Patent Publication Number: US-8126352-B2

Title: Image forming apparatus and developer cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-085287, filed on Mar. 28, 2007, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an image forming apparatus such as a laser printer, and a developer cartridge mountable therein. 
     BACKGROUND 
     A process unit including a drum cartridge and developer cartridges is provided to an image forming apparatus such as a laser printer. In the drum cartridge, photosensitive drums are held. In the developer cartridges, toners are housed, and developing rollers to supply the toners to the photosensitive drums are held. In order for the developer cartridge to be replaceable with a new cartridge when toner in a developer cartridge runs out, the developer cartridge is removably mounted on the drum cartridge. 
     Among such types of image forming apparatuses, there is an image forming apparatus in which developing rollers are made capable of being pressed against and spaced from photosensitive drums (for example, see JP-A-2003-84647). In this image forming apparatus, during image formation, in order to satisfactorily transfer the toners to the photosensitive drums from the developing rollers, developer cartridges are pressed to make the developing rollers contact the photosensitive drums in a pressed state. On the other hand, during non-image formation, in order to prevent deformation and the like in the developing rollers by continuously pressing the same areas of the developing rollers by the photosensitive drums in non-rotating state, the developing rollers are spaced from the photosensitive drums. 
     Further, there is an image forming apparatus in which a memory is mounted on a cartridge removably mounted on the apparatus body, and information on history of image forming operations is recorded in the memory (for example, see JP-A-2001-215862). 
     However, in accordance with an image forming apparatus having a structure in which developing rollers are capable of being pressed against and spaced from photosensitive drums, the developer cartridge is moved in accordance with a pressing and spacing operation thereof. Therefore, when a memory is mounted on a developer cartridge, it is impossible to secure a connection between a terminal attached to the memory and terminals provided to the apparatus body, which makes it impossible to satisfactorily perform read/write of information to the memory. 
     SUMMARY 
     An object of one aspect of the present invention is to provide an image forming apparatus capable of satisfactorily carrying out read/write of information with respect to a memory element provided to the developing device in a structure in which a developing device is provided to be movable in order to make a developer carrier contact and be spaced with respect to an image carrier. 
     Further, an object of another aspect of the present invention is to provide a developer cartridge capable of satisfactorily carrying out read/write of information with respect to a memory element disposed in the case in a structure in which a case is provided to be movable in an image forming apparatus body in order to make a developer carrier contact and be spaced with respect to an image carrier. 
     According to a first aspect of the invention, there is provided an image forming apparatus comprising: an image carrier; a developing device configured to hold a developer carrier to supply developer to the image carrier, the developing device movable to a contacting position where the developer carrier contacts the image carrier and to a spaced position where the developer carrier is spaced from the image carrier; and a memory element disposed in the developing device, wherein the developing device comprises: a pressing force input portion configured to receive pressing force to make the developer carrier contact the image carrier; and a spacing force input portion configured to receive spacing force to make the developing device move from the contacting position to the spaced position, and wherein at least one of the pressing force input portion and the spacing force input portion comprises a terminal electrically connected to the memory element. 
     According to a second aspect of the invention, there is provided a developer cartridge removably mountable to an image forming apparatus having an image carrier, the developer cartridge comprising: a developer carrier configured to supply developer to the image carrier; a case that holds the developer carrier; a memory element disposed in the case; a pressing force input portion configured to receive pressing force to make the developer carrier contact the image carrier; and a spacing force input portion configured to receive spacing force to make the developer carrier be spaced from the image carrier, wherein at least one of the pressing force input portion and the spacing force input portion comprises a terminal electrically connected to the memory element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional side view showing one embodiment of a color laser printer as an example of an image forming apparatus of the present invention; 
         FIG. 2  is a perspective view of a drum unit shown in  FIG. 1  and a developer cartridge in the process of being attached/detached with respect to the drum unit, which are viewed from the left front side thereof; 
         FIG. 3  is a perspective view of the developer cartridge shown in  FIG. 2 , which is viewed from the left front side thereof; 
         FIG. 4  is a plan view of the developer cartridge shown in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of a handle supporting part shown in  FIG. 2 ; 
         FIG. 6  is a perspective view of a body casing and the drum unit shown in  FIG. 1 , which are viewed from above the right front thereof, and  FIG. 6  shows a state in which outer covering plates and a front cover of the body casing are detached, and the drum unit is mounted into the body casing; 
         FIG. 7  is a perspective view of the drum unit, right and left rails and spacing and pressing mechanisms shown in  FIG. 6 , which are viewed from above the right front thereof; 
         FIG. 8  is a perspective view of the rails and the spacing and pressing mechanisms shown in  FIG. 7 , which are viewed from above the right front thereof; 
         FIG. 9  is a perspective view of translation cam members, intermediate members, and a synchronous movement mechanism shown in  FIG. 8 , which are viewed from above the right front thereof; 
         FIGS. 10A to 10E  are perspective views for explanation of actions of the translation cam member and the intermediate members shown in  FIG. 9 ; 
         FIG. 11  is a right side view of the translation cam member and the intermediate members in a state of  FIG. 10A ; 
         FIG. 12  is a right side view of the translation cam member and the intermediate members in a state of  FIG. 10C ; 
         FIG. 13  is a right side view of the translation cam member and the intermediate members in a state of  FIG. 10E ; and 
         FIG. 14  is a perspective view showing another embodiment of the developer cartridge (an embodiment having plate spring-shaped members). 
     
    
    
     DESCRIPTION 
     1. Overall Configuration of Color Laser Printer 
       FIG. 1  is a sectional side view showing one embodiment of a color laser printer as an example of an image forming apparatus of the present invention. 
     This color laser printer  1  is a transverse-mounted tandem type color laser printer in which a plurality of photosensitive drums  27  are disposed in parallel in a horizontal direction. 
     The color laser printer  1  includes a sheet feeding unit  4  to feed a sheet  3 , an image forming unit  5  to form an image on the sheet  3  fed, and a sheet discharging unit  6  to discharge the sheet  3  on which the image has been formed, in a body casing  2 . 
     (1) Body Casing 
     The body casing  2  is formed in a box shape whose side view is a substantially rectangular shape and defines therein a drum housing space  7  in which a drum unit  24  described later is housed. 
     An opening  8  communicated with the drum housing space  7  is formed at one side surface of the body casing  2 . Further, a front cover  9  to open and close the opening  8  is provided at the side surface at which the opening  8  is formed. This front cover  9  is made to fall over to the side of the body casing  2  to open the opening  8 , and is made to stand up along the one side surface of the body casing  2  to close the opening  8 . In a state in which the opening  8  is open, the drum unit  24  can be mounted to and removed from the drum housing space  7  via the opening  8 . 
