Patent Publication Number: US-2011069978-A1

Title: Image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to image forming apparatuses such as electrophotographic copying machines, electrophotographic printers, etc. 
     The inventors of the present invention have proposed a method for detecting the amount of the developer (which hereafter may be referred to as toner) remaining in a developing apparatus (which hereafter may be referred to as developing device) (Japanese Laid-open Patent Application H04-234777). This method is for detecting the amount of the toner remaining in a developing device equipped with a toner bearing member for developing an electrostatic latent image by supplying an image bearing member with toner, a toner supplying member for supplying the toner bearing member with toner by being in contact with the toner bearing member. More concretely, a developing device is provided with a member for coating a toner bearing member with toner (toner bearing member coating member). The toner bearing member coating member is supported by an electrically conductive member, so that an alternating voltage can be applied to the toner bearing member from a development bias power source. Thus, the amount of the toner remaining in the developing device is detected (estimated) by measuring the voltage induced in the electrically conductive supporting member for the developer bearing member coating member. The magnitude of the voltage induced in the electrically conductive supporting member is affected by the amount of the electrostatic capacity between the toner bearing member and electrically conductive supporting member. When a developing device is full of toner, the area between its toner bearing member and electrically conductive supporting member is full of toner. However, as the toner in the developing device is consumed, the area between the toner bearing member and electrically conductive supporting member reduces. Thus, the amount of the electrostatic capacity of the area between the toner bearing member and electrically conductive supporting member when the developing device is full of toner, is different from that when the amount of the toner in the developing device has been reduced by consumption. Therefore, the amount of voltage induced in the electrically conductive member when the developing device is full of toner, is different from that when the amount of the toner in the developing device is less because of the consumption. This phenomenon is used to detect (estimate) the amount of the toner in the developing device. This method does not require a space dedicated to the detection (estimation) of the amount of the toner remaining in a developing device. 
     It has become evident that the above described prior art suffers from the problem that even if no toner in a developing device is consumed, the amount of the electrostatic capacity between the toner bearing member and electrically conductive supporting member is affected by the changes in the toner density in the developing device. Ordinarily, during an image forming operation, the toner in a developing device in an image forming apparatus is circulated in the device, while being fully stirred, by the rotation of the toner bearing member, and the rotation or the like of the toner conveying member. However, if the developing device in the image forming apparatus is kept unattended for a long time after the completion of the image forming operation, the body of the toner in the developing device becomes packed downward by its own weight, increasing in density. Consequently, the area between the toner bearing member and development bearing member coating member is increased in toner density. In other words, even if the developing device remains the same in the amount of the toner therein, it sometimes varies in the detected amount of the electrostatic capacity between the toner bearing member and toner bearing member coating member. In order to solve this problem, the developing device has to be made uniform in toner density before the amount of the toner in the developing device is detected. In other words, before the amount of the toner in the developing device is detected, the developing device has to be rotated to stir the toner in the developing device to make the toner uniform in density. Thus, a certain length of time is necessary each time the toner remainder amount in the developing device is detected. This results in the reduction in the throughput of the image forming apparatus. In addition, the additional driving of the developing device contributes to the further frictional wear and deterioration of the developing device, being therefore likely to affect the service life of the developing device. 
     The present invention is intended to improve the above described prior art which relates to the toner remainder amount detecting function of an image forming apparatus and a developing device therefor. Thus, the primary object of the present invention is to provide an image forming apparatus capable of accurately detecting (estimating) the amount of the toner remaining in its developing device(s) regardless of the environment in which the developing device (image forming apparatus) is used, and/or the condition in which the developing device (image forming apparatus) is left unattended. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is to provide an image forming apparatus capable of accurately detecting (estimating) the amount of the toner remaining in its developing device(s) regardless of the environment in which the developing device (image forming apparatus) is used, and/or the condition in which the developing device (image forming apparatus) is left unattended. 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising an image bearing member for bearing an electrostatic latent image on a surface thereof; a developing device including a developer accommodating chamber for accommodating a developer, a developer carrying member, provided in said developer accommodating chamber and having a first electrode member, for developing the electrostatic latent image, a developer feeding member, provided in said developer accommodating chamber in contact with said developer carrying member and having a foam layer around a second electrode member, for supplying the developer to said developer carrying member; a holding unit holding said developing device, said holding unit being movable between a first position in which the developer is accumulated on a nip between said developer carrying member and said developer feeding member and a second position in which the developer accumulated at said nip in the first position falls; and a detecting device for detecting a developer remainder amount in said developer accommodating chamber on the basis of a change of an electrostatic capacity between said first electrode member and said second electrode member. 
     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 
         FIG. 1(   a ) is a schematic sectional view of the image forming apparatus in the first preferred embodiment of the present invention, and shows the general structure of the apparatus.  FIG. 1(   b ) is an enlarged schematic sectional view of the developing device of the apparatus shown in  FIG. 1(   a ), and shows the developing apparatus when it is in its first position. 
         FIG. 2(   a ) is an enlarged schematic sectional view of the developing device of the apparatus shown in  FIG. 1(   a ), and shows the developing apparatus when it is in its second position.  FIG. 2(   b ) is a schematic drawing of the developing apparatus, and the components related to the operation of the developing apparatus, and shows the method for measuring the amount of airflow through the developer application roller. 
         FIG. 3(   a ) is a graph which shows the relationship between the amount of the toner in the developing device, and the amount of the toner in the sponge portion of the developer application roller.  FIG. 3(   b ) is a graph which shows the relationship between the amount of the toner in the sponge portion of the developer application roller, and the amount of the electrostatic capacity. 
         FIG. 4(   a ) is a graph which shows the relationship between the changes in the amount of the electrostatic capacity detected by a toner remainder amount detecting apparatus immediately after the developing device was moved to its second position, and the length of time which elapsed after the movement of the detecting apparatus.  FIG. 4(   b ) is a graph which shows the relationship between the amount of the output of the toner remainder amount detecting apparatus, and the amount of the toner remainder in the developer container. 
         FIG. 5(   a ) is a block diagram of the toner remainder amount detecting apparatus, and  FIG. 5(   b ) is a graph which shows the relationship between the amount (weight) of the body of toner in the developing device, and the toner remainder amount detection output. 
         FIG. 6(   a ) is a schematic sectional view of the developing device of the image forming apparatus in the second preferred embodiment, when the developing device is in its first attitude.  FIG. 6(   b ) is a combination of a schematic sectional view of the developing device in the second embodiment, when the device is in its second attitude, and a block diagram of the developer remainder amount detecting apparatus in the second embodiment. 
         FIG. 7(   a ) is a graph which shows the relationship between the changes in the amount of the electrostatic capacity detected by the toner remainder amount detecting apparatus immediately after the developing device was moved to its second position, and the length of time which elapsed after the movement of the detecting apparatus.  FIG. 7(   b ) is a graph which shows the change in the relationship between the amount of the output of the toner remainder amount detecting apparatus, and the amount of the toner in the developer container. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the appended drawings. Incidentally, the measurement and shape of the structural components of the image forming apparatus in each of the preferred embodiments of the present invention, and the positional relationship among them, should be altered as necessary according to the structure of an apparatus to which the present invention is applied, and the various conditions under which the apparatus is used. In other words, the following embodiments of the present is not intended to limit the present invention in scope. 
