Abstract:
A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus includes an electrophotographic photosensitive drum; a charging roller for electrically charging the electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum; an input electrode extended along a longitudinal direction of the developing roller; an output electrode extended along a longitudinal direction of the developing roller; a grounding contact for electrically grounding the photosensitive drum to a main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the grounding contact being exposed at an end surface of a cartridge frame provided at one longitudinal end of the photosensitive drum and being disposed across an axis of the photosensitive drum; a charging bias contact for receiving a charging bias voltage to be applied to the charging roller from the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the charging bias contact being exposed and facing downwardly adjacent one longitudinal end of the photosensitive drum when the cartridge is mounted to the main assembly of the apparatus; a developing bias contact for receiving a developing bias to be applied to the developing roller from the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the developing bias contact being exposed and facing downwardly adjacent one longitudinal end of the photosensitive drum when the cartridge is mounted to the main assembly of the apparatus, and the developing bias contact being disposed at a side opposite from the charging bias contact with the photosensitive drum interposed therebetween with respect to a direction crossing a longitudinal direction of the photosensitive drum; an input electrical contact for receiving an input bias to be applied to the input electrode from the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the input electrical contact being exposed at an end surface of a cartridge frame provided adjacent a longitudinal end of the photosensitive drum; and an output contact for transmitting, to the main assembly of apparatus, an output produced on the basis of a value corresponding to an electrostatic capacity between the input electrode and the output electrode and an electrostatic capacity between the developing roller and the output electrode to detect substantially real time a remaining amount of the developer in the cartridge by the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the output contact being exposed at an end surface of a cartridge frame provided adjacent a longitudinal end of the photosensitive drum.

Description:
FIELD OF THE INVENTION AND RELATED ART  
         [0001]    The present invention relates to a process cartridge and an electrophotographic image forming apparatus.  
           [0002]    An electrophotographic image forming apparatus means an apparatus which forms an image on recording medium with the use of an electrophotographic image formation method. As for the examples of an electrophotographic image forming apparatus, an electrophotographic copying machine, an electrophotographic printer (laser beam printer, LED printer, or the like), a facsimile machine, a word processor, or the like, are included.  
           [0003]    A process cartridge means a cartridge in which a charging means, a developing means or cleaning means, and an electrophotographic photoconductive drum, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. It also means a cartridge in which at least one means among a charging means, a developing means, and a cleaning means, and an electrophotographic photoconductive drum, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus, or a cartridge in which a minimum of a developing means, and an electrophotographic photoconductive member, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus.  
           [0004]    An electrophotographic image forming apparatus, which employs an electrophotographic image formation process, also employs a process cartridge system, in which an electrophotographic photoconductive member, and a single, or a plurality of, processing means, which act on the electrophotographic photoconductive drum, are integrally disposed in a cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus. This system enables a user to maintain the apparatus without relying on service personnel, drastically improving operational efficiency. Thus, a process cartridge system is widely in use in the field of an electrophotographic image forming apparatus.  
           [0005]    In the case of an electrophotographic image forming apparatus employing a process cartridge system, a user him/herself replaces a cartridge. Therefore, some of the electrophotographic image forming apparatuses are equipped with a developer amount detecting means for informing the user of the remaining amount of the developer. As for a developer amount detecting means, there is a method in which a plurality of electrodes are disposed within a process cartridge, and the changes in the electrostatic capacity among the electrodes is detected to estimate the remaining amount of the developer.  
           [0006]    According to a process cartridge system, as a cartridge is inserted into the apparatus main assembly, electrical connection must be established between the cartridge and apparatus main assembly. Therefore, a cartridge is provided with electrical contacts (for example, U.S. Pat. No. 6,272,299).  
           [0007]    According to U.S. Pat. No. 6,272,299, the electrical contacts are optimally positioned to reduce in size a process cartridge and an electrophotographic image forming apparatus.  
           [0008]    The present invention is a result of the further development of the aforementioned prior arts regarding the positioning of the electrical contacts of a process cartridge and an electrophotographic image forming apparatus.  
         SUMMARY OF THE INVENTION  
         [0009]    The primary object of the present invention is to provide a smaller process cartridge which contains input and output electrical contacts which make it possible for the remaining amount of the developer to be continually detected by the image forming apparatus main assembly side, and an electrophotographic image forming apparatus in which such a process cartridge can be removably mounted.  
           [0010]    Another object of the present invention is to provide a smaller process cartridge, which contains input and output electrical contacts which make it possible for the remaining amount of the developer to be continually detected by the image forming apparatus main assembly side, and in which the input and output electrical contacts are positioned at one of the lengthwise ends of the process cartridge to improve the accuracy with which the remaining amount of the developer is detected by the image forming apparatus main assembly side, and an electrophotographic image forming apparatus in which such a process cartridge can be removably mounted.  
           [0011]    Another object of the present invention is to provide a smaller process cartridge, the size of which is realized by optimally positioning the electrical contacts, inclusive of both input and output electrical contacts, and an electrophotographic image forming apparatus in which such a process cartridge can be removably mountable.  
           [0012]    Another object of the present invention is to provide a process cartridge in which various electrodes thereof are disposed at one end of the process cartridge in terms of the lengthwise direction of the electrophotographic photoconductive member to make it possible to reduce the size of the high voltage circuit on the image forming apparatus main assembly side, and an electrophotographic image forming apparatus in which such a process cartridge can be removably mounted.  