     In addition, in the following descriptions, the side at which the front cover  9  is provided (on the right side in  FIG. 1 ) is defined as a front side (front face side), and the opposite side (on the left side in  FIG. 1 ) is defined as a rear side (back face side). Further, the view from the front side of the color laser printer  1  is defined as a standard for the right and left. With respect to the drum unit  24 , unless there is a particular reference thereto, it will be described with a direction in a state in which the drum unit  24  is mounted in the body casing  2  as a standard. 
     (2) Sheet Feeding Unit 
     The sheet feeding unit  4  includes a sheet feeding tray  10  removably mounted on the bottom inside the body casing  2 . A feed roller  11  is disposed above the front end of the sheet feeding tray  10 . Further, the sheet feeding unit  4  includes a substantially U-shaped sheet feeding path  12  formed between the upper side of the front end of the sheet feeding tray  10  and a conveyor belt  41  described later. A separation roller  13 , a separation pad  14 , a pinch roller  15 , a paper powder removing roller  16 , and a pair of registration rollers  17  are allocated on the sheet feeding path  12 . 
     The sheets  3  stuck at the sheet feeding tray  10  are sent out one by one to the sheet feeding path  12  by rotation of the feed roller  11 . Each sheet  3  sent out is picked up between the separation roller  13  and the separation pad  14 . Then, the sheet  3  passes through between the pinch roller  15  and the paper powder removing roller  16 , and paper powder is removed by the paper powder removing roller  16 . Thereafter, the sheet  3  is conveyed to the registration rollers  17 . The registration rollers  17  send out the sheet  3  onto the conveyor belt  41  (described later) after registration. 
     (3) Image Forming Unit 
     The image forming unit  5  includes a scanner unit  20 , a process unit  21 , a transfer unit  22 , and a fixing unit  23 . 
     (3-1) Scanner Unit 
     The scanner unit  20  is disposed at the upper portion of the body casing  2 . This scanner unit  20  includes optical members such as a laser, a mirror, a lens, and the like, and emits four laser beams at the four photosensitive drums  27  described later. As shown by the broken lines in  FIG. 1 , the surfaces of the photosensitive drums  27  are irradiated with the respective laser beams. 
     (3-2) Process Unit 
     The process unit  21  is disposed below the scanner unit  20  and above the sheet feeding unit  4 . The process unit  21  includes the drum unit  24 , and four developer cartridges  25  corresponding to the respective colors of black, yellow, magenta, and cyan. 
     The drum unit  24  is inserted from the opening  8  and provided to be slidable in a horizontal direction. This drum unit  24  includes four drum sub-units  26  corresponding to the respective colors. 
     The respective drum sub-units  26  are respectively disposed in parallel at intervals in an anteroposterior direction. That is, a black drum sub-unit  26 K, a yellow drum sub-unit  26 Y, a magenta drum sub-unit  26 M, and a cyan drum sub-unit  26 C are respectively disposed at intervals in this order from the front side to the rear side. 
     The respective drum sub-units  26  have the photosensitive drums  27 , scorotron type electrifiers  28 , and cleaning brushes  29 . 
     The photosensitive drums  27  as an example of image carriers are disposed in a longitudinal direction, and are provided to be rotatable centering on those central axis lines. 
     The scorotron type electrifiers  28  are disposed to face the photosensitive drums  27  with a distance therebetween at the obliquely upward rear side of the photosensitive drums  27 . 
     The cleaning brushes  29  are disposed so as to face to contact the photosensitive drums  27  at the back of the photosensitive drums  27 . 
     The developer cartridges  25  as an example of a developing device are provided to correspond to the drum sub-units  26  of the respective colors as shown in  FIG. 1 . That is, a black developer cartridge  25 K is provided to correspond to the black drum sub-unit  26 K, a yellow developer cartridge  25 Y is provided to correspond to the yellow drum sub-unit  26 Y, a magenta developer cartridge  25 M is provided to correspond to the magenta drum sub-unit  26 M, and a cyan developer cartridge  25 C is provided to correspond to the cyan drum sub-unit  26 C. 
     Each of the respective developer cartridges  25  includes an agitator  31 , a supply roller  32 , a developing roller  33 , and a layer thickness regulating blade  34  in the case  30 . 
     The case  30  is formed in a box shape having opening portion  35  at the lower end. The inside of the case  30  is partitioned into toner housing chamber  37  at the upper side and development chamber  38  at the lower side by a partition wall  36 . 
     The toner housing chamber  37  and the development chamber  38  are communicated with one another so as to be capable of supplying toner from the toner housing chamber  37  to the development chamber  38 . 
     Toner of the color corresponding to the respective developer cartridge  25  is housed in the toner housing chamber  37 . Positive charged polymerized toner including one nonmagnetic component in which respective coloring agent of yellow, magenta, cyan, and black is mixed so as to correspond to the respective color is used as toner of the respective color. 
     The agitator  31  is disposed in the toner housing chamber  37  and provided so as to be rotatable around an axis line extending in a longitudinal direction. 
     The supply roller  32  is disposed in the vicinities of the partition wall  36  in the development chamber  38 . 
     The supply roller  32  as an example of developer carrier is disposed at the obliquely downward lower side of the supply roller  32  in the development chamber  38 . A portion of the circumferential surface of the developing roller  33  is exposed from the opening portion  35  of the case  30 . 
     The supply roller  32  and the developing roller  33  is provided so as to be rotatable around an axis line extending in a longitudinal direction. Further, the supply roller  32  and the developing roller  33  are pressed to contact each other with their circumferential surface. 
     The layer thickness regulating blade  34  is disposed in the development chamber  38 . The layer thickness regulating blade  34  is structured such that a rubber member is provided to one end of a plate spring-shaped member made of metal, and the other end of the plate spring-shaped member is fixed to the case  30 , and the rubber member is provided so as to press the developing roller  33  from above. 
     In the developer cartridge  25 , the toner housed in the toner housing chamber  37  is discharged to the development chamber  38  while being agitated by the agitator  31 . The toner discharged to the development chamber  38  is supplied to the supply roller  32 . The toner supplied to the supply roller  32  is supplied to the developing roller  33  by rotation of the supply roller  32 . At this time, the toner is frictionally electrified to have straight polarity between the supply roller  32  and the developing roller  33  to which developing bias is applied. Then, excess toner is scratched off from the developing roller  33  by the layer thickness regulating blade  34  in accordance with rotation of the developing roller  33 , and thin layers of toner with a constant thickness is carried on the developing roller  33 . 
     On the other hand, in the drum sub-unit  26  corresponding to the respective developer cartridge  25 , the surface of the photosensitive drum  27  is positively charged uniformly by corona discharge of the scorotron type electrifier  28 . Then, the surface of the photosensitive drum  27  having been positively charged is irradiated with laser beams from the scanner unit  20 , which forms an electrostatic latent image corresponding to an image to be formed on the sheet  3 . 
