatus 
     An image forming apparatus  1  according to the first exemplary embodiment is configured as, for example, a color printer. The image forming apparatus I includes plural image forming devices  10  that form a toner image which is developed with toners which configure developer, an intermediate transfer device  20  that holds each of the toner images formed by each of the image forming devices  10  and that transports the toner image to a secondary transfer position at which the toner image is finally secondarily transferred onto recording paper  5 , which is an example of a recording medium, a paper feeding device  50  that houses and transports the recording paper  5  which is required to be supplied to the secondary transfer position of the intermediate transfer device  20 , and a fixing device  40  that fixes the toner image which has been secondarily transferred by the intermediate transfer device  20  on the recording paper  5 . In  FIG. 1 , a main body of the image forming apparatus  1  is indicated by  1   a , and the main body la includes a supporting structure member, an exterior cover, and the like. In addition, a dashed line in  FIG. 1  indicates a main transporting path on which the recording paper  5  is transported in the apparatus main body  1  a. 
     The image forming devices  10  are configured with the four image forming devices  10 Y,  10 M,  10 C, and  10 K that are dedicated to form a toner image in each of four colors, such as yellow (Y), magenta (M), cyan (C), and black (K). These four image forming devices  10  (Y, M, C, and K) are disposed so as to be arranged in one line in a space inside the main body la in a horizontal direction. 
     As illustrated in  FIG. 1  and  FIG. 2 , the image forming devices  10  (Y, M, C, and K) include rotating photoconductor drums  11  (Y, M, C, and K) respectively, which are an example of an image carrier. In the vicinity of the photoconductor drams  11  (Y, M, C, and K), mainly the following devices are disposed as an example of a toner image forming unit. The devices that are mainly disposed are charging devices  12  (Y, M, C, and K) that charge a circumferential surface (image holding surface) of the photoconductor drums  11  (Y, M, C, and K) on which image forming is possible such that the circumferential surface is charged to have the required electric potential, exposure devices  13  (Y, M, C, and K) that irradiate the charged circumferential surfaces of the photoconductor drums  11  (Y, M, C, and K) with light based on image information (signal) to form an electrostatic latent image in each color which has a potential difference, developing devices  14  (Y, M, C, and K) that are an example of a developing unit which develop the electrostatic latent image with the toner in the developer in the corresponding color (Y, M, C, and K) and turn into a toner image, primary transfer devices  15  (Y, M, C, and K) that are an example of a primary transfer unit which transfers each of the toner images onto the intermediate transfer device  20 , and drum cleaning devices  16  (Y, M, C, and K) that clean the image holding surface of the photoconductor drum  11  after a primary transfer by eliminating attached substances, such as the toner which has remained and attached to the image holding surface. 
     The photoconductor drum  11  forms the image holding surface that has a photoconductive layer (photosensitive layer), which is made of photosensitive materials, on the grounded circumferential surface of a cylindrical or columnar base member. The photoconductor drum  11  is supported so as to be capable of rotating in a direction indicated by an arrow A by motive power being transmitted from a driving device (not illustrated), 
     The charging device  12  is configured as a contact-type charging roll that is disposed in a state of maintaining contact with the photoconductor drum  11 . Charging voltage is supplied to the charging device  12 . In a case where the developing device  14  conducts reversal developing, electric current or voltage that has the same polarity with the toner charging polarity (negative polarity) supplied from the developing device  14  is supplied as the charging voltage. A non-contact type charging device including a scorotron that is disposed in a state of not being in contact with the surface of the photoconductor drum  11  maybe used as the charging device  12 . 
     The exposure device  13  forms an electrostatic latent image by the charged circumferential surface of the photoconductor drum  11  being deflection-scanned by the semiconductor laser  131  emitting light (a solid line with an arrowhead) configured depending on image information input to the image forming apparatus I. The exposure devices  13  corresponding to the image forming devices  10 Y,  10 M,  10 C, and  10 K for yellow (Y), magenta (M), cyan (C), and black (K) are provided. Once it becomes time to form a latent image, full-color or black-and-white image information (signal) input to the image forming apparatus  1  by any unit is transmitted to the exposure device  13 . As the exposure device  13 , an LED printer head may be used, which forms an electrostatic latent image by the photoconductor drum  11  being irradiated with light corresponding to image information, emitted by a light emitting diode (LED) that includes plural light emitting elements placed along an axial direction of each photoconductor drum  11  of the image forming device  10 . 
