Abstract:
A cartridge mountable in an image forming apparatus includes a first unit that stores developer and a second unit that accommodates the first unit. The first unit includes a first detected part configured to be displaced irreversibly from a first-unit new-product position to a first-unit used position upon receipt of a driving force from the image forming apparatus, the first detected part contacting a detector provided in the image forming apparatus while being displaced from the first-unit new-product position to the first-unit used position to be detected by the detector. The second unit includes a second detected part configured to be displaced irreversibly from a second-unit new-product position to a second-unit used position upon receipt of a driving force from the image forming apparatus, the second detected part contacting the detector while being displaced from the second-unit new-product position to the second-unit used position to be detected by the detector.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/141,863 filed Dec. 27, 2013, which claims priority from Japanese Patent Application No. 2012-286698 filed Dec. 28, 2012. The entire contents of the priority applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an image forming apparatus and a cartridge that is detachably mounted in a body of the image forming apparatus. 
     BACKGROUND 
     One conventional cartridge that is detachably mounted in a body of an image forming apparatus is configured of a toner case that accommodates toner, and a process case in which the toner case is detachably mounted (see Japanese Patent Application Publication No. 2011-203493). In this conventional image forming apparatus, a photosensitive drum provided in the process case, and a sensor gear is provided on the toner case. The sensor gear has a contact protrusion and is capable of rotating irreversibly in one direction. When the cartridge is mounted in the body of the image forming apparatus, the sensor gear is driven to rotate by a driving force inputted from the body of the image forming apparatus. When the toner case is a new product, the contact protrusion will contact an actuator provided in the body as the sensor gear rotates, enabling the image forming apparatus to acquire information on the toner case, such as whether the toner case is new. 
     SUMMARY 
     When the cartridge used in the image forming apparatus is configured of two units, as in the above example, it would be desirable to have an ability to detect whether both units are new. However, new-product detection for two units would require separate actuators, separate photosensors for detecting the motion of these actuators, and the like, leading to a rise in manufacturing costs. 
     In view of the foregoing, it is an object of the present invention to provide an image forming apparatus equipped with a cartridge that is configured of two units, and a low-cost solution for acquiring information (new-product detection) on both units. 
     In order to attain the above and other objects, there is provided a cartridge configured to be detachably mountable in an image forming apparatus provided with a detector. The cartridge includes: a first unit configured to store developer therein; and a second unit having a photosensitive drum and configured to detachably accommodate the first unit. The first unit includes a first detected part configured to be displaced irreversibly from a first-unit new-product position to a first-unit used position upon receipt of a driving force from the image forming apparatus, the first detected part being configured to contact the detector while being displaced from the first-unit new-product position to the first-unit used position to permit the first detected part to be detected by the detector. The second unit includes a second detected part configured to be displaced irreversibly from a second-unit new-product position to a second-unit used position upon receipt of a driving force from the image forming apparatus, the second detected part being configured to contact the detector while being displaced from the second-unit new-product position to the second-unit used position to permit the second detected part to be detected by the detector. 
     According to another aspect of the present invention, there is also provided an image forming apparatus configured to detachably accommodate the cartridge configured of the first unit and the second unit. The detector includes: a contact arm, a biasing member, a biasing member and a light-receiving element. The contact arm is configured to be contacted by each of the first detected part and the second detected part and to pivotally move between the detection position and the non-detection position in accordance with contact and separation relative to each of the first detected part and the second detected part. The biasing member is configured to apply a biasing force to the contact arm to bias the contact arm toward the non-detection position. The light-emitting element is configured to emit light to detect whether the contact arm pivotally moves, and the light-receiving element is configured to receive the light from the light-emitting element. The contact arm further includes a first shielding portion and a second shielding portion. The first shielding portion is configured to enter between the light-emitting element and the light-receiving element to shield the light when one of the first detected part and the second detected part is separated from the contact arm and configured to be retracted from between the light-emitting element and the light-receiving element when the one of the first detected part and the second detected part contacts the contact arm. The second shielding portion is configured to enter between the light-emitting element and the light-receiving element to shield the light when a remaining one of the first detected part and the second detected part further contacts the contact arm while the one of the first detected part and the second detected part is in contact with the contact arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a schematic cross-sectional diagram illustrating a general configuration of a laser printer according to a first embodiment of the present invention; 
         FIG. 2A  is a perspective view of a developing unit according to the first embodiment; 
         FIG. 2B  is a perspective view of the developing unit according to the first embodiment, wherein a cover has been moved; 
         FIG. 3  is a perspective view of a first sensor gear and an agitator gear provided on the developing unit of the first embodiment; 
         FIG. 4A  is a perspective view of a drum unit according to the first embodiment; 
         FIG. 4B  is an enlarged view of a second sensor gear and its peripheral components provided on the drum unit according to the first embodiment; 
         FIG. 5  is a perspective view of the developing unit according to the first embodiment as viewed from below; 
         FIG. 6  is a perspective view showing a structure of a sensing mechanism provided in the laser printer according to the first embodiment, the sensing mechanism including a contact arm; 
         FIG. 7  is a side view of a process cartridge of the first embodiment in which the new developing unit according to the first embodiment is mounted in the new drum unit according to the first embodiment, wherein a portion of the drum unit and the developing unit are shown; 
         FIG. 8  is a side view of the process cartridge according to the first embodiment, wherein a second detected part of the second sensor gear has contacted the contact arm after the state shown in  FIG. 7 ; 
         FIG. 9  is a side view of the process cartridge according to the first embodiment, wherein the second detected part has been displaced to a used position after the state shown in  FIG. 8 ; 
