Patent Publication Number: US-10310428-B2

Title: Image forming apparatus and method of controlling the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2017-070322, which was filed on Mar. 31, 2017, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND 
     Technical Field 
     The following disclosure relates to an image forming apparatus including a supplier configured to supply a developer from a developer storage to a developing device and also relates to a method of controlling the image forming apparatus. 
     Description of Related Art 
     There has been known an image forming apparatus including: a developing device having a developing roller; and a supplier configured to add or supply new or fresh toner into the developing device as needed. In the known apparatus, the toner is supplied into the developing device in an amount corresponding to an amount of consumption of the toner based on a dot count, so as to keep a constant amount the toner in a developing chamber. 
     SUMMARY 
     In the case where an error such as a paper jam occurs in the disclosed apparatus in the middle of supplying the toner into the developing device, it is needed to stop rotating the developing roller and suspend the supply of the toner. In such a case, if the toner is supplied in a state in which the rotation of the developing roller is stopped and the toner in the developing chamber is not agitated, there may be caused a risk that the supplied toner and the toner in the developing chamber are not agitated. 
     Accordingly, one aspect of the present disclosure relates to a technique of obviating a state in which the supplied toner and the toner in the developing device are not agitated. 
     One aspect of the present disclosure provides an image forming apparatus, including: a photoconductor; an exposing device configured to expose the photoconductor and form an electrostatic latent image on the photoconductor; a developing device including a developing roller configured to form a developer image on the photoconductor; a developer storage storing developer; a supplier configured to supply the developer from the developer storage to the developing device; and a controller configured to execute: a rotating process of rotating the developing roller; a developing process of developing, by the developing device, the electrostatic latent image on the photoconductor; a supplying process of supplying, by the supplier, the developer to the developing device; and a stopping process of stopping rotation of the developing roller after the supplying process has been suspended in a case where the supplying process is being executed. 
     Another aspect of the present disclosure provides a method of controlling an image forming apparatus, including: a photoconductor; an exposing device configured to expose the photoconductor and form an electrostatic latent image on the photoconductor; a developing device including a developing roller configured to form a developer image on the photoconductor; a developer storage storing developer; and a supplier configured to supply the developer from the developer storage to the developing device, the method comprising: a rotating step of rotating the developing roller; a developing step of developing, by the developing device, the electrostatic latent image on the photoconductor; a supplying step of supplying, by the supplier, the developer to the developing device; and a stopping step of stopping rotation of the developing roller after the supplying step has been suspended in a case where the supplying step is being executed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of one embodiment, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a view showing a general structure of a printer according to one embodiment; 
         FIG. 2  is a cross-sectional view of a process cartridge; 
         FIG. 3  is a cross-sectional view taken along line I-I in  FIG. 2 ; 
         FIG. 4A  is a view showing a relationship among members when a transmitting mechanism is in a disconnected state; 
         FIG. 4B  is a view showing a relationship among the members when the transmitting mechanism is in the disconnected state; 
         FIG. 4C  is a view showing a relationship among the members when the transmitting mechanism is in the disconnected state; 
         FIG. 5A  is a view showing a relationship among the members when the transmitting mechanism is in a connected state; 
         FIG. 5B  is a view showing a relationship among the members when the transmitting mechanism is in the connected state; 
         FIG. 5C  is a view showing a relationship among the members when the transmitting mechanism is in the connected state; 
         FIG. 6  is a block diagram showing a relationship between a controller and members of the image forming apparatus; 
         FIG. 7  is a flowchart indicating an operation of the controller; 
         FIG. 8  is a flowchart indicating a toner amount recognition process; 
         FIG. 9  is a flowchart indicating an exposure process; 
         FIG. 10  is a flowchart indicating an end determining process; 
         FIG. 11  is a flowchart indicating a conveyance switching process; and 
         FIG. 12  is a flowchart indicating a conveyance switching process according to a modification. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     There will be next explained in detail one embodiment of the present disclosure referring to the drawings. In the following explanation, directions are defined based on directions indicated in  FIG. 1 . That is, a right side and a left side in  FIG. 1  are respectively defined as a front side and a rear side, and a side corresponding to a back surface of the sheet of  FIG. 1  and a side corresponding to a front surface of the sheet of  FIG. 1  are respectively defined as a right side and a left side. Further, an up-down direction in  FIG. 1  is defined as an up-down direction. 
     As shown in  FIG. 1 , a printer  100  as one example of an image forming apparatus includes, in a printer housing  120 , a feeder portion  130  configured to supply a sheet S as one example of a sheet, an image forming portion  140  configured to form an image on the sheet S, a controller  200 , a motor  300  as one example of a drive source, and a return conveyor mechanism  400 . A drive force of the motor  300  is transmitted to the feeder portion  130  and the image forming portion  140 . 
     The feeder portion  130  includes a sheet supply tray  131  removably mounted on a lower portion of the printer housing  120  and a conveyor mechanism  132  configured to convey the sheet S in the sheet supply tray  131  toward a transfer roller  183 . The conveyor mechanism  132  includes: a sheet supply mechanism  133  configured to convey the sheet S in the sheet supply tray  131  toward registration rollers  134 ; and the registration rollers  134  for properly positioning each position in the leading edge of the sheet S being conveyed. A first sheet sensor  101 , as one example of a detector, is provided downstream of the registration rollers  134  in a conveyance direction of the sheet S. The first sheet sensor  101  is configured to detect the sheet S conveyed from the registration rollers  134  toward the transfer roller  183 . The first sheet sensor  101  is disposed nearer to the registration rollers  134  than to the transfer roller  183 . 
     The first sheet sensor  101  includes, for instance, a swing lever configured to swing by being pushed by the sheet S that is being conveyed and an optical sensor configured to detect swinging of the swing lever. In the present embodiment, the first sheet sensor  101  is in an ON state while the sheet S is passing, namely, while the swing lever is being laid down by the sheet S. 
     A third sheet sensor  103  is provided upstream of the registration rollers  134  in the conveyance direction of the sheet S. The third sheet sensor  103  is configured to detect the sheet S conveyed toward the registration rollers  134  from the sheet supply mechanism  133  or the return conveyor mechanism  400 . The third sheet sensor is similar in construction to the first sheet sensor  101 . The registration rollers  134  come into contact with the conveyed sheet S in a state in which the rotation of the registration rollers  134  is stopped, and the registration rollers  134  starts to rotate when a predetermined time elapses after a time point of detection of the sheet S by the third sheet sensor  103 , thereby properly positioning the leading edge of the sheet S. 
     The image forming portion  140  includes an exposing device  150 , a process unit  160 , and a fixing device  170 . 
     The exposing device  150  of a laser scanner unit is provided in an upper portion of the printer housing  120  and includes a laser light emitter, a polygon mirror, lenses, and reflective mirrors. In the exposing device  150 , a laser beam is applied to a surface of a photoconductive drum  181  by high-speed scanning. 