     &lt;General Structure of Image Forming Apparatus&gt; 
       FIG. 1(   a ) is a schematic sectional view of the image forming apparatus in this embodiment, and shows the general structure of the apparatus. This image forming apparatus is an electrophotographic full-color image forming apparatus which uses four developers different in color. This image forming apparatus forms an image on recording medium P, which is in the form of a sheet, based on the electrical image formation signal inputted into the controller portion  100  (controlling means: CPU) of the apparatus from a host apparatus  200 , such as an image reader (original reading apparatus), a personal computer, a facsimile, etc. The controller portion  100  (which hereafter will be referred to simply as controller  100 ) exchanges various electrical information with the host apparatus  200 , and the control panel portion  300  of the image forming apparatus, and also, controls the overall operation of the image forming apparatus, based on preset control programs and referential tables. The image forming apparatus has an electrophotographic photosensitive member  1  (which hereafter will be referred to as drum  1 ), which is a rotatable image bearing member, on the peripheral surface of which an electrostatic latent image is. It has also: a charging means  2 , which is a processing means for processing the peripheral surface of the drum  1 ; a drum exposing means  3 ; developing apparatuses  5  ( 5   a,    5   b,    5   c,  and  5   d ); a transferring means  6 ; and a drum cleaning means  7 . The drum  1  is rotated about its axis at a preset speed in the counterclockwise direction, that is, the direction indicated by an arrow mark R 1 . The charging means  2  is a means which uniformly charges the peripheral surface of the drum  1  to preset polarity (which in this embodiment is negative) and potential level. The charging means  2  in this embodiment is a charge roller of the contact type. The drum exposing means  3  is a means which forms an electrostatic latent image on the peripheral surface of the drum  1 . The drum exposing means  3  in this embodiment is a laser-based scanner unit. This unit  3  scans (exposes) the uniformly charged portion of the peripheral surface of the drum  1 , in the drum exposing portion A. More specifically, the unit  3  projects a beam L of laser light upon a deflection mirror  4 , while modulating the beam L with image formation information inputted, one for each of primary colors, into the controller  100  from the host apparatus  200 . Thus, the uniformly charged portion of the peripheral surface of the drum  1  is scanned by the beam L deflected by the mirror  4 . Consequently, an electrostatic latent image is effected on the peripheral surface of the drum  1 . The electrostatic latent image forming method used in this embodiment is such a drum exposing method that exposes the uniformly charged portion of the peripheral surface of the drum  1  according to the image formation information. The developing apparatus  5  is a means for developing the electrostatic latent image on the peripheral surface of the drum  1  into a visible image, that is, an image formed of developer (toner), which hereafter may be referred to as a developer image or a toner image. The image forming apparatus in this embodiment has multiple developing devices (developing apparatuses), more specifically, first to fourth developing apparatuses  5  ( 5   a,    5   b,    5   c,  and  5   d,  which are in the form of a cartridge (development cartridge)). These developing devices are held by a rotary  50 , which is a developing device holding member (holder unit) rotatable about its central axis  51  in such a manner that a given developing device can be positioned in a preset position (in terms of the rotational angle of rotary  50 ). The rotary  50  is provided with four chambers in which the four developing devices  5  are removably mountable, one for one. The four developing device holding chambers extend in the direction parallel to the axial direction of the holder  50 . The size of each chamber in terms of the angle in the rotational direction of the rotary  50  is 90 degrees. The rotary  50  is rotatable by a driving means (motor or the like, which is unshown in drawings), which is under the control of the controller  100 . It is rotatable in steps of 90 degree angle, in the clockwise direction, that is, the direction indicated by an arrow mark R 2 . Thus, the first to fourth developing devices  5   a,    5   b,    5   c,  and  5   d  are sequentially movable to a development position C where they oppose the peripheral surface of the drum  1  and can develop the electrostatic latent image on the drum  1  into a toner image. Hereafter, the position into which any of the developing apparatuses in the rotary holder  50  is to be moved to oppose the drum  1  will be referred to as the position C of the developing apparatus  5 . Further, a position into which a given developing device  5  is moved from the position C as the rotary  50  is rotated by 90° in the abovementioned direction, will be referred to as a position F. Further, the position into which the developing device  5  will be placed as the rotary  50  is rotated from the position F by 90 degrees (180° from position C) in the abovementioned direction, will be referred to as a position E. Further, the position in which the developing apparatus  5  will be as it is rotated 90° (270° from position C) from the position E in the abovementioned direction, will be referred to as a position G. 
     The first to fourth developing devices  5   a,    5   b,    5   c,  and  5   d  in this embodiment are of the contact type. They develop an electrostatic latent image in reverse with the use of developer T, which is nonmagnetic toner and is negatively chargeable. The developing device  5   a,  that is, the first developing device, is a developing device for developing an electrostatic latent image into a yellow toner image. It contains yellow (Y) toner in its developer storage chamber. The developing device  5   b,  that is, the second developing device, is a developing device for developing an electrostatic latent image into a magenta (M) toner image. It contains magenta (M) toner in its developer storage chamber. The developing device  5   c,  that is, the third developing device, is a developing device for developing an electrostatic latent image into a cyan toner image. It contains cyan (C) toner in its developer storage chamber. The developing device  5   d,  that is, the fourth developing device, is a developing device for developing an electrostatic latent image into a black (Bk) toner image. It contains black (Bk) toner in its developer storage chamber. The transferring means  6  is a means for transferring the toner image on the peripheral surface of the drum  1  onto recording medium. The transferring means  6  in this embodiment is in the form of an intermediary transfer belt unit, and may be referred to as an intermediary transfer belt unit, hereafter. This unit  6  has an intermediary transferring member  61 , which is an intermediary transfer medium and is in the form of a dielectric and flexible endless belt. The unit  6  has also a first transfer roller  62 , a belt driving roller  63  (driver roller), a backup roller  64  (which backs up endless belt against second transfer roller  66 ), and a tension roller  65 . The first transfer roller  62  is kept pressed upon the peripheral surface of the drum  1  with the presence of the belt  61  between the roller  62  and drum  1 . The area of contact between the drum  1  and belt  61  is the first transfer nip B. There is a second transfer roller  66 , which is kept pressed upon the belt  61  (kept pressed against backup roller  64  with presence of the belt  61  between rollers  64  and  66 ). The second transfer roller  66  is movable by a second transfer roller moving mechanism (unshown), so that it can be kept in a position (first position) in which it is kept pressed against the belt-backing roller  64  with the presence of the belt  61  between the belt-backing roller  64  and second transfer roller  66 , or a position (second position) in which it is kept separated from the belt  61 . When the second transfer roller  66  is not used for transfer, it is kept in its second position. When it has to be used for transfer, it is moved into its first position with a preset timing. As the second transfer roller  66  is moved into the first position, a nip is formed between the second transfer roller  66  and belt  61 . This nip is the second transfer nip D. The unit  6  has also a belt cleaning means  67 , which is for cleaning the outward surface of the belt  61 . The cleaning means  67  is in the adjacencies of where the belt  61  is in contact with the peripheral surface of the tension roller  65 . The belt cleaning means  67  is movable by a belt cleaning means moving mechanism (unshown) so that it can be kept in a position (first position) in which its cleaning member is kept in contact with the outward surface of the belt  61 , and a position (second position) in which the cleaning member is kept separated from the outward surface of the belt  61 . When the cleaning means  67  is not used for cleaning, it is kept in the second position. When it has to be used for cleaning, it is moved into the first position with a preset timing. The drum cleaning means  7  is a means for removing the toner (first transfer residual toner) remaining on the peripheral surface of the drum  1  after the first transfer of the toner image onto the belt  61 . It is in the form of a blade (cleaning blade). After being removed from the peripheral surface of the drum  1 , the first transfer residual toner is stored in the cleaning means container  71 . As an image formation start signal is inputted, the controller  100  begins to drive the main motor (unshown), whereby the drum  1  begins to be rotated in the counterclockwise direction, that is, the direction indicated by an arrow mark R 1  at a preset speed. Further, the rotary  50  is rotated so that the first developing device  5   a  is moved into the position C. As the developing device  5   a  is moved into the position C, the driving force from the main motor begins to be transmitted to the developing device  5   a,  and a preset development bias is applied to the developing device  5   a.  Further, the laser-based scanner unit begins to be driven, and the belt  61  begins to be circularly driven in the clockwise direction, that is, the direction indicated by an arrow mark R 3  (so that the peripheral surface of drum  1  and the peripheral surface of the developing member of developing device  5   a  move in the same direction in their interface) at a speed which corresponds to the rotational speed of the drum  1 . As for the second transfer roller  66  and belt cleaning means  67 , they are kept in their second positions where they remain separated from the belt  61 . To the charge roller  2 , a preset charge bias is applied. Thus, the peripheral surface of the rotating drum  1  is uniformly charged to preset polarity (which in this embodiment is negative) and potential level. The uniformly charged portion of the peripheral surface of the drum  1  is scanned (exposed) by the beam L of laser light outputted from the laser-based scanner unit  3 , while being modulated with the image formation signals for the formation of a monochromatic image of the yellow component obtained by the color separation of the original full-color image. Consequently, an electrostatic image, which corresponds in pattern to the yellow monochromatic image to be formed on the peripheral surface of the drum  1 , is effected on the peripheral surface of the drum  1 . This electrostatic latent image is developed into a toner image (developer image) of yellow color by the first developing device  5   a  which is in the position C. In this embodiment, the electrostatic latent image is developed in reverse with the use of negative toner, that is, toner which is the same in polarity (negative) as the polarity to which the peripheral surface of the drum  1  is charged. Then, the yellow toner image is transferred (first transfer) onto the outward surface of the belt  61  in the first transfer nip B. In order to transfer (first transfer) the yellow toner image, a transfer bias (first transfer bias), which is preset in potential level and is opposite in polarity (positive) to the polarity to which toner is charged, is applied to the primary transfer roller  62  with preset control timing. After the first transfer, the peripheral surface of the drum  1  is cleaned by the drum cleaning means  7 . After the completion of the first transfer of the yellow toner image, that is, the transfer of the yellow toner image onto the belt  61 , the rotary  50  is rotated 90° in the clockwise direction, whereby the second developing device  5   b  is moved into the position C. Then, the charging, exposing, and developing processes for forming a monochromatic image of the magenta (M) color, that is, another color component of the original full-color image, on the peripheral surface of the drum  1  are carried out. Then, the thus formed magenta (M) toner image is transferred (first transfer) onto the belt  61 , in the first transfer nip B, in such a manner that it is layered onto the yellow toner image, in alignment with the yellow toner image on the belt  61 . After the first transfer of the magenta (M) toner image onto the belt  61 , the rotary  50  is rotated 90° in the clockwise direction, whereby the third developing device  5   c  is moved into the position C. Then, the charging, exposing, and developing processes for forming a monochromatic image of the cyan (C) color, that is, another color component of the original full-color image, on the peripheral surface of the drum  1  are carried out. Then, the thus formed cyan (C) toner image is transferred (first transfer) onto the belt  61 , in the first transfer nip B, in such a manner that it is layered onto the aligned combination of the yellow and magenta toner images on the belt  61 , in alignment with the combination. After the first transfer of the cyan (C) toner image onto the belt  61 , the rotary  50  is rotated 90° in the clockwise direction, whereby the third developing device  5   d  is moved into the position C. Then, the charging, exposing, and developing processes for forming a monochromatic image of the black (Bk) color, that is, another color component of the original full-color image, on the peripheral surface of the drum  1  are carried out. Then, the thus formed black (Bk) toner image is transferred (first transfer) onto the belt  61 , in the first transfer nip B, in such a manner that it is layered onto the aligned combination of the yellow, magenta, and cyan toner images on the belt  61 , in alignment with the combination. As a result, an unfixed full-color toner image is synthetically effected on the belt  61 , from the four monochromatic images of Y+M+C+Bk colors, one for one. 