         FIG. 10  is a side view of the process cartridge according to the first embodiment, wherein a first detected part of the first sensor gear has contacted the contact arm after the state shown in  FIG. 9 ; 
         FIGS. 11A-11D  are timing charts showing output of a photosensor according to the first embodiment; 
         FIG. 12A  is a side view showing a configuration of first and second sensor gears and peripheral components, including a contact arm, according to a second embodiment of the present invention, wherein both of first and second detected parts are in a new-product position; 
         FIG. 12B  is a side view showing the configuration of the first and second sensor gears and peripheral components, including the contact arm, according to the second embodiment, wherein the second detected part is in contact with the contact arm; 
         FIG. 13A  is a side view showing the configuration of the first and second sensor gears and peripheral components, including the contact arm, according to the second embodiment, wherein the first detected part contacts the contact arm while the second detected part is in contact with the contact arm; 
         FIG. 13B  is a side view showing the configuration of the first and second sensor gears and peripheral components, including the contact arm, according to the second embodiment, wherein the contact between the first detected part and the contact arm is broken while the second detected part remains in contact with the contact arm; 
         FIGS. 14A-14D  are timing charts showing output of a photosensor according to the second embodiment; 
         FIG. 15  is a side view of a new process cartridge according to a third embodiment of the present invention, wherein a first detected part and a second detected part are both in their new-product position; 
         FIG. 16A  is a side view showing a configuration of first and second sensor gears and peripheral components thereof (including a contact arm) according to the third embodiment, wherein the second detected part is in contact with the contact arm after the state shown in  FIG. 15 ; 
         FIG. 16B  is a side view showing the configuration of the first and second sensor gears and peripheral components thereof according to the third embodiment, wherein the second detected part has been displaced to its used position after the state shown in  FIG. 16A ; 
         FIG. 16C  is a side view showing the configuration of the first and second sensor gears and peripheral components thereof according to the third embodiment, wherein the first detected part is in contact with the contact arm after the state show in  FIG. 16B ; 
         FIG. 17A  is a side view showing the configuration of the first and second sensor gears and their peripheral components of a new process cartridge according to the third embodiment, wherein a third detected part provided on the first sensor gear is in contact with the contact arm after the state of  FIG. 16C  (after new-product detection is performed); 
         FIG. 17B  is a side view showing the configuration of the first and second sensor gears and peripheral components of a used process cartridge according to the third embodiment, wherein the third detected part is in contact with the contact arm; 
         FIG. 18  is a side view showing a portion of a drum unit and a developing unit according to a first modification of the present invention; and 
         FIG. 19  is a side view showing a portion of a drum unit and a developing unit according to a second modification of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A process cartridge  5  as an example of a cartridge according to a first embodiment of the present invention will be described with reference to  FIGS. 1 through 11 ( d ). 
     A laser printer  1  is an example of an image forming apparatus of the first embodiment that is configured to detachably accommodate the process cartridge  5 . 
     1. Overall Structure of the Laser Printer 
     In the following description, directions related to the laser printer  1  will be given based on the perspective of a user using the laser printer  1 . Specifically, the right side of the laser printer  1  in  FIG. 1  will be considered the front side, and the left side of the printer  1  in  FIG. 1  will be considered the rear side. Further, the near side in  FIG. 1  will be considered the left side, and the far side in  FIG. 1  will be considered the right side. A vertical direction in  FIG. 1  will be referred to as a top-down direction with regard to the laser printer  1 . 
     The laser printer  1  is configured to form a toner image, transfer the toner image onto a sheet S, and thermally fix the toner image on the sheet S. 
     As shown in  FIG. 1 , the laser printer  1  is provided with a main casing  2  within which provided are a sheet-feeding unit  3 , an exposing unit  4 , the process cartridge  5 , and a fixing unit  8 . 
     The main casing  2  is provided with a front cover  21 . When the front cover  21  configured to be opened and closed to expose and cover an aperture formed in a front end portion of the main casing  2 . 
     The sheet-feeding unit  3  is disposed at a lower portion of the main casing  2 . The sheet-feeding unit  3  mainly includes a sheet tray  31  for accommodating the sheets S, a sheet-lifting plate  32 , and a sheet-feeding mechanism  33 . The sheets S stacked in the sheet tray  31  are lifted upward by the sheet-lifting plate  32 , and are separated one by one by the sheet-feeding mechanism  33  to be conveyed to the process cartridge  5 . 
     The exposing unit  4  is disposed in an upper portion of the main casing  2 . The exposing unit  4  includes a laser source (not shown), a polygon mirror, lenses, and a reflection minor (shown without reference numerals). In the exposing unit  4 , the laser source emits a laser beam, a path of which is indicated by a chain line in  FIG. 1 , based on image data. The laser beam is irradiated on a surface of a photosensitive drum  61  at a high speed, thereby exposing the surface of the photosensitive drum  61  to light. 
     The process cartridge  5  is configured to be disposed below the exposing unit  4  when mounted in the main casing  2 . The process cartridge  5  is configured to be received in the main casing  2  through the aperture formed in the main casing  2  when the front cover  21  is opened. 
     The process cartridge  5  includes a drum unit  6  and a developing unit  7 . 
     The drum unit  6  mainly includes a photosensitive drum  61 , a charger  62  and a transfer roller  63 . 
     The developing unit  7  is configured to be mounted in and removed from the drum unit  6  and includes a developing roller  71 , a supply roller  72 , a thickness regulation blade  73 , a toner accommodation chamber  74  for accommodating toner, and an agitator  75 . 
     In the process cartridge  5 , the charger  62  applies a uniform charge to a peripheral surface of the photosensitive drum  61 . Subsequently, the exposing unit  4  exposes the peripheral surface of the photosensitive drum  61  to light, thereby forming an electrostatic latent image on the peripheral surface of the photosensitive drum  61  based on the image data. In the meantime, while the agitator  75  agitates the toner stored in the toner accommodation chamber  74 , the supply roller  72  supplies the toner onto the developing roller  71 . As the developing roller  71  rotates, the thickness regulation blade  73  regulates the thickness of toner on the developing roller  71 . The toner is thus carried on the peripheral surface of the developing roller  71  as a thin layer of uniform thickness. 
     The toner on the developing roller  71  is then supplied to the latent image formed on the peripheral surface of the photosensitive drum  61 , thereby developing the latent image into a visible toner image. Subsequently, the toner image is transferred onto the sheet S conveyed from the sheet-feeding unit  3  as the sheet S passes between the photosensitive drum  61  and the transfer roller  63 . 