     The process unit  160  includes the photoconductive drum  181  as one example of a photoconductor, a charger  182 , the transfer roller  183  as one example of a transfer device, and a process cartridge PC. Toner, as one example of a developer, is stored in the process cartridge PC. 
     The process cartridge PC is mountable on and removable from the printer housing  120  through an opening  122  which is opened and closed by a front cover  123  pivotably provided on a front wall of the printer housing  120 . The process cartridge PC will be later explained in detail. 
     In the process unit  160 , the surface of the photoconductive drum  181  that rotates is uniformly charged by the charger  182  and is subsequently exposed to a high-speed scanning of a laser beam from the exposing device  150 . Thus, an electrostatic latent image based on image data is formed on the surface of the photoconductive drum  181 . 
     Subsequently, the toner in the process cartridge PC is supplied to the electrostatic latent image on the photoconductive drum  181 , so that a toner image is formed on the surface of the photoconductive drum  181 . Thereafter, the sheet S is conveyed between the photoconductive drum  181  and the transfer roller  183 , so that the toner image formed on the surface of the photoconductive drum  181  is transferred onto the sheet S. 
     The fixing device  170  includes a heating roller  171  and a pressure roller  172  pressed onto the heating roller  171 . The fixing device  170  thermally fixes the toner transferred onto the sheet S while the sheet S is passing between the heating roller  171  and the pressure roller  172 . A second sheet sensor  102  is disposed downstream of the fixing device  170  in the conveyance direction of the sheet S. The second sheet sensor  102  is configured to detect passage of the sheet S discharged from the fixing device  170 . The second sheet sensor  102  is similar in construction to the first sheet sensor  101  described above. 
     The sheet S that has been subjected to thermal fixation of the toner by the fixing device  170  is conveyed to a discharge roller R disposed downstream of the fixing device  170  and is subsequently discharged onto the sheet discharge tray  121  by the discharge roller R. 
     In duplex printing to form images on both surfaces of the sheet S, the discharge roller R rotates reversely before an entirety of the sheet S is discharged onto the sheet discharge tray  121 , so that the sheet S is pulled back into the printer housing  120 . The sheet S pulled back into the printer housing  120  is permitted to pass rearward of the fixing device  170  by switching of a flapper  110  and is subsequently conveyed to the return conveyor mechanism  400 . 
     The return conveyor mechanism  400  is a mechanism for turning, upside down, the sheet S on which the toner image has been formed on its first surface by the fixing device  170  and returning or re-conveying the sheet S to the upstream side of the registration rollers  134 . The return conveyor mechanism  400  is disposed between the image forming portion  140  and the sheet supply tray  131 . The return conveyor mechanism  400  includes a guide member  410  and a plurality of return rollers  420 . 
     The guide member  410  is a guide for changing, frontward, the direction of the sheet S which passes rearward of the fixing device  170  and is conveyed downward. The return rollers  420  are configured to return the sheet S guided by the guide member  410  to the upstream side of the registration rollers  134 . 
     The return rollers  420  are configured to rotate in a predetermined direction by the drive force of the motor  300 , irrespective of the rotational direction of the motor  300 . That is, the return rollers  420  rotate in a direction to convey the sheet S toward the registration rollers  134  both of when the motor  300  rotates forwardly and when the motor  300  rotates reversely. 
     The sheet S conveyed by the return conveyor mechanism  400  is sent to the registration rollers  134  with the sheet S turned upside down. After the leading edge of the sheet S is properly positioned by the registration rollers  134 , the sheet S is conveyed again to between the photoconductive drum  181  and the transfer roller  183 , and the toner image on the photoconductive drum  181  is transferred to a second surface of the sheet S. 
     As shown in  FIG. 6 , the motor  300  is connected to the developing roller  12  (specifically, to the coupling CP) via a clutch mechanism  310 . Further, the motor  300  is connected to the discharge roller R. The clutch mechanism  310  is configured to perform transmission and cutoff of the drive force by an electromagnetic clutch or a solenoid, for instance. In this configuration, when the motor  300  rotates forwardly, the discharge roller R rotates in a direction to discharge the sheet S to the sheet discharge tray  121 . When the motor  300  rotates reversely, the discharge roller R rotates in a direction to pull the sheet S back into the printer housing  120 . In rotating the motor  300  reversely, the transmission of the drive force is cut off by the clutch mechanism  310 , so that the developing roller  12  stops rotating. 
     As shown in  FIG. 2 , the process cartridge PC includes a developing cartridge  1  as one example of a developing device and a toner cartridge  2  as one example of a developer storage. 
     The developing cartridge  1  includes a housing  11 , a developing roller  12 , a supply roller  13 , a layer-thickness limiting blade  14 , and a first agitator  15  as one example of an agitator. The housing  11  houses the developer therein. The housing  11  supports the layer-thickness limiting blade  14  and rotatably supports the developing roller  12 , the supply roller  13 , and the first agitator  15 . 
     The developing roller  12  is configured to supply the toner to the electrostatic latent image formed on the photoconductive drum  181 . The developing roller  12  is rotatable about a rotation axis extending in a right-left direction. 
     The supply roller  13  is configured to supply, to the developing roller  12 , the toner in the housing  11 . The layer-thickness limiting blade  14  is a member for limiting a thickness of the toner on the developing roller  12 . 
     The first agitator  15  includes: a shaft portion  15 A rotatable about a first axis X 1  which is its rotation axis parallel to a rotation axis of the developing roller  12 ; and an agitating blade  15 B fixed to the shaft portion  15 A. The housing  11  rotatably supports the shaft portion  15 A. The agitating blade  15 B is configured to rotate clockwise in  FIG. 2  together with the shaft portion  15 A, so as to agitate the toner in the housing  11 . 
     As shown in  FIG. 3 , the printer  100  includes an optical sensor  190  configured to detect an amount of the toner in the housing  11 . The optical sensor  190  includes a light emitter  191  for emitting light into an inside of the housing  11  and a light receiver  192  for receiving the light which has been emitted from the light emitter  191  and which has passed through the inside the housing  11 . The light emitter  191  and the light receiver  192  are provided on the printer housing  120 . Specifically, the light emitter  191  is disposed on one of opposite sides of the housing  11  in the right-left direction, and the light receiver  192  is disposed on the other of the opposite sides of the housing  11  in the right-left direction. 
     The housing  11  includes light guide portions  11 B which permit the light emitted from the light emitter  191  to pass through the inside of the housing  11 , so as to guide the light to the light receiver  192 . The light guide portions  11 B are formed on respective wall surfaces of the housing  11  in the right-left direction. Each light guide portion  11 B is formed of a light transmitting member that enables transmission of the light from the light emitter  191 . The wall surfaces of the housing  11  in the right-left direction are formed of a material that does not allow transmission of the light from the light emitter  191 . As shown in  FIG. 2 , the light guide portions  11 B are located at a height level higher than the first axis X 1 . Thus, the light emitted from the light emitter  191  passes between the first axis X 1  and an auger  22  (which will be explained) in the up-down direction. 
