Abstract:
A developing cartridge may include multiple rotary members, at least one of the rotary members configured to be detected by an image forming apparatus. In one example, the rotary members may include engagement portions configured to engage with one another to rotate the rotary members. Additionally or alternatively, in a case where one rotary member is in a driven position, the other rotary member may be rotatable a predefined amount from a non-driving state in which the other rotary member is rotatably disengaged from the one rotary member, to a driving state in which the other rotary member rotatably engages the one rotary member with the engagement portions in contact with one another.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/229,106 filed Mar. 28, 2014, which is a continuation of U.S. patent application Ser. No. 13/053,020 filed Mar. 21, 2011, issued as U.S. Pat. No. 8,712,286 on Apr. 29, 2014, which claims priority from Japanese Patent Application No. 2010-068576, filed on Mar. 24, 2010, the entire subject matter of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Aspects of the present invention relate to a developing cartridge which is detachably mounted in an apparatus main body of an image forming apparatus such as a laser printer. 
     BACKGROUND 
     In an image forming apparatus such as a laser printer, a developing cartridge is detachably mounted in an apparatus main body. Toner is accommodated within the developing cartridge. When toner in the developing cartridge is used up, the developing cartridge is removed from the apparatus main body. Then, a new developing cartridge is mounted in the apparatus main body. In addition, when a sheet is jammed in the apparatus main body, there may be a situation in which the developing cartridge is removed from the apparatus main body, and after the jam is resolved, the developing cartridge is remounted in the apparatus main body. 
     In this type of image forming apparatuses, there is proposed an image forming apparatus in which a detection gear having an abutment projection is provided on a side surface of a developing cartridge, and when the developing cartridge is mounted in an apparatus main body, information on the developing cartridge is obtained based on rotation of the detection gear. 
     The detection gear is provided to be rotatable about an axis which extends in a direction which orthogonally intersects the side surface of the developing cartridge. Gear teeth are formed on a circumferential surface of the detection gear except a part thereof. Namely, the detection gear is a partly non-tooth gear. In addition, a transmission gear is provided on the side surface of the developing cartridge to be rotatable about an axis which extends in parallel to the axis of the detection gear with a space therebetween. The transmission gear rotates integrally with an agitator for agitating toner accommodated in the developing cartridge. Gear teeth are formed on a circumferential surface of the transmission gear so as to extend along the full circumference thereof. With a new developing cartridge, the gear teeth of the detection gear mesh with the gear teeth of the detection gear. When the developing cartridge is mounted in the apparatus main body, a driving force of a motor is inputted into the transmission gear, and the driving force is transmitted from the detection gear to the detection gear via the gear teeth of these gears. 
     With the driving force so transmitted, the detection gear rotates, and the abutment projection moves as the detection gear rotates. A sensor is provided in the apparatus main body for detecting a passage of the abutment projection while the abutment projection is regarded as a detection target. Then, whether the developing cartridge is new or used is determined based on whether or not the passage of the abutment projection is detected by the sensor within a predetermined length of time after the start of driving of the motor. When the detection gear continues to rotate so that a non-tooth portion of the detection gear comes to oppose the gear teeth of the transmission gear, the mesh engagement of the gear teeth of the transmission gear with the gear teeth of the detection gear is released, whereby the detection gear stops rotating (for example, see JP-A-2006-267994). 
     SUMMARY 
     Accordingly, an aspect of the present invention is to provide a developing cartridge which is superior to the conventional one in the configuration including a detectable member such as an abutment projection. 
     According to an illustrative embodiment of the present invention, there is provided a developing cartridge which is detachably mounted in an apparatus main body of an image forming apparatus, the developing cartridge comprising: a housing including a first side wall and a second side wall which are provided to oppose each other, the housing configured to accommodate developer therein; a receiving member provided on an outer side of the first side wall to be rotatable about a first axis which extends in an opposing direction of the first side wall and the second side wall, the receiving member configured to couple with a driving force output member provided in the apparatus main body to receive a driving force from the driving force output member; a developing roller provided between the first side wall and the second side wall to be rotatable about a second axis which extends in parallel to the first axis with a space therebetween, the developing roller configured to rotate by the driving force received by the receiving member; a first rotary member provided on the outer side of the first side wall to be rotatable about a third axis which extends in parallel to the first axis with a space therebetween, the first rotary member configured to rotate by the driving force received by the receiving member; a second rotary member provided on the outer side of the first side wall to be rotatable about a fourth axis which extends in parallel to the third axis with a space therebetween, the second rotary member configured to take a driven position where the second rotary member rotates by the driving force transmitted from the first rotary member and a non-driven position where the transmission of the driving force from the first rotary member is cut off; a detectable member provided on the outer side of the first side wall and configured to move in association with the rotation of the second rotary member and function as a detection target to be detected by a detection member provided in the apparatus main body; and a first engagement portion provided on the outer side of the first side wall in a position separated from a fifth axis which extends in parallel to the first axis with a space therebetween, the first engagement portion configured to rotate about the fifth axis by the driving force received by the receiving member, wherein the second rotary member includes a second engagement portion which is provided in a position separated from the fourth axis, wherein when the second rotary member is in the non-driven position, the second engagement portion is provided on a rotating locus drawn by the first engagement portion, and wherein the first engagement portion is configured to engage with the second engagement portion as the first engagement portion rotates, so that the second engagement portion moves rotationally about the fourth axis by a force received from the first engagement portion, whereby the second rotary member rotates from the non-driven position to the driven position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects of the present invention will become more apparent and more readily appreciated from the following description of illustrative embodiments of the present invention taken in conjunction with the attached drawings, in which: 
         FIG. 1  is a sectional view of a laser printer in which a developing cartridge according to an illustrative embodiment of the present invention is mounted; 
         FIG. 2A  is a perspective view of the developing cartridge as viewed from the left rear thereof; 
         FIG. 2B  is a left side view of the developing cartridge shown in  FIG. 2A  with a gear cover attached; 
         FIG. 2C  is a left side view of the developing cartridge shown in  FIG. 2A ; 
         FIG. 2D  is a left side of the developing cartridge shown in  FIG. 2A  with a part of a detectable rotary member detached; 
         FIG. 2E  is a perspective view of a part of the developing cartridge shown in  FIG. 2A  in an enlarged manner; 
         FIG. 3A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state immediately after the developing cartridge is mounted in a body casing; 
         FIG. 3B  is a left side view of the developing cartridge shown in  FIG. 3A  with a gear cover attached; 
         FIG. 3C  is a left side view of the developing cartridge shown in  FIG. 3A ; 
         FIG. 3D  is a left side of the developing cartridge shown in  FIG. 3A  with a part of the detectable rotary member detached; 
         FIG. 4A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 3A ; 
         FIG. 4B  is a left side view of the developing cartridge shown in  FIG. 4A  with the gear cover attached; 
         FIG. 4C  is a left side view of the developing cartridge shown in  FIG. 4A ; 
         FIG. 4D  is a left side of the developing cartridge shown in  FIG. 4A  with a part of the detectable rotary member detached; 
         FIG. 5A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 4A ; 
         FIG. 5B  is a left side view of the developing cartridge shown in  FIG. 5A  with the gear cover attached; 
         FIG. 5C  is a left side view of the developing cartridge shown in  FIG. 5A ; 
         FIG. 5D  is a left side of the developing cartridge shown in  FIG. 5A  with a part of the detectable rotary member detached; 
         FIG. 6A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 5A ; 
         FIG. 6B  is a left side view of the developing cartridge shown in  FIG. 6A  with the gear cover attached; 
         FIG. 6C  is a left side view of the developing cartridge shown in  FIG. 6A ; 
         FIG. 6D  is a left side of the developing cartridge shown in  FIG. 6A  with a part of the detectable rotary member detached; 
         FIG. 7A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 6A ; 
         FIG. 7B  is a left side view of the developing cartridge shown in  FIG. 7A  with the gear cover attached; 
         FIG. 7C  is a left side view of the developing cartridge shown in  FIG. 7A ; 
         FIG. 7D  is a left side of the developing cartridge shown in  FIG. 7A  with a part of the detectable rotary member detached; 