     When the electrostatic latent image formed on the surface of the photosensitive drum  27  is made to face the developing roller  33  by rotation of the photosensitive drum  27 , the positively-charged toner carried on the surface of the developing roller  33  is supplied to the electrostatic latent image (i.e., a portion, which is exposed to the laser beams to lower their electric potential, of the surface of the photosensitive drum  27  positively-charged uniformly). In accordance therewith, the electrostatic latent image is made to be a visible image, and a toner image is carried on the surface of the photosensitive drum  27 . 
     (3-3) Transfer Unit 
     The transfer unit  22  is disposed above the sheet feeding unit  4  and under the process unit  21  in the body casing  2 . This transfer unit  22  includes a driving roller  39 , a driven roller  40 , the conveyor belt  41 , and transfer rollers  42 . 
     The driving roller  39  and the driven roller  40  are disposed to face one another with a distance in an anteroposterior direction. The conveyor belt  41  is made of an endless belt, and is wound around between the driving roller  39  and the driven roller  40 . 
     When the driving roller  39  is rotated, the conveyor belt  41  revolves to move so as to rotate in a direction opposite to the photosensitive drums  27  at transfer positions facing to contact the respective photosensitive drums  27  between the driving roller  39  and the driven roller  40 . 
     The transfer rollers  42  are respectively provided so as to face the respective photosensitive drums  27  with the conveyor belts  41  therebetween in the conveyor belt  41  wound around between the driving roller  39  and the driven roller  40 . The respective transfer rollers  42  are provided so as to rotate by being driven in a direction the same as the direction of revolving movement of the conveyor belt  41  at the transfer positions facing to contact the conveyor belt  41 . 
     The sheet  3  fed from the sheet feeding unit  4  is conveyed from the front side toward the rear side by the conveyor belt  41 , and passes through sequentially the transfer positions corresponding to the respective photosensitive drums  27 . Then, when the sheet  3  passes through the respective transfer positions, the toner images carried on the photosensitive drums  27  are transferred onto the sheet  3  by working of transfer biases applied to the transfer rollers  42 . In accordance therewith, a color image is formed on the sheet  3 . 
     In addition, transfer residual toners remaining on the photosensitive drums  27  after the transfer are recovered by the developing rollers  33 . Further, paper powder from the sheet  3  adhered to the photosensitive drums  27  after the transfer is recovered by the cleaning brushes  29 . 
     (3-4) Fixing Unit 
     The fixing unit  23  is disposed behind the transfer unit  22 , and includes a heating roller  43  and a pressing roller  44  to press the heating roller  43 . 
     In the fixing unit  23 , the color image transferred to the sheet  3  is heat-fixed onto the sheet  3  by being heated and pressed while the sheet  3  passes through between the heating roller  43  and the pressing roller  44 . 
     (4) Sheet Discharging Unit 
     The sheet discharging unit  6  includes a substantially C-shaped sheet discharging path  45  which is open frontward. On this sheet discharging path  45 , a conveyor roller  46 , a pinch roller  47 , and a pair of discharge rollers  48  are allocated. The sheet  3  conveyed from the fixing unit  23  is conveyed along the sheet discharging path  45  by the conveyor roller  46  and the pinch roller  47 , and is discharged onto a sheet discharging tray  49  formed at the superior surface of the body casing  2  by the discharge rollers  48 . 
     2. Drum Unit 
       FIG. 2  is a perspective view of the drum unit  24  and the developer cartridge  25  in the process of being mounted and removed with respect to the drum unit  24 , which are viewed from the left front side thereof. 
     The drum unit  24  includes a front beam  101  disposed at the front side of the four drum sub-units  26 , a rear beam  102  disposed at the rear side of the four drum sub-units  26 , and a pair of side plates  103  sandwiching the four drum sub-units  26 , the front beam  101 , and the rear beam  102  from the both sides in a longitudinal direction. 
     (1) Drum Sub-Unit 
     The drum sub-unit  26  has a pair of side frames  104  disposed to face one another with a distance in a longitudinal direction, and a center frame  105  provided to bridge in a longitudinal direction over the both side frames  104 . 
     The respective side frames  104  are formed of resin material into flat plate shapes. 
     Guide slots  106  to guide the mounting and removal of the developer cartridge  25  with respect to the drum sub-unit  26  are formed to the respective side frames  104 . The guide slots  106  are formed in a substantially vertical direction from the top edges at the rear sides of the side frames  104  up to the vicinities of the bottoms at the front sides of the side frames  104 . Collar members  208  (described later) are slidably received into the guide slots  106 . 
     The scorotron type electrifier  28  and the cleaning brush  29  (see  FIG. 1 ) are held at the center frame  105 . 
     (2) Front Beam 
     The front beam  101  is formed of a resin material. 
     This front beam  101  includes a near side gripper  107  attached to the central part in a longitudinal direction, and a supporting shaft  108  supporting the near side gripper  107 . 
     The near side gripper  107  is formed into a shape whose front view is a substantially U-shape. The respective free ends of the near side gripper  107  are supported rotatably by the supporting shaft  108 . In accordance therewith, it is possible to swing the near side gripper  107  to a housed position at which the near side gripper  107  stands up along the front beam  101 , and to an operative position at which the near side gripper  107  is made to fall over to the front side of the front beam  101 . 
     The supporting shaft  108  is disposed so as to run through the front beam  101  in a longitudinal direction, and is supported by the front beam  101 . The both ends of the supporting shaft  108  run through the side plates  103  to project outward. 
     (3) Rear Beam 
     The rear beam  102  is formed of a resin material. 
     A back side gripper  109  is integrally formed at the central part in a longitudinal direction with the rear beam  102 . 
     The back side gripper  109  is formed into a shape whose back view is a substantially U-shape, which projects upward from the rear beam  102 . 
     (4) Side Plates 
     The respective side plates  103  are formed of steel plates. The respective side plates  103  are formed into shapes whose side views are substantially elongate rectangular plate shapes, which extend in an anteroposterior direction. Then, with respect to the respective side plates  103 , the front ends thereof are fixed to the front beam  101 , and the rear ends thereof are fixed to the rear beam  102 . The respective side plates  103  hold the four drum sub-units  26  so as to sandwich those from the both sides. 
     The upper ends of the respective side plates  103  are bent outward into L-shapes on cross sections. In accordance therewith, flange portions  110  extending outward over the anteroposterior direction are formed at the upper ends of the respective side plates  103 . 