     The toner cartridge  2  is mountable on and removable from the developing cartridge  1 . The toner cartridge  2  includes: a housing  21  in which the toner is stored; the auger  22 , as one example of a supplier, configured to supply the toner in the housing  21  to the developing cartridge  1 ; and a second agitator  23  configured to rotate clockwise in  FIG. 2  so as to agitate the toner in the housing  21 . 
     The auger  22  is rotatable about a rotation shaft  22 A extending in the right-left direction. The auger  22  is configured to rotate so as to convey the toner in the housing  21  in the axial direction. Specifically, the auger  22  is a screw auger including the rotation shaft  22 A and a plate  22 B helically provided around the rotation shaft  22 A. The plate  22 B of the auger  22  is formed integrally with the rotation shaft  22 A. 
     The housing  21  includes an outlet  21 A through which the toner in the housing  21  is supplied to the developing cartridge  1 . The housing  11  of the developing cartridge  1  includes an inlet  11 A facing the outlet  21 A. The outlet  21 A and the inlet  11 A are located below the auger  22  and on one end side of the auger  22  in the axial direction. In this configuration, as shown in  FIG. 3 , when the auger  22  rotates, the toner is conveyed toward the one end side in the axial direction by the helical plate  22 B, so that the toner is supplied into the housing  11  through the outlet  21 A and the inlet  11 A. 
     The auger  22  includes an auger gear  22 G as one example of a transmission gear. The auger gear  22 G is a gear for transmitting a drive force to the auger  22 . The auger gear  22 G is fixed to the shaft of the auger  22 . 
     The second agitator  23  includes a shaft portion  23 A parallel to the right-left direction and an agitating blade  23 B provided on the shaft portion  23 A. A second agitator gear  23 G is fixed to one end portion of the shaft portion  23 A of the second agitator  23 . The second agitator gear  23 G is in mesh with the auger gear  22 G. 
     As shown in  FIG. 4A , the developing cartridge  1  includes a coupling CP, a developing gear Gd, a supply gear Gs, a fourth gear  40 , and a transmitting mechanism TM. The coupling CP is configured to rotate clockwise in  FIG. 4A  when the drive force is input thereto from the motor  300  ( FIG. 1 ). The coupling CP includes a coupling gear Gc. 
     The developing gear Gd is a gear for driving the developing roller  12 . The developing gear Gd is in mesh with the coupling gear Gc. The supply gear Gs is a gear for driving the supply roller  13 . The supply gear Gs is in mesh with the coupling gear Gc. 
     The fourth gear  40  is rotatable about a fourth axis X 4  extending in the axial direction. The fourth gear  40  includes a large-diameter gear  41  which is in mesh with the coupling gear Gc and a small-diameter gear  42  ( FIG. 4C ) having a smaller outside diameter than the large-diameter gear  41 . The small-diameter gear  42  rotates together with the large-diameter gear  41 . The small-diameter gear  42  is located between the housing  11  and the large-diameter gear  41  in the axial direction. The fourth gear  40  rotates counterclockwise in  FIG. 4A  when the drive force of the motor  300  is input to the coupling CP. 
     The transmitting mechanism TM is a mechanism for transmitting the drive force of the motor  300  to the auger  22 . A state of the transmitting mechanism TM is switchable between: a disconnected state in which the drive force is not transmitted to the auger  22 ; and a connected state in which the drive force is transmitted to the auger  22 . The transmitting mechanism TM includes mainly a first gear G 1 , a second gear G 2 , a lever  50 , a supporter  60 , and a third gear  30 . 
     The first gear G 1  is fixed to the shaft portion  15 A of the first agitator  15 . Thus, the first gear G 1  rotates about the first axis X 1  together with the first agitator  15 . As shown in  FIG. 4C , the first gear G 1  is in mesh with the small-diameter gear  42  of the fourth gear  40 . Thus, the drive force of the motor  300  is input to the first gear G 1 . The first gear G 1  to which the drive force is input rotates clockwise in  FIG. 4C . 
     The second gear G 2  is rotatable about a second axis X 2  extending in the axial direction. The second gear G 2  is pivotable about the first gear G 1  while being in mesh with the first gear G 1 . Specifically, the second gear G 2  is revolvable about the first axis X 1  and pivots between: a first position shown in  FIG. 4C ; and a second position shown in  FIG. 5C . When the second gear G 2  is positioned at the first position, the second gear G 2  is out of mesh with the auger gear  22 G. When the second gear G 2  is positioned at the second position, the second gear G 2  is in mesh with the auger gear  22 G. 
     The supporter  60  rotatably supports the first gear G 1  and the second gear G 2 . The supporter  60  is pivotable about the first axis X 1  with the second gear G 2  between a first position and a second position. 
     As shown in  FIG. 4A , the third gear  30  is rotatable about a third axis X 3  extending in the axial direction. The third gear  30  includes: a cam  31  for pressing, counterclockwise in  FIG. 4A , a pressed portion  61  which is a lower end portion of the supporter  60 ; and a spring engaging portion  34 . The spring engaging portion  34  has a dimension (height) in the axial direction smaller than that of the cam  31 , so that the spring engaging portion  34  does not come into contact with the pressed portion  61  of the supporter  60 . The spring engaging portion  34  is disposed opposite to the cam  31  with the third axis X 3  interposed therebetween. The cam  31  and the spring engaging portion  34  have an identical shape as viewed in the axial direction and are configured to be biased by a second spring SP 2 . The second gear G 2  is placed at the first position when the pressed portion  61  of the supporter  60  is supported by the cam  31  as shown in  FIG. 4A , and the second gear G 2  is movable to the second position when the cam  31  is moved away from the supporter  60  as shown in  FIG. 5A . 
     When the second gear G 2  is positioned at the first position, the cam  31  is biased counterclockwise in  FIG. 4A  by the second spring SP 2 . When the second gear G 2  is positioned at the second position, the spring engaging portion  34  is biased counterclockwise in  FIG. 5A  by the second spring SP 2 . The biasing force of the second spring SP 2  when the second gear G 2  is positioned at the first position is received by a first engaging portion  51 B of the lever  50  via a protruding portion  37  provided for the third gear  30 , as shown in  FIG. 4B . The biasing force of the second spring SP 2  when the second gear G 2  is positioned at the second position is received by a second engaging portion  52 B of the lever  50  via the protruding portion  37 , as shown in  FIG. 5B . 
     As shown in  FIG. 4C , the third gear  30  includes two gear toothed portions  35 A,  35 B and two missing tooth portions  36 A,  36 B. When the second gear G 2  is positioned at the first position, one of the two missing tooth portions, namely, the missing tooth portion  36 A, is opposed to the first gear G 1 . When the second gear G 2  is positioned at the second position, the other of the two missing tooth portions, namely, the missing tooth portion  36 B, is opposed to the first gear G 1  ( FIG. 5C ). 