     The fixing unit  8  is disposed rearward of the process cartridge  5  within the main casing  2 . The fixing unit  8  includes a heat roller  81  and a pressure roller  82  disposed in opposition to each other. The pressure roller  82  is in pressure-contact with the heat roller  81 . In the fixing unit  8 , the toner image transferred onto the sheet S is thermally fixed thereon as the sheet S passes between the heat roller  81  and the pressure roller  82 . The sheet S with the toner image fixed thereon is finally discharged onto a discharge tray  22  formed on an upper surface of the main casing  2  by conveying rollers  23  and discharge rollers  24 . 
     2. Detailed Description of the Process Cartridge 
     A detailed structure of the process cartridge  5  will be described with reference to  FIGS. 2 to 5 . 
     In the following description of the process cartridge  5 , the process cartridge  5  is assumed to be new (in a state where the process cartridge  5  is shipped as a new product), unless otherwise defined. In other words, the process cartridge  5  is assumed to be in a state shown in  FIG. 7  where a first detected part  115  and a second detected part  215  are at a new-product position, as will be described later. 
     The developing unit  7  includes a developing-unit frame  70  configuring an external appearance of the developing unit  7 . In addition to the developing roller  71  and thickness regulation blade  73  described above, the developing unit  7  also includes a drive-transmitting mechanism  76 , a first sensor gear  110 , and a cover  77 . The developing-unit frame  70  has a left surface to which the cover  77  is attached for covering the drive-transmitting mechanism  76  and first sensor gear  110 , as shown in  FIGS. 2A and 2B . 
     The drive-transmitting mechanism  76  is provided on the left surface of the developing-unit frame  70  and is configured of an input gear  73 G into which a driving force is inputted from the main casing  2 , a developing-roller gear  71 G and a supply-roller gear  72 G engaged with the input gear  73 G, and an agitator gear  75 G engaged with the input gear  73 G through an intermediary gear  74 G. The developing-roller gear  71 G, supply-roller gear  72 G, and agitator gear  75 G transmit the driving force to the developing roller  71 , supply roller  72 , and agitator  75 , respectively. 
     The first sensor gear  110  primarily includes a gear part  111 , and a first detected part  115 . The first detected part  115  can be irreversibly rotated (displaced) from the new-product position shown in  FIGS. 3 and 7  to a used position in which a toothless portion  113  described later confronts the agitator gear  75 G. 
     As shown in  FIG. 3 , the gear part  111  is arranged such that its circumferential surface confronts the agitator gear  75 G. The circumferential surface of the gear part  111  is provided with a toothed portion  112  and the toothless portion  113  (see  FIG. 7 ). A protruding part  114  is also provided on the circumferential surface of the gear part  111  at the downstream end of the toothed portion  112  with respect to a direction in which the first sensor gear  110  rotates (indicated by an arrow in  FIG. 3 ). 
     When the toothed portion  112  faces and engages with the agitator gear  75 G, a driving force is transmitted from the agitator gear  75 G to the toothed portion  112 , rotating the first sensor gear  110 . However, when the toothless portion  113  confronts the agitator gear  75 G, the driving force is not transmitted from the agitator gear  75 G and thus the first sensor gear  110  is not rotated. 
     The protruding part  114  protrudes radially outward from the peripheral surface of the gear part  111  at a position offset from the gear teeth of the agitator gear  75 G in a left-right direction (axial direction of the first sensor gear  110 ). When the first detected part  115  is in the new-product position shown in  FIG. 3 , the protruding part  114  and the gear teeth of the agitator gear  75 G overlap in the left-right direction but do not interfere with (contact) each other. 
     The first detected part  115  is provided on a left surface of the gear part  111  and protrudes leftward therefrom at a position offset radially from the rotational center of the gear part  111 . 
     The agitator gear  75 G has a left surface on which a protruding part  75 A is provided. The protruding part  75 A protrudes leftward from the agitator gear  75 G at a position offset radially from the rotational center of the same. The protruding part  75 A rotates (is displaced) along with the rotation of the agitator gear  75 G in a direction of the arrow indicated in  FIG. 3 . The protruding part  75 A is positioned to contact the protruding part  114  on the first sensor gear  110  in order to start the first sensor gear  110  rotating. 
     In addition to the photosensitive drum  61  and the charger  62  (see  FIG. 1 ) described above, the drum unit  6  further includes a drum-unit frame  60  configuring an external appearance of the drum unit  6  on which transmission gears  64  and  65 , and a second sensor gear  210  are provided, as shown in  FIG. 4A . 
     As shown in  FIG. 4B , the transmission gears  64  and  65  function to transmit a driving force to the second sensor gear  210 . The transmission gears  64  and  65  have respective inner gear parts  64 A and  65 A disposed on the inside in the left-right direction (right side), and outer gear parts  64 B and  65 B disposed on the outside in the left-right direction (left side). The outer gear part  64 B is engaged with the inner gear part  65 A, and the outer gear part  65 B can engage with a toothed portion  212  of the second sensor gear  210  described later. 
     When the developing unit  7  is viewed from its bottom, as shown in  FIG. 5 , a bottom portion of the agitator gear  75 G is exposed through the cover  77 . When the developing unit  7  is mounted in the drum unit  6 , the agitator gear  75 G engages with the inner gear part  64 A of the transmission gear  64  shown in  FIG. 4B . In other words, the drum unit  6  is configured such that the driving force from the developing unit  7  is inputted into the second sensor gear  210 . This construction can contribute to a lower production cost than when separate structures are provided for inputting driving forces into the first sensor gear  110  and second sensor gear  210 . 
     The second sensor gear  210  primarily includes a gear part  211 , and a second detected part  215 . The second sensor gear  210  is configured so that the second detected part  215  is irreversibly rotated (displaced) from the new-product position shown in  FIG. 7  to the used position shown in  FIG. 9 . 
     As shown in  FIG. 4B , the gear part  211  is arranged such that its circumferential surface confronts the outer gear part  65 B of the transmission gear  65 . The gear part  211  has a circumferential surface on which the toothed portion  212  and a toothless portion  213  are provided. When the toothed portion  212  is positioned opposite the outer gear part  65 B and is engaged with the gear teeth of the outer gear part  65 B, a driving force can be transmitted from the transmission gear  65  to the toothed portion  212  for rotating the second sensor gear  210 . However, when the toothless portion  213  faces the outer gear part  65 B, a driving force cannot be transmitted from the transmission gear  65  and thus the second sensor gear  210  is not rotated. 