           [0013]    According to an aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus comprising an electrophotographic photosensitive drum; a charging roller for electrically charging the electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum; an input electrode extended along a longitudinal direction of the developing roller; an output electrode extended along a longitudinal direction of the developing roller; a grounding contact for electrically grounding the photosensitive drum to a main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the grounding contact being exposed at an end surface of a cartridge frame provided at one longitudinal end of the photosensitive drum and being disposed across an axis of the photosensitive drum; a charging bias contact for receiving a charging bias voltage to be applied to the charging roller from the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the charging bias contact being exposed and facing downwardly adjacent one longitudinal end of the photosensitive drum when the cartridge is mounted to the main assembly of the apparatus; a developing bias contact for receiving a developing bias to be applied to the developing roller from the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the developing bias contact being exposed, and facing downwardly adjacent one longitudinal end of the photosensitive drum when the cartridge is mounted to the main assembly of the apparatus, and the developing bias contact being disposed at a side opposite from the charging bias contact with the photosensitive drum interposed therebetween with respect to a direction crossing a longitudinal direction of the photosensitive drum; an input electrical contact for receiving an input bias to be applied to the input electrode from the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the input electrical contact being exposed at an end surface of a cartridge frame provided adjacent a longitudinal end of the photosensitive drum; and an output contact for transmitting, to the main assembly of apparatus, an output produced on the basis of a value corresponding to an electrostatic capacity between the input electrode and the output electrode and an electrostatic capacity between the developing roller and the output electrode to detect substantially real time a remaining amount of the developer in the cartridge by the main assembly of the apparatus when the cartridge is mounted to the main assembly of the apparatus, the output contact being exposed at an end surface of a cartridge frame provided adjacent a longitudinal end of the photosensitive drum.  
           [0014]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic sectional view of an electrophotographic image forming apparatus in an embodiment of the present invention.  
         [0016]    [0016]FIG. 2 is a sectional view of the process cartridge in the embodiment of the present invention.  
         [0017]    [0017]FIG. 3 is a perspective view of the top portion of the image forming apparatus in the embodiment of the present invention, the cover of which is open.  
         [0018]    [0018]FIG. 4 is a perspective view of the cleaning unit in the embodiment of the present invention, as seen from below.  
         [0019]    [0019]FIG. 5 is a sectional view of the grounding electrical contact of the photoconductive drum in the embodiment of the present invention, for showing the structure thereof.  
         [0020]    [0020]FIG. 6 is a sectional view of the charge bias electrical contact in the embodiment of the present invention, for showing the structure thereof.  
         [0021]    [0021]FIG. 7 is a diagram of the developer amount detection circuit in the embodiment of the present invention.  
         [0022]    [0022]FIG. 8 is a partially exploded perspective view of the developing means holding frame in the embodiment of the present invention, for showing how the first and third electrodes are attached to the developing means holding frame.  
         [0023]    [0023]FIG. 9 is a partially exploded perspective view of the developing means holding frame in the embodiment of the present invention, for showing how the second electrode is attached to the developing means holding frame.  
         [0024]    [0024]FIG. 10 is a perspective view of the developing holding frame and developer container in the embodiment of the present invention, for showing how the developing means holding frame and developer container are joined with each other after the attachment of the first to third electrodes to the developing means holding frame.  
         [0025]    [0025]FIG. 11 is a side view of the process cartridge B, for showing the positioning of the external electrical contacts.  
         [0026]    [0026]FIG. 12 is a perspective view of the process cartridge B as seen from below. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    (Embodiment 1)  
         [0028]    (General Description of Image Forming Apparatus)  
         [0029]    First, an example of an electrophotographic image forming apparatus in which a process cartridge in accordance with the present invention is removably mountable will be described. FIG. 1 is a sectional view of the electrophotographic image forming apparatus A in this embodiment of the present invention, and FIG. 2 is a sectional view of the process cartridge B in this embodiment.  
         [0030]    The image forming apparatus A has an electrophotographic photoconductive drum  7  (which hereinafter will be referred to as photoconductive drum). The photoconductive drum  7  is charged by a charge roller  8  as a charging means, and is exposed to a beam of laser light emitted, while being modulated with the image formation information, from an optical means  1  comprising a laser diode, a polygon mirror, a lens, a deflection mirror, and the like. As a result, an electrostatic latent image in accordance with the image formation information, is formed on the peripheral surface of the photoconductive drum  7 . This latent image is developed into a developer image, or a visible image, by a developing means.  
         [0031]    The developing means comprises a development roller  12  as a developer bearing member for delivering developer to the photoconductive drum  7 , and a development blade  18  as a regulating member for regulating the amount by which developer is adhered to the peripheral surface of the development roller  12 . The developing means also comprises a developing means holding frame  13  for holding the development roller  12  and development blade  18 , and a developer holding frame  11  for holding developer. The developing means holding frame  13  in which the development roller  12  and development blade  18  are held, and the developer holding frame  11  in which developer is held, are joined to form a development unit  20  or a developing apparatus.  
         [0032]    The developing means holding frame  13  has a development chamber  13   a . The developer held in the developer holding portion  14  adjoining the development chamber  13   a  is conveyed toward the development roller  12  in the development chamber  13   a , by the rotation of a developer conveying member  15 . The developing means holding frame  13  is provided with a developer stirring member  16 , which is disposed adjacent to the development roller  12  and is rotationally drivable. The developer stirring member  16  circulates the developer within the development chamber  13   a , after the developer is delivered from the developer holding portion  14 . The developer is magnetic, and the development roller  12  contains a stationary magnet  17 . Therefore, the developer adheres to the peripheral surface of the development roller  12 .  
         [0033]    As the development roller  12  is rotated, the developer is conveyed, while being given tribo-electrical charge by the development blade  18 . As a result, a developer layer with a predetermined thickness is formed on the peripheral surface of the development roller  12 , and is conveyed to the development region of the photoconductive drum  7 . In the development region, the developer is transferred onto the areas of the peripheral surface of the photoconductive drum  7 , correspondent to the latent image, forming a development image, on the peripheral surface of the photoconductive drum  7 . The development roller  12  is connected to a development bias circuit with which the main assembly of the image forming apparatus A is provided. Normally, development bias voltage, which is a combination of AC and DC voltages, is applied to the development roller  12 .  
         [0034]    Meanwhile, in synchronism with the formation of the aforementioned developer image, a recording medium  2 , which has been set in a sheet feeder cassette  3   a , is delivered to a transfer station by a pickup roller  3   b , and conveyer roller pairs  3   c ,  3   d , and  3   e . In the transfer station, a transfer roller  4  as a transferring means is disposed. As voltage is applied to the transfer roller  4 , the developer image on the photoconductive drum  7  is transferred onto the recording medium  2 .  
