Abstract:
A developer cartridge includes a developer storage portion for retaining developer. The developer storage portion includes an opening portion. The developer cartridge further includes a shutter member for opening and closing the opening portion; and a first protrusion portion disposed on at least one of end portions of the developer storage portion in a longitudinal direction thereof. The first protrusion portion extends outwardly in the longitudinal direction.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
       [0001]    The present invention relates to a developer cartridge and an image forming apparatus. 
         [0002]    Conventionally, in an image forming apparatus such as a printer, a copier, a facsimile, a MFP (Multi-functional Product), and the likes, for example, in a printer using an electro-photographic process, a photosensitive drum, a charging roller, a developing roller, a cleaning device, and the like, are integrally formed in an image forming unit (process cartridge) to improve maintenance property. Further, the image forming unit is provided to be attachable to and detachable from a main body of the printer; that is, an apparatus main body. 
         [0003]    Specifically, in a color printer, a capacity of toner is limited due to a size of the printer. Further, it is required to store toner in a plurality of colors in a limited space. Accordingly, a toner cartridge is provided attachable to and detachable from a main body of an image forming unit while toner is contained in the toner cartridge. Further, the toner cartridge is replaced as toner is consumed. The toner cartridge is provided with an engagement portion at an end portion thereof in a longitudinal direction for engaging with the image forming unit main body, so that a position of the toner cartridge is determined with respect to the image forming unit main body. 
         [0004]    In the color printer, it is necessary to form an image with a high-definition without color shift. When an image with a high-definition without color shift is formed, it is necessary to provide parts relating to a printing operation with high dimension accuracy and assembly accuracy. Specifically, it is necessary to attach with high accuracy the image forming unit in which attachment and detachment operations are executed (refer to Patent Reference). Patent Reference Japanese Patent Publication No. 2004-170790 
         [0005]    In the conventional printer, the toner cartridge is positioned with respect to the image forming unit main body. Accordingly, a relative position of the toner cartridge and the image forming unit main body remains unchanged. However, when rotation bodies inside the image forming unit main body such as a photosensitive drum, a developing roller, or the like rotate during a formation of an image or a printing operation, the image forming unit main body may twist, thereby lowering image quality. 
         [0006]    In view of the problems described above, an object of the present invention is to provide an image forming unit and an image forming apparatus capable of solving the problems of the conventional printer. In the image forming unit and the image forming apparatus, it is possible to prevent a main body of an image forming unit from twisting while forming an image, thereby improving image quality. 
         [0007]    Further objects and advantages of the invention will be apparent from the following description of the invention. 
       SUMMARY OF THE INVENTION 
       [0008]    In order to attain the objects described above, according to the present invention, a developer cartridge includes a developer storage portion for retaining developer. The developer storage portion includes an opening portion. The developer cartridge further includes a shutter member for opening and closing the opening portion; and a first protrusion portion disposed on at least one of end portions of the developer storage portion in a longitudinal direction thereof. The first protrusion portion extends outwardly in the longitudinal direction. 
         [0009]    In the present invention, the developer cartridge includes the first protrusion portion disposed on at least one of the end portions of the developer storage portion in the longitudinal direction thereof. Further, the first protrusion portion extends outwardly in the longitudinal direction. Accordingly, when the toner cartridge is attached to an image forming unit, it is possible to prevent the image forming unit from twisting. As a result, it is possible to form images on a left side and a right side with little difference. Further, it is possible to prevent a load torque of the image forming unit from increasing, and to prevent a set dimension such as an overlay amount and a space amount from changing, thereby improving image quality. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an exploded perspective view showing an image forming unit according to a first embodiment of the present invention; 
           [0011]      FIG. 2  is a schematic view showing the printer according to the first embodiment of the present invention; 
           [0012]      FIG. 3  is a sectional view showing the image forming unit according to the first embodiment of the present invention; 
           [0013]      FIG. 4  is an exploded perspective view showing an image forming unit according to a comparative example; 
           [0014]      FIG. 5  is a view showing a left side surface portion of the image forming unit according to the comparative example; 
           [0015]      FIG. 6  is a view showing a right side surface portion of the image forming unit according to the comparative example; 
           [0016]      FIG. 7  is a view showing a lever in an unlocked state according to the comparative example; 
           [0017]      FIG. 8  is a view showing the lever in a locked state according to the comparative example; 
           [0018]      FIG. 9  is a perspective view No.  1  showing a main portion of a toner cartridge according to the first embodiment of the present invention; 
           [0019]      FIG. 10  is a perspective view No.  2  showing the main portion of the toner cartridge according to the first embodiment of the present invention; 
           [0020]      FIG. 11  is a perspective view No.  1  showing a main portion of the image forming unit main body according to the first embodiment of the present invention; 
           [0021]      FIG. 12  is a perspective view No.  2  showing the main portion of the image forming unit main body according to the first embodiment of the present invention; 
           [0022]      FIG. 13  is an exploded perspective view No.  1  showing a structure of a regulating groove member according to the first embodiment of the present invention; 
           [0023]      FIG. 14  is an exploded perspective view No.  2  showing the structure of the regulating groove member according to the first embodiment of the present invention; 
           [0024]      FIG. 15  is view showing a process of fixing the cover according to the first embodiment of the present invention; 
           [0025]      FIG. 16  is a view showing a modified example of the regulating protrusion according to the first embodiment of the present invention; 
           [0026]      FIG. 17  is a perspective view showing a main portion of the image forming unit according to the first embodiment of the present invention; 
           [0027]      FIG. 18  is a view No.  1  for explaining a mechanism of generating twisting according to the first embodiment of the present invention; 
           [0028]      FIG. 19  is a figure No.  2  for explaining the mechanism of generating twisting according to the first embodiment; 
           [0029]      FIG. 20  is a figure No.  3  for explaining the mechanism of generating twisting according to the first embodiment; 
           [0030]      FIG. 21  is a view showing an example No.  1  of a regulating groove member according to the first embodiment of the present invention; 
           [0031]      FIG. 22  is a view showing an example No.  2  of the regulating groove member according to the first embodiment of the present invention; 
           [0032]      FIG. 23  is a view showing an example No.  3  of the regulating groove member according to the first embodiment of the present invention; 
           [0033]      FIG. 24  is a left side view of the image forming unit according to the first embodiment of the present invention; 
           [0034]      FIG. 25  is a right side view of the image forming unit according to the first embodiment of the present invention; 
           [0035]      FIG. 26  is an exploded perspective view showing an image forming unit according to a second embodiment of the present invention; 
           [0036]      FIG. 27  is a perspective view No.  1  showing a main portion of a toner cartridge according to the second embodiment of the present invention; 
           [0037]      FIG. 28  is a perspective view No.  2  showing the main portion of the toner cartridge according to the second embodiment of the present invention; 
           [0038]      FIG. 29  is a perspective view No.  1  showing a main portion of an image forming unit main body according to the second embodiment of the present invention; 
           [0039]      FIG. 30  is a perspective view No.  2  showing the main portion of the image forming unit main body according to the second embodiment of the present invention; 
           [0040]      FIG. 31  is a view showing a fitting portion of a regulating protrusion and a regulating groove according to the second embodiment of the present invention; 
           [0041]      FIG. 32  is a view showing a modified example of the regulating protrusion according to the second embodiment of the present invention; 
           [0042]      FIG. 33  is a left side view of the image forming unit according to the second embodiment of the present invention; 
           [0043]      FIG. 34  is a right side view of the image forming unit according to the second embodiment of the present invention; 
           [0044]      FIG. 35  is an exploded perspective view No.  1  showing a configuration of a regulating groove according to the second embodiment of the present invention; 
           [0045]      FIG. 36  is an exploded perspective view No.  2  showing the configuration of the regulating groove according to the second embodiment of the present invention; 
           [0046]      FIG. 37  is a view showing an operation of a fitting portion of a regulating protrusion and the regulating groove according to the second embodiment of the present invention; 
           [0047]      FIG. 38  is an exploded perspective view of an image forming unit according to a third embodiment of the present invention; 
           [0048]      FIG. 39  is an exploded perspective view No.  1  showing a configuration of a regulating groove according to the third embodiment of the present invention; 
           [0049]      FIG. 40  is an exploded perspective view No.  2  showing the configuration of the regulating groove according to the third embodiment of the present invention; 
           [0050]      FIG. 41  is a perspective view No.  1  showing a main portion of a toner cartridge according to the third embodiment of the present invention; 
           [0051]      FIG. 42  is a perspective view No.  2  showing the main portion of the toner cartridge according to the third embodiment of the present invention; 
           [0052]      FIG. 43  is a perspective view No.  1  showing a main portion of an image forming unit main body according to the third embodiment of the present invention; 
           [0053]      FIG. 44  is a perspective view No.  2  showing the main portion of the image forming unit main body according to the third embodiment of the present invention; 
           [0054]      FIG. 45  is a perspective view of the image forming unit according to the third embodiment of the present invention; 
           [0055]      FIG. 46  is a side view of the image forming unit according to the third embodiment of the present invention; and 
           [0056]      FIG. 47  is a plan view of the image forming unit according to the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0057]    Hereunder, embodiments of the present invention will be explained with reference to the accompanying drawings. In the following description, a printer will be explained as an image forming apparatus. 