     That is, the rotary  50  is rotated by the rotary driving means to move one of the developing devices  5  into the position C where the developing device  5  opposes the drum  1 . Then, this developing device  5  is used to develop the electrostatic latent image on the drum  1  into a toner image. In the case of the image forming apparatus in this embodiment, this operational sequence is repeated multiple (four) times to form a full-color toner image on the outward surface of the belt  61 . Incidentally, the order in which the four monochromatic images, different in color (Y, M, C, and Bk) are sequentially formed on the drum  1  does not need to be as described above, that is, Y+M+C+Bk. That is, it may be altered as necessary or desired. After the formation of an unfixed full-color toner image on the belt  61 , the aforementioned second transfer roller  66  is moved into its first position, that is, the position in which the roller  66  is kept in contact with the belt  61 , before the leading edge of the unfixed full-color toner image on the belt  61  is moved by the movement of the belt  61  to where the second transfer roller  66  is. Further, the belt cleaning means  67  also is moved to its first position, that is, the position in which the cleaning means  67  is kept in contact with the belt  61 . Meanwhile, one of the sheets of recording medium P, which is the third recording image bearing means, in the recording medium feeding-and-conveying portion (unshown), is separated from the rest and conveyed into the main assembly of the image forming apparatus. Then, the sheet of recording medium P (which hereafter will be referred to simply as recording medium P) is introduced into the interface between the second transfer belt  66  and belt  61  by a registration roller unit (unshown) with a preset timing. To the second transfer roller  66 , a second transfer bias, which is preset in potential level and is opposite (positive) in static electricity polarity to toner, is applied, whereby the unfixed full-color toner image, that is, unfixed image made up of the layered four monochromatic toner images, different in color, on the belt  61 , is transferred together (second transfer) onto the recording medium P, as if it is peeled away from the belt  61 , while the recording medium P is conveyed through the second transfer nip D while remaining pinched by the second transfer roller  66  and belt  61 . Then, the recording medium P is separated from the belt  61 , and introduced into the fixation unit  8 . In the fixation unit  8 , the recording medium P and the four unfixed monochromatic toner images (making up unfixed full-color toner image) thereon, are subjected to heat and pressure as they are conveyed through the fixation nip of the fixation unit  8 . Consequently, the four monochromatic toner images become fixed (after being melted and mixed) to the recording medium P. Thereafter, the recording medium P is discharged from the fixation unit  8 , and then, is discharged, as a completed full-color copy, into the delivery portion (unshown) of the image forming apparatus. After the separation of the recording medium P from the belt  61 , the secondary transfer residual toner, that is, the toner remaining on the belt  61  after the second transfer, is removed by the belt cleaning means  67 . 
     As soon as a job for outputting one copy, or a job for continuously outputting multiple copies ends, the controller  100  puts the image forming apparatus on standby, and waits for the inputting of the next image formation start signal. That is, it stops driving the drum  1 , laser-based scanner unit  3 , belt  61 , etc.. Further it moves the second transfer roller  66  and belt cleaning means  67  to the positions one for one where they are kept inactive. When the image forming apparatus is in the monochromatic image formation mode, only the fourth developing device  5   d,  that is, the developing apparatus for forming a black monochromatic image is used for image formation. As soon as a job for outputting one copy in monochromatic image formation mode, or a job for continuously outputting multiple copies ends in the monochromatic image formation mode, the controller  100  puts the image forming apparatus on standby, and waits for the inputting of the next image formation start signal. 
     &lt;Developing Device  5 &gt; 
     The first to fourth developing devices  5   a,    5   b,    5   c , and  5   d  in this embodiment are the same in structure, although they are different in the color of the developer (toner) contained therein.  FIG. 1(   b ) is an enlarged schematic sectional view of one of the developing devices in this embodiment. The developing device  5  has: a developer container  21  in which toner T is held; a development roller  25  which is a developer bearing member for bearing the developer for developing an electrostatic latent image on the drum  1 ; and a development roller coating member  24  which is a member for supplying the development roller  25  with toner by being virtually in contact with the development roller  25 . The developing device  5  has also: a regulation blade which is a member for forming the body of the toner borne on the development roller  25  into a toner layer which is preset in thickness; and a seal  26  for preventing the toner from leaking out through the gap between the development roller  25  and developer container  21 . The developer container  21  is a long and narrow container, and is positioned so that its lengthwise direction is parallel to the axial direction of the drum  1 . Its downwardly facing wall has a long and narrow opening, which faces the drum  1 , and the lengthwise direction of which is parallel to the axial line of the drum  1 . The development roller  25  is positioned so that its peripheral surface faces this opening, and also, so that it is parallel to the lengthwise direction of the developer container  21 . It is rotatably supported by the developer container  21 . More specifically, the lengthwise end walls of the developer container  21  are provided with a pair of bearings (unshown), and the development roller  25  is rotatably supported by the pair of bearings. The development roller  25  in this embodiment is 13 mm in diameter. It comprises: an electrically conductive metallic core  28 , which is 8 mm in diameter; a base layer  28   a  which is made of silicon rubber and covers the entirety of the peripheral surface of the metallic core  28 ; and a surface layer  28   b  which is made of acrylic urethane rubber and covers the entirety of the outer surface of the base layer  28   a.  The development roller  25  is 10 4 -10 12  Ω·cm in volume resistivity. The development roller coating roller  24  comprises: an electrically conductive metallic core  29 , which is 6 mm in diameter; and a urethane sponge layer  29   a,  whose cells are interconnected, and which covers the entirety of the peripheral surface of the metallic core  29 . It is a urethane sponge roller with a diameter of 15 mm, and is 10 4 -10 12  Ω·cm in volume resistivity. That is, the development roller coating roller  24  comprises a sponge layer whose cells are interconnected. Incidentally, although, in this embodiment, a roller having interconnected cells is used as the development sleeve coating roller  24 , any roller may be used as the development roller coating roller  24 , as long as the roller is structured so that toner is allowed to penetrate into the roller. For example, it may be a roller comprising a foamed layer having independent cells as long as it is structured so that toner is allowed to penetrate into the roller. An elastic layer formed of a substance having interconnected cells is greater in the amount by which it can internally hold toner than an elastic layer formed of independent cells. Therefore, a development roller coating roller having interconnected cells cell, is better suited for measuring the amount of the “electrostatic capacity”, which will be described later. The distance between the rotational axis  28  of the development roller  25  and the rotational axis  29  of the development sleeve coating member  24  is 13 mm. Thus, it appears as if the urethane sponge roller  29   a  of the development sleeve coating member  24  had penetrated into the development roller  25  by 1.0 mm. The regulation blade  27  is positioned so that as the development roller  25  is rotated, its opposite edge from the edge by which it is anchored, is placed virtually in contact with the peripheral surface of the development roller  25  and forms the body of the toner on the peripheral surface of the development roller  25  into a thin and uniform layer of the toner. It is a flexible member made of copper phosphate, urethane rubber, etc. The regulation blade  27  is solidly attached to the developer container  21 , with one of its long edge portions attached to the top edge portion of the aforementioned opening of the container  21 . The leak prevention seal  26  is a flexible member and is attached to the container  21  by one of its long edge portions. The other long edge is in contact with the development roller  25 , one the bottom side of the container  21 , covering thereby the gap between the development roller  25  and container  21  to prevent the toner in the developer container  21  from leaking out through the gap. The seal  26  is attached to the bottom edge of the aforementioned opening of the container  21 . 
