Patent Publication Number: US-8971734-B2

Title: Image forming apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a remaining amount detection of a toner which is a developer in an electrophotographic image forming apparatus such as a laser printer, a copying machine or a facsimile machine. 
     BACKGROUND ART 
     In a convention image forming apparatus, there is an example in which the remaining amount of the toner in a toner container is detected by an electrostatic capacity detecting device. For example, in a remaining toner amount detecting device described in Japanese Patent No. 4137703, a flexible member including a member to be detected at its end is connected with a stirring member and is rotated by rotation of the stirring member, so that the flexible member enters the toner and rotates. At this time, when a connecting portion between the flexible member and the stirring member enters the toner, the entire flexible member continuously enters the toner at the same portion while being deformed with flexibility, so that the flexible member draws the same locus in the toner and is rotationally moved. Therefore, also a member to be detected provided at the end of the flexible member draws the same locus as that of the flexible member and is rotationally moved. Further, when the amount of the toner is decreased to less than a certain level and the connecting portion with the stirring member does not enter the toner, the neighborhood of the end of the flexible member slides on the toner surface and also the member to be detected slides and moves on the toner surface. Here, when the amount of the toner is decreased to less than the certain level and a height of the toner surface is gradually lowered, a position of the member to be detected which slides and moves on the toner surface is also gradually lowered. That is, when the toner amount is decreased to less than the certain level, depending on a remaining toner amount, the position of the member to be detected which moves on the toner surface is also lowered. 
     On the other hand, an electrostatic capacity sensor detects an electrostatic capacity between itself and the member to be detected which moves on the toner surface, and the electrostatic capacity changes depending on a distance between the both members. Further, the electrostatic capacity sensor is disposed at a lower portion of the toner container and therefore when the toner amount is decreased to less than the certain level and the position of the member to be detected which moves on the toner surface is lowered, the distance between the electric signal sensor and the member to be detected becomes short and thus the electrostatic capacity between the both members becomes large. That is, the electrostatic capacity between the electrostatic capacity sensor and the member to be detected changes depending on the remaining toner amount. 
     Further, in the conventional image forming apparatus, a permeability sensor is used in a device for detecting the amount of the toner in a developing unit. As an example of the device for detecting the amount of the toner by using the permeability sensor, e.g., there is the detecting device as disclosed in Japanese Laid-Open Patent Application (JP-A) 2002-132036. JP-A 2002-132036 discloses the toner amount detecting device which uses a flexible first stirring blade deformed toward a rear side with respect to a rotational direction by stirring the toner, a rigid second stirring blade provided at the rear side of the first stirring blade with respect to the rotational direction, and the permeability sensor provided outside the bottom of the developing unit. This device detects a state of a rotating operation of a metal material provided on each of the stirring blades by the permeability sensor provided outside the bottom of the developing unit. Further, this device is constituted so that in the case where the toner amount in the developing unit is large, the first stirring blade and the second stirring blade integrally perform the rotating operation and so that in the case where the toner amount in the developing unit is small, the first stirring blade and the second stirring blade separately perform the rotating operation without being deformed. In this case, when the toner amount is detected by using the permeability sensor, a change in permeability per rotation of a rotation shaft is detected once in the case where the toner amount in the developing unit is large and is detected twice in the case where the toner amount in the developing unit is small. The toner amount detecting device detects the toner amount in the developing unit on the basis of the change in number of this detection. 
     However, the above-described remaining toner amount detecting device is accompanied with the following problem. In the case where the toner is filled at the certain level or more, the connecting portion between the stirring member and the flexible member enters the toner and therefore the loci drawn by the flexible member and the member to be detected do not little change. That is, in the case where the toner is filled at the certain level or more, the detected electrostatic capacity also does not little change. Therefore, in the case where the toner is present in a certain amount or more, the remaining toner amount cannot be accurately detected in real time. 
     Further, the detecting device of JP-A 2002-132036 involves the following problem. In the case where the first and second stirring blades integrally perform the rotating operation and therefore a signal detected by the permeability sensor indicates one change of the permeability per rotation of the rotation shaft. On the other hand, in the case where the toner amount is small, the first stirring blade is little deformed and thus the first and second stirring blade do not integrally perform the rotating operation. At this time, the signal detected by the permeability sensor indicates two changes of the permeability per rotation of the rotation shaft. Thus, selective detection of the amount of the toner or the presence/absence of the toner is made depending on the number (once or twice) of the change in magnetic field detected by the permeability sensor. For this reason, it is difficult to detect the change in toner amount in real time. 
     DISCLOSURE OF THE INVENTION 
     The present invention has been accomplished in these circumstances. A principal object of the present invention is to provide an image forming apparatus capable of detecting a remaining toner amount in real time from a full state to an empty state and capable of detecting the remaining toner amount even when stirring member is operated at high speed. 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising: a rotatable member which is provided on and rotatable about a rotation shaft in a detachably mountable developing unit containing a developer and has flexibility so that it is flexed depending on a physical resistance of the developer; an electroconductive member to be detected which is provided on the rotatable member; a detecting electrode provided in a neighborhood of an outer wall surface of a bottom of the developing unit; converting means for detecting an electrostatic capacity between the member to be detected and the detecting electrode and for converting the electrostatic capacity into an electric signal; measuring means for measuring a time duration in which the electric signal converted by the converting means exceeds a predetermined threshold; and discriminating means for discriminating an amount of the developer on the basis of the time duration measured by the measuring means. 
     According to another aspect of the present invention, there is provided an image forming apparatus comprising: a rotatable member which is provided on and rotatable about a rotation shaft in a detachably mountable developing unit containing a developer and has flexibility so that it is flexed depending on a resistance of the developer; an electroconductive member to be detected which is provided on the rotatable member; a detecting electrode provided in a neighborhood of an outer wall surface of a bottom of the developing unit; converting means for detecting an electrostatic capacity between the member to be detected and the detecting electrode and for converting the electrostatic capacity into an electric signal; measuring means for measuring a detection level of the electric signal converted by the converting means; and discriminating means for discriminating an amount of the developer on the basis of the detection level measured by the measuring means. 
