Patent Publication Number: US-11644769-B2

Title: Image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2021-039505 filed on Mar. 11, 2021, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The present disclosure relates to an image forming apparatus. 
     As image forming apparatuses of an electrophotographic type such as copiers and printers, there are known devices that develop, using developer, an electrostatic latent image formed on the surface of a photosensitive drum as an image carrying member to form a toner image that is then transferred to a sheet. 
     For example, a conventional image forming apparatus includes a first toner container and a second toner container that store toner to be supplied to a single developing device. In such an image forming apparatus, when one container is empty, it is possible to supply toner from the other container to the developing device. This helps reduce the number of times of the image forming operation being stopped due to the replacement of the toner container and the time spent for it. 
     SUMMARY 
     According to one aspect of what is disclosed herein, an image forming apparatus includes a developing device, a first container, a second container, and a toner supply device. The developing device supplies toner to an image carrying member. The first container and second containers store the toner to be supplied to the developing device. The toner supply device supplies the toner in the first and second containers to the developing device. The toner supply device includes a supply pipe, a first conveying pipe, a second conveying pipe, a first conveying member, a second conveying member, and a conveying driving portion. The supply pipe is a single supply pipe that is connected to the developing device and through which the toner flows into the developing device. The first conveying pipe is connected between the first container and the supply pipe and through which the toner is conveyed from the first container toward the supply pipe. The second conveying pipe is connected between the second container and the supply pipe and through which the toner is conveyed from the second container toward the supply pipe. The first conveying member is rotatably arranged in the first conveying pipe and conveys the toner from the first container toward the supply pipe. The second conveying member is rotatably arranged in the second conveying pipe and conveys the toner from the second container toward the supply pipe. The conveying driving portion rotates selectively one of the first and second conveying members. The rotary shaft of the first conveying member and the rotary shaft of the second conveying member are arranged so as to form a predetermined axial angle. The conveying driving portion includes a motor, a first gear, a second gear, a third gear, a swing gear, an idle gear, and a fourth gear. The motor rotates the first and second conveying members. The first gear is fixed to the output shaft of the motor. The second gear is fixed coaxially with the rotary shaft of the second conveying member. The third gear is arranged away from, parallel to, the second gear. The swing gear meshes with the first gear and in addition meshes selectively with one of the second and third gears by swinging on the outer circumference of the first gear. The idle gear meshes with the third gear. The fourth gear has the axial angle between its input and output shafts and is fixed coaxially with the rotary shaft of the first conveying member to mesh with the idle gear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic sectional front view of an image forming apparatus according to an embodiment of the present disclosure; 
         FIG.  2    is a block diagram showing an outline of the construction of the image forming apparatus in  FIG.  1   ; 
         FIG.  3    is a schematic sectional front view of and around an image forming portion in the image forming apparatus in  FIG.  1   ; 
         FIG.  4    is a perspective view of and around a toner supply device in the image forming apparatus in  FIG.  1   ; 
         FIG.  5    is a front view of and around the toner supply device in  FIG.  4   ; 
         FIG.  6    is a side view of and around the toner supply device in  FIG.  4   ; 
         FIG.  7    is a perspective view of the toner supply device in  FIG.  4   ; 
         FIG.  8    is a plan view of the toner supply device in  FIG.  4   ; 
         FIG.  9    is a perspective view of a first conveying pipe, a second conveying pipe, and a conveying driving portion in the toner supply device in  FIG.  7   ; 
         FIG.  10    is a side view of the first and second conveying pipes and the conveying driving portion in the toner supply device in  FIG.  7   ; 
         FIG.  11    is a perspective view of a first conveying member, a second conveying member, and the conveying driving portion in the toner supply device in  FIG.  9   ; and 
         FIG.  12    is a sectional back view of and around the conveying driving portion in the toner supply device in  FIG.  10   . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described below with reference to the accompanying drawings. The present disclosure is, however, not limited to what is specifically described below. 
       FIG.  1    is a schematic sectional front view of an image forming apparatus  1  according to an embodiment.  FIG.  2    is a block diagram showing an outline of the construction of the image forming apparatus  1  in  FIG.  1   .  FIG.  3    is a sectional view of and around an image forming portion  20  in the image forming apparatus  1  in  FIG.  1   . One example of the image forming apparatus  1  according to the embodiment is a color printer of a tandem-type which transfers a toner image onto a sheet S using the intermediate transfer belt  31 . The image forming apparatus  1  may be what is called a multifunction peripheral provided with the functions of, for example, printing, scanning (image reading), and facsimile transmission. 
     As shown in  FIGS.  1 ,  2 , and  3   , the image forming apparatus  1  includes, in its main body  2 , a sheet feeding portion  3 , a sheet conveying portion  4 , an exposure portion  5 , the image forming portion  20 , a transfer portion  30 , a fixing portion  6 , a sheet discharge portion  7 , and a control portion  8 . 