     As for the development of an electrostatic latent image formed on the drum  1  by the developing device  5 , first, the developing device  5  is moved by the rotation of the rotary  50  by the angle necessary to move the developing device  5  into the position C (first position) where it faces the drum  1  as shown in  FIGS. 1(   a ) and  1 ( b ). In this embodiment, the main assembly of the image forming apparatus is structured so that as the developing device  5  is moved into the position C, it becomes upright (first attitude) in which the opposite side of the developer container  21  from the side having the aforementioned opening faces upward, whereas the side having the opening faces downward, and development roller  25  comes into contact with the drum  1 . While the electrostatic latent image is developed by the developing device  5 , the development roller  25  remains in contact with the drum  1 . That is, the developing method used in this embodiment is the developing method of the so-called contact type. When the developing device  5  is in the position C, the mechanical force for driving the developing device  5  and development bias are inputted into the developing device  5  from the mechanical driving means (unshown) and electric power source E, respectively, of the main assembly of the image forming apparatus during image formation. Referring to  FIG. 1(   b ), the development roller  25  is rotated at a preset speed in the clockwise direction, that is, the direction indicated by an arrow mark R 4 . Thus, the direction in which the peripheral surface of the development roller  25  moves in the interface between the development roller  25  and drum  1  is the same as the rotational direction R 1  of the drum  1 . Further, the development roller coating roller  24 , which supplies the development roller  25  with toner by being in contact with the development roller  25 , is rotated at a preset speed in the clockwise direction, that is, the direction indicated by an arrow mark R 5 . Thus, the direction in which the peripheral surface of the developer roller coating roller  24  moves in the interface between the roller  24  and development roller  25  is opposite (counter) to the rotational direction R 4  of the development roller  25 . As the development roller coating roller  24  and development roller  25  rotate, the peripheral surface of the development roller  25  is coated with toner by the development roller coating roller  24 . Then, the body of the coated toner on the peripheral surface of the development roller  25  is formed into a thin layer by the regulation blade  27 . Then, this thin layer of toner is moved to the development position C by the subsequent rotation of the development roller  25  to be applied to the peripheral surface of the drum  1 . Further, a preset development bias, which in this embodiment is a DC voltage, is applied to the development roller  25  from a development bias application power source V, whereby the toner particles in the thin layer of toner on the peripheral surface of the development roller  25  transfer onto the specific points (points with low potential) of the electrostatic latent image on the peripheral surface of the drum  1 . In other words, the electrostatic latent image is developed into a visible image (image formed of toner). The toner particles which were not used for the development of the electrostatic latent image are conveyed back into the developer container  21  by the subsequent rotation of the development roller  25 , and are removed from the peripheral surface of the development roller  25  by the development roller coating roller  24 . As the toner particles are removed from the peripheral surface of the development roller  25 , the portion of the peripheral surface of the development roller  25 , from which the toner particles have just been removed, is coated again with the toner in the developer container  21 , by the development roller coating roller  24 . The above described sequence is repeated to develop the electrostatic latent image on the peripheral surface of the drum  1 . 
     When the developing device  5  is in the position C, its attitude is upright (first attitude) as described above. Thus, the toner T in the developer container  21  is kept in the bottom side of the developer container  21 , that is, the side where the development roller coating roller  24  is present, by gravity. Designated by a referential code Ta is the top surface of the body of the toner T (developer) in the developer container  21 . It is when the developing device  5  is in this attitude (upright) that the development roller coating roller  24  can be supplied with the toner T so that the development roller  25  can be coated with the toner T by the development roller coating roller  24 . That is, it is when the developing device  5  is in this attitude (upright) that the toner T is in an area X, which is the top adjacencies of the nip between the developer bearing member (development roller  25 ) and developer supplying member (development roller coating roller  24 ), and therefore, the developing device  5  is capable of developing the electrostatic latent image on the peripheral surface of the drum  1 . When the image forming apparatus is in an ordinary image forming operation, the developing device  5  is upright in the position C, that is, the development position, and the toner T in the developer container  21  is only on the bottom side of the developer container  21  because of the presence of gravity, which makes the area X and its adjacencies relatively high in toner density. This condition is ideal for image formation for the following reason. That is, if the area X and its adjacencies reduce in toner density during an ordinary toner image forming operation, it becomes impossible for the development roller  25  to be supplied with a sufficient amount of toner, sometimes causing thereby the image forming apparatus to output images having white spots or the like. This is why the area X and its adjacencies are desired to be high in toner density. When the developing device  5  is in the position F, its attitude is horizontal, and the development roller side of the developer container  25  is on the bottom side. When the developing device  5  is in the position E, its attitude is the upside-down attitude (second position), that is, the reverse attitude relative to the attitude in which the developing device  5  is in the position C. Further, when the developing device  5  is in the position G, it is in such a horizontal attitude that the development roller side of the developing device  5  faces upward. 
     &lt;Method for Detecting (Estimating) Remaining Amount of Toner in Developing Device&gt; 
     As the first to fourth developing devices  5  ( 5   a ,  5   b,    5   c,  and  5   d ) are used for image formation, the toner in each developing device  5  is consumed. Thus, the image forming apparatus is provided with a toner remainder amount detecting apparatus  100   a  (toner remainder amount detection circuit) for detecting the amount of toner remainder in each of the developing devices  5 . As the amount of toner detected by the toner remainder amount detecting apparatus  100   a  falls to a threshold value preset for predicting the remaining length of the service left of a developing device  5 , or warning a user of an imminent ending of the service life of a developing device  5 , the controller  100  causes the display portion  300   a  of the control panel  300  to display the predicted remaining length of the service life of the developing device  5 , or the warning about the imminent ending of the service life of the developing device, prompting thereby a user to prepare a replacement developing device  5 , or to replace the developing device  5  in order to ensure that the image forming apparatus will remain at a preset level in terms of image quality. The old developing device (developing device in image forming apparatus) is replaced with a new developing device (replacement developing device) through the following preset procedural sequence, in which a developing device  5  having run out of toner (developer) is removed from the development device chamber of the rotary  50  through the preset developing device removal sequence, and a replacement developing device (new developing device, which is identical to removed one) is mounted into the emptied developing device chamber through the preset procedural sequence for mounting a developing device. In this embodiment, the amount of the toner remaining in a given developing device is detected when the developing device is in the second attitude ( FIG. 1(   a )); a developing device  5  which is in the position in which it is in the first attitude ( FIG. 1(   b )) is moved to the position in which it is in the second attitude ( FIG. 1(   a )). The first attitude of the developing device  5  is the attitude in which the developing device  5  can develop the electrostatic latent image on the drum  1 , that is, the attitude in which the development roller coating roller  24  can be coated with the toner T. The second attitude of the developing device  5  is the attitude into which the developing device  5  is changed in attitude from the first attitude, and in which the toner on the development roller coating roller  24  returns to the developer container  21 . The first attitude of the developing device  5  in this embodiment is the attitude in which the developing device  5  is in the position C (first position). The second attitude of the developing device  5  in this embodiment is the attitude in which the developing device  5  is in the position E (second position). As for the method for detecting the amount of toner remaining in the developing device  5  after the developing device  5  is changed in attitude into the second attitude, an AC bias is applied to the electrically conductive metallic core  29  of the development roller coating roller  24  (which functions as first electrode) by the toner (developer) remainder amount detecting apparatus  100   a.  Then, the amount of toner remaining in the developer container  21  is detected (estimated) by calculating the amount of the electrostatic capacity from the electrical voltage induced in the electrically conductive metallic core  28  (second electrode) of the development roller  25 . Hereafter, “electrostatic capacity” means the electrostatic capacity between the development roller coating roller  24  and development roller  25 . More concretely, the electrostatic capacity between the metallic core  28  of the development roller  25  and the metallic core  29  of the development roller coating roller  24  is measured. Further, in terms of the calculation of the amount of the “electrostatic capacity”, it is not always necessary to calculate the electrostatic capacity itself, such as 100 pf. That is, the amount of the toner remaining in the developing device  5  may be obtained by measuring the amount of voltage induced in the metallic core in response to the change in the amount of the electrostatic capacity, in the form of the voltage value or current value. 