     As illustrated in  FIG. 2 , each of the developing devices  14  (Y, M, C, and K) includes a developing roll  141 , a supply transport member  142 , an agitation transport member  143 , a layer thickness regulating member  144 , and the like being disposed in a device housing  140  in which an opening portion and a housing chamber for the developer  4  are formed. The developing roll  141  is an example of a developer holding member that holds and transports the developer  4  to a developing region which faces the photoconductor drum  11 . The supply transport member  142 , including a screw auger, agitates and supplies the developer  4  to the developing roil  141 . The agitation transport member  143 , including the screw auger, agitates and transports the developer  4  while exchanging the developer  4  with the supply transport member  142 . The layer thickness regulating member  144  regulates an amount of the developer (layer thickness) held by the developing roll  141 . A two-component developer that contains a non-magnetic toner and magnetic carrier is used as the developer  4  in each of the four colors (Y, M, C, and K). The developing devices  14  (Y, M, C, and K) will be described in detail later. 
     The primary transfer devices  15  (Y, M, C, and K) are contact-type transfer devices that rotate while maintaining contact with the circumference of the photoconductor drum  11  via an intermediate transfer belt  21  and that include a primary transfer roll to which primary transfer voltage is supplied. As the primary transfer voltage, voltage of direct current that has reverse polarity with respect to the toner charging polarity is supplied from a power source device (not illustrated). 
     As illustrated in  FIG. 2 , the drum cleaning device  16  includes a container-shaped main body  16   a  of which a part is opened, a cleaning plate  16   b  that is disposed so as to be in contact with, at a required pressure, the circumferential surface of the photoconductor drum  11  after the primary transfer, and that cleans the photoconductor drum  11  by eliminating attached substances, including a residual toner, and a sending member  16   c , including the screw auger, which recovers and transports the attached substances, including the toner, eliminated by the cleaning plate  16   b  so as to be sent out to a recovery system (not illustrated), and the like. A plate shaped member (for example, cleaning blade) made of rubber or the like is used as the cleaning plate  16   b.    
     As illustrated in  FIG. 1 , the intermediate transfer device  20  is disposed at a position below each of the image forming devices  10  (Y, M, C, and K). The intermediate transfer device  20  mainly includes the intermediate transfer belt  21 , plural belt supporting rolls  22  to  26 , a secondary transfer device  30 , and a belt cleaning device  27 . The intermediate transfer belt  21  passes through a primary transfer position between the photoconductor drum  11  and the primary transfer device  15  (primary transfer roll), and rotates in a direction indicated by an arrow B. The plural belt supporting rolls  22  to  26  rotatably support the intermediate transfer belt  21  by holding the intermediate transfer belt  21  from an inner surface thereof in a desirable state. The secondary transfer device  30  is an example of a secondary transfer unit that has a secondary transfer roll  31  which is disposed on an outer peripheral surface (image holding surface) side of the intermediate transfer belt  21  supported by the belt supporting roll  26 , and that secondarily transfers the toner image on the intermediate transfer belt  21  onto the recording paper  5 . The belt cleaning device  27  cleans the intermediate transfer belt  21  by eliminating the attached substances, including paper dust and a toner that remain on and are attached to the outer peripheral surface of the intermediate transfer belt  21 , after passing through the secondary transfer device  30 . 
     An endless belt that is made of, for example, a material obtained by a carbon black or other resistance adjusting agents being dispersed in a polyimide resin, a polyamide resin or other synthetic resins is used as the intermediate transfer belt  21 . In addition, the belt supporting roll  22  is configured as a driving roll that is rotation-driven by the driving device (not illustrated). The belt supporting rolls  23  and  24  are configured as surfacing rolls that form image forming surfaces of the intermediate transfer belt  21 . The belt supporting roll  25  is configured as a tension applying roll that exerts tension on the intermediate transfer belt  21 , and as a meandering correction roll that corrects the belt walk of the intermediate transfer belt  21 . The belt supporting roll  26  is configured as a rear surface supporting roll of the secondary transfer. 
     As illustrated in  FIG. 1 , the secondary transfer device  30  is a contact-type transfer device that is provided with the secondary transfer roll  31  which rotates while maintaining contact with the peripheral surface of the intermediate transfer belt  21  and which configures the secondary transfer unit to which secondary transfer voltage is supplied, in the secondary transfer position that is an outer peripheral surface portion of the intermediate transfer belt  21  supported by the belt supporting roll  26  of the intermediate transfer device  20 . The secondary transfer device  30  includes the secondary transfer roll  31  and the belt supporting roll  26  that is a backup roll. In addition, the voltage of direct current that has the opposite polarity to the toner charging polarity or the same polarity as the toner charging polarity is supplied as the secondary transfer voltage to the secondary transfer roll  31  or the belt supporting roll  26 . 