     The sheet feeding portion  3  stores a plurality of sheets S and, during printing, feeds them out one after another separately. The sheet conveying portion  4  conveys a sheet S fed out from the sheet feeding portion  3  to a secondary transfer portion  33  and then to the fixing portion  6 , and then discharges the sheet S after fixing through a sheet discharge port  4   a  to the sheet discharge portion  7 . When two-side printing is performed, the sheet conveying portion  4  switches, with a branch portion  4   b , the conveying direction of the sheet S after fixing on its first side to an inverting conveying portion  4   c , and conveys the sheet S to the secondary transfer portion  33  and then to the fixing portion  6  once again. The exposure portion  5  shines, toward the image forming portion  20 , laser light that is controlled based on image data. 
     The image forming portion  20  is arranged under the intermediate transfer belt  31 . The image forming portion  20  includes an image forming portion for yellow  20 Y, an image forming portion for cyan  20 C, an image forming portion for magenta  20 M, and an image forming portion for black  20 B. These four image forming portions  20  have basically similar structures. Thus, in the following description, the letters “Y”, “C”, “M”, and “B” distinguishing different colors may be omitted unless distinction is needed. 
     As shown in  FIG.  3   , the image forming portion  20  includes a photosensitive drum (image carrying member)  21  that is supported so as to be rotatable in a predetermined direction (clockwise in  FIG.  3   ). The image forming portion  20  further includes, arranged around the photosensitive drum  21  along its rotation direction, a charging portion  22 , a developing device  40 , and a drum cleaning portion  23 . A primary transfer portion  32  is arranged between the developing device  40  and the drum cleaning portion  23 . 
     The photosensitive drum  21  has a photosensitive layer around its outer circumferential face. The charging portion  22  electrically charges the outer circumferential face of the photosensitive drum  21  to a predetermined potential. The exposure portion  5  exposes to light the outer circumferential face of the photosensitive drum  21  charged by the charging portion  22  to form on it an electrostatic latent image of the document image. The developing device  40  attaches toner to the electrostatic latent image to form a toner image. The four image forming portions  20  form toner images of different colors respectively. After the toner image is primarily transferred to the outer circumferential face of the intermediate transfer belt  31 , the drum cleaning portion  23  performs cleaning by removing toner and the like left on the outer circumferential face of the photosensitive drum  21 . In this way, the image forming portion  20  forms an image on the sheet S. 
     As shown in  FIG.  1   , the transfer portion  30  includes an intermediate transfer belt  31 , primary transfer portions  32 Y,  32 C,  32 M, and  32 B, a secondary transfer portion  33 , and a belt cleaning portion  34 . The intermediate transfer belt  31  is arranged above the four image forming portions  20 . The intermediate transfer belt  31  is an intermediate transfer member which is supported so as to be rotatable in a predetermined direction (counter-clockwise in  FIG.  1   ) and to which the toner images formed on the four image forming portions  20  are sequentially superposed on each other and thereby primarily transferred. The four image forming portions  20  are arranged in what is called a tandem formation in which they are arranged in a row from upstream to downstream in the rotation direction of the intermediate transfer belt  31 . 
     The primary transfer portions  32 Y,  32 C,  32 M, and  32 B are arranged across the intermediate transfer belt  31  over the image forming portions for different colors  20 Y,  20 C.  20 M, and  20 B. The secondary transfer portion  33  is arranged upstream of the fixing portion  6  in the sheet conveying direction in the sheet conveying portion  4  and downstream of the image forming portions for different colors  20 Y,  20 C,  20 M, and  20 B in the rotation direction of the intermediate transfer belt  31  in the transfer portion  30 . The belt cleaning portion  34  is arranged upstream of the image forming portions for different colors  20 Y,  20 C,  20 M, and  20 B in the rotation direction of the intermediate transfer belt  31 . 
     A toner image is primarily transferred to the outer circumferential face of the intermediate transfer belt  31  in the primary transfer portions for different colors  32 Y,  32 C,  32 M, and  32 B. Then, as the intermediate transfer belt  31  rotates, the toner images on the four image forming portions  20  are sequentially superposed on each other and thereby transferred to the intermediate transfer belt  31  with predetermined timing. In this way, a color toner image with the toner images of four colors, namely yellow, cyan, magenta, and black, superposed together is formed on the outer circumferential face of the intermediate transfer belt  31 . 
     The color toner image on the outer circumferential face of the intermediate transfer belt  31  is transferred to a sheet S conveyed in synchronism by the sheet conveying portion  4  at the secondary transfer nips formed in the secondary transfer portion  33 . The belt cleaning portion  34 , after secondary transfer, performs cleaning by removing toner and the like left on the outer circumferential face of the intermediate transfer belt  31 . 
     The fixing portion  6  is arranged above the secondary transfer portion  33 . The fixing portion  6  heats and presses the sheet S having the toner image transferred to it to fix the toner image to the sheet S. 
     The sheet discharge portion  7  is arranged above the transfer portion  30 . The sheet S having the toner images fixed to it and thus having undergone printing is conveyed to the sheet discharge portion  7 . 