       First Embodiment 
       [0058]    A first embodiment of the present invention will be explained.  FIG. 2  is a schematic view showing a printer according to the first embodiment of the present invention. 
         [0059]    As shown in  FIG. 2 , a sheet supply cassette  11  is provided in a main body of the printer; that is, a bottom portion of the main body of the printer. The sheet supply cassette  11  is a media storage portion to accommodate a sheet (not shown) as a medium. A sheet feeding mechanism of the printer enables the sheet to be adjacent to a front edge of the sheet supply cassette  11 , so that each sheet is fed separately. The sheet feeding mechanism has sheet supply rollers  12   a  and  12   b  and a separation roller  13 . 
         [0060]    In the embodiment, the sheet fed through the sheet feeding mechanism is carried to a carrying roller portion  14  provided in an upper portion. Further, the sheet is carried to a carrying roller portion  15 . Then, the sheet is carried through a transfer belt  17  as the transfer belt  17  travels. The transfer belt  17  is a first transfer member and a carrying member. Further, the sheet is fed through between image forming units and transfer rollers; that is, between  16 Bk and  51 Bk,  16 Y and  51 Y,  16 M and  51 M, and  16 C and  51 C. 
         [0061]    In the embodiment, the image forming units  16 Bk,  16 Y,  16 M, and  16 C are a plurality of image forming portions for forming a toner image as a developer image in each of black, yellow, magenta and cyan, respectively. The transfer rollers  51 Bk,  51 Y,  51 M, and  51 C are second transfer members. The transfer unit comprises the transfer belt  17 , the transfer rollers  51 Bk,  51 Y,  51 M, and  51 C, and the likes. 
         [0062]    The transfer rollers  51 Bk,  51 Y,  51 M, and  51 C transfer and overlap a toner image in each color to the sheet to form a color toner image. Photosensitive drums  52 Bk,  52 Y,  52 M, and  52 C form the toner image in each color in the image forming units  16 Bk,  16 Y,  16 M, and  16 C, respectively. The photosensitive drums  52 Bk,  52 Y,  52 M, and  52 C function as image supporting members. 
         [0063]    Then, the sheet is carried to a fixing device  18  to fix the color toner image on the sheet and form a color image. After the sheet ejected from the fixing device  18  is carried with a carrying roller portion  19 , the sheet is ejected to outside of the apparatus main body with an ejection roller portion  20 . 
         [0064]    LED heads  21 Bk,  21 Y,  21 M, and  21 C are provided adjacent to the image forming units  16 Bk,  16 Y,  16 M, and  16 C to face the photosensitive drums  52 Bk,  52 Y,  52 M, and  52 C, respectively. Each of the LED heads  21 Bk,  21 Y,  21 M, and  21 C is an exposure device. The LED heads  21 Bk,  21 Y,  21 M, and  21 C expose surfaces of the photosensitive drums  52 Bk,  52 Y,  52 M, and  52 C, respectively, to form an electrostatic latent image. 
         [0065]    The image forming units  16 Bk,  16 Y,  16 M, and  16 C are provided to be attachable to and detachable from the apparatus main body. Accordingly, a main body cover  23  can be opened and closed on a top portion of the apparatus main body. The LED heads  21 Bk,  21 Y,  21 M, and  21 C are held with the main body cover  23 . 
         [0066]    The image forming units  16 Bk,  16 Y,  16 M, and  16 C will be explained next. The image forming units  16 Bk,  16 Y,  16 M, and  16 C have an identical configuration. Accordingly, only the image forming unit  16 Bk will be explained, and explanations of the image forming units  16 Y,  16 M, and  16 C are omitted. 
         [0067]      FIG. 3  is a sectional view showing the image forming unit according to the first embodiment of the present invention. 
         [0068]    The image forming unit  16 Bk is provided with the photosensitive drum  52 Bk; a charging roller  45 ; a developing roller  46 ; a toner supply roller  47 ; a developing blade  48 ; and a cleaning blade  49 . The charging roller  45  charges a surface of the photosensitive drum  52 Bk evenly. The developing roller  46  is a developer image supporting member to hold toner as a developer. The toner supply roller  47  is a developer supply member to supply toner to the developing roller  46 . The developing blade  48  is a developer regulating member to uniformly form a thin of toner on the developing roller  46 . The cleaning blade  49  is a cleaning device to remove toner remaining in the photosensitive drum  52 Bk after the transfer. 
         [0069]    The photosensitive drum  52 Bk comprises a conductive base layer made of aluminum or the like and a surface layer made of an organic photosensitive. The charging roller  45  is formed of a conductive metal shaft coated with a semi-conductive rubber such as epichlorohydrin rubber or the like in a roll shape. The developing roller  46  is formed of a conductive metal shaft coated with a semi-conductive rubber such as a silicone or the like. The toner supply roller  47  is formed of a conductive metal shaft coated with a rubber that is mixed with a foaming agent in order to improve a transportation property of toner. 
         [0070]    The charging roller  45 , the developing roller  46 , and the cleaning blade  49  are provided to contact with the photosensitive drum  52 Bk. Further, the toner supply roller  47  and the developing blade  48  are provided to contact with the developing roller  46 . Power sources (not shown) of the developing roller  46 , the toner supply roller  47 , and the developing blade  48  are connected to the developing roller  46 , the toner supply roller  47 , and the developing blade  48 , respectively. Accordingly, bias voltages are applied to the developing roller  46 , the toner supply roller  47  and the developing blade  48 , respectively. 
