Patent Publication Number: US-11036162-B1

Title: Powder transport apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-219972 filed Dec. 4, 2019. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a powder transport apparatus. 
     2. Related Art 
     JP-A-2010-176074 discloses a developing device. The developing device includes a developer accommodating unit that accommodates a developer containing toner and a magnetic carrier, a developer transport path through which the developer is transported inside the developer accommodating unit, a developer transport member that is provided in the developer transport path and transports the developer towards a predetermined direction while agitating the developer, and a developing roller that carries the developer in the developer transport path and supplies the toner contained in the developer to a photoconductor drum. The developer transport member includes a rotation shaft and a spiral blade provided on an outer periphery of the rotation shaft. The spiral blade is configured with a multiplex spiral structure that includes one or more ring-shaped spiral blades having a large outer diameter and one or more spiral blades having a small outer diameter. A spiral pitch of the ring-shaped spiral blade having the large outer diameter is the same as a spiral pitch of the spiral blade having the smaller outer diameter. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to preventing powder from accumulating in a first connection port as compared with a powder transport apparatus in which a transport force of a second transport member at a portion of the second transport member where the second transport member faces the first connection port is the same as a transport force of the second transport member at a portion of the second transport member where the second transport member faces a partition wall. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a powder transport apparatus including a housing, a first transport member, and a second transport member. The housing includes a first transport path and a second transport path that are separated by a partition wall extending in one direction. The first transport path and the second transport path are connected to each other by a first connection port and a second connection port. The first connection port and the second connection port are separated in the one direction with the partition wall interposed therebetween. The first transport member is provided in the first transport path. The first transport member is configured to transport powder in a direction extending from the first connection port towards the second connection port. The second transport member is provided in the second transport path. The second transport member is configured to transport the powder in a direction extending from the second connection port towards the first connection port. A transport force of the second transport member at a portion of the second transport member where the second transport member faces the first connection port is smaller than a transport force of the second transport member at a portion where the second transport member faces the partition wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a front view illustrating an image forming apparatus according to an exemplary embodiment; 
         FIG. 2  is a front cross-sectional view illustrating a developing device according to the exemplary embodiment; 
         FIG. 3  is a plan cross-sectional view illustrating the developing device illustrated in  FIG. 2 ; and 
         FIG. 4  is an enlarged plan cross-sectional view illustrating a part of the developing device illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     An example of a developing device and an image forming apparatus according to an exemplary embodiment of the present disclosure will be described with reference to the drawings. 
     In the following description, in a front view of an image forming apparatus  10  when viewed from a side where a user (not illustrated) stands, apparatus upper and lower directions (vertical directions) is described as H directions, apparatus width directions (horizontal directions) is described as W directions, apparatus depth directions (horizontal directions) is described as D directions. When one side and the other side of each of the apparatus upper and lower directions, the apparatus width directions, and the apparatus depth directions need to be distinguished from each other, an upper side is described as a +H side, a lower side is described as a −H side, a right side is described as a +W side, a left side is described as a −W side, a far side is described as a +D side, and a near side is described as a −D side in the front view of the image forming apparatus  10 . 
     Image Forming Apparatus  10   
     The image forming apparatus  10  according to the exemplary embodiment is a monocolor image forming apparatus that forms and fixes a monochrome toner image on a sheet member P which is an example of a recording medium. As illustrated in  FIG. 1 , the image forming apparatus  10  includes an accommodating unit  12 , a discharge unit  18 , a transport unit  14 , an image forming unit  30 , a fixing unit  16 , and a toner cartridge  20 . The image forming apparatus according to the exemplary embodiment of the present disclosure is not limited to the monocolor image forming apparatus. For example, the image forming apparatus according to the exemplary embodiment of the present disclosure may be a color image forming apparatus that expresses colors by combining two or more colors, such as four colors of yellow (Y), magenta (M), cyan (C), and black (K). 
     The accommodating unit  12  has a function of accommodating the sheet members P. 
     The sheet member P on which an image is formed by the image forming unit  30  and fixed by the fixing unit  16  is discharged to the discharge unit  18 . 