     The control portion  8  includes a CPU, an image processing portion, a storage portion, and other electronic circuits and components (none of these are illustrated). The CPU, based on control programs and data stored in the storage portion, controls the operation of different components provided in the image forming apparatus  1  to perform processing related to the functions of the image forming apparatus  1 . The sheet feeding portion  3 , the sheet conveying portion  4 , the exposure portion  5 , the image forming portion  20 , the transfer portion  30 , and the fixing portion  6  individually receive commands from the control portion  8  and coordinate to perform printing on the sheet S. The storage portion is composed of a combination of, for example, a non-volatile storage device such as a program ROM (read-only memory) and a data ROM and a volatile storage device such as a RAM (random-access memory). 
     Next, the construction of and around the developing device  40  will be described with reference to  FIG.  3   . The developing devices  40  for different colors have basically a similar structure; thus, for their components, the suffixes distinguishing different colors will be omitted and no overlapping description will be repeated. 
     The developing device  40  feeds toner to the outer circumferential face of the photosensitive drum  21 . The developing device  40  includes a developer container  41 , a first stirring/conveying member  42 , a second stirring/conveying member  43 , a developing roller  44 , and a regulating member  45 . 
     The developer container  41  is in an elongate shape extending in the axial direction of the photosensitive drum  21  (i.e., in the depth direction with respect to the plane of  FIG.  3   ), and is arranged with its longitudinal direction aligned horizontally. The developer container  41  stores, as developer, for example, magnetic one-component developer containing magnetic toner. Developer may instead be, for example, non-magnetic one-component developer or two-component developer containing toner and magnetic carrier. The developer container  41  includes a partition portion  411 , a first conveying chamber  412 , and a second conveying chamber  413 . 
     The partition portion  411  is provided in a lower part inside the developer container  41 . The partition portion  411  is provided in the lower part of the developer container  41 , substantially in a middle part of it in the direction (the left-right direction in  FIG.  3   ) intersecting with the axial direction, and extends in the axial and up-down directions. The partition portion  411  divides the inside of the developer container  41  in the direction (the left-right direction in  FIG.  3   ) intersecting with the axial direction. The developer container  41  has, in opposite end parts of the partition portion  411  in the axial direction (the depth direction with respect to the plane of  FIG.  3   ), a communication portion (not shown) between the first and second conveying chambers  412  and  413 . 
     The first and second conveying chambers  412  and  413  are provided inside the developer container  41 . The first and second conveying chambers  412  and  413  are formed by partitioning the inside of the developer container  41  with the partition portion  411  and are arranged side by side. The second conveying chamber  413  is arranged inside the developer container  41 , adjacently below the region in which the developing roller  44  is arranged. The first conveying chamber  412  is arranged inside the developer container  41 , in a region farther away from the developing roller  44  than the second conveying chamber  413 . The first conveying chamber  412  is supplied with toner via a supply pipe connecting portion  412   a  shown in  FIG.  3   . 
     The first stirring/conveying member  42  is arranged inside the first conveying chamber  412 . The second stirring/conveying member  43  is arranged inside the second conveying chamber  413 . The second stirring/conveying member  43  is located close to the developing roller  44  and extends parallel to it. The first and second stirring/conveying members  42  and  43  are supported on the developer container  41  so as to be rotatable about axes that extend parallel to the photosensitive drum  21 . The first and second stirring/conveying members  42  and  43 , by rotating about their axes, stir and convey developer in opposite directions along the axial direction of their rotation. 
     As the first and second stirring/conveying members  42  and  43  rotate, developer circulates between the first and second conveying chambers  412  and  413  via the communication portions arranged in the opposite end parts of the partition portion  411  in the axial direction. In the first and second conveying chambers  412  and  413 , toner fed from outside is stirred and electrostatically charged. 
     The developing roller  44  is arranged inside the developer container  41 , above the second stirring/conveying member  43 . The developing roller  44  is supported on the developer container  41  so as to be rotatable about an axis that extends parallel to the axis of the photosensitive drum  21 . The developing roller  44  includes, for example, a cylindrical developing sleeve that rotates counter-clockwise in  FIG.  3    and a developing roller-side magnetic pole that is fixed inside the developing sleeve (neither is shown). 
     Part of an outer circumferential face of the developing roller  44  is exposed out of the developer container  41  so as to face the photosensitive drum  21  in proximity to it. In a region of the developing roller  44  opposite the photosensitive drum  21 , the developing roller  44  holds on its outer circumferential face the toner to be fed to the outer circumferential face of the photosensitive drum  21 . The developing roller  44  attaches the toner in the second conveying chamber  413  to the electrostatic latent image on the outer circumferential face of the photosensitive drum  21  to form a toner image. 
     The regulating member  45  is arranged in a region where the developing roller  44  and the photosensitive drum  21  face each other, upstream of the developing roller  44  in its rotation direction. The regulating member  45  is arranged opposite the developing roller  44  in proximity to it with a predetermined distance left between its tip end and the outer circumferential face of the developing roller  44 . The regulating member  45  extends over the entire region of the developing roller  44  in the axial direction (the depth direction with respect to the plane of  FIG.  3   ). The regulating member  45  regulates the layer thickness of developer (toner) held on the outer circumferential face of the developing roller  44 . 