         FIG. 7E  is a perspective view of a part of the developing cartridge shown in  FIG. 7A  in an enlarged manner; 
         FIG. 8A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 7A ; 
         FIG. 8B  is a left side view of the developing cartridge shown in  FIG. 8A  with the gear cover attached; 
         FIG. 8C  is a left side view of the developing cartridge shown in  FIG. 8A ; 
         FIG. 8D  is a left side of the developing cartridge shown in  FIG. 8A  with a part of the detectable rotary member detached; 
         FIG. 9A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 8A ; 
         FIG. 9B  is a left side view of the developing cartridge shown in  FIG. 9A  with the gear cover attached; 
         FIG. 9C  is a left side view of the developing cartridge shown in  FIG. 9A ; 
         FIG. 9D  is a left side of the developing cartridge shown in  FIG. 9A  with a part of the detectable rotary member detached; 
         FIG. 10A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 9A ; 
         FIG. 10B  is a left side view of the developing cartridge shown in  FIG. 10A  with the gear cover attached; 
         FIG. 10C  is a left side view of the developing cartridge shown in  FIG. 10A ; 
         FIG. 10D  is a left side of the developing cartridge shown in  FIG. 10A  with a part of the detectable rotary member detached; 
         FIG. 11A  is a perspective view of the developing cartridge as viewed from the left rear thereof which shows a state following the state shown in  FIG. 10A ; 
         FIG. 11B  is a left side view of the developing cartridge shown in  FIG. 11A  with the gear cover attached; 
         FIG. 11C  is a left side view of the developing cartridge shown in  FIG. 11A ; 
         FIG. 11D  is a left side of the developing cartridge shown in  FIG. 11A  with a part of the detectable rotary member detached; 
         FIG. 12  is a timing chart showing operation timings of a main part when mounting of the developing cartridge is detected and the developing cartridge mounted is detected as new; 
         FIG. 13  is a timing chart showing other operation timings (operation timings with a third detection portion omitted) of the main part when mounting of the developing cartridge is detected and the developing cartridge mounted is detected as new; 
         FIG. 14  is a plan view showing a configuration (Modified Example 1) in which an engagement portion is formed separately from an agitator gear; 
         FIG. 15  is an illustrative side view showing a configuration (Modified Example 2) in which an engagement portion is formed on a gear different from an agitator gear; 
         FIG. 16  is a side view showing a configuration (Modified Example 3) in which a first detectable portion and a second detectable portion are integrated; 
         FIG. 17  is an illustrative side view showing a configuration (Modified Example 4) which employs alternative of a non-tooth portion of a detectable rotary member; 
         FIG. 18  is an example of a flowchart for detecting mounting of the developing cartridge and detecting whether or not the developing cartridge mounted is new (an example in which whether or not the developing cartridge is mounted is determined before the driving of a motor); and 
         FIG. 19  is another example of a flowchart for detecting mounting of the developing cartridge and detecting whether or not the developing cartridge mounted is new (an example in which whether or not the developing cartridge is mounted is determined after the driving of a motor). 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an illustrative embodiment of the present invention will be described in detail by reference to the accompanying drawings. 
     1. Overall Configuration of Laser Printer 
     As shown in  FIG. 1 , a laser printer  1  (an example of an image forming apparatus) includes a body casing  2  (an example of an apparatus main body). A cartridge mount/removal opening  3  is formed in one side wall of the body casing  2 , and a front cover  4  is provided for opening and closing the cartridge mount/removal opening  3 . 
     Note that in the following description, the side of the laser printer  1  where the front cover  4  is provided is referred to as a front side thereof. Upper, lower, left and right sides of the laser printer are so determined based a situation in which the laser printer  1  is viewed from the front side thereof In addition, a front and rear of a developing cartridge  7  is so determined based on a situation in which the developing cartridge  7  is mounted in the body casing  2 , and upper, lower, left and right sides thereof are so determined based on a situation in which the developing cartridge  7  is viewed from the front side thereof. 
     A process cartridge  5  is mounted in the body casing  2  in a position which is situated slightly further forwards than a center thereof. With the front cover  4  opened, the process cartridge  5  is mounted in and removed from the body casing  2  via the cartridge mount/removal opening  3 . 
     The process cartridge  5  includes a drum cartridge  6  and a developing cartridge  7  which is detachably attached in the drum cartridge  7 . 
     The drum cartridge  6  includes a drum frame  8 . A photosensitive drum  9  is held rotatably at a rear end portion of the drum frame  8 . In addition, a charger  10  and a transfer roller  11  are held in the drum frame  8 . The charger  10  and the transfer roller  11  are provided at the rear of and below the photosensitive drum  9 . 
     A portion of the drum frame  8  situated further forwards than the photosensitive drum  9  is configured as a developing cartridge attachment portion  12 , and the developing cartridge  7  is mounted in this developing cartridge attachment portion  12 . 
     The developing cartridge  7  includes a housing  13  which accommodates toner therein. A toner accommodation compartment  14  and a developing compartment  15 , which communicate with each other, are formed in an interior of the housing  13  so as to be situated adjacent to each other in a front-rear direction. 
     An agitator  16  is provided in the toner accommodation compartment  14  to be rotatable about an agitator rotating axis  17  which extends in a left-right direction. Toner accommodated in the toner accommodation compartment  14  is supplied from the toner accommodation compartment  14  to the developing compartment  15  while being agitated by rotation of the agitator  16 . 
     A developing roller  18  and a supply roller  19  are provided in the developing compartment  15  to be rotatable about a developing rotating axis  20  and a supplying rotating axis  21 , respectively, which extend in the left-right direction. The developing roller  18  is provided so that a part of a circumferential surface thereof is exposed from a rear end portion of the housing  13 . The developing cartridge  7  is attached in the drum cartridge  6  so that the circumferential surface of the developing roller  18  is brought into contact with a circumferential surface of the photosensitive drum  9 . The supply roller  19  is provided so that a circumferential surface thereof is brought into contact with the circumferential surface of the developing roller  18  from the front and below the developing roller  18 . Toner in the developing compartment  15  is supplied to the circumferential surface of the developing roller  18  by the supply roller  19  and is carried on the circumferential surface of the developing roller  18  in the form of a thin layer. 
     An exposing unit  22  which emits a laser beam is provided above the process cartridge  5  in the body casing  2 . 
     When forming an image, the photosensitive drum  9  is rotated clockwise as viewed in  FIG. 1  at a constant speed. The circumferential surface (the surface) of the photosensitive drum  9  is charged uniformly by discharge from the charger  10 . On the other hand, a laser beam is emitted from the exposing unit  22  based on image data received from a personal computer (not shown) which is connected to the printer  1 . The laser beam passes between the charger  10  and the developing cartridge  7  and is shone on to the circumferential surface of the photosensitive drum  9  which is uniformly positively charged so as to expose the circumferential surface of the photosensitive drum  9  selectively. By this exposure, electric charges are selectively removed from the portion of the photosensitive drum  9  which is so exposed, whereby an electrostatic latent image is formed on the circumferential surface of the photosensitive drum  9 . When the latent image comes to confront the developing roller  18  as a result of rotation of the photosensitive drum  9 , toner is supplied to the latent image from the developing roller  18 , whereby a toner image is formed on the circumferential surface of the photosensitive drum  9 . 
     A sheet feeding cassette  23  is provided at a bottom portion of the body casing  2 . A pickup roller  24  is provided above the sheet feeding cassette  23  for feeding sheets out of the sheet feeding cassette  23 . 
     In addition, a conveying path  25 , which has an S-shape as viewed from a side thereof, is formed in the body casing  2 . This conveying path  25  extends from the sheet feeding cassette  23  to reach a sheet discharging tray  26  which is formed on an upper surface of the body casing  2  by way of a nip between the photosensitive drum  9  and the transfer roller  11 . Provided on the conveying path  25  are a separation roller  27  and a separation pad  28 , which are provided so as to oppose each other, a pair of sheet feeding rollers  29 , a pair of registration rollers  30  and a pair sheet discharging rollers  31 . 
     Sheets P which are fed out of the sheet feeding cassette  23  are fed in between the separation roller  27  and the separation pad  28  so as pass therebetween sheet by sheet. Thereafter, the sheet P is conveyed towards the registration rollers by the sheet feeding rollers  29 . Then, the sheet P is registered by the registration rollers  30  and is thereafter conveyed towards between the photosensitive drum  9  and the transfer roller  11  by the registration rollers  30 . 
     When the toner image comes to face the sheet P passing between the photosensitive drum  9  and the transfer roller  11  as a result of rotation of the photosensitive drum  9 , the toner image on the circumferential surface of the photosensitive drum  9  is electrically attracted by the transfer roller  11  so as to be transferred to the sheet P. 