     The transport unit  14  has a function of transporting the sheet member P accommodated in the accommodating unit  12  to a transfer position T where an image is to be formed by transfer. The transport unit  14  further has a function of transporting the sheet member P on which the image is fixed by the fixing unit  16 , which will be described later, to the discharge unit  18  to discharge the sheet member P. 
     The image forming unit  30  has a function of forming an image on the sheet member P by an electrophotographic process. Specifically, the image forming unit  30  includes a photoconductor drum  32 , a charging roller  34 , an exposure device  36 , a developing device  40  (an example of a powder transport apparatus), and a transfer roller  38 . The photoconductor drum  32  is an example of an image carrier that carries a latent image. The charging roller  34  is an example of a charging device that charges the photoconductor drum  32 . The exposure device  36  exposes the photoconductor drum  32  charged by the charging roller  34  to form an electrostatic latent image (an example of a latent image) on the photoconductor drum  32 . The developing device  40  develops the electrostatic latent image formed on the photoconductor drum  32  by the exposure device  36  into a toner image using a developer G (an example of powder) that contains toner. The developer G is accommodated in the developing device  40 . The developing device  40  will be described later in detail. 
     The transfer roller  38  faces and is in contact with the photoconductor drum  32 . A nip region N which is an example of the transfer position T is formed between the transfer roller  38  and the photoconductor drum  32 . The transfer roller  38  and the photoconductor drum  32  sandwich the sheet member P transported to the nip region N by the transport unit  14  while the transfer roller  38  is rotated, so as to transfer the toner image formed on the photoconductor drum  32  to the sheet member P and transport the sheet member P to the fixing unit  16 . As illustrated in  FIG. 1 , the transfer roller  38  is rotated counterclockwise and the photoconductor drum  32  is rotated clockwise at this time as viewed from the front side in the exemplary embodiment. The transfer roller  38  is an example of a transfer unit and transfers the toner image formed on the photoconductor drum  32  to the sheet member P. 
     In the present exemplary embodiment, the fixing unit  16  is a fixing device that fixes the toner image, which is transferred to the sheet member P by the transfer roller  38 , onto the sheet member P by heating and pressurizing the sheet member P. 
     The toner cartridge  20  accommodates the developer G that contains the toner and a magnetic carrier. The toner cartridge  20  is connected with a second transport path  54  of the developing device  40  (which will be described later) by a supply path (not illustrated). When the toner is consumed in the developing device  40  by a development operation of the developing device  40 , the toner cartridge  20  supplies the developer G to the second transport path  54  of the developing device  40 . 
     Developing Device  40   
     Next, the developing device  40  will be described. 
     As illustrated in  FIGS. 2 and 3 , the developing device  40  extends in the apparatus depth directions and includes a housing  50 , a developing roller  42 , a layer regulating member  44 , a first transport member  60 , and a second transport member  70 . In the exemplary embodiment, the developing device  40  is disposed at the −H side and the +W side of the photoconductor drum  32 . The housing  50  accommodates the developer G therein. 
     As illustrated in  FIG. 3 , the housing  50  includes a bottom wall extending in the apparatus depth directions in a plan view, a peripheral wall standing at the +H side of a periphery of the bottom wall, and a first partition wall  56   a  and a second partition wall  56   b . The first partition wall  56   a  and the second partition wall  56   b  stand at a center portion of the bottom wall in the apparatus width directions towards the +H side and extend in the apparatus depth directions. The first partition wall  56   a  and the second partition wall  56   b  stand while arranged side by side in the apparatus depth directions. The first partition wall  56   a  stands at the −D side, and the second partition wall  56   b  stands at the +D side. The first partition wall  56   a  and the second partition wall  56   b  will be described later in detail. As illustrated in  FIG. 2 , a cross section of the bottom wall as viewed from the front side has such a shape that two semicircle arc portions open towards the +H side and are arranged adjacent to each other in the apparatus width direction. The first partition wall  56   a  and the second partition wall  56   b  stand at a boundary portion between the two semicircle arc portions. A space defined by the bottom wall and the peripheral wall of the housing  50  is divided into a first transport path  52  and a second transport path  54  in the apparatus width directions by the first partition wall  56   a  and the second partition wall  56   b . In the exemplary embodiment, a space at the −W side of the first partition wall  56   a  and the second partition wall  56   b  serves as the first transport path  52 , and a space at the +W side of the first partition wall  56   a  and the second partition wall  56   b  serves as the second transport path  54 . That is, the first transport path  52  and the second transport path  54  are separated by the first partition wall  56   a  and the second partition wall  56   b . The first transport path  52  and the second transport path  54  accommodate the developer G. End walls at both sides of the peripheral wall in the apparatus depth directions serve as bearing portions that rotatably support a shaft body  62  of the first transport member  60  and a shaft body  72  of the second transport member  70 . The first transport member  60  and the second transport member  70  (which will be described later) are respectively provided in the first transport path  52  and the second transport path  54 . 