     The toner in the developer container  41  is stirred, circulated, and electrostatically charged in the first and second conveying chambers  412  and  413 , and is then passed to the outer circumferential face of the developing roller  44  by the second stirring/conveying member  43 . Having its layer thickness regulated by the regulating member  45 , the toner, as the developing roller  44  rotates, is conveyed to the region where the developing roller  44  and the photosensitive drum  21  face each other. When a predetermined developing voltage is applied to the developing roller  44 , due to the potential difference from that on the outer circumferential face of the photosensitive drum  21 , the toner held on the outer circumferential face of the developing roller  44  flies through the developing space toward the outer circumferential face of the photosensitive drum  21 , thereby the electrostatic latent image on the outer circumferential face of the photosensitive drum  21  is developed. 
     In connection with the supply of toner to the developing device  40 , the image forming apparatus  1  includes a first container  51 , a second container  52 , and a toner supply device  60  (see  FIG.  4   ). The first and second containers  51  and  52  and the toner supply device  60  are arranged above the developing device  40 . The first and second containers  51  and  52  and the toner supply device  60  are provided one of each for each of four colors of yellow, cyan, magenta, and black. 
     Next, the construction of and around the toner supply device  60  will be described with reference to  FIGS.  4  to  12   .  FIG.  4    is a perspective view of and around the toner supply device  60  in the image forming apparatus  1  in  FIG.  1   .  FIGS.  5  and  6    are a front view and a side view, respectively, of and around the toner supply device  60  in  FIG.  4   .  FIGS.  7  and  8    are a perspective view and a plan view, respectively, of and around the toner supply device  60  in  FIG.  4   .  FIGS.  9  and  10    are a perspective view and a side view, respectively, of a first conveying pipe  66  and a second conveying pipe  67  in the toner supply device  60  in  FIG.  7   .  FIG.  11    is a perspective view of a first conveying member  68  and a second conveying member  69  in the toner supply device  60  in  FIG.  9   .  FIG.  12    is a sectional back view of and around a conveying driving portion  70  in the toner supply device  60  in  FIG.  10   . 
     The first container  51 , the second container  52 , and the toner supply device  60  include the following: a first and a second container  51 Y and  52 Y and a toner supply device  60 Y for yellow; a first and a second container  51 C and  52 C and a toner supply device  60 C for cyan; a first and a second container  51 M and  52  M and a toner supply device  60 M for magenta; and a first and a second container  51 B and  52 B and a toner supply device  60 B for black. The first and second containers  51  and  52  and the toner supply device  60  for different colors have basically a similar structure. Thus, in the following description, the suffixes “Y”, “C”, “M”, and “B” distinguishing different colors are often omitted, unless distinction is needed. 
     The first container  51  is arranged above the second container  52 . The second container  52  is arranged below the first container  51 . The first and second containers  51  and  52  are arranged, as seen from in front, deviated from each other in the array direction of the image forming portions  20  and the toner supply devices  60 . The first and second containers  51  and  52  are removable from the main body  2  and stores toner to be supplied to the developing device  40 . 
     The first and second containers  51  and  52  are in an elongate cylindrical shape extending in the axial direction Dx of the photosensitive drum  21 , and are arranged with their longitudinal direction aligned horizontally. Formed on the circumference wall of the first and second containers  51  and  52  are helical projecting portions  51   s  and  52   s  that project inward in the radial direction and that extend in the longitudinal direction. 
     The first and second containers  51  and  52  are each closed at one end (front side) in the axial direction Dx and each have an opening (not shown) at the other end (rear side) in the axial direction Dx. The first and second containers  51  and  52  are, at the rear side, i.e., open side, that is open, respectively connected to a first container connecting portion  61  and a second container connecting portion  62  in the toner supply device  60 . The first and second containers  51  and  52  are supported on the toner supply device  60  so as to be rotatable about their axes that extend parallel to the axial direction Dx of the photosensitive drum  21 . 
     The first and second containers  51  and  52  are rotated by a driver (not shown) about their axes that extend parallel to the axial direction Dx of the photosensitive drum  21 . As the first and second containers  51  and  52  rotate, the toner inside is conveyed by the helical projecting portions  51   s  and  52   s  toward the rear side, i.e., open side. Thus, the toner in the first and second containers  51  and  52  flows into the toner supply device  60  through the opening. 
     The toner supply device  60  is arranged at the rear side of the first and second containers  51  and  52 . The four toner supply devices  60  are arranged in a row in the same order as the four image forming portions  20 . The toner supply device  60  supplies the toner in the first and second containers  51  and  52  to the developing device  40 . 
     The toner supply device  60  includes the first and second container connecting portions  61  and  62 , a supply pipe  63 , a first and a second vertical pipe  64  and  65 , the first and second conveying pipes  66  and  67 , the first and second conveying members  68  and  69 , the conveying driving portion  70 , and a rotation sensing portion  80 . 