     The second detected part  215  is provided on a right surface of the gear part  211 . The second detected part  215  protrudes rightward from the gear part  211  at a position offset radially from a rotational center thereof. 
     As shown in  FIG. 7 , the first sensor gear  110  and second sensor gear  210  are juxtaposed (aligned with each other) in the left-right direction (axial direction) when the developing unit  7  is mounted in the drum unit  6  (only the transmission gears  64  and  65  and the second sensor gear  210  are shown in  FIG. 7 ). This arrangement enables the process cartridge  5  to be made more compact vertically than a structure in which the second sensor gear  210  is positioned above the first sensor gear  110 , for example. 
     3. Structure of the Laser Printer Related to Sensing a Process Cartridge 
     A detailed structure of the laser printer  1  concerned with sensing the process cartridge  5  (the drum unit  6  and developing unit  7 ) will be described next with respect to  FIG. 6 . 
     The laser printer  1  includes a drive mechanism (not shown) that is well known in the art. The drive mechanism can input a driving force into the input gear  73 G of the process cartridge  5  (developing unit  7 ) while the process cartridge  5  is mounted in the main casing  2 . The laser printer  1  is also provided with a sensing mechanism  9  and a control unit  10  shown in  FIG. 6 . 
     The sensing mechanism  9  is primarily configured of a pivotally movable contact arm  91 , a coil spring  92  that applies a force to the contact arm  91  for returning the contact arm  91  to a non-contact state (hereinafter called a “non-detection position”), and a photosensor  93  for sensing the pivotal movement of the contact arm  91 . The contact arm  91  pivotally moves when contacted by the first detected part  115  or second detected part  215 . 
     The contact arm  91  primarily includes a shaft part  91 A, a contact part  91 B, and an arm part  91 D. The shaft part  91 A is rotatably supported on a wall  25  provided inside the main casing  2 . Specifically, the contact part  91 B is provided on a right end of the shaft part  91 A, while the arm part  91 D is provided on a left end of the shaft part  91 A. The contact part  91 B is provided on the right side of the wall  25  (the side nearest the process cartridge  5 ). The arm part  91 D is provided on the left side of the wall  25  (the side opposite the process cartridge  5  with respect to the wall  25 ). The contact part  91 B is a plate-shaped part that is arranged in a position for contacting the first detected part  115  and second detected part  215 . The contact part  91 B extends generally upward from the right end of the shaft part  91 A in a radial direction of the shaft part  91 A. The arm part  91 D extends radially outward from the left end of the shaft part  91 A in the general front-rear direction. A light-shielding part  91 E having a plate shape is formed on a rear end of the arm part  91 D. 
     The coil spring  92  has one end anchored on a front end of the arm part  91 D, and another end anchored to a spring-anchoring part  25 A formed on the left surface of the wall  25 . In the present embodiment, the photosensor  93 , shaft part  91 A, and spring-anchoring part  25 A fall along a general straight line when viewed in the left-right direction. Accordingly, when the first detected part  115  and second detected part  215  are not in contact with the contact arm  91 , the urging force of the coil spring  92  urges the light-shielding part  91 E toward the non-detection position between a light-emitting element  93 A and a light-receiving element  93 B described later. 
     The photosensor  93  is fixed to a sensor-mounting part  25 B formed on the left surface of the wall  25 . The photosensor  93  has the light-emitting element  93 A and the light-receiving element  93 B positioned to confront each other in the left-right direction. The light-emitting element  93 A is configured to emit light toward the light-receiving element  93 B, and the light-receiving element  93 B is configured to receive the light emitted from the light-emitting element  93 A. When the contact arm  91  is in the non-detection position, the light-shielding part  91 E is positioned between the light-emitting element  93 A and light-receiving element  93 B, as shown in  FIG. 6 . Therefore, the light-receiving element  93 B cannot receive the light from the light-emitting element  93 A at this time. However, when the contact part  91 B is contacted by the first detected part  115  or second detected part  215 , the contact arm  91  pivotally moves, causing the light-shielding part  91 E to move out from between the light-emitting element  93 A and light-receiving element  93 B. At this time, the light-receiving element  93 B can receive the light emitted from the light-emitting element  93 A. The light-receiving element  93 B is configured to output a prescribed signal to the control unit  10  when light is received. 
     The control unit  10  functions to control operations of the laser printer  1 . In the present embodiment, the control unit  10  executes an operation for driving the developing roller  71 , supply roller  72 , agitator  75 , and the like in a preliminary rotation (hereinafter called an “idle rotation operation”) when the process cartridge  5  is mounted in the main casing  2  (such as when a signal is received from a sensor provided for detecting opening and closing of the front cover  21  indicating that the front cover  21  has been closed). While the idle rotation operation will be described later in greater detail, the control unit  10  determines whether the drum unit  6  and developing unit  7  are new products during this operation based on the signal received from the light-receiving element  93 B. 
     4. Operations for Detecting the Process Cartridge 
     Next, operations of the laser printer  1  for detecting the process cartridge  5  (drum unit  6  and developing unit  7 ) will be described with reference to  FIGS. 7 through 11D . 
     When the first detected part  115  is in the new-product position shown in  FIG. 7  (when the developing unit  7  is new), the first sensor gear  110  is oriented such that the protruding part  114  points generally toward the rotational center of the agitator gear  75 G, and the toothed portion  112  is not engaged with the agitator gear  75 G. On the other hand, when the second detected part  215  is in the new-product position (when the drum unit  6  is new), the second sensor gear  210  is oriented such that the toothed portion  212  faces and engages with the transmission gear  65  (outer gear part  65 B). In the first embodiment, the first detected part  115  and second detected part  215  are disposed to overlap each other in the left-right direction when both are in the new-product position. 
     In order to execute the idle rotation operation, the control unit  10  controls the drive mechanism (not shown) when the process cartridge  5  is mounted in the main casing  2  to input a driving force into the process cartridge  5  (and specifically, the input gear  73 G). When the driving force is inputted into the process cartridge  5 , the driving force is transmitted from the agitator gear  75 G to the toothed portion  212  of the second sensor gear  210  via the transmission gears  64  and  65 , and the second sensor gear  210  begins to rotate. 