     As illustrated in  FIG. 2 , the housing  50  includes a projection wall and a cover portion. The projection wall projects from an upper end of a side wall that is the peripheral wall defining the first transport path  52  to a side opposite to the first partition wall  56   a  and the second partition wall  56   b  as viewed from the front side. The cover portion covers the peripheral wall and the projection wall from above. A roller chamber  55  is formed between the projection wall and the cover portion. In the roller chamber  55 , the developing roller  42  which will be described later is disposed. The roller chamber  55  is disposed above the first transport path  52 . The housing  50  has an opening  51  that allows the developing roller  42  to face the photoconductor drum  32 . 
     As illustrated in  FIG. 3 , the first partition wall  56   a  and the second partition wall  56   b  are separated from each other in the apparatus depth directions with a first connection port  58   a  being interposed therebetween. The first partition wall  56   a  is separated from an end wall (the peripheral wall) at the −D side with a second connection port  58   b  being interposed between the first partition wall  56   a  and the end wall in the apparatus depth directions. In other words, the first connection port  58   a  and the second connection port  58   b  are separated from each other in the apparatus depth directions with the first partition wall  56   a  being interposed therebetween. The first partition wall  56   a  is an example of a partition wall. The first connection port  58   a  and the second connection port  58   b  connect the first transport path  52  and the second transport path  54 . 
     As illustrated in  FIG. 2 , the developing roller  42  is a roller-shaped member. The developing roller  42  is disposed in the roller chamber  55  above the first transport path  52  and faces the photoconductor drum  32  with the opening  51  being interposed between the developing roller  42  and the photoconductor drum  32 . That is, the developing roller  42  is disposed above the first transport member  60  provided in the first transport path  52 . Accordingly, the first transport member  60  (which will be described later) is required to have not only a transport force in the apparatus depth directions but also a transport force to lift the developer G towards the developing roller  42  above the first transport member  60 . The developing roller  42  holds, with a magnetic force, the developer G that contains the magnetic carrier and that is accommodated in the first transport path  52 , so as to form a layer of the developer G on a surface of the developing roller  42 . The developing roller  42  is rotated in such a state to transport the developer G to a position where the developer G faces the photoconductor drum  32 . At this time, the developing roller  42  is rotated counterclockwise as viewed from the front side in the exemplary embodiment, as illustrated in  FIG. 2 . The toner contained in the developer G that is transported to the position where the developer G faces the photoconductor drum  32  by the developing roller  42  adheres to the electrostatic latent image formed on the photoconductor drum  32 , whereby the developing device  40  develops the electrostatic latent image into a toner image. When the developing roller  42  and the first transport member  60  are projected onto a plane that is parallel to the apparatus width directions, the developing roller  42  and the first transport member  60  overlap each other at least partially (see  FIG. 2 ). It is noted that in  FIG. 3 , the developing roller  42  is illustrated at a position separated from the first transport member  60  in the apparatus width directions in order to illustrate the entire first transport member  60 . 
     As illustrated in  FIG. 2 , the layer regulating member  44  is a roller-shaped member and is disposed on the +W side of the developing roller  42  and on the +H side of the first transport member  60 . The layer regulating member  44  regulates, to a predetermined thickness, the layer of the developer G that is carried by the developing roller  42  and that is to be transported to the position where the developer G faces the photoconductor drum  32 . When the layer regulating member  44  and the first transport member  60  are projected to a plane that is parallel to the apparatus width directions, the layer regulating member  44  and the first transport member  60  overlap each other at least partially (see  FIG. 2 ). It is noted that the layer regulating member  44  is omitted in  FIG. 3  in order to illustrate the entire first transport member  60 . 