     The first container connecting portion  61  is arranged in an upper part of the toner supply device  60 , above the second container connecting portion  62 . The first container connecting portion  61  has a toner circulation path (not shown) inside. The first container connecting portion  61  is connected to the first container  51  at its open side and rotatably supports the first container  51 . The downstream end of the first container connecting portion  61  in the toner circulation direction is connected to the first vertical pipe  64 . When the toner in the first container  51  is supplied to the developing device  40 , the toner flows from the first container  51  into the first container connecting portion  61  and then flows through and then out of the first container connecting portion  61  toward the first vertical pipe  64 . 
     The second container connecting portion  62  is arranged in an upper part of the toner supply device  60 , below the first container connecting portion  61 . The second container connecting portion  62  has a toner circulation path (not shown) inside. The second container connecting portion  62  is connected to the second container  52  at its open side and rotatably supports the second container  52 . The downstream end of the second container connecting portion  62  in the toner circulation direction is connected to the second vertical pipe  65 . When the toner in the second container  52  is supplied to the developing device  40 , the toner flows from the second container  52  into the second container connecting portion  62  and then flows through and then out of the second container connecting portion  62  toward the second vertical pipe  65 . 
     The supply pipe  63  is arranged in a lower part of the toner supply device  60 . The toner supply device  60  includes the single supply pipe  63 . The supply pipe  63  is formed in a cylindrical shape extending in the up-down direction. The top end of the supply pipe  63  is connected to a confluence portion  60   a  of the first and second conveying pipes  66  and  67 . The bottom end of the supply pipe  63  is connected to the supply pipe connecting portion  412   a  in the developing device  40 . When the toner in the first and second containers  51  and  52  is supplied to the developing device  40 , the toner flows via the confluence portion  60   a  into the supply pipe  63  and then flows through the supply pipe  63  into the developing device  40 . 
     The first vertical pipe  64  is arranged between the first container connecting portion  61  and the first conveying pipe  66 . The first vertical pipe  64  is formed in a cylindrical shape extending in the up-down direction. The top end of the first vertical pipe  64  is connected to the first container connecting portion  61 . The bottom end of the first vertical pipe  64  is connected to the first conveying pipe  66 . When the toner in the first container  51  is supplied to the developing device  40 , the toner flows via the first container connecting portion  61  into the first vertical pipe  64  and then flows through and then out of the first vertical pipe  64  toward the first conveying pipe  66 . 
     The second vertical pipe  65  is arranged between the second container connecting portion  62  and the second conveying pipe  67 . The second vertical pipe  65  is formed in a cylindrical shape extending in the up-down direction. The top end of the second vertical pipe  65  is connected to the second container connecting portion  62 . The bottom end of the second vertical pipe  65  is connected to the second conveying pipe  67 . When the toner in the second container  52  is supplied to the developing device  40 , the toner flows via the second container connecting portion  62  into the second vertical pipe  65  and then flows through and then out of the second vertical pipe  65  toward the second conveying pipe  67 . 
     Since the first container  51  and the first container connecting portion  61  are arranged above the second container  52  and the second container connecting portion  62 , the first vertical pipe  64  is longer in the up-down direction than the second vertical pipe  65 . Since the second container  52  and the second container connecting portion  62  are arranged below the first container  51  and the first container connecting portion  61 , the second vertical pipe  65  is shorter in the up-down direction than the first vertical pipe  64 . The first and second vertical pipes  64  and  65  are arranged at the same position in the axial direction Dx of the photosensitive drum  21 . In other words, the first and second vertical pipes  64  and  65  are arranged side by side along a straight line perpendicular to the axial direction Dx. 
     The first conveying pipe  66  is arranged between the first vertical pipe  64  and the supply pipe  63  in the up-down direction. The first conveying pipe  66  is formed in a cylindrical shape extending in the horizontal direction. To one end of the first conveying pipe  66  in its extending direction, the first vertical pipe  64  is connected. The other end of the first conveying pipe  66  in its extending direction is connected to the confluence portion  60   a  When the toner in the first container  51  is supplied to the developing device  40 , the toner flows from the first vertical pipe  64  into the first conveying pipe  66  and then flows through and then out of the first conveying pipe  66  toward the confluence portion  60   a . In other words, the first conveying pipe  66  is connected between the first container  51  and the supply pipe  63 , and the toner is conveyed from the first container  51  toward the supply pipe  63 . 
     The second conveying pipe  67  is arranged between the second vertical pipe  65  and the supply pipe  63  in the up-down direction. The second conveying pipe  67  is formed in a cylindrical shape extending in the horizontal direction. To one end of the second conveying pipe  67  in its extending direction, the second vertical pipe  65  is connected. The other end of the second conveying pipe  67  in its extending direction is connected to the confluence portion  60   a . When the toner in the second container  52  is supplied to the developing device  40 , the toner flows from the second vertical pipe  65  into the second conveying pipe  67  and then flows through and then out of the second conveying pipe  67  toward the confluence portion  60   a . In other words, the second conveying pipe  67  is connected between the second container  52  and the supply pipe  63 , and the toner is conveyed from the second container  52  toward the supply pipe  63 . 