     As shown in  FIG. 4B , the lever  50  is pivotable about the first axis X 1  and is biased counterclockwise by a first spring SP 1 . The engaging portions  51 B,  52 B described above are provided at one end of the lever  50 . At the other end of the lever  50 , there is provided a receiving portion  53 D which is engageable with a driving lever DL provided on the printer housing  120 . The driving lever DL pivots about a pivot shaft DS provided on the printer housing  120 . 
     In the thus constructed transmitting mechanism TM, when the driving lever DL pivots counterclockwise from the state shown in  FIG. 4A , the lever  50  is pivoted clockwise by the driving lever DL against the biasing force of the first spring SP 1 . As a result, the first engaging portion  51 B of the lever  50  shown in  FIG. 4B  is disengaged from the protruding portion  37 . 
     When the first engaging portion  51 B is disengaged from the protruding portion  37 , the third gear  30  is rotated counterclockwise by the biasing force of the second spring SP 2 . As a result, the first gear toothed portion  35 A of the third gear  30  shown in  FIG. 4C  is brought into mesh with the first gear G 1 . 
     When the first gear toothed portion  35 A is brought into mesh with the first gear G 1 , the third gear  30  to which the drive force is transmitted from the first gear G 1  is further rotated. As a result, the cam  31  shown in  FIG. 4A  pivots in a direction away from the pressed portion  61  which is the lower end portion of the supporter  60 . 
     When the cam  31  thus pivots, the supporter  60  that has been supported by the cam  31  pivots from the first position to the second position. Specifically, the supporter  60  receives a friction force from the first gear G 1  that rotates clockwise, so that the supporter  60  pivots in the same direction as the rotational direction of the first gear G 1 . 
     When the supporter  60  thus pivots, the second gear G 2  supported by the supporter  60  also pivots from the first position to the second position. Further, the second gear G 2  receives the drive force from the first gear G 1 , so that the second gear G 2  rotates counterclockwise. As a result, the second gear G 2  is brought into mesh with the auger gear  22 G, so that the auger  22  is rotated. That is, the state of the transmitting mechanism TM is switched from the disconnected state to the connected state, whereby the developing roller  12 , the supply roller  13 , the first agitator  15 , the auger  22 , and the second agitator  23  are rotated by the drive force of the motor  300 . 
     When the third gear  30  further rotates, the spring engaging portion  34  pivots toward the second spring SP 2  so as to once contract the second spring SP 2 . Thereafter, the spring engaging portion  34  pivots in a direction away from the second spring SP 2 , so that the spring engaging portion  34  is biased counterclockwise by the second spring SP 2 . As shown in  FIG. 5C , when the first gear toothed portion  35 A of the third gear  30  becomes out of mesh with the first gear G 1 , the transmission of the drive force from the first gear G 1  to the third gear  30  is cut off. In this instance, the second spring SP 2  biases the spring engaging portion  34  as described above, so that the third gear  30  slightly rotates by the biasing force of the second spring SP 2  and the protruding portion  37  shown in  FIG. 5B  comes into engagement with the second engaging portion  52 B of the lever  50 . As a result, as shown in  FIG. 5A , the third gear  30  stops rotating, so that the cam  31  is kept at a position away from the pressed portion  61  of the supporter  60 . Thus, the second gear G 2  is kept positioned at the second position. 
     When the driving lever DL is returned from the state of  FIG. 5A  to its original position (shown in  FIG. 4A ), the lever  50  is returned to its original position by the biasing force of the first spring SP 1 . Thus, the second engaging portion  52 B is disengaged from the protruding portion  37 , and the cam  31  pivots to and stops at the position shown in  FIG. 4A  according to a motion similar to that described above. The pressed portion  61  of the supporter  60  is pushed by the cam  31  which thus pivots. As a result, the pressed portion of the supporter pivots counterclockwise, so that the second gear G 2  moves from the second position to the first position. That is, the state of the transmitting mechanism TM is switched from the connected state to the disconnected state, whereby the auger  22  and the second agitator  23  stop rotating whereas the developing roller  12 , the supply roller  13 , and the first agitator  15  keep rotating. 
     As shown in  FIG. 6 , the controller  200  includes a CPU, a RAM, a ROM, a nonvolatile memory, an ASIC, and an input/output circuit. The controller  200  executes control by executing various arithmetic processing based on a print command output from an external computer, signals output from the sensors  101 - 103 ,  190 , and programs and data stored in the ROM, for instance, so as to control the motor  300 , the clutch mechanism  310 , the driving lever DL, and so on. The controller  200  is configured to execute a developing process, a usage-amount obtaining process, a supplying process, a detecting process, a stopping process, and a threshold correcting process. In other words, the controller  200  operates based on the programs so as to function as a means to execute the processes described above. Further, a controlling method by the controller  200  includes steps of executing the processes. 
     The developing process is a process of developing an electrostatic latent image on the photoconductive drum  181 . Specifically, in a state in which an appropriate voltage is applied to the developing roller  12 , the controller  200  executes an exposure process in which the controller blinks the exposing device  150  based on image data in accordance with the print command, so as to execute the developing process. Further, the controller  200  causes the first agitator  15  to rotate at a first speed V 1  in the developing process. 
     The usage-amount obtaining process is a process of obtaining a usage amount Qu of the toner in the developing process. In the usage-amount obtaining process, the controller  200  obtains the usage amount Qu based on the number of dots of binary image data used in the exposure. 
     In the case where the number of dots per unit area is not greater than a predetermined value, the number of dots may be regarded as the predetermined value. In a toner saving mode, for instance, the usage amount Qu may be calculated so as to be smaller by multiplying the number of dots by a coefficient less than 1. 
     The controller  200  has a function of executing the usage-amount obtaining process after a toner image corresponding to an image for one sheet S has been formed on the photoconductive drum  181  in the developing process. Specifically, in the present embodiment, the controller  200  executes the usage-amount obtaining process after the state of the second sheet sensor  102  has been switched from ON to OFF, namely, after the sheet S has passed through the fixing device  170 . 
     The supplying process is a process of supplying the toner by the auger  22  to the developing cartridge  1 . The controller  200  executes the supplying process on the condition that the usage amount Qu from a time point of execution of a preceding supplying process up to a current time point becomes equal to or greater than a first threshold TH 1 . Specifically, in the present embodiment, the controller  200  sets a flag F 1  for executing the supplying process to 1 in the case where an increase amount Qu 1  of the usage amount Qu from the time point of execution of the preceding supplying process up to the current time point becomes equal to or greater than the first threshold TH 1 . In this configuration, the supplying process is executed every time when the usage amount Qu of the toner becomes equal to or greater than the first threshold TH 1 . 