     According to another aspect of the present invention, there is provided an image forming apparatus comprising: a rotatable member which is provided on and rotatable about a rotation shaft in a detachably mountable developing unit containing a developer and has flexibility so that it is flexed depending on a resistance of the developer; an electroconductive member to be detected which is provided on the rotatable member; a detecting electrode provided in a neighborhood of an outer wall surface of a bottom of the developing unit; converting means for detecting an electrostatic capacity between the member to be detected and the detecting electrode and for converting the electrostatic capacity into an electric signal; first measuring means for measuring a time duration in which the electric signal converted by the converting means exceeds a predetermined threshold; second measuring means for measuring a detection level of the electric signal converted by the converting means; discriminating means for discriminating an amount of the developer on the basis of the time duration measured by the first measuring means or the detection level measured by the second measuring means; and control means for effecting control so that the discriminating means discriminates, when the discriminating means discriminates that the amount of the developer is less than a predetermined amount on the basis of the time duration measured by the first measuring means, the amount of the developer on the basis of the detection level measured by the second measuring means and so that the discriminating means discriminates, when the discriminates that the amount of the developer is not less than the predetermined amount on the basis of the time duration measured by the first measuring means, the amount of the developer on the basis of the time duration measured by the first measuring means. 
     According to another aspect of the present invention, there is provided an image forming apparatus comprising: a detachably mountable developing unit for accommodating a developer; a first member which includes a first electrode and is rotatable about a rotation shaft in the developing unit; a second member which performs a rotating operation about the rotation shaft in the developing unit; a second electrode provided on an outer casing of the developing unit; outputting means for detecting an electrostatic capacity between the first electrode and the second electrode and for outputting data regarding the detected electrostatic capacity; and discriminating means for discriminating an amount of the developer in the developing unit on the basis of the data outputted from the outputting means. 
     According to another aspect of the present invention, there is provided an image forming apparatus comprising: a detachably mountable developing unit for accommodating a developer; a first member which comprises a first electrode and is rotatable about a rotation shaft in the developing unit; a second member which comprises a second electrode and is provided at a predetermined angle formed between itself and the first member with respect to the rotation shaft of the first member; a third electrode provided on an outer casing of the developing unit; outputting means for detecting an electrostatic capacity between the first electrode and the third electrode or between the second electrode and the third electrode and for outputting information on the detected electrostatic capacity; and discriminating means for discriminating an amount of the developer in the developing unit on the basis of the information outputted from the outputting means, wherein the discriminating means discriminates the amount of the developer on the basis of a difference between a time when the outputting means detects the electrostatic capacity between the first electrode and the third electrode and a time when the outputting means detects the electrostatic capacity between the second electrode and the third electrode. 
     According to a further aspect of the present invention, there is provided an image forming apparatus comprising: a detachably mountable developing unit for accommodating a developer; a first member which comprises a first electrode and is rotatable about a rotation shaft in the developing unit; a second member which comprises a second electrode and is provided at a predetermined angle formed between itself and the first member with respect to the rotation shaft of the first member; a third electrode provided on an outer casing of the developing unit; outputting means for detecting an electrostatic capacity between the first electrode and the third electrode or between the second electrode and the third electrode and for outputting information on the detected electrostatic capacity; and discriminating means for discriminating an amount of the developer in the developing unit on the basis of the information outputted from the outputting means, wherein the discriminating means discriminates the amount of the developer on the basis of a difference between the information on the electrostatic capacity between the first electrode and the third electrode outputted by the outputting means and the information on the electrostatic capacity between the second electrode and the third electrode outputted by the outputting means. 
     These and other objects, features and advantages of the present invention will become more apparent upon a 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  is a sectional view showing a structure of an image forming apparatus in Embodiments 1 to 3. 
       Parts (a) and (b) of  FIG. 2  are sectional views of a developing unit in Embodiment 1, and (c) of  FIG. 2  is a perspective view of a detecting Mylar and an electrode to be detected. 
         FIG. 3  is a circuit diagram of a remaining toner amount detection in Embodiment 1. 
       Parts (a) to (c) of  FIG. 4  are a characteristic graph, a waveform and a table T, respectively, for the remaining toner amount detection in Embodiment 1. 
         FIG. 5  is a flow chart of the remaining toner amount detection in Embodiment 1. 
       Parts (a) and (b) of  FIG. 6  is a characteristic graph and a table L, respectively, for the remaining toner amount detection in Embodiment 2. 
         FIG. 7  is a flow chart of the remaining toner amount detection in Embodiment 2. 
       Parts (a) and (b) of  FIG. 8  are sectional views of a developing unit in Embodiment 3, and (c) of  FIG. 8  is a perspective view of a detecting Mylar and electrodes to be detected. 
         FIG. 9  is a sectional view of a developing unit and an electrostatic capacity sensor in Embodiments 4 to 6. 
       Parts (a) and (b) of  FIG. 10  are a perspective view of a developing unit and a circuit diagram of an electrostatic capacity sensor and its peripheral portions, respectively, in Embodiments 4 to 6. 
       Parts (a) to (c) of  FIG. 11  are sectional views showing operations of a stirring Mylar and a detecting Mylar of the developing unit in Embodiments 4 to 6. 
       Parts (a) to (d) of  FIG. 12  are sectional views each showing an operation of the detecting Mylar in Embodiments 4 to 6, wherein (a) and (b) show the case where the toner amount is large and (c) and (d) show the case where the toner amount is small. 
       Parts (a) and (b) of  FIG. 13  are a characteristic graph and a table T 1 , respectively, in Embodiment 4. 
         FIG. 14  is a flow chart showing a processing sequence of remaining toner amount detection in Embodiment 4. 
         FIG. 15  is a graph showing a state in which a detection level of the electrostatic capacity sensor is changed by free fall of the detecting Mylar. 