     The belt cleaning device  27  has the same configuration as that of the chum cleaning device  16 . The belt cleaning device  27  includes a container-shaped main body of which a part is opened, a cleaning plate (not illustrated) that is disposed so as to be in contact with, at a required pressure, the peripheral surface of the intermediate transfer belt  21  after the secondary transfer, and that cleans the intermediate transfer belt  21  by eliminating the attached substances, including a residual toner, and a sending member (not illustrated), including the screw auger, which recovers and transports the attached substances, including the toner, eliminated by the cleaning plate so as to be sent out to a recovery system, and the like. 
     The fixing device  40  includes a heating rotation member  41 , a pressurizing rotating body  42 , and the like. The heating rotation member  41  is in the form of a belt or roll heated by a heating unit such that a surface temperature thereof is maintained at a required temperature. The pressurizing rotating body  42  is in the form of a roll or a belt that rotates in a substantially axial direction of the heating rotation member  41  while maintaining contact with the heating rotation member  41  at a predetermined pressure. In the fixing device  40 , a contact portion in which the heating rotation member  41  is in contact with the pressurizing rotating body  42  is a fixing processing portion that conducts required fixing processing (heating and pressurizing). 
     The paper feeding device  50  is disposed at a position below the intermediate transfer device  20 . The paper feeding device  50  mainly include plural paper housing members (or a single paper housing member)  51  that house a desirable size and type of the recording paper  5  in a state of being stacked, and a sending device  52  that sends out the recording paper  5  one at a time from the paper housing member  51 . The paper housing member  51  is attached, for example, such that the paper housing member  51  may be pulled toward the front side of the main body la (side where a user faces when operating the apparatus). 
     Examples of the recording paper  5  include plain paper that is used in an electrophotographic system copying machine and printer, thin paper including tracing paper, and an OHP sheet. It is preferable to make the surface of the recording paper  5  as smooth as possible, and for example, coated paper that is obtained by coating the surface of plain paper with a resin or the like, art paper for printing and other so-called pasteboards which have a relatively heavy basis weight may be appropriately used in order to further improve the smoothness of image surface after the fixing. 
     A sheet transporting path  55  including plural paper transport roll pairs (or single paper transport roll pair)  53  and  54  that transport the recording paper  5 , which has been sent out from the paper feeding device  50 , to the secondary transfer position, and a transporting guide (not illustrated) is provided between the paper feeding device  50  and the secondary transfer device  30 . The paper transport roll pair  54 , for example, is configured as rolls (registration rolls) that adjust the transport timing of the recording paper  5 . In addition, a transporting belt  56  that transports the recording paper  5  after the secondary transfer, which has been sent out from the secondary transfer roll  31  of the secondary transfer device  30 , to the fixing device  40  is provided between the secondary transfer device  30  and the fixing device  40 . A paper output roll pair  57  that outputs the fixed recording paper  5 , which has been sent out from the fixing device  40 , to a paper output unit (not illustrated) provided on a side surface of the main body la is disposed in a portion close to a paper output port formed in the main body  1   a.    
     In addition, the paper feeding device  50  includes plural paper transport roll pairs  58  that transport the recording paper  5  from a paper housing member (not illustrated) which is large in capacity and is disposed outside the main body la, and a sheet transporting path  59  including a transporting guide (not illustrated), and the like. 
     In  FIG. 1 , each of plural reference numerals  145  (Y, M, C, and K) are placed in a direction orthogonal to the surface of the paper, and each indicates a toner cartridge that houses at least a developer containing a toner to be supplied to the corresponding developing devices  14  (Y, M, C, and. K). In this exemplary embodiment, the toner is housed in the toner cartridges  145  (Y, M, C, and K), and the toner is replenished with a small amount of carrier for trickle development. 
     In addition, a reference numeral  100  in  FIG. 1  indicates a control unit that performs an overall control of an operation of the image forming apparatus  1 . The control unit  100  includes a central processing unit (CPU) (not illustrated), a read-only memory (ROM), a random access memory (RAM), a bus that connects the CPU, the ROM, and the like, and a communication interface. 
     Operation of Image Forming Apparatus 
     Hereinafter, a basic image forming operation conducted by the image forming apparatus  1  will be described. 
     Here, an operation of forming a full-color image formed by toner images in four colors (Y, M, C, and K) in combination by using the four image forming devices  10  (Y, M, C, and K) will be described. 
     Once the image forming apparatus  1  receives command information requiring an image forming operation (printing), the four image forming devices  10  (Y, M, C, and K), the intermediate transfer device  20 , the secondary transfer device  30 , the fixing device  40 , and the like start. 
     In each of the image forming devices  10  (Y, M, C, and K), first, each of the photoconductor drums  11  rotates in the direction indicated by the arrow A, and each of the charging devices  12  charges a surface of each of the photoconductor drums  11  to have required polarity (negative polarity in the first exemplary embodiment) and electric potential. Then, each of the exposure devices  13  irradiates the charged surface of the photoconductor drum  11  with light emitted based on an image signal obtained by converting image information input in the image forming apparatus  1  to each of color components (Y, M, C, and K), and forms, on the surface, an electrostatic latent image in each color component configured by required potential difference. 
