Patent Publication Number: US-11385589-B2

Title: Image forming apparatus with detachable drum unit and developing unit

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Applications No. 2020-107824 filed on Jun. 23, 2020, No. 2020-107822 filed on Jun. 23, 2020 and No. 2020-107823 filed on Jun. 23, 2020, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an image forming apparatus including a drum unit and a developing unit that are each attached in a detachable manner. 
     An electrophotographic image forming apparatus may include a drum unit and a developing unit that are each attached, in a detachable manner, to an apparatus main body. The drum unit includes a photoconductor drum and the developing unit includes a developing roller that supplies developer to the surface of the photoconductor drum. 
     For example, there is known an image forming apparatus in which the apparatus main body includes a guide portion that guides the drum unit and the developing unit respectively to predetermined attachment positions. 
     SUMMARY 
     An image forming apparatus according to an aspect of the present disclosure includes an apparatus main body, a drum unit, and a developing unit. The apparatus main body has an opening that is closed by a cover portion. The drum unit includes a rotatably supported photoconductor drum and is attached through the opening to an inside of the apparatus main body in a detachable manner. The developing unit includes a rotatably supported developing roller and a developing unit projection and is attached to the drum unit in a detachable manner. The developing unit projection is formed to project out from opposite sides of the developing unit along an extension line of a rotation shaft of the developing roller. The apparatus main body includes a first developing projection guide portion configured to guide the developing unit projection from a first start position to a relay position in the apparatus main body, the relay position located closer to the photoconductor drum than the first start position. The drum unit includes a second developing projection guide portion configured to, succeeding from the first developing projection guide portion, guide the developing unit projection from the relay position to a first end position, the first end position located closer to the photoconductor drum than the relay position. 
     An image forming apparatus according to another aspect of the present disclosure includes a drum unit, a developing unit, and a biasing mechanism. The drum unit is provided in an apparatus main body and includes a rotatably supported photoconductor drum. The developing unit includes a rotatably supported developing roller, a primary gear, and a secondary gear and is configured to be attached to the drum unit. The primary gear receives a rotational force from a drive portion provided in the apparatus main body. The secondary gear is integrally provided with a rotation shaft of the developing roller and receives a rotational force from the primary gear. The biasing mechanism elastically biases the developing unit toward the photoconductor drum. The developing unit includes a first developing unit projection and a second developing unit projection. The first developing unit projection is formed to project out from opposite sides of the developing unit along an extension line of a rotation shaft of the developing roller. The second developing unit projection is provided on an opposite side to the first developing unit projection with respect to the primary gear in a state where the developing unit has been attached to the drum unit. The second developing unit projection is formed to project out from the opposite sides in parallel to the first developing unit projection. The drum unit includes a first support surface and a second support surface. The first support surface supports the first developing unit projection against a moment of a force that is applied from the primary gear to the developing unit via the secondary gear, the first support surface being parallel to a biasing direction of the biasing mechanism. The second support surface supports the second developing unit projection against the moment of the force, the second support surface being parallel to the biasing direction. 
     An image forming apparatus according to a still another aspect of the present disclosure includes an apparatus main body, a drum unit, and a developing unit. The apparatus main body has an opening that is closed by a cover portion. The drum unit includes a rotatably supported photoconductor drum and is attached through the opening to the apparatus main body in a detachable manner. The developing unit includes a rotatably supported developing roller and is attached to the drum unit in a detachable manner. The drum unit forms an attachment space in which the developing unit is disposed, and includes a handle portion configured to be gripped by a hand that accesses the handle portion through the attachment space. By being attached to the drum unit, the developing unit closes a path including the attachment space through which the handle portion is accessed by the hand. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section diagram of an image forming apparatus according to an embodiment. 
         FIG. 2  is a perspective diagram of a drum unit in the image forming apparatus according to the embodiment. 
         FIG. 3  is a perspective diagram of a developing unit in the image forming apparatus according to the embodiment. 
         FIG. 4  is a perspective diagram of the drum unit and the developing unit in the image forming apparatus according to the embodiment. 
         FIG. 5  is a cross-section diagram of the drum unit in the image forming apparatus according to the embodiment. 
         FIG. 6  is a first cross-section diagram of the drum unit and the developing unit in the image forming apparatus according to the embodiment. 
         FIG. 7  is a second cross-section diagram of the drum unit and the developing unit in the image forming apparatus according to the embodiment. 