     Further, the rear ends of the respective side plates  103  are formed into shapes whose upper ends extend backward and whose side views are substantially L-shapes. Then, two roller members  111  are provided rotatably to the portions extending backward therefrom. The two roller members  111  are disposed to place a spacer  112  therebetween in an anteroposterior direction. The roller member  111  at the front side is disposed under the flange portion  110 . The roller member  111  at the rear side is disposed behind the rear end of the flange portion  110 . 
     3. Developer Cartridge 
       FIG. 3  is a perspective view of the developer cartridge  25  viewed from the left front side thereof. Further,  FIG. 4  is a plan view of the developer cartridge  25 . In addition, in  FIG. 4 , the grip member is in a fallen over state. 
     (1) Developer Cartridge 
     The case  30  of the developer cartridge  25  integrally has a pair of side walls  201  facing one another in a longitudinal direction, an upper wall  202  provided to bridge between the top edges of the both side walls  201 , a front wall  202  provided to bridge between the front edges of the both side walls  201 , and a rear wall  204  provided to bridge between the rear edges of the both side walls  201  (see  FIG. 4 ). The opening portion  35  (see  FIG. 1 ) to expose the developing roller  33  is formed by the bottom edges of the side walls  201 , the front wall  203 , and the rear wall  204 . 
     A gear cover  205  is attached to the side wall  201  on the left side. A cylindrical gear disposing portion  206  is formed to project on the gear cover  205 . In the gear disposing portion  206 , a passive gear  207  to which a coupling shaft (not shown) provided in the body casing  2  is coupled is disposed in the gear disposing portion  206 . The agitator  31 , the supply roller  32 , and the developing roller  33  are made to rotate by driving force inputted to the passive gear  207  from the coupling shaft. 
     The shaft of the developing roller  33  runs through the gear cover  205  to project under the gear disposing portion  206 , and the collar member  208  is attached to the leading end of the shaft. Further, the shaft of the developing roller  33  runs through the side wall  201  on the right side to project, and the collar member  208  (see  FIG. 4 ) is attached to the leading end thereof as well. Substantially cylindrical spacing protrusions  209  projecting outward from the connecting portions with the upper end of the rear wall  204  are formed at the upper ends of the both side walls  201 . The spacing protrusions  209  as an example of spacing force input portions are formed of conductive material. 
     A handle  210  gripped at the time of moving the developer cartridge  25  is provided to the upper wall  202 . The handle  210  as an example of a grip member is formed in a laminar shape long in a longitudinal direction, and is provided to be capable of being swung to a standing state in which the handle  210  stands up to be substantially perpendicular to the upper wall  202 , and to a fallen over state in which the handle  210  is made to fall over to the front side from the standing state to approach the upper wall  202 . 
     Handle supporting portions  211  whose side views are substantially semicircular shapes, which project upward are integrally formed with the both ends of the rear end of the upper wall  202 . As shown in  FIG. 3 , through holes  212  running through in a longitudinal direction are formed in the handle supporting portions  211  as an example of the shaft insertion portions. On the other hand, notch parts  213  into which the handle supporting portions  211  can be fitted are formed at the both ends of the rear end of the handle  210 . Elastically deformable portions  214  whose plane views are substantially L-shapes, and in which the base ends are coupled to their left sides, are provided to the respective notch parts  213 . With respect to the elastically deformable portions  214 , free ends thereof face the right side surfaces of the notch parts  213  with a distance in a longitudinal direction, and the handle supporting portions  211  are fitted into between the free ends of the elastically deformable portions  214  and the right side surfaces of the notch parts  213 . That is, each deformable portion  214  has one portion (an example of a fixed portion) fixed to the handle  210  at the notch part  213  and another portion (an example of a free portion) unfixed to the handle  210 . Then, supporting shafts  215  (see  FIG. 3 ) as an example of shafts are respectively provided to project in a direction coming close to one another at the free ends of the elastically deformable portions  214  and the right side surfaces of the notch parts  213 . The supporting shafts  215  are formed of conductive material. In a state in which an interval between the supporting shafts  215  is broadened by deforming the elastically deformable portions  214 , the handle supporting portions  211  are fitted into the respective notch parts  213 . Thereafter, the deformation of the elastically deformable portions  214  is cancelled, and the respective supporting shafts  215  are inserted into the through holes  212  of the handle supporting portions  211 , and therefore, the handle  210  is attached to the handle supporting portions  211  so as to be capable of being swung. The elastically deformable portion  214  and/or the supporting shaft  215  serves as an example of a second connecting portion. 
       FIG. 5  is a cross-sectional view of the handle supporting portion  211 . 
     As shown in  FIG. 5 , a ring-shaped member  216  formed of a conductive shrinkable material is fitted to the inside of the through hole  212  of the handle supporting portion  211 . The ring-shaped member  216  is formed of, for example, polyurethane rubber into which carbon black particles are added, silicon rubber, or the like. The handle supporting portion  211  and/or the ring-shaped member  216  serves as an example of a first connecting portion. 
     The supporting shaft  215  is inserted into the ring-shaped member  216 . The radial of the supporting shaft  215  is formed to be smaller than an internal diameter R 1  of the ring-shaped member  216 , and gaps are formed between the circumferential surface of the supporting shaft  215  and the internal circumferential surface of the ring-shaped member  216 . A plurality of protrusions  217  are formed integrally with the supporting shaft  215  on the circumferential surface of the supporting shaft  215 . A height of each protrusion  217  (a volume of protrusion) is designed such that a length R 2  from the center of the supporting shaft  215  to a tip of each protrusion  217  is made greater than the internal diameter R 1  of the ring-shaped member  216 . In accordance therewith, the respective protrusions  217  contact the internal circumferential surface of the ring-shaped member  216 , and the supporting shaft  215  is supported rotatably with low resistance by the ring-shaped member  216 , and is provided to be capable of having electrical continuity with the ring-shaped member  216 . 
     As shown in  FIG. 3 , spring guide members  218  are formed at the both ends of the front end of the upper wall  202 . The respective spring guide members  218  face the respective handle supporting portions  211  with a distance in an anteroposterior direction. Elastically contacting members  219  as an example of elastic members, which are capable of elastically moving forward and backward in a vertical direction are provided in the respective spring guide members  218 . 
     Concave portions  220  capable of receiving the corresponding elastically contacting members  219  are formed at positions corresponding to the elastically contacting members  219  on the bottom surface of the handle  210  (a plane opposite to the upper wall  202 ). In a state in which the handle  210  is made to fall over into a fallen over state, the respective elastically contacting members  219  are received in the respective concave portions  220 , and the leading ends of the respective elastically contacting members  219  contact the bottom surfaces of the respective concave portions  220  (the bottom of the handle  210 ). 
     Further, a grip hole  221  whose plane view is a substantially rectangular shape, which is long in a longitudinal direction, is formed at the central part in a longitudinal direction. In accordance therewith, it is possible to grip the handle  210  by inserting fingers into the grip hole  221 . 