       Parts (a) and (b) of  FIG. 16  are a characteristic graph depending on sensor sensitivity and a characteristic graph in which the sensor sensitivity is changed depending on a remaining toner amount, respectively, in Embodiment 5. 
       Parts (a) to (c) of  FIG. 17  are characteristic tables each showing the remaining toner amount depending on the sensor sensitivity in Embodiment 5. 
         FIG. 18  is a flow chart showing a processing sequence of remaining toner amount detection in Embodiment 5. 
       Parts (a) and (b) of  FIG. 19  are a characteristic graph and a table T 4 , respectively, in Embodiment 6. 
         FIG. 20  is a flow chart showing a processing sequence of remaining toner amount detection in Embodiment 6. 
       Part (a) of  FIG. 21  is a sectional view of a developing unit and an electrostatic capacity sensor substrate in Embodiments 7 and 9, and (b) of  FIG. 21  is a perspective view of a detecting Mylar and an electrode to be detected. 
         FIG. 22  is a circuit diagram of remaining toner amount detection in Embodiments 7 to 10. 
       Parts (a) and (b) of  FIG. 23  are sectional views each showing a developing unit and an electrostatic capacity sensor substrate in Embodiment 7. 
       Parts (a) to (c) of  FIG. 24  are a characteristic graph, a waveform and a table T, respectively, for remaining toner amount detection in Embodiments 7 and 8. 
         FIGS. 25A and 25B  are a flow chart of the remaining toner amount detection in Embodiments 7 and 8. 
         FIG. 26  is a sectional view of a developing unit and an electrostatic capacity sensor substrate in Embodiments 8 and 10. 
       Parts (a) to (c) of  FIG. 27  are a characteristic graph, a waveform and a table N, respectively, in Embodiments 9 and 10. 
         FIGS. 28A and 28B  are a flow chart of remaining toner amount detection in Embodiments 9 and 10. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiment 1 
     [Image Forming Apparatus] 
       FIG. 1  is a sectional view showing a general structure of a color laser printer which is an image forming apparatus in this embodiment. The color laser printer (hereinafter referred to as a main assembly  101 ) includes process cartridges  5 Y,  5 M,  5 C and  5 K which are detachably mountable to the main assembly  101 . These four process cartridges  5 Y,  5 M,  5 C and  5 K have the same structure but are different in that they form images with developers (hereinafter referred to as toners) of yellow (Y), magenta (M), cyan (C) and black (K), respectively. Hereinafter, the suffixes Y, M, C and K will be omitted in some cases except to the case where the description is made with respect to a specific color. The process cartridge  5  is constituted by 3 units consisting of a developing unit, an image forming unit and a residual toner unit. The developing unit includes a developing roller  3 , a toner supplying roller  12 , a toner container  23  and a polyester (terephthalate) stirring film stirring (Mylar)  34 . Further, the image forming unit includes a photosensitive drum  1  which is an image bearing member, and a charging roller  2 . The residual toner unit includes a cleaning blade  4  and a residual toner collecting container  24 . 
     Below the process cartridge  5 , a laser unit  7  is provided and exposes the photosensitive drum  1  to light on the basis of an image signal. The photosensitive drum  1  is charged to a predetermined negative potential by the charging roller  2  and then an electrostatic latent image is formed thereon by the laser unit  7 . The electrostatic latent image is reversely developed by deposition of the negative toner by the developing roller  3 , so that toner images of Y, M, C and K are formed. An intermediary transfer belt unit is constituted by an intermediary transfer belt  8 , a driving roller  9  and a secondary transfer opposite roller  10 . Inside the intermediary transfer belt  8 , a primary transfer roller  6  is provided opposed to an associated photosensitive drum  1 , and a transfer bias is applied to the primary transfer roller  6  by a bias applying device (not shown). 
     The respective photosensitive drums  1  are rotated in arrow directions indicated in the photosensitive drums  1 , and the intermediary transfer belt  8  is rotated in an arrow A direction. Then, a positive bias is applied to the primary rollers  6 , so that the toner images on the photosensitive drums  1  are successively primary-transferred onto the intermediary transfer belt  8  from the toner image on the photosensitive drum  1 Y and then are conveyed to a secondary transfer roller  11  in a superposition state of the four color toner images. A sheet feeding device includes a sheet (paper) feeding roller  14  for feeding a transfer(-receiving) material P from a sheet feeding cassette  13  which accommodates sheets of the transfer material P and a conveying roller pair  15  for conveying the fed transfer material P. The transfer material P fed from the sheet feeding device is conveyed to the secondary transfer roller  11  by a registration roller pair  16 . 
     In the transfer of the toner images from the intermediary transfer belt  8  onto the transfer material P, by applying a positive bias to the primary transfer roller  11 , the four color toner images on the intermediary transfer belt  8  are secondary-transferred onto the conveyed transfer material P. The transfer material P after the toner image transfer is conveyed into a fixing device  17  and is heated and pressed by a fixing film  18  and a pressing roller  19 , so that the toner images are fixed on the surface of the transfer material P. The transfer material P on which the toner images are fixed is discharged by a discharging roller pair  20 . On the other hand, the toner remaining on the surface of the photosensitive drum  1  after the toner image transfer is removed by the cleaning blade, so that the removed toner is collected in the residual toner collecting container  24 . Further, the toner remaining on the intermediary transfer belt  8  after the secondary transfer onto the transfer material P is removed by a transfer belt cleaning blade  21 , so that the removed toner is collected in a residual toner collecting container  22 . 
     Further, a control board (substrate)  80  in  FIG. 1  is a board for effecting control of the main assembly, and on the control board  80 , a one-chip microcomputer  40  (hereinafter referred to as CPU) and a storing portion including RAM, ROM and the like for storing data or the like for tables are mounted. The CPU  40  effects integrated control of the operation of the main assembly, such as control of driving sources (not shown) relating to the conveyance of the transfer material P and driving sources (not shown) for the process cartridges  5 , control relating to image formation, and control relating to failure detection. A video controller  42  controls light emission of a laser in the laser unit on the basis of image data. Further, the video controller  42  also interfaces with a user via a control panel (not shown). On the control panel, a remaining amount of the toner of each color is displayed in the form of a bar chart (graph). 