     Then, each of the image forming devices  10  (Y, M, C, and K) supplies the corresponding color (Y, M, C, and K) toners that have been charged to have the required polarity (negative polarity) from each of the developing rolls  141  to electrostatically attach the corresponding color toner onto the electrostatic latent image in each color component formed on the photoconductor drum  11 , thereby developing the electrostatic latent image. As a result of the developing, the electrostatic latent image in each color component formed on the photoconductor drum  11  is obtained as a toner image in each of the four colors (Y, M, C, and K) that has been developed with each of the corresponding color toners. 
     Next, once the toner image in each color formed on the photoconductor drum  11  of each of the image forming devices  10  (Y, M, C, and K) is transported to the primary transfer position, the primary transfer device  15  primarily transfers the toner image in each color such that the toner images are sequentially superimposed on the intermediate transfer belt  21  of intermediate transfer device  20  which rotates in the direction indicated by the arrow B. 
     In addition, in each of the image forming devices  10  in which the primary transfer has been completed, the drum cleaning device  16  scrapes and removes the attached substances to clean the surface of the photoconductor drum  11 . Accordingly, each of the image forming devices  10  returns to a state where another image forming operation can be implemented. 
     Next, the intermediate transfer device  20  holds the toner image primarily transferred by the rotation of the intermediate transfer belt  21 , and transports to the secondary transfer position. The paper feeding device  50  sends out the required recording paper  5  onto the sheet transporting path  55  in accordance with the image forming operation. On the sheet transporting path  55 , the paper transport roll pair  54  that is the registration roll sends out and supplies the recording paper  5  to the secondary transfer position in accordance with transfer timing. 
     The secondary transfer roll  31  of the secondary transfer device  30  collectively and secondarily transfers the toner image on the intermediate transfer belt  21  onto the recording paper  5  at the secondary transfer position. In addition, in the intermediate transfer device  20  in which the secondary transfer has been completed, the belt cleaning device  27  cleans the intermediate transfer belt  21  by eliminating the toner and other attached substances that have remained on the surface of the intermediate transfer belt  21  after the secondary transfer. 
     Next, the recording paper  5  on which the toner image has been secondarily transferred is transported to the fixing device  40  via the transporting belt  56  after being peeled off from the intermediate transfer belt  21  and the secondary transfer roll  31 . In the fixing device  40 , necessary fixing processing (heating and pressurizing) is implemented, and an unfixed toner image is fixed onto the recording paper  5  by the secondarily transferred recording paper  5  being put at and then passed through the contact portion between the rotating heating rotation member  41  and the rotating pressurizing rotating body  42 . Finally, when an image forming operation in which an image is formed only on one side is implemented, the recording paper  5  on which fixing has been completed is output by the paper output roll pair  57  to the paper output unit (not illustrated) disposed in the side of the main body  1   a.    
     As a result of the operation described above, the recording paper  5  on which a full-color image formed by the four color toner images in combination is formed is printed out. 
     Configuration of Developing Device 
       FIG. 2  is a sectional view illustrating a configuration of the developing device according to the first exemplary embodiment. 
     The developing device  14  includes the device housing  140  that is an example of a device housing member. The device housing  140  mainly has a lower housing  140   a  that is disposed in a lower portion of the developing device  14 , and an upper housing  140   b  that is disposed in an upper portion of the developing device  14 . The lower housing  140   a  and the upper housing  140   b  are bonded to each other via a spacer member (not illustrated), and a developer housing chamber  146  that houses the two-component developer  4  is fainted in the device housing  140 . An opening portion  147  is provided in a region of the device housing  140  facing the photoconductor drum  11 . In addition, in the device housing  140 , the developing roll  141  that is an example of the developer holding member is disposed so as to be capable of rotating in an arrow direction such that a part thereof is exposed from the opening portion  147 . The developing roll  141  is disposed so as to be fixed to an inner portion, and has a magnet roll  141   b  in which a magnetic pole of required polarity is disposed at a required position, and a developing sleeve  141   a  that is disposed in an outer circumference of the magnet roll  141   b  so as to be rotatable at a required speed in the arrow direction. The developing sleeve  141   a  is shaped into a cylinder made of nonmagnetic materials, such as aluminum and n on-magnetic stainless steel. 
