Patent Publication Number: US-7587156-B2

Title: Replaceable process cartridge and image forming apparatus using the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This patent specification is based on Japanese patent application, No. JP 2006-167660 filed on Jun. 16, 2006 in the Japan Patent Office, the entire contents of which are incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a process cartridge and an image forming apparatus using the same, and more particularly to an effectively replaceable process cartridge and an image forming apparatus using the same. 
   2. Discussion of the Background 
   Image forming apparatuses include copiers, facsimiles, printers, plotters, multi-functional devices thereof, etc. Some image forming apparatuses may use an electrophotographic method to form an image on a recording medium. Such image forming apparatuses include a plurality of components such as a photoconductor drum, a developing roller, a charger, a cleaner, etc. 
   In consideration of size reduction or ease of maintenance, some image forming apparatuses are provided with a process cartridge for visualizing an electrostatic latent image on an image carrier with developer including toner. The process cartridge includes a plurality of components, and is configured to be detachably mountable to an image forming apparatus. 
   Such a process cartridge may be configured with a plurality of units. For example, a process cartridge may include a first unit having an image carrier, and a second unit having a developer carrier, which may be rotatably coupled to each other with a coupling member. 
   A process cartridge having such a configuration includes a photoconductor unit as the first unit and a developing unit as the second unit. The photoconductor unit also includes a photoconductor drum serving as an image carrier, while the developing unit includes a developing roller serving as a developer carrier. A coupling member for coupling the two units is disposed at a position in a direction in which an engaging pressure is applied between gears of the photoconductor drum and the developing roller. The coupling member is also supported so as to be movable along a direction perpendicular to the engaging pressure direction. 
   Thus, during driving of the photoconductor drum, the coupling member is positioned so as not to generate a rotational moment for unintentionally rotating the developing unit. Thereby the pressing force of the developing roller may be stably applied to the photoconductor drum to form a desired image. 
   Another conventional process cartridge having two units includes coupling pins for coupling the two units with each other. The two units are coupled so as to pivot around the coupling pins. The coupling pins are configured to project toward the outside of the process cartridge along the longitudinal direction of the two units. 
   Guide grooves are provided on an image forming apparatus using the process cartridge. When the process cartridge is mounted to or detached from the image forming apparatus, the coupling pins are put into or pulled out of the image forming apparatus along the guide groove. 
   For such a process cartridge, to reduce operating costs or environmental load, separate replacement of components is increasingly preferred to the whole replacement of the process cartridge as conventionally performed. Therefore a need exists for a process cartridge including replaceable components that are quick and easy to reuse. 
   However, a conventional process cartridge does not take sufficient consideration of the operability of components during disassembly and assembly thereof. For example, a process cartridge including coupling pins as described can be disassembled by clipping the end faces of the coupling pins with a tool. However, after disassembly, some time and effort are needed for re-inserting the coupling pins to reassemble the process cartridge. 
   In an image forming apparatus using a process cartridge as described above, a developing gap is formed between an image carrier and a developer carrier. 
   In a method of measuring such a developing gap, first, a measuring device is inserted into the developing gap, and a filling material stored in the measuring device is filled into and drawn from the developing gap. At this time, a portion of the measuring device expands and shrinks in the developing gap. The portion is provided with flat plates on both end surfaces thereof. The flat plates are brought into contact with both walls of the developing gap. Then the developing gap is measured with a detector of the measuring device. 
   In another method of measuring the developing gap, the developing gap is determined based on the width of a transmitting light flux measured by an optical dimension measuring device. 
   However, for the developing gap as described above, adjusting methods thereof are not sufficiently described compared to the measuring methods. 
   SUMMARY OF THE INVENTION 
   This patent specification describes a replaceable process cartridge and an image forming apparatus using the same. In an example of a preferred embodiment of the present invention, a process cartridge for use in an image forming apparatus includes a first unit, a second unit, and a coupling shaft. The first unit includes an image carrier, while the second unit includes a developer carrier. The coupling shaft is configured to couple the first unit and the second unit so as to be pivotable relative to each other. A distance between the image carrier and the developer carrier is adjustable by pivoting at least one of the first unit and the second unit without releasing the coupling of the first unit and the second unit via the coupling shaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  is a front view illustrating a folded state of a process cartridge according to an exemplary embodiment of the present invention; 
       FIG. 2  is a perspective view illustrating a folded state of the process cartridge of  FIG. 1 ; 
       FIG. 3  is a front view illustrating an unfolded state of the process cartridge of  FIG. 1 ; 
       FIG. 4  is a perspective view illustrating an unfolded state of the process cartridge of  FIG. 1 ; 
       FIG. 5  is a front view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 6  is a perspective view illustrating an unfolded state of the process cartridge of  FIG. 5 ; 
       FIG. 7  is a front view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 8  is a perspective view illustrating a folded state of the process cartridge of  FIG. 7 ; 
       FIG. 9  is a front view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 10  is a perspective view illustrating an unfolded state of the process cartridge of  FIG. 9 ; 
       FIG. 11  is a front view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 12  is a front view illustrating an unfolded state of the process cartridge of  FIG. 11 ; 
       FIG. 13  is a front view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 14  is a front view illustrating an unfolded state of the process cartridge of  FIG. 13 ; 
       FIG. 15  is a front view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 16  is a front view illustrating an unfolded state of the process cartridge of  FIG. 15 ; 
       FIG. 17  is a sectional view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 18  is a perspective view illustrating a folded state of the process cartridge of  FIG. 17 ; 
       FIG. 19  is a sectional view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 20  is a perspective view illustrating a folded state of the process cartridge of  FIG. 19 ; 
       FIG. 21  is a sectional view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 22  is an explanatory view illustrating a method of fixing a sealing member in the process cartridge of  FIG. 17 ; 
       FIG. 23  is a sectional view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 24  is a perspective view illustrating a folded state of the process cartridge of  FIG. 23 ; 
       FIG. 25  is a sectional view illustrating a folded state of a process cartridge according to another exemplary embodiment of the present invention; 
       FIG. 26  is a perspective view illustrating a folded state of the process cartridge of  FIG. 25 ; 
       FIG. 27  is a sectional view illustrating an unfolded state of the process cartridge of  FIG. 25 ; 
       FIG. 28  is a schematic view illustrating a configuration of an image forming apparatus according to an exemplary embodiment of the present invention; 
       FIG. 29  is a sectional view illustrating an assembled state of a disassemblable process cartridge according to another exemplary embodiment of the present invention; and 
       FIG. 30  is a schematic view illustrating a configuration of an image forming apparatus, including the process cartridge of  FIG. 29 , according to another exemplary embodiment of the present invention. 
   

   The accompanying drawings are intended to depict exemplary embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to  FIG. 1 , a process cartridge  60  according to an example embodiment of the present invention is described. 
   As illustrated in  FIG. 1 , the process cartridge  60  includes a photoconductor drum  1 , a photoconductor cleaner  2 , a charger  3 , a waste toner container  4 , first support members  5   a , hinge pins  6 , a developing roller  7 , a developer transporter  8 , a toner supplying agitator  9 , and second support members  10   a.    
   The photoconductor drum  1  is surrounded by the charger  3 , the developing roller  7 , and the photoconductor cleaner  2  along a rotational direction thereof indicated by an arrow A in  FIG. 1 . The waste toner container  4  is disposed near the photoconductor cleaner  2 . 
   The photoconductor drum  1  serves as an image carrier. A surface portion of the photoconductor drum  1  between the charger  3  and the developing roller  7  serves as an exposed portion to be irradiated by light. Another surface portion of the photoconductor drum  1  between the developing roller  7  and the photoconductor cleaner  2  serves as a transfer section together with a transfer unit (not illustrated). At the transfer section, the image forming apparatus  100  transfers a toner image, which is carried on the photoconductor drum  2 , onto a sheet medium. 
   The process cartridge  60  includes a drum unit  5  and a developing unit  10 . In an embodiment of the present invention, the drum unit  5  is a first unit of the process cartridge  60 , while the developing unit  10  is a second unit thereof. Alternatively, the developing unit  10  may be a first unit of the process cartridge  60 , while the drum unit  5  may be a second unit thereof. 