     [Constitution of Developing Unit] 
     Parts (a) and (b) of  FIG. 2  are sectional views each showing a developing unit and an electrostatic capacity sensor substrate  331  which constitute the process cartridge  5 , wherein (a) shows a state in which the remaining toner amount is about 50% and (b) shows a state in which the remaining toner amount is about 10%. The toner  28  of a color corresponding to each of Y, M, C and K is stirred by the polyester stirring film  34  accommodated in the developing unit. The polyester stirring film  34  is provided on a rotation shaft  25  and is rotated about the rotation shaft  25  in a direction indicated by an arrow in a toner container  23 . Further, the rotation shaft  25  is provided with a polyester (terephthalate) detecting film (detecting Mylar)  351  which is a rotatable member, having flexibility, for detecting the remaining toner amount. As the polyester detecting film  351 , a general-purpose Mylar film is used. A thickness of the polyester stirring film  34  was 150 μm, and a thickness of the polyester detecting film  351  was 75 μm. Therefore, the polyester detecting film  351  is larger in warp degree than the polyester stirring film  34 . The polyester detecting film  351  is provided with an electroconductive electrode to be detected  361  (member to be detected). Further, an electrostatic capacity sensor electrode  321  for detecting electrostatic capacity functions as a remaining toner amount detecting sensor. The electrostatic capacity sensor electrode  321  is provided in the neighborhood of an outer wall surface of the bottom of the toner container  23  when the process cartridge  5  is mounted in the main assembly  101 . On the electrostatic capacity sensor substrate  331 , an electrostatic capacity sensor IC  33  is mounted, and the electrostatic capacity sensor electrode  321  and a reference electrode  320  are formed in a copper foil pattern. Further, on the electrostatic capacity sensor substrate  331 , peripheral circuit parts of the electrostatic capacity IC  33  are mounted. The electrode to be detected  361  is used for moving electric charges from the electrostatic capacity sensor electrode  321 . 
     As shown in (a) of  FIG. 2 , when the polyester detecting film  351  is rotated, in the case where the remaining toner amount is large, the polyester detecting film  351  is subjected to physical resistance of the toner to be deformed toward a rear side of a rotational direction, thus being largely flexed (bent). Thus, in the case where the remaining toner amount is large, the polyester detecting film  351  passes through a position remote from the electrostatic capacity sensor electrode  321  and therefore the electrostatic capacity is detected as a low level, so that a time duration in which a detection level exceeds a threshold, i.e., a detection time duration, becomes short. On the other hand, as shown in (b) of  FIG. 2 , in the case where the remaining toner amount is small, the polyester detecting film  351  is less deformed and passes through a position close to the electrostatic capacity sensor electrode  321  and therefore the electrostatic capacity is detected at a high level, so that the detection time duration also becomes long. In this embodiment, by using this principle, detection of the remaining toner amount is effected. Part (c) of  FIG. 2  is a perspective view showing a positional relationship between the polyester detecting film  351  and the electrode to be detected  361 . A radial length of the electrode to be detected  361  is 30 mm. The length of each of the polyester detecting film  351  and the electrode to be detected  361  with respect to the direction of the rotation shaft  35  may only be required that the polyester detecting film  351  or the electrode to be detected  361  covers at least the detection surface of the electrostatic capacity sensor electrode  321 . The radial length of each of the polyester detecting film  351  and the electrode to be detected  361  is required to be to the extent that an end of the polyester detecting film  351  or the electrode to be detected  361  is contacted to the bottom (surface) of the toner container  23  and is flexed in a state in which there is no toner  28 . Further, the polyester detecting film  351  is a member which is softer than that of the polyester stirring film  34  but its material and thickness are not limited to those described above. 
     [Circuit Diagram of Remaining Toner Amount Detection] 
       FIG. 3  is a circuit view of the remaining toner amount detection. A bypass capacitor  46  removes noise of an analog power source terminal AVDD of the electrostatic capacity sensor IC  33 . Further, a bypass capacitor  47  removes noise of a digital power source terminal DVDD of the electrostatic capacity sensor IC  33 . Each of fixed resistors  43  to  45  divides a DC power source voltage of 5.0 and is connected with a THON input terminal or a THOFF input terminal of the electrostatic capacity sensor IC  33 , and constants are set so that a voltage of the THON input terminal is 1.4 V and a voltage of the THOFF input terminal is 0.8 V. To an SREF terminal, the reference electrode  320  is connected, and to an SIN  1  terminal, the electrostatic capacity sensor electrode  321  is connected. The reference electrode  320  is a copper foil pattern having the same area as that of the electrostatic capacity sensor electrode  321 . The electrode sensor IC  33  outputs level data, which is electric signals obtained by converting a detected electrostatic capacity, from a P 01  output terminal and an SDN output terminal to the CPU  40  via a serial communication line. 
     [Characteristic of Remaining Toner Amount Detection] 
     Next, a remaining toner amount detection characteristic in this embodiment will be described with reference to (a) to (c) of  FIG. 4 . Part (a) of  FIG. 4  is a waveform data showing a relationship between a detection level of the electrostatic capacity sensor IC  33  and a time (msec) when the remaining toner amount is 10%. The CPU  40  (first measuring means) measures the time duration in which the detection level of the electrostatic capacity sensor IC  33  is 60 or more, so that the time duration is 12.5 msec. Part (b) of  FIG. 4  is a characteristic graph showing a relationship between the remaining toner amount (%) and the time duration (msec) in which the detection level of the electrostatic capacity sensor IC  33  is 60 or more. When the remaining toner amount is 0%, the time duration in which the detection level of the electrostatic capacity sensor IC  33  or 60 or more is 13.7 msec. On the other hand, when the remaining toner amount is 100%, the time duration in which the detection level of the electrostatic capacity sensor IC  33  is 60 or more is 8.0 msec. Part (c) of  FIG. 4  is a table T showing a relationship between the remaining toner amount (%) and the time duration (msec) in which the detection level of the electrostatic capacity sensor IC  33  is 60 or more. The data of this table T are stored in a storing portion of the control board  80 . The remaining toner amount between numerical values in the table is obtained by linear interpolation of known remaining toner amounts. Here, the calculated detection levels are values in this embodiment and therefore when a condition is changed, the calculated detection level is also changed. This is true for the numerical values in the table T for calculating the remaining toner amount. 