         [0071]    In the embodiment, a toner cartridge (not shown) is provided to be attachable to and detachable from a main body of the image forming unit  16 Bk; that is, an image forming unit main body. The toner cartridge is a developer container to accommodate toner. The image forming unit main body is provided with a housing  27 . The housing  27  is provided with side housings (not shown); a bottom housing  28  as a first case; a top housing  29  as a second case; and a cover  62  as a third case. 
         [0072]    The photosensitive drum  52 Bk and the charging roller  45  are supported freely rotatably through the side housings (not shown) of the bottom housing  28  on both ends in an axis direction. Further, the developing roller  46 , the toner supply roller  47 , and the developing blade  48  constitute a development device, and are supported through the side housings on both ends in the axis direction. 
         [0073]    In the embodiment, the LED head  21 Bk is provided to be adjacent to the image forming unit  16 Bk ( FIG. 2 ). An opening  30  for exposure is formed in the top housing  29 , so that light emitted from the LED head  21 Bk is irradiated a surface of the photosensitive drum  52 Bk in a downstream side of the charging roller  45  in a rotational direction (rotational direction when an image is formed) of the photosensitive drum  52 Bk and an upstream side of the developing roller  46 . 
         [0074]    In the printer with the configuration described above, the developing roller  46  and the toner supply roller  47  are rotated counterclockwise in  FIG. 3  through a driving motor (not shown) while printing. The driving motor is a driving portion for supplying the developer. The toner supply roller  47  supplies toner to the developing roller  46 . Further, toner supplied to the developing roller  46  is carried to a contact portion of the developing roller  46  and the developing blade  48  as the developing roller  46  rotates. The developing blade  48  scrapes off excess toner to be in a thin film, and the thin film is carried to the photosensitive drum  52 Bk as the developing roller  46  rotates. 
         [0075]    In the embodiment, the photosensitive drum  52 Bk is rotated in a specific direction (clockwise in  FIG. 3 ) through driving a drum monitor (not shown) that is a driving portion for forming an image. A surface of the photosensitive drum  52 Bk is charged evenly through the charging roller  45  as the photosensitive drum  52 Bk rotates, and is exposed through the LED head  21 Bk ( FIG. 2 ) to form an electrostatic latent image. Further, a toner image is formed through statically adhering toner on the developing roller  46  to the electrostatic latent image. 
         [0076]    A comparative example of the image forming unit  16 Bk will be explained next. 
         [0077]      FIG. 4  is an exploded perspective view showing the image forming unit according to the comparative example.  FIG. 5  is a view showing a left side surface portion of the image forming unit according to the comparative example.  FIG. 6  is a view showing a right side surface portion of the image forming unit according to the comparative example.  FIG. 7  is a view showing a lever in an unlocked state according to the comparative example.  FIG. 8  is a view showing the lever in a locked state according to the comparative example. 
         [0078]    As shown in  FIG. 4 , in the image forming unit  16 Bk, side housings  60  and  61  as a pair of supporting members are provided on both end portions (right end portion and left end portion with respect to a sheet transportation direction) of the image forming unit main body. The main members such as the photosensitive drum  52 Bk, the developing roller  46 , the toner supply roller  47 , and the likes are rotatable or fixed to be held at a specific position through the side housings  60  and  61  while securing a specific amount of nip. 
         [0079]    In the comparative example, the side housings  60  and  61  are provided with two pairs of protrusion portions  60   a  and  60   b , and  61   a  and  61   b , to determine positions thereof with respect to the apparatus main body through protruding toward outside of the image forming unit  16 Bk. Further, the cover  62  as a housing is provided between the side housings  60  and  61 . Moreover, the cover  62  is provided with an opening portion  62   c  to supply toner from a toner cartridge  26  to inside of the image forming unit main body. Further, walls of both ends of the cover  62  are provided with protrusion portions  62   a  and  62   b , respectively, to fix the toner cartridge  26  to the image forming unit main body. The protrusion portions  62   a  and  62   b  are integrally formed inwardly in the cover  62 . 
         [0080]    The toner cartridge  26  is provided with a discharge port (not shown), a housing  26   a , a lever  26   b , and a shutter (not shown), and the likes. The discharge port is provided for discharging toner. The housing  26   a  having a box shape and an open-end portion is provided for storing toner. The lever  26   b  is provided outside the toner cartridge  26 . The shutter is provided for opening and closing the discharge port, and is interlocked with the lever  26   b  to be rotated. Fitting portions  26   c  and  26   d  to fit with the protrusion portions  62   a  and  62   b  provided in the cover  62 , respectively, are provided on side surfaces of the toner cartridge  26 . 
         [0081]    As described above, the toner cartridge  26  is attached to the image forming unit main body in a state in which the protrusion portions  62   a  and  62   b  and the fitting portions  26   c  and  26   d  are fitted into each other, respectively. Further, as shown in  FIGS. 7 and 8 , the toner cartridge  26  is fixed to the image forming unit main body through rotating the lever  26   b.    
         [0082]    In the comparative example, two pairs of grooves  24   a  and  24   b , and  25   a  and  25   b  are provided in a pair of fixed walls  24  and  25  provided in the apparatus main body, respectively. The image forming unit  16 Bk can be attached to a specific position of the apparatus main body through fitting the protrusion portions  60   a ,  60   b ,  61   a , and  61   b  into the grooves  24   a ,  24   b ,  25   a , and  25   b.    
         [0083]    After the image forming unit  16 Bk is attached to the apparatus main body, the main body cover  23  ( FIG. 2 ) is closed. An urging member (not shown) is provided in the main body cover  23  for urging the image forming unit  16 B downwardly to prevent the image forming unit  16 Bk from being displaced while printing. Accordingly, the image forming unit  16 Bk fixed to the apparatus main body can receive a rotation transmitted from a motor (not shown) through a driving gear  31  on one end portion and carry out a printing operation. 
         [0084]    In the comparative example, a plurality of the rotation bodies (rollers) such as the photosensitive drum  52 Bk, the charging roller  45 , the developing roller  46 , the toner supply roller  47 , and the like is provided inside of the image forming unit  16 Bk. Each of rotary shafts of the rotation bodies is parallel to the other rotary shafts, and contacts with the other rotation bodies in one or two points. The both ends of each of the rotation bodies are supported through the side housings  60  and  61 . 
         [0085]    In the comparative example, the side housings  60  and  61  are connected through the bottom housing  28  ( FIG. 3 ) and the top housing  29  ( FIG. 3 ). Further, the rotation bodies are surrounded by the external housing  27  ( FIG. 3 ) that is formed of a plate member made of a resin. The bottom housing  28  and the top housing  29  have plate shapes to avoid the rotation bodies. Accordingly, the bottom housing  28  and the top housing  29  have small resistance against twisting. 
         [0086]    As a result, when the rotation bodies rotate during the printing operation, the image forming unit  16 Bk is twisted through a frictional resistance of the contact portions of the rotation bodies. Accordingly, images formed on a right side and a left side may become uneven. Further, a load torque of the image forming unit  16 Bk can be increased. In addition, a setup dimension of an overlay amount, a space amount, and the likes, can be varied. Accordingly, image quality will be deteriorated. 
         [0087]    To this end, a reinforcing rib may be formed inwardly on the bottom housing  28 , the top housing  29 , or an inner circumferential surface of the bottom housing  28  or the top housing  29 . In this case, the reinforcing rib and the rotation bodies contact each other. Further, the reinforcing rib may be formed outwardly. In this case, a size of the image forming unit  16 Bk becomes large. 