   The drum unit  5  may include the photoconductor drum  1 , the photoconductor cleaner  2 , the charger  3 , and the waste toner container  4 . In such a configuration, the photoconductor drum  1 , the photoconductor cleaner  2 , the charger  3 , and the waste toner container  4  are attached to a frame of the drum unit  5 . 
   The developing unit  10  includes the developing roller  7 , the developer transporter  8 , and the toner supply agitator  9 . In such a configuration, the developing roller  7 , the developer transporter  8 , and the toner supply agitator  9  are attached to a frame of the developing unit  10 . 
   The developing roller  7  serves as a developer carrier. The developer transporter  8  includes a conveying screw for conveying a developer containing toner to the developing roller  7 . The toner supply agitator  9  includes another conveying screw for conveying and agitating toner and carrier particles. 
   In  FIG. 1 , the photoconductor drum  1  has an axis O extending along a longitudinal direction thereof. The axis O of the photoconductor drum  1  is disposed so as to be parallel with the axis of the developing roller  7 . 
   The hinge pins  6  are provided so as to be parallel with the axis O. Each hinge pin  6  serves as a common shaft for coupling the drum unit  5  and the developing unit  10 . 
   The first support members  5   a  protrude from the drum unit  5 , while the second support members  10   a  protrude from the developer unit  7 . Each of the first support members  5   a  and the second support members  10   a  has an engaging hole  11 . The hinge pins  6  are inserted into the corresponding engaging holes  11  of the first support members  5   a  and the second support members  10   a  along a direction being parallel with the axis O of the photoconductor drum  1 . Thereby the first support member  5   a  and the second support member  10   a  are engaged with and supported by the hinge pins  6 . 
   Thus the drum unit  5  and the developer unit  10  are pivotably coupled with each other by the hinge pins  6  to integrally form the process cartridge  60 . The central axis  14  of each hinge pin  6  is set to a position so that the frames of the photoconductive unit  5  and the developing unit  10  do not interfere with each other when the photoconductor drum  1  and the developing roller  7  pivot in a direction moving away from each other. 
   As described above, in an embodiment of the present invention, the drum unit  5  and the developing unit  10  is coupled via the two sets of the hinge pins  6 , the first support members  5   a , and the second support members  10   a . However, the drum unit  5  and the developing unit  10  may be also coupled via one set of the hinge pin  6 , the first support member  5   a , and the second support member  10   a . Alternatively, the drum unit  5  and the developing unit  10  may be coupled via three or more sets of the hinge pin  6 , the first support member  5   a , and the second support member  10   a.    
   As illustrated in  FIG. 2 , a bearing  12  is provided to an end face of the drum unit  5 . Although not illustrated in  FIG. 2 , another bearing  12  is provided on the opposite end surface of the drum unit  5 . The photoconductor drum  1  is held in the drum unit  5  via the bearings  12  so the photoconductor drum  1  can rotate smoothly. 
   Similarly, the developing roller  7  is held in the developing unit  10  via bearings  13 , which are provided to end faces of the developing unit  10 . Thus, the developing roller  7  is smoothly rotatable in the developing unit  10 . Accordingly, the process cartridge  60  can suppress an accidental drop or a positional shift of the photoconductor drum  1  and the developing roller  7 . 
     FIGS. 3 and 4  illustrate unfolded states of the process cartridge  60  of  FIGS. 1 and 2 , respectively. In the unfolded states, the upper side of the photoconductor drum  1  is exposed to the outside. Thus, replacement and maintenance operations of the photoconductor drum  1  can be facilitated. 
   Similarly, in the unfolded states as illustrated in  FIGS. 3 and 4 , the upper side of the developing unit  10  is also exposed to the outside. Thus, replacement and maintenance operations of the developing roller  7 , the developer transporter  8 , and the toner supply agitator  9  can be facilitated. 
   After finishing such a replacement or maintenance operation of the components of the process cartridge  60 , the process cartridge  60  is re-installed in an image forming apparatus. The drum unit  5  and the developing unit  10  are pivoted around the hinge pins  6  so as to come close to each other. Thereby the process cartridge  60  returns to the folded state, as illustrated in  FIGS. 1 and 2 , in which the photoconductor drum  1 , the developing roller  7 , and the other components are operably positioned. Thus, the photoconductor drum  1  and the developing roller  7  can be positioned adjacent to each other. 
   Further, when needed, the process cartridge  60  can be ejected from the image forming apparatus and returned to the unfolded state as illustrated in  FIG. 3  or  4 . In such an unfolded state, the upper side of the process cartridge  60  is exposed to the outside as described above. At this time, the photoconductor drum  1  and the developing roller  7  are positioned away from each other, thus facilitating a component replacement of the process cartridge  60 . 
   When the process cartridge  60  is folded as illustrated in  FIG. 1  or  2 , the developer transporter  8  and the toner supply agitator  9  are arranged side by side in the developing unit  10 . The developing roller  7  is disposed above the developer transporter  8  and the toner supply agitator  9 . 
   The drum unit  5  is positioned obliquely upward of the developing unit  10 . The photoconductor drum  1  of the drum unit  5  is positioned obliquely upward of the developing roller  7 . 
   On the other hand, when the process cartridge  60  is unfolded as illustrated in  FIG. 3  or  4 , the drum unit  5  pivots approximately 90 degrees around the hinge pins  6  in the counterclockwise direction. At this time, the developing unit  10  is held at the position as illustrated in  FIG. 1  or  2 . 
   In an exemplary embodiment of the present invention, each hinge pin  6  serves as a common shaft for foldably and unfoldably coupling the drum unit  5  and the developing unit  10 . Thus, an operator can separate the drum unit  5  and the developing unit  10  from each other by moving any one thereof along the longitudinal direction of the photoconductor drum  1 . 
   Then, in order to suppress an accidental separation of the drum unit  5  and the developing unit  10 , at least one of the hinge pins  6  may be provided with a stopper for limiting the movement of the drum unit  5  and the developing unit  10  along the longitudinal direction of the photoconductor drum  1 . 
   As described above, the drum unit  5  including the photoconductor drum  1  and the developing unit  10  including the developing roller  7  are foldably and unfoldably coupled with each other by the hinge pins  6 , which serve as the common shafts relative to the two units. Thereby the process cartridge  60  can switch between the folded state and the unfolded state without releasing the coupling of the drum unit  5  and the developing unit  10 . 
   Thus, the process cartridge  60  can transform into the unfolded state suitable for maintenance without being disassembled. Further, the process cartridge  60  can return to the folded state so as to be operable in the image forming apparatus  100 . 
   As described above, the photoconductor drum  1  is held via the bearings  12  on the frame of the drum unit  5 , while the developing roller  7  is held via the bearings  13  on the frame of the developing unit  10 . The respective frames of the drum unit  5  and the developing unit  10  are pivotably coupled to given axes being in parallel with the longitudinal direction of the photoconductor drum  1 . 
   Thus, without using a coupling member, such as a faceplate, for precisely coupling the frames of the drum unit  5  and the developing unit  10 , the process cartridge  60  can restore original positions of the photoconductor drum  1  and the developing roller  7  by determining engaging points of the drum unit  5  and the developing unit  10  on the pivot trajectory thereof. Further, the photoconductor drum  1  and the developing roller  7  can pivot in a direction of moving away from each other, and therefore replacement and maintenance operations can be facilitated. 
   Thus, in an exemplary embodiment of the present invention, a process cartridge can be provided with a relatively simple configuration, increased positioning precision, and increased replaceability of components. 
   Next, a process cartridge  61  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 5 and 6 . 
   The process cartridge  61  has substantially identical configurations to the process cartridge  60  in that a drum unit  5  and a developing unit  10  are foldably and unfoldably coupled by hinge pins  6  to each other. The identical components or members are represented by identical numeral and letter codes to  FIGS. 1 to 4 , and repeated descriptions thereof are omitted. 