     [Flow Chart of Remaining Toner Amount Detection] 
     Then, flow of the remaining toner amount detection will be described with reference to a flow chart of  FIG. 5 . Similarly as in the flow chart of  FIG. 5 , processing in flow charts in subsequent Embodiments is performed by the CPU  40 . However, the present invention is not limited thereto but in the case where e.g., an application-specific integrated circuit (ASIC) is mounted in the image forming apparatus, the ASIC may have a function of any of steps. First, the CPU  40  rotates the polyester stirring film  34  and the polyester detecting film  351  (S 101 ). The CPU  40  performs serial communication with the electrostatic capacity sensor IC  33  to set an initial value and then starts reading of the detection level of the electrostatic capacity sensor IC  33  (S 102 ). In the case where the CPU  40  discriminates that the detection level is 40 or less for 0.5 sec or more (S 103 , YES), the CPU  40  discriminates that the detection level is an initial state level at a position where there is no electrode to be detected  361 . The CPU  40  then discriminates, when the detection level of the electrostatic capacity sensor IC  33  is 60 or more (S 104 , YES), that a sensor signal rises and sets a timer at zero (S 105 ). The value of 60 used for the discrimination in S 104  is a so-called rising threshold. Then, the CPU  40  starts the timer for measuring the time duration (S 106 ). The CPU  40  discriminates, when the detection level of the electrostatic capacity sensor IC  33  is 50 or less (S 107 , YES) that the sensor signal falls (S 108 ). The value of 50 used for the discrimination in S 107  is a so-called falling threshold. Then, the CPU  40  stops the timer (S 108 ). Here, the reason why the detection level rising threshold is 60 and the detection level falling threshold is 50 is that hysteresis is provided and thus a malfunction due to noise is prevented. Next, the CPU  40  reads the timer value (S 109 ) and checks the value against a table T (S 110 ). Then, the CPU  40  notifies a video controller  42  of a remaining toner amount corresponding to the checked value (S 111 ) and then ends the remaining toner amount detection. 
     Here, a period of the polyester detecting film  351  is about 1 sec in this embodiment. The CPU  40  makes, when it discriminates that a state in which the detection level of is not 40 or less for 0.5 sec or more is continued for 2.0 sec or more (S 103 , NO and S 114 , YES), the following discrimination. That is, the CPU  40  discriminates that the electrostatic capacity sensor IC  33  fails, that the electrode to be detected  361  is in a state in which it stops at the detection position or that abnormal communication between the CPU  40  and the electrostatic capacity sensor IC  33  occurs (S 115 ). In this case, the CPU  40  notifies the video controller of the failure, the state or the abnormality (S 115 ) and then ends the remaining toner amount detection. Incidentally, in the case where the CPU  40  discriminates that the state in which the detection level is not 40 or less for 0.5 sec or more is not continued for 2.0 sec or more (S 103 , NO and S 114 , NO), the CPU  40  continues the processing of S 103 . Further, in the case where the CPU  40  discriminates that the detection level is less than 60 in S 104  and then 2.0 sec or more elapses (S 104 , NO and S 113 , YES), the electrode to be detected  361  cannot be detected and therefore the CPU  50  discriminates that the abnormality occurs, and notifies the video controller  42  of the abnormality (S 115 ) and then ends the remaining toner amount detection. In the case where the CPU  40  discriminates that the detection level is less than 60 in S 104  and then 2.0 sec or more do not elapse (S 104 , NO and S 113 , NO), the CPU  40  continues the processing of S 104 . In the case where the CPU  40  discriminates that the detection level is not 50 or less and 2.0 sec or more elapses after the start of the timer (S 107 , NO and S 112 , YES), the CPU  40  discriminates that the electrode to be detected  361  is stagnated at the detection position or that the electrostatic capacity sensor IC  33  causes abnormality, and then notifies the video controller  42  of the stagnation or the abnormality (S 115 ) and ends the remaining toner amount detection. Incidentally, in the case where the CPU  40  discriminates that 2.0 sec or more does not elapse from the timer start (S 112 , NO), the CPU  40  continues the processing of S 107 . 
     Incidentally, in the sequence in this embodiment, an example in which the time duration was measured on the basis of an absolute value of the detection level was described. However, a sequence in which a stable initial level is detected and the rising and falling times are measured with the detected level +α as the threshold to detect the time duration and thereafter the measured time duration is checked against the table T may also be employed. Thus, the CPU  40  can detect the remaining toner amount in real time by measuring the time duration in which the electrostatic capacity sensor IC  33  detects the electrode to be detected  361  and then by checking the measured time duration against the table T. 
     According to this embodiment, by the above-described constitution and operation, the following effects are achieved. First, the time duration in which the electrode to be detected  361  is detected in the remaining toner amount from 100% to 0% is monotonically increased, so that it is possible to detect the remaining toner amount in real time from the full state of the toner to the empty state of the toner. Further, in the electrostatic capacity sensor type, a reaction speed is fast and therefore speed-up of the detection time and the image forming operation can be performed simultaneously. Further, the warpage of the polyester detecting film  351  is stable depending on the remaining toner amount even when the polyester detecting film  351  is rotated at high speed and therefore the remaining toner amount detection can be effected in real time. 
     As described above, according to this embodiment, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detect with high accuracy. 