         FIG. 8  is a cross-section diagram of a portion including a drum projection guide portion and a developing projection guide portion in the image forming apparatus according to the embodiment. 
         FIG. 9  is a perspective diagram of a portion including the drum projection guide portion and the developing projection guide portion in the image forming apparatus according to the embodiment. 
         FIG. 10  is a diagram showing an end portion of a first developing projection guide portion and a second developing projection guide portion in the image forming apparatus according to the embodiment. 
         FIG. 11  is a cross-section diagram of a biasing mechanism and its surroundings in the image forming apparatus according to the embodiment. 
         FIG. 12  is a side diagram of the drum unit and the developing unit in the image forming apparatus according to the embodiment. 
         FIG. 13  is a perspective diagram of fitting portions provided in a drum unit and a developing unit in an application example of the image forming apparatus according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes an embodiment of the present disclosure with reference to the accompanying drawings. It should be noted that the following embodiment is an example of a specific embodiment of the present disclosure and should not limit the technical scope of the present disclosure. 
     [Entire Configuration of Image Forming Apparatus  10 ] 
     An image forming apparatus  10  according to the embodiment executes a print process by an electrophotographic method. The print process is executed to form an image on a sheet. 
     As shown in  FIG. 1 , the image forming apparatus  10  includes an apparatus main body  100  and a cover portion  101 , wherein a main opening  102  is formed in an upper portion of the apparatus main body  100 , and the cover portion  101  closes the main opening  102 . The cover portion  101  is configured to open and close the main opening  102 . The cover portion  101  is supported by the apparatus main body  100  in such a way as to pivot vertically. 
     The apparatus main body  100  is a main housing storing a sheet cassette  1 , a sheet feed device  2 , a sheet conveying device  3 , a drum unit  4 , a developing unit  5 , a fixing device  6 , and an exposure device  7 . 
     A plurality of sheets are stacked in the sheet cassette  1 . The sheet feed device  2  feeds the sheets stacked in the sheet cassette  1  one by one to a sheet conveyance path  30 . The sheet conveying device  3  includes a plurality of pairs of conveyance rollers  31  that convey the sheet along the sheet conveyance path  30 . The sheet conveying device  3  discharges the sheet with an image formed thereon, from the sheet conveyance path  30  to a discharge tray  101   a . The discharge tray  101   a  is formed in the cover portion  101  (see  FIG. 1 ). 
     As shown in  FIG. 5  to  FIG. 7 , the drum unit  4  includes a first unit housing  40 , a photoconductor drum  41 , a charging device  42 , and a transfer roller  44 . The first unit housing  40  supports the photoconductor drum  41 , the charging device  42 , and the transfer roller  44 . 
       FIG. 6  is a cross-section diagram of the drum unit  4  and the developing unit  5  taken along a J-J plane shown in  FIG. 4 . In addition,  FIG. 7  is a cross-section diagram of the drum unit  4  and the developing unit  5  taken along a K-K plane shown in  FIG. 4 . 
     The photoconductor drum  41  and the transfer roller  44  are rotatably supported by the first unit housing  40 . The photoconductor drum  41  is rotatably supported by a rotation shaft  41   a,  and the rotation shaft  41   a  is supported by the first unit housing  40 . 
     The charging device  42  electrically charges the surface of the photoconductor drum  41 . The exposure device  7  writes an electrostatic latent image on the surface of the photoconductor drum  41 . The electrostatic latent image is developed as a toner image by the developing unit  5 . 
     The transfer roller  44  transfers the toner image from the photoconductor drum  41  to the sheet. The first unit housing  40  includes a sheet introducing portion  403  that guides the sheet to a transfer position between the photoconductor drum  41  and the transfer roller  44  (see  FIG. 5 ,  FIG. 6 ). 
     As shown in  FIG. 6  and  FIG. 7 , the developing unit  5  includes a second unit housing  50  and a developing roller  51 . The second unit housing  50  includes a developer case  50   a  that stores toner. 
     The second unit housing  50  rotatably supports the developing roller  51 . Specifically, the developing roller  51  is integrally provided with a rotation shaft  51   a,  and the rotation shaft  51   a  is rotatably supported by the second unit housing  50 . 
     The developing roller  51  supplies the toner in the developer case  50   a  to the surface of the photoconductor drum  41 , thereby developing, as a toner image, the electrostatic latent image formed on the surface of the photoconductor drum  41 . The developing unit  5  also includes a stirring member  52  configured to stir the developer in the developer case  50   a.    