     Here, the first threshold TH 1  is set to satisfy the following expression (1):
 
 M≤TH 1≤2 M . . .    (1)
 
M: maximum usage amount of toner for sheet S having a maximum size that can be printed
 
     The controller  200  has a function of supplying a predetermined amount of the toner to the developing cartridge  1  in the supplying process. In the supplying process, the controller  200  causes the auger  22  to rotate by the predetermined number of times. Specifically, the controller  200  causes, in the supplying process, the auger  22  to rotate at a predetermined rotational speed for a predetermined length of time. Here, the predetermined length of time corresponds to an execution period Td of the supplying process. 
     Here, an amount MF of the toner supplied to the developing cartridge  1  in the supplying process is set so as to satisfy the following expression (2):
 
 TH 1≤ MF≤ 2 M . . .    (2)
 
TH 1 : first threshold
 
M: maximum usage amount of toner for sheet S having a maximum size that can be printed
 
     In the present embodiment, the increase amount Qu 1  of the usage amount Qu is updated to a value obtained by subtracting the first threshold TH 1  every time when the supplying process is executed, specifically, every time when the flag F 1  is set to 1. Further, the usage amount Qu is counted as a total usage amount Qus and reset to an initial value every time when the toner cartridge  2  is replaced with new one. 
     The controller  200  has a function of starting, based on the signal indicative of detection of the sheet S by the first sheet sensor  101 , the supplying process before the formation of the electrostatic latent image for the sheet S is started. Specifically, the controller  200  starts the supplying process when a first predetermined length of time T 1  elapses from a time point when the state of the first sheet sensor  101  has been switched from OFF to ON. 
     Here, where a length of time before a time point of starting of the exposure process for the sheet S detected by the first sheet sensor  101  from the time point when the ON state of the first sheet sensor  101  has been established is defined as a third predetermined length of time T 3 , the first predetermined length of time T 1  is set so as to satisfy the following expression (3):
 
 T 1 &lt;T 3 . . .   (3)
 
     When the controller  200  starts the supplying process, the controller  200  controls the transmitting mechanism TM such that the state of the transmitting mechanism TM is switched from the disconnected state to the connected state by pivoting the driving lever DL counterclockwise in  FIG. 4 . The controller  200  ends the supplying process when an execution period Td elapses from a time point of starting of the supplying process. 
     The detecting process is a process of detecting, by the optical sensor  190 , the amount of the toner in the developing cartridge  1 , on the condition that the usage amount Qu from a time point of execution of a preceding detecting process up to a current time point becomes equal to or greater than a second threshold TH 2  larger than the first threshold TH 1 . Specifically, in the present embodiment, the controller  200  executes the detecting process when an increase amount Qu 2  of the usage amount Qu from the time point of execution of the preceding detecting process up to the current time point becomes equal to or greater than the second threshold TH 2 . In this configuration, the detecting process is executed every time when the usage amount Qu of the developer becomes equal to or greater than the second threshold TH 2 . The controller  200  executes the detecting process in a period in which the developing process is not being executed. 
     Here, the second threshold TH 2  may be set to a value more than twice as large as the first threshold TH 1 , e.g., a value ten times as large as the first threshold TH 1 , for instance. The increase amount Qu 2  of the usage amount Qu is updated to a value obtained by subtracting the second threshold TH 2  every time when the detecting process is executed. The increase amount Qu 1  and the increase amount Qu 2  are updated independently of each other. 
     In the case where the usage amount Qu becomes equal to or greater than the second threshold TH 2  during execution of the print job, the controller  200  suspends the print job and executes the detecting process. In the detecting process, the controller  200  controls the motor  300  such that the first agitator  15  rotates at a second speed V 2  lower than the first speed V 1 . Thus, the rotational speed of the first agitator  15  is lower in the detecting process than in the developing process. 
     In the case where the amount of the toner detected in the detecting process, namely, an amount Qr of the toner contained in the developing cartridge  1  (toner amount Qr), is larger than a predetermined amount Qth, the controller  200  executes control not to execute the supplying process. In the case where the toner amount Qr in the developing cartridge  1  detected in the detecting process is larger than the predetermined amount Qth, the controller  200  sets a flag F 2  to 1. On the other hand, in the case where the toner amount Qr is equal to or smaller than the predetermined amount Qth, the controller  200  sets the flag F 2  to 0. When the flag F 2  is 1, the supplying process is not executed. The supplying process is executed when the detecting process is again executed and the flag F 2  is set to 0. Here, the predetermined amount Qth is set to be a relatively large value, e.g., a value corresponding to about 70-90% of the volume of the developing cartridge  1 . 
     The toner in the developing cartridge  1  is deteriorated due to frictional charging between the developing roller  12  and the supply roller  13 . In this case, charging capability is lowered, for instance. For good printing, it is desirable that the toner in the developing cartridge  1  be composed of deteriorated toner and fresh toner mixed in an appropriate ratio. It is further desirable that the deteriorated toner and the fresh toner are agitated so as to be evenly distributed in the developing cartridge  1 . It is accordingly desirable that the amount of the toner in the developing cartridge  1  be held within a predetermined range. In the present embodiment, the supplying process is not executed when the toner amount Qr is larger than the predetermined amount Qth (Qr&gt;Qth). Thus, in the case where the toner amount Qr in the developing cartridge  1  is too large, it is possible to wait until the toner amount in the developing cartridge  1  decreases to an appropriate amount, thus enabling the toner amount to be held within the predetermined range. 
     The stopping process is a process of stopping rotation of the developing roller  12 . In the stopping process, the rotation of the developing roller  12  is stopped after the supplying process has been suspended in the case where the rotation of the developing roller  12  is stopped in a period in which the supplying process is being executed. Specifically, the controller  200  suspends the supplying process in the stopping process in the case where the developer is being supplied to the developing cartridge  1  in the supplying process. More specifically, the controller  200  switches, in the stopping process, the state of the transmitting mechanism TM from the connected state to the disconnected state, so as to suspend the supplying process. Thereafter, the controller  200  disengages the clutch mechanism  310  so as to cut off the transmission of the drive force from the motor  300  to the coupling CP. As a result, the developing roller  12  stops rotating. 
     The threshold correcting process is a process of correcting the first threshold TH 1  to a value smaller than that before the suspension of the supplying process, in the case where the supplying process is suspended by the execution of the stopping process. Specifically, the controller  200  sets an initial value of the first threshold TH 1  to a value γ. In the case where the controller  200  suspends the supplying process, namely, in the case where the controller  200  stops the supply of the toner by the auger  22  before the execution period Td elapses, the first threshold TH 1  is corrected to a value 0.5 γ smaller than the value γ. For instance, the first threshold TH 1  is corrected to a smaller value by multiplying the first threshold TH 1  by a coefficient less than 1 or by subtracting a predetermined value from the first threshold TH 1 . This configuration enables timing of starting the next the supplying process to be advanced. 
     There will be next explained an operation of the controller  200  in detail. 
     As shown in  FIG. 7 , when the print job is started, the controller  200  executes a printing preparation process (S 1 ). Specifically, at Step S 1 , the controller  200  controls the motor  300  to be in an ON state and applies a voltage to the developing roller  12 , the charger  182 , and so on. Thus, the developing roller  12  is rotated. In this instance, the controller  200  controls the motor  300  to rotate at a predetermined rotational speed such that a rotational speed Vr of the first agitator  15  is equal to the first speed V 1 . 