     Embodiment 2 
     In Embodiment 1, the remaining toner amount was measured with the time duration in which the electrostatic capacity sensor IC  33  detected the electrode to be detected  361 . In this embodiment, the remaining toner amount is measured in a range of e.g., 30% or more (predetermined amount or more), i.e., from 30% to 100% in the type in Embodiment 1 and thereafter in a range of, e.g., less than 30% (less than the predetermined amount), a detection again (sensitivity) of the electrostatic capacity sensor IC  33  is switched and then the level of the electrostatic capacity is detected. Then, on the basis of the detected level of the electrostatic capacity, the CPU (second measuring means) measures the remaining toner amount. Incidentally, the constitutions in  FIGS. 1 ,  2  and  3  described in Embodiment 1 are also applicable to a color laser printer in this embodiment. Further, constituent elements identical to those in Embodiment 1 are represented by the same reference numerals or symbols and will be omitted from detailed description. 
     [Characteristic of Remaining Toner Amount Detection] 
     Next, a remaining toner amount detection characteristic in this embodiment will be described with reference to (a) and (b) of  FIG. 6 . Part (a) of  FIG. 6  is a characteristic graph showing a relationship between the remaining toner amount (%) and the detection level of the electrostatic capacity sensor IC  33 . When the remaining toner amount is large, the polyester detecting film  351  is subjected to the resistance of the toner  28  and is largely warped, and the electrode to be detected  361  passes through a position remote from the electrostatic capacity sensor electrode  321  and therefore the electrostatic capacity between the electrode to be detected  361  and the electrostatic capacity sensor electrode  321  becomes small. On the other hand, when the amount of the toner  28  is small, the electrode to be detected  361  passes through a position close to the electrostatic capacity sensor electrode  321  and therefore the electrostatic capacity between the electrode to be detected  361  and the electrostatic capacity sensor electrode  321  becomes large. Part (b) of  FIG. 6  is a table L showing a relationship between the remaining toner amount (%) and the detection level of the electrostatic capacity sensor IC  33 . The data of this table L are stored in a storing portion of the control board  80 . Incidentally, the sensitivity of the electrostatic capacity sensor IC  33  for the table L and the sensitivity of the electrostatic capacity sensor IC  33  for the table T in Embodiment 1 are different from each other. For example, the detection level of the electrostatic capacity sensor IC  33  corresponding to the remaining toner amount of 10% in the table L is 190 but the detection level of the electrostatic capacity sensor IC  33  corresponding to the remaining toner amount of 10% in the table T is about 80 which is a different value. The remaining toner amount between numerical values in the table is obtained by linear interpolation of known remaining toner amounts. Here, the calculated detection levels are values in this embodiment and therefore when a condition is changed, the calculated detection level is also changed. This is true for the numerical values in the table L for calculating the remaining toner amount. 
     [Flow Chart of Remaining Toner Amount Detection] 
     Then, flow of the remaining toner amount detection in this embodiment after the remaining toner amount becomes less than 30% will be described with reference to a flow chart of  FIG. 7 . 
     Here, a period of the polyester detecting film  351  is one turn per about 1 sec also in this embodiment similarly as in Embodiment 1. The processing operations in S 201  and S 202  are the same as those in S 101  and S 102  in  FIG. 5  and therefore will be omitted from description. In the case where the CPU  40  discriminates that the detection level is 165 or less for 0.5 sec or more, the CPU  40  discriminates that the detection level is the initial state level at the position where there is no electrode to be detected  361  and stores an average of the values during 0.5 sec or more as an initial value (S 203 , YES and S 204 ). The CPU  40  makes, when it discriminates that the detection level of is not 165 or less for 0.5 sec or more and 2.0 sec or more elapses (S 203 , NO and S 214 , YES), the following discrimination. That is, the CPU  40  discriminates that any of the electrostatic capacity sensor IC  33  abnormal and notifies the video controller of the abnormality (S 215 ) and then ends the remaining toner amount detection. Incidentally, in the case where the CPU  40  discriminates that 2.0 sec or more does not elapse from the start of reading of the electrostatic capacity detection level (S 214 , NO), the CPU  40  continues the processing of SO 203 . 
     Next, in order to detect that the electrode to be detected  361  reaches the detection position, the CPU  40  monitors the detection level whether or not the detection level is (initial value)+10 or more (S 205 ). In the case where the CPU  40  discriminates that the detection level is not (initial value)+10 or more and (initial value)±9 is continued for 2.0 sec or more (S 213 , YES), the CPU  40  discriminates that the polyester detecting film  351  or the electrode to be detected  361  is abnormal and then notifies the video controller  42  of the abnormality (S 215 ) and ends the remaining toner amount detection. Incidentally, in the case where the CPU  40  discriminates that the detection level of (initial value) ±9 does not continued for 2.0 sec or more (S 213 , NO), the CPU  40  continues the processing of S 205 . In the case where the CPU  40  discriminates that the detection level is (initial value)+10 or more during the monitoring (S 205 , YES), the CPU discriminates that the electrode to be detected  361  reaches the detection position, and starts continued reading and then stores a read detection level value (S 206 ). Further, in the case where the CPU  40  discriminates that the detection level of (initial value)+10 or more is continued for 8 msec (S 207 , YES), the CPU  40  discriminates that the detection level as a normal value and stores its maximum (S 208 ). Incidentally, in the case where the CPU  40  discriminates that the detection level of (initial value)+10 or more is not continued for 8 msec (S 207 , NO), the CPU  40  continues the processing of S 105 . In the case where the CPU  40  discriminates that data of the maximum do not correspond to 10 data (S 209 , NO), the sequence is returned to the processing of S 205  (S 209 ). 
     The CPU  40  calculates, when the data of maximum correspond to 10 data (S 209 , YES), an average (remaining toner amount detection value) of the 10 data of the maximum (S 210 ) and checks the average against the table L (S 211 ). The CPU  40  obtains the remaining toner amount between numerical values in the table by linear interpolation of known remaining toner amounts. Thereafter, the CPU  40  notifies the video controller  42  of the checked remaining toner amount (S 212 ) and then ends the remaining toner amount detection. 