         [0088]    Further, a dimension variance at an engagement portion of the apparatus main body and the image forming unit  16 Bk can be made small to prevent the image forming unit  16 Bk from twisting. However, when the dimension difference at the engagement portion is made small, a protrusion of the image forming unit  16 Bk side can be caught on the apparatus main body side. Thus, the image forming unit  16 Bk cannot be set in a regular position with respect to the apparatus main body during up and down operation of the image forming unit  16 Bk when the image forming unit  16 Bk is attached to or detached from the apparatus main body. Accordingly, image quality will be deteriorated. 
         [0089]    In view of the problem of the comparative example, in the first embodiment, the image forming unit  16 Bk is fitted to the toner cartridge  26  through a specific fitting configuration, so that the image forming unit  16 Bk does not twist in a large extent. 
         [0090]      FIG. 1  is an exploded perspective view showing the image forming unit according to the first embodiment of the present invention.  FIG. 9  is a perspective view No.  1  showing a main portion of the toner cartridge according to the first embodiment of the present invention.  FIG. 10  is a perspective view No.  2  showing the main portion of the toner cartridge according to the first embodiment of the present invention. 
         [0091]    Further,  FIG. 11  is a perspective view No.  1  showing a main portion of the image forming unit main body according to the first embodiment of the present invention.  FIG. 12  is a perspective view No.  2  showing the main portion of the image forming unit main body according to the first embodiment of the present invention.  FIG. 13  is an exploded perspective view No.  1  showing a structure of a regulating groove member according to the first embodiment of the present invention.  FIG. 14  is an exploded perspective view No.  2  showing the structure of the regulating groove member according to the first embodiment of the present invention.  FIG. 15  is view showing a process of fixing the cover according to the first embodiment of the present invention.  FIG. 16  is a view showing a modified example of the regulating protrusion according to the first embodiment of the present invention. 
         [0092]    As shown in  FIGS. 1 and 3 , both ends of the external housing  27  ( FIG. 3 ) of the image forming unit  16 Bk are provided with the side housings  60  and  61 , respectively, as the supporting members. The side housings  60  and  61  support the rotation bodies to be freely rotatable. Further, the side housings  60  and  61  support the cleaning blade  49  and the like. In addition, the cover  62  is provided to surround parts held between the side housings  60  and  61 . 
         [0093]    The cover  62  is provided with a storage portion  62   f  to accommodate the toner cartridge  26 . Further, when the toner cartridge  26  is attached to an inner circumference surface of sidewalls m 1  and m 2 , fixed raised portions  62   d  and  62   e  are provided as a first engaging portion to fix the toner cartridge  26  to be integrated with the cover  62  to slope at a specific angle. The sidewalls m 1  and m 2  constitute both end portions of the cover  62  in an axis direction of the rotation bodies in the storage portion  62   f.    
         [0094]    In the embodiment, as shown in  FIGS. 13 and 14 , regulating groove members  60   c  and  61   c  are provided as first regulating elements near the fixed raised portions  62   d  and  62   e , respectively. The regulating groove members  60   c  and  61   c  penetrate through the cover  62 , and are integrated with the side housings  60  and  61 , respectively. Further, grooves  60   k  and  61   k  that are sloped at a specific angle are provided in the regulating groove members  60   c  and  61   c , respectively. Each of the grooves  60   k  and  61   k  comprises side surfaces j 1  and j 2  and a bottom surface j 3 . The side surfaces j 1  and j 2  constitute regulating surfaces. 
         [0095]    In the embodiment, the toner cartridge  26  comprises the housing  26   a  having a box shape with one open end portion and a case having a box shape provided with a cap  26   e  to close an opening portion of the housing  26   a . Further, the toner cartridge  26  accommodates toner therein to supply toner from a toner discharge port  26   i  provided in a center bottom portion of the housing  26   a  to the image forming unit main body. Further, a shutter (not shown) is provided for opening and closing the toner discharge port  26   i . The shutter opens and closes the toner discharge portion  26   i  through interlocking with the lever  26   b  provided on an external edge surface of the toner cartridge  26 . 
         [0096]    In the embodiment, as shown in  FIG. 15 , the cover  62  is positioned through a fitting of holes  62   g  and  62   h  and protrusion portions  60   d  and  61   d , respectively. The holes  62   g  and  62   h  are first engagement elements provided inside of the cover  62 , while the protrusion portions  60   d  and  61   d  having circular shapes are second engagement elements provided integrally with the side housings  60  and  61 . In the state, the cover  62  is fixed from above through screws  63   a  and  63   b  as fixing elements. 
         [0097]    In the embodiment, fixed portions  26   j  and  26   k  having recessed shapes are provided integrally with the lever  26   b  and the cap  26   e , respectively, on a side surface of the toner cartridge  26  upon attachment to the image forming unit  16 Bk. The fixed portions  26   j  and  26   k  are second engaging portions to engage with the fixed raised portions  62   d  and  62   e , respectively. 
         [0098]    In the embodiment, regulating protrusions  26   g  and  26   h  having columnar shapes are formed integrally with the cap  26   e  and the housing  26   a  near the fixed raised portions  62   d  and  62   e , respectively. The regulating protrusions  26   g  and  26   h  extend to protrude outwardly from an edge surface of the toner cartridge  26  to fit with the regulating groove members  60   c  and  61   c , respectively, upon attachment. Further, the regulating protrusions  26   g  and  26   h  are second regulating elements to regulate rotations of the side housings  60  and  61 , respectively. Outer diameters (widths) of the regulating protrusions  26   g  and  26   h  are set to be slightly smaller than widths of the grooves  60   k  and  61   k , respectively. 
         [0099]    In this case, it is preferred to limit sizes of certain parts so that a fitting is to be smooth and a manufacturing cost does not increase. For example, it is preferred that each of the grooves  60   k  and  61   k  has a width equal to or greater than 6.0 mm and equal to or less than 6.05 mm; each of the regulating protrusions  26   g  and  26   h  has an outer diameter equal to or greater than 5.93 mm and equal to or less than 5.98 mm. Further, it is preferred that a space equal to or greater than 0.02 mm and equal to or less than 0.12 mm is formed. 
         [0100]    When the space is less than 0.02 mm, it is difficult to smoothly attach and detach the toner cartridge  26  to and from the image forming unit. Specifically, when toner is adhered to the regulating protrusions  26   g  and  26   h , the regulating groove members  60   c  and  61   c , and the likes, it is difficult to attach and detach the toner cartridge  26  to and from the image forming unit main body. 
         [0101]    On the other hand, when the space is greater than 0.12 mm, the grooves  60   k  and  61   k  become loose with respect to the regulating groove members  60   c  are  61   c , respectively. Accordingly, it is difficult to prevent the image forming unit  16 Bk from twisting. 
         [0102]    In the embodiment, the regulating protrusions  26   g  and  26   h  are formed integrally with the housing  26   a  and cap  26   e , respectively, when the toner cartridge  26  is structured with relatively high rigidity. On the other hand, when the toner cartridge  26  is structured with relatively low rigidity, as shown in  FIG. 16 , a shaft  35  made of a metal having a circle section is provided to pierce side portions of the toner cartridge  26 . A length of the shaft  35  is to be the same as the distance from a protrusion edge surface of one end to that of the other end. Accordingly, portions p 1  and p 2  protruded from the side surfaces of the toner cartridge  26  can be used as the regulating protrusions on both ends. 