     Next, the principle based on which the amount of the toner remaining in the developing device  5  is detected (estimated) will be described. One of the distinctive properties of the development roller coating roller  24  (which hereafter will be referred to simply as coating roller  24 ) in this embodiment is that it changes in the amount by which toner can be retained in the urethane sponge layer  29   a,  the cells of which are interconnected, is affected by the optimization of the airflow amount, which is one of the physical properties of the sponge layer  29   a.  The airflow amount indicates the amount by which air flows between the opening, at the peripheral surface of the urethane layer, of given cell, and the inward of the cell, per unit length of time. That is, the airflow amount is likely to reduce as the surface cells and internal cells are reduced in size, and therefore, increase in density. On the other hand, the amount of airflow is likely to increase as the surface and internal cells are increased in size. Thus, the amount by which toner can be retained in the sponge layer is affected by the change in the amount of airflow. Next, the method for measuring the amount of the airflow through the developer roller coating roller  24  will be described. Referring to  FIG. 2(   b ) which is a schematic drawing for describing the method for measuring the amount of the airflow through the developer roller coating roller  24 , a piece of acrylic plate  301  having a hole  301   a,  which is 10 mm in diameter, is placed in contact with the urethane sponge layer  29   a  of the coating roller  24  in such a manner that the hole  301   a  faces the sponge layer  29   a . Then, a hose  302 , which is larger in internal diameter than the hole  301   a  is connected to the hole  301   a.  Then, the amount of the airflow through the sponge layer  29   a , hole  301   a  and hose  302  is measured with an airflow measuring device  303  (KZ type Air Permeability Tester: product of Daiei Kagaku Seiki). The capacity of the pump  304  is 10.8 liter/min without the coating roller  24 . According to the experiments carried out by the inventors of the present invention, the amount of the airflow through the urethane sponge layer  29   a  (cells of which are interconnected) of the coating roller  24  was desired to be no less than 2 liter/min. Shown in  FIG. 3(   a ) are the changes which occurred to the relationship between the amount of the toner in the sponge layer  29   a  of the coating roller  24  and the amount of the toner in the developing device  5  when the urethane layer  29   a  was optimized in the amount of airflow. Referring to  FIG. 3(   a ), as the amount of the toner in the developer container  21  reduced, the amount of the toner in the sponge layer  29   a  of the coating roller  24  also reduced. It is evident from this result that there is a correlation between the amount by which toner is retained in the sponge layer  29   a  of the coating roller  24  and the total amount of the toner in the developer container  21 . Further, the changes in the relationship between the amount of the toner in the sponge layer  29   a  of the coating roller  24  and the amount of the electrostatic capacity between the coating roller  24  and development roller  25  were measured. The results of the measurement is shown in  FIG. 3(   b ). The amount of the electrostatic capacity was measured by the LCR meter ZM2354 (product of NF, Co., Ltd). Referring to  FIG. 3(   b ), the relationship between the amount of the toner in the sponge layer and the amount of the electrostatic capacity is virtually linear. It is evident from these results that there is a correlation between the amount by which toner can be retained in the sponge layer  26   a  of the coating roller  24  and the amount of the electrostatic capacity between the coating roller  24  and development roller  25 . In other words, the amount of the toner in the developer container  21  can be estimated by measuring the amount of the electrostatic capacity between the coating roller  24  and the development roller  25 . 
     In this embodiment, the amount of the toner in the developer container  21  is detected (estimated) by measuring the amount of electrostatic capacity between the coating roller  24  and development roller  25  of the developing device  5  after the developing device  5  is changed in attitude from the first attitude, that is, the attitude in which it is when it is in the first position, to the second attitude, that is, the attitude in which it is when it is in the second position. More concretely, the image forming apparatus is provided with a developing device positioning unit which changes the developing device  5  in position from the first attitude (position) C in which toner can be supplied from the toner storage chamber of the developing device  5 , which primarily stores toner, into the development chamber, that is, the chamber in which the coating roller  24  and development roller  25  are present, to the second attitude (position) E in which toner returns from the development chamber to the toner storage chamber. The amount of the toner remaining in the developing device  5  is detected while the developing device  5  is kept in the second attitude. Therefore, the amount of the electrostatic capacity is not affected by the change in the toner density, and the environment in which the developing device (image forming apparatus) is used, or left unused. Thus, the amount of the toner remaining in the developer container  21  can be precisely and reliably detected (estimated) by using the changes in the amount of the electrostatic capacity. 
     According to the above-described toner remainder amount detecting method, the measurement of the amount of the electrostatic capacity between the coating roller  24  and development roller  25  is started immediately after the developing device  5  is moved into the second position E, and the changes which occur to the amount of the electrostatic capacity during a preset length of time is mathematically calculated. It is based on the thus obtained value that the amount of the toner in the developer storage chamber  21  is obtained by calculation. Next, these steps for estimating the amount of the toner remaining in the developer container  21  are described in more detail. First, the behavior of the toner T in the developer container  21  of the developing device  5  will be described. The attitude of the developing device  5  in the position C (development position) is upright. Thus, the toner T in the developer container  21  is kept in only the bottom side of the developer container  2  by gravity. Therefore, a large amount of toner is in the area X, that is, the area in the top adjacencies of the nip between the development roller  25  and coating roller  24  in terms of gravity direction. In this embodiment, it is in the area X, which is on the upstream side of the nip between the coating roller  24  and development roller  25  in terms of the rotational direction of the development roller  25  that a large amount of toner is present. As the rotary  50  rotates 90°, the developing device  5  changes in position from the position C to the position F, and then, as the rotary  50  further rotates by additional 90°, the developing device  5  changes in position from the position F to the position E (which is 180° away from position C). When the developing device  5  is in the position E, the attitude of the developing device  5  is upside-down, and therefore, the portion of the body of the toner T, which was in the area X, falls from the area X due to the presence of gravity. That is, the attitude of the developing apparatus in the second position is the position in which the developer which is on the nip and its adjacencies when the developing apparatus is in the first position falls. Eventually, there will be no toner in the adjacencies of the coating roller  24  as shown in  FIG. 2(   a ). Therefore, the amount of electrostatic capacity between the metallic core  28  of the development roller  25  and the metallic core  29  of the developer supply roller  24  when the developing device  5  is in the position C is different from that when the developing device  5  is in the position E. In this embodiment, the position C shown in  FIG. 1(   a ) is the first position, and the position E shown in  FIG. 1(   a ) is the second position. It is when the developing device  5  is in the position E that the amount of the toner remaining in the developing device  5  is detected by the toner remainder amount detecting apparatus  100   a.  The toner remainder amount detecting apparatus  100   a  is the “detecting apparatus for detecting the amount of the developer remaining in the developer storage chamber of the developing device  5 , based on the changes in the amount of the electrostatic capacity between the first and second electrodes, which occurs during a preset length of time immediately after the developing apparatus is moved from the first position to the second position by the developing device positioning unit”. The results of the operation in which the amount of the electrostatic capacity began to be detected by the toner remainder amount detecting apparatus  100   a  immediately after the movement of the developing device  5  into the position E are shown in  FIG. 4(   a ). For example, in a case where the amount of the toner T in the developer container  21  is relatively large, such as immediately after the developing device  5  began to be used for the first time, the output of the toner remainder amount detecting apparatus  100   a  changes, as indicated by a line “a” in  FIG. 4(   a ), immediately after the movement of the developing device  5  into the position E. That is, the amount of the electrostatic capacity detected by the toner remainder amount detecting apparatus  100   a  during a period A in  FIG. 4(   a ) is greater than that when the amount of the toner in the adjacencies of the metallic core  29  of the coating roller  24  is only the toner in the sponge layer of the coating roller  24 . This phenomenon occurs because not all toner particles fall from the coating roller  24  immediately after the movement of the developing device  5  into the position E, and therefore, there is a certain amount of toner still remaining on the coating roller  24 . Thus, the amount of the electrostatic capacity detected during the period A is greater than the amount of the electrostatic capacity, which corresponds to only the amount of the toner in the sponge layer of the coating roller  24 . Thus, as the toner T continuously falls because of the presence of by gravity, the output (detected amount of electrostatic capacity) of the toner remainder amount detecting apparatus  100   a  gradually reduces. Eventually, no toner will remain in the adjacencies of the coating roller  24 , and the top surface Ta of the body of the toner T in the developer container  21  falls below the coating roller  24 , as shown in  FIG. 2(   a ). Thus, the output stabilizes. Referring to  FIG. 4(   a ), a period B is when the output of the toner remainder amount detecting apparatus  100   a  is stable. In comparison, in a case where the service life of the developing device  5  has been reduced to roughly half by its usage, the output of the toner remainder amount detecting apparatus  100   a  changes as indicated by the line “i” in  FIG. 4(   a ). That is, the period A is shorter because the toner T in the developer container  21  has been substantially consumed. Therefore, the state in which no toner is in the adjacencies of the coating roller  24 , that is, the state in which the surface Ta of the body of the toner T in the developer container  21  is below the coating roller  24 , occurs sooner. Further, toward the end of the service life of the developing device  5 , the changes in the output of the toner remainder amount detecting apparatus  100  becomes as indicated by line “u”. In this case, there is already not much toner in the adjacencies of the coating roller  24 , and the surface Ta of the body of the toner T is below the coating roller  24 . Therefore, the output of the toner remainder amount detecting apparatus  100   a  is not as high as that detected in the period A. Therefore, the output of the toner remainder amount detecting apparatus  100   a  becomes stable as soon as the developing device  5  is moved into the position E. 