     According to this embodiment, by the above-described constitution and operation, the following effects are achieved. First, in the electrostatic capacity sensor type, a reaction speed is fast and therefore speed-up of the detection time and the image forming operation can be performed simultaneously. Further, the warpage of the polyester stirring film  34  is stable depending on the remaining toner amount even when the polyester detecting film  351  is rotated at high speed and therefore the remaining toner amount detection can be effected. Further, by combining the sequence of the time duration detection with timing when the electrostatic capacity is changed in Embodiment 1 with the sequence of the electrostatic capacity level detection in this embodiment, the present invention can meet process cartridges having various constitutions. Incidentally, the remaining toner amount of 0% to 100% may also be detected by only the sequence of the electrostatic capacity level detection. 
     As described above, according to this embodiment, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detect with high accuracy. 
     Embodiment 3 
     In Embodiments 1 and 2, the process cartridge  5  in which the electrode to be detected  361  was provided with the single polyester detecting film  351  was described as an example. In this embodiment, an example in which the electrode to be detected  361  is divided will be described. With respect to a color laser printer in this embodiment, the constitutions and flow charts in  FIGS. 1 and 2  to  7  described in Embodiments 1 and 2 are applied. Further, constituent elements identical to those in Embodiments 1 and 2 are represented by the same reference numerals or symbols and will be omitted from detailed description. 
     Parts (a) and (b) of  FIG. 8  are sectional views each showing a developing unit and an electrostatic capacity sensor substrate  331  which constitute the process cartridge  5  in this embodiment, wherein (a) shows a state in which the remaining toner amount is about 50% and (b) shows a state in which the remaining toner amount is about 10%. The electrode to be detected  361  is divided into two electrodes consisting of an electrode to be detected  361   a  and an electrode to be detected  361   b . The electrode to be detected  361   a  is provided in the neighborhood of the rotation shaft  25  and the electrode to be detected  361   b  is provided in the neighborhood of an end of the polyester detecting film  351 . A length from an edge of the electrode to be detected  361   a  at the rotation shaft  25  side to an edge of the electrode to be detected  361   b  at the polyester detecting film  351  end side is the same as that in Embodiments 1 and 2, i.e., 30 mm ((c) of  FIG. 8 ). By using such a constitution, the electrostatic capacity of the electrode to be detected  361   a  and the electrode to be detected  361   b  in total is detected and therefore the maximum of the detection levels is lowered but the above constitution is applicable in the case where the sensitivity of the electrostatic capacity sensor IC  33  can be ensured. 
     According to this embodiment, by the above-described constitution and operation, the following effects are achieved. The area of the electrode to be detected  361  becomes small and correspondingly a cost is lowered. Further, in the case where the warp degree of the polyester detecting film  351  is reduced by rigidity of the electrode to be detected  361  when the large electrode to be detected  361  is used as in Embodiments 1 and 2, by employing the electrode to be detected  361   a  and the electrode to be detected  361   a  in this embodiment, a sufficient warp degree can be ensured. Incidentally, in Embodiments 1 and 3, for easy understanding, an example in which reference to the table T was made in one detecting operation was shown. However, by effecting control such that data for plural times of the detection is averaged and thereafter reference to an associated table T is made, further enhancement of the detection accuracy can be expected. 
     Further, in Embodiments 1 to 3, an example in which the developing unit was integrally constituted was described. However, in a toner container of a supply type in which the developing roller and the toner container is separately provided, by providing the electrode to be detected and the polyester detecting film, the present invention is applicable. 
     As described above, according to this embodiment, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detect with high accuracy. 
     Embodiment 4 
     A constitution of an image forming apparatus in this embodiment is the same as that described in Embodiment 1 and therefore will be omitted from description. 
     [Constitution of Developing Unit and Electrostatic Capacity Sensor] 
       FIG. 9  is a sectional view of a developing unit and an electrostatic capacity sensor, provided in the neighborhood of the bottom of the developing unit, which constitute a process cartridge  5 B. Inside the process cartridge  5 B shown in  FIG. 9 , a developing roller  3 B and a toner supply roller  12 B are provided, and in a toner container  23 B, a toner  28 B of an associated color and a polyester stirring film  34 B for stirring the toner  28 B are present. The polyester stirring film  34 B (second member) is provided on a rotation shaft  29 B in the toner container  23 B and performs a circulation operation around the rotation shaft  29 B which performs a rotating operation by an unshown motor. Further, the rotation shaft  29 B is also provided with a polyester detecting film  351 B (first member), having flexibility, for detecting a remaining amount of the toner  28 B, and the polyester detecting film  351 B is rotatable around the rotation shaft  28 B. Further, the polyester detecting film  351 B is provided with an electroconductive electrode to be detected  361 B (first electrode) in the neighborhood of its circumferential end. 
     Further, an electrostatic capacity sensor substrate  331 B provided in the neighborhood of the bottom of the process cartridge  5 B is provided in the main assembly  101  and thereon, an electrostatic capacity sensor  33 B and its peripheral circuit parts (not shown) are mounted. The electrostatic capacity sensor  33 B detects a change in electrostatic capacity by an electrostatic capacity sensor electrode  321 B by using a difference between the electrostatic capacity by the electrostatic capacity sensor electrode  321 B and the electrostatic capacity by a reference electrode  320 B. On the electrostatic capacity sensor substrate  331 B, the electrostatic capacity sensor electrode  321 B and the reference electrode  320 B are formed in a copper foil pattern. The bottom of an outer casing of the developing unit approaches the electrostatic capacity sensor electrode  321 B (second electrode) when the process cartridge  5 B is mounted in the main assembly  101 . The electrostatic capacity sensor  33 B detects, in this state, the electrostatic capacity generated by the approach of the electrode to be detected  361 B, provided on the polyester detecting film  351 B, toward the electrostatic capacity sensor electrode  321 B. 