         [0035]    After receiving the developer image, the recording medium  2  is conveyed to a fixing means  5  by a conveyance guide  3   f . The fixing means  5  is provided with a driving roller  5   c , and a fixing roller  5   b  containing a heater  5   a . As the recording medium  2 , onto which the developer image has just been transferred, is passed through the fixing means  5 , heat and pressure are applied to the recording medium  2  and the developer image thereon, by the fixing means  5 . As a result, the developer image is fixed to the recording medium  2 .  
         [0036]    Thereafter, the recording medium  2  is further conveyed by discharge roller pairs  3   g  and  3   h , and then is discharged into a delivery tray  6  through an inverting path  3   j . The delivery tray  6  constitutes a part of the top surface of the image forming apparatus A. Incidentally, it is possible to pivot a pivotable flapper  3   k  to discharge the recording medium  2  without sending the recording medium  2  through the inverting path  3   j . In this embodiment, the aforementioned pickup roller  3   b , conveying roller pairs  3   c ,  3   d , and  3   e , conveyance guide  3   f , and discharge roller pairs  3   g  and  3   h , together make up a conveying means.  
         [0037]    After the transfer of the developer image onto the recording medium  2  by the transfer roller  4 , the developer particles remaining on the peripheral surface of the photoconductive drum  7  are removed by a cleaning means  9 , preparing the photoconductive drum  7  for the following rotational cycle for image formation. The cleaning means  9  is provided with an elastic cleaning blade  9   a , which is placed in contact with the peripheral surface of the photoconductive drum  7  to scrape down the developer particles remaining on the peripheral surface of the photoconductive drum  7 . The removed developer particles are collected into a removed developer bin  9   b.    
         [0038]    (Description of Process Cartridge)  
         [0039]    Referring to FIG. 2, the process cartridge B in this embodiment comprises the developing means holding frame  13  provided with a developing means, and the developer holding frame  11 . The developing means holding frame  13  and developer holding frame  11  are welded to each other, forming a development unit  20  (developing apparatus). The developer holding frame  11  comprises the developer holding portion  14 , and a developer outlet  47  through which the developer in the developer holding portion  14  is supplied to the developing means holding frame  13 . Within the developer holding portion  14 , a developer conveying member  15  is rotationally supported. The developer outlet  47  remains sealed with a developer seal  48  until the process cartridge B is used for the first time; in other words, when the process cartridge B is used for the first time, the developer seal  48  is pulled out by a user in order to enable the developer to be supplied to the developing means holding frame  13 . The developing means holding frame  13  holds the development roller  12  as a developing means, and the development blade  18 .  
         [0040]    The drum holding frame  21  holds the cleaning means  9  such as the cleaning blade  9   a  or the like, the photoconductive drum  7 , and the charge roller  8 , making up a cleaning unit  19 .  
         [0041]    The development unit  20  and cleaning unit  19  are integrally joined into the process cartridge B.  
         [0042]    Next, referring to FIG. 3, a method for mounting the process cartridge B into the image forming apparatus main assembly, or dismounting the process cartridge B from the image forming apparatus main assembly, will be described.  
         [0043]    [0043]FIG. 3 is a perspective view of the image forming apparatus A, the cover  35  of which is open. The image forming apparatus A is provided with the left and right guide rails  26 L and  26 R ( 26 R is not shown), which are on the internal surfaces of the left and right side walls, respectively, of the image forming apparatus A, being inclined downward in terms of the direction in which the process cartridge B is inserted. The image forming apparatus A is also provided with the left and right positioning grooves  26   b L and  26   b R ( 26   b R is not shown). These guide rails  26 L and  26 R and positioning guides  26   b L and  26   b R are exposed as the cover  35  is opened by being rotated about the hinge  35   a  (FIG. 1). In comparison, the process cartridge B is provided with the left and right cylindrical guides, the axial lines of which are in alignment with the axial line of the photoconductive drum  7 . It is also provided with the left and right positioning guides, which are long and narrow and are behind the cylindrical guides, one for one, in terms of the direction in which the process cartridge B is inserted into the apparatus main assembly. In order to mount the process cartridge B into the image forming apparatus A, first, the left and right cylindrical guides of the process cartridge B and the left and right positioning guides of the process cartridge B are inserted into the guide rails  26 L and  26 R, and then, the cylindrical guides are fitted into the corresponding positioning grooves  26   b L and  26   b R of the image forming apparatus main assembly A.  
         [0044]    On the contrary, in order to dismount the process cartridge B in the image forming apparatus main assembly A, the above described process cartridge mounting steps are carried out in reverse; the process cartridge B is pulled out following the guide rails  26 L and  26 R.  
         [0045]    (Description of Cleaning Unit)  
         [0046]    To the drum holding frame  21 , the photoconductive drum  7 , charge roller  8 , cleaning means, and the like, are integrally attached to make up the cleaning unit  19 .  
         [0047]    [0047]FIG. 4 is a perspective view of the cleaning unit  19  as seen from below. As is evident from the drawing, the drum holding frame  21  is provided with a plurality of electrical contacts in addition to the aforementioned various components. More specifically, it is provided with: (1) cylindrical guide  21   a L (which hereinafter will be designated by a referential code  40  when it is referred to as grounding contact) as a grounding contact connected to the photoconductive drum  7  to ground the photoconductive drum  7  through the image forming apparatus main assembly A; and (2) a charge bias contact  28  connected to the charge roller shaft for applying charge bias to the charge roller  8 .  
         [0048]    Referring to FIG. 5, the grounding contact  40  is an integral part of a flange  41  formed of electrically conductive substance. The flange  41  is also provided with a drum shaft  27 , which is also an integral part of the flange  41 , and the axial line of which is in alignment with the center of the grounding contact  40 . Further, the photoconductive drum  7  comprises a drum cylinder  7   a , and a grounding plate  7   b  in contact with drum cylinder  7   a . Thus, the photoconductive drum  7  is kept grounded by keeping a grounding plate  7   b  pressed directly upon the drum shaft  27 .  