         [0103]    Next, a mechanism that twisting is generated in the image forming unit  16 Bk will be explained. 
         [0104]      FIG. 17  is a perspective view showing a main portion of the image forming unit according to the first embodiment of the present invention.  FIG. 18  is a view No.  1  for explaining a mechanism of generating twisting according to the first embodiment of the present invention.  FIG. 19  is a figure No.  2  for explaining the mechanism of generating twisting according to the first embodiment.  FIG. 20  is a figure No.  3  for explaining the mechanism of generating twisting according to the first embodiment. 
         [0105]    As shown in  FIG. 17 , the photosensitive drum  52 Bk, the developing roller  46 , and the toner supply roller  47  are provided between the side housings  60  and  61 . Accordingly, shaft supporting holes  60   f  and  61   f  are provided in the side housings  60  and  61 , respectively, to support the photosensitive drum  52 Bk. Further, bearings b 1  and b 3  are provided in the side housings  60  and  61 , respectively, to support the developing roller  46 , while bearings b 2  and b 4  are provided in the side housings  60  and  61 , respectively, to support the toner supply roller  47 . Still further, the side housings  60  and  61  support the photosensitive drum  52 Bk, the developing roller  46 , and the toner supply roller to be rotatable. 
         [0106]    In the embodiment, as shown in  FIG. 18 , gear rows are provided on one end portion (edge portion on right side with respect to a sheet transportation direction) of the image forming unit  16 Bk, so that the rotation bodies such as the photosensitive drum  52 Bk, the developing roller  46 , and the toner supply roller  47  rotate. Further, a driving gear  32  for the image forming unit  16 Bk is provided in the apparatus main body. As shown in  FIG. 19 , the driving gear  32  and a gear  33  of the gear rows are meshed. 
         [0107]    When a rotation is transmitted to the gear  33  through the driving gear  32 , the image forming unit  16 Bk starts to operate. As shown in  FIG. 19 , a drive load of the image forming unit  16 Bk itself is added to the gear  33  of the photosensitive drum  52 Bk in one end portion side of the image forming unit  16 Bk. Accordingly, when the photosensitive drum  52 Bk rotates in a counterclockwise direction, the image forming unit  16 Bk itself rotates in a direction indicated by an arrow A (counterclockwise direction). 
         [0108]    In the embodiment, the developing roller  46  and the toner supply roller  47  contact in the same direction (clockwise direction), and are rotated at different speeds on the other end portion side of the image forming unit  16 Bk. Accordingly, as shown in  FIG. 20 , due to the frictional resistance generated at the time, the image forming unit  16 Bk itself is to be rotated in a direction indicated by an arrow B (clockwise direction). As a result, the image forming unit  16 Bk is twisted. 
         [0109]    The twisting is generated around the rotary shaft of the photosensitive drum  52 Bk. Accordingly, it is effective to regulate the twisting through the regulating surfaces extending in a vertical direction with respect to the circumference direction around the rotary shaft of the photosensitive drum  52 B. All of the twisting forces is regulated. 
         [0110]    When an angle formed by the regulating surfaces with respect to a circumference direction is less than 90°, forces applied to the regulating surfaces are dispersed. Accordingly, a component parallel to the regulating surfaces is generated. As a result, positions of the side housings  60  and  61  or the regulating protrusions  26   g  and  26   h  are displaced. 
         [0111]    In the embodiment, the regulating groove members  60   c  and  61   c  are provided in the side housings  60  and  61 . The side housings  60  and  61  support the rotation bodies such as photosensitive drum  52 Bk, the developing roller  46 , and the toner supply roller  47  causing twisting. The regulating groove members  60   c  and  61   c  are engaged with the regulating protrusions  26   g  and  26   h  of the toner cartridge  26 , respectively. Forces applied to the side housings  60  and  61  are regulated to prevent the image forming unit  16 Bk from twisting. 
         [0112]    Next, an angle to be regulated through the regulating groove members  60   c  and  61   c ; that is, a groove angle as a regulating angle will be explained. 
         [0113]      FIG. 21  is a view showing an example No.  1  of a regulating groove member according to the first embodiment of the present invention.  FIG. 22  is a view showing an example No.  2  of the regulating groove member according to the first embodiment of the present invention.  FIG. 23  is a view showing an example No.  3  of the regulating groove member according to the first embodiment of the present invention. 
         [0114]    As shown in  FIG. 21 ,  26   h  denotes a regulating protrusion; sh 1  denotes the rotary shaft of the photosensitive drum  52 Bk; and  61   c , a  61   c ′ and a  61   c ″ denote regulating groove members. An angle formed by a line X 1  and the side surfaces j 1  and j 2  is a groove angle a. The line X 1  connects the rotary shaft sh 1  and the regulating protrusion  26   h . The side surfaces j 1  and j 2  sandwich the regulating protrusion  26   h  of the regulating groove members  61   c ,  61   c ′, and  61   c″.    
         [0115]    As shown in  FIG. 21 , when the side surfaces j 1  and j 2  of the groove  61   k  of the regulating groove member  61   c ′ are formed along a vertical direction, the groove angle a has a sharp angle. As shown in  FIG. 22 , when the side surfaces j 1  and j 2  of the groove  61   k  of the regulating groove member  61   c  are provided to be parallel to the line X 1 , the groove angle a becomes 0°. As shown in  FIG. 23 , when the side surfaces j 1  and j 2  of the groove  61   k  of the regulating groove member  61   c ″ are perpendicular to the line X 1 , the groove angle a becomes 90°. 
         [0116]    It is preferred that the groove angle a is a sharp angle. When the angle a becomes closer to 0°, it is possible to reduce the twisting more effectively. That is, the twisting of the image forming unit  16 Bk is generated due to a displacement caused by a rotation of the side housings  60  and  61  around the rotary shaft sh 1  of the photosensitive drum  52 Bk. Accordingly, it is most effective that the side surfaces j 1  and j 2  sandwich the regulating protrusion  26   h  from both sides in which the regulating protrusion  26   h  is provided to regulate, so that the regulating protrusion  26   h  does not move. The side surfaces j 1  and j 2  are provided in a direction perpendicular to a circumference direction on a circumference around the rotary shaft sh 1  of the photosensitive drum  52 Bk. 
         [0117]    When the groove angle a is 90°, the regulating surface becomes parallel to a moving direction of the regulating protrusion  26   h . Accordingly, the regulation does not work. 
         [0118]    In the embodiment, adjacent surfaces of the fixed raised portions  62   d  and  62   e  and the fixed portions  26   j  and  26   k , respectively, and the side surfaces j 1  and j 2  of the regulating groove member  61   c  are provided to be parallel to each other and in the same angle with respect to a vertical direction. Accordingly, the toner cartridge  26  can be attached to and detached from or fix to the image forming unit main body, and the image forming unit  16 Bk can be attached to and detached from or fixed to the apparatus main body. 
         [0119]    Next, an operation of the image forming unit  16 Bk of the configuration will be explained. 
         [0120]      FIG. 24  is a left side view of the image forming unit according to the first embodiment of the present invention.  FIG. 25  is a right side view of the image forming unit according to the first embodiment of the present invention. 