     After Step S 1 , the controller  200  executes a sheet feeding process (S 60 ). At Step S 60 , when the sheet S is supplied from the sheet supply tray  131 , the controller  200  causes the sheet supply mechanism  133  to pick up the sheet S and subsequently controls the registration rollers  134  based on the signal from the third sheet sensor  103 , so that the sheet S is fed toward the transfer roller  183 . When the sheet S that has been re-conveyed by the return conveyor mechanism  400  is fed toward the transfer roller  183 , the controller  200  controls the registration rollers  134  based on the signal from the third sheet sensor  103 , so that the sheet S is fed toward the transfer roller  183 . 
     After Step S 60 , the controller  200  determines whether the sheet S conveyed toward the transfer roller  183  needs to be re-conveyed after printing (S 2 ). Specifically, the controller  200  determines, based on the print command, whether printing on the second surface of the sheet S is needed after printing on the first surface of the sheet S when duplex printing is performed. 
     When it is determined at Step S 2  that the reconveyance is needed (Yes), the controller  200  sets a flag F 3  to 1 (S 3 ), the flag F 3  indicating that the reconveyance is needed. After Step S 3  or when a negative decision is made at Step S 2  (No), the controller  200  determines whether the ON state of the first sheet sensor  101  has been established (S 5 ). When it is determined that at Step S 5  that the first sheet sensor  101  is in the ON state (Yes), the controller  200  determines whether the flag F 1  for executing the supplying process is “1” (S 6 ). 
     When it is determined at Step S 6  that the flag F 1  is 1 (F 1 =1) (Yes), the controller  200  starts the supplying process when the first predetermined length of time T 1  elapses from the time point when the first sheet sensor  101  has become ON (S 7 ). In the case where the supplying process is already being executed at Step S 7 , the controller  200  executes no process and proceeds to next process. 
     After Step S 7  or when a negative decision is made at Step S 6  (No), the controller  200  determines whether the state of the second sheet sensor  102  has been switched from ON to OFF (S 9 ). When it is determined at Step S 9  that the state of the second sheet sensor  102  is in the OFF state (Yes), the controller  200  executes a toner amount recognition process (S 10 ). The toner amount recognition process will be later explained in detail. 
     After Step S 10 , the controller  200  determines whether the flag F 3  is 1 (S 11 ), the flag F 3  indicating that the reconveyance is needed. When it is determined at Step S 11  that the flag F 3  is 1 (F 3 = 1 ) (Yes), the controller  200  executes a conveyance switching process (S 12 ). The conveyance switching process will be later explained in detail. 
     After Step S 12  or when a negative decision is made at Step S 11  (No), the controller  200  determines whether the print job is ended (S 13 ). When it is determined at Step S 13  that the print job is not yet ended (No), the control flow goes back to Step S 60 . On the other hand, when it is determined at Step S 13  that the print job is ended (Yes), the controller  200  ends the present control. 
     As shown in  FIG. 8 , in the toner amount recognition process, the controller  200  executes the usage-amount obtaining process (S 31 ), so as to calculate the usage amount Qu of the toner. After Step S 31 , the controller  200  determines whether or not the flag F 2  is 0, the flag F 2  being for indicating that the toner amount in the developing cartridge  1  is larger than the predetermined amount (S 32 ). When it is determined at Step S 32  that the flag F 2  is 0 (F 2 =0) (Yes), the controller  200  determines whether or not the increase amount Qu 1  of the usage amount Qu from the time point of execution of the preceding supplying process up to the current time point is equal to or greater than the first threshold TH 1  (S 33 ). 
     When it is determined at Step S 33  that the increase amount Qu 1  is equal to or greater than the first threshold TH 1  (Qu 1 ≥TH 1 ) (Yes), the controller  200  sets the flag F 1  for starting the supplying process, to 1 (S 34 ). After Step S 34 , the controller  200  updates the increase amount Qu 1  to Qu 1 −TH 1  (S 35 ). 
     After Step S 35  or when a negative decision is made at Step S 32 , Step S 33  (No), the controller  200  determines whether or not the increase amount Qu 2  of the usage amount Qu from the time point of execution of the preceding detecting process up to the current time point is equal to or greater than the second threshold TH 2  (S 36 ). When it is determined at Step S 36  that the increase amount Qu 2  is equal to or greater than the second threshold TH 2  (Qu 2 ≥TH 2 ) (Yes), the controller  200  suspends the print job (S 37 ). Specifically, the controller  200  stops, at Step S 37 , pickup of the sheet S by the sheet supply mechanism  133 . 
     After Step S 37 , the controller  200  decreases the rotational speed of the motor  300  to a value lower than the current value, whereby the rotational speed Vr of the first agitator  15  is decreased to the second speed V 2  lower than the first speed V 1  (S 38 ). Thus, the first agitator  15  rotates more slowly than in printing. 
     After Step S 38 , namely, after the rotational speed of the first agitator  15  has been lowered, the controller  200  executes the detecting process (S 39 ). Thus, the detecting process can be appropriately executed. After the detecting process is executed, the controller  200  updates the increase amount Qu 2  to Qu 2 −TH 2 . 
     After Step S 39 , the controller  200  determines whether the toner amount Qr detected in the detecting process is larger than the predetermined amount Qth (S 40 ). When it is determined at Step S 40  that the toner amount Qr is larger than the predetermined amount Qth (Qr&gt;Qth) (Yes), the controller  200  sets the flag F 2  to 1 (S 41 ), the flag F 2  indicating that the toner amount in the developing cartridge  1  is larger than the predetermined amount. When a negative decision is made at Step S 36 , S 40  (No), the controller  200  sets the flag F 2  described above to 0 (S 42 ). The controller  200  ends the present control after Step S 41  or Step S 42 . 
     The controller  200  executes the exposure process shown in  FIG. 9  based on the print command. 
     In the exposure process of  FIG. 9 , when a print command is received, the controller  200  determines whether the ON state of the first sheet sensor  101  has been established (S 51 ). When it is determined at Step S 51  that the ON state of the first sheet sensor  101  has been established (Yes), the controller  200  starts the exposure process when the third predetermined length of time T 3  elapses from the time point when the ON state of the first sheet sensor  101  has been established (S 52 ). Here, the time of start of the supplying process is a time after the first predetermined length of time T 1  shorter than the third predetermined length of time T 3  has elapsed from the time point of the establishment of the ON state of the first sheet sensor  101 . Accordingly, the supplying process is started before the exposure process is started. 
     At Step S 52 , the controller  200  executes the exposure process for one sheet. That is, the controller  200  executes the exposure process for a predetermined execution time length Te. 