         [0049]    Next, referring to FIG. 6, the charge bias electrical contact  28   a  is electrically in contact with the charge roller shaft  8   a  of the charge roller  8  through a compound spring  8   b  in contact with the charge roller shaft  8   a . This spring  8   b  comprises a coil spring portion  8   b   1  and a straight wire spring portion  8   b   2 . A charge bias electrical contact member  28  has the charge bias electrical contact  28   a  and a spring seat  28   b . Thus, the charge bias received from the apparatus main assembly through the charge bias electrical contact  28   a  is applied to the charge roller  8  through the spring seat  28   b , coil spring portion  8   b   1 , and straight wire spring portion  8   b   2 . A charge roller bearing  8   c  is fitted in the guide groove  21   b  of the drum holding frame  21 . The charge bias electrical contact  28   a  is attached to the drum holding frame  21  in such a manner that it faces downward when the process cartridge B is in the image forming apparatus main assembly A.  
         [0050]    The above described two electrical contacts (grounding contact  40  and charge bias contact member  28 ) are disposed at the same end of the process cartridge B in terms of the lengthwise direction of the photoconductive drum  7 .  
         [0051]    (Description of Developer Amount Detecting Means)  
         [0052]    In this embodiment, the process cartridge B is provided with a developer amount detecting means which continually detects the remaining amount of the developer in the developer chamber  13   a  as the developer is consumed.  
         [0053]    Referring to FIG. 2, in this embodiment, the developing means holding frame  13  is provided with first, second, and third electrodes  81 ,  82 , and  83 , which constitute the measurement electrodes of the developer amount detecting means. These electrodes are disposed in parallel to the development roller  12 . More specifically, the first electrode  81  is disposed close, and in parallel, to the development roller  12 , and the third electrode  83  is attached to the bottom portion of the developing means holding frame  13 . The first and third electrodes  81  and  83  are connected to each other within the developing means holding frame  13 , being therefore equal in electrical potential level.  
         [0054]    The second electrode  82  is disposed closer to the developer holding frame  11  than the first electrode  81 , and is disposed in the upper portion of the developing means holding frame  13 , opposing the first electrode  81 . With the provision of this structural arrangement, as electrical voltage is applied to either the first electrode  81  or second electrode  82 , static electricity is induced between the electrodes, and the amount of this static electricity is measured by the detection circuit provided on the image forming apparatus main assembly A side to detect the amount of the developer remaining in the process cartridge B.  
         [0055]    More specifically, as developer enters between the electrodes, the electrostatic capacity between the electrodes changes. Thus, the amount of the developer between the electrodes can be detected by detecting the changes in this electrostatic capacity. In this embodiment, the second electrode  82  is used as the input electrode through which voltage is applied, and the first and third electrodes  81  and  83  are used as the output electrodes.  
         [0056]    The aforementioned first, second, and third electrodes  81 ,  82 , and  83  are disposed where the developer enters the developing means holding frame  13  after being conveyed toward the developing means holding frame  13  by the developer conveying member  15  in the developer holding frame  11 . When there is a substantial amount of developer in the process cartridge B, the developer is pushed into the space surrounded by the electrodes, by the developer conveying member  15 , and therefore, the value of the electrostatic capacity between the electrodes remains at a high level. As the use of the process cartridge B continues, the developer therein is continuously consumed, and the level of the developer between the electrodes gradually falls, reducing accordingly the electrostatic capacity between the electrodes. Thus, the remaining amount of the developer can be continually detected based on the reduction in the electrostatic capacity between the electrodes.  
         [0057]    In this embodiment, the development bias applied to the development roller  12  is used as the input voltage, and the electrostatic capacity between the development roller  12  and first electrode  81  is detected to detect the state in which there remains no developer in the process cartridge B. In other words, the detecting means is enabled to continually detect the amount of the developer by detecting the changes in the electrostatic capacity.  
         [0058]    (Description of Detection Circuit)  
         [0059]    [0059]FIG. 7 is a diagram of an example of the developer amount detection circuit in the image forming apparatus in this embodiment.  
         [0060]    The developer amount detection circuit  200  comprises a detecting portion  80 , a development bias circuit  201 , a control circuit  202 , and an amplification circuit  204 . The detecting portion  80  is made up of the aforementioned first, second, and third electrodes  81 ,  82 , and  83 , and the development roller  12 . It induces the static electricity used for detecting the developer amount. This detecting portion  80  is on the process cartridge B side.  
         [0061]    In comparison, the development bias circuit  201 , control circuit  202 , and amplification circuit  204  are on the image forming apparatus main assembly A side.  
         [0062]    The process cartridge B is provided with a development bias electrical contact member  22 , which is electrically in contact with the development roller  12 , whereas the image forming apparatus main assembly A is provided with an electrical contact  103 , which is in contact with the development bias circuit  201 . As the process cartridge B is inserted into the image forming apparatus main assembly A, the development bias electrical contact  22   a  of the development bias electrical contact member  22  and the electrical contact  103  on the image forming apparatus main assembly A side, are placed electrically in contact with each other. To the development roller  12 , development bias is applied from the development bias circuit  201  of the image forming apparatus main assembly A through the electrical contact  103  and development bias electrical contact  22   a.    
         [0063]    Further, the process cartridge B is provided with an output electrical contact  23   a  and an input electrical contact  29   a , which constitute the electrical contacts through which electrical connection is made between the process cartridge B and the image forming apparatus A. These contacts  23   a  and  29   a  are located at one of the end walls of the process cartridge B in terms of the lengthwise direction of the process cartridge B, and come into contact with the electrical contacts  30  and  31  provided on the image forming apparatus A side, as the process cartridge B is mounted into the image forming apparatus main assembly A.  
         [0064]    The electrostatic capacity Ca of the detecting portion  80  is the combination of the electrostatic capacity between the second and first electrodes  82  and  81 , and the electrostatic capacity between the second and third electrodes  82  and  83 . It changes in response to the developer amount.  