     First Transport Member  60   
     As illustrated in  FIG. 3 , the first transport member  60  includes the shaft body  62  and a spiral blade  64 . The first transport member  60  is provided in the first transport path  52 . The shaft body  62  extends in the apparatus depth directions and is rotatably supported by end walls at a first transport path  52  side. The shaft body  62  has a larger diameter than that of a shaft body  72  of the second transport member  70  which will be described later. In this manner, the first transport member  60  is regarded as a member having a smaller space capable of accommodating the developer G in the first transport path  52  than a space in the second transport path  54 . The spiral blade  64  includes two spiral blade bodies that are provided around the shaft body  62  from a portion of the shaft body  62  where the shaft body  62  faces the second partition wall  56   b  to a portion of the shaft body  62  where the shaft body  62  faces the second connection port  58   b . The two spiral blade bodies extend in the apparatus depth directions. In the exemplary embodiment, when the shaft body  62  is rotated clockwise as viewed from the front side, the spiral blade  64  supplies the developer G accommodated in the first transport path  52  to the developing roller  42  while transporting the developer G in a direction extending from the first connection port  58   a  towards the second connection port  58   b  (that is, towards the −D side). 
     In the exemplary embodiment, an outer diameter of the two spiral blades constituted by the spiral blade  64 , that is, a blade diameter, is a predetermined diameter D 1 . A pitch of the spiral blade  64  is a predetermined pitch P 1 . Accordingly, the spiral blade  64  transports a predetermined amount of the developer G from a portion where the spiral blade  64  faces the second connection port  58   b  to a portion where the spiral blade  64  faces the first connection port  58   a . In other words, the first transport member  60  that transports the developer G has the same transport force, which is provided by the spiral blade  64 , in the apparatus depth directions. In the present disclosure, the term “transport force” refers to an amount of the developer G per pitch of the spiral blade that is transported per rotation of the transport member [g/rotation]. That is, a transport force of the first transport member  60  at the portion of the transport member  60  where the transport member  60  faces the second connection port  58   b  is equal to the transport force of the first transport member  60  at a portion of the first transport member  60  where the first transport member  60  faces the first partition wall  56   a . Moreover, a transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b  is equal to the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the first connection port  58   a . In other words, the transport force of the first transport member  60  is the same from the portion of the first transport member  60  where the first transport member  60  faces the first connection port  58   a  up to the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b . In the present disclosure, the phrase that “the transport force is the same” refers to that transport forces at two or more portions of a transport member fall within a range of ±10% of an average value of the transport forces. For example, when two portions of a transport member are compared, transport forces at the two portions are the same if the number of spiral blades, pitches, blade diameters, and shaft diameters are the same. It is noted that the phrase “the same” does not refer to that parameters are completely identical, but allow that the parameters are not completely identical due to a dimensional error or a design error. 
     Second Transport Member  70   
     As illustrated in  FIG. 3 , the second transport member  70  includes the shaft body  72 , a first spiral blade  74 , a second spiral blade  76 , and a third spiral blade  78 . The second transport member  70  is provided in the second transport path  54 . The shaft body  72  extends in the apparatus depth directions and is rotatably supported by end walls at a second transport path  54  side. 
     The first spiral blade  74  includes two spiral blade bodies that are provided around the shaft body  72  from a portion of the shaft body  72  where the shaft body  72  faces the first partition wall  56   a  to a portion of the shaft body  72  where the shaft body  72  faces the second connection port  58   b . The two spiral blade bodies extend in the apparatus depth directions. In the exemplary embodiment, when the shaft body  72  is rotated clockwise as viewed from the front side, the first spiral blade  74  agitates the developer G around the first spiral blade  74  while transporting the developer G in a direction extending from the second connection port  58   b  towards the first connection port  58   a  (towards the +D side). In the exemplary embodiment, a blade diameter of the first spiral blade  74  is the predetermined diameter D 1  as illustrated in  FIG. 4 . A pitch of the first spiral blade  74  is the predetermined pitch P 1 . Accordingly, a transport force of the second transport member  70  at a portion of the second transport member  70  where the second transport member  70  faces the second connection port  58   b  is equal to a transport force of the second transport member  70  at a portion of the second transport member  70  where the second transport member  70  faces the first partition wall  56   a.    