     In this embodiment, the output of the toner remainder amount detecting apparatus  100   a  is mathematically processed as follows, in consideration of the above described behavior of the toner T and the resultant changes in the output value of the toner remainder mount detecting apparatus  100   a:  1) the outputs of the apparatus  100   a  during the period B, which correspond to the amount of the toner in the sponge layer of the coating roller  24 , is averaged to obtain a toner remainder amount detection output R, which is used as a background value. 2) the value T obtained by the surface integration of the difference which will be described below, with respect to the length of time the amount of the electrostatic capacity was detected by the toner remainder amount detecting apparatus  100   a  is the toner remainder amount detection output R. The abovementioned difference is the value obtained by subtracting the background value from the value of the amount of the electrostatic capacity measured by the apparatus  100   a  during the period A. Therefore, it reflects the amount of the toner particles which failed to fall from the coating roller  24 , being therefore greater than the amount of the electrostatic capacity which reflects the actual amount of the toner in the sponge layer. The toner remainder amount detection output R is measured after the attitude of the developing device  5  is changed to the upside-down, that is, the second attitude. In other words, the output R is measured when there is virtually no toner in the adjacencies of the coating roller  24 . Therefore, it does not fluctuate; the amount of the electrostatic capacity does not fluctuate. Thus, it can be used to accurately estimate the amount of the toner in the sponge layer of the coating roller  24  the toner remainder amount detection output R does not reflects the above described changes in the amount of the electrostatic capacity. In other words, it can be used to accurately estimate the amount of the toner in the sponge layer of the coating roller  24 . The amount of the toner in the sponge layer of the coating roller  24  tends to reduces as the amount of the toner in the developer container  21  reduces. However, in the area of the developer container  21 , in which the amount of toner is relatively large, the ratio by which the amount of the toner in the sponge layer of the coating roller  24  reduces, relative to the amount by which the toner in the developer container  21  reduces, is relatively small. In other words, the toner remainder amount detecting apparatus  100   a  in this embodiment, which detects the changes in the amount of the electrostatic capacity between the coating roller  24  and development roller  25 , is low in terms of the level of accuracy with which the amount of the toner remainder in the developer container  21  is detected. Thus, the toner remainder amount detection output T is obtained to improve the toner remainder amount detecting apparatus  100   a  in this embodiment, in the accuracy with which it detects the toner remainder amount in the developer container  21  when the amount of the toner in the developer container  21  is relatively large. The changes in the relationship between the toner remainder amount detection output T and the amount of the toner in the developer container  21  is shown in  FIG. 4(   b ). It was discovered that until the amount of the toner in the developer container  21  falls to a certain value, the amount by which the toner remainder amount detection output T reduces is virtually proportional to the amount by which the amount of the toner in the developer container  21  reduces, as shown in  FIG. 4(   b ). Thus, when the amount of the toner in the developer container  21  is relatively large, the correlation between the toner remainder amount detection output T and the total amount of the toner in the developer container  21  is used to estimated the amount of the toner remaining in the developer container  21 . That is, the amount of the toner in the developer container  21  can be highly accurately detected (estimated) from when a brand-new developing device  5  is used for the first time to when its service life expires, by such mathematical calculation that complimentarily uses the toner remainder amount detection output R and toner remainder amount detection output T. In this embodiment, the correlation between the value obtained by the surface integration of the toner remainder amount detection output, with respect to the length of time the amount of the electrostatic capacity is measured is used to estimate the toner remainder amount in the developer container  21 . However, the similar results can be obtained by subjecting the toner remainder amount detection output to a mathematical process that shows the correlation between the toner remainder amount detection output and the amount of the toner in the developer container  21 , for example, the rate of the change in the amount of the electrostatic capacity, which is obtainable by the differentiation of the amount of the electrostatic capacity with respect to time (elapsed time). Next, the case in which the amount of the toner remainder in the developer container  21  is detected (estimated) by the differentiation of the amount of the electrostatic capacity with respect to time (elapsed time) will be described. As the amount of the toner in the developer container  21  further reduces, the amount of the electrostatic capacity changes from the amount represented by the line “a” in  FIG. 4(   a ) to the amount represented by the line “u”. That is, as the amount of the toner in the developer container  21  reduces, the value obtained by the differentiation of the amount of the electrostatic capacity, with respect to the elapsed time (period A) becomes virtually zero. Therefore, it is possible to detect (estimate) the amount of the toner remainder in the developer container  21 , based on the value obtained by differentiating the amount of the electrostatic capacity with respect to the elapsed time. That is, it is possible detect the amount of the toner remainder in the developer container  21  based on the value obtained by the differentiation of the amount of the electrostatic capacity with respect to the elapsed time. For example, if the value obtained by the differentiation of the amount of the electrostatic capacity with respect to the elapsed time exceeds a preset threshold value, it may be determined that the amount of the toner in the developer container  21  fell below a preset value. In this embodiment, the amount of the electrostatic capacity between the developer supplying member  24  and developer bearing member  25  begins to be measured immediately after the developing device  5  is moved into the second position E, and the amount of the developer in the developer container  21  is calculated (estimated) based on the value obtained by differentiating the measured amount of the electrostatic capacity, that is, the output of the toner remainder amount detecting apparatus  100   a,  with respect to the elapsed time. 
     Next, a detecting device  30  and an integrating device  31  which make up the toner remainder amount detecting apparatus  100   a  is described.  FIG. 5(   a ) is a schematic diagram which shows the equivalent circuits of the condenser C 1  (which comprises coating roller  24  and development roller  25 ), detecting device  30 , integrating device  31 , electric power source  33  for toner remainder amount detection bias, electric power source  34  for development bias, etc. The toner remainder amount detection bias, which is an AC bias, is supplied from the electric power source  33  for the toner remainder amount detection. The detecting device  30  comprises a resistor R and a diode D. The output of the condenser C 1  is picked up as the voltage of the resistor R, and is half-wave rectified. The half-wave rectified voltage is integrated by the integrating device  31 , which is a condenser C 2  in  FIG. 4(   a ), becoming thereby a DC voltage. The detected voltage is subject to the above described mathematical process by the CPU  32 , to obtain the toner remainder amount detection output R and toner remainder amount detection output T. In this embodiment, the application of the AC bias to the developing device  5  from the electric power source  33  for toner remainder amount detection bias, and the toner remainder amount detection by the detecting device  30 , integrating device  31 , and CPU  32 , are started immediately after the movement of the developing device  5  from the position F to the position E. Next, referring to  FIG. 5(   b ), the display of the amount of the toner remaining in the developing device  5  is described. The value displayed to show the amount of the toner in the developing device  5  immediately after a developing device  5  is used for the first time is obviously 100%. As an image forming operation continues, the amount of the toner T in the developer container  21  reduces, and therefore, the output T of the toner remainder amount detecting apparatus  100   a  reduces as described above, reducing thereby the value displayed to show the amount (percentage) of the toner remainder in the developer container  21 . In this embodiment, as the actual amount of the toner in the developer container  21  falls to roughly 40%, the output T of the toner remainder amount detecting apparatus  100   a  falls to virtually zero. That is, as the actual amount of the toner in the developer container  21  falls to roughly 40%, no toner remains in the adjacencies of the coating roller  24 , that is, the surface Ta of the body of the toner T in the developer container  21  falls below the coating roller  24 . From this point on, the estimated amount (percentage) of the toner in the developer container  21  is displayed based on the toner remainder amount detection output R. Then, as the output T falls to a preset value, “0%” is displayed as a warning on the display portion  300   a  of the control panel  300  to inform a user that a specific developing device ( 5 ) is “running out of toner”, or that it is time for the replacement of the specific developing device ( 5 ). Incidentally, as the output T falls to a preset value, the on-going image forming operation may be interrupted, in addition to displaying “0%” or “running out of toner”. As described above, the image forming apparatus in this embodiment can accurately detect the amount of the toner remaining in the developer container  21 , and convey to a user the information about the amount of the toner in the developer container  21 . In this embodiment, the toner remainder amount detecting operation is started immediately after the transfer of the developing device  5  from the position F to the position E. However, it is not mandatory that the operation is started immediately after the transfer of the developing device  5  from the position F to the position E. That is, as long as the changes in the amount of the electrostatic capacity can be detected, the timing with which the toner remainder amount detecting operation is started may be slightly before or after the transfer of the developing device  5  into the position E. 