     A fixing unit  32  is provided on the conveying path  25  in a position situated further downstream in the conveying direction of the sheet P than the transfer roller  11 . 
     The sheet P to which the toner image is transferred is conveyed along the conveying path  25  and passes the fixing unit  32 . In the fixing unit  32 , the toner image is transformed into an image which is fixed on the sheet P by virtue of heat and pressure. 
     This printer  1  has, as operation modes, a single-side printing mode in which an image (a toner image) is formed on one side of a sheet P and a double-side printing mode in which after an image is formed on one side a sheet P, an image is formed on the other side of the sheet P which is opposite to the one side where the image has already been formed. 
     In the single-side printing mode, the sheet P on one side of which the image is formed is discharged into the sheet discharging tray  26  by the sheet discharging rollers  31 . 
     A reversely conveying path  33  is formed in the body casing  2  so as to realize the double-side printing mode. The reversely conveying path  33  starts from a position in proximity to the sheet discharging rollers  31 , extends between the conveying path  25  and the sheet feeding cassette  23  and is finally connected to a portion on the conveying path  25  which is situated between the sheet feeding rollers  29  and the registration rollers  30 . Provided on the reversely conveying path  33  are a pair of first reversely conveying rollers  34  and a pair of second reversely conveying rollers  35 . 
     In the double-side printing mode, after an image is formed on one side of a sheet P, the sheet P is not discharged into the sheet discharging tray  26  but is fed into the reversely conveying path  33 . Then, the sheet P is conveyed along the reversely conveying path  33  by the first reversely conveying rollers  34  and the second reversely conveying rollers  35  and is turned inside out so as to be fed into the conveying path  25  in a posture in which the other side of the sheet P on which no image is formed faces the circumferential surface of the photosensitive drum  9 . Then, an image is formed on the other side of the sheet P, whereby the formation of the images on both the sides of the sheet P is performed. 
     2. Developing Cartridge 
     (1) Housing 
     As shown in  FIG. 2A , the housing  13  of the developing cartridge  7  has a box shape which is opened at a rear side. Specifically, the housing  13  has a first side wall  41  and a second side wall  42 . The first side wall  41  and a second side wall  42  oppose each other in the left-right direction. The first and second side walls  41 ,  42  each have a plate-like shape and extend in the front-rear direction. In addition, the housing  13  has an upper wall  43  and a lower wall  44  which extend between upper end portions and lower end portions of the first side wall  41  and the second side wall  42 , respectively. A front end portion of the lower wall  44  extends upwards while being curved and is connected to a front end portion of the upper wall  43 . 
     (2) Gears 
     As shown in  FIGS. 2A, 2C , an input gear  45  (an example of a receiving member), a developing gear  46 , a supply gear  47 , an intermediate gear  48 , an agitator gear  49  (an example of a first rotary gear), and a detectable rotary member  50  (an example of a second rotary gear) are provided on an outer side (a left-hand side) of the first side wall  41  which is situated at a left-hand side of the housing  13 . 
     (2-1) Input Gear 
     The input gear  45  is provided at an upper portion of a rear end of the first side wall  41 . The input gear  45  is provided to be rotatable about an input gear rotation shaft  51  which extends in the left-right direction. The input gear rotation shaft  51  is held in the first side wall  41  so as not to rotate. 
     The input gear  45  has integrally a large-diameter gear portion  52 , a small-diameter gear portion  53  and a coupling portion  54 . The large-diameter gear portion  52 , the small-diameter gear portion  53  and the coupling portion  54  are aligned in that order from the first side wall  41  side. 
     The large-diameter gear portion  52  has a disc shape whose axis coincides with the input gear rotation shaft  51 . Gear teeth (for example, inclined gear teeth) are formed on a circumferential surface of the large-diameter gear portion  52  along the full circumference thereof. 
     The small-diameter gear portion  53  has a disc shape whose axis coincides with the input gear rotation shaft  51  and is formed smaller in diameter than the large-diameter gear portion  52 . Gear teeth (for example, inclined gear teeth) are formed on a circumferential surface of the small-diameter gear portion  53  along the full circumference thereof. 
     The coupling portion  54  has a disc shape whose axis coincides with the input gear rotation shaft  51  and has a circumferential surface which is smaller in diameter than the circumferential surface of the small-diameter gear portion  53 . A coupling recess portion  55  is formed in a left-hand side surface of the coupling portion  54 . A distal end portion of a driving force output member  56  (refer to  FIG. 2A ) which is provided in the body casing  2  is inserted into the coupling recess portion  55  in such a state that the developing cartridge  7  is mounted in the body casing  2 . 
     The driving force output member  56  is provided so as to advance and retreat in the left-right direction. With the developing cartridge  7  mounted in the body casing  2 , the driving force output member  56  advances rightwards along an axis of the input gear rotational shaft  51 , so that the distal end portion thereof is inserted into the coupling recess portion  55 , whereby the driving force output member  56  and the coupling recess portion  55  are coupled together so as not to rotate relatively. Therefore, when the driving force output member  56  is rotated by a driving force from a motor (not shown) in the body casing  2 , a rotation force of the driving force output member  56  is received by the input gear  45 , whereby the input gear  45  rotates together with the driving force output member  56 . Specifically, the coupling recess portion  55  has a receiving surface which contacts the driving force output member  56  to receive the rotation force of the driving force output member  56 . 
     (2-2) Developing Gear 
     The developing gear  46  is provided at the rear of and below the input gear  45 . The developing gear  46  is attached to a developing roller shaft  57  that the developing roller  18  possesses so as not to rotate relatively. The developing roller shaft  57  is rotatably provided in the first side wall  41 , and an axis of the developing roller shaft  57  constitutes a developing rotation axis  20  (refer to  FIG. 1 ) (an example of a second axis) which is a rotation axis of the developing roller  18 . Gear teeth are formed on a circumferential surface of the developing gear  46  along the full circumference thereof, and the gear teeth mesh with the gear teeth of the large-diameter gear portion  52  of the input gear  45 . 
     (2-3) Supply Gear 
     The supply gear  47  is provided below the input gear  45 . The developing gear  47  is attached to a supply roller shaft  58  that the supply roller  19  (refer to  FIG. 1 ) possesses so as not to rotate relatively. The supply roller shaft  58  is rotatably provided in the first side wall  41 , and an axis of the supply roller shaft  58  constitutes a supplying rotation axis  20  (refer to  FIG. 1 ) which is a rotation axis of the supply roller  19 . Gear teeth are formed on a circumferential surface of the supply gear  47  along the full circumference thereof, and the gear teeth mesh with the gear teeth of the small-diameter gear portion  53  of the input gear  45 . 
     (2-4) Intermediate Gear 
     The intermediate gear  48  is provided in front of the input gear  45 . The intermediate gear  48  is provided to be rotatable about an intermediate gear rotation shaft  59  which extends in the left-right direction. The intermediate gear rotation shaft  59  is held in the first side wall  41  so as not to rotate. 
     The intermediate gear  48  integrally has a small-diameter portion  60  having a disc shape with a relatively small outside diameter and a large-diameter portion  61  having a cylindrical shape with a relatively large outside diameter. The small-diameter portion  60  and the large-diameter portion  61  are aligned in that order from the first side wall  41  side. Axes of the small-diameter portion  60  and the large-diameter portion  61  coincide with an axis of the intermediate gear rotation shaft  59 . 
     Gear teeth are formed on a circumferential surface of the small-diameter portion  60  along the full circumference thereof. 
     Gear teeth are formed on an circumferential surface of the large-diameter portion  61  along the full circumference thereof. The gear teeth of the large-diameter portion  61  mesh with the gear teeth of the small-diameter gear portion  53  of the input gear  45 . 
     (2-5) Agitator Gear 
     The agitator gear  49  is provided at the front of and below the intermediate gear  48 . As shown in  FIG. 2C , the agitator gear  49  is attached to an agitator rotation shaft  62  so as not to rotate relatively. Specifically, the agitator rotation shaft  62  penetrates the first side wall  41  in the left-right direction. In the housing  13 , the agitator  16  is attached to the agitator rotation shaft  62 . A part of a circumferential surface of a left end portion of the agitator rotation shaft  62  is cut out so that the left end portion of the agitator rotation shaft  62  has a D-shape as viewed from a side thereof. Then, on the outer side of the first side wall  41 , the left end portion of the agitator shaft rotation shaft  62  is inserted through a shaft insertion hole  63  having a D-shape as viewed from a side thereof which is formed so as to penetrate the agitator gear  49  in the left-right direction, whereby the agitator gear  49  is attached to the agitator rotation shaft  62  so as not to rotate relatively. 