     The first and second conveying pipes  66  and  67  are arranged so that their respective extension lines intersect with each other at their confluence portion  60   a  sides with respect to their extending directions. In other words, the first and second conveying pipes  66  and  67  are arranged such that the angle between their extending directions is an acute angle in the horizontal direction, that is, in a V-shape as seen from the up-down direction. 
     The first conveying member  68  is arranged inside the first conveying pipe  66 . The first conveying member  68  includes a rotary shaft  681  that is provided between opposite ends of the cylindrical first conveying pipe  66  in the axial direction and a first conveying blade  682  that is formed on the outer circumferential surface of the rotary shaft  681  and extends in a helical shape along the axial direction. The first conveying member  68  is supported inside the first conveying pipe  66  so as to be rotatable about an axis that extends in the horizontal direction. One end part of the first conveying member  68  in the axial direction is located in the confluence portion  60   a.    
     The first conveying member  68 , as it rotates about the axis, stirs and conveys the toner in the first conveying pipe  66  along the toner conveying direction f 1  (see  FIGS.  8 ,  9 , and  10   ) that is parallel to the rotation axis. The first conveying member  68  conveys the toner in the first conveying pipe  66  from the first vertical pipe  64  toward the confluence portion  60   a . In other words, the first conveying member  68  conveys the toner from the first container  51  toward the supply pipe  63 . 
     The second conveying member  69  is arranged inside the second conveying pipe  67 . The second conveying member  69  includes a rotary shaft  691  that is provided between opposite ends of the cylindrical second conveying pipe  67  in the axial direction and a second conveying blade  692  that is formed on the outer circumferential surface of the rotary shaft  691  and extends in a helical shape along the axial direction. The second conveying member  69  is supported inside the second conveying pipe  67  so as to be rotatable about the axis that extends in the horizontal direction. One end part of the second conveying member  69  in the axial direction is located in the confluence portion  60   a.    
     The second conveying member  69 , as it rotates about the axis, stirs and conveys the toner in the second conveying pipe  67  along the toner conveying direction f 2  (see  FIGS.  8 ,  9   , and  10 ) that is parallel to the rotation axis. The second conveying member  69  conveys the toner in the second conveying pipe  67  from the second vertical pipe  65  toward the confluence portion  60   a  In other words, the second conveying member  69  conveys the toner from the second container  52  toward the supply pipe  63 . 
     The first and second conveying pipes  66  and  67  are, as mentioned above, arranged in a V-shape as seen from the up-down direction. That is, the rotary shaft  681  of the first conveying member  68  and the rotary shaft  691  of the second conveying member  69  are arranged so as to form a predetermined axial angle α. 
     The conveying driving portion  70  is arranged in a rear part of the toner supply device  60 , upstream of the first and second conveying pipes  66  and  67  in the toner conveying direction. The conveying driving portion  70  includes a motor  71 , a first gear  72 , a second gear  73 , a third gear  74 , a swing gear  75 , an idle gear  76 , and a fourth gear  77 . 
     The motor  71  generates a driving force for rotating the first and second conveying members  68  and  69 . The motor  71  is controlled by the control portion  8 . To the motor  71 , an output shaft  711  is coupled. The output shaft  711  is arranged below the second conveying member  69  and extends parallel to the rotary shaft  691  of the second conveying member  69 . 
     The first gear  72  is fixed to the output shaft  711  of the motor  71 . The first gear  72  is located below the second gear  73 , the third gear  74 , and the swing gear  75 . The first gear  72  is rotated by the motor  71 . The first gear  72  meshes with the swing gear  75  to transmit the driving force of the motor  71  to the swing gear  75 . 
     The second gear  73  is located above the swing gear  75 . The second gear  73  is fixed coaxially with the rotary shaft  691  of the second conveying member  69 . The second gear  73  receives the driving force of the motor  71  from the swing gear  75  to rotate together with the second conveying member  69 . 
     The third gear  74  is located above the swing gear  75 . The third gear  74  is arranged away from, parallel to, the second gear  73 . The third gear  74  is located closer, than the second gear  73 , to the first conveying member  68 . The third gear  74  receives the driving force of the motor  71  from the swing gear  75  to rotate. 
     The swing gear  75  is located above the first gear  72 , below the second and third gears  73  and  74 . The swing gear  75  stays in mesh with the first gear  72  all the time. The rotary shaft  751  of the swing gear  75  is rotatably supported inside an arcuate guide  78 . The arcuate guide  78  is formed in an arcuate shape extending in the circumferential direction of the first gear  72 . Thus, the swing gear  75  meshes with the first gear  72  to swing on its outer circumference. The swing gear  75 , by swinging, selectively meshes with one of the second and third gears  73  and  74 . The swing gear  75  transmits the driving force of the motor  71  received via the first gear  72  to one of the second and third gears  73  and  74 . 