     The second spiral blade  76  includes two spiral blade bodies that are provided at a portion of the shaft body  72  where the shaft body  72  faces the first connection port  58   a . The two spiral blade bodies extend in the apparatus depth directions. In the exemplary embodiment, when the shaft body  72  is rotated clockwise as viewed from the front side, the second spiral blade  76  agitates the developer G around the second spiral blade  76  while transporting the developer G in a direction extending from the second connection port  58   b  towards the first connection port  58   a  (towards the +D side). 
     A blade diameter of the second spiral blade  76  is a predetermined diameter D 2 . The blade diameter D 2  of the second spiral blade  76  is smaller than the blade diameter D 1  of the first spiral blade  74 . A pitch of the second spiral blade  76  is equal to the pitch P 1  of the first spiral blade  74 . Accordingly, a transport force of the second spiral blade  76  is smaller than a transport force of the first spiral blade  74 . That is, a transport force of the second transport member  70  at a portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is smaller than the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first partition wall  56   a . The transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is smaller than the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the second connection port  58   b.    
     The second spiral blade  76  is continuously connected to the first spiral blade  74  at a boundary between the first partition wall  56   a  and the first connection port  58   a  in the apparatus depth directions. In the exemplary embodiment, the first spiral blade  74  and the second spiral blade  76  are continuously connected to each other via a stepped portion  75  at the boundary between the first partition wall  56   a  and the first connection port  58   a  in the apparatus depth directions. The stepped portion  75  between the first spiral blade  74  and the second spiral blade  76  may be positioned at any position within a range of +3 [mm] from the boundary in the apparatus depth directions. Further, the stepped portion  75  between the first spiral blade  74  and the second spiral blade  76  may be positioned at the −D side of the boundary within a range of 3 [mm] from the boundary. 
     The third spiral blade  78  includes a single spiral blade body that is provided at a portion of the shaft body  72  where the shaft body  72  faces the second partition wall  56   b . The single spiral blade extends in the apparatus depth directions. That is, the third spiral blade  78  is provided at a portion of the shaft body  72  at an opposite side to the first spiral blade  74  with the second spiral blade  76  being interposed between the third spiral blade  78  and the first spiral blade  74 . In the exemplary embodiment, when the shaft body  72  is rotated clockwise as viewed from the −D side, the third spiral blade  78  agitates the developer G around the third spiral blade  78  while transporting the developer G in a direction towards the first connection port  58   a  (towards the −D side). 
     In the exemplary embodiment, a blade diameter of the third spiral blade  78  is equal to the blade diameter D 1  of the first spiral blade  74 . That is, the blade diameter of the third spiral blade  78  is larger than the blade diameter D 2  of the second spiral blade  76 . A pitch of the third spiral blade  78  is a predetermined pitch P 2 . The pitch P 2  of the third spiral blade  78  is smaller than the pitch P 1  of the first spiral blade  74 . 
     In the exemplary embodiment, the third spiral blade  78  is not continuous with the second spiral blade  76  at a boundary between the second partition wall  56   b  and the first connection port  58   a.    
     The first transport member  60  and the second transport member  70  are separately connected to a driving device such as a motor (not illustrated), and are rotated in conjunction with each other. The first transport member  60  and the second transport member  70  rotate in conjunction with each other, so that the developer G flows from the second transport path  54  towards the first transport path  52  via the first connection port  58   a  and flows from the first transport path  52  towards the second transport path  54  via the second connection port  58   b . Accordingly, a circulation path for the developer G including the first transport path  52 , the second connection port  58   b , the second transport path  54 , and the first connection port  58   a  is formed in the developing device  40 . 
     Functions and Effects 
     Next, functions and effects of the exemplary embodiment of the present disclosure will be described. When the same components or the like as those of the image forming apparatus  10  according to the exemplary embodiment are used in a comparative example in describing the comparative example and a comparative apparatus to be compared with the exemplary embodiment of the present disclosure in the following description, numerals and names of the components and the like are used as they are. 