     When the second sensor gear  210  rotates upon input of the driving force inputted from the main casing  2 , the second detected part  215  is displaced counterclockwise from the new-product position shown in  FIG. 7  to a position contacting the contact part  91 B of the contact arm  91 , as shown in  FIG. 8 . This contact forces the contact arm  91  to pivot. As the contact arm  91  pivots, the light-shielding part  91 E is retracted from the photosensor  93  (from between the light-emitting element  93 A and light-receiving element  93 B), causing the light-receiving element  93 B to detect light and output a signal to the control unit  10 . 
     As the second sensor gear  210  continues to rotate, the second detected part  215  slides over the contact part  91 B, allowing the contact arm  91  to return to its non-detection position, as shown in  FIG. 9 . At this time, the light-receiving element  93 B no longer outputs a signal. 
     As shown in  FIGS. 11A and 11B , the control unit  10  determines that the drum unit  6  is new if the photosensor  93  outputs a signal (enters the ON state) and subsequently halts output of the signal (returns to the OFF state) within a predetermined first time interval T 1  following the start of the idle rotation operation. After the second sensor gear  210  has rotated until the toothless portion  213  faces the transmission gear  65  and the second detected part  215  is displaced to the used position shown in  FIG. 9 , the driving force is no longer transmitted to the second sensor gear  210 . Hence, the second sensor gear  210  comes to a halt and can no longer rotate thereafter. 
     On the other hand, if the second detected part  215  of the drum unit  6  mounted in the main casing  2  is already in the used position when the control unit  10  begins the idle rotation operation, the sensing mechanism  9  will not detect the second detected part  215  (the OFF state of the photosensor  93  will be continuous) during the first time interval T 1 , as in the examples of  FIGS. 11C and 11D . Consequently, the control unit  10  will determine that the drum unit  6  is a used product. 
     Through the current stage of the process described above, the first sensor gear  110  has remained motionless because the toothed portion  112  is not engaged with the agitator gear  75 G. However, the protruding part  75 A of the agitator gear  75 G also moves along with the rotation of the agitator gear  75 G and contacts the protruding part  114  of the first sensor gear  110 . When the protruding part  114  is pushed by the protruding part  75 A, the first sensor gear  110  begins to rotate counterclockwise in the drawings so that the toothed portion  112  becomes engaged with the agitator gear  75 G. Through this engagement, a driving force is inputted into the toothed portion  112  from the main casing  2 , rotating the first sensor gear  110 . 
     As the first sensor gear  110  rotates, the first detected part  115  is displaced counterclockwise in the drawings from the new-product position and contacts the contact part  91 B of the contact arm  91 , as shown in  FIG. 10 . As in the case of the second detected part  215 , contact from the first detected part  115  causes the contact arm  91  to pivot so that the photosensor  93  outputs a signal to the control unit  10 . Although not illustrated in the drawings, the first detected part  115  slides over the contact part  91 B as the first sensor gear  110  continues to rotate, allowing the contact arm  91  to return to its non-detection position and halting signal output to the control unit  10 . 
     As illustrated in  FIGS. 11A and 11C , the control unit  10  determines that the developing unit  7  is new when the photosensor  93  outputs a signal (enters the ON state) and subsequently halts output of the signal (returns to the OFF state) during a predetermined second time interval T 2  following the first time interval T 1 . While not shown in the drawings, after the first sensor gear  110  has rotated so that the toothless portion  113  faces the agitator gear  75 G and the first detected part  115  has been displaced to the used position, the driving force is no longer transmitted to the first sensor gear  110 . Accordingly, the first sensor gear  110  is halted and cannot rotate thereafter. 
     If the control unit  10  initiates the idle rotation operation after a developing unit  7  having a first detected part  115  in the used position is mounted in the main casing  2 , the sensing mechanism  9  will not detect the first detected part  115  during the second time interval T 2 , as illustrated in  FIGS. 11B and 11D . In this case, the control unit  10  determines that the developing unit  7  is a used product. 
     Therefore, if both the drum unit  6  and developing unit  7  of the mounted process cartridge  5  are new, the sensing mechanism  9  will detect both the first detected part  115  and the second detected part  215 . Accordingly, the signal outputted from the photosensor  93  will change according to the sequence OFF-*ON-*OFF within each of the first time interval T 1  and second time interval T 2 , as in the example of  FIG. 11A . On the other hand, if only the drum unit  6  is new, the sensing mechanism  9  will only detect the second detected part  215  and the changes in signal state will occur only in the first time interval T 1 , as in the example of  FIG. 11B . If only the developing unit  7  is new, then the sensing mechanism  9  will detect only the first detected part  115  and the signal changes will appear only in the second time interval T 2 , as in the example of  FIG. 11C . If both the drum unit  6  and developing unit  7  are used products, then the sensing mechanism  9  will detect neither the first detected part  115  nor the second detected part  215  and the signal will remain unchanged (in the OFF state) during both the first time interval T 1  and second time interval T 2 , as in the example of  FIG. 11D . 
     According to the first embodiment described above, the sensing mechanism  9  can detect both the first detected part  115  (the developing unit  7 ) and the second detected part  215  (the drum unit  6 ). Therefore, there is no need to provide separate detecting means for each of the drum unit  6  and developing unit  7 , enabling the drum unit  6  and developing unit  7  to be detected at a lower cost. 
     Further, since the first detected part  115  and second detected part  215  are configured to contact the contact arm  91  (sensing mechanism  9 ) at different timings in the present embodiment, the sensing mechanism  9  can differentiate between contact by the first detected part  115  and contact by the second detected part  215 , thereby enabling separate detection of the first detected part  115  and second detected part  215 . 
     Further, since the driving force from the main casing  2  is transmitted to the drum unit  6  via the developing unit  7  in the present embodiment, separate mechanisms for inputting a driving force to each of the drum unit  6  and the developing unit  7  are not necessary to be provided in the laser printer  1 . This construction contributes to a reduction in production cost. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIGS. 12A-14D , wherein like parts and components are designated with the same reference numerals with those of the first embodiment to avoid duplicating description. 