     The idle gear  76  is arranged between the third and fourth gears  74  and  77 . The idle gear  76  meshes with both the third and fourth gears  74  and  77 . The idle gear  76  transmits the driving force of the motor  71  received via the third gear  74  to the fourth gear  77 . 
     The fourth gear  77  is fixed coaxially with the rotary shaft  681  of the first conveying member  68 . The fourth gear  77  meshes with the idle gear  76 . The rotary shaft  761  of the idle gear  76  is parallel to the rotary shaft of the second gear  73  (the rotary shaft  691  of the second conveying member  69 ). That is, the fourth gear  77  is a gear that has an axial angle α between the input shaft (the rotary shaft  761  of the idle gear  76 ) and the output shaft (the rotary shaft  681  of the first conveying member  68 ). 
     When the motor  71  is driven to rotate the first gear  72  clockwise in  FIG.  12   , the swing gear  75  receives the driving force from the first gear  72  to rotate, and moves, along the arcuate guide  78 , on the outer circumference of the first gear  72  clockwise in  FIG.  12   . Thus, the swing gear  75  meshes with the third gear  74  to transmit the driving force of the motor  71  to the third gear  74 . The driving force of the motor  71  that has been transmitted to the third gear  74  is transmitted to the fourth gear  77  via the idle gear  76 . The first conveying member  68  is then rotated by the conveying driving portion  70  via the fourth gear  77  to convey the toner in the toner conveying direction f 1 . On the other hand, the second conveying member  69  stops rotating. 
     When the motor  71  is driven to rotate the first gear  72  counterclockwise in  FIG.  12   , the swing gear  75  receives the driving force from the first gear  72  to rotate, and moves, along the arcuate guide  78 , on the outer circumference of the first gear  72  counterclockwise in  FIG.  12   . Thus, the swing gear  75  meshes with the second gear  73  to transmit the driving force of the motor  71  to the second gear  73 . The second conveying member  69  is then rotated by the conveying driving portion  70  via the second gear  73  to convey the toner in the toner conveying direction f 2 . On the other hand, the first conveying member  68  stops rotating. 
     In this way, the conveying driving portion  70  rotates one of the first and second conveying members  68  and  69  selectively. 
     According to the above construction, the first and second conveying members  68  and  69  are arranged so as to form a predetermined axial angle α; thus it is possible to efficiently convey the toner toward the single supply pipe  63 . In addition, with a minimum structure composed of a combination of six gears, the conveying driving portion  70  can selectively drive one of the first and second conveying members  68  and  69 . Thus, the image forming apparatus  1  is configured to be able to efficiently supply toner from the two containers to the single developing device  40 , and this helps reduce cost and size. 
     For example, the fourth gear  77  is a conical gear of which the tooth top faces and the tooth bottom faces lie on a conical surface. The angle formed by the generatrix of the conical surface and the rotation axis of the first conveying member  68  equals the axial angle α. With this construction, even when there is an axial angle α between the rotary shaft  681  of the first conveying member  68  and the rotary shaft  691  of the second conveying member  69 , it is possible to make the idle gear  76 , which is a flat gear, mesh with the fourth gear  77 . In this way, it is possible to reduce the number of gears in the gear train between the third and fourth gears  74  and  77 , and this helps avoid a complex gear structure. 
     In addition, as shown in  FIG.  12   , the rotation axes of the second gear  73 , the third gear  74 , the idle gear  76 , and the fourth gear  77  lie on the plane P including the rotation axes of the first and second conveying members  68  and  69 . With this construction, the driving force of the motor  71  transmitted from the swing gear  75  to the second and third gears  73  and  74  can be transmitted to the first and second conveying members  68  and  69  evenly. Thus, the toner conveyance performance of the first and second conveying members  68  and  69  can be stabilized evenly. 
     In addition, as shown in  FIG.  12   , the swing gear  75  is located below the second and third gears  73  and  74 . With this construction, it is possible to mesh with more ease the swing gear  75  that swings on the outer circumference of the first gear  72  with the second and third gears  73  and  74 . This makes it possible to smoothly switch the transmission of the driving force between the first and second conveying members  68  and  69 . Thus, it is possible to efficiently supply the toner to the developing device  40 . 
     The second gear  73 , the third gear  74 , the idle gear  76 , and the fourth gear  77  all have the same number of teeth. With this structure, it is possible to easily make the number of revolutions equal between the first and second conveying members  68  and  69 . Thus, it is possible to easily make the toner conveying force equal between the first and second conveying members  68  and  69 . 
     The rotation sensing portion  80  is arranged in a rear part of the toner supply device  60 , upstream of the second conveying pipe  67  in the toner conveying direction with respect to the conveying driving portion  70 . The rotation sensing portion  80  includes a first sensing shaft  81 , a second sensing shaft  82 , and an optical sensor  83 . 