     In the exemplary embodiment, the rotation direction of the developing sleeve  141   a  is set to a direction reverse to the rotation direction of the photoconductor drum  11 . In other words, the rotation direction of the photoconductor drum  11  is set to a clockwise direction as illustrated in  FIG. 2 . On the other hand, the rotation direction of the developing sleeve  141   a  is set to a counterclockwise direction. As a result, the outer circumferential surface of the developing sleeve  141   a  in the developing region facing the photoconductor drum  11  moves in the same direction as a moving direction of the surface of the photoconductor drum  11 . The rotation direction of the developing sleeve  141   a  may be set to the same direction as the rotation direction of the photoconductor drum  11 . 
     The supply transporting member  142  that includes a screw auger (supply auger) which pumps up the developer  4  in the developer housing chamber  146  and supplies to the developing roll  141  is disposed obliquely downward with respect to the developing roll  141  in the device housing  140 . The agitation transporting member  143  that includes a screw auger (admix auger) which agitates and transports the developer  4  supplied into the device housing  140  is disposed on a rear surface side in the horizontal direction of the supply transporting member  142  in the device housing  140 . The agitation transporting member  143  is rotation-driven in the clockwise direction by the driving device (not illustrated). 
     Since the supply transporting member  142  and the agitation transporting member  143  are housed in the lower housing  140   a , a first housing portion  148  and a second housing portion  149  that are shaped into a substantially semi-cylinder are provided. The first housing portion  148  and the second housing portion  149  are partitioned by a partition wall  150  that is provided in the lower housing  140   a.    
     In addition, first and second passage portions  151  and  152  that pass on the developer  4  are respectively provided at both ends in a longitudinal direction of the partition wall  150  between the supply transporting member  142  and the agitation transporting member  143  as illustrated in  FIG. 3B . In addition, one end of the agitation transporting member  143  in the axial direction thereof extends so as to protrude toward a rear surface side of the device housing  140 . A rectangular tubular supplying unit  153  corresponding to an extended portion  143   c  of the agitation transporting member  143  is provided so as to protrude in the device housing  140 . In addition, a supply port  154  to which the developer  4  in a color corresponding to the toner cartridges  145  (Y, M, C, and K) is supplied is opened to an upper surface of the supplying unit  153 . 
     The supply transporting member  142  and the agitation transporting member  143  have rotary shafts  142   a  and  143   a  that are shaped into a column, and transporting blades  142   b  and  143   b  that are shaped into a spiral so as to be integrated with the outer circumferences of the rotary shafts  142   a  and  143   a  in the axial direction as illustrated in  FIG. 3B . 
     In the course of using the developing device  14 , the developer  4  degrades with time by the toner, external additives of the toner, or the like being attached to the carrier that configure the two-component developer  4 . The performance of the carrier to triboelectrically charge the toner deteriorates when the toner and the carrier are agitated and transported in a state of being mixed together. It is known that, once the performance of the carrier to triboelectrically charge the toner deteriorates, the toner does not get charged successfully and deterioration of image quality, including decreased concentration and fogging, attributable to unsuccessful charging occurs. 
     In the developing device  14  according to the exemplary embodiment, a so-called trickle development method is adopted in which excessive developer out of the developer  4  housed in the device housing  140  is gradually discharged to the outside while the developer  4  that contains the carrier is supplied to the device housing  140  of the developing device  14 , in order to suppress the deterioration of image quality due to the unsuccessfully charged toner. 
     As illustrated in  FIG. 4 , in the device housing  140  of the developing device  14 , the discharge transport blades  155  are provided in an end of the agitation transporting member  143  on a downstream side in the transport direction. The discharge transport blades  155  discharge the excess developer  4 . A transport direction in which the discharge transport blades  155  transport the developer  4  is opposite to that in which the transport blades  143   b  of the agitation transporting member  143  transport the developer  4 . In addition, a pitch of the discharge transport blades  155  is set to be narrower (smaller) than that of the transport blades  143   b  of the agitation transporting member  143 . The discharge transport blade  155  has a lower developer transport capacity than the transport blade  143   b  of the agitation transporting member  143 . The discharge transport blades  155  transport the developer  4 , which is transported to the downstream side by the transport blades  143   b  of the agitation transporting member  143  in accordance with the rotation of the agitation transporting member  143 , so as to push the developer  4  back to the upstream side. The developer  4  pushed back to the upstream side passes through the first passage portion  151 , and then the developer  4  is passed onto the supply transporting member  142 . Accordingly, a total amount of the developer  4  housed in the device housing  140  is usually maintained at a required value. 