     The drum unit  6  of the second embodiment is provided with a second sensor gear  220 , instead of the second sensor gear  210 . The developing unit  7  has the same configuration as the first embodiment. 
     As shown in  FIG. 12A , the second sensor gear  220  of the second embodiment primarily includes the gear part  211  having the toothed portion  212  and toothless portion  213 , and a second detected part  225 . 
     The second detected part  225  is provided on the right surface of the gear part  211 . The second detected part  225  has a fan-like shape in a left-right view and protrudes rightward (away from the viewer in  FIG. 12 ) from the gear part  211  at a position offset radially from the rotational center thereof. The fan-shaped second detected part  225  has an arc-shaped outer peripheral edge that is configured to contact the contact arm  91 . 
     The contact arm  91  of the second embodiment primarily includes the shaft part  91 A (see  FIG. 6 ), the contact part  91 B, the arm part  91 D, an offshoot arm  91 G, a first light-shielding part  91 E, and a second light-shielding part  91 F. 
     When the contact arm  91  is in a non-contact state, the first light-shielding part  91 E is positioned inside the photosensor  93  (between the light-emitting element  93 A and light-receiving element  93 B) for interrupting light emitted from the light-emitting element  93 A, as in the first embodiment. The first light-shielding part  91 E is formed in a shape identical to the light-shielding part  91 E described in the first embodiment. 
     The offshoot arm  91 G extends diagonally downward and rearward from a point near the center of the arm part  91 D. The second light-shielding part  91 F has a plate shape and is provided on a distal end of the offshoot arm  91 G. 
     First, to facilitate understanding of the second embodiment, operations for sensing the process cartridge  5  will be described for a process cartridge  5  in which only the drum unit  6  is new. In this description, movement of the first sensor gear  110  depicted in the drawings will be ignored since the contact arm  91  (sensing mechanism  9 ) does not detect the first detected part  115  of the developing unit  7 , as described in the first embodiment. 
     When the second sensor gear  220  rotates from the driving force inputted from the agitator gear  75 G, the second detected part  225  is displaced from the new-product position shown in  FIG. 12A  to a position contacting the contact part  91 B of the contact arm  91 , as shown in  FIG. 12B . This contact forces the contact arm  91  to pivot. As the contact arm  91  pivots, the first light-shielding part  91 E is retracted from the photosensor  93 , causing the photosensor  93  to detect light and to output an ON signal to the control unit  10 . Since the outer peripheral edge of the second detected part  225  that contacts the contact arm  91  has an arc shape in the second embodiment, the second detected part  225  maintains contact with the contact arm  91  for a prescribed time (fourth time interval T 4  described later). While not illustrated in the drawings, the second detected part  225  slides over the contact part  91 B as the second sensor gear  220  continues to rotate. Once contact between the second detected part  225  and contact part  91 B is released, the contact arm  91  returns to its non-detection position, causing the photosensor  93  to stop outputting the ON signal to the control unit  10  and to enter an OFF state. 
     As shown in  FIG. 14B , the control unit  10  determines that the drum unit  6  is new if an ON signal is detected after a predetermined third time interval T 3  following the start of the idle rotation operation, and again detects an OFF state after an additional predetermined fourth time interval T 4  following the third time interval T 3 . After the second sensor gear  220  has rotated until the toothless portion  213  faces the transmission gear  65  and the second detected part  225  is displaced to the used position, the second sensor gear  220  comes to a halt and can no longer rotate thereafter. Accordingly, the contact arm  91  will no longer detect the second detected part  225 . Hence, when a drum unit  6  whose second detected part  225  is already in the used position is mounted in the main casing  2 , the control unit  10  will determine that the drum unit  6  is a used product because the signal variations described above are not detected. 
     Based on the above description, operations for sensing a process cartridge  5  in which both the drum unit  6  and developing unit  7  are new will be described next. 
     When a driving force is inputted from the agitator gear  75 G, the second sensor gear  220  rotates, as illustrated in  FIGS. 12A and 12B , until the second detected part  225  contacts the contact arm  91 , causing the contact arm  91  to pivot. Due to the pivoting contact arm  91 , the photosensor  93  begins outputting an ON signal to the control unit  10  after the third time interval T 3  has elapsed, as illustrated in  FIG. 14A . 
     Subsequently, the protruding part  75 A of the agitator gear  75 G contacts the protruding part  114  of the first sensor gear  110  while the second detected part  225  is still in contact with the contact arm  91 , and the first sensor gear  110  begins to rotate. As the first sensor gear  110  rotates, the first detected part  115  is displaced from the new-product position shown in  FIG. 12B  and comes into contact with the contact part  91 B of the contact arm  91  when the second detected part  225  is still in contact with the same, as shown in  FIG. 13A . 
     As the contact arm  91  pivots clockwise in the drawings from the position shown in  FIG. 12B  to the position shown in  FIG. 13A , the second light-shielding part  91 F moves to a position between the light-emitting element  93 A and light-receiving element  93 B to interrupt the light emitted from the light-emitting element  93 A. As the first sensor gear  110  continues to rotate, the first detected part  115  slides over the contact part  91 B and separates from the contact arm  91 , as illustrated in  FIG. 13B . At this time, the contact arm  91  returns to a state of contact only with the second detected part  225 , and the light-receiving element  93 B once again receives light. 
     Through the process described above, the photosensor  93  halts output of the ON signal to the control unit  10  and enters an OFF state, then subsequently resumes outputting the ON signal to the control unit  10 , all within the fourth time interval T 4 . In the preferred embodiment, the control unit  10  determines that the developing unit  7  is new when the signal changes and returns to the original state. When the drum unit  6  and developing unit  7  of the process cartridge  5  are both new, the signal outputted when sensing the process cartridge  5  first changes from ON to OFF and back to ON again. From this variation, the control unit  10  can determine that the developing unit  7  is new. 