     Moreover, pressing protrusions  222  as an example of pressing force input portions, whose side views are substantially cylindrical shapes, are provided at the both ends of the front end of the handle  210 . The respective pressing protrusions  222  are formed of conductive material. The respective pressing protrusions  222  are formed to have lengths such that the apical surfaces are located on the plane including the apical surfaces of the spacing protrusions  209  projecting to the same side. Further, the respective pressing protrusions  222  are disposed at positions lower than the spacing protrusions  209  in a state in which the developer cartridge  25  is mounted in the drum sub-unit  26 , and the handle  210  is made to fall over in a fallen over state. 
     A memory chip  223  as an example of a memory element is attached to the front wall  203  as shown in  FIG. 3 . One ends of two wirings  224  are connected to the memory chip  223 . The respective wirings  224  extend toward the handle supporting portions  211 , and as shown in  FIG. 5 , the other ends thereof are connected to the ring-shaped members  216 . Further, at the respective sides, the spacing protrusions  209  and the ring-shaped members  216  are electrically connected to one another via wirings  225  as shown in  FIG. 4 . Moreover, at the respective sides, the pressing protrusions  222  and the supporting shafts  215  are electrically connected to one another via wirings  226 . 
     In accordance therewith, the memory chip  223  and the respective spacing protrusions  209  are electrically connected to one another via the wirings  224 , the ring-shaped members  216 , and the wirings  225 , and the respective spacing protrusions  209  serve as terminals for reading/writing information with respect to the memory chip  223 . Further, the memory chip  223  and the respective pressing protrusions  222  are electrically connected to one another via the wirings  224 , the ring-shaped members  216 , the supporting shafts  215 , and the wirings  226 , and the respective pressing protrusions  222  as well serve as terminals for reading/writing information with respect to the memory chip  223 . 
     As information written into the memory chip  223 , a number of operations of image formation (a number of sheets to be printed) executed by use of the developer cartridge  25 , an ID code unique to the developer cartridge  25 , and the like can be exemplified. 
     In the present embodiment, the spacing protrusions  209 , the supporting shafts  215 , and the pressing protrusions  222  are formed of polyacetal or the like. 
     (2) Mounting and Removal of Developer Cartridge with Respect to Drum Unit 
     With respect to the developer cartridge  25  corresponding to each color, the handle  210  is gripped by inserting fingers into the grip hole  221  of the handle  210 , and as shown in  FIG. 2 , the developer cartridge  25  is mounted to the drum sub-unit  26  corresponding to the developer cartridge  25  from above the drum unit  24 . 
     In greater detail, the collar members  208  at the both ends in an axial direction of the developing roller  33  of the developer cartridge  25  are inserted into the guide slots  106  of the respective side frames  104  of the corresponding drum sub-unit  26 , and the developer cartridge  25  is pushed downward along the guide slots  106  into the drum sub-unit  26 . When the developing roller  33  contacts the photosensitive drum  27 , it is restricted from pushing the developer cartridge  25  thereto. Then, the developer cartridge  25  is made to fall over in a direction in which the upper end thereof leans against the center frame  105  at the front side centering on the shaft of the developing roller  33  due to its own weight of the developer cartridge  25 , and the front wall  203  of the case  30  contacts the center frame  105  to be supported. In accordance therewith, the developer cartridge  25  is positioned with respect to the drum sub-unit  26 , and the mounting of the developer cartridge  25  into the drum sub-unit  26  is achieved. 
     In this way, after the developer cartridge  25  is mounted, when the handle  210  in a standing state is released from a hand, the handle  210  is made to fall over from a standing state to a fallen over state with the supporting shafts  215  as fulcrums due to its own weight. 
     On the other hand, provided that, in a state in which the developer cartridge  25  is mounted into the drum unit  24  (drum sub-unit  26 ), the handle  210  is gripped, and the handle  210  is pulled up to a standing state from a fallen over state, and is lifted up, it is possible to remove the developer cartridge  25  from the drum unit  24 . 
     4. Rail and Spacing and Pressing Mechanism 
       FIG. 6  is a perspective view of the body casing  2  and the drum unit  24  which are viewed from above the right front thereof.  FIG. 6  shows a state in which the outer covering plate and the front cover  9  of the body casing  2  are detached, and the drum unit  24  is mounted into the body casing  2 . 
     The body casing  2  includes a pair of body frames  301  disposed to face one another in a longitudinal direction with the drum unit  24  therebetween. In the inner surfaces of the respective body frames  301 , there are provided: rails  302  to guide the mounting and removal of the drum unit  24 ; and spacing and pressing mechanisms  303  to space and press the developing rollers  33  of the developer cartridge  25  mounted into the drum unit  24 , with respect to the photosensitive drum  27 . 
       FIG. 7  is a perspective view of the drum unit  24 , the right and left rails  302 , and the spacing and pressing mechanisms  303 , which are viewed from above the right front thereof. Further,  FIG. 8  is a perspective view of the right and left rails  302  and the spacing and pressing mechanisms  303  which are viewed from above the right front thereof. 
     (1) Rails 
     The right and left rails  302  are disposed to face one another in a longitudinal direction with the drum unit  24  therebetween. The respective rails  302  integrally have rail fixing parts  304  disposed to face one another at the front end faces of the body frames  301 , rail main body parts  305  extending in an anteroposterior direction (horizontal direction) along the inner surfaces of the body frames  301 , and joining parts  306  which join the rail fixing parts  304  and the rail main body parts  305 . 
     The rail fixing parts  304  are fixed to the front end faces of the body frames  301  with screws  307 . 
     The rail main body parts  305  are formed into substantially L-shapes on cross sections whose lower ends are bent to the inner sides (the right side in a case of the left rail main body part  305 , and the left side in a case of the right rail main body part  305 ), and the flange portions  110  of the respective side plates  103  of the drum unit  24  are placed on the portions thereof extending horizontally in a state in which the drum unit  24  is mounted into the body casing  2 . 
     Roller supporting shafts  308  are supported so as to run through the joining parts  306  in a longitudinal direction. Rail rollers  309  supported rotatably by the roller supporting shafts  308  are disposed on the planes of the respective joining parts  306  facing one another. The uppermost end portions of the circumferential surfaces of the rail rollers  309  are located above the lower end portions (portions extending horizontally) of the rail main body parts  305 . 
     (2) Mounting of Drum Unit into Body Casing 
     In order to mount the drum unit  24  into the body casing  2 , first, the drum unit  24  is lifted up by gripping respectively the near side gripper  107  and the back side gripper  109  (see  FIG. 2 ) of the drum unit  24  with both hands. Then, referring to  FIG. 1 , the opening  8  is opened by making the front cover  9  fall over, and the drum unit  24  is made to go into the drum housing space  7  from the opening  8 . 