         [0121]    As shown in  FIG. 24 , when the toner cartridge  26  is attached to the image forming unit main body, the toner cartridge  26  is inserted into the cover  62 . Then, the regulating protrusions  26   g  and  26   h  of the toner cartridge  26  and the regulating groove members  60   c  and  61   c  are fitted into each other, respectively. When the lever  26   b  is rotated, the toner cartridge  26  can be fixed to the image forming unit main body. 
         [0122]    When the printing operation is executed in this state, as described above, the image forming unit  16 Bk attempts to twist. However, the regulating groove members  60   c  and  61   c  of the image forming unit main body contact the regulating protrusions  26   g  and  26   h , respectively. The regulating protrusions  26   g  and  26   h  are supported through the rigidity of the toner cartridge  26 . Accordingly, the twisting is prevented. 
         [0123]    As described above, in the embodiment, the toner cartridge  26  is provided with the regulating protrusions  26   g  and  26   h . Further, the regulating groove members  60   c  and  61   c  are provided in the image forming unit main body, so that the groove angle a becomes a sharp angle. Accordingly, the twisting of the image forming unit  16 Bk can be prevented. Further, the images formed on right side and a left side can be even. As a result, an increase of a load torque of the image forming unit  16 Bk and changes of the set dimensions of an overlay amount and a space amount are prevented. Accordingly, the image quality is improved. 
       Second Embodiment 
       [0124]    A second embodiment of the present invention will be explained next. Components in the second embodiment similar to those in the first embodiment are designated with the same reference numerals. The components in the second embodiment similar to those in the first embodiment provide the same effects. 
         [0125]      FIG. 26  is an exploded perspective view showing an image forming unit according to the second embodiment of the present invention.  FIG. 27  is a perspective view No.  1  showing a main portion of a toner cartridge according to the second embodiment of the present invention.  FIG. 28  is a perspective view No.  2  showing the main portion of the toner cartridge according to the second embodiment of the present invention. 
         [0126]    Further,  FIG. 29  is a perspective view No.  1  showing a main portion of an image forming unit main body according to the second embodiment of the present invention.  FIG. 30  is a perspective view No.  2  showing the main portion of the image forming unit main body according to the second embodiment of the present invention.  FIG. 31  is a view showing a fitting portion of a regulating protrusion and a regulating groove according to the second embodiment of the present invention.  FIG. 32  is a view showing a modified example of the regulating protrusion according to the second embodiment of the present invention. 
         [0127]    In the embodiment, fixed raised portions  62   i  and  62   j  are provided in a vertical direction inside of the sidewalls of the both end portions of the cover  62  in a storage portion  62   f  of the image forming unit  16 Bk. The fixed raised portions  62   i  and  62   j  are first engaging portions having the same shapes as those in the first embodiment. 
         [0128]    In the embodiment, the regulating groove members  60   e  and  61   e  are provided as first regulating elements near the fixed raised portions  62   i  and  62   j  piercing the cover  62  to be integrated with the side housings  60  and  61 , respectively. Further, the grooves  60   k  and  61   k  are provided in the regulating groove members  60   e  and  61   e , respectively. Each of the grooves  60   k  and  61   k  comprises the side surfaces j 1  and j 2  and the bottom surface j 3 . Further, the regulating surfaces comprise the side surfaces j 1  and j 2 . 
         [0129]    In the embodiment, in the side surfaces of the toner cartridge  26 , fixed portions  26   n  and  26   o  having recessed shapes are provided to be integrated with the lever  26   b  and the cap  26   e , respectively. The fixed portions  26   n  and  26   o  are second engagement portions to fit with the fixed raised portions  62   i  and  62   j  when attached to the image forming unit main body. 
         [0130]    Further, regulating protrusions  26   l  and  26   m  are provided to protrude from side surfaces of the toner cartridge  26  and to be integrated with the housing  26   a  and the cap  26   e , respectively, near the fixed portions  26   n  and  26   o . The regulating protrusions  26   l  and  26   m  are second regulating elements having rectangular column shapes in which vertical direction dimensions C are made larger than horizontal direction dimensions B ( FIG. 31 ). 
         [0131]    The horizontal direction dimensions B of the regulating protrusions  26   l  and  26   m  are to be slightly smaller than the widths of the grooves  60   k  and  61   k , respectively. Further, the vertical direction dimensions C of the  26   l  and  26   m  are to be slightly smaller than the depths of the grooves  60   k  and  61   k , respectively. 
         [0132]    In the embodiment, fitting portions comprise the regulating groove members  60   e  and  61   e  and the regulating protrusions  26   l  and  26   m , respectively. The regulating groove members  60   e  and  61   e  and the regulating protrusions  26   l  and  26   m  are fitted into each other. Accordingly, the side surfaces j 1  and j 2  of the grooves  60   k  and  61   k  of the regulating groove members  60   e  and  61   e  can regulate the side surfaces of the regulating protrusions  26   l  and  26   m  in a vertical direction, respectively. 
         [0133]    In the embodiment, certain parts are formed in limited sizes, so that the regulating protrusions  26   l  and  26   m  can fit into the regulating groove members  60   e  and  61   e  smoothly, and the manufacturing cost does not increase. More specifically, each of the regulating protrusions  26   l  and  26   m  has the horizontal direction dimension B equal to or greater than 4.93 mm and equal to or less than 4.98 mm; each of the grooves  60   k  and  61   k  has a width equal to or greater than 5.0 mm and equal to or less than 5.05 mm. Further, a space equal to or greater than 0.02 mm and equal to or less than 0.12 mm is provided. 
         [0134]    When the space is less than 0.02 mm, the toner cartridge  26  is difficult to smoothly attach to or detach from the image forming unit main body. Specifically, when toner is adhered to the regulating protrusions  26   l  and  26   m  or the regulating groove members  60   e  and  61   e , the toner cartridge  26  is difficult to attach to or detach from the image forming unit main body. 
         [0135]    On the other hand, when the space is greater than 0.12 mm, the regulating protrusions  26   l  and  26   m  become loose with respect to the regulating groove members  60   e  and  61   e , respectively. Accordingly, the twisting of the image forming unit  16 Bk is not effectively prevented. 
         [0136]    Further, a space is formed between each lower surface of the regulating protrusions  26   l  and  26   m  and each bottom surface j 3  of the regulating groove members  60   e  and  61   e . The dimension of the space is determined considering variations of the dimensions within general tolerance according to the manufacturing method of the side housings  60  and  61 , the toner cartridge  26 , and the likes. 
         [0137]    Normally, when a molded component has a dimension equal to or less than 10 mm, the general tolerance is to be plus or minus 0.2 mm. Accordingly, it is preferred that the space greater than 0.4 mm is formed, so that the regulating protrusions  26   l  and  26   m  and the regulating groove members  60   e  and  61   e , respectively, do not contact each other. 
         [0138]    In the embodiment, the regulating protrusions  26   l  and  26   m  do not need to be in rectangular columnar shapes, and may be in shapes having a plurality of the regulating portions. In this case, the regulating protrusions  26   l  and  26   m  have more than two regulating portions contacting with the side surfaces j 1  and j 2  of the grooves  60   k  or  61   k  on a point, line, surface, or the like over a distance longer than the horizontal direction dimension. For example, as shown in  FIG. 32 , the regulating portions h 2  and h 3  having circular shapes are swollen on top and bottom edges of a main body h 1  to provide the regulating protrusions. 