     Excess developer out of the developer  4  that is housed in the second housing portion  149  and that is transported to the downstream side by the transport blades  143   b  of the agitation transporting member  143  crosses the discharge transport blades  155  and is transported to the downstream side in a case where the total amount of the developer  4  housed in the device housing  140  of the developing device  14  exceeds the required value. The agitation transporting member  143  is provided with auxiliary transport blades  156  downstream of the discharge transport blades  155  as illustrated in  FIG. 5 . The auxiliary transport blades  156  transport the developer  4  to the downstream side of the agitation transporting member  143  in the transport direction. A pitch of the auxiliary transport blades  156  is substantially equal to the pitch of the discharge transport blades  155 , and the outer diameter of the auxiliary transport blade  156  is set to be smaller than that of the discharge transport blade  155 . In addition, a transporting passage (not illustrated) formed in the outer circumference of the auxiliary transporting blade  156  is set to be small in accordance with the outer diameter of the auxiliary transporting blade  156 . Accordingly, an amount of the developer transported by the auxiliary transport blades  156  is significantly smaller than an amount of the developer transported by the discharge transport blades  155 . In addition, in the device housing  140  disposed in a front end of the auxiliary transporting blades  156  in the axial direction, a discharge port (not illustrated) that discharges the excess developer outside the device housing  140  is provided to open downward. The excess developer that has been discharged from the discharge port is recovered by a recovery device (not illustrated). 
     In addition, in the exemplary embodiment, a toner concentration sensor  160  that is an example of a detecting unit is provided upstream of the discharge transport blades  155  in the transport direction as illustrated in  FIG. 4 . The toner concentration sensor  160  detects a toner concentration of the developer  4  housed in the device housing  140 . The discharge transport blades  155  discharges the excess developer in the developer  4 . The toner concentration sensor  160  is disposed at a position adjacent to the end of the agitation transporting member  143  on the downstream side in the transport direction and adjacent to an upstream side of the first passage portion  151 . A magnetic permeability sensor that acquires toner concentration in the developer  4  by detecting magnetic permeability of the developer  4  is used as the toner concentration sensor  160 . As illustrated in  FIG. 2 , the toner concentration sensor  160  is provided such that a detecting unit  161  that is shaped into a column and that is attached to an inner wall of the second housing portion  149 , which houses the agitation transporting member  143 , is exposed. 
     In addition, as an example of an agitating member, a flat plate shaped paddle  162  is provided so as to be integrated with the agitation transporting member  143  in a region facing the detecting unit  161  of the toner concentration sensor  160  as illustrated in  FIG. 5  and  FIG. 6 . The paddle  162  suppresses that the developer  4  is attached to the detecting unit  161  due to agitating of the developer  4 , which is in front of the detecting unit  161  of the toner concentration sensor  160 , along a circumferential direction, resulting in occurrence of a detection error. 
     Recently, there has been a tendency in which the developing device  14  that has the aforementioned configuration runs at a high speed as rotation speeds of the developing roll  141  and the agitation transporting member  143  as well as the photoconductor drum  11  are increased to meet a requirement for increased productivity of the image forming apparatus  1 . It has been determined that the developer  4  housed in the second housing portion  149  is scrapped up and scattered beyond the discharge transport blades  155  by the paddle  162  agitating the developer  4  in the circumferential direction of the rotary shaft  143   a , and the developer  4  reaches the auxiliary transport blades  156  in a case where the rotation speeds of the developing roll  141  and the like of the developing device  14  have increased as illustrated in  FIG. 7 . 
     Once the developer  4  that has been scrapped up by the paddle  162  of the agitation transporting member  143  reaches the auxiliary transporting blades  156 , the developer  4  that should not be discharged because an amount of the developer housed in the second housing portion  149  does not exceed the required value ends up being discharged from the discharge port by the auxiliary transporting blades  156 . Accordingly, the developer  4  housed in the device housing  140  is excessively discharged, and the total amount of the developer  4  in the device housing  140  decreases so as to be smaller than the amount that the developer should remain in the device housing  140 . Then, the amount of the developer  4  supplied to the developing roll  141  by the supply transporting member  142  decreases, and image quality defects, including decreased concentration, may occur on the image that should be developed on the surface of the photoconductor drum  11 . 
     In the exemplary embodiment, as illustrated in  FIG. 4  and  FIG. 5 , a cutout portion  163  that is an example of a non-application portion that prevents action of a force for transporting the developer  4  radially outward from the rotary shaft  143   a  is provided in the paddle  162 , in order to suppress the occurrence of excessive discharge of the developer  4  that is caused by the increased rotation speeds of the developing roll  141  and the like. 
     Furthermore, in the region facing the detecting unit  161  of the toner concentration sensor  160 , the paddle  162  of the developing device  14  according to the exemplary embodiment is provided with the cutout portion  163  that has a required width W, in a portion connected to the transporting blade  143   b  located downstream of the agitation transporting member  143  in the developer transport direction as illustrated in  FIG. 4  and  FIG. 5 . The cutout portion  163  provided in the paddle  162  is configured as the non-application portion that cannot permit action of a force for transporting the developer  4  radially outward because the cutout portion  163  does not come into contact with the developer  4  even in a case where the paddle  162  has rotated. 