     Embodiment 2 
     The image forming apparatus and developing devices in this embodiment are practically the same in structure as those in the first embodiment, except that those in this embodiment are provided with an antenna dedicated to the detection of the toner remainder amount detection output T. The effects of this embodiment are the same as the above-described effects of the first embodiment. 
     &lt;Developing Device&gt; 
     The first to fourth developing devices  5   a,    5   b,    5   c , and  5   d  in this embodiment are the same in structure although they are different in the color of the developer (toner) contained therein. Further, they are the same in structure as those in the first embodiment. Thus, the components, portions, etc., of the image forming apparatus in this embodiment, which are the same as the counterparts in the first embodiment are given the same referential codes, and are not described.  FIG. 6(   b ) is an enlarged schematic sectional view of one of the developing devices  5  in this embodiment, which is in the position C. The developing device  5  has: a developer container  21 , which is a developer storage chamber for storing toner T; a development roller  25  which is a developer bearing member for bearing the developer for developing an electrostatic latent image on the drum  1 ; and a development roller coating member  24  which is a member for supplying the development roller  25  with toner by being virtually in contact with the development roller  25 . The developing device has also: a regulation blade which is a member for forming the body of the toner borne on the development roller  25 , into a toner layer which is preset in thickness; and a seal  26  for preventing the toner in the developer container  21  from leaking out through the gap between the development roller  25  and developer container  21 . Further, the developing device has an antenna  40  (first electrode), which is in the adjacencies of the development roller coating roller  24  which is the developer supplying member for supplying the development roller  25  with toner by being placed in contact with the development roller  25 . The antenna  40  is positioned so that it extends in the lengthwise direction of the developer container  21 , through the area X, which will be described later. 
     &lt;Method for Detecting Amount of Toner Remaining in Developer Container Using Antenna&gt; 
     The image forming apparatus and developing devices in this embodiment are virtually the same in structure as those in the above described first embodiment, except that the developing devices in this embodiment have the antenna  40  dedicated to the detection of the toner remainder amount detection output T. The toner remainder amount detecting method described in regard to the description of the first embodiment can also be used by the image forming apparatus and developing devices in this embodiment. In addition, in the case of this embodiment, the toner remainder amount can be detected with the use of the antenna. The operation for detecting the amount of the toner remaining in the developing device  5  with the use of the antenna is also carried out after the developing device  5  is changed in attitude from the first attitude ( FIG. 6(   a )) into the second attitude ( FIG. 6(   b )). Also in this embodiment, the first attitude of the developing device  5  is the attitude in the developing device  5  is when it is in the position C. The second attitude is the attitude in which the developing device  5  is in the position E (second position). The toner remainder amount detecting method which uses the antenna  40  is as follows: an AC bias is applied to the electrically conductive metallic core  28  of the development roller  25  by the toner remainder amount detecting apparatus  100   a.  Then, the amount of the toner remaining in the developer container  21  is detected (estimated) from the amounts of voltage and electrostatic capacity induced in the antenna  40  (which is electrically conductive). Hereafter, the output of the toner remainder amount detecting apparatus  100   a  which detects the amount of the electrostatic capacity through the antenna  40  is referred to as the electrostatic capacity detection output S. The above described operation for detecting the amount of the electrostatic capacity, that is, the operation which detects the amount of the electrostatic capacity between the development roller  25  and antenna  40  is started immediately after the developing device  5  is transferred to the second position E, and the changes which occurs to the electrostatic capacity detection output S during a preset length of time (detection time) is subjected to mathematically process, with respect to the preset length of time. Next, the method for calculating (estimating) the amount of the developer in the developer storage chamber  21  is described in detail. First, the behavior of the toner T in the developer container  21  is described. When the developing device  5  is in the position C, that is, the development position, its attitude is upright. Thus, the toner T in the developer container  21  is kept in only the bottom side of the developer container  21   2  by gravity. Therefore, a large amount of toner is in the area X, that is, the top adjacencies of the nip between the development roller  25  and coating roller  24  in terms of gravity direction. In this embodiment, it is in the area X, which is on the upstream side of the nip between the coating roller  24  and development roller  25  in terms of the rotational direction of the development roller  25  that a large amount of toner is present. The antenna  40  is positioned so that it extends in the lengthwise direction of the developing device  5  through the area X. As the rotary  50  rotates 90°, the developing device  5  changes in position from the position C to the position F, and then, as the rotary  50  further rotates by additional 90°, the developing device  5  changes in position from the position F to the position E (which is 180° away from position C). When the developing device  5  is in the position E, the attitude of the developing device  5  is upside-down, and therefore, the portion of the body of the toner T, which was in the area X, is made to fall away from the coating roller  24  by gravity. Eventually, there will be no toner in the adjacencies of the antenna  40  as shown in  FIG. 6(   b ). In this embodiment, the position C shown in  FIG. 6(   a ) is referred to as the first position, and the position E shown in  FIG. 1(   a ) is referred to as the second position. It is when the developing device  5  is in the position E that the amount of the toner remaining in the developing device  5  is detected by the toner remainder amount detecting apparatus  100   a.  The results of the operation in which the amount of the electrostatic capacity began to be detected by the toner remainder amount detecting apparatus  100   a  immediately after the movement of the developing device  5  into the position E are shown in  FIG. 7(   a ). For example, when the amount of toner T in the developer container  21  is relatively large, such as immediately after the developing device  5  began to be used for the first time, the electrostatic capacity detection output S changes as indicated by a line “a”, immediately after the movement of the developing device  5  into the position E. That is, the output S is greater in value during a preset length of time within the period A, where a substantial amount of toner, which did not fall immediately after the movement of the developing device  5  into the position E, is still in the adjacencies of the antenna  40 . Thus, as the portion of the toner T, which remained in the adjacencies of the antenna  40 , continues to fall away from the coating roller  24 , the electrostatic capacity detection output S gradually reduces. Eventually, no toner will remain in the adjacencies of the antenna  40 . Thus, the output S stabilizes. Referring to  FIG. 7(   a ), a period B is the period in which the electrostatic capacity detection output S is stable. In comparison, when the service life of the developing device  5  has been reduced to roughly half by its usage, the electrostatic capacity detection output S changes as indicated by the line “i” in  FIG. 7(   a ). That is, because the toner T in the developer container  21  has been substantially consumed, the period A is relatively short. Therefore, the state in which no toner is in the adjacencies of the antenna  40  comes sooner. Toward the end of the service life of the developing device  5 , the electrostatic capacity detection output S becomes as indicated by line “u”. During this period in the service life of the developing device  5 , there is not much toner left in the adjacencies of the antenna  40  anyway, and therefore, the output S is not going to be as high as that in the period A. Thus, the electrostatic capacity detection output S becomes stable in value immediately after the movement of the developing device  5  into the position E. 
     In this embodiment, the output of the toner remainder amount detecting apparatus  100   a  is mathematically processed as follows, in consideration of the above-described behavior of the toner T and the resultant changes in the electrostatic capacity detection output S. In the first place, the electrostatic capacity detection output S in the period B is such an output that is obtained when there is virtually no toner in the adjacencies of the antenna  40 . Therefore, it is stable regardless of the state of the usage of the developing device, that is, the amount of the usage of the toner in the developer container  21 . Thus, the outputs of the apparatus  100   a  during the period B are averaged to obtain a background value U. Then, the difference obtained by subtracting the background value U from the electrostatic capacity detection output S is surface-integrated, with respect to the length of time the amount of the electrostatic capacity is detected, to obtain a toner remainder amount detection output V. Since the toner T in the developer container  21  behaves as described above, the toner remainder amount detection output V reduces in proportion to the toner remainder amount in the developer container  21  as the amount of the toner in the developer container  21  gradually reduces to a preset value. The preset value is the value at which no toner will be in the adjacencies of the antenna  40 . That is, the electrostatic capacity detection output S becomes stable, making stable the background value, and therefore, the toner remainder detection output V becomes a preset value, which is zero in this embodiment. As soon as the toner reminder amount detection output V becomes zero, the image forming apparatus starts the second toner remainder amount detecting apparatus. The first toner remainder amount detecting apparatus in this embodiment is the same as the above described toner remainder amount detecting apparatus in the first embodiment. The second toner remainder amount detecting apparatus applies an AC bias to the metallic core  29  of the coating roller  24  by the toner remainder amount detecting apparatus  100   a . Then, it detects (estimates) the amount of the toner in the developer container  21  based on the amount of voltage and electrostatic capacity induced in the metallic core  28  (which is electrically conductive) of the development roller  25 . The second toner remainder amount detecting apparatus outputs a toner remainder amount detection output W. The toner reminder amount detection output W is the output of the second toner remainder amount detection apparatus when the output of the toner remainder amount detection output V is zero, that is, when there is virtually no toner is in the adjacencies of the antenna  40 . When the developing device  5  is in the second position, that is, when the developing device  5  is upside-down in attitude, there is no excess amount of toner in the adjacencies of the coating roller  24 . Therefore, there is no change in the electrostatic capacity, making it possible to accurately estimate the amount of the toner in the sponge layer of the coating roller  24 . As for the toner remainder amount detection output W, it is likely that as the amount of the toner in the developer container  21  reduces, the amount of the toner in the sponge layer of the coating roller  24  also reduces. The area of the developer container  21 , which is relatively large in the amount of the toner, is smaller in the ratio between the rate with which the amount of the toner in the sponge layer of the coating roller  24  reduces, relative to the rate with which the amount of the toner in the developer container  21  reduces is small. That is, when the amount of the toner in the developer container  21  is relatively large, the accuracy with which the amount of the toner in the developer container  21  is detectable is relatively low. Thus, in this embodiment, the developing device  5  is provided with an electrically conductive antenna to obtain the electrostatic amount detection output S, in order to improve the image forming apparatus in terms of the accuracy with which the amount of the toner in the developer container  21  is detected when the amount of the toner in the developer container  21  is relatively large. 