     The agitator rotation shaft  62  is held rotatably in the first side wall  41  and the second side wall  42  (refer to  FIG. 2A ). By being so held, the agitator  16  and the agitator gear  49  can rotate together with the agitator rotation shaft  62  about an axis of the agitator rotation shaft  62  which is an agitator rotation axis  17  (refer to  FIG. 1 ). 
     The agitator gear  49  integrally has a large-diameter gear portion  64 , a small-diameter gear portion  65  and an engagement portion  66 . 
     The large-diameter gear portion  64  has a disc shape whose axis coincides with the agitator rotation shaft  62 . Gear teeth are formed on a circumferential surface of the large-diameter gear portion  64  along the full circumference thereof. The gear teeth of the large-diameter gear portion  64  mesh with the gear teeth of the small-diameter portion of the intermediate gear  48 . 
     The small-diameter gear portion  65  is formed on a side of the large-diameter gear portion  64  which is opposite to a side thereof which opposes the first side wall  41 , has a disc shape whose axis coincides with the agitator rotation shaft  62  and is formed smaller in diameter than the large-diameter gear portion  64 . Gear teeth  67  (an example of first gear teeth) are formed on a circumferential surface of the small-diameter gear portion  65  along the full circumference thereof. 
     The engagement portion  66  is provided on a left end face of the small-diameter gear portion  65 . The engagement portion  66  has its height in the left-right direction and has a substantially triangular shape as viewed from a side thereof which extends in a radial direction of the small-diameter gear portion  65 . An end portion of the engagement portion  66  which is opposite to an end portion which opposes the agitator rotation shaft  62  has the same shape, when viewed from a side thereof, as one of the gear teeth  67  of the small-diameter gear portion  65  and is completely superimposed on one gear teeth  67  in the left-right direction. 
     (2-6) Detectable Rotary Member 
     The detectable rotary member  50  is provided in front of the agitator gear  49 . As shown in  FIGS. 2A to 2D , the detectable rotary member  50  is provided to be rotatable about a rotation shaft  68  which extends in the left-right direction. The rotation shaft  68  is held in the first side wall  41  so as not to rotate. 
     The detectable rotary member  50  integrally has a partly non-tooth gear portion  69 , a raised portion  70 , a cylindrical portion  71 , a first detectable portion  72  (an example of a detectable member), a second detectable portion  73  and a third detectable portion  74 . 
     As shown in  FIG. 2D , the partly non-tooth gear portion  69  has a double-cylinder shape whose axis coincides with the rotation shaft  68 . 
     Gear teeth  76  (an example of second gear teeth) are formed on a part of a circumferential surface of an outer cylindrical portion, that is, on an outermost circumferential surface of the partly non-tooth gear portion  69 . Specifically, a portion of the outermost circumferential surface of the partly non-tooth gear portion  69  whose central angle is about 230.degree. is configured as a non-tooth portion  77  (an example of a cut-off mechanism), and the gear teeth  76  are formed on the other portion than the non-tooth portion  77  of the outermost circumferential surface whose central angle is about 130.degree. The gear teeth  76  have a gear width which is larger than that of the gear teeth  67  of the small-diameter gear portion  65  of the agitator gear  49 , and right end faces of the gear teeth  76  are provided on the same plane as right end faces of the gear teeth  67 . By adopting this configuration, left end portions of the gear teeth  76  do not mesh with the gear teeth  67  irrespective of the rotational position of the detectable rotary member  50 , and portions of the gear teeth  76  other than the left end portions mesh with the gear teeth  67  depending on the rotational position of the detectable rotary member  50 . 
     An engagement portion  78  is formed at an upstream side end portion in the rotating direction of the detectable rotary member  50  (counterclockwise in  FIG. 2D ) of the non-tooth portion  77 . As shown in  FIG. 2E , the engagement portion  78  has a triangular shape as viewed from a side thereof and extends in a radial direction of the detectable rotary member  50  a length which is substantially the same as a height of the gear teeth  76 . The engagement portion  78  opposes a left end portion of the gear tooth  76  which is provided at a most downstream end in the rotating direction of the train of gear teeth  76  with a space defined therebetween in the rotating direction. Here, the engagement portion  78  does not oppose a right end portion of the gear tooth  76  in the rotating direction which is provided at the most downstream end in the rotating direction of the train of gear teeth  76  (specifically, a portion of the gear tooth  76  which is situated further rightwards than the left end portion (described above) which does not mesh with the gear teeth  67 ). By this configuration, the engagement portion  78  is not brought into abutment with the gear teeth  67  of the small-diameter gear portion  65  of the agitator gear  49  irrespective of the rotational position of the detectable rotary member  50 . A rotational locus drawn by the engagement portion  78  when the detectable rotary member  50  rotates partly overlaps a rotational locus drawn by the engagement portion  66  when the agitator gear  49  rotates. 
     A pressed portion  79  is formed integrally on an inner cylindrical portion of the partly non-tooth gear portion  69 . The pressed portion  79  has a first radially extending portion  80  which extends radially from a circumferential surface of the inner cylindrical portion, a rotating direction extending portion  81  which extends in the rotating direction of the detectable rotary member  50  from a distal end portion of the first radially extending portion  80  towards a downstream side in the rotating direction and a second radially extending portion  82  which extends from a distal end portion of the rotating direction extending portion  81  towards the circumferential surface of the cylindrical portion. The first radially extending portion  80  extends in a direction which substantially orthogonally intersects a line which connects the gear tooth  76  of the gear teeth  76  which is provided at the most downstream side and the rotation shaft  68  (in detail, a direction which forms an angle of about 85.degree. with respect to the line). In addition, the rotating direction extending portion  81  is formed to extend along an arc which is centered at an axis of the rotation shaft  68  and whose central angle is about 80.degree. and opposes the non-tooth portion  77 . 
     The raised portion  70  has a cylindrical shape whose axis coincides with the rotation shaft  68 . A through hole (not shown) is formed in the raised portion  70  along its axis, and the rotation shaft  68  is inserted through the through hole. 
     The cylindrical portion  71  has a cylindrical shape and projects from a left end face of the raised portion  70 . A left end portion of the rotation shaft  68  is inserted into the cylindrical portion  71 . 
     The first detectable portion  72  extends from the cylindrical portion  71  in a radial direction of the raised portion  70  on a left end face of the raised portion  70 . In the rotating direction of the detectable rotary member  50 , a distal end portion of the first detectable portion  72  is provided substantially in the same position as a central portion of the train of gear teeth  76  of the partly non-tooth gear portion  69 . 
     The second detectable portion  73  extends from the cylindrical portion  71  on the left end face of the raised portion  70  in a substantially opposite direction to the direction in which the first detectable portion  72  extends. In the rotating direction of the detectable rotary member  50 , a distal end portion  73 A of the second detectable portion  73  is provided in the same position as a central portion of the non-tooth portion  77  of the partly non-tooth gear portion  69 . In addition, the distal end portion  73 A projects to the outside of a rotating locus drawn by the first detectable portion  72  when the detectable rotary member  50  rotates to thereby constitute an abutment portion with which an interference member  91  (described later) is brought into abutment. 
     The third detectable portion  74  is provided upstream of the first detectable portion  72  and downstream of the second detectable portion  73  in the rotating direction (counterclockwise in  FIG. 2B ) of the detectable rotary member  50  and extends in a direction which orthogonally intersects the direction in which the first detectable portion  72  extends and a direction in which the third detectable portion  74  extends. 
     (3) Wire Spring 
     As shown in  FIG. 2D , a cylindrical boss  83  is formed on the outer side of the first side wall  41  so as to project therefrom in front of the detectable rotary member  50 . A wire spring  84  (an example of a holding member) is wound round the boss  83 . One end portion of the wire spring  84  is fixed to the first side wall  41 . The other end portion of the wire spring  84  extends towards the rotation shaft  68  of the detectable rotary member  50 . The wire spring  84  is curved at an intermediate portion along the length thereof. A distal end portion of the wire spring  84  is brought into abutment with the pressed portion  79  of the partly non-tooth gear portion  69  from a front side thereof to thereby press the pressed portion  79  to the rear. 