         [0139]    Further, in the embodiment, the regulating protrusions  26   l  and  26   m  and the grooves  60   k  and  61   k  are provided in an attachment and detachment direction of the toner cartridge  26  from the image forming unit main body or a vertical direction. The regulating protrusions  26   l  and  26   m  and the grooves  60   k  and  61   k  can be provided to be tilted by a specific angle, as far as the toner cartridge  26  can be attached to or detached form the image forming unit main body smoothly. 
         [0140]    Next, an operation of the image forming unit  16 Bk of the configuration will be explained. 
         [0141]      FIG. 33  is a left side view of the image forming unit according to the second embodiment of the present invention.  FIG. 34  is a right side view of the image forming unit according to the second embodiment of the present invention.  FIG. 35  is an exploded perspective view No.  1  showing a configuration of the regulating groove according to the second embodiment of the present invention.  FIG. 36  is an exploded perspective view No.  2  showing the configuration of the regulating groove according to the second embodiment of the present invention.  FIG. 37  is a view showing an operation of a fitting portion of the regulating protrusion and the regulating groove according to the second embodiment of the present invention. 
         [0142]    As shown in  FIG. 33 , when the toner cartridge  26  is attached to the image forming unit main body, the toner cartridge  26  is inserted into inside of the cover  62 . Then, the regulating protrusions  26   l  and  26   m  of the toner cartridge  26  are fitted into the regulating groove members  60   e  and  61   e  inside of the cover  62 , respectively. Further, when the lever  26   b  is rotated, the toner cartridge  26  can be fixed to the image forming unit main body. 
         [0143]    At this time, in the fitting portion, the side surfaces of the regulating protrusions  26   l  and  26   m  contact with the side surfaces j 1  and j 2  of the grooves  60   k  and  61   k , respectively. Accordingly, movements of the regulating protrusions  26   l  and  26   m  in a perpendicular direction with respect to the side surfaces j 1  and j 2  are regulated. In addition, rotations of the regulating protrusions  26   l  and  26   m  are also regulated. 
         [0144]    That is, as shown in  FIG. 37 , even when the side housing  60  tries to rotate in a direction indicated by an arrow, the side surfaces of the regulating protrusion  26   l  contact with the side surfaces j 1  of the groove  60   k  at points q 1  and q 2  separated by a distance L in a vertical direction. Accordingly, a rotation of the regulating protrusion  26   l  is regulated. When the distance L becomes larger, the twisting of the side housing  60  is regulated more effectively. A state of the contact changes in one to two points depending on the vertical direction dimension C and spaces between the regulating protrusions  26   l  and  26   m  and the grooves  60   k  and  61   k , respectively. 
         [0145]    When a printing operation is executed in this state, as described above, the image forming unit  16 Bk attempts to twist. However, the regulating groove members  60   e  and  61   e  of the image forming unit main body contact with the regulating protrusions  26   l  and  26   m , respectively. The regulating protrusions  26   l  and  26   m  are supported on the toner cartridge  26 . Accordingly, twisting is prevented. 
         [0146]    As described, in the embodiment, the regulating protrusion  26   l  and  26   m  are provided to protrude from the both side surfaces of the toner cartridge  26 . Further, the regulating groove members  60   e  and  61   e  are provided in the side housings  60  and  61 , respectively, inside of the image forming unit  16 Bk. Accordingly, the twisting of the image forming unit  16 Bk can be prevented. As a result, images formed on a right side and a left side can become even. Further, an increase of a load torque of the image forming unit  16 Bk and changes of the set dimensions of an overlay amount and a space amount are prevented. Accordingly, image quality is improved. 
         [0147]    Further, the two side surfaces of the regulating protrusions  26   l  and  26   m  contact with the side surfaces j 1  and j 2  of the grooves  60   k  and  61   k , respectively, at two points q 1  and q 2 . Accordingly, there are no differences in the regulating force due to angles (slopes) of the regulating protrusions  26   l  or  26   m  and the side surfaces j 1  and j 2 . That is, the angle can be determined freely. 
       Third Embodiment 
       [0148]    A third embodiment of the present invention will be explained next. Components in the third embodiment similar to those in the first and second embodiments are designated with the same reference numerals. The components in the third embodiment similar to those in the first and second embodiments provide the same effects. 
         [0149]      FIG. 38  is an exploded perspective view of an image forming unit according to the third embodiment of the present invention.  FIG. 39  is an exploded perspective view No.  1  showing a configuration of a regulating groove according to the third embodiment of the present invention.  FIG. 40  is an exploded perspective view No.  2  showing the configuration of the regulating groove according to the third embodiment of the present invention.  FIG. 41  is a perspective view No.  1  showing a main portion of a toner cartridge according to the third embodiment of the present invention.  FIG. 42  is a perspective view No.  2  showing the main portion of the toner cartridge according to the third embodiment of the present invention. 
         [0150]    Further,  FIG. 43  is a perspective view No.  1  showing a main portion of an image forming unit main body according to the third embodiment of the present invention.  FIG. 44  is a perspective view No.  2  showing the main portion of the image forming unit main body according to the third embodiment of the present invention. 
         [0151]    In the embodiment, in the storage portion  62   f  of the image forming unit  16 Bk, the fixed raised portions  62   i  and  62   j  are provided in a vertical direction inside of the sidewalls of the both end portions of the cover  62  in the same position as in the second embodiment. The fixed raised portions  62   i  and  62   j  are first engagement portions having the same shapes. 
         [0152]    As shown in  FIGS. 39 and 40 , regulating groove members  60   g  and  60   h  and regulating groove members  61   g  and  61   h  are provided integrally with the side housings  60  and  61  near the fixed raised portion  62   i  and  62   j , respectively. The regulating groove members  60   g ,  60   h ,  61   g , and  61   h  pierce the cover  62 . Further, the regulating groove members  60   g  and  60   h  and the regulating groove members  61   g  and  61   h  are two pairs of first regulating elements arranged in a horizontal direction sandwiching the fixed raised portions  62   i  and  62   j , respectively. 
         [0153]    In the embodiment, when the toner cartridge  26  is attached to the image forming unit main body, the fixed portions  26   n  and  26   o  having recessed shapes are integrally formed with the lever  26   b  and the cap  26   e , respectively, on the side surfaces of the toner cartridge  26 . The fixed portions  26   n  and  26   o  are second engaging portions to fit into the fixed raised portions  62   i  and  62   j , respectively. 
         [0154]    Further, regulating protrusions  26   p  and  26   q  and regulating protrusions  26   r  and  26   s  are integrally formed with the housing  26   a  and the cap  26   e  to protrude from the side surfaces of the toner cartridge  26  near the fixed portions  26   n  and  26   o . The regulating protrusions  26   p ,  26   q ,  26   r , and  26   s  having columnar shapes are second regulating elements. 
         [0155]    The regulating protrusions  26   p  and  26   r  extend from an end portion of the front side in a bottom edge of the side surface of the toner cartridge  26  downwardly in a vertical direction. Further, when the toner cartridge  26  is attached to the image forming unit main body, outer circumference surfaces of the regulating protrusions  26   p  and  26   r  are fitted into the grooves  60   k  and  61   k  of the regulating groove members  60   g  and  61   g , respectively. 