     On the other hand, the paddle  162  in the related art is provided in the transport direction of the agitation transporting member  143  as if the paddle  162  connects the adjacent transporting blades  143   b  as illustrated in  FIG. 7 . Accordingly, in a case where the paddle  162  has been rotated, the entire region of the paddle  162  in the transport direction comes into contact with the developer  4 , and a force for transporting the developer  4  radially outward acts. Therefore, once the rotation speeds of the developing roll  141 , the agitation transporting member  143 , and the like are increased, the developer  4  gets scrapped up and scattered. 
     Operation of Characteristic Portions of Developing Device 
     In the developing device  14  according to the first exemplary embodiment, each of the developing roll  141 , the supply transporting member  142 , and the agitation transporting member  143  is rotation-driven by the driving device (not illustrated) in the directions indicated by the arrows, in accordance with an image forming operation as illustrated in  FIG. 2 . The developer  4  housed in the device housing  140  is agitated and transported in accordance with the rotations of the supply transporting member  142  and the agitation transporting member  143 , and is supplied from the supply transporting member  142  to the developing roll  141 . Then, the developer  4  is transported to the developing region facing photoconductor drum  11  by the developing roll  141 , and the electrostatic latent image is developed on the surface of the photoconductor drum  11 . 
     In addition, developer is newly supplied from the supply port  154  to the device housing  140  at required timing as illustrated in  FIG. 3B . The developer newly supplied to the device housing  140  is agitated with the developer  4  housed in the device housing  140  while the new developer is transported by the agitation transporting member  143 . Then the developer is transported to the supply transporting member  142  via the first and second passage portions  151  and  152  to be supplied to the developing roll  141 . 
     As described above, once the new developer is gradually supplied to the device housing  140  of the developing device  14 , the total amount of the developer  4  housed in the device housing  140  exceeds the required value. In a case where the total amount of the developer  4  housed in the device housing  140  has exceeded the required value, the excess developer out of the developer  4  that is housed in the second housing portion  149  and that is transported to the downstream side by the transport blades  143   b  of the agitation transporting member  143  crosses the discharge transport blades  155  and is transported to the downstream side as illustrated in  FIG. 4  and  FIG. 5 . Then, the excess developer is discharged by the auxiliary transport blades  156  from the discharge port (not illustrated) of the device housing  140  to the outside. 
     There is a tendency in which the developing device  14  that has the aforementioned configuration runs at a high speed as the rotation speeds of the developing roll  141 , the agitation transporting member  143 , and the like are increased to meet the requirement for increased productivity of the image forming apparatus  1 . The developer  4  housed in the second housing portion  149  becomes likely to be scrapped up and scattered by the paddle  162  of the agitation transporting member  143  in a case where the rotation speeds of the developing roll  141  and the like of the developing device  14  have increased. 
     In the exemplary embodiment, as illustrated in  FIG. 4  and  FIG. 5 , the cutout portion  163  is provided in the end of the paddle  162  on the downstream side in the developer transport direction. The cutout portion  163  prevents action of the force for transporting the developer  4  outward in radial directions of the rotary shaft  143   a . Accordingly, as illustrated in  FIG. 8 , in the paddle  162  of the developing device  14  according to the exemplary embodiment, the amount of the developer  4  scrapped up by the paddle  162  in accordance with the rotation of the agitation transporting member  143  decreases by a size of the cutout portion  163  provided. That is, the cutout portion  163  suppresses the developer  4  scrapped up and scattered by the paddle  162  from crossing the discharge transport blades  155  and reaching the auxiliary transport blades  156  located on the downstream side. 
     Accordingly, the developing device  14  according to the exemplary embodiment suppress or prevent the developer  4  from being scrapped up and scattered by the paddle  162 , reaching the auxiliary transporting blades  156 , and being discharged from the discharge port by the auxiliary transporting blades  156  even in a case where the rotation speeds of the developing roll  141 , the agitation transporting member  143 , and the like have been increased. For this reason, the developing device  14  may maintain the total amount of the developer  4  in the device housing  140  at an approximately appropriate value and avoid the occurrence of decreased developing concentration and the like even in a case where the rotation speeds of the developing roll  141 , the agitation transporting member  143 , and the like have been increased. 
     Experiment Example 
     The inventors produce a benchmark model of a image forming apparatus  1  as illustrated in  FIG. 2  and conducts an experiment to confirm a total amount of the developer  4  in the device housing  140  of the developing device  1 , 4  in order to confirm effects of the developing device according to the first exemplary embodiment described above. The productivity of the image forming apparatus  1  is set to 100 ppm at which 100 images per minute are printed onto A4 size recording paper  5 . 