     The first sensing shaft  81  is connected coaxially with, so as to extend, the rotary shaft  741  of the third gear  74 . The first sensing shaft  81  is coupled to the first conveying member  68  via the third gear  74 , the idle gear  76 , and the fourth gear  77  and rotates together with the first conveying member  68 . The first sensing shaft  81  rotates in the same direction and at the same speed as the first conveying member  68 . The first sensing shaft  81  is, in this embodiment, located adjacent to the second sensing shaft  82  and extends parallel to the second sensing shaft  82 . 
     The first sensing shaft  81  includes, for example, two first light-shielding plates  811 . The two first light-shielding plates  811  extend outward in the radial direction of the first sensing shaft  81  and are arrayed at angular intervals of 180 degrees from each other in the circumferential direction. As the first sensing shaft  81  rotates, the first light-shielding plate  811  moves into and out of the optical path of the optical sensor  83 . 
     The second sensing shaft  82  is connected coaxially with, so as to extend, the rotary shaft of the second gear  73 . The second gear  73  is fixed coaxially with the rotary shaft  691  of the second conveying member  69 . That is, the second sensing shaft  82  is coupled to the second conveying member  69  and rotates together with the second conveying member  69 . The second sensing shaft  82  rotates in the same direction and at the same speed as the second conveying member  69 . 
     The second sensing shaft  82  includes, for example, two second light-shielding plates  821 . The two second light-shielding plates  821  extend outward in the radial direction of the second sensing shaft  82  and are arrayed at angular intervals of 180 degrees from each other in the circumferential direction. As the second sensing shaft  82  rotates, the second light-shielding plate  821  moves into and out of the optical path of the optical sensor  83 . 
     The optical sensor  83  is arranged above between the first and second sensing shafts  81  and  82 . The rotation sensing portion  80  includes the single optical sensor  83 . The optical sensor  83  is, for example, a transmission type sensor. It includes a light emitting portion and a light receiving portion (neither is shown) and has an optical path passing from the light emitting portion to the light receiving portion. The optical sensor  83  senses whether the optical path is blocked (light-shielded) or not blocked (light-transmitted). 
     The first light-shielding plate  811  of the first sensing shaft  81  and the second light-shielding plate  821  of the second sensing shaft  82  move into and out of the optical path of the optical sensor  83 . Thus, the optical sensor  83  senses the rotation of the first and second sensing shafts  81  and  82 . That is, the optical sensor  83  senses the rotation of the second and third gears  73  and  74 . The optical sensor  83  outputs to the control portion  8  a signal related to the sensed rotation of the second and third gears  73  and  74 . 
     The control portion  8  receives the output signal of the optical sensor  83 . The control portion  8  has a remaining quantity sensing portion  8   a  shown in  FIG.  2   . The function of the remaining quantity sensing portion  8   a  is achieved on a software basis by the CPU performing arithmetic operation in accordance with a program stored in the storage portion. The remaining quantity sensing portion  8   a  may be configured as an electrical hardware circuit. 
     The remaining quantity sensing portion  8   a , based on the output signal of the optical sensor  83 , senses the remaining quantity of toner in the first and second containers  51  and  52 . More specifically, the remaining quantity sensing portion  8   a  counts the number of revolutions of the second and third gears  73  and  74  based on the output signal of the optical sensor  83  and, based on the number of revolutions, senses the remaining quantity of the toner in the first and second containers  51  and  52 . 
     The remaining quantity sensing portion  8   a  counts the number of revolutions of the third gear  74  (the first conveying member  68 ) based on the output signal of the optical sensor  83  and, based on the number of revolutions, senses the toner in the first container  51  being empty. The control portion  8  controls the motor  71  to stop the rotation of the first conveying member  68  and thereby stops the supply of toner from the first container  51  to the developing device  40 . Next, the control portion  8  rotates the motor  71  reversely to rotate the second gear  73  (the second conveying member  69 ) and thereby starts the supply of toner from the second container  52  to the developing device  40 . 
     Similarly, the remaining quantity sensing portion  8   a  senses the toner in the second container  52  being empty based on the number of revolutions of the second gear  73  (second conveying member  69 ). Next, the control portion  8  controls the motor  71  to rotate the third gear  74  (the first conveying member  68 ) and thereby start the supply of toner from the first container  51  to the developing device  40 . 
     According to the above construction, with the single optical sensor  83 , it is possible to separately detect the rotation of the second gear  73  (the second conveying member  69 ) and the third gear  74  (the first conveying member  68 ). Thus, with a cost- and size-reduced construction, it is possible to accurately detect the remaining quantity of toner in the two containers (first and second containers  51  and  52 ) that supply toner to the single developing device  40 . 
     The description given above of embodiments of the present disclosure is in no way meant to limit the scope of the present disclosure; the present disclosure can be implemented with any modifications made without departing from the spirit of the present disclosure. 
     For example, while in the embodiment described above, the image forming apparatus  1  is assumed to be a color-printing image forming apparatus of what is called a tandem type in which images of a plurality of colors are formed so as to be sequentially superposed on each other, this is not meant as any limitation to that and similar types. The image forming apparatus may be a color-printing image forming apparatus of any type other than a tandem type, or may be an image forming apparatus for monochrome printing.