     The drum unit  4  and the developing unit  5  are individually attached to the apparatus main body  100 . In the present embodiment, the drum unit  4  is attached through the main opening  102  to the inside of the apparatus main body  100  in a detachable manner. In addition, in a state where the drum unit  4  has been attached to the inside of the apparatus main body  100 , the developing unit  5  is attached through the main opening  102  to the inside of the apparatus main body  100  in a detachable manner. 
     Meanwhile, the accuracy of the position of the developing roller  51  with respect to the photoconductor drum  41  has a great influence on the image quality. In a case where the drum unit  4  and the developing unit  5  are individually attached to the apparatus main body  100 , the error of the position of the developing roller  51  with respect to the photoconductor drum  41  may be increased by a combination of errors of positions of the drum unit  4  and the developing unit  5  in the apparatus main body  100 . 
     On the other hand, the image forming apparatus  10  has a structure to enhance the accuracy of the attachment position of the developing roller  51  with respect to the photoconductor drum  41 . 
     In addition, the image forming apparatus  10  includes a biasing mechanism  45  configured to elastically bias the developing unit  5  toward the photoconductor drum  41  such that the developing roller  51  is held at a position close to the photoconductor drum  41  (see  FIG. 7 ,  FIG. 11 ). In addition, the developing unit  5  includes gears  53  and  54  configured to transmit a rotational force from a drive portion provided in the apparatus main body  100  to the developing roller  51  (see  FIG. 12 ). In addition, a moment M 1  of a force applied to the developing unit  5  via the gears  53  and  54  may act as a force that positionally shifts the developing unit  5  against the biasing force of the biasing mechanism  45  (see  FIG. 12 ). The positional shift of the developing unit  5  has an adverse effect on the image quality. 
     The image forming apparatus  10  also has a structure to prevent the moment M 1  of the force applied to the developing unit  5  from acting as a force that positionally shifts the developing unit  5  against the biasing force of the biasing mechanism  45 . 
     In addition, the photoconductor drum  41  and the developing roller  51  are disposed close to each other. As a result, if the drum unit  4  and the developing unit  5  are removed by an erroneous procedure, the photoconductor drum  41  or the developing roller  51  may be damaged by coming in contact with a near member. 
     The image forming apparatus  10  also has a structure to prevent the drum unit  4  and the developing unit  5  from being removed by an erroneous procedure. The following describes structures of the drum unit  4  and the developing unit  5 . 
     The first unit housing  40  of the drum unit  4  forms an attachment space  400  in which the developing unit  5  is disposed (see  FIG. 5 ). The developing unit  5  is attached, in a detachable manner, to the first unit housing  40  of the drum unit  4  that has been attached to the apparatus main body  100 . 
     That is, the developing unit  5  is attached to the apparatus main body  100  by being attached to the first unit housing  40  of the drum unit  4  that has been attached to the apparatus main body  100 . In addition, the drum unit  4  can be removed from the apparatus main body  100  after the developing unit  5  is removed from the first unit housing  40  of the drum unit  4 . 
     As shown in  FIG. 2 ,  FIG. 4 , and  FIG. 12 , the drum unit  4  includes a first drum unit projection  401  that projects out from opposite sides of the drum unit  4  along an extension line of the rotation shaft  41   a  of the photoconductor drum  41 . Furthermore, the drum unit  4  includes a second drum unit projection  402  that projects out from the opposite sides of the drum unit  4  in parallel to the first drum unit projection  401 . 
     As shown in  FIG. 1  and  FIG. 8 , the apparatus main body  100  includes a first drum projection guide portion  103  and a second drum projection guide portion  104  that are provided on inner surfaces of a pair of side walls facing each other. The first drum projection guide portion  103  and the second drum projection guide portion  104  are provided as a structure for facilitating the attachment of the drum unit  4 . 
     The first drum projection guide portion  103  is a guide rail configured to guide the first drum unit projection  401  from a first drum introduction position P 11  to a first drum attachment position P 12  in the apparatus main body  100 . 
     The second drum projection guide portion  104  is a guide rail configured to guide the second drum unit projection  402  from a second drum introduction position P 21  to a second drum attachment position P 22  in the apparatus main body  100 . 