         [0065]    Regarding the detecting portion  80 , the electrode, as an impedance element, on the input side, that is, the second electrode  82  in this embodiment, is connected, through the development bias electrical contact  22 , to the development bias circuit  201  and control circuit  202 , which make up the development bias applying means. In this embodiment, the second electrode  82  is the input electrode, and is connected to the development bias circuit  201  through the input electrical contact  29   a  and the electrical contact  30  of the image forming apparatus main assembly A. It is also connected to the control circuit  202  through the power routing member  36  of the image forming apparatus main assembly A.  
         [0066]    The other electrodes, or output electrodes, of the detecting portion  80 , that is, the first and third electrodes  81  and  83  in this embodiment, are connected to the control circuit  202  through the output electrical contact  23   a , and the electrical contact  31  of the apparatus main assembly, and also the power routing member  37  of the image forming apparatus main assembly A.  
         [0067]    The control circuit  202  is provided with a referential capacity element Cb, which is connected to the development bias circuit  202 , in the image forming apparatus main assembly A. The referential capacity element Cb uses the AC current I 1  supplied from the development bias circuit  201  to set up a referential voltage V 1  for detecting the developer amount. In the control circuit  202 , the AC current I 1  supplied to the referential capacity element Cb is divided by the volume VR 1 , creating AC current I 1 , which is used to set up the referential voltage V 1  by adding the amount V 2  by which voltage is reduced by a resistor R 2 , to the voltage V 3  set up by resistors R 3  and R 4 .  
         [0068]    The amplification circuit  204  is provided with a comparator for calculating voltage difference; the AC current I 2  applied to the detecting portion  80  is inputted into the amplification circuit  204 , and is outputted as the detected value V 4  (V 1 −I 2  R 5 ) of the developer amount. This output value is used as the detected value of the amount of the remaining developer. The information regarding the amount of the remaining developer detected as described above is reported to a user through a display (unshown) with which the image forming apparatus main assembly A is provided.  
         [0069]    In the case of the image forming apparatus in this embodiment, the remaining amount of the developer in the process cartridge B is continually detected, and the amount of the developer consumption can be displayed based on the information regarding the remaining amount of the developer. Therefore, it is possible to prompt a user to prepare a brand-new process cartridge. Further, it is possible to prompt a user to replace the process cartridge, based on the detected information that there is no developer in the process cartridge B in the image forming apparatus main assembly A.  
         [0070]    (Description of Structure for Electrode Attachment)  
         [0071]    Next, referring to FIGS. 8 and 9, the structure for attaching the first, second, and third electrodes  81 ,  82 , and  83  of the developer amount detecting means, to the developing apparatus structure. The developer amount detecting means comprising the first, second, and third electrodes  81 ,  82 , and  83  detects the developer amount by detecting the electrostatic capacity of the space between the first and second electrodes  81  and  82 , and the space between the third and second electrodes  83  and  82 . Therefore, the positional accuracy of each electrode is extremely important. Further, one of the objects of the developer amount detecting means is to accurately detect when the formation of an image with unintended white spots begins due to the depletion of the developer. Thus, each electrode should be disposed close to the development roller  12  which will be in contact with the developer until the developer is completely depleted. This is why the electrodes  81 ,  82 , and  83  in this embodiment are attached to the development frame, that is, developing means holding frame  13  as shown in FIGS. 8 and 9.  
         [0072]    (First and Third Electrodes)  
         [0073]    [0073]FIG. 8 is a perspective view of the developing means holding frame  13  for showing how the first and third electrodes  81  and  83  are attached to the developing means holding frame  13 . As shown in the drawing, the first electrode  81  is accurately positioned relative to the developing means holding frame  13  by the positioning bosses  13   c  on the electrode attachment surface  13   b  of the developing means holding frame  13 , and is pasted to the surface  13   b  with the use of two-sided tape. One of the lengthwise ends of the first electrode  81  is provided with an arm portion  81   a , and the end of the arm portion  81   a  is partially cut and bent upright, forming a portion  81   b , which fits into the groove  13   d  of the developing means holding frame  13 . Next to the groove  13   d  of the developing means holding frame  13 , a side hole  13   e  is provided, which extends from the inward side of the developing means holding frame  13  to the outward side of the developing means holding frame  13 , and the position of which corresponds to the hole  81   c  of the uprightly bent portion  81   b.    
         [0074]    The third electrode  83  is a piece of thin plate. The lengthwise ends of the third electrode  83  are provided with arm portions  83   a  and  83   b , one for one, which are virtually perpendicular to the main portion of the third electrode  83  between the two arm portions  83   a  and  83   b . The arm portions  83   a  and  83   b  are provided with positioning holes  83   e  and  83   f , respectively, into which the positioning bosses  13   k  fit, one for one. The end of the arm portion  83   a  is cut and bent upright, forming a portion  83   c , which is virtually perpendicular to the main section of the arm portion  83   a  and the main section of the third electrode  83 . This uprightly bent portion  83   c  of the arm portion  83   a  of the third electrode  83  is the same in shape as the uprightly bent portion  81   b  of the first electrode  81 . In order to attach the third electrode  83  to the developing means holding frame  13 , first, the positioning bosses  13   k  are put through the positioning holes  83   e  and  83   f  of the arm portion  83   a  and  83   b , one for one, placing the arm portions  83   a  and  83   b  in contact with the electrode attachment surfaces  13   i  and  13   j , respectively, and then, is secured with the use of screws.  
         [0075]    During the above process, the end portion of the arm portion  83   a  with the uprightly bent portion  83   c  fits into the groove  13   d  of the developing means holding frame  13 . The uprightly bent portion  83   c  is provided with a hole  83   d , which is positioned next, and in parallel, to the uprightly bent portion  81   b , as the third electrode  83  is attached to the developing means holding frame  13 .  
         [0076]    The side hole  13   e  of the developing means holding frame  13  is matched in shape and size to an elastic seal  24  to accommodate the elastic seal  24 , which is pressed into the side hole  13   e  from the outward side of the developing means holding frame  13 . After the insertion of the elastic seal  24  into the side hole  13   e , a U-shaped electrode  25  formed of a piece of cylindrical rod is inserted into the side hole  13   e , more precisely, the hole of the elastic seal  24 , of the developing means holding frame  13 , and then, the holes  81   c  and  83   d , within the developing means holding frame  13 . As a result, the first electrode  81 , third electrode  83 , and electrode  25 , become electrically connected.  