     Referring to  FIG. 7(   b ), the portion of the developer container  21 , which is large in the amount of the toner, is smaller in the ratio of the rate with which the toner in the sponge layer of the coating roller  24  reduces, relative to the rate with which the toner in the developer container  21  reduces, and therefore, is lower in the accuracy with which the amount of the toner remainder in the developer container  21  can be detected. Therefore, when the amount of the toner in the developer container  21  is relatively large, the amount of the toner remainder in the developer container  21  is calculated (estimated) based on the decrease in the toner remainder amount detection output V. Then, as the amount of the toner remaining in the developer container  21  falls to a preset value (35% in this embodiment), that is, as the value of the toner remainder amount detection output V falls to zero, the amount of the toner remainder in the developer container  21  begins to be calculated based on the toner remainder amount detection output W, which is the ratio of the rate with which the amount of the toner in the sponge layer of the coating roller  24 , relative to the ratio with which the amount of the toner remainder in the developer container  21  reduces. That is, the toner remainder amount detection output V and toner remainder amount detection output W are complimentarily used to mathematically estimate the amount of the toner remaining in the developer container  21 . Therefore, the amount of the toner remaining in the developer container  21  can be highly precisely detected from when a given developing device begins to be used for the first time to when it runs out of the toner. In this embodiment, the correlation between the value obtained by surface-integrating the electrostatic capacity detection output, with respect to the length of the electrostatic capacity detection time, and the amount of the toner remainder in the developer container  21 , is used to calculate (estimate) the amount of the toner remaining in the developer container  21 . However, the same effects can also be obtained by a mathematical process which shows the relationship between the time-differentiation which shows the rate of change in the electrostatic capacity amount detection output, and the amount of the toner remainder in the developer container  21 . That is, the amount of the electrostatic capacity between the antenna  40  (electrode) and developer bearing member  25  begins to be measured immediately after the movement of the developing device  5  into the second position E, and the amount of the developer in the developer storage chamber is calculated based on the value obtained by time-differentiating the electrostatic capacity detection output. 
       FIG. 6(   b ) shows the structure of the toner remainder amount detecting apparatus  100   a  in this embodiment. A toner remainder amount detection bias, which is an AC bias, is applied from the electric power source  33  for toner remainder amount detection bias. The image forming apparatus is structured so that the toner remainder amount detection bias can be selectively supplied to the metallic core (which is electrically conductive) of the development roller  25 , or that of the coating roller  24 . Further, the toner remainder amount detection circuit, which comprises a detecting device  30 , etc., are selectively connectible to the antenna  40 , or the electrically conductive metallic core of the development roller  25 . Referring to  FIG. 6(   b ), in this embodiment, the toner remainder amount detection bias is switchable to the development roller  25 , and the toner remainder amount detection circuit is switchable to the antenna  40 . Further, the toner remainder amount detection bias is switchable to the coating roller  24 , and the toner remainder amount detection circuit is switchable to the development roller  25 . The reason why these biases are made switchable is to make it possible for the toner remainder amount to be accurately detectable to the end of the service life of a given developing device. The antenna  40  is unlikely to retain toner. Thus, as the developing device  5  is changed in position to measure the amount of the electrostatic capacity between the development roller  25  and antenna  40  after the amount of the toner in the developing device  5  has become small, the toner which was in the adjacencies of the antenna before the position change immediately disappears, making it therefore difficult to detect the changes in the amount of the electrostatic capacity. In comparison, the coating roller  24  has the foamed layer, being therefore likely to retain a certain amount of toner. Thus, even after the substantial amount of reduction in the amount of the toner remainder in the developing device  5 , the change in the amount of the electrostatic capacity between the development roller  25  and coating roller  24  is likely to be gentle even after the change in the position of the developing device  5 , making it possible to measure the amount of the electrostatic capacity. As described above, the electrode for measuring the amount of the electrostatic capacity may be switched according to the amount of the toner remainder in the developing device  5 . As for the reason for the switch, when the coating roller  24  is used as the electrode, there is the toner in the coating roller  24 . Therefore, while the amount of the electrostatic capacity is measured within the period B shown in  FIG. 4(   a ), the amount of the electrostatic capacity is changed by the amount of the toner remainder in the developer container  21 . Although the amount of the electrostatic capacity measured during the period B is canceled as the background, there is a possibility that it will still affect the measurement accuracy. Thus, while the large amount of toner still remains in the developer container  21 , the amount of the electrostatic capacity between the antenna  40  and development roller  25  is measured to make it unnecessary to take the background value into consideration (period B in  FIG. 7(   b )), so that the amount of the electrostatic capacity can be measure with a higher level of accuracy. If it is determined from the amount of the electrostatic capacity between the antenna  40  and development roller  25  that the amount of the toner in the developer container  21  fell below a preset value, the coating roller  24  begins to be used as the electrode for measuring the amount of the electrostatic capacity. Incidentally, if the amount of the developer in the developer container  21  can be detected at a satisfactory level of accuracy by measuring the amount of the electrostatic capacity between the development roller  25  and antenna  40  to the end of the service life of a developing device, the image forming apparatus does not need to be provided with the abovementioned switching means. The means, in this embodiment, for displaying the amount of the toner remaining in a given developing device is the same as the above described one in the first embodiment, and therefore, is not described here. 
     As described above, the present invention can make it possible for an image forming apparatus to accurately detect the amount of the toner remaining in a given developing device in the apparatus, and inform a user of the information (amount of toner remainder in developing device). In the above described embodiments of the present invention, the operation for detecting the toner remainder amount in the developer container  21  was started immediately after the developing device  5  was moved from the position F to the position E. However, it is not mandatory that the operation is started immediately after the movement of the developing device  5  into the position E. In other words, as long as the changes in the amount of the electrostatic capacity can be detected, the timing with which the operation is to be started may be slightly before or after the transfer of the developing device  5  into the position E. Incidentally, the image forming apparatus in the second embodiment was structured so that the amount of the electrostatic capacity between the antenna  40  and development roller  25  is measured. However, this setup is not mandatory. That is, as long as the amount of the electrostatic capacity is changed by the change in the position of the developing device  5 , the apparatus may be structured so that the amount of the electrostatic capacity between the antenna  40  and coating roller  24  is measured. Further, instead of using the development roller  25  or coating roller  24  as one of the electrodes, two or more antennas may be provided to be used as electrodes for electrostatic capacity detection, so that the amount of the electrostatic capacity between two antennas is measured for the detection of the amount of the toner remainder in the developing device  5 . Further, in consideration of the fact that it is only for estimating the amount of the toner in a developing device  5  that the amount of the “electrostatic capacity” is obtained by calculation, it is not mandatory to obtain the amount, such as 100 pf, of the electrostatic capacity. That is, the amount of the toner remaining in a developing device  5  may be calculated (estimated) by measuring the voltage which is induced in the metallic core of the development roller  25  or coating roller  24 , and the amount of which is affected by the changes in the amount of the electrostatic capacity, by the detection circuit, or by measuring the electric current flowed by the voltage, by the detection circuit. 
     [Miscellanies] 
     1) Image forming apparatuses to which the present invention is applicable are not limited to those of the electrophotographic type; not only is the present invention is applicable to electrophotographic image forming apparatuses, but also, image forming apparatuses of the electrostatic recording type, which use an electrostatically recordable dielectric member as an image bearing member, and image forming apparatuses of the magnetic recording type, which use a magnetically recordable member as an image bearing member. 2) Not only is the present invention applicable to developing apparatuses of the above described type, but also, those of the non-contact type, which use nonmagnetic toner as developer, and those of the contact type or non-contact type, which use magnetic toner as developer. 
     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. 
     This application claims priority from Japanese Patent Applications Nos. 216900/2009 and 159297/2010 filed Sep. 18, 2009 and Jul. 14, 2010, respectively, which are hereby incorporated by reference.