     FIG. 5  illustrates a folded state where the drum unit  5  and the developing unit  10  are folded toward each other. In the folded state of  FIG. 5 , a photoconductor drum  1  and a developing roller  7  are operably positioned. An arrow B indicates a conveyance direction of a sheet medium for recording an image. 
     FIG. 6  illustrates an unfolded state where the drum unit  5  and the developing unit  10  are unfolded away from each other. 
   The developing unit  10  is provided with protrusions  20  on a surface thereof. Specifically, the protrusions  20  are disposed outside a conveying width β of a sheet medium so as not to interfere with the developing roller  7 . 
   On the other hand, the drum unit  5  includes recesses  21 . The recesses  21  are disposed on the drum unit  5 . Specifically, the recesses  21  are disposed outside the conveying width β of a sheet medium so as not to interfere with the photoconductor drum  1 . 
   When the drum unit  5  and the developing unit  10  pivot around the central axes  14  of the hinge pins  6  from the unfolded state of  FIG. 6  until the folded state of  FIG. 5 , the protrusions  20  are brought into contact with the recesses  21 . 
   Thereby the pivoting movement of the drum unit  5  and the developing unit  10  stops before the photoconductor drum  1  and the developing roller  7  abut against each other. Then the positions of the drum unit  5  and the developing unit  10  are held by the moment of the weight of the drum unit  5 . 
   According to an embodiment of the present invention, the process cartridge  61  includes such a stopping portion, which is formed of the protrusions  20  and the recesses  21  between the drum unit  5  and the developing unit  10 . 
   Thus, an interference between the photoconductor drum  1  and the developing roller  7  can be suppressed when the photoconductor drum  1  and the developing roller  7  come close to each other during a replacement operation of components. 
   The recesses  21  may be positioning recesses or holes for engaging with the protrusions  20  and appropriately positioning the drum unit  5  and the developing unit  10 . 
   Such a configuration allows the process cartridge  61  to effectively restore the positions of components, which leads to the reduction of scratches and dents on a coating of the photoconductor drum  1  during a replacement operation of components, etc. 
   As described above, the process cartridge  61  includes a mechanism of regulating the distance between the photoconductor drum  1  and the developing roller  7 . 
   Thus, an interference between the photoconductor drum  1  and the developing roller  7  can be effectively suppressed during disassembly and assembly of the process cartridge  61 . 
   Thus scratches on the coating of the photoconductor drum  1  or an image degradation due to a deformation of the photoconductor drum  1  or the developing roller  7  can also be suppressed. 
   In the process cartridge  61  according to an exemplary embodiment of the present invention, the protrusions  20  are provided on the developing unit  10 , while the recesses  21  are provided on the drum unit  5 . Alternatively, the protrusions  20  may be provided on the drum unit  5 , while the recesses  21  may be provided on the developing unit  10 . 
   Next, a process cartridge  62  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 7 and 8 . 
   The process cartridge  62  has substantially identical configurations to the process cartridge  60  or  61  in that a drum unit  5  and a developing unit  10  are foldably and unfoldably coupled by hinge pins  6  to each other. The identical components or members are represented by identical numeral and letter codes of  FIGS. 1 to 6 , and repeated descriptions thereof are omitted. 
     FIGS. 7 and 8  illustrate folded states where the drum unit  5  and the developing unit  10  are folded toward each other. 
   As illustrated in  FIGS. 7 and 8 , the developing unit  10  is provided with holes  23  on a surface thereof. Specifically, the holes  23  are disposed outside a conveying width β of a sheet medium as illustrated in  FIG. 8 . 
   The drum unit  5  is provided with stoppers  24 . The stoppers  24  protrude from a surface of the drum unit  5  toward the developing unit  10 . 
   The drum unit  5  and the developing unit  10  pivot toward each other around the central axes  14  of the hinge pins  6  so that a photoconductor drum  1  and a developing roller  7  are operably positioned. 
   When the stoppers  24  are inserted into the corresponding holes  23 , the pivoting of the drum unit  5  and the developing unit  10  stops. At this time, if the stoppers  24  and the holes  23  are firmly engaged with each other, the drum unit  5  and the developing unit  10  can be held together in a fixed state. 
   Each stopper  24  may further include an engaging portion for regulating the movement of the drum unit  5  and the developing unit  10  along a longitudinal direction of the photoconductor drum  1 . 
   Further, the stoppers  24  may be configured to have a rigidity capable of slightly bending toward the inside of the developing unit  10 . Thus, when the drum unit  5  and the developing unit  10  pivot around the central axes  14  so as to come close to each other, the stoppers  24  can be smoothly inserted into the holes  23 . 
   According to an exemplary embodiment of the present invention, as illustrated in  FIGS. 7 and 8 , when the photoconductor drum  1  and the developing roller  7  come close to each other, the stoppers  24  of the drum unit  5  are engagingly inserted into the corresponding holes  23  of the developing unit  10 . Thus, the photoconductor drum  1  and the developing roller  7  can securely hold a distance so as not to interfere with each other. 
   In the process cartridge  62  according to an exemplary embodiment of the present invention, the holes  23  are provided on the developing unit  10 , while the stoppers  24  are provided on the drum unit  5 . Alternatively, the holes  23  may be provided on the drum unit  5 , while the stoppers  24  may be provided on the developing unit  10 . 
   Further, the configuration of the process cartridge  62  as described above may be used together with the configuration of the process cartridge  61  as illustrated in  FIGS. 5 and 6 . 
   For the process cartridge  62  according to an embodiment of the present invention, the drum unit  5  and the developing unit  10  pivot around the central axes  14  so that the photoconductor drum  1  and the developing roller  7  come close to each other. 
   When the photoconductor drum  1  and the developing roller  7  are closed so as to be operably positioned, a protruding portion of each stopper  24  of the drum unit  5  engages with the corresponding hole  23  of the developing unit  10 . A base portion of each stopper  24  is flatly shaped so as to regulate the extent in which the protruding portion of each stopper  24  is inserted into the hole  23 . 
   Thereby the drum unit  5  and the developing unit  10  can hold the folded state as described above. The folded state can be released with a single touch operation. Thus, the process cartridge  62  can hold and release the folded state of the drum unit  5  and the developing unit  10  without using a fastening member such as a screw. 
   In other words, the drum unit  5  and the developing unit  10  do not necessarily need a fastening member or a locking mechanism. Therefore the efficiency of the assembly operation of the process cartridge  62  can be increased. 
   Next, a process cartridge  63  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 9 and 10 . 
   As illustrated in  FIGS. 9 and 10 , for the process cartridge  63 , holes  23   a  are provided on a developing unit  10 , while protruding stoppers  24   a  are provided on a drum unit  5 . When a photoconductor drum  1  and a developing roller  7  come close to each other, the protruding stoppers  24   a  are engagingly inserted into the corresponding holes  23   a.    
   Thus, the photoconductor drum  1  and the developing roller  7  can hold a distance so as not to interfere with each other. 
   As illustrated in  FIG. 10 , each of the protruding stoppers  24   a  has a hook portion for stopping a pivoting of the photoconductor drum  1  and the developing roller  7  in a direction of moving away from each other. When the photoconductor drum  1  and the developing roller  7  are folded as illustrated in  FIG. 9 , the protruding stoppers  24   a  are inserted into the corresponding holes  23   a.    
   The developing unit  10  is provided with springs  25  or other biasing members such as sponge seals (not illustrated). The springs  25  are disposed at positions on a surface of the developing unit  10  facing the drum unit  5 . The springs  25  or other biasing members bias the photoconductor drum  1  and the developing roller  7  away from each other. 
   The drum unit  5  is provided with concaves  27  for receiving the biasing force of the springs  25 . Thus the process cartridge  63  is configured to have a biasing force when the drum unit  5  and the developing unit  10  are folded as illustrated in  FIG. 9 . 
   As illustrated in  FIG. 10 , the holes  23   a , the protruding stoppers  24   a , the springs  25 , and the concaves  27  are disposed outside a conveying width β of a sheet medium. 