     At this time, the respective roller members  111  provided to the rear ends of the drum unit  24  are moved to roll on the rail main body parts  305  of the rails  302 . Further, the back gripper  109  is released from a hand, the both flange portions  110  of the drum unit  24  are respectively placed on the right and left rail rollers  309 . When the drum unit  24  is pushed backward in this state, the respective roller members  111  move to roll on the rail main body parts  305 , and the flange portions  110  slide on the respective rail rollers  309 , which makes the drum unit  24  move smoothly. Further, the spacing protrusions  209  and the pressing protrusions  222  of the respective developer cartridges  25  slide on a cum housing portion  323  of a holder fixing portion  322  described later. 
     Then, when the respective roller members  111  drop out of the rails  302  to the back side, and the flange portions  110  drop out of the respective rail rollers  309  to the back side of the respective rail rollers  309 , and the respective flange portions  110  are placed on the portions of the rail main body parts  305  extending horizontally, the pressing protrusions  222  and the spacing protrusions  209  of the respective developer cartridges  25  are respectively received in pressing protrusion receiving parts  325  and spacing protrusion receiving parts  326  described later, which completes the mounting of the drum unit  24  into the body casing  2 . 
     Thereafter, the front cover  9  is closed by releasing the hand from the near side gripper  107 , and the opening  8  is closed with the front cover  9 . When the front cover  9  is closed, the near side gripper  107  turns from a standing state to the housed position with the supporting shafts  108  as fulcrums so as to interlock thereto. 
     (3) Spacing and Pressing Mechanism 
     As shown in  FIG. 8 , the spacing and pressing mechanism  303  includes a pair of translation cam members  310 , cam holders  312  to hold the respective translation cam members  310  so as to rectilinearly move those in an anteroposterior direction, and a synchronous movement mechanism  313  to rectilinearly move the pair of translation cam members  310  so as to synchronize those. 
       FIG. 9  is a perspective view of the translation cam members  310  and the synchronous movement mechanism  313  which are viewed from above the right front thereof. That is, in  FIG. 9 , a perspective view in which illustrations of the cam holders  312  are omitted, and the spacing and pressing mechanism  303  is viewed from above the right front thereof, is shown. Further,  FIGS. 10A to 10E  are perspective views for explanation of actions of the translation cam members  310 . Moreover,  FIG. 11  is a right side view of the translation cam member  310  in a state of  FIG. 1A ,  FIG. 12  is aright side view of the translation cam member  310  in a state of  FIG. 10C , and  FIG. 13  is a right side view of the translation cam member  310  in a state of  FIG. 10E . 
     With respect to the translation cam member  310 , respective members (described hereinafter) are formed of conductive materials. The translation cam member  310  includes a laminar cam body plate  314  extending in an anteroposterior direction along the inner surface of the body frame  301  (see  FIG. 6 ), four operational members  315  provided to the inner surface of the cam body plate  314  (planes facing one another of the cam body plates  314  of the respective translation cam member  310 ), and intermediate members  311  disposed behind the respective operational members  315 . 
     Four rectangular holes  316  in substantially rectangular shapes which are long in an anteroposterior direction are formed at regular intervals in an anteroposterior direction at the cam body plate  314 . 
     The four operational members  315  are disposed at the respective front sides of the four rectangular holes  316 . The respective operational members  315  integrally include pressing force application portions  317  which are formed in shapes whose side views are crank shapes, and extend along the upper edge of the cam body plate  314 , and which are to press the pressing protrusions  222  of the developer cartridges  25  downward, contacting/spacing force application portions  318  which extend along the bottom edge of the cam body plate  314 , and which are to make the intermediate members  311  turn as will be described later, and joining parts  319  which join the rear ends of the pressing force application portions  317  and the front ends of the contacting/spacing force application portions  318 . 
     As shown in  FIG. 11  to  FIG. 13 , projected protruding portions  320  projecting upward are formed at the rear ends of the contacting/spacing force application portions  318 . 
     Further, the most anterior operational member  315  has a shape different from those of the other three operational members  315  (hereinafter called “the three posterior operational members  315 ”). That is, the pressing force application portion  317  of the most anterior operational member  315  is formed longer in its length in an anteroposterior direction as compared with those of the pressing force application portions  317  of the three posterior operational members  315 . Further, the contacting/spacing force application portion  318  of the most anterior operational member  315  is formed shorter in its length in an anteroposterior direction as compared with those of the contacting/spacing force application portions  318  of the three posterior operational members  315 . Due to such differences in shapes (sizes), as will be described later, it is possible to make the developing rollers  33  of all the developer cartridges  25  press the photosensitive drums  27 , to make only the developing roller  33  of the black developer cartridge  25 K press the photosensitive drum  27 , or to make the developing rollers  33  of all the developer cartridges  25  be spaced from the photosensitive drums  27 . 
     The respective intermediate members  311  face the respective rectangular holes  316  in a longitudinal direction. As shown in  FIG. 11  to  FIG. 13 , the respective intermediate members  311  are formed in shapes whose side views are substantially L-shapes, and are formed in block shapes having thicknesses in a longitudinal direction. Intermediate member supporting shafts  321  run through one ends of the respective intermediate members  311  in a longitudinal direction, and the intermediate members  311  are supported rotatably by the intermediate member supporting shafts  321 . In a state in which the respective intermediate members  311  are not contacted with the contacting/spacing force application portions  318  (see FIG.  11 ), the lower ends thereof face the protruding portions  320  of the contacting/spacing force application portions  318  with a distance in an anteroposterior direction. 
     As shown in  FIG. 7 , the intermediate member supporting shafts  321  are disposed at regular intervals (intervals equal to intervals among the respective spacing protrusions  209  in a state in which the four developer cartridges  25  are mounted into the drum unit  24 ) to each other in an anteroposterior direction. The respective intermediate member supporting shafts  321  extend in the longitudinal direction of the cam body plates  314  due to the intermediate members  311  supported thereby being inserted into the rectangular holes  316  which the intermediate members face, and one ends thereof are supported to be unable to rotate on the cam holder  312 . 
     As shown in  FIG. 8 , the cam holder  312  integrally has the laminar holder fixing part  322  extending in an anteroposterior direction along the inner surface of the body frame  301 , and a cam housing portion  323  continuing at the bottom edge of the holder fixing part  322 . 