         [0077]    (Second Electrode)  
         [0078]    [0078]FIG. 9 is a drawing for showing how the second electrode is attached to the developing means holding frame  13 . As shown in FIG. 9, the second electrode  82  is formed of a piece of thin plate, and is virtually perpendicularly bent in terms of the direction perpendicular to the lengthwise direction of the process cartridge B. It has a pair of arm portions  82   a , which are located at its lengthwise ends, one for one. Each arm portion  82   a  of the second electrode  82  is provided with a positioning hole  82   b , in which the positioning boss  13   h  of the developing means holding frame  13  fits, and a screw hole  82   c.    
         [0079]    In order to attach the second electrode  82  to the developing means holding frame  13 , first, the bosses  13   h  of the developing means holding frame  13  are fitted into the corresponding positioning holes  82   b  of the second electrode  82  to accurately position the second electrode  82  relative to the developing means holding frame  13 , and then, a pair of small screws are screwed into the corresponding holes  13   q  with a female thread, through the corresponding screw holes  82   c , securing thereby the second electrode  82  to the developing means holding frame  13 . During this process, one of the small screws (screw on the front side in FIG. 9) is put through the screw hole  32   c  of a plate electrode  32  so that the plate electrode  32  is placed in contact with the second electrode  82  as it is secured to the developing means holding frame  13 . The plate electrode  32  provides the outward electrical connection for the second electrode  82 . In order to prevent the presence of the second electrode  82  from interfering with the process for attaching the first electrode  81 , it is desired that the second electrode  82  is attached after the attachment of the first electrode  81 .  
         [0080]    Thereafter, a holder  90 , which rotationally supports the development roller  12  with the interposition of a bearing, is attached to one of the lengthwise end of the developing means holding frame  13  as shown in FIG. 9 (development roller  12  is placed in the holder  90  after the joining of the developing means holding frame  13  and developer holding frame  11  by ultrasonic welding, which will be described later). To this holder  90 , a plate output electrode  23  for placing the image forming apparatus A electrically in contact with the process cartridge B, and a development bias electrical contact  22  for supplying development bias voltage to the development roller  12 , are attached.  
         [0081]    In the virtually square hole  90   a , with which the holder  90  is provided, a part of the plate electrode  23 , which constitutes the output electrical contact  23   a  for placing the image forming apparatus A electrically in contact with the process cartridge B, is fitted. The output plate electrode  23  is provided with a contact portion  23   b . As the holder  90  is attached to the developing means holding frame  13 , the contact portion  23   b  comes into contact with the cylindrical electrode  25 , placing the output electrical contact  23   a  electrically in contact with the first and third electrodes  81  and  83 .  
         [0082]    To the holder  90 , the development bias contact member  22  is attached, electrically connecting the image forming apparatus A and development roller  12 . The development bias contact member  22  is provided with the development bias electrical contact  22   a  and a contact portion  22   b . As the holder  90  is attached to the developing means holding frame  13 , the contact portion  22   b  comes into contact with the sleeve electrode  12   a  attached to the development roller  12 , becoming electrically connected to the sleeve electrode  12   a.    
         [0083]    As described above, the second electrode  82  is different in electrical potential level from the first and third electrodes  81  and  83 . Thus, if the second electrode  82  is placed in a manner to oppose the first electrode  81  or third electrode  83 , static electricity is induced between them. This is also true with power routing electrodes. In other words, even if the power routing plate electrode for the second electrode  82  is placed in a manner to oppose the first electrode  81  and/or third electrode  83 , static electricity is induced between the power routing plate electrode and the first electrode  81  and/or third electrode  83 , reducing the accuracy with which the amount of the remaining developer is detected. Incidentally, a power routing plate electrode means a plate electrode, the sole function of which is to conduct electrical power from one point to another. Since the plate electrode  32  is the power routing plate electrode for the second electrode  82 , it is routed from the developing means holding frame  13  to the developer holding frame  11  in such a manner that it does not oppose the power routing plate electrode  23  for the first and third electrodes  81  and  83 .  
         [0084]    Next, referring to FIG. 10, the structure for keeping the developing means holding frame  13  joined with the developer holding means  11  having the developer storing portion  14  will be described. FIG. 10 is a perspective view of the developing means holding frame  13  and developer holding means  11 , for showing how the two frames are joined with each other after the attachment of the first to third electrodes  81 ,  82 , and  83  to the developing means holding frame  13 .  
         [0085]    As shown in FIG. 10, to the surface of the developer holding frame  11 , by which the developer holding frame  11  is joined with the developing means holding frame  13 , a developer seal  48  for sealing the developer supplying opening of the developer holding frame  11  is attached (which is shown in a broken line, since it is attached to the hidden side of the developer holding frame  11  in the drawing). The surface of the developing means holding frame  13 , by which the developing means holding frame  13  is joined with the developer holding frame  11 , is provided with ribs  13   f  and  13   g , which fit into the grooves (unshown) with which the developer holding frame  11  is provided. The ribs  13   f  and  13   g  are located in the adjacencies of the top and bottom edges, respectively, of the developer supplying opening of the developing means holding frame  13 , and extend in parallel in the lengthwise direction of the developing means holding frame  13 . The top surface of each of the ribs  13   f  and  13   g  is provided with a triangular rib for ultrasonic welding.  
         [0086]    To the lengthwise ends of the developing means holding frame  13 , sealing members  38  and  39  are pasted to prevent the developer from leaking from between the developing means holding frame  13  and developer holding frame  11 . Further, in order to prevent the developer from leaking from around the power routing plate electrode  32  for conducting electric power to the developer holding frame  11 , a sealing member  46  is pasted to the developing means holding frame  13  in a manner to surround the contact portion  26   a  of the plate electrode  32 . Incidentally, the sealing members  38 ,  39 , and  46  are formed of elastic spongy substance.  