   The biasing force of the springs  25  presses the hook portions of the protruding stoppers  24   a  against corresponding engaging surfaces of the holes  23   a . Thus, the drum unit  5  and the developing unit  10  can hold the folded state as illustrated in  FIG. 9 . 
   Further, similar to the process cartridge  62 , the protruding stoppers  24   a  have a rigidity capable of slightly bending toward the inside of the developing unit  10 . 
   Thus, when the drum unit  5  and the developing unit  10  pivot around the central axis  14  so as to come close to each other, the stoppers  24   a  can be smoothly inserted into the holes  23   a.    
   In an exemplary embodiment of the present invention, the protruding stoppers  24   a  have hook portions. The springs  25  or other biasing members such as sponge seals are disposed at positions on a surface of the developing unit  10  facing the drum unit  5  so as to bias the photoconductor drum  1  and the developing roller  7  away from each other. 
   In such a configuration, when the drum unit  5  and the developing unit  10  pivot so that the photoconductor drum  1  and the developing roller  7  come close to each other so as to be operably positioned, the hook portions of the protruding stoppers  24   a  are biased against the engaging surfaces of the holes  23   a  as illustrated in  FIG. 9 . Thereby the frame of the developing unit  10  can be appropriately positioned. 
   Thus, without using any fastening member, the process cartridge  63  can hold the folded state where the photoconductor drum  1  and the developing roller  7  are operably positioned. 
   As described above, the process cartridge  62  does not necessarily need a fastening member, such as a screw, or a locking mechanism to hold and release the folded state as illustrated in  FIG. 7  or  8  while the distance between the photoconductor drum  1  and the developing roller  7  is preferably held with relatively high precision. 
   Such process cartridge  62  may need a precise engagement between the stoppers  24  and the holes  23  to preferably suppress looseness of engagement between the stoppers  24  and the holes  23  so that the drum unit  5  and the developing unit  10  may be effectively positioned with each other when folded. Consequently, the process cartridge  62  may need some time and effort in the manufacturing of components thereof. 
   On the other hand, the process cartridge  63  can hold a preferable positional relationship between the photoconductor drum  1  and the developing roller  7  by a relatively simple configuration as described above. Thus, the time and effort may be reduced in the manufacturing of components thereof. 
   Next, a process cartridge  64  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 11 and 12 . 
     FIG. 11  illustrates a folded state where the drum unit  5  and the developing unit  10  are folded toward each other. 
     FIG. 12  is an unfolded state where the drum unit  5  and the developing unit  10  are unfolded away from each other. 
   The configuration of the process cartridge  64  according to an exemplary embodiment of the present invention can be applied to any of the process cartridges  60  to  64  according to the above-described exemplary embodiments. 
   Similar to the above-described exemplary embodiments, a drum unit  5  is provided with first support members  5   a , while a developing unit  10  is provided with second support members  10   a . Each of the first support members  5   a  and the second support members  10   a  has an engaging hole  11 . 
   Hinge pins  6  are inserted into the corresponding engaging holes  11  of the first support members  5   a  and the second support members  10   a  in parallel with a longitudinal direction of a photoconductor drum  1 . Thus, the hinge pins  6  pivotably couple the drum unit  5  and the developing unit  10  to integrally form the process cartridge  64 . 
   When the process cartridge  64  is mounted on an image forming apparatus, the process cartridge  64  is in a folded state as illustrated in  FIG. 11 . On the other hand, after the process cartridge  64  is withdrawn from the image forming apparatus, the process cartridge  64  can take a position as illustrated in  FIG. 12 , in which the drum unit  5  and the developing unit  10  are unfolded so as to be convenient for component replacement. 
   When the photoconductor drum  1  and the developing roller  7  are positioned substantially farthest away from each other as illustrated in  FIG. 12 , flat surfaces  65  and  66  of the drum unit  5  and the developing unit  10  fit a plane α. In other words, in the unfolded state, the drum unit  5  and the developing unit  10  have flat surfaces  65  and  66 , respectively, for simultaneously contacting the plane α to stably support the process cartridge  64  as a whole. 
   In an exemplary embodiment of the present invention, the flat surface  65  of the drum unit  5  forms a vertical plane when the process cartridge  64  is folded as illustrated in  FIG. 11 . Then, the flat surface  66  of the developing unit  10  is disposed in parallel with a horizontal plane being perpendicular to the flat surface  65 . 
   When the process cartridge  64  is unfolded as illustrated in  FIG. 12 , the flat surfaces  65  and  66  contact the plane α to stably support the process cartridge  64  as a whole. 
   Thus, in the unfolded state of  FIG. 12 , the flat surfaces  65  and  66  contact the plane α, and the process cartridge  64  stably fits to a flat face such as table face. Accordingly, a replacement operation of components can be facilitated. 
   Next, a process cartridge  70  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 13 and 14 . 
   The process cartridge  70  has a different layout of components in a drum unit  5  and a developing unit  10  from any of the process cartridges  60  to  64  as described above. Therefore, the process cartridge  70  has also different in the outer shapes of the drum unit  5  and the developing unit  10 . 
     FIG. 13  illustrates a folded state of the process cartridge  70  where the drum unit  5  and the developing unit  10  are folded toward each other. 
     FIG. 14  illustrates an unfolded state thereof where the drum unit  5  and the developing unit  10  are unfolded away from each other. 
   As illustrated in  FIGS. 13 and 14 , the process cartridge  70  includes the drum unit  5  and the developing unit  10 , both of which have rectangular shapes. 
   In  FIGS. 13 and 14 , identical numeral and letter codes are used for the other components having substantially identical functions to the above-described exemplary embodiments. 
   When the process cartridge  70  is folded as illustrated in  FIG. 13 , the drum unit  5  is stacked on the developing unit  10 . When the drum unit  5  pivots approximately 90 degrees to the left around the hinge pins  6  from the position of  FIG. 13 , the process cartridge  70  is unfolded as illustrated in  FIG. 14 . 
   The drum unit  5  and the developing unit  10  have flat surfaces  65  and  66  to fit a plane α when a photoconductor drum  1  and a developing roller  7  are substantially farthest away from each other as illustrated in  FIG. 14 . 
   In other words, in the unfolded state, the drum unit  5  and the developing unit  10  have the flat surfaces  65  and  66 , respectively, for simultaneously contacting the plane α to stably support the process cartridge  70  as a whole. 
   In an exemplary embodiment of the present invention, the flat surface  65  of the drum unit  5  forms a vertical plane when the process cartridge  64  is in the folded state as illustrated in  FIG. 13 . At this time, the flat surface  66  of the developing unit  10  is disposed in parallel with a horizontal plane being perpendicular to the flat surface  65 . 
   When the process cartridge  70  is in the unfolded state as illustrated in  FIG. 14 , the flat surfaces  65  and  66  contact the identical plane α to stably support the process cartridge  70  as a whole. 
   In an exemplary embodiment of the present, when the drum unit  5  and the developing unit  10  are pivoted into a position suitable for component replacement, respective surfaces of the drum unit  5  and the developing unit  10  stably fit a flat surface of a workbench or so forth. Therefore, an operator can perform a replacement operation of components while suppressing an unintentional move of the process cartridge  70 . Thus, operators such as service or repair persons can effectively perform assembly and disassembly operations of the process cartridge  70  in a more compact space on a table or floor. 
   Next, a process cartridge  80  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 15 and 16 . 
   Similar to the above-described exemplary embodiments, a developing unit  10  has engaging holes  11 . Hinge pins  6  are inserted into the engaging hole  11  in parallel with a longitudinal direction of a photoconductor drum  1 . Thereby the hinge pins  6  pivotably couple the drum unit  5  and the developing unit  10 . 
   In the process cartridge  80 , a developing roller unit  30  is formed as a single unit separately from the developing unit  10 . The developing roller unit  30  includes a developing roller  7 , while the developing unit  10  includes a developer transporter  8  and a toner supply agitator  9 . 
   The developing unit  10  has engaging holes  32 . Hinge pins  31  are inserted into the engaging holes  32  in parallel with a longitudinal direction of the photoconductor drum  1 . Thus, the hinge pins  31  pivotably couple the developing unit  10  and the developing roller unit  30 . 