         [0156]    In the embodiment, the regulating protrusions  26   q  and  26   s  extend from an end portion of rear side in a bottom edge of the side surfaces of the toner cartridge  26  upwardly in a horizontal direction. Further, when the toner cartridge  26  is attached to the image forming unit main body, outer circumference surfaces of the regulating protrusions  26   q  and  26   s  are fitted into the grooves  60   k  and  61   k  of the regulating groove members  60   h  and  61   h , respectively. Each of the grooves  60   k  and  61   k  is provided with the side surfaces j 1  and j 2  and the bottom surface j 3 . 
         [0157]    In the embodiment, outer diameters of the regulating protrusions  26   p  and  26   r  are slightly smaller than widths of the grooves  60   k  and  61   k , respectively. Further, lengths of the regulating protrusions  26   p  and  26   r  in a vertical direction are made smaller enough than the groove depths of the grooves  60   k  and  61   k , respectively. 
         [0158]    Further, outer diameters of the regulating protrusions  26   q  and  26   s  are slightly smaller than widths of the grooves  60   k  and  61   k , respectively. Lengths of the regulating protrusions  26   q  and  26   s  in a horizontal direction are made long enough to cover the lengths of the grooves  60   k  and  61   k , respectively. 
         [0159]    In the embodiment, fitting portions comprise the regulating groove members  60   g ,  60   h ,  61   g , and  61   h  and the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s , respectively. Further, the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s  fit into the regulating groove members  60   g ,  60   h ,  61   g , and  61   h , respectively. Accordingly, the side surfaces of the regulating protrusions  26   p  and  26   q  and the regulating protrusions  26   r  and  26   s  contact the side surfaces j 1  and j 2  of the grooves  60   k  and  61   k , respectively, to regulate. 
         [0160]    In the embodiment, dimensions of the outer diameters and the spaces are determined, so that the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s  can smoothly fit into the regulating groove members  60   g ,  60   h ,  61   g , and  61   h , respectively, and the manufacturing cost will not be high. 
         [0161]    More specifically, each of the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s  has an outer diameter equal to or greater than 5.93 mm and equal to or less than 5.98 mm. Further, each of the grooves  60   k  and  61   k  has a width equal to or greater than 6.0 mm and equal to or less than 6.05 mm. Further, a space equal to or greater than 0.02 mm and equal to or less than 0.12 mm is provided. 
         [0162]    When the space is less than 0.02 mm, the toner cartridge  26  is difficult to smoothly attach to and detach from the image forming unit main body. More specifically, when toner is adhered to the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s , or the regulating groove members  60   g ,  60   h ,  61   g , and  61   h , the toner cartridge  26  is difficult to attach to or detach from the image forming unit main body. 
         [0163]    On the other hand, when the space is greater than 0.12 mm, the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s  become loose with respect to the regulating groove members  60   g ,  60   h ,  61   g , and  61   h , respectively. Accordingly, it is difficult to prevent the twisting of the image forming unit  16 Bk. 
         [0164]    Next, an operation of the image forming unit  16 Bk of the configuration will be explained. 
         [0165]      FIG. 45  is a perspective view of the image forming unit according to the third embodiment of the present invention.  FIG. 46  is a side view of the image forming unit according to the third embodiment of the present invention.  FIG. 47  is a plan view of the image forming unit according to the third embodiment of the present invention. 
         [0166]    When the toner cartridge  26  is attached to the image forming unit main body, as shown in  FIG. 45 , the toner cartridge  26  is inserted inside of the cover  62 . Next, the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s  of the toner cartridge  26  are fitted into the regulating groove members  60   g ,  60   h ,  61   g , and  61   h , respectively, inside of the cover  62 . When the lever  26   b  is rotated, the toner cartridge  26  can be fixed to the image forming unit main body. 
         [0167]    In the embodiment, in the fitting portions of the regulating protrusions  26   p  and  26   r  and the regulating groove members  60   g  and  61   g , the side surfaces of the regulating protrusions  26   p  and  26   r  contact the side surfaces j 1  and j 2  of the grooves  60   k  and  61   k , respectively. Accordingly, the regulating protrusions  26   p  and  26   r  are regulated not to move in a direction perpendicular to the side the surfaces j 1  and j 2 . Further, rotations of the regulating protrusions  26   p  and  26   r  are regulated. 
         [0168]    In the fitting portions of the regulating protrusions  26   p  and  26   r  and the regulating groove members  60   g  and  61   g , axes of the regulating protrusions  26   p  and  26   r  are regulated not to incline in a direction perpendicular to a rotary shaft of the photosensitive drum  52 Bk (direction indicated by an arrow D) or displace. However, the axes of the regulating protrusions  26   p  and  26   r  do not regulate not to incline in a direction parallel to the rotary shaft of the photosensitive drum  52 Bk (direction indicated by an arrow E), displace, or rotate around the axes of the regulating protrusions  26   p  and  26   r  (rotate to a direction indicated by an arrow F), respectively. Further, the regulating protrusions  26   p  and  26   r  regulate the side housings  60  and  61  to rotate around the rotary shaft of the photosensitive drum  52 Bk, respectively. 
         [0169]    On the other hand, in the fitting portions of the regulating protrusions  26   q  and  26   s  and the regulating groove members  60   h  and  61   h , the axes of the regulating protrusions  26   q  and  26   s  are regulated not to incline or rotate inside of the surface in a horizontal direction parallel to the rotary shaft of the photosensitive drum  52 Bk (rotate to a direction indicated by an arrow G). 
         [0170]    The regulating protrusions  26   q  and  26   s  regulate a rotation of the side housings  60  and  61  around the rotary shaft of the photosensitive drum  52 Bk, respectively. However, angles of the grooves  60   k  and  61   k  with respect to the rotation direction of the photosensitive drum  52 Bk are large. Accordingly, the regulating force becomes small. 
         [0171]    In the embodiment, the regulating protrusions  26   p  and  26   r  and the grooves  60   k  and  61   k  are provided in a direction in which the toner cartridge  26  is attached to or detached from the image forming unit main body or a vertical direction. Alternatively, the regulating protrusions  26   p  and  26   r  and the grooves  60   k  and  61   k  may be provided to be tilted at a specific angle, as far as the toner cartridge  26  can be smoothly attached to or detached form the image forming unit main body. 
         [0172]    As described, in the embodiment, the regulating protrusions  26   p ,  26   q ,  26   r , and  26   s  are provided to protrude from both side surfaces of the toner cartridge  26 . Further, the regulating groove members  60   g  and  61   h  and the regulating groove members  60   g  and  61   h  are provided in the side housings  60  and  61  inside of the image forming unit  16 Bk, respectively. Accordingly, twisting of the image forming unit  16 Bk can be prevented. Thus, images formed on a left side and a right side become even. Accordingly, an increase of a load torque of the image forming unit  16 Bk and changes of the set dimensions of an overlay amount and a space amount are prevented. Accordingly, image quality will be improved. 
         [0173]    In the embodiments described above, an example applied to the printer as an image forming apparatus was explained. 
         [0174]    The present invention can be applied to a copier, a facsimile, MFP, or the likes, in which an image forming unit is attachable to or detachable from an apparatus main body and a toner cartridge is attachable to or detachable from the image forming unit main body. 
         [0175]    The present invention is not limited to the embodiments. Variations are possible within a scope of the present invention. The variations are not to be excluded from the present invention. 
         [0176]    The disclosure of Japanese Patent Application No. 2007-053125, filed on Mar. 2, 2007 is incorporated in the application by reference. 
         [0177]    While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.