     The developing device  40  according to the exemplary embodiment has a configuration in which the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is smaller than the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first partition wall  56   a  (this configuration will be referred to as a first configuration). The developing device  40  having the first configuration and a second configuration is compared with a developing device according to a first comparative example described below. 
     First Comparative Example 
     In the developing device according to the first comparative example, a spiral blade having a blade diameter of the predetermined diameter D is provided at a portion of the shaft body  72  of the second transport member  70  where the shaft body  72  faces the first connection port  58   a . Accordingly, in the first comparative example, the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is equal to the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first partition wall  56   a . In the first comparative example, the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is equal to the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the second connection port  58   b . Configurations of the first comparative example are the same as those of the exemplary embodiment other than the above-described points. 
     In a developing device including a circulation path, the developer G transported by the portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is pushed by a spiral blade formed at the portion towards the +D side and flows from the second transport path  54  to the first transport path  52  via the first connection port  58   a . Therefore, a part of the developer G in the second transport path  54  is likely to accumulate around the first connection port  58   a.    
     On the other hand, since the developing device  40  according to the exemplary embodiment has the first configuration, the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is smaller than the transport force of the second transport member  70  at that portion in the first comparative example. Therefore, an amount of the developer G accumulating around the first connection port  58   a  in the second transport path  54  in the developing device  40  having the first configuration is small as compared with the developing device of the first comparative example. Therefore, the developer G is prevented from accumulating around the first connection port  58   a  in the developing device  40  having the first configuration as compared with the developing device of the first comparative example. 
     The developing device  40  according to the exemplary embodiment has a configuration in which the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the first connection port  58   a  is smaller than the transport force of the second transport member  70  at the portion of the second transport member  70  where the second transport member  70  faces the second connection port  58   b  (this configuration will be referred to as the second configuration). Similar to the developing device  40  having the first configuration, the developer G is prevented from accumulating around the first connection port  58   a  in the developing device  40  having the second configuration as compared with the developing device of the first comparative example. 
     The developing device  40  according to the exemplary embodiment has a configuration in which the blade diameter D 2  of the second spiral blade  76  of the second transport member  70  is smaller than the blade diameter D 1  of the first spiral blade  74  (this configuration will be referred to as a third configuration). The developing device  40  having the third configuration is compared with a developing device of a second comparative example as described below. 
     Second Comparative Example 
     In the developing device according to the second comparative example, the blade diameter of the second spiral blade of the second transport member  70  is the predetermined diameter D 1 , and the pitch of the second spiral blade is a pitch P 3  which is smaller than the pitch P 1  of the first spiral blade  74 . Accordingly, the transport force of the second spiral blade in the second comparative example is equal to the transport force of the second spiral blade  76  in the exemplary embodiment. Configurations of the second comparative example are the same as those of the exemplary embodiment other than the above-described points. 
     In a developing device having a circulation path, the developer G around the second spiral blade may scatter in a direction along a centrifugal force applied by the second spiral blade along with the rotation of the second transport member  70 . In particular, when the pitch of the second spiral blade is small, if the second spiral blade is rotated so as to enclose the magnetic carrier of the developer Q the enclosed developer G may be scattered without being transported. 
     On the other hand, since the developing device  40  of the exemplary embodiment has the third configuration, the centrifugal force applied by the second spiral blade  76  is reduced as compared with the developing device of the second comparative example. Therefore, the developer G is prevented from scattering. Since the pitch of the second spiral blade  76  in the developing device  40  according to the exemplary embodiment is larger than the pitch of the second spiral blade in the second comparative example, the second spiral blade  76  is less likely to enclose the magnetic carrier of the developer G. Accordingly, the developer G is prevented from scattering in the developing device  40  according to the exemplary embodiment as compared with the developing device of the second comparative example. It is noted that the second comparative example described above is included in the technical idea of the present disclosure as a modification of the exemplary embodiment. 