     After Step S 52 , the controller  200  determines whether the print job is ended (S 53 ). When it is determined at Step S 53  that the print job is not yet ended (No), the control flow goes back to Step SM. When it is determined at Step S 53  that the print job is ended (Yes), the controller  200  ends the present control. 
     In the case where the controller  200  starts the supplying process, the controller  200  executes an end determining process shown in  FIG. 10 . As shown in  FIG. 10 , in the end determining process, the controller  200  determines whether the execution period Td has elapsed from the time point of starting of the supplying process (S 71 ). When it is determined at Step S 71  that the execution period Td has elapsed (Yes), the controller  200  ends the supplying process (S 72 ). After Step S 72 , the controller  200  sets the flag F 1  back to 0 and ends the present control. 
     As shown in  FIG. 11 , in the conveyance switching process, the controller  200  determines whether the supplying process is being executed (S 81 ). The determination as to whether the supplying process is being executed may be made as follows, for instance. In the case where the supplying process is started at Step S 7 , a flag different from the flag F 1  for starting the supplying process may be set, and it may be determined whether or not this flag is 1. This flag may be set back to 0 together with the flag F 1  when the supplying process is ended. 
     When it is determined at Step S 81  that the supplying process is not being executed (No), the controller  200  disengages the clutch mechanism  310  so as to cut off the transmission of the drive force from the motor  300  to the coupling CP (S 85 ). Thus, the rotation of the developing roller  12 , etc., is stopped. 
     When it is determined at Step S 81  that the supplying process is being executed (Yes), the controller  200  switches the state of the transmitting mechanism TM from the connected state to the disconnected state, so as to suspend the supplying process (S 82 ). That is, when the supplying process is being executed, the supplying process is suspended (S 82 ) before the rotation of the developing roller  12 , etc., is stopped at Step S 85 . 
     After Step S 82 , the controller  200  corrects the first threshold TH 1  to a smaller value (S 83 ). Specifically, in the case where the first threshold TH 1  is γ, the controller  200  corrects the first threshold TH 1  to 0.5 γ smaller than γ. 
     After Step S 83 , the controller  200  sets the flag F 1  back to 0 (S 84 ), and the control flow goes to Step S 85 . After Step S 85 , the controller  200  controls the motor  300  to rotate reversely, so that the sheet S is re-conveyed (S 86 ). 
     After Step S 86 , the controller  200  determines whether or not the state of the third sheet sensor  103  is switched from OFF to ON (S 87 ). When it is determined at Step S 87  that the third sheet sensor  103  is in the ON state (Yes), the controller  200  controls the motor  300  to rotate forwardly (S 88 ). 
     After Step S 88 , the controller  200  engages the clutch mechanism  310 , so as to permit the drive force to be transmitted from the motor  300  to the coupling CP (S 89 ). After Step S 89 , the controller  200  sets the flag F 3  indicating that the reconveyance is needed, back to 0 (S 90 ), and ends the present control. 
     There will be next explained a concrete example of the operation of the controller  200 . 
     As shown in  FIG. 7 , when the controller  200  receives the print command of double-sided successive printing, the controller  200  repeats the processes of Step S 1 -S 13  (S 13 : No). Thus, every time when printing is performed on the first surface and the second surface of the sheet, the usage-amount obtaining process ( FIG. 8 : S 31 ) is executed. When the usage amount Qu which is successively added up every time when the usage-amount obtaining process is executed becomes equal to or greater than the first threshold TH 1  (S 33 : Yes), the flag F 1  is set to 1 (S 34 ). 
     When the sheet S to be next printed passes the first sheet sensor  101  (S 5 : Yes), an affirmative decision is made at Step S 6  (Yes), and the supplying process is started (S 7 ). When the conveyance switching process is executed in the period in which the supplying process is being executed, an affirmative decision is made at Step S 81  of  FIG. 11  (Yes), and the supplying process is suspended (S 82 ). That is, the supplying process is suspended before the developing roller  12  stops rotating at Step S 85 . In this configuration, the state of the transmitting mechanism TM is switched from the connected state to the disconnected state in a state in which the gears of the process cartridge PC are rotating. It is thus possible to reduce a resistance when the second gear G 2  is disengaged from the auger gear  22 G, so that the transmitting mechanism TM is appropriately switched to the disconnected state. 
     The present embodiment offers the following advantageous effects. 
     In the case where the sheet S is re-conveyed in the period in which the supplying process is being executed, namely, in the case where the rotation of the developing roller  12  is stopped in the period in which the supplying process is being executed, the supplying process is first suspended, and thereafter the rotation of the developing roller  12  is stopped. In other words, in the case where the rotation of the developing roller  12  needs to be stopped in the period in which the supplying process is being executed, the supplying process is first suspended, and thereafter the rotation of the developing roller  12  is stopped. It is accordingly possible to obviate an adverse influence caused when the toner supplied from the auger  22  is not agitated in the developing cartridge  1 . 
     When the supplying process is suspended by the execution of the stopping process, the first threshold TH 1  is corrected to a smaller value, so as to advance timing of starting of next supplying process. It is thus possible to obviate a shortage of the toner in the developing cartridge  1  due to the suspension of the supplying process. 
     The supplying process is started before the formation of the electrostatic latent image is started. This configuration prevents or reduces disturbance of the electrostatic latent image on the photoconductive drum  181  due to vibration caused at the time of starting the supplying process, namely, vibration caused at the time of switching the state of the transmitting mechanism TM. Further, detection, by the first sheet sensor  101 , of the sheet S conveyed toward the transfer roller  183  triggers the starting of the supplying process, and the supplying process is started before the formation of the electrostatic latent image for that sheet S is started, so that the toner is supplied into the developing cartridge  1  before the developing process for that sheet S is executed. Thus, when the developing process is executed, the condition of the toner in the developing cartridge  1 , namely, the ratio between deteriorated toner and fresh toner, is better than that before the starting of the supplying process, so as to prevent or reduce deterioration in the image quality. 
     The toner cartridge  2  is mountable on and removable from the developing cartridge  1 . When the amount of the toner in the toner cartridge  2  becomes less than a usable amount, only the toner cartridge  2  can be replaced without replacing the developing roller  12 . 
     The detecting process is executed in a period in which the print job is suspended, namely, in a period in which the developing process is not being executed, enabling accurate detection of the toner amount in the developing cartridge  1  by the optical sensor  190 . Further, the frequency of execution of the detecting process is lower than that of the supplying process. Thus, the detecting process can be executed in the case where there is a possibility that the toner amount in the developing cartridge  1  varies by a plurality of times of execution of the supplying processes. 
     The first agitator  15  is operated in the detecting process at the first speed V 1  lower than the second speed V 2 . This configuration prevents or reduces flying or scattering of the toner in the developing cartridge  1  in the detecting process and enables accurate detection of the toner amount by the optical sensor  190 . 
     When the condition for starting the detecting process is satisfied in a period in which the print job is being executed, the print job is suspended and the detecting process is executed. This configuration enables the toner amount in the developing cartridge  1  to be recognized at an earlier stage even in the case where the number of pages to be successively printed is large. 