     After the control unit  10  determines that the developing unit  7  is new, the second sensor gear  220  continues to rotate and the second detected part  225  slides off the contact part  91 B, halting output of the ON signal to the control unit  10 . Since the control unit  10  detects the OFF state at the point the fourth time interval T 4  has elapsed, the control unit  10  determines that the drum unit  6  is new. 
     Next, operations for sensing a process cartridge  5  will be described for a case in which only the developing unit  7  is new. In this case, the contact arm  91  does not detect the second detected part  225  of the drum unit  6 . Therefore, only the first detected part  115  contacts the contact arm  91 . 
     As the first sensor gear  110  rotates, the first detected part  115  is displaced from the new product position shown in  FIG. 12A  and contacts the contact arm  91 , causing the contact arm  91  to pivot so that the first light-shielding part  91 E is retracted from the photosensor  93  (see  FIG. 12B ). The contact arm  91  continues to pivot until the second light-shielding part  91 F is positioned between the light-emitting element  93 A and light-receiving element  93 B, as shown in  FIG. 13A . As the first sensor gear  110  continues to rotate, the first detected part  115  slides over the contact arm  91 , allowing the contact arm  91  to return from its state in  FIG. 13A  to its non-detection position shown in  FIG. 12A , after passing through the state shown in  FIG. 12B . Through this operation, the signal outputted to the control unit  10  changes in the order OFF→ON→OFF→ON→OFF during the fourth time interval T 4 , as illustrated in  FIG. 14C . Accordingly, the control unit  10  determines that the developing unit  7  is new. 
     If both the drum unit  6  and developing unit  7  of the process cartridge  5  mounted in the main casing  2  are used, the contact arm  91  will detect neither the first detected part  115  nor the second detected part  225 . Hence, the control unit  10  will detect no signal changes, as illustrated in  FIG. 14D . In this case, the control unit  10  determines that both the drum unit  6  and developing unit  7  are used products. 
     As in the first embodiment, the sensing mechanism  9  according to the second embodiment can detect both the drum unit  6  and developing unit  7  at a low cost. Moreover, the sensing mechanism  9  in the second embodiment can detect contact by the first detected part  115  while detecting contact by the second detected part  225 . 
     In the second embodiment, the first detected part  115  is configured to contact the contact arm  91  and subsequently separate from the same while the second detected part  225  remains in contact with the contact arm  91 , but the opposite configuration may be used. Namely, the second detected part may be configured to contact the contact arm and subsequently separate from the same while the first detected part remains in contact with the contact arm. 
     Third Embodiment 
     A third embodiment of the present invention will be described with reference to  FIGS. 15 to 17B , wherein like parts and components are designated with the same reference numerals with those of the first embodiment to avoid duplicating description. 
     As shown in  FIG. 15 , the drum unit  6  according to the third embodiment has a second sensor gear  230 , and the developing unit  7  according to the third embodiment has a first sensor gear  130 . 
     The second sensor gear  230  primarily includes a gear part  231  having the toothed portion  212 , which is capable of engaging with the agitator gear  75 G, and toothless portion  213 ; and a second detected part  235 . The second detected part  235  is provided on a left surface of the gear part  231  and protrudes leftward from the gear part  231  at a position offset radially from a rotational center thereof. 
     The first sensor gear  130  is configured of the gear part  111  having the toothed portion  112 , toothless portion  113 , and protruding part  114 ; the first detected part  115 ; and a third detected part  136 . The third detected part  136  is provided on the left surface of the gear part  111  and protrudes leftward from the gear part  111  at a position offset radially from the rotational center thereof and forward (upstream in the rotational direction) of the first detected part  115 . 
     In the third embodiment, the first detected part  115  and second detected part  235  are provided on opposite sides of the contact arm  91  (the sensing mechanism  9 ) when the process cartridge  5  is mounted in the main casing  2 . Further, the first sensor gear  130  and second sensor gear  230  are arranged in a generally vertical relationship with the contact arm  91  interposed therebetween when the process cartridge  5  is mounted in the main casing  2 . This configuration enables the process cartridge  5  to be made more compact in the left-right dimension (the axial direction of the photosensitive drum  61 ). 
     The contact arm  91  primarily includes the shaft part  91 A (see  FIG. 6 ), a first contact part  91 B, a second contact part  91 C, the arm part  91 D, and the first light-shielding part  91 E. The first contact part  91 B is formed in a shape identical to the contact part  91 B described in the first embodiment. The second contact part  91 C has a plate shape and extends radially outward (in a general downward direction) from the right end of the shaft part  91 A. 
     Next, operations for sensing the process cartridge  5  will be described. 
     When a driving force is inputted from the main casing  2 , the second sensor gear  230  begins to rotate and the second detected part  235  is displaced from the new-product position shown in  FIG. 15  and contacts the second contact part  91 C of the contact arm  91 , as shown in  FIG. 16A , causing the contact arm  91  to pivot upward. When the contact arm  91  pivots, the photosensor  93  outputs a signal to the control unit  10 . 
     As the second sensor gear  230  continues to rotate, the second detected part  235  slides over the second contact part  91 C, allowing the contact arm  91  to return to its non-detection position as shown in  FIG. 16B . As a result, the contact arm  91  halts output of the signal to the control unit  10 , whereby the control unit  10  can determine that the drum unit  6  is a new product. When the toothless portion  213  subsequently confronts the agitator gear  75 G and the second detected part  235  is displaced to the used position, the second sensor gear  230  comes to a halt and can no longer rotate thereafter. 
     In the meantime, the protruding part  75 A contacts the protruding part  114 , causing the first sensor gear  130  to begin rotating. As the first sensor gear  130  rotates, the first detected part  115  is displaced from the new-product position shown in  FIG. 16B  until the first detected part  115  contacts the first contact part  91 B of the contact arm  91 , as shown in  FIG. 16C , causing the contact arm  91  to pivot upward. While not shown in the drawings, the first detected part  115  slides over the first contact part  91 B as the first sensor gear  130  continues to rotate, allowing the contact arm  91  to return to the non-detection position. As a result, the control unit  10  determines that the developing unit  7  is a new product. 