   From the folded state as illustrated in  FIG. 15 , the drum unit  5  is pivoted around the hinge pin  6  so as to be unfolded relative to the developing unit  10 . Then the developing roller unit  30  is exposed to the outside. 
   When the developing roller unit  30  is pivoted around the hinge pin  31  away from the developing unit  10 , the developer transporter  8  and the toner supply agitator  9  are exposed to the outside. Thus, a replacement or refill operation of developer can be facilitated. 
   At this time, the developing roller  7  of the developing roller unit  30  is also exposed to the outside. Thus, maintenance and replacement operations of the developing roller  7  can also be facilitated. 
   In an exemplary embodiment of the present invention, the developing roller unit  30  may be configured to have a surface capable of stably fitting a plane α as illustrated in  FIG. 16  when the process cartridge  80  is unfolded. 
   Any of the above-described process cartridges  60  to  64 ,  70 , and  80  can adjust the gap between the photoconductor drum  1  and the developing roller  7  in a relatively simple manner. For example, the gap can be adjusted by changing the height of the protrusions  20 , the first support members  5   a , or the second support members  10   a , which is provided on the drum unit  5  or the developing unit  10 . 
   Thus, when the process cartridge is in the unfolded state, an operator can perform a component replacement operation or a maintenance operation such as the gap adjustment. After finishing the replacement or maintenance operation, the drum unit  5  and the developing unit  10  are pivoted toward each other. Thus, the process cartridge  80  can restore the folded state. 
   Next, a process cartridge  91  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 17 and 18 . 
     FIG. 17  is a sectional view illustrating a folded state of the process cartridge  91 . 
     FIG. 18  is a perspective view illustrating a folded state of the process cartridge  91  illustrated in  FIG. 17 . 
   As illustrated in  FIGS. 17 and 18 , the process cartridge  91  includes a drum unit  5  as a first unit and a developing unit  10  as a second unit. The drum unit  5  also includes a photoconductor drum  1 , while the developing unit  10  includes a developing roller  7 . 
   The drum unit  5  is integrally provided with two support members  5   a , while the developing unit  10  is integrally provided with two support members  10   a . The respective supports  5   a  are coupled with the corresponding support members  10   a  via hinge pins  6  as illustrated in  FIG. 18 . The hinge pins  6  are disposed so as to have substantially identical axes relative to each other. The drum unit  5  and the developing unit  10  are pivoted around the hinge pins  6  so as to be folded and unfolded relative to each other. 
   The hinge pins  6  are disposed at positions so that the drum unit  5  and the developing unit  10  do not interfere with each other when the drum unit  5  and the developing unit  10  pivot around the hinge pins  6 . 
   As described above,  FIGS. 17 and 18  illustrate folded states of the process cartridge  91 . 
   When the drum unit  5  and the developing unit  10  are unfolded away form each other, the process cartridge  91  takes a similar position as illustrated in  FIG. 3  or  FIG. 27  (described later). In the unfolded state, the upper side of the drum unit  5  is exposed to the outside. Thus, replacement and maintenance operations of the photoconductor drum  1  can be facilitated. 
   At this time, the upper side of the developing unit  10  is also exposed to the outside. Thus, replacement and maintenance operations of the developing roller  7 , the developer transporter  8 , and the toner supply agitator  9  can also be facilitated. In this regard, an interface line  40 , as illustrated in  FIGS. 17 and 18 , represents an interface between the drum unit  5  and the developing unit  10 , which is formed when the process cartridge  91  is folded. 
   As illustrated in  FIG. 17 , the drum unit  5  also includes a photoconductor cleaner  2 , a charger  3 , and a waste toner container  4  besides the photoconductor drum  1 . The developing unit  10  also includes a developer transporter  8  and a toner supply agitator  9  besides the developing roller  7 . 
   A central axis O of the photoconductor drum  1  is disposed in parallel with a central axis O 7  of the developing roller  7 . The folded state of the process cartridge  91  is held by a locking mechanism. 
   In the folded state, a through space  49  is formed along a normal line direction of a virtual plane h 1 -h 1  including both the central axes O and O 7 . 
   The through space  49  passes through between the drum unit  5  and the developing unit  10  so as to include a processing gap PG. The processing gap PG is a distance between outer surfaces of the photoconductor drum  1  and the developing roller  7 . 
   The process cartridge  91  has openings  50  and  51  on side portions of the drum unit  5 . The through space  49  passes through the process cartridge  91  via the openings  50  and  51 . 
   When measuring the processing gap PG, a measuring device  52  is positioned outside the process cartridge  91 , which is folded as illustrated in  FIG. 17 . 
   The measuring device  52  includes an irradiation aperture  52   a  from which light is irradiated for measuring the processing gap PG. The measuring device  52  also includes a sensor  52   b  for receiving the light irradiated from the irradiation aperture  52   a.    
   The irradiation aperture  52   a  is positioned outside an opening  50 , while the sensor  52   b  is positioned outside an opening  51 . The irradiation aperture  52   a  faces the sensor  52   b  via the through space  49 . 
   Light  53 , which is irradiated from the irradiation aperture  52   a , sequentially goes through the opening  50 , the processing gap PG, and the opening  51 . Then the sensor  52   b  detects the light  53  and determines the width of the processing gap PG. 
   Currently, many image forming sections of image forming apparatuses are integrally formed as compact-size process cartridges to facilitate maintenance and replacement operations. In such a process cartridge, the width of the processing gap PG have some effect on the quality of an image formed on a recording medium. Therefore, the processing gap PG is preferably adjustable to obtain a desired image quality. 
   However, a conventional process cartridge may need to be disassembled in order to remeasure the width of the processing gap PG after the assembly thereof. Alternatively, for another conventional process cartridge, the processing gap PG is measured by detecting a pressure applied from a contact terminal. In this case, a photoconductor drum may be replaced with a specialized drum for measurement. Therefore, such a conventional process cartridge may need some time and effort for the measurement of the processing gap PG. Additionally, the processing gap PG is not measured for the photoconductor drum actually used in an image forming apparatus. 
   In an exemplary embodiment of the invention, the measuring device  52  measures the processing gap PG by transmitting the light  53  after the assembly of the process cartridge  91 . As described above, the process cartridge  91  has the through space  49  including the processing gap PG. The through space  49  passes through between the drum unit  5  and the developing unit  10  along a normal line direction of the virtual plane h 1 -h 1 , which includes the central axis O of the photoconductor drum  1  and the central axis O 7  of the developing roller  7 . 
   Then the measuring device  52  transmits the light  53  from the outside of the through space  49 . Thus, the processing gap PG can be measured without disassembling the process cartridge  91 . 
   Further, the measurement of the processing gap PG on a manufacturing line can be facilitated, thus resulting in more effective quality assurance. Even if a failure occurs in the process cartridge  91  on the manufacturing line, the failure can be analyzed without disassembling the process cartridge  91 . 
   Next, a process cartridge  92  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 19 and 20 . 
   The process cartridge  92  has substantially identical configurations to the process cartridge  91  as illustrated in  FIGS. 17 and 18 . The identical components or members are represented by identical codes of  FIGS. 17 and 18 , and repeated descriptions thereof are omitted. 
   As illustrated in  FIGS. 17 and 18 , the process cartridge  91  has the openings  50  and  51  on the ends of the through space  49 . When the openings  50  and  51  remain open, the process cartridge  91  may have lower dustproof performance, which may lead to image deterioration due to dust. 
   Hence, according to an exemplary embodiment of the present invention, the process cartridge  92  is configured so as to have an increased dustproof performance. 
   Specifically, the process cartridge  92  includes a through space  49 , openings  50  and  51 , and transparent boards  54  and  55 . The transparent boards  54  and  55  are disposed so as to close the openings  50  and  51 , respectively. The transparent boards  54  and  55  are also supported at side-wall portions of a drum unit  5  and a developing unit  10  by the outer frame of the process cartridge  92 . 