     The holder fixing part  322  is fixed to the inner surface of the body frame  301  with screws  324 . The cam housing portion  323  is formed in a substantially sideways-square U-shape on cross section which extends from the entire length of the bottom edge of the holder fixing part  322  to a direction of being separated away from the inner surface of the body frame  301 , and is bent downward, and is further bent to a direction of approaching the inner surface of the body frame  301 . In the cam housing portion  323 , the pressing protrusion receiving parts  325  capable of receiving the pressing protrusions  222  of the developer cartridge  25  and the spacing protrusion receiving parts  326  capable of receiving the spacing protrusions  209  of the developer cartridge  25  are alternately formed four each thereof by sequentially notching the cam housing portion  323  from the upper surface to the side surface. That is, in the cam housing portion  323 , the four pressing protrusion receiving parts  325  are formed in an anteroposterior direction at regular intervals which are the same as the intervals among the respective pressing protrusions  222  in a state in which the respective developer cartridges  25  are mounted into the drum unit  24 . Further, the four spacing protrusion receiving parts  326  are formed in an anteroposterior direction at regular intervals which are the same as the intervals among the respective spacing protrusions  209  in a state in which the respective developer cartridges  25  are mounted into the drum unit  24 . The respective spacing protrusion receiving parts  326  are disposed behind the respective pressing protrusion receiving parts  325 . In a state in which the spacing protrusions  209  are received in the respective spacing protrusion receiving parts  326 , the respective spacing protrusions  209  face the respective intermediate members  311  from above. 
     The synchronous movement mechanism  313  is configured to transmit driving force for rectilinear travel to the right translation cam member  310  from the left translation cam member  310  in accordance with a rectilinear travel of the left translation cam member  310 . 
     That is, as shown in  FIG. 9 , the synchronous movement mechanism  313  includes a left rack gear  327  formed on the upper surface of the rear end of the left translation cam member  310 , a left pinion gear  328  engaged with the left rack gear  327 , a right rack gear  329  formed on the upper surface of the rear end of the right translation cam member  310 , a right pinion gear  330  engaged with the right rack gear  329 , and a connecting shaft  331  to which the left pinion gear  328  and the right pinion gear  330  are attached to be unable to rotate relatively. 
     Further, an input rack gear  332  to which driving force of a motor (not shown) is inputted is provided on the outer surface of the cam body plate  314  in the left translation cam member  310 . In the present embodiment, the translation cam members  310  are formed of polyacetal or the like. 
     (4) Spacing and Pressing Operations 
     The operations of the spacing and pressing mechanism  303  will be described with mainly reference to FIG.  10  to  FIG. 13 . 
     As shown in  FIG. 10A  and  FIG. 11 , in a state in which the translation cam member  310  is moved to the most anterior position, the contacting/spacing force application portions  318  of the respective operational members  315  and the intermediate members  311  disposed respectively behind those face one another in a noncontact state at intervals in an anteroposterior direction. Intervals greater than the intervals between the contacting/spacing force application portions  318  and the intermediate members  311  disposed respectively behind those of the three posterior operational members  315  are formed between the contacting/spacing force application portions  318  and the intermediate member  311  disposed behind it of the most anterior operational member  315 . 
     In this state, the respective developer cartridges  25  are disposed at contacting positions at which the developing rollers  33  and the photosensitive drums  27  contact each other. Then, the pressing force application portions  317  of the respective operational members  315  contact the pressing protrusions  222  of the respective developer cartridges  25  from above to press the respective pressing protrusions  222  downward. Due to the respective pressing protrusions  222  being pressed downward, in the respective developer cartridges  25 , the handles  210  are turned with the supporting shafts  215  as fulcrums into a pressed state, and the elastically contacting members  219  are pressed down by the handles  210  (concave portions  220 ). Pressing force inputted to the respective pressing protrusions  222  from the pressing force application portions  317  are adjusted to be appropriate force due to the elasticity of the elastically contacting members  219  to bias the cases  30  downward. In accordance therewith, the developing rollers  33  are pressed onto the photosensitive drums  27 . 
     From this state, when driving force of the motor (not shown) is inputted to the input rack gear  332 , and the left translation cam member  310  is moved backward, the left pinion gear  328  rotates in accordance with the movement of the left translation cam member  310 , and the rotation of the left pinion gear  328  is transmitted to the right pinion gear  330  via the connecting shaft  331 . Then, the right pinion gear  330  rotates in the same direction of the left pinion gear  328 , which makes the right translation cam member  310  move backward. 
     As the backward movement of the translation cam member  310  progresses, the engagement among the pressing force application portions  317  of the three posterior operational members  315  and the pressing protrusions  222  of the developer cartridges  25  is cancelled, and the pressing onto the pressing protrusions  222  by the pressing force application portions  317  is cancelled. Further, as shown in  FIG. 10B , the contacting/spacing force application portions  318  of the three posterior operational members  315  contact the lower ends of the intermediate members  311  disposed respectively behind those to press the lower ends of the respective intermediate members  311  backward, and the respective intermediate members  311  turn to be lifted upward with the intermediate member supporting shafts  321  as fulcrums. In the process of the turning of the respective intermediate members  311 , the respective intermediate members  311  contact the spacing protrusions  209  positioned respectively thereabove from beneath, and upward spacing forces are applied to the spacing protrusions  209  from the respective intermediate members  311 . In accordance therewith, the yellow developer cartridge  25 Y, the magenta developer cartridge  25 M, and the cyan developer cartridge  25 C are lifted up upward. 
     Then, as the backward movement of the translation cam member  310  further progresses, and when one ends (ends at the sides through which the intermediate member supporting shafts  321  are inserted) of the intermediate members  311  contact the upper surfaces of the contacting/spacing force application portions  318  of the three posterior operational members  315  as shown in  FIG. 10C  and  FIG. 12 , the yellow developer cartridge  25 Y, the magenta developer cartridge  25 M, and the cyan developer cartridge  25 C are disposed at spaced positions, and the developing rollers  33  of the yellow developer cartridge  25 Y, the magenta developer cartridge  25 M, and the cyan developer cartridge  25 C are spaced from the photosensitive drums  27 . At this time, the pressing protrusions  222  of the black developer cartridge  25 K are pressed by the pressing force application portions  317  of the operational members  315 . In accordance therewith, only the developing roller  33  of the black developer cartridge  25 K is made into a state of being pressed onto the photosensitive drum  27 . 
     Thereafter, as the backward movement of the translation cam member  310  further progresses, the engagement between the pressing force application portions  317  of the most anterior operational member  315  and the pressing protrusions  222  of the black developer cartridge  25 K is cancelled, and the pressing onto the pressing protrusions  222  by the pressing force application portions  317  is cancelled. Further, as shown in  FIG. 10D , the contacting/spacing force application portion  318  of the most anterior operational member  315  contacts the lower end of the intermediate member  311  disposed behind it to press the lower end of the intermediate member  311  backward, and the intermediate member  311  turns to be lifted upward with the intermediate member supporting shaft  321  as a fulcrum. In the process of the turning of the intermediate member  311 , the intermediate member  311  contacts the spacing protrusions  209  of the black developer cartridge  25 K positioned thereabove from beneath, and upward spacing force is applied to the spacing protrusions  209  from the intermediate member  311 . Therefore, the black developer cartridge  25 K is lifted upward. 