       FIG. 9  is a graph illustrating the results of an experiment example. 
     As is apparent from  FIG. 9 , it is determined that total amounts of the developer  4  in the device housing  140  of the developing device  14  have substantially reached a set value of 480 g. 
       FIG. 10  is a graph illustrating the results of a reference example. In the reference example, the paddle  162  has been removed altogether from the agitation transporting member  143 , and the paddle  162  has been configured such that the force for transporting the developer  4  radially outward does not act at all. 
     In the case of the reference example, as is apparent from  FIG. 10 , it is determined that once the total amount of the developer  4  in the device housing  140  substantially approaches the set value of the 480 g, a developer discharge amount per minute may be increased rapidly and the total amount of the developer  4  in the device housing  140  may be maintained approximately at the set value even if the rotation speeds of the developing roll  141  and the like are increased to a speed corresponding to the productivity of 100 ppm. 
     Comparative Example 
     As a comparative example, the inventors produce a benchmark product of a image forming apparatus I that employs the developing device  14  of the related art in which the paddle  162  is provided over the entire region between the adjacent transporting blades  143   b  in the developer transport direction of the agitation transporting member  143  as illustrated in  FIG. 7 . Then, the inventors conduct an experiment to confirm a total amount of the developer  4  in the device housing  140  of the developing device  14 . The productivity of the image forming apparatus  1  is set to 100 ppm at which 100 images per minute arc printed onto A4 size recording paper  5 . 
       FIG. 11  is a graph illustrating the results of the comparative example. The scale of the vertical axis of  FIG. 11  is different from those of  FIG. 9  and  FIG. 10 . 
     As is apparent in  FIG. 11 , it is determined that the developer discharge amount increases rapidly and the developer  4  in the device housing  140  is excessively discharged before the total amount of the developer  4  in the device housing  140  of the developing device  14  substantially approaches the set value of 480 g. 
     As described above, according to the exemplary embodiment, the paddle  162  that retains the developer  4  in the region corresponding to the toner concentration sensor  160  well suppress the excessive discharge of the developer  4  compared with a case where the non-application portion that prevents action of the power for transporting the developer  4  radially outward is not provided. 
     Second Exemplary Embodiment 
       FIGS. 12A to 12G  are enlarged views illustrating main parts of the developing device according to a second exemplary embodiment of the invention. 
     In the second exemplary embodiment, the shape of each cutout portion  163  provided in the paddle  162  differs from each other as illustrated in  FIGS. 12A to 12G . 
     In the exemplary embodiment illustrated in  FIG. 12A , the paddle  162  is configured with plural plate members  164  each of which has a substantially regular triangle shape in front view. The cutout portions  163  are provided between the plate members  164  and on the downstream side of the paddle  162  in the developer transport direction. 
     In the exemplary embodiment illustrated in  FIG. 12B , the paddle  162  is configured with a plate member  165 . The plate member  165  has such a triangle shape that a height of the triangle gets smaller linearly from the upstream side toward the downstream side in the developer transport direction. The cutout portion  163  is provided on the plate member  165 . 
     In the exemplary embodiment illustrated in  FIG. 12C , the cutout portion  163  is provided in the paddle  162  having a flat plate shape. An area of the cutout portion  163  increases toward the downstream side in the developer transport direction. 
     In the exemplary embodiment illustrated in  FIG. 12D , the cutout portion  163  is provided in an upper portion of the paddle  162  that is feinted as a flat plate  167 . An area of the cutout portion  163  increases toward the downstream side in the developer transport direction. 
     In the exemplary embodiment illustrated in  FIG. 12E , the paddle  162  that is formed as a flat plate  168  is disposed such that the tip portion  168   a  at the outer circumference of the rotary shaft  143   a  is tilted toward the upstream side in the rotation direction. The cutout portion  163  that prevents action of a force for transporting the developer radially outward is provided at a base end portion  168   b  of the flat plate  168 . 
     In the exemplary embodiment illustrated in  FIG. 12F , the paddle  162  is configured of plural rod-like members  169 , instead of a flat plate, which are erected on the outer circumference of the rotary shaft  143   a , and the cutout portions  163  that prevents action of the force for transporting the developer radially outward is provided between the plural rod-like members  169 . 
     In the exemplary embodiment illustrated in  FIG. 12G , the paddle  162  is configured of plural flat plate shaped members  170 , instead of an unbroken flat plate, which are erected so as to be tilted on the outer circumference of the rotary shaft  143   a , and the cutout portions  163  that prevents action of the force for transporting the developer radially outward is provided between the plural flat plate shaped members  170 . 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.