   Thus, the transparent board  54  is fixed on the outer frame of the process cartridge  92  so as to close the opening  50 . The transparent board  55  is fixed on the outer frame of the process cartridge  92  so as to close the opening  51 . 
   The transparent boards  54  and  55  are also fixed on the outer frame of the process cartridge  92  with an adhesive seal or a screw. Thus, by closing the opening  50  and  51 , the entry of dust from the outside of the process cartridge  92  may be suppressed. 
   The transparent boards  54  and  55  are transparent to light. Therefore, in a similar way to the process cartridge  91 , the process cartridge  92  can measure a processing gap PG, which is a distance between outer surfaces of the photoconductor drum  1  and the developing roller  7 , by using a measuring device  52 . 
   Further, by closing the openings  54  and  55 , the process cartridge  92  can suppress the entry of dirt and dust into the interior thereof. Thus, the process cartridge  92  can reduce the time for a cleaning step as generally performed in the manufacturing process thereof. 
   As a result, for example, setting of clean rooms may become unnecessary in the manufacturing facilities. Thus, the time and cost for dust protection in the manufacturing facilities can be reduced, resulting in a reduction of the manufacturing cost of the process cartridge  92 . 
   Next, a process cartridge  93  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 21 and 22 . 
   The process cartridge  93  has substantially identical configurations to the process cartridge  91  as illustrated in  FIGS. 17 and 18 . The identical components or members are represented by identical numeral and letter codes to  FIGS. 17 and 18 , and repeated descriptions thereof are omitted. 
   The process cartridge  93  includes a sealing member  72 , such as a seal or a cover, for sealing opening portions of the drum unit  5  and the developing unit  10 . The sealing member  72  is disposed within a through space  49 . When the process cartridge  93  is folded, the sealing member  72  can be relatively simply attached to and detached from the process cartridge  93  by an operation from the outside thereof. 
   In an exemplary embodiment of the invention, the process cartridge  93  includes the sealing member  72  as a member that is disposed within the through space  49 . However, the member disposed within the through space  49  is not limited to the sealing member  72 , and may be other members or components. 
   As illustrated in  FIGS. 21 and 22 , the sealing member  72  has a size capable of going through an opening  50 . The sealing member  72  is partially or wholly disposed within the through space  49  in the process cartridge  93 . Light  53 , which is irradiated from an irradiation aperture  52   a , is partially or wholly shielded by the sealing member  72 . Therefore, a process gap PG between outer surfaces of a photoconductor drum  1  and a developing roller  7  might not be properly measured. 
   Hence, according to an exemplary embodiment of the present invention, the sealing member  72  is provided with engaging holes  16 , while the developing unit  10  is provided with protrusions  15 . The protrusions  15  are inserted into the corresponding engaging holes  16 . 
   Each of the protrusions  15  has a groove  15   a . Stoppers  17 , such as molded E-shape rings, are engaged with the corresponding grooves  15   a  in a direction indicated by an arrow W in  FIG. 22 . 
   Thus, the movement of the sealing member  72  can be regulated, and the stoppers  17  can be detached from the groove  15   a  by hand or tool. 
   When detaching the sealing member  72 , first, the stoppers  17  are disengaged from the grooves  15   a  by hand or tool. At this time, an operator can perform the disengaging operation from the outside of the process cartridge  93 . 
   Then the sealing member  72  is pulled out from the protrusions  15  and is taken out of the process cartridge  60  via the opening  50 . Thereby the object shielding the light  53  is taken out of the through space  49 . Thus, the process gap PG can be measured by a measuring device  52 . 
   When the sealing member  72  remains within the through space  49 , an operator may need some effort for a check, replacement, or positional adjustment operation of the sealing member  72 . Hence, according to an exemplary embodiment of the present invention, the protrusions  15  are provided on the developing unit  10 , while the engaging holes  16  are formed on the sealing member  72 . 
   Further, the stoppers  17  are configured to be engageable with and disengageable from the grooves  15   a  of the protrusions  15 . Thus, the process cartridge  93  can facilitate replacement and adjustment operations of the sealing member  72 . 
   Thus, even if the sealing member  72  is provided within the through space  49 , the sealing member  72  can be removed from the through space  49  and the processing gap PG can be optically measured by the measuring device  52 . 
   Further, a measurement operation of the process gap PG on a manufacturing line can be facilitated, which may result in a more effective quality assurance of the process cartridge  93 . Furthermore, even if a failure occurs in the process cartridge  93  on the manufacturing line, the failure may be analyzed without disassembling the process cartridge  93 . 
   The process cartridge  93  according to an exemplary embodiment of the present invention may further include transparent boards  54  and  55  as described in the process cartridge  92 . 
   Next, a process cartridge  94  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 23 and 24 . 
     FIG. 23  is a sectional view illustrating a folded state of the process cartridge  94 . 
     FIG. 24  is a perspective view illustrating a folded state of the process cartridge  94  of  FIG. 23 . 
   The process cartridge  94  has substantially identical configurations to the process cartridge  91  of  FIGS. 17 and 18 . The identical components or members are represented by identical numeral and letter codes of  FIGS. 17 and 18 , and repeated descriptions thereof are omitted. 
   As illustrated in  FIG. 23 , a sealing member  72  has a size capable of going through an opening  50 . The sealing member  72  is partially or wholly disposed within the through space  49  in the process cartridge  94 . The position of the sealing member  72  is regulated by stoppers  26  with respect to a direction, as indicated by an arrow “a”, from the opening  50  toward the through space  49 . The stoppers  26  are provided on the developer unit  10 . 
   As illustrated in  FIG. 23 , the sealing member  72  is mounted on an upper surface of the developing unit  10 . In such a configuration, light  53 , which is irradiated from an irradiation aperture  52   a , is partially or wholly shielded by the sealing member  72 . Therefore, a process gap PG between outer surfaces of a photoconductor drum  1  and a developing roller  7  might not be properly measured. 
   Hence, according to an exemplary embodiment of the present invention, elongate holes  75  are formed at lateral sides of a top board  71  of the developing unit  10 . Levers  76  are disposed so as to pass through the corresponding elongate holes  75 . Each lever  76  is fitted with the upper board  71  by a shaft  77  at a mid point thereof. Thus each lever  76  is configured so as to be swingable around the shaft  77 . 
   From the lower end of each lever  76 , a lever shaft  76 L extends in a direction substantially perpendicular to a side wall of the developing unit  10 . 
   As illustrated in  FIG. 24 , the side wall of the developing unit  10  has an elongate hole  78 . Similarly the opposite side wall has another elongate hole  78 . 
   Each elongate hole  78  is formed in an arc shape around the shaft  77 . From the elongate hole  78 , one end of each lever shaft  76 L extends toward the outside of the process cartridge  94 . Thus an operator can operate the end of each lever shaft  76 L. 
   An upper portion of each lever  76  is formed in an L shape. The end of the upper portion is configured as a hook portion  76   a . The sealing member  72  has recesses  72   a  for engaging with the hook portions  76   a . As described above, each lever  76  is configured so as to be swingable around the shaft  77 . 
   When each lever shaft  76 L is positioned at a rear end of the elongate hole  78 , the hook portion  76   a  is detached from the recess  72   a . On the other hand, when the lever shaft  76 L is positioned at a front end of the elongate hole  78 , the hook portion  76   a  is inserted into the recess  72   a  to fix the sealing member  72 . Each lever shaft  76 L is releasably held by a holding member (not illustrated) at respective positions in the front and rear ends of the elongate hole  78 . 
   As described above, for example, when each lever  76  swings in a direction indicated by an arrow “b” in  FIG. 24 , the hook portion  76   a  thereof is inserted into the recess  72   a  of the sealing member  72 , thereby stopping the swinging of the lever  76 . Thus the sealing member  72  is fixedly pressed against each stopper  26 . At this time, if the recess  72   a  and the hook portion  76   a  are firmly engaged with each other, the lever  76  and the sealing member  72  can be held together in a fixed state. 
   When the lever  76  and the sealing member  72  are fixed each other, the fixed state can be released by applying an external force to the lever  76  in a direction indicated by an arrow “c” in  FIG. 23 . 