     Then, as the backward movement of the translation cam member  310  further progresses, and when one end (an end at the side through which the intermediate member supporting shaft  321  is inserted) of the intermediate member  311  contacts the upper surface of the contacting/spacing force application portion  318  of the most anterior operational member  315  as shown in  FIG. 10E  and  FIG. 13 , the black developer cartridge  25 K is moved to a spaced position, and the developing roller  33  of the black developer cartridge  25 K is spaced from the photosensitive drum  27 . In accordance therewith, the developing rollers  33  of all the developer cartridges  25  are spaced from the photosensitive drums  27 . 
     In addition, provided that the translation cam member  310  is moved forward from the state shown in  FIG. 10E , it is possible to return to the respective states shown in  FIGS. 10A to 10D . At this time, the protruding portions  320  of the respective contacting/spacing force application portions  318  are latched onto the intermediate members  311  to make the intermediate members  311  turn to a direction of being spaced from the spacing protrusions  209  (downward). 
     5. Effects 
     Both of the pressing protrusions  222  to which pressing force to make the developing roller  33  contact the photosensitive drum  27  in a pressed state is inputted and the spacing protrusions  209  to which spacing force to make the developing roller  33  be spaced from the photosensitive drum  27  is inputted function as terminals electrically connected to the memory chip  223  disposed in the case  30  of the developer cartridge  25 . When pressing force is inputted to the pressing protrusions  222  (at the time of inputting pressing force), the pressing force application portions  317  to input pressing force contact the pressing protrusions  222 . Further, when spacing force is inputted to the spacing protrusions  209  (at the time of inputting spacing force), the intermediate members  311  to input spacing force contact the spacing protrusions  209 . Then, because the pressing force application portions  317  and the intermediate members  311  are formed of conductive materials, provided that the pressing force application portions  317  and the intermediate members  311 , and a read-writer (not shown) to read and write information with respect to the memory chip  223  are electrically connected to one another, at the time of inputting pressing force and the time of inputting spacing force, it is possible to reliably achieve an electrical connection between the read-writer and the memory chip  223 . As a result, even with a structure in which the developer cartridges  25  are provided to be movable, it is possible to satisfactorily carry out read/write information with respect to the memory chips  223  disposed in the developer cartridges  25 . 
     Further, because the handle  210  is provided to the case  30 , it is possible to move the developer cartridges  25  (to carry the developer cartridges  25 , and to mount and remove the developer cartridges  25  with respect to the body casing  2 ) by gripping the handle  210 . Further, because the hand of an operator does not contact the memory chip  223  disposed in the case by gripping the handle  210  at the time of moving the developer cartridges  25 , it is possible to prevent stains by contacting the memory chip  223  with the hand. Moreover, because the pressing protrusions  222  are formed to the handle  210 , and the elastically contacting members  219  are provided between the handle  210  and the case  30 , it is possible to adjust pressing force to be inputted to the pressing protrusions  222  due to the elasticity of the elastically contacting members  219 . As a result, it is possible to make the developing roller  33  contact the photosensitive drum  27  in an appropriate pressed state. 
     Further, the pressing protrusions  222  formed to the handle  210  function as terminals as well. The handle  210  includes the supporting shafts  215  formed of conductive materials, and the supporting shafts  215  are electrically connected to the pressing protrusions  222 . On the other hand, the ring-shaped members  216  formed of conductive materials are provided to the through holes  212  of the handle supporting portions  211  through which the supporting shafts  215  are inserted. The ring-shaped members  216  are electrically connected to the memory chip  223 . Then, the plurality of protrusions  217  are formed on the circumferential surfaces of the supporting shafts  215 , and those protrusions  217  contact the ring-shaped members  216  externally fitted to the supporting shafts  215 . In accordance therewith, even when the handle  210  is swung with the supporting shafts  215  as fulcrums, it is possible to secure the contact between the supporting shafts  215  and the ring-shaped members  216 , and it is possible to secure an electrical connection between the memory chip  223  and the pressing protrusions  222  functioning as terminals as well. 
     6. Another Embodiment 
       FIG. 14  is a perspective view showing another embodiment of the developer cartridge  25 . In  FIG. 14 , portions corresponding to the respective parts described above are denoted by the same reference numerals of the respective parts. Further, in the following descriptions, detailed descriptions of the respective parts denoted by the same reference numerals will be omitted. 
     In this developer cartridge  25 , the handle  210  is not provided, and plate spring-shaped members  401  are provided to the both ends of the upper wall  202  of the case  30 . 
     The respective plate spring-shaped members  401  are fixed to the upper surface of the upper wall  202  at one ends  402  thereof with screws  403 . The left plate spring-shaped member  401  is bent upward from the one end  402 , and is further bent to extend to the left. The right plate spring-shaped member  401  is bent upward from the one end  402 , and is further bent to extend to the right. Then, the other ends  404  of the respective plate spring-shaped members  401  extend outward from the side walls  201  of the case  30  so as to form pressing protrusions to which pressing forces from the pressing force application portions  317  of the spacing and pressing mechanism  303  are inputted. 
     In such a structure, the pressing force application portions  317  of the spacing and pressing mechanism  303  contact the other ends  404  of the respective plate spring-shaped members  401  from above to press the other ends  404  downward. Pressing forces inputted to the other ends  404  from the pressing force application portions  317  are adjusted to be appropriate forces due to the elastic deformation of the plate spring-shaped members  401  to bias the case  30  downward. In accordance therewith, the developing roller  33  is pressed onto the photosensitive drum  27 . 
     The two wirings  224  extending from the memory chip  223  are respectively connected to the one ends  402  of the right and left respective plate spring-shaped members  401 . Further, at the right and left respective sides, the spacing protrusions  209  are electrically connected to the one ends  402  of the plate spring-shaped members  401  via wirings  405 . 
     In accordance with this structure as well, effects which are the same as those of the developer cartridge  25  shown in  FIG. 3  and  FIG. 4  can be performed. 
     7. Modified Example 
     The present invention is not limited to the tandem type color laser printer  1 , and may be applied to an intermediate transfer type color laser printer, or may be applied to a monochrome laser printer. 
     Further, in the above-described embodiment, the example that the respective members of the translation cam member  310  are formed of conductive materials has been shown. However, it is not limited thereto. That is, in the translation cam member  310 , conductive sheet metals are disposed to only the contact portions between the pressing protrusions  222  and the spacing protrusions  209 , and the sheet metals and a controller at the body side may be wired.