     The developing device  40  according to the exemplary embodiment includes a configuration in which the third spiral blade  78  that transports the developer G towards the first connection port  58   a  is provided at the portion at the opposite side to the first spiral blade  74  with the second spiral blade  76  of the shaft body  72  of the second transport member  70  being interposed between the third spiral blade  78  and the first spiral blade  74 , and the blade diameter of the third spiral blade  78  is larger than the blade diameter of the second spiral blade  76  (this configuration will be referred to as a seventh configuration). The developer G in the second transport path  54  is less likely to be transported to a third spiral blade  78  side relative to the first connection port  58   a  in the developing device  40  having the seventh configuration as compared with a configuration in which the blade diameter of the third spiral blade  78  is smaller than the blade diameter of the second spiral blade  76 . Therefore, the developer G in the second transport path  54  is prevented from accumulating at the third spiral blade  78  side relative to the first connection port  58   a  in the developing device  40  having the seventh configuration as compared with a configuration in which the third spiral blade transports the developer G towards the +D side. 
     The developing device  40  according to the exemplary embodiment has a configuration in which the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b  is equal to the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the first partition wall  56   a  (this configuration will be referred to as a fourth configuration). In the developing device having the circulation path, circulation of the developer G in the circulation path is unstable when the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b  is different from the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the first partition wall  56   a . Therefore, the circulation of the developer G is stable in the developing device  40  having the fourth configuration as compared with a configuration in which the transport force of the shaft body  62  of the first transport member  60  at the portion of the shaft body  62  where the shaft body  62  faces the second connection port  58   b  is smaller than the transport force of the spiral blade  64  at the portion of the spiral blade  64  where the spiral blade  64  faces the first partition wall  56   a.    
     The developing device  40  according to the exemplary embodiment has a configuration in which the first transport member  60  is provided with the spiral blade  64  on the shaft body  62  having a larger diameter than the shaft body  72  of the second transport member  70  (this configuration will be referred as a fifth configuration). When the developing device having the circulation path has the fifth configuration, a space of the first transport path  52  capable of accommodating the developer G is smaller than a space of the second transport path  54  capable of accommodating the developer G. Therefore, the developer G is likely to accumulate around the first connection port  58   a . However, since the developing device  40  according to the exemplary embodiment has the first configuration, an amount of the developer G accumulating around the first connection port  58   a  in the second transport path  54  is small as compared with the developing device of the first comparative example that has the fifth configuration. Therefore, in the developing device  40  having the first and fifth configurations, the developer G is prevented from accumulating around the first connection port  58   a  as compared with the developing device of the first comparative example which has the fifth configuration. 
     The developing device  40  according to the exemplary embodiment has a configuration in which the developing roller  42  is disposed above the first transport member  60  (this configuration will be referred to as a sixth configuration). When the developing device having the circulation path has the fifth configuration and the sixth configuration, the developer G in the first transport path  52  is lifted in a direction against the gravity by the first transport member  60  and supplied to the developing roller  42 . Therefore, the developer G is likely to accumulate around the first connection port  58   a . However, since the developing device  40  according to the exemplary embodiment has the first configuration, the amount of the developer G accumulating around the first connection port  58   a  in the second transport path  54  is small as compared with the developing device according to the first comparative example that has the fifth configuration and the sixth configuration. Therefore, in the developing device  40  having the first, fifth, and sixth configurations, the developer G is prevented from accumulating around the first connection port  58   a  as compared with the developing device of the first comparative example that has the fifth and sixth configurations. 
     The developing device  40  according to the exemplary embodiment has a configuration in which the first transport member  60  has the same transport force from the portion of the first transport member  60  where the first transport member  60  faces the first connection port  58   a  up to the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b  (this configuration will be referred to as an eighth configuration). Therefore, developing spots are prevented in the developing device  40  having the eighth configuration as compared with a configuration in which the transport force of the shaft body  62  of the first transport member  60  at the portion of the shaft body  62  where the shaft body  62  faces the second connection port  58   b  is smaller than the transport force of the shaft body  62  at the portion where the shaft body  62  faces the first connection port  58   a.    
     In addition, the image forming apparatus  10  including the developing device  40  according to the exemplary embodiment prevents image spots in an image formed on the sheet member P due to the developer G accumulating around the first connection port  58   a  as compared with an image forming apparatus including the developing device of the first comparative example. 
     As described above, the specific exemplary embodiment of the present disclosure has been described in detail. It is noted that the present disclosure is not limited to the above-described exemplary embodiment. Various modifications, changes, and improvements may be made within the scope of the technical idea of the present disclosure. 