     The supplying process is not executed when the toner amount Qr detected in the detecting process is larger than the predetermined amount Qth, so as to prevent the toner from being excessively supplied into the developing cartridge  1 . 
     The first threshold TH 1  is set so as to satisfy the expression (1). It is thus possible to prevent shortage of the toner in the developing cartridge  1  even when printing, in which the amount of the toner used for one sheet S is maximal, is successively performed on a plurality of sheets S. 
     In the case where the developing roller  12  and the auger  22  are driven by the same motor  300  common thereto, the load of the motor  300  changes when the state of the transmitting mechanism TM is switched from the disconnected state to the connected state. In this case, the rotation of the developing roller  12  becomes unstable, and the rotation of the photoconductive drum  181  that contacts the developing roller  12  accordingly becomes unstable. If the exposure process is executed in such a state, the electrostatic latent image tends to disturb. In the present embodiment, however, the supplying process is started before the exposure process is executed, namely, the transmitting mechanism TM is switched. It is thus possible to prevent or reduce disturbance of the electrostatic latent image. 
     It is to be understood that the present disclosure is not limited to the details of the illustrated embodiment but may be embodied otherwise as described below. In the following explanation, the same reference signs as used in the illustrated embodiment are used to identify the same components and processes as those in the illustrated embodiment, and a detailed explanation thereof is dispensed with. 
     In the illustrated embodiment, the first threshold TH 1  is corrected to a smaller value in the case where the supplying process is suspended. The present disclosure is not limited to this configuration. For instance, the controller  200  may execute: when the supplying process is suspended, an already-supplied amount calculating process of calculating an already-supplied amount of the toner that has been supplied from a time point of starting of the supplying process to a time point of suspension of the supplying process; and a post-suspension supplying process of supplying, by the auger  22  to the developing cartridge, the toner in an amount corresponding to a difference between: a predetermined amount which is a supply amount in the case where the supplying process is normally ended, namely, an amount that should be supplied in the supplying process; and the already-supplied amount. 
     Specifically, a conveyance switching process indicated in a flowchart of  FIG. 12  is executed. The flowchart of  FIG. 12  is partly changed from the flowchart of  FIG. 11 . The flowchart of  FIG. 12  includes new Steps S 100 , S 101  in place of Step S 83  of  FIG. 11 , and new Steps S 102 -S 104  between Step S 89  and Step S 90  of  FIG. 11 . 
     When the controller  200  suspends the supplying process (S 82 ), the controller  200  executes the already-supplied amount calculating process (S 100 ). Specifically, the controller  200  calculates at Step S 100  the already-supplied amount of the toner that has been supplied from the time point of starting of the supplying process to the time point of suspension of the supplying process. In this configuration, the already-supplied amount of the toner is calculated as a former time TF which is a length of time that has been elapsed from the time point of starting of the supplying process to the time point of suspension of the supplying process. After Step S 100 , the controller  200  sets a flag F 4  to 1 (S 101 ), the flag F 4  indicating that the already-supplied amount of the toner (the former time) has been calculated. 
     After the controller  200  has restarted the transmission of the drive force to the coupling CP at Step S 89 , the controller  200  determines whether or not the flag F 4  is 1 (S 102 ). When it is determined at Step S 102  that the flag F 4  is 1 (F 4 =1) (Yes), the controller  200  executes the post-suspension supplying process (S 103 ). 
     At Step S 103 , the controller  200  calculates the amount of the toner corresponding to the difference between: the predetermined amount which is the supply amount of the toner in the case where the supplying process is normally ended; and the already-supplied amount of the toner. The controller  200  controls the auger  22  to supply the calculated amount of the toner to the developing cartridge  1 . Specifically, the controller  200  calculates, as the toner amount corresponding to the difference, a latter time TL obtained by subtracting the former time TF from the execution period Td of the supplying process. The controller  200  controls the transmitting mechanism TM to be kept in the connected state during the latter time TL. 
     According to this configuration, the toner that could not be supplied to the developing cartridge  1  due to the suspension of the supplying process can be supplied by execution of the post-suspension supplying process. Accordingly, the toner amount in the developing cartridge  1  can be kept appropriate. 
     In the illustrated embodiment, the auger  22  having the helical plate  22 B is illustrated as one example of the supplier. The present disclosure is not limited to this configuration. For instance, the supplier may be configured to include a rotation shaft and a flat plate provided in parallel with the rotation shaft. 
     In the illustrated embodiment, the clutch mechanism  310  employs an electromagnetic clutch or the like and is controlled by the controller  200  so as to be engaged or disengaged. The clutch mechanism  310  may employ a one-way clutch mechanism such that the drive force is not transmitted to the developing roller  12  in reverse rotation of the motor  300 . 
     In the illustrated embodiment, the execution period Td of the supplying process is represented as a constant time. The execution period Td may be a time corresponding to a period in which the auger  22  is rotated by the predetermined number of times. In an arrangement in which the printing speed is changeable, for instance, the execution period Td may be configured to change in accordance with the printing speed such that the number of rotations of the auger  22  is constant for any printing speed. 
     In the illustrated embodiment, the photoconductive drum  181  is illustrated as one example of the photoconductor. The present disclosure is not limited to this configuration. The photoconductive drum  181  may be a belt-like photoconductor, for instance. 
     In the illustrated embodiment, the developing device and the developer storage are separately constituted. The present disclosure is not limited to this configuration. The developing device and the developer storage may be constituted integrally with each other. 
     In the illustrated embodiment, the usage amount Qu is obtained in the usage-amount obtaining process based on the number of dots of the image data. The present disclosure is not limited to this configuration. For instance, the usage amount may be obtained based on the number of printed sheets, the number of rotations of the photoconductive drum, or the number of detections of the sheet by the first sheet sensor or the second sheet sensor. 
     In the illustrated embodiment, the first agitator  15  having the single agitating blade  15 B is illustrated as one example of the agitator. The present disclosure is not limited to this configuration. For instance, the agitator may include a plurality of agitating blades. 
     In the illustrated embodiment, the transfer roller  183  that contacts the photoconductive drum  181  is illustrated as one example of the transfer device. The present disclosure is not limited to this configuration. For instance, the transfer device may be a transfer member, in an intermediate transfer system, facing an intermediate transfer belt that contacts the photoconductor. 
     In the illustrated embodiment, the first sheet sensor  101  is illustrated as one example of the detector. The present disclosure is not limited to this configuration. For instance, the detector may be a third sheet sensor provided upstream of the registration rollers in the conveyance direction. 
     In the illustrated embodiment, examples of the sheet S include thick paper, a post card, and thin paper. The present disclosure is not limited to this configuration. The sheet S may be an OHP sheet, for instance 
     The exposing device  150  may be an exposure head including a light emitting element such as an LED and configured to expose the photoconductor in close proximity to the photoconductor. 
     The elements explained in the illustrated embodiment and the modification may be suitably combined.