     Once the toothless portion  113  has rotated opposite the agitator gear  75 G and the first detected part  115  and third detected part  136  have been displaced to their used positions, as shown in  FIG. 17A , the first sensor gear  130  comes to a halt and can no longer rotate thereafter. At this time, the third detected part  136  has contacted the first contact part  91 B of the contact arm  91  and caused the contact arm  91  to pivot clockwise in the drawings. Consequently, the photosensor  93  outputs an ON signal to the control unit  10 , enabling the control unit  10  to determine that the developing unit  7  (the process cartridge  5 ) is in the mounted state. 
     If both the first detected part  115  and second detected part  235  are in their used positions when the process cartridge  5  is mounted in the main casing  2 , the contact arm  91  will detect neither the first detected part  115  nor the second detected part  235 . Hence, the control unit  10  will determine that both the drum unit  6  and developing unit  7  are used. In this case, the third detected part  136  will still contact the first contact part  91 B of the contact arm  91  as the process cartridge  5  is mounted in the main casing  2 , causing the contact arm  91  to pivot counterclockwise in the drawings, as illustrated in  FIG. 17B . Accordingly, the control unit  10  can detect that the process cartridge  5  is in a mounted state. 
     In the third embodiment described above, the sensing mechanism  9  can detect both the drum unit  6  and developing unit  7  at a low cost. Moreover, the sensing mechanism  9  according to the third embodiment can detect whether the process cartridge  5  is in a mounted state. Therefore, it is not necessary to provide separate means for detecting when the process cartridge  5  is in a mounted state, allowing for further reduction in manufacturing costs. 
     &lt;Variations and Modifications&gt; 
     In the first embodiment described above, the first detected part  115  and second detected part  215  cause the contact arm  91  to pivot in the same direction when contacting the contact arm  91 , but the present invention is not limited to this configuration. 
     For example,  FIG. 18  shows a first modification of the present invention. The drum unit  6  of the first modification is provided with a second sensor gear  240 . The second sensor gear  240  has the toothed portion  212  for engaging the outer gear part  64 B of the transmission gear  64 . In addition to the contact part  91 B, the contact arm  91  of the first modification includes a second contact part  91 H configured to be contacted by the second detected part  235  of the second sensor gear  240 . With this configuration, the direction in which the contact arm  91  is pivoted when the first detected part  115  contacts the first contact part  91 B can be opposite the direction in which the contact arm  91  pivots when the second detected part  235  of the second sensor gear  240  contacts the second contact part  91 H. 
     However, the space required for displacing the contact arm  91  can be reduced when the first and second detected parts are configured to displace the contact arm  91  in the same direction, as in the first to third embodiments. Accordingly, the structures in the depicted embodiments make effective use of space inside the main casing  2 , enabling the laser printer  1  to be made more compact. Further, configuring the first and second detected parts to displace the contact arm  91  in the same direction simplifies the structure for detecting contact by the first detected part while simultaneously detecting contact by the second detected part, as described in the second embodiment. 
     In the depicted first to third embodiments, the detected parts (the first detected part  115 , second detected part  215 , and the like) are provided on rotary bodies (the first sensor gear  110 , second sensor gear  210 , and the like), but the present invention is not limited to this configuration. 
     For example, the detected parts may be provided on a movable body that can move in a prescribed direction.  FIG. 19  shows an example of such configuration as a second modification of the present invention. 
     As shown in  FIG. 19 , the drum unit  6  of the second modification is provided with a transmission gear  66 , and a movable body  250  on which a second detected part  255  is provided. More specifically, the transmission gear  66  includes an inner gear part  66 A, and an outer gear part  66 B. The inner gear part  66 A has both a toothed part and a toothless part (not indicated with reference numerals in  FIG. 19 ). When the toothed part confronts the agitator gear  75 G, the driving force of the agitator gear  75 G is transmitted to the inner gear part  66 A. The outer gear part  66 B is juxtaposed with the inner gear part  66 A and rotates together with the same. The movable body  250  is supported on guides provided in the drum-unit frame  60  so as to be capable of sliding in the general front-rear direction. The movable body  250  has a rack gear part  251  that engages with the outer gear part  66 B of the transmission gear  66 . The second detected part  255  protrudes upward from a front end of the movable body  250 . 
     With this configuration, when a driving force is transmitted from the agitator gear  75 G to the inner gear part  66 A, the outer gear part  66 B rotating together with the inner gear part  66 A and engaged with the rack gear part  251  moves the movable body  250  (and the second detected part  255 ) generally forward. The second detected part  255  contacts a second contact part  91 J that protrudes in a general downward direction from the contact arm  91 , causing the contact arm  91  to pivot. As the second detected part  255  slides over the second contact part  91 J, the contact arm  91  is allowed to return to its non-detection position. 
     In the first and third embodiments described above, the first detected part  115  is configured to contact the contact arm  91  (sensing mechanism  9 ) after the sensing mechanism  9  has detected the second detected part  215  (or  235 ). However, the operations described in these embodiments may be performed in reverse order; namely, the second detected part may be configured to contact the sensing mechanism after the sensing mechanism has detected the first detected part. 
     In the embodiments described above, the developing unit  7  inputs a driving force into the drum unit  6  in order to displace the second detected part (the second detected part  215  and the like). However, the image forming apparatus may be configured to input the driving force from the device body into the drum unit directly, for example. Alternatively, the drum unit may be configured to transmit a driving force inputted from the device body into the developing unit for displacing the first detected part. 
     In the embodiments described above, the developing unit  7  having the developing roller  71  and toner-accommodating section  74  serves as the claimed first unit, and the drum unit  6  having the photosensitive drum  61  serves as the claimed second unit. However, the first unit may be a unit possessing a toner-accommodating section (such as a toner cartridge), while the second unit may be a unit possessing a photosensitive member and a developing roller. 
     The sensing mechanism  9  of the depicted embodiments employs the coil spring  92  for applying a biasing force to the contact arm  91 . Instead of the coil spring, a torsion spring or a leaf spring may be available. 
     The laser printer  1  depicted in the first to third embodiments is a monochrome printer capable of forming black and white images only, but the present invention may also be applied to a color printer capable of forming colored images. Further, the present invention may also be embodied as a copier or a multifunction device provided with a scanning function, such as a flatbed scanner. 
     While the invention has been described in detail with reference to the specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.