   The sealing member  72  is moved toward the opening  50  by further rotating the lever  76  in the direction indicated by the arrow “c”. Then the sealing member  72  can be taken from the process cartridge  94  to the outside. 
   Thus, even when the process cartridge  94  remains folded, attaching and detaching operations of the sealing member  72  can be effectively performed. Similarly, when the process cartridge  94  is unfolded, the attaching and detaching operations of the sealing member  72  can also be facilitated. 
   By removing the sealing member  72  as described above, the object shielding the light  53  is removed from the through space  49 . Thus the processing gap PG can be measured by a measuring device  52 . 
   Therefore, according to the present example embodiment, even if the sealing member  72  is disposed within the through space  49 , the sealing member  72  can be taken out of the process cartridge  94  by an operation from the outside thereof. Thus, the process cartridge  94  can optically measure the processing gap PG by the measuring device  52 . 
   Next, a process cartridge  95  according to another exemplary embodiment of the present invention is described with reference to  FIGS. 25 to 27 . 
     FIG. 25  is a sectional view illustrating a folded state of the process cartridge  95 . 
     FIG. 26  is a perspective view illustrating a folded state of the process cartridge  95  of  FIG. 25 . 
     FIG. 27  is a sectional view illustrating a unfolded state of the process cartridge  95 . 
   The process cartridge  95  has substantially identical configurations to the process cartridge  91  of  FIGS. 17 and 18 . The identical components or members are represented by identical numeral and letter codes to  FIGS. 17 and 18 , and repeated descriptions thereof are omitted. 
   As illustrated in  FIG. 26 , a drum unit  5  is provided with bearings  82  at side surfaces thereof. The bearings  82  hold a photoconductor drum  1  in the drum unit  5 . Thereby, the photoconductor drum  1  is smoothly rotatable. 
   A developing unit  10  is provided with bearings  83  at side surfaces thereof. The bearings  83  hold a developing roller  7  in the developing unit  10 . Thereby the developing roller  7  is smoothly rotatable in the developing unit  10 . 
   Thus, similar to the process cartridges  91  to  94  according to the above-described example embodiments, the process cartridge  95  can suppress an accidental drop or unintentional positional shift of the photoconductor drum  1  and the developing roller  7  during a pivoting operation of the drum unit  5  and the developing unit  10 . 
   When the process cartridge  95  is mounted on an image forming apparatus, the process cartridge  95  is folded as illustrated in  FIGS. 25 and 26 . Thus, the photoconductor drum  1  and the developing roller  7  are operably positioned. After the process cartridge  95  is withdrawn from the image forming apparatus for component replacement, the process cartridge  95  is unfolded as illustrated in  FIG. 27 . Thus, the photoconductor drum  1  and the developing roller  7  are positioned away from each other so as to be suitable for component replacement. 
     FIG. 27  is a sectional view illustrating a folded state of the process cartridge  95 . In the unfolded state as illustrated in  FIG. 25 , a sealing member  72  is partially or wholly positioned within a through space  49 . The sealing member  72  is provided with engaging holes  96 . The developing unit  10  is provided with a top board  71  having protrusions  97 . 
   The protrusions  97  are inserted into the corresponding engaging holes  96 . Further, stoppers  19 , such as molded E-shape rings, are engaged into grooves, which are formed on the protrusions  97  to fix the sealing member  72 . The stoppers  19  can be disengaged from the grooves by hand or tool. 
   After the sealing member  72  is taken out of the process cartridge  95 , the process cartridge  95  is unfolded as illustrated in  FIG. 27 . The stoppers  19  are disengaged from the protrusions  97  by hand or tool from the outside of the process cartridge  95 . Then the sealing member  72  is pulled out of the protrusions  97 . Thus, the sealing member  72  can be taken out of the process cartridge  95 . 
   After the detachment of the sealing member  72 , the process cartridge  95  is folded as illustrated in  FIG. 25 . At this time, the sealing member  72  has been removed from the through space  49 . Therefore a process gap PG, which is a distance between outer surfaces of a photoconductor drum  1  and a developing roller  7 , can be measured by a measuring device  52  as described in the above exemplary embodiments. 
   According to an exemplary embodiment of the present invention, the process cartridge  95  is foldably and unfoldably configured by pivoting the drum unit  5  and the developing unit  10  relative to each other around a common shaft. Therefore the process cartridge  95  is switchable between the folded and unfolded states. 
   In the unfolded state as illustrated in  FIG. 27 , the sealing member  72  can be attached to and detached from the through space  49 . Further operations such as check, positional adjustment, and component replacement can be performed for the sealing member  72  in the through space  49 . 
   Thus components, such as the drum unit  5  and the developing unit  10 , which are conventionally discarded as a whole after use, can be repeatedly reused. Therefore the manufacturing cost and the environmental load of the process cartridge  95  can be reduced. 
   Next, an image forming apparatus  100  according to an exemplary embodiment of the present invention is described with reference to  FIG. 28 . 
   For example, the above-described process cartridge  60  can be mounted on the image forming apparatus  100  as illustrated in  FIG. 28 . In an exemplary embodiment of the present invention, only the process cartridge  60  is described as a process cartridge used in the image forming apparatus  100 . However, any of the other process cartridges  61  to  64 ,  70 ,  80 ,  91  to  95  as described above can be used in the image forming apparatus  100 . 
   As illustrated in  FIG. 28 , the image forming apparatus  100  is provided with an image scanner  370  at the uppermost portion thereof. Under the image scanner  370  are disposed in turn an internal output tray  360 , a fixing device  330 , an image forming section including any of the process cartridge  60 , a sheet feeder  361  including a sheet tray for storing sheet media S. 
   The process cartridge  60  is detachably mounted on the image forming apparatus  100 . Under the process cartridge  60  is disposed an optical writing device  290 . The charger  3  charges the surface of the photoconductor drum  1 . The optical writing device  290  irradiates a light beam on the charged surface of the photoconductor drum  1  so that a desired image is appropriately formed on a sheet medium S. Thus, an electrostatically latent image is carried on the surface of the photoconductor drum  1 . 
   The latent image is visualized with developer including toner while passing through a nip between the photoconductor drum  1  and the developing roller  7 . The visualized toner image on the photoconductor drum  1  is transferred on the sheet medium S. The sheet medium S is conveyed along a conveyance path, which is indicated by a dashed line starting from the sheet feeder  361 . 
   After the transfer process, the sheet medium S is conveyed to the fixing device  330  along the conveyance path by the rotation of conveying rollers. The toner image on the sheet medium S is fixed while passing through a nip region of the fixing device  330 . 
   After the sheet medium S exits the fixing device  330 , the conveyance path of the sheet medium S is branched into two paths by a branching mechanism. 
   For the one path, the sheet medium S is inversely conveyed, and is ejected from a pair of ejecting rollers  350  to the internal output tray  360 . 
   For the other path, the sheet medium S is conveyed through a pair of ejecting rollers  380  to a post-processing device (not illustrated). 
   As described above, the image forming apparatus  100  is provided with the process cartridge  60  including the photoconductor drum  1  and the developing roller  7 . The process cartridge  60  is detachably mounted on the image forming apparatus  100 . The developing roller  7  visualizes an electrostatic latent image formed on the photoconductor drum  1  with developer including toner. The visualized toner image is transferred and fixed on a sheet medium S to obtain an desired image. 
   Use of the process cartridge  60  for the image forming apparatus  100  can facilitate maintenance and inspecting operations of components of the process cartridge  60 . 
   Next, a process cartridge  96  according to another exemplary embodiment of the present invention is described with reference to  FIG. 29 . The process cartridge  96  is configured to be disassembled and reassembled. 
     FIG. 29  is a sectional view illustrating an assembled state of the process cartridge  96 . The process cartridge  96  includes a drum unit  5 ′ as a first unit and a developing unit  10 ′ as a second unit. The drum unit  5 ′ and the developing unit  10 ′ also includes a photoconductor drum  1 ′ and a developing roller  7 ′, respectively. 