     (4) Gear Cover 
     As shown in  FIG. 2B , a gear cover  85  is attached to the outer side of the first side wall  41 . The gear cover  85  covers the input gear  45 , the supply gear  47 , the intermediate gear  48 , the agitator gear  49 , the detectable rotary member  50  and the wire spring  84  altogether. Formed in this gear cover  85  are an opening  86  which enables the coupling portion  54  of the input gear  45  to be exposed and an opening  87  which enables the raised portion  70 , the cylindrical portion  71 , the first detectable portion  72 , the second detectable portion  73  and the third detectable portion  74  of the detectable rotary member  50  to be exposed. 
     3. Interference Member 
     As shown in  FIG. 3A , the interference member  91  is provided in the body casing  2  in a position which opposes the first side wall  41  of the developing cartridge  7  in the left-right direction and opposes the second detectable portion  73  in an up-down direction. The interference member  91  includes a support portion  92  and an operating portion  93 . The support portion  92  has a plate shape, is thick in the up-down direction and extends in the front-rear direction. The operating portion  93  has a plate shape, extends obliquely upwards and rearwards from an intermediate portion in the front-rear direction on an upper surface of the support portion  92  and is bent to extend further to the rear with a space defined between the support portion  92  and itself. 
     4. Detection Mechanism 
     As shown in  FIGS. 3A to 3C , a detection mechanism is provided in the body casing  2  for detecting the first detectable portion  72 , the second detectable portion  73  and the third detectable portion  74 . This detection mechanism includes an actuator  94  and a light sensor  95  (an example of a detection member). 
     The actuator  94  integrally includes a swing shaft  96  which extends in the left-right direction, an abutment lever  97  which extends downwards from a right end portion of the swing shaft  96  and an optical path interruption lever  98  which extends upwards from a portion of the swing shaft  96  which is spaced away to the left from the portion where the abutment lever  97  is connected. The swing shaft  96  is held rotatably on an inner wall portion (not shown) of the body casing  2 . The abutment lever  97  and the optical path interruption lever  98  intersect each other at an angle of about 130.degree. 
     The actuator  94  can swing to a detecting posture in which the abutment lever  97  extends substantially perpendicularly downwards from the swing shaft  96  and the optical path interruption lever  98  extends forwards and upwards from the swing shaft  96  as shown in  FIG. 3C  and a non-detecting posture in which the optical path interruption lever  98  extends substantially perpendicularly upwards from the swing shaft  96  and the abutment lever  97  extends forwards and downwards from the swing shaft  96 . The actuator  94  is designed to take the non-detecting posture by a spring force of a spring (not shown) in such a state that no other external force than the spring force is exerted thereon. 
     The light sensor  95  includes a light emitting element and a light receiving element which are provided to oppose each other in the left-right direction. The light sensor  95  is provided in a position where an optical path extending from the light emitting element to the light receiving element is interrupted by the optical path interruption lever  98  of the actuator  94  which is taking the detecting posture. The light sensor  95  continues to output an ON signal while the optical path extending from the light emitting element to the light receiving element is being interrupted by the optical path interruption lever  98  and continues to output an OFF signal while the optical path is not interrupted (light from the light emitting element reaches the light receiving element). 
     5. Detection of Mounting of Developing Cartridge and Detection of Whether Developing Cartridge is New or Used 
     As shown in  FIGS. 2A to 2C , with a new developing cartridge  7 , the second detectable portion  73  extends perpendicularly downwards from the cylindrical portion  71 . In addition, as shown in  FIG. 2D , with a new developing cartridge  7 , the engagement portion  78  is provided in the position situated outside the rotating locus drawn by the engagement portion  66  when the agitator gear  49  rotates. Specifically, the engagement portion  78  is situated in such a position as to oppose an upper end portion of the small-diameter gear portion  65  of the agitator gear  49  in the front-rear direction when viewed from a side thereof. 
     A rotating position of the detectable rotary member  50  when the engagement portion  78  is provided in the above position corresponds to an example of a third rotational position which is different from a first rotational position and a second rotational position (described later). 
     The developing cartridge  7  is mounted in the body casing  2  with the front cover  4  open. When a new developing cartridge  7  is mounted in the body casing  2 , in the midst of mounting thereof, as shown in  FIGS. 3A to 3C , the distal end portion  73 A of the second detectable portion  73  is brought into abutment with an upper surface of a sloping portion of the operating portion  93  of the interference member  91 . By a rearward movement of the developing cartridge  7  as a result of mounting thereof into the body casing  2 , the distal end portion  73 A of the second detectable portion  73  slides on an upper surface of the sloping portion of the operating portion  93  in a rubbing manner and is lifted upwards in accordance with the inclination of the sloping surface. By the distal end portion  73 A being lifted upwards, the detectable rotary member  50  rotates clockwise when viewed in  FIGS. 3B to 3D  through about 10.degree. (T 1  to T 2  in  FIG. 12 ), whereby the engagement portion  78  is provided on the rotating locus of the engagement portion  66  as shown in  FIG. 3D . 
     When the mounting of the developing cartridge  7  is completed, as shown in  FIGS. 3A to 3C , a distal end portion of the first detectable portion  72  is brought into abutment with a lower end portion of the abutment lever  97  of the actuator  94 , whereby the lower end portion is pressed to the rear, causing the actuator  94  to take the detecting posture. As a result, the optical path extending from the light emitting element to the light receiving element is interrupted by the optical path interruption lever  98 , whereby an ON signal is outputted from the light sensor  95  (T 1  in  FIG. 12 ). In this way, an indirect detection of the first detectable portion by the light sensor  95  is performed. 
     The rotational position of the detectable rotary member  50  corresponds to an example of a first rotational position where the first detectable portion  72  is detected by the light sensor  95 , and a non-driven position where the transmission of the driving force from the agitator gear  49  to the detectable rotary member  50  is cut off. 
     When the mounting of the developing cartridge  7  is completed and the front cover  4  is closed, a warming-up operation of the laser printer  1  is started. In this warming-up operation, the driving force output member (refer to  FIG. 2A ) is inserted in the coupling recess portion  55  of the input gear  45  so that a driving force is inputted into the input gear  45  from the driving force output member  56 , whereby the input gear  45  rotates. Then, the developing gear  46 , the supply gear  47  and the intermediate gear  48  rotate in association with the rotation of the input gear  45 , whereby the developing roller  18  and the supply roller  19  rotates. The agitator gear  49  rotates (T 3  in  FIG. 12 ) in association with the rotation of the intermediate gear  48 , whereby the agitator  16  (refer to  FIG. 1 ) rotates. Toner in the developing cartridge  7  is loosened by the rotation of the agitator  16 . 
     As  FIGS. 4C, 5C and 6C  show sequential rotational positions of the agitator gear  49 , the agitator gear  49  rotates clockwise in  FIGS. 4C, 5C, 6C . As the agitator gear  49  rotates, the engagement portion  66  is not in contact with the engagement portion  78 , and the gear teeth  76  of the partly non-tooth gear portion  69  of the agitator gear  49  do not mesh with the gear teeth  67  of the agitator gear  49 . Therefore, as shown in  FIGS. 4A to 4D, 5A to 5D and 6A to 6D , the detectable rotary member  50  does not rotate, and the rotational position of the detectable rotary member  50  does not change. 
     Then, when the rotation of the agitator gear  49  progresses, as shown in  FIGS. 7A, 7C, 7D , the engagement portion  66  comes into abutment with the engagement portion  78 . Specifically, as shown in  FIG. 7E , the engagement portion  66  comes into abutment with the engagement portion from the above. 
     Then, when the rotation of the agitator  49  progresses further, as shown in  FIGS. 8A, 8C, 8D , the engagement portion  78  is pressed against by the engagement portion  66 , and the detectable rotary member  50  rotates counterclockwise in  FIGS. 8A, 8C, 8D  (T 4  in  FIG. 12 ), whereby the gear teeth  76  of the partly non-tooth gear portion  69  of the detectable rotary member  50  mesh with the gear teeth  67  of the agitator gear  49 . 
     This rotational position of the detectable rotary member  50  corresponds to an example of a driven position where the detectable rotary member  50  is rotated by the driving force transmitted from the agitator gear  49 . 
     Thereafter, the gear teeth  76  moves by following the rotation of the agitator gear  49 , whereby the detectable rotary member  50  rotates. As a result of the rotation of the detectable rotary member  50 , as shown in  FIGS. 9A to 9C , the distal end portion of the first detectable portion  72  moves away from the abutment lever  97 , and the actuator  94  changes its posture from the detecting posture to the non-detecting posture. As a result, the optical path interruption lever  98  moves out of the optical path which extends from the light emitting element to the light receiving element of the light sensor  95 , whereby an OFF signal is outputted from the light sensor  95  (T 5  in  FIG. 12 ). 