         [0087]    After the placement of various components into the developer holding frame  11  and developing means holding frame  13 , ultrasonic vibrations are applied to the two frames while pressing them upon each other, with the ribs  13   f  and  13   g  of the developing means holding frame  13  fitted in the corresponding grooves of the developer holding frame  11 . Consequently, the aforementioned triangular top ribs of the ribs  13   f  and  13   g  are melted by the ultrasonic vibrations, and weld to the bottoms of the grooves; in other words, the developer holding frame  11  and developing means holding frame  13  are welded to each other.  
         [0088]    In the case of this structural arrangement, a power routing plate electrode  29  is attached to the developer holding frame  11 . The plate electrode  29  is provided with an input electrical contact  29   a  for making connection with the image forming apparatus main assembly A, and a contact portion  29   b  for making connection with the plate electrode  32 . The plate electrode  29  is attached to the exterior of the developer holding frame  11 , with its contact portion  29   b  being positioned in a manner to clasp the lengthwise end portion of the flange  11   a  of the developer holding frame  11  and oppose the contact portion  32   a . Further, the plate electrode  29  is extended following the outward side of the flange  11   a  of the developer holding frame  11 , and a joggle  11   b  protruding, in the lengthwise direction of the developer holding frame  11 , from the lengthwise end surface of the developer holding frame  11  is fitted in the hole of the plate electrode  29 , securing thereby the plate electrode  29  to the developer holding frame  11 . The input contact portion  29   b  of the plate electrode  29  is bent so that it conforms to the contact seat  11   c  of the developer holding frame  11 . The surface of the input electrical contact  29   a , which constitutes the actual electrical contact, faces outward, like the output electrical contact  23   a , in terms of the lengthwise direction of the process cartridge B.  
         [0089]    The electrical connection between the plate electrode  29  and plate electrode  32  is made by the contact between the contact portion  29   b  and contact portion  32   a , which physically come into contact with each other, becoming thereby electrically connected with each other, as the developing means holding frame  13  and developer holding frame  11  are joined with each other. The plate electrode  29  is disposed so that the plane of the main section of the electrode  29  becomes virtually perpendicular to the plane of the arm portion  83   a  of the third electrode  83 , preventing the surface of the main section of the electrode  29  from facing the surface of the arm portion  83   a  of the third electrode  83 . In other words, the utmost effort is made not to induce static electricity between the plate electrode  29  and arm portion  83   a . The plate electrodes  23  and  29  are also disposed so that their surfaces do not oppose each other. Further, the two plate electrodes  29  and  23  are disposed on the developing means holding frame  13  side and developer holding frame  11  side, respectively, preventing static electricity from being induced between the two electrodes  29  and  23 .  
         [0090]    In other words, in the case of the process cartridge B in this embodiment, the power routing plate electrode  32  is attached to the developing means holding frame  13 , avoiding the situation that the plate electrode  29  on the voltage application side and the plate electrode on the power output side are attached to the same frame. Therefore, static electricity is not induced between the plate electrodes  29  and  23 , preventing the reduction in the accuracy with which the amount of the remaining developer is detected.  
         [0091]    Referring to FIGS. 12 and 13, after the above described process cartridge assembly processes, the output and input electrical contacts  23   a  and  29   a  of the developer amount detecting means are attached to the process cartridge B, close to each other, being separated by the developer seal placed between the developing means holding frame  13  and developer holding frame  11 . The external electrical contact point  22   a  of the development bias electrical contact  22  is disposed on the bottom surface of the process cartridge B. Further, the ground electrical contact  40  and charge bias electrical contact  28  are disposed on the side and bottom surfaces, respectively, of the cleaning unit  19 .  
         [0092]    Referring to FIG. 3, the image forming apparatus A is provided with electrical contacts  30  and  31 , which make contact with the input and output electrical contacts  29   a  and  23   a , respectively, of the developer amount detecting means. The electrical contacts  30  and  31  are attached to an electrical contact holder  42 , forming an electrical contact unit  43 , which is attached to the frame of the image forming apparatus main assembly A. The image forming apparatus A is also provided with electrical contacts  103  and  44  which make contact with the development bias electrical contact  22  and charge bias electrical contact  28  of the process cartridge B. The electrical contacts  103  and  44  project upward from the internal surface of the bottom wall of the image forming apparatus A. Further, the image forming apparatus A is provided with a ground electrical contact member  45  which makes contact with the ground electrical contact  40 , and which is attached to the internal surface of the side wall of the image forming apparatus main assembly A, in a manner to align with the positioning groove  26   b L (into which the drum shaft  27  fits) of the guide rail  26 L in terms of the lengthwise direction of the process cartridge B. The grounding electrical contact member  45  is grounded through the apparatus main assembly chassis.  
         [0093]    As the process cartridge B is inserted into the image forming apparatus main assembly A in the direction indicated by an arrow mark X, the input and output electrical contacts  23   a  and  29   a  of the developer amount detecting means come physically into contact, being therefore electrically connected, with the electrical contacts  30  and  31 , respectively, on the internal surface of one the side walls of the image forming apparatus main assembly A. Further, the development bias electrical contact  22   a  and charge bias electrical contact  28   a , come physically in contact, being therefore electrically connected, with the electrical contacts  103  and  44  protruding from the internal surface of the bottom wall of the image forming apparatus main assembly. Further, the grounding electrical contact  40  comes physically in contact, being therefore electrically connected, with the grounding contact member on the apparatus main assembly side (FIG. 5).  
         [0094]    The above described structure of the process cartridge can be summarized as follows.  