     The first drum introduction position P 11  and the second drum introduction position P 21  are located along the main opening  102  in the apparatus main body  100 . In addition, the first drum attachment position P 12  is located further away from the main opening  102  than the first drum introduction position P 11 . Similarly, the second drum attachment position P 22  is located further away from the main opening  102  than the second drum introduction position P 21 . 
     When the first drum unit projection  401  is located at the first drum attachment position P 12 , and the second drum unit projection  402  is located at the second drum attachment position P 22 , the drum unit  4  is in a state of being correctly attached to the apparatus main body  100 . 
     As shown in  FIG. 3 ,  FIG. 4 , and  FIG. 12 , the second unit housing  50  of the developing unit  5  includes a first developing unit projection  501  and a second developing unit projection  502 . The first developing unit projection  501  is formed to project out from opposite sides of the developing unit  5  along an extension line of the rotation shaft  51   a  of the developing roller  51 . The second developing unit projection  502  is formed to project out from the opposite sides in parallel to the first developing unit projection  501 . 
     As shown in  FIG. 1  and  FIG. 8 , the apparatus main body  100  includes a first developing projection guide portion  105  that is provided on inner surfaces of a pair of side walls facing each other. Furthermore, the first unit housing  40  of the drum unit  4  includes a second developing projection guide portion  405  that is formed on opposite side plates of the attachment space  400 . The first developing projection guide portion  105  and the second developing projection guide portion  405  are provided as a structure for facilitating the attachment of the developing unit  5 . 
     As shown in  FIG. 8  and  FIG. 10 , the first developing projection guide portion  105  includes a guide rail  105   a  configured to guide the first developing unit projection  501  from a developing unit introduction position P 31  to a relay position P 32  in the apparatus main body  100 . The developing unit introduction position P 31  is located along the main opening  102  in the apparatus main body  100 . The relay position P 32  is located closer to the photoconductor drum  41  than the developing unit introduction position P 31 . 
     Furthermore, the first developing projection guide portion  105  guides the second developing unit projection  502 . The first developing projection guide portion  105  guides both the first developing unit projection  501  and the second developing unit projection  502  and thereby stabilizes the attitude of the developing unit  5  during the detachment. 
     As shown in  FIG. 10 , the second developing projection guide portion  405  is disposed inside the attachment space  400  to face a downstream end portion  105   b  of the guide rail  105   a , and succeeding from the first developing projection guide portion  105 , guides the first developing unit projection  501  from the relay position P 32  to a developing unit attachment position P 33 . The developing unit attachment position P 33  is closer to the photoconductor drum  41  than the relay position P 32 . 
     The second developing projection guide portion  405  is formed in a recessed shape at the developing unit attachment position P 33  such that the first developing unit projection  501  is fitted to the second developing projection guide portion  405 . The first developing unit projection  501  is positioned by the second developing projection guide portion  405 . 
     In the present embodiment, the first developing unit projection  501  is guided by the second developing projection guide portion  405  of the drum unit  4  to the developing unit attachment position P 33 . This makes it possible for the developing roller  51  to be positioned with high accuracy with respect to the photoconductor drum  41  without being influenced by an error of the position of the developing unit  5  in the apparatus main body  100 . 
     The first drum unit projection  401  is formed to project further than the first developing unit projection  501  from the opposite sides, and be thinner than the first developing unit projection  501 . In other words, the first drum unit projection  401  is formed to project, from the opposite sides, to positions that are not reached by tips of the first developing unit projection  501 , and the first developing unit projection  501  is thicker than the first drum unit projection  401 . 
     In addition, a partial path of the first drum projection guide portion  103  overlaps with a partial path of the first developing projection guide portion  105  to form a guide path  103   a  (see  FIG. 8 ,  FIG. 9 ). 
     In the present embodiment, a partial path of the first drum projection guide portion  103  including the first drum introduction position P 11  overlaps with a partial path of the first developing projection guide portion  105  including the developing unit introduction position P 31 . 
     In addition, the first drum projection guide portion  103  forms, at outside the first developing projection guide portion  105 , a guide path that is narrower in width than the first developing projection guide portion  105 . Here, the outside is the opposite side to a region in which the photoconductor drum  41  and the developing roller  51  are disposed, in a direction along the rotation shaft  41   a  of the photoconductor drum  41  and the rotation shaft  51   a  of the developing roller  51 . 