     Thereafter, when the rotation of the agitator gear  49  and the detectable rotary member  50  progresses, as shown in  FIGS. 10A to 10C , a distal end portion of the third detectable portion  74  comes into abutment with the lower end portion of the abutment lever  97 , whereby the lower end portion is pressed to the rear, causing the actuator  94  to change its posture again from the non-detecting posture to the detecting posture. As a result, the optical path extending from the light emitting element to the light receiving element of the light sensor  95  is interrupted by the optical path interruption lever  98 , whereby an ON signal is outputted from the light sensor  95  (T 6  in  FIG. 12 ). This attains an indirect detection of the third detectable portion  74  by the light sensor  95 . 
     Then, when the rotation of the agitator gear  49  and the detectable rotary member  50  progresses further, the distal end portion of the third detectable portion  74  moves away from the abutment lever  97  of the actuator  94 , whereby the actuator  94  changes its posture again from the detecting posture to the non-detecting posture. As a result, the optical path interruption lever moves out of the optical path extending from the light emitting element to the light receiving element of the light sensor  95 , whereby an OFF signal is outputted from the light sensor  95  (T 7  in  FIG. 12 ). 
     Thereafter, when the rotation of the agitator gear  49  and the detectable rotary member  50  progresses further, as shown in  FIGS. 11A to 11C , the distal end portion  73 A of the second detectable portion  73  comes into abutment with the lower end portion of the abutment lever  97 , whereby the lower end portion is pressed to the rear, causing the actuator  94  to change its posture again from the non-detecting posture to the detecting posture. As a result, the optical path extending from the light emitting element to the light receiving element of the light sensor  95  is interrupted by the optical path interruption lever  98 , whereby an ON signal is outputted from the light sensor  95  (T 8  in  FIG. 12 ). This attains an indirect detection of the second detectable portion  73  by the light sensor  95 . 
     The rotational position of the detectable rotary member  50  corresponds to an example of a second rotational position where the second detectable portion  73  is detected by the light sensor  95 . 
     Then, as shown in  FIG. 11D , when the rotation of the agitator gear  49  and the detectable rotary member  50  progresses further and the meshing engagement of the gear teeth  76  of the detectable rotary member  50  with the gear teeth  67  of the agitator gear  49  is released, the detectable rotary member stop rotating (T 9  in  FIG. 12 ). Thereafter, by the pressed portion  79  of the detectable rotary member  50  being pressed to the rear by the wire spring  84 , the rotational position of the detectable rotary member  50  is held in the rotational position thereof when the meshing engagement of the gear teeth  76  of the detectable rotary member  50  with the gear teeth  67  of the agitator gear  49  is released, whereby the detectable rotary member  50  does not rotate in any way. 
     When a predetermined length of time elapses after the front cover  4  is closed, the warming-up operation ends, and the motor (not shown) stops rotating the driving force output member  56 , whereby the input of the driving force from the driving force output member  56  into the input gear  45  is stopped. 
     In this way, when the new developing cartridge  7  is mounted into the body casing  2  for the first time, there occurs twice the situation in which the OFF signal is outputted from the light sensor  95 . Consequently, when there occurs twice the situation in which the OFF signal is outputted from the light sensor  95  after the developing cartridge  7  is mounted into the body casing  2 , it can be determined that the developing cartridge  7  mounted is new. 
     Further, if the developing cartridge  7  is new, when the developing cartridge  7  is mounted into the body casing  2 , the distal end portion of the first detectable portion  72  presses the lower end portion of the abutment lever  97  of the actuator  94  to the rear, whereby the actuator  94  takes the detecting posture, and the ON signal is outputted from the light sensor  95 . In addition, even if the developing cartridge  7  is not new or used, when the developing cartridge  7  is mounted into the body casing  2 , the distal end portion  73 A of the second detectable portion  73  presses the lower end portion of the abutment lever  97  of the actuator  94  to the rear, whereby the actuator  94  takes the detecting posture, and the ON signal is outputted from the light sensor  95 . Consequently, irrespective of the developing cartridge  7  being new or used, the ON signal is outputted from the light sensor  95  in such a state that the developing cartridge  7  is mounted in the body casing  2 . Therefore, whether or not the developing cartridge  7  is mounted in the body casing  2  can be determined based on whether or not the ON signal is outputted from the light sensor  95 . 
     It is noted that the third detectable portion  74  may be omitted. If the third detectable portion  74  is omitted, when the developing cartridge  7  is mounted into the body casing  2 , as shown in  FIG. 13 , no ON signal is outputted from the light sensor  95  during a time T 6  to T 7 , and there occurs only once the situation in which the OFF signal is outputted from the light sensor  95 . Consequently, it can be determined from the fact that the situation occurs once in which the OFF signal is outputted from the light sensor  95  that the developing cartridge  7  mounted is new. 
     For example, the developing cartridge  7  on which the third detectable portion  74  is provided accommodates a relatively large amount of toner in the housing  13  thereof, while the developing cartridge  7  from which the third detectable portion  74  is omitted accommodates a relatively small amount of toner in the housing  13  thereof. When these developing cartridges  7  are mounted into the body casing  2  selectively, the type of the developing cartridge  7  mounted can be determined by the number of times of occurrence of the situation in which the OFF signal is outputted from the light sensor  95  after the new developing cartridge  7  is mounted in the body casing  2 . 
     These determinations of whether or not the developing cartridge  7  is mounted in the body casing  2  and whether the developing cartridge  7  mounted is new or used are executed by a control unit (not shown) that a microcomputer has. Specifically, the control unit executes, for example, operations shown in a flowchart in  FIG. 18  to determine whether or not the developing cartridge  7  is mounted in the body casing  2  and whether the developing cartridge  7  mounted is new or used. 
     The flowchart shown in  FIG. 18  is executed in response to the closure of the front cover  4 . 
     When the front cover  4  is closed, firstly, it is checked whether or not the output signal from the light sensor  95  is the ON signal (ON) (S 1 ). 
     If the output signal from the light sensor  95  is the ON signal (S 1 : YES), the warming-up operation is started, and the driving of the motor is started to rotate the driving force output member  56  in such a state that the driving force output member  56  is coupled to the coupling recess portion  55  of the input gear  45  (S 2 ). 
     While the motor is being driven, the state of the output signal from the light sensor  95  is monitored at all times (S 3 ). Namely, output signals from the light sensor  95  are sampled at a predetermined cycle by the control unit, and whether the output signal from the light sensor  95  is the ON signal or the OFF signal is checked repeatedly. When the output signal from the light sensor  95  is switched from the ON signal to the OFF signal, every time the switching occurs, the value of a counter within the control unit is increased (by one). The value of the counter is reset to zero when this operation starts. 
     When a predetermined length of time elapses from the start of driving of the motor (S 4 : YES), the driving of the motor is stopped, and the warming-up operation ends. 
     Then, it is checked whether or not the OFF signal is outputted from the light sensor  95  during the period of time when the motor is driven (the monitoring period) (S 5 ). Specifically, it is checked whether the value of the counter is 1 or 2, or zero. 
     If the value of the counter is 1 or 2, it is determined that the developing cartridge  7  mounted is new (S 6 ). In an example which is in greater detail, if the value of the counter is 1, it is determined that the developing cartridge  7  mounted is new and accommodates the relatively small amount of toner, while if the value of the counter is 2, it is determined that the developing cartridge  7  mounted is new and accommodates the relatively large amount of toner. 
     On the other hand, if the value of the counter is zero, it is determined that the developing cartridge  7  mounted is used (S 7 ). 
     In addition, if the output signal from the light sensor  95  immediately after the front cover  4  is closed is the OFF signal (S 1 : NO), it is determined that no developing cartridge  7  is mounted in the body casing  2  (S 8 ). 
     6. Functions and Advantages 
     (1) Function and Advantage 1 
     As described above, the input gear  45 , the agitator gear  49  and the detectable rotary member  50  are provided on the outer side of the first side wall  41  of the housing  13  to be rotatable about the respective axes of the input gear rotation shaft  51 , the agitator rotation shaft  62  and the rotation shaft  68  which extend in parallel to each other. The axes of the input gear rotation shaft  51 , the agitator rotation shaft  62  and the rotation shaft  68  are examples of a first axis, a third axis and a fourth axis. In addition, the developing roller  18  is provided between the first side wall  41  and the second side wall  42  to be rotatable about the developing rotation axis  20 . 