         [0095]    The process cartridge B removably mountable in the main assembly of an electrophotographic image forming apparatus A comprises:  
         [0096]    the electrophotographic photoconductive drum  7 ;  
         [0097]    the charge roller  8  for charging the electrophotographic photoconductive drum  7 ;  
         [0098]    the development roller  12  for developing an electrostatic latent image formed on the electrophotographic photoconductive drum  7 ;  
         [0099]    the input electrode  82  extended in the lengthwise direction of the development roller  12 , along the development roller  12 ;  
         [0100]    the output electrode  81  extended in the lengthwise direction of the development roller  12 , along the development roller  12 ; and  
         [0101]    the grounding electrical contact  40  which is for keeping the photoconductive drum  7  grounded to the apparatus main assembly when the process cartridge B is in the apparatus main assembly, and which is exposed from one end of the cartridge frame  50  in terms of the lengthwise direction of the photoconductive drum  7 , with its center coinciding with the axial line of the photoconductive drum  7 ;  
         [0102]    the charge bias electrical contact  28   a  which is for receiving the charge bias from the apparatus main assembly and applying the received charge bias to the charge roller  8 , and which is exposed from one end of the cartridge frame  50  in terms of the lengthwise direction of the photoconductive drum  7 , in such a manner that it faces downward when the process cartridge B is in the apparatus main assembly;  
         [0103]    the development bias electrical contact  22   a  which is for receiving the development bias from the apparatus main assembly and applying the received development bias to the development roller  12 , and which is exposed from one end of the cartridge frame  50  in terms of the lengthwise direction of the photoconductive drum  7 , being positioned opposite to the charge bias electrical contact  28   a  with respect to the photoconductive drum  7  in terms of the direction perpendicular to the lengthwise direction of the photoconductive drum  7 , in such a manner that it faces downward when the process cartridge B is in the apparatus main assembly;  
         [0104]    the input electrical contact  29   a  which is for receiving the input bias from the apparatus main assembly and applying the received input bias to the input electrode  82 , and which is exposed from one of the end walls of the cartridge frame  50  in terms of the lengthwise direction of the photoconductive drum  7 ;  
         [0105]    the output electrical contact  23   a  which is for transmitting to the apparatus main assembly, the output value reflecting the electrostatic capacity between the input electrode  82  and output electrode  81 , and the electrostatic capacity between the development roller  12  and output electrode  81 , in order to enable the apparatus main assembly to continually detect the amount of the developer remaining in the process cartridge B, and which is exposed from one of the end walls of the cartridge frame  50  in terms of the lengthwise direction of the photoconductive drum  7 .  
         [0106]    To the input electrode  82 , AC bias is applied through the input electrode  29   a.    
         [0107]    The cartridge frame  50  comprises the developer holding frame  11  having the developer holding portion  14  for holding the developer used by the development roller  12  for developing an electrostatic latent image, the developing means holding frame  13  for supporting the development roller  12 , and the drum holding frame  21  for supporting the photoconductive drum  7  and charge roller  8 . The input electrical contact  29   a  is attached to the developer holding frame  11 , and the output electrical contact  23   a  is attached to the developing means holding frame  13 .  
         [0108]    The process cartridge B has the developer supplying opening  47  for supplying the developer held in the developer holding portion  14 , to the development roller  12 . The input electrical contact  29   a  is disposed on one side of the path through which the developer seal  48 , which is sealing the developer supplying opening  47 , is pulled out, whereas the output electrical contacts  23   a  are disposed on the other side.  
         [0109]    The input electrode  82  is attached to the developer holding frame  11 , whereas the output electrode  81  is attached to the developing means holding frame  13 .  
         [0110]    The grounding electrical contact  40  and charge bias electrical contact  28   a  are attached to the drum holding frame  21 , whereas the development bias electrical contact  22   a  is attached to the developing means holding frame  13 .  
         [0111]    The development bias electrical contact  22   a  is also used for receiving the development bias applied to the development roller  12 , in order to detect the value reflecting the electrostatic capacity between the development roller  12  and output electrode  81 .  
         [0112]    According to the above described embodiment of the present invention, the output electrical contact  23   a  and input electrical contact  29   a  are disposed on the same end of the process cartridge B in terms of the lengthwise direction of the photoconductive drum  7 , close to each other. Therefore, the electrical contact unit  43  which is attached to the image forming apparatus main assembly A can be reduced in size, which in turn makes it possible to reduce the size and cost of the image forming apparatus main assembly A.  
         [0113]    The charge bias electrical contact  28   a , development bias electrical contact  22   a , grounding electrical contact  40 , input electrical contact  29   a , and output electrical contact  23   a  are all disposed on the same lengthwise end of the process cartridge B. Therefore, it is possible to reduce the distance the wiring for connecting the high voltage circuit of the image forming apparatus main assembly to the process cartridge B must be routed, which in turn makes it possible to reduce the size and cost of the image forming apparatus A.  
         [0114]    Further, it is possible to reduce the distance the power routing members  36  and  37  must be routed to connect the electrical contact unit  48  to the developer amount detection circuit  200 . Therefore, it is possible to prevent the problem that the developer amount detection accuracy is reduced by the instability in the electrostatic capacities among the power routing members.  
         [0115]    As described above, according to this embodiment of the present invention, the output electrical contact  23   a  and input electrical contact  29   a  are disposed at the same end of the process cartridge B in terms of the lengthwise direction of the photoconductive drum  7 , close to each other. Therefore, the electrical contact unit  43  provided on the image forming apparatus main assembly A side in correspondence to the electrical contacts  23   a  and  29   a  can be reduced in size, which in turns makes it possible to reduce the size and cost of the image forming apparatus A.  
         [0116]    Further, the charge bias electrical contact  28   a , development bias electrical contact  22   a , grounding electrical contact  40 , input electrical contact  29   a , and output electrical contact  23   a  are all disposed on the same lengthwise end of the process cartridge B. Therefore, it is possible to reduce the distance the power routing members for connecting the high voltage circuit of the image forming apparatus main assembly to the process cartridge B must be routed, which in turn makes it possible to reduce the size and cost of the image forming apparatus A.  
         [0117]    Further, it is possible to reduce the distance the power routing members  36  and  37  must be routed to connect the electrical contact unit  48  to the developer amount detection circuit  200 . Therefore, it is possible to prevent the problem that the developer amount detection accuracy is reduced by the instability in the electrostatic capacities among the power routing members.  
         [0118]    According to the present invention, each of the various electrical contacts of a process cartridge could be optimally positioned, making it possible to reduce a process cartridge in size.  
         [0119]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.