     In the present embodiment, each of the first drum projection guide portion  103  and the first developing projection guide portion  105  is formed to be a groove (see  FIG. 9 ). The first drum projection guide portion  103  is a groove that is narrower in width and deeper than the first developing projection guide portion  105 . 
     As a result, the partial path of the first drum projection guide portion  103  overlapping with the first developing projection guide portion  105  is a groove that is narrow in width, deep, and formed in a groove of the first developing projection guide portion  105  (see  FIG. 9 ). 
     Furthermore, the first unit housing  40  of the drum unit  4  includes a projection support portion  406  that supports the second developing unit projection  502  (see  FIG. 12 ). 
     When the developing unit  5  is attached to the drum unit  4 , the first developing unit projection  501  is guided to the developing unit attachment position P 33  by the first drum projection guide portion  103  and the first developing projection guide portion  105 , and the second developing unit projection  502  is placed to the projection support portion  406 . With this, the developing unit  5  is attached to the drum unit  4 . 
     The photoconductor drum  41  and the developing roller  51  are disposed close to each other in the apparatus main body  100 . As a result, there may be a case where a partial path of the first drum projection guide portion  103  needs to be overlapped with a partial path of the first developing projection guide portion  105 . The present embodiment is applicable to such a case. 
     As shown in  FIG. 7  and  FIG. 11 , the drum unit  4  further includes the biasing mechanism  45 . The biasing mechanism  45  elastically biases the developing unit  5  in a predetermined biasing direction D 1 . The biasing direction D 1  is a direction in which the first developing unit projection  501  moves from the relay position P 32  to the developing unit attachment position P 33 . That is, the biasing mechanism  45  elastically biases the biasing mechanism  45  toward the photoconductor drum  41 . 
     It is noted that the developing unit introduction position P 31  is an example of a first start position, and the developing unit attachment position P 33  is an example of a first end position. In addition, the first drum introduction position P 11  is an example of a second start position, and the first drum attachment position P 12  is an example of a second end position. 
     As shown in  FIG. 12 , the developing unit  5  further includes a primary gear  53  and a secondary gear  54 . A coupling  53   a  is formed on a side of the primary gear  53 , and the apparatus main body  100  is provided with a drive portion that is engaged with the coupling  53   a . The primary gear  53  is a pinion gear to which a rotational force is transmitted from the drive portion via the coupling  53   a.    
     The secondary gear  54  is a pinion gear that is integrally formed with the rotation shaft  51   a  of the developing roller  51 . A rotational force is transmitted from the primary gear  53  to the secondary gear  54 . The secondary gear  54  is rotatably supported by the second unit housing  50 . 
     As shown in  FIG. 12 , in a state where the developing unit  5  has been attached to the drum unit  4 , the second developing unit projection  502  is on the opposite side to the first developing unit projection  501  with respect to the primary gear  53 . 
     When the primary gear  53  is rotationally driven, the moment M 1  of the force is applied from the primary gear  53  to the developing unit  5  via the secondary gear  54  (see  FIG. 12 ). 
     The second developing projection guide portion  405  includes a first support surface  405   a  that supports the first developing unit projection  501  against the moment M 1  of the force (see  FIG. 5 ,  FIG. 10 ,  FIG. 12 ). The first support surface  405   a  is parallel to the biasing direction D 1  of the biasing mechanism  45 . 
     In addition, the projection support portion  406  includes a second support surface  406   a  that supports the second developing unit projection  502  against the moment M 1  of the force (see  FIG. 12 ). As is the case with the first support surface  405   a,  the second support surface  406   a  is parallel to the biasing direction Dl. 
     Since the first support surface  405   a  and the second support surface  406   a  are parallel to the biasing direction D 1 , the moment M 1  of the force acts on the first support surface  405   a  and the second support surface  406   a  in a direction perpendicular to the biasing direction D 1 . 
     Accordingly, it is avoided that the moment M 1  of the force acts as a force that causes the developing unit  5  to positionally shift against the biasing force of the biasing mechanism  45 . As a result, the developing roller  51  is held with high positional accuracy with respect to the photoconductor drum  41 . 
     As shown in  FIG. 2  and  FIG. 5 , the first unit housing  40  of the drum unit  4  includes a first handle portion  404 . The first handle portion  404  is gripped by a hand of a worker when the drum unit  4  is attached to the apparatus main body  100 , or when the drum unit  4  is removed from the apparatus main body  100 . 