     The driving force output member  56  provided in the body casing  2  is coupled to the input gear  45 , and the driving force is inputted thereto from the driving force output member  56 . The developing roller  18  and the agitator gear  49  rotate by the driving force inputted into the input gear  45  (the driving force that the input gear  45  receives from the driving force output member  56 ), whereby the engagement portion  66  provided on the agitator gear  49  rotates about the axis of the agitator rotation shaft  62  (an example of a fifth axis which is on the same axis as the third axis). 
     The detectable rotary member  50  has the gear teeth  76  and the engagement portion  78 . The gear teeth  76  mesh with the gear teeth  67  of the agitator gear  49  when the rotational position of the detectable rotary member  50  is in a driven position, that is, when the rotational position of the detectable rotary member  50  stays within a range which ranges from the rotational position of the detectable rotary member  50  shown in  FIG. 8D  to the rotational position of the detectable rotary member  50  shown in  FIG. 11D . The engagement portion  78  is provided on the rotating locus of the engagement portion  66  when the rotational position of the detectable rotary member  50  is in a non-driven position which is the other rotational positions than the driven position, that is, when the rotational position of the detectable rotary member  50  is in the rotational positions shown in  FIGS. 3D, 4D, 5D, 6D, 7D . 
     Therefore, when the agitator gear  49  and the engagement portion  66  rotates by the driving force that the input gear  45  receives when the rotational position of the detectable rotary member  50  is in the non-driven position, the engagement portion  66  is brought into engagement with the engagement portion  78  which is provided on the rotating locus thereof. At this time, since the gear teeth  76  do not mesh with the gear teeth  67  of the agitator gear  49 , the detectable rotary member  50  does not change the rotational position thereof to stay still until the engagement portion  66  is brought into engagement with the engagement portion  78 . After the engagement of the engagement portion  66  with the engagement portion  78 , by the engagement portion  66  rotating further, the force is exerted on the engagement portion  78  from the engagement portion  66 , whereby the detectable rotary member  50  starts rotating. Then, when the rotational position of the detectable rotary member  50  comes in the driven position, the gear teeth  76  mesh with the agitator gear  49 , whereafter the detectable rotary member  50  rotates by the driving force transmitted from the agitator gear  49 . 
     In the laser printer  1 , the developing cartridge  7  is mounted in the body casing  2 , and the warming-up operation is performed in response to the mounting of the developing cartridge  7 . In this warming-up operation, the detectable rotary member  50  does not rotate right after the start of driving of the driving force output member  56  (right after the start of inputting of the driving force into the input gear  45 ), and the detectable rotary member  50  starts rotating after the passage of the time required from the start of driving of the driving force output member  56  to the engagement of the engagement portion  66  with the engagement portion  78 . By this configuration, the detectable rotary member  50  is allowed to rotate stably after the driving force that is inputted into the input gear  45  from the driving force output member  56  has become stable. The first detectable portion  72 , the second detectable portion  73  and the third detectable portion  74  move in association with the rotation of the detectable rotary member  50 . Consequently, the first detectable portion  72 , the second detectable portion  73  and the third detectable portion  74  are allowed to move at stable speeds. Consequently, the developing cartridge  7  is superior to the conventional developing cartridge. 
     (2) Function and Advantage 2 
     The developing cartridge  7  includes the agitator  16 . The agitator  16  rotates about the axis of the agitator rotation shaft  62  (an example of a sixth axis which is on the same axis as the third axis). Toner accommodated in the housing  13  can be agitated by the rotating agitator  16 . 
     With a new developing cartridge  7 , there may be a situation in which toner in the housing  13  solidifies. In this case, a large load (resistance) is exerted on the agitator  16  which rotates integrally with the agitator gear  49  immediately after the new developing cartridge  7  is mounted in the body casing  2  and the agitator gear  49  starts rotating by the driving force that the input gear  45  receives from the driving force output member  56 . Then, when the toner is started to be loosened, the load exerted on the agitator  16  is reduced, and the magnitude of the load is stabilized at a constant level. That is, the rotation of the agitator gear  40  becomes unstable from the start of rotation of the agitator gear  49  until the loosening of the solidified toner. 
     The detectable rotary member  50  does not follow the rotation of the agitator gear  49  immediately after the driving force output member  56  is started to be driven (immediately after the driving force is started to be inputted into the input gear  45 ). The detectable rotary member  50  starts to follow the rotation of the agitator gear  49  after the passage of the time required from the start of driving of the driving force output member  56  until the engagement of the engagement portion  66  with the engagement portion  78 . Consequently, the detectable rotary member  50  is allowed to follow the rotation of the agitator gear  49  after the toner solidified in the housing  13  is loosened. As a result, the rotation of the detectable rotary member  50  can be stabilized further, thereby making it possible to allow the first detectable portion  72  and the second detectable portion  73  to move at the stable speed. 
     (3) Function and Advantage 3 
     The detectable rotary member  50  has the first detectable portion  72  and the second detectable portion  73 . Then, the detectable rotary member  50  rotates, by following the rotation of the agitator gear  49 , from the first rotational position where the distal end portion of the first detectable portion  72  is brought into abutment with the lower end portion of the abutment lever  97  to the second rotational position where the distal end portion of the second detectable portion  73  is brought into abutment with the lower end portion of the abutment lever  97 . By this configuration, when the detectable rotary member  50  rotates after the developing cartridge  7  is mounted in the body casing  2 , since both the first detectable portion  72  and the second detectable portion  73  are detected by the light sensor  95 , information that the developing cartridge  7  mounted is new can be obtained based on the detection of those detectable portions. 
     (4) Function and Advantage 4 
     When the rotational position of the detectable rotary member  50  is in the second rotational position, the gear teeth  76  do not mesh with the agitator  49 , and the detectable rotary member  50  is made free relative to the agitator gear  49 . 
     (5) Function and Advantage (5) 
     The developing cartridge  7  includes the wire spring  84 . According to this configuration, even though the second detectable portion  73  is brought into abutment with the abutment lever  97  of the actuator  94  to thereby exert the pressing force of the spring (not shown) provided on the actuator  94  on the second detectable portion  73 , the state is held in a state where the detectable rotary member  50  stays in the second rotational position by the pressed portion  79  of the detectable rotary member  50  being pressed by the wire spring  84 . Therefore, the second detectable portion  73  continues to be detected by the light sensor  95  while the developing cartridge  7  is mounted in the body casing  2 . Consequently, whether or not the developing cartridge  7  is mounted in the body casing  2  can be determined well based on whether or not the second detectable portion  73  is detected by the light sensor  95 . 
     (6) Function and Advantage 6 
     The interference member  91  is fixed in the body casing  2 . Then, in the process of mounting the developing cartridge  7  into the body casing  2 , the interference member  91  contacts the second detectable portion  73 , whereby the detectable rotary member  50  rotates from the third rotational position where the engagement portion  78  is provided out of the rotating locus drawn by the engagement portion  66  when the agitator gear  49  rotates to the first rotational position. 
     (7) Function and Advantage 7 
     In such a state where the detectable rotary member  50  stays in the third rotational position, the engagement portion  78  is provided out of the rotating locus of the engagement portion  66 . When the detectable rotary member  50  rotates from the third rotational position to the first rotational position, the engagement portion  78  is provided on the rotating locus of the engagement portion  66 . Consequently, when the engagement portion  6  moves thereafter, the engagement portion  66  is allowed to be surely brought into engagement with the engagement portion  78 . 
     (8) Function and Advantage 8 
     The first detectable portion  72  and the second detectable portion  73  extend in the radius direction of the rotation of the detectable rotary member  50 . The second detectable portion  73  projects outside the rotating locus drawn by the first detectable portion  72  when the detectable rotary member  50  rotates, and the projecting portion or the radially extending portion  82  constitutes an abutment portion with which the interference member  91  is brought into abutment when the developing cartridge  7  is mounted into the body casing  2 . By this configuration, while the interference member  91  is allowed to be surely brought into abutment with the second detectable portion  73 , the first detectable portion  72  can be prevented from being brought into abutment with the interference member  91  when the detectable rotary member  50  rotates. 