     For example, in the exemplary embodiment, the first spiral blade  74  and the second spiral blade  76  are continuously connected via the stepped portion  75  at the boundary between the first partition wall  56   a  and the first connection port  58   a  in the apparatus depth directions. However, the first spiral blade  74  and the second spiral blade  76  may be continuously connected via a gradual change portion in the apparatus depth direction. The gradual change portion is a spiral blade that is provided between the first spiral blade  74  and the second spiral blade  76  and has a blade diameter changing gradually from D 1  to D 2 . A boundary between the second spiral blade  76  and the gradual change portion may be positioned at any position within a range of +3 mm from the boundary between the first partition wall  56   a  and the first connection port  58   a . The boundary between the second spiral blade  76  and the gradual change portion may be positioned within a range of 3 mm at the −D side from the boundary between the first partition wall  56   a  and the first connection port  58   a.    
     According to the exemplary embodiment, the second transport member  70  includes the third spiral blade  78  that has a larger blade diameter than that of the second spiral blade  76  and that transports the developer G towards the first connection port  58   a . Alternatively, the second transport member  70  may not include the third spiral blade  78  that is provided at a portion at an opposite side to the first spiral blade  74  with the second spiral blade  76  being interposed between the third spiral blade  78  and the first spiral blade  74 . The third spiral blade  78  may have a smaller blade diameter than that of the second spiral blade  76 . The third spiral blade  78  may transport the developer G in a direction opposite to the direction extending from the first connection port  58   a  towards the second connection port  58   b.    
     According to the exemplary embodiment, the first transport member  60  includes the spiral blade  64  that has the predetermined blade diameter D 1  and the predetermined pitch P 1 , and that is provided around the shaft body  62 . Alternatively, the spiral blade  64  may have neither the predetermined blade diameter nor the predetermined pitch. According to the exemplary embodiment, the first transport member  60  has the same transport force from the portion of the first transport member  60  where the first transport member  60  faces the first connection port  58   a  up to the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b . Alternatively, the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b  may be different from the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the first partition wall  56   a , or may be different from the transport force of the first transport member  60  at the portion of the first transport member  60  where the first transport member  60  faces the first connection port  58   a . That is, the first transport member  60  may not have the same transport force from the portion of the first transport member  60  where the first transport member  60  faces the first connection port  58   a  up to the portion of the first transport member  60  where the first transport member  60  faces the second connection port  58   b.    
     According to the exemplary embodiment, the shaft body  62  of the first transport member  60  has a larger diameter than that of the shaft body  72  of the second transport member  70 . Alternatively, the shaft body  62  of the first transport member  60  may have a smaller diameter than that of the shaft body  72  of the second transport member  70 . 
     According to the exemplary embodiment, the developing roller  42  is disposed above the first transport member  60 . Alternatively, the developing roller  42  may be disposed beside the first transport member  60 . 
     An example in which the present disclosure is applied to a developing device of an electrophotographic process as a powder transport apparatus is described in the above-described exemplary embodiment. It is noted that the present disclosure is not limited thereto and may be applied to applications other than developing. 
     For example, a powder coating device may be implemented by using a developer of the above-described exemplary embodiment as coating powder. Specifically, the developing device according to the above-described exemplary embodiment is used as a powder coating head using an electrostatic powder coating method, and a conductive sheet-shaped medium is transported while being brought close to the powder coating head. A bias voltage is applied between the powder coating head and the conductive sheet-like medium, so that a charged coating powder (for example, heat curing toner) is coated onto the sheet-shaped medium. Thereafter, a surface of the sheet-shaped medium is coated with the powder when the sheet-shaped medium is heated. 
     The present disclosure may be applied to other manufacturing devices using powder. For example, the present disclosure may be applied to a device that transports carbon black used in manufacturing in a manufacturing device that manufactures an electrode body for a secondary battery. 
     In addition, application of powder is not limited, and the powder may be powder for use in medicine, powder for use in food, or the like. Alternatively, a form of a device is not limited as long as the device is a device using powder such as a manufacturing device, a processing device, and an inspection device. 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure 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 disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.