     FIG. 29  illustrates an assembled state of the process cartridge  96  where the drum unit  5 ′ and the developing unit  10 ′ are assembled together to integrally form the process cartridge  96 . 
   In the process cartridge  96 , two sets of the drum units  5 ′ and the developing units  10 ′ are arranged along a longitudinal direction of the photoconductor drum  1 ′. The drum unit  5 ′ and the developing unit  10 ′ are configured to be disassembled and assembled. In the assembled state as illustrated in  FIG. 29 , a through space  49 ′ is formed so as to pass through between the drum unit  5 ′ and the developing unit  10 ′. The through space  49 ′ is substantially identical in configuration and function with the through space  49  as described above with reference to  FIG. 17 . 
   When the process cartridge  96  is disassembled, the drum unit  5 ′ and the developing unit  10 ′ can be separated from each other unlike the drum unit  5  and the developing unit  10  as illustrated in  FIG. 3 . The process cartridge  96  does not include support members, such as the support members  5   a  and  10   a  of  FIG. 17 , for foldably and unfoldably coupling the drum unit  5 ′ and the developing unit  10 ′. Therefore in the disassembled state, the drum unit  5 ′ and the developing unit  10 ′ are separated from each other unlike the above-described exemplary embodiments. 
   For the disassembled state, for example, if the process cartridge  96  is configured so that the drum unit  5 ′ is disposed on the developing unit  10 ′, an upper portion of the drum unit  5 ′ is open to the outside of the process cartridge  96 . Such a configuration can facilitate replacement and maintenance operations of the photoconductor drum  1 ′. 
   Alternatively, if the process cartridge  96  is configured so that an upper portion of the developing unit  10 ′ is open to the outside of the process cartridge  96 . Such a configuration can facilitate replacement and maintenance operations of a developer transporter  8 ′ and a toner supplying agitator  9 ′. 
   In an exemplary embodiment of the present invention, an engaging member or a fastening member, such as a screw, may be used for positioning the drum unit  5 ′ and the developing unit  10 ′ at the assembly thereof. An interface line  40 ′ of  FIG. 29  represents an interface formed between the drum unit  5 ′ and the developing unit  10 ′ after the assembly thereof. 
   As illustrated in  FIG. 29 , the drum unit  5 ′ includes a photoconductor cleaner  2 ′, a charger  3 ′, and a waste toner container  4 ′ besides the photoconductor drum  1 ′. The developing unit  10 ′ includes the developer transporter  8 ′ and the toner supplying agitator  9 ′ besides the developing roller  7 ′. 
   A central axis O′ of the photoconductor drum  1 ′ is disposed in parallel with a central axis O 7 ′ of the developing roller  7 ′. When the process cartridge  96  is assembled and folded, the through space  49 ′ is formed along a normal line direction of a virtual plane h 1 ′-h 1  including both the central axes O′ and O 7 ′. The through space  49 ′ also passes through between the drum unit  5 ′ and the developing unit  10 ′ so as to include a processing gap PG′. The processing gap PG′ is a distance between the outer surfaces of the photoconductor drum  1  and the developing roller  7 . 
   The process cartridge  96  is provided with openings  50 ′ and  51 ′ on side portions of the drum unit  5 ′. The through space  49 ′ passes through the process cartridge  96  via the openings  50 ′ and  51 ′. 
   When measuring the processing gap PG′, a measuring device  52  is positioned outside the process cartridge  96 , which is in the assembled state. The measuring device  52  includes an irradiation aperture  52   a  from which light is irradiated for measuring the processing gap PG. The measuring device  52  also includes a sensor  52   b  for receiving the light irradiated from the irradiation aperture  52   a.    
   The irradiation aperture  52   a  is positioned outside the opening  50 ′, while the sensor  52   b  is positioned outside the opening  51 ′. The irradiation aperture  52   a  faces the sensor  52   b  via the through space  49 ′. Light  53 , which is irradiated from the irradiation aperture  52   a , sequentially goes through the opening  50 ′, the processing gap PG′, and the opening  51 ′. Then the sensor  52   b  detects the light  53  and determines the width of the processing gap PG′. 
   Currently, many image forming sections of image forming apparatuses are integrally configured as compact-size process cartridges to facilitate maintenance and replacement operations thereof. In such a process cartridge, the width of the processing gap PG′ between outer surfaces of a photoconductor drum and a developing roller has some effect on the quality of an image formed on a recording medium. Therefore the processing gap PG′ is preferably adjustable to obtain a desired image quality. 
   However, a conventional process cartridge may need to be disassembled in order to remeasure the width of the processing gap PG′ after the assembly thereof. 
   Alternatively, for another conventional process cartridge, the processing gap PG′ is measured by detecting a pressure applied from a contact terminal. In this case, a photoconductor drum may be replaced with a specialized drum for measurement. Therefore, such a conventional process cartridge may need some time and effort in the measurement of the processing gap PG′. Additionally, the processing gap PG′ is not measured for the photoconductor drum actually used in an image forming apparatus. 
   Hence, according to an example embodiment of the present invention, the measuring device  52  measures the processing gap PG′ by transmitting the light  53  after the assembly of the process cartridge  96 . As described above, the process cartridge  96  is provided with the through space  49 ′ including the processing gap PG′. The through space  49 ′ passes through between the drum unit  5 ′ and the developing unit  10 ′ along the normal line direction of the virtual plane h 1 ′-h 1 ′, which includes the central axis O′ of the photoconductor drum  1 ′ and the central axis O 7 ′ of the developing roller  7 ′. 
   The measuring device  52  transmits the light  53  from the outside of the through space  49 , and therefore the processing gap PG′ can be measured without disassembling the process cartridge  91 . 
   Thus, the measurement of the processing gap PG′ on a manufacturing line can be facilitated, resulting in more effective quality assurance. Further, even if a failure occurs in the process cartridge  96  on the manufacturing line, the failure may be analyzed without disassembling the process cartridge  96 . In particular, such a configuration of the process cartridge  96 , in which two independent units are assembled together, is advantageous in that disassembly and assembly operations are not necessarily needed for the measurement of the processing gap PG′ or the failure analysis as described above. 
   For example, for the process cartridge  91  as illustrated in  FIG. 7 , the drum unit  5  and the developing unit  10  are coupled with each other. On the other hand, for the process cartridge  96  as illustrated in  FIG. 29 , the drum unit  5 ′ and the developing unit  10 ′ are not coupled with each other. The two units are assembled to integrally form the process cartridge  96 . 
   The process cartridge  91  and the process cartridge  96  are different in whether or not the two units are coupled, while are substantially identical in the configuration of the through space. 
   Any one configuration of the process cartridges  92  to  94  may be applied to the process cartridge  96  as illustrated in  FIG. 29 . 
   For example, in accordance with the process cartridge  92 , the process cartridge  96  may include transparent boards  54  and  55 , which are disposed so as to close openings of the through space  49 ′. Further, transparent boards  54  and  55  may be supported by an outer frame of the process cartridge  96 . 
   Alternatively, in accordance with the process cartridge  93  or  94 , a component, which is supported on the process cartridge  96 , may be disposed within the through space  49 ′ so as to be attachable to and detachable from the process cartridge  96 . 
   For example, the sealing member  72  may be disposed within the through space  49 ′. Further, a lever  76  and other associated members may be used for the process cartridge  96 . Thereby the sealing member  72  can be attached to and detached from the process cartridge  96  by an operation from the outside of the process cartridge  96 . 
   Moreover any one configuration of the other process cartridges  60  to  64 ,  70 ,  80 ,  90 ,  91 ,  95  as described above is applicable to the process cartridge  96  as illustrated in  FIG. 29 . 
   Furthermore, as illustrated in  FIG. 30 , the process cartridge  96  of  FIG. 29  can be mounted on the image forming apparatus  100  as described with reference to  FIG. 28 . In  FIG. 30 , components and members, which are identical in configurations and functions, are represented by identical numeral and letter codes with  FIG. 28  or  FIG. 29 . Therefore, repeated descriptions are omitted. 
   Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.