     The first handle portion  404  is configured to be gripped by a hand that accesses it through the attachment space  400 . In other words, when the attachment space  400  is closed, the first handle portion  404  cannot be gripped. 
     As shown in  FIG. 3  and  FIG. 4 , the second unit housing  50  of the developing unit  5  includes a second handle portion  503 . The second handle portion  503  is gripped by a hand of a worker when the developing unit  5  is attached to the drum unit  4 , or when the developing unit  5  is removed from the drum unit  4 . 
     As shown in  FIG. 4  and  FIG. 6 , by being attached to the drum unit  4 , the developing unit  5  closes a path including the attachment space  400  through which the first handle portion  404  is accessed by the hand. Accordingly, it is possible to avoid an erroneous operation of lifting the drum unit  4  before the developing unit  5  is removed from the drum unit  4 . 
     The structure of the first handle portion  404  prevents the photoconductor drum  41  or the developing roller  51  from being damaged due to lifting of the drum unit  4  before the separation of the developing roller  51  from the photoconductor drum  41 . 
     As shown in  FIG. 11 , the biasing mechanism  45  includes an abutting member  451  and a spring  452 . The abutting member  451  is supported in such a way as to be displaced between a predetermined reference position and an action position, wherein the action position is further away from the photoconductor drum  41  than the reference position. 
     In  FIG. 11 , the abutting member  451  located at the reference position is indicated by an imaginary line (a two-dot chain line), and the abutting member  451  located at the action position is indicated by a solid line. The biasing direction D 1  matches a direction in which the abutting member  451  moves from the action position to the reference position. 
     The abutting member  451  abuts on the developing unit  5  attached to the drum unit  4 , and thereby is displaced from the reference position to the action position. 
     The spring  452  elastically biases the abutting member  451  toward the photoconductor drum  41 . This allows the spring  452  to bias the developing unit  5  toward the photoconductor drum  41  via the abutting member  451 . The spring  452  is an example of an elastic member. It is noted that rubber may be adopted instead of the spring  452 . 
     On the other hand, the apparatus main body  100  includes a locking portion  106  that is configured to lock a locked portion  451   a  of the abutting member  451 . The locking portion  106  locks the abutting member  451  located at the action position, thereby restricting the drum unit  4  from moving in a direction of being removed from the apparatus main body  100 . 
     When the abutting member  451  is displaced from the action position to the reference position by the biasing force of the spring  452 , the locking of the abutting member  451  by the locking portion  106  is released. 
     The structure where the locking portion  106  locks the abutting member  451  prevents, in a more reliable manner, the photoconductor drum  41  or the developing roller  51  from being damaged due to lifting of the drum unit  4  before the separation of the developing roller  51  from the photoconductor drum  41 . 
     [Application Example] 
     Next, the following describes the drum unit  4  and the developing unit  5  according to an application example applicable to the image forming apparatus  10  with reference to  FIG. 13 . In the present application example, the drum unit  4  and the developing unit  5  include fitting portions  407  and  504  shown in  FIG. 13 . 
     Specifically, the first unit housing  40  of the drum unit  4  includes one or more fitting recessed portions  407  of a recessed shape, and the second unit housing  50  of the developing unit  5  includes one or more fitting projection portions  504  of a projecting shape. 
     In the example shown in  FIG. 13 , three fitting recessed portions  407  are formed in the first handle portion  404 . In addition, three fitting projection portions  504  are formed in the second unit housing  50  in correspondence with the three fitting recessed portions  407 . 
     The fitting projection portions  504  are configured to be fitted to the fitting recessed portions  407  only when the developing unit  5  is attached to the drum unit  4  in a predetermined normal direction. The fitting projection portions  504  prevent the developing unit  5  from being attached to the drum unit  4  in a direction other than the normal direction. 
     That is, when an attempt is made to attach the developing unit  5  to the drum unit  4  in a direction other than the normal direction, the fitting projection portions  504  are caught by any part of the drum unit  4 , and the developing unit  5  is not completely stored in the attachment space  400  of the drum unit  4 . 
     The fitting recessed portions  407  and the fitting projection portions  504  prevent the developing unit  5  from being attached to the drum unit  4  in an incomplete state. 
     It is noted that the second unit housing  50  of the developing unit  5  may include one or more fitting recessed portions  407 , and the first unit housing  40  of the drum unit  4  may include one or more fitting projection portions  504 . 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.