     (9) Function and Advantage 9 
     In addition, since the first detectable portion  72  and the second detectable portion  73  are provided away from each other in the rotating direction of the detectable rotary member  50 , even though the detectable rotary member  50  does not rotate through 360.degree., the rotational position of the detectable rotary member  50  is changed to the first rotational position where the first detectable portion  72  is detected by the light sensor  95  to the second rotational position where the second detectable portion  73  is detected by the light sensor  95 . Therefore, due to the detectable rotary member  50  including the first detectable portion  72  and the second detectable portion  73 , the detection of the first detectable portion  72  and the second detectable portion  73  by the light sensor  95  can be performed without rotating the detectable rotary member  50  through 360.degree., while due to the detectable rotary member  50  including the partly non-tooth gear portion  69 , the transmission of the driving force from the agitator gear  49  to the detectable rotary member  50  can be cut off. 
     For example, it might be considered that both the determination of whether or not the developing cartridge  7  mounted is new and the determination of whether or not the developing cartridge  7  is mounted in the body casing  2  can be implemented by detecting only the first detectable portion  72  by the light sensor  95  with the second detectable portion  73  omitted. 
     In this case, it is necessary that the first detectable portion  72  comes into abutment with the abutment lever  97  of the actuator  94  so that the first detectable portion  72  is detected by the light sensor  95  at a time when the new developing cartridge  7  is mounted in the body casing  2 . Then, it is necessary that after the first detectable portion  72  temporarily moves away from the abutment lever  97  by the rotation of the detectable rotary member  50 , the detectable rotary member  50  rotates through 360.degree. after the mounting of the developing cartridge  7 , causing the first detectable portion  72  to come into abutment with the abutment lever  97  again so that the first detectable portion  72  is detected by the light sensor  95 . Further, the transmission of the driving force from the agitator gear  49  to the detectable rotary member  50  has to be cut off at a time when the detectable rotary member  50  rotates through 360.degree. 
     These three requirements cannot be satisfied by the configuration in which the partly non-tooth gear portion  69  is provided. To satisfy those requirements, a complex mechanism such as a clutch mechanism has to be provided, which makes the configuration of the developing cartridge  7  (the laser printer  1 ) complex and increases the manufacturing costs thereof. 
     By including the second detectable portion  73  separately from the first detectable portion  72  and including the partly non-tooth gear portion  69 , the three requirements can be satisfied which are necessary to determine well whether or not the developing cartridge  7  mounted new or used and whether or not the developing cartridge  7  is mounted in the body casing  2 . 
     7. Modified Examples 
     (1) Modified Example 1 
     In the laser printer  1 , the engagement portion  66  is formed integrally on the small-diameter gear portion  65  of the agitator gear  49 . As shown in  FIG. 14 , however, for example, a cylindrical connecting member  141  may be provided as a separate member from a small-diameter gear portion  65 . In this case, an engagement portion  66  is formed on the connecting member  141  so as to project from a circumferential surface of the connecting member  141 , and the connecting member  141  is connected to the small-diameter gear portion  65  to rotate together therewith (so as not to rotate relatively). 
     In this case, the small-diameter gear portion  65  and the connecting member  141  can rotate together by fitting two bosses  142  provided on the connecting member  141  so as to extend towards the small-diameter gear portion  65  in recess portions  143  provided in the small-diameter gear portion  65 . 
     (2) Modified Example 2 
     In addition, as shown in  FIG. 15 , an engagement portion  66  may be formed on a different gear  151  to which a driving force is transmitted from an intermediate gear  48  so as to project from a circumferential surface of the gear  151  at a distal end thereof, so that an engagement portion  78  is pressed by the gear  151  when it rotates. In this case, a detectable rotary member  50  rotates to a position where a partly non-tooth gear portion  69  receives a drive force from a small-diameter gear portion  65  of an agitator gear  49  by firstly the engagement portion  78  being brought into contact with the engagement portion  66  provided on the gear  151 . 
     (3) Modified Example 3 
     A first detectable portion  72  and a second detectable portion  73  may be integrated together. For example, as shown in  FIG. 16 , connecting portions  161 ,  162 , which extend along an outer circumferential surface of a cylindrical portion  71  and constitute an example of a non-detecting portion, are formed between the first detectable portion  72  and a third detectable portion  74  and between the third detectable portion  74  and the second detectable portion  73 , respectively, so that the first detectable portion  72 , the second detectable portion  73  and the third detectable portion  74  are integrated together. 
     In this case, a configuration may be adopted in which an abutment lever  97  of an actuator  94  is brought into abutment with connecting portions  161 ,  162 . In this configuration, a height of the connecting portions  161 ,  162  (a length of a detectable rotary member  50  in the direction of turning radius) is formed smaller than lengths of the first detectable portion  72  and the second detectable portion  73  and is formed to such an extent that even though an abutment lever  97  of an actuator  94  is brought into abutment with the connecting portions  161 ,  162 , an optical path interruption lever  98  of the actuator  94  is prevented from moving out of an optical path of the light sensor  95 . 
     (4) Modified Example 4 
     In the laser printer  1 , the partly non-tooth gear portion  69  is provided on the detectable rotary member  50 , and the gear teeth  76  are formed on the outermost circumferential surface of the partly non-tooth gear portion  69 . However, the following configuration may be adopted in place of the cylindrical portion on an outer side of the partly non-tooth gear portion  69 . For example, as shown in  FIG. 17 , a fan-shaped main body  171  which is centered at a rotation shaft  68  of a detectable rotary member  50  and a resistance imparting member  173  may be provided. At least an outer circumferential surface of the resistance imparting member  173  is formed of a material such as a rubber having a relatively large friction coefficient, and the resistance imparting member  173  is wound round an outer circumference of a wall portion  172  erected along a circumferential edge of the main body  171 . In this case, gear teeth  67  may be formed or may not be formed on a circumferential surface of a small-diameter gear portion  65  of an agitator gear  49 . The main body  171  and the resistance imparting member  173  are sized so that an angle formed by two planes of the outer circumferential surface of the resistance imparting member  173  is about 230.degree. and that those plane do not contact the small-diameter gear portion  65  but an arc surface of the outer circumferential surface of the resistance imparting member  173  contacts the circumferential surface of the small-diameter gear portion  65 . 
     (5) Modified Example 5 
     To determine whether or not the developing cartridge  7  is mounted in the body casing  2  and whether the developing cartridge  7  mounted is new or used, the control unit executes operations shown in a flowchart in  FIG. 19  in place of the operations shown in the flowchart in  FIG. 18 . 
     The flowchart in  FIG. 19  is executed in response to the closure of the front cover  4 . 
     When the front cover  4  is closed, a warming-up operation is started, and the motor (not shown) is started to be driven to rotate the driving force output member  56  in such a state that the driving force output member  56  is coupled to the coupling recess portion  55  of the input gear  45  (S 11 ). 
     While the motor is being driven, the state of an output signal from the light sensor  95  is monitored at all times (S 12 ). Namely, output signals of the light sensor  95  are sampled at a predetermined cycle by the control unit so as to check repeatedly whether the output signal from the light sensor  95  is an ON signal or an OFF signal. When the output signal from the light sensor  95  is switched from the ON signal to the OFF signal, every time the output signal is so switched, the value of the counter in the control unit is increased (by one). The value of the counter is reset to zero when this operation is started. 
     The driving of the motor is stopped after the passage of a predetermined length of time from the start of driving of the motor (S 13 : YES), and the warming-up operation ends. 
     Thereafter, it is checked whether or not the output signal from the light sensor  95  is the ON signal (ON) (S 14 ). 
     If the output signal from the light sensor  95  is the ON signal (S 14 : YES), it is checked whether or not the OFF signal is outputted from the light sensor  95  during a period of time when the motor is driven (a monitoring period) (S 15 ). Specifically, it is checked whether the value of the counter in the control unit is 1 or 2. 
     If the value of the counter is 1 or 2, it is determined that the developing cartridge  7  mounted is new (S 16 ). In an example which is greater detail, if the value of the counter is 1, it is determined that the developing cartridge  7  is new and accommodates a relatively small amount of toner. If the value of the counter is 2, it is determined that the developing cartridge  7  is new and accommodates a relatively large amount of toner. 
     On the other hand, if the value of the counter is zero, it is determined that the developing cartridge  7  is used (S 17 ). 
     In addition, if the output signal from the light sensor  95  at a point in time when the warming-up operation ends is the OFF signal (S 14 : NO), it is determined that no developing cartridge  7  is mounted in the body casing  2  (S 18 ). 
     While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.