     Part (a) of  FIG. 10  is a perspective view of the process cartridge  5 B. The polyester detecting film  351 B is rotatable around the rotation shaft  29 B. For that reason, in the case where the polyester detecting film  351 B performs the rotating operation in a direction (upward direction) opposite to the gravitation direction, the polyester detecting film  351 B is rotated together with the toner  28 B by the rotation of the rotation shaft  29 B while being raised by the polyester stirring film  34 B. On the other hand, in the case where the polyester detecting film  351 B performs the rotating operation in the gravitation direction (downward direction), the polyester detecting film  351 B falls freely by its own weight, after the toner  28 B falls, in advance of the polyester stirring film  34 B. Incidentally, a constitution of the polyester detecting film  351 B may only be required that the polyester detecting film  351 B falls onto the toner  28 B after the toner  28 B stirred by the polyester stirring film  34 B falls and thus is not limited to that shown in (a) of  FIG. 10 . 
     Further, the electrostatic capacity sensor  33 B and its peripheral circuit parts may also be required to be capable of detecting the electrostatic capacity and thus can be replaced with analog integrated circuit parts. In this embodiment, the electrostatic capacity sensor electrode  321 B is formed on the electrostatic capacity sensor substrate  331 B provided in the main assembly  101  but may only be required to be provided in the neighborhood of the bottom of the developing unit and may also be directly molded on, e.g., the bottom of the developing unit. In that case, it is preferable that electrical contacts are provided on the electrostatic capacity sensor substrate  331 B and the electrostatic capacity sensor electrode  321 B so as to electrically connect the electrostatic capacity sensor substrate  331 B and the electrostatic capacity sensor electrode  321 B when the process cartridge  5 B is mounted in the main assembly  101 . 
     [Circuit Constitution of Electrostatic Capacity Sensor] 
     Part (b) of  FIG. 10  is a circuit diagram showing a connection relationship among the electrostatic capacity sensor  33 B, the CPU  40 , the reference electrode  320 B and the electrostatic capacity sensor electrode  321 B. In (b) of  FIG. 10 , AVDD of the electrostatic capacity sensor  33 B is an analog power source terminal and DVDD of the electrostatic capacity sensor  33 B is a digital power source terminal and in order to remove noise of these power source terminals, bypass capacitors  46 B and  47 B are provided respectively. To an SREF terminal, the reference electrode  320 B is connected, and to an SIN terminal, the electrostatic capacity sensor electrode  321 B is connected. Further, between the CPU  40 B and the electrostatic capacity sensor  33 B, data transfer by serial communication is effected. From the CPU  40 B, a clock signal for communication synchronization is supplied to a CL terminal of the electrostatic capacity sensor  33 B. Via an SD terminal, from the electrostatic capacity sensor  33 B, 8-bit detection data corresponding to a detected value of the electrostatic capacity is outputted. On the other hand, setting data for controlling the electrostatic capacity sensor  33 B is inputted from the CPU  40 B to the electrostatic capacity sensor  33 B via the SD terminal. 
     As described above, the electrostatic capacity  33 B detects the change in electrostatic capacity of the electrostatic capacity sensor  33 B by detecting a difference between the electrostatic capacity by the electrode to be detected  361 B and the electrostatic capacity sensor electrode  321 B and the electrostatic capacity by the reference electrode  320 B. The electrostatic capacity sensor  33 B is provided with an amplifier circuit for amplifying the detected difference of the electrostatic capacity. The sensitivity of the electrostatic capacity sensor  33 B indicating an amplification factor of the amplifier circuit can be set from the CPU  40 B to the electrostatic capacity sensor  33 B and can be set at 92 levels from 1 to 92. In the case where the sensitivity of the electrostatic capacity sensor  33 B is set at 92 which is high, the electrostatic capacity sensor  33 B can grasp a more minute change in electrostatic capacity and therefore can detect the electrostatic capacity even when the electrode to be detected  361 B is remote from the electrostatic capacity sensor electrode  321 B. On the other hand, in the case where the sensitivity of the electrostatic capacity sensor  33 B is set at 1 which is low, the electrostatic capacity sensor  33 B cannot grasp the change in electrostatic capacity when the change in electrostatic capacity is small and therefore cannot detect the change in electrostatic capacity when the electrode to be detected  361 B is remote from the electrostatic capacity sensor electrode  321 B. In the electrostatic capacity sensor electrode  321 B in this embodiment, a circuit for adjusting the sensitivity is mounted. The electrostatic capacity sensor may only be required to have a constitution capable of changing the sensitivity when the electrostatic capacity between the electrostatic capacity sensor electrode  321 B and the electrode to be detected  361 B is detected and is not limited to the electrostatic capacity sensor used in this embodiment. 
     [Operation of Polyester Stirring Film and Polyester Detecting Film] 
     Parts (a) to (d) of  FIG. 11  are sectional views each showing an operation of the polyester stirring film  34 B and the polyester detecting film  351 B which are used for detecting the remaining amount of the toner  28 B in the toner container  23 B. Part (a) of  FIG. 11  shows an initial state of the rotating operation. The polyester stirring film  34 B is in a state in which its end portion is located at a highest point, and the polyester detecting film  351 B is rotatable around the rotation shaft  29 B and therefore is in a state in which it falls freely and rests on the toner  28 B. Part (b) of  FIG. 11  shows an intermediate state in which the polyester stirring film  34 B performs the rotating operation together with the polyester detecting film  351 B. From the state of (a) of  FIG. 11 , the rotation shaft  29  is rotated and with the rotation, the polyester stirring film  34 B is rotated to contact the polyester detecting film  351 B which rests on the toner  28 B. Then the polyester stirring film  34 B performs the upward rotating operation with the polyester detecting film  351 B and at the same time the toner  28 B is also pushed upward. The toner  28 B has flowability and therefore before the polyester stirring film  34 B reaches the highest point, the toner  28 B start falling from the polyester stirring film  34 B onto the bottom of the toner container  23 B by its own weight and is gradually accumulated on the bottom of the toner container. Part (c) of  FIG. 11  shows a state in which the polyester stirring film  34 B reaches the highest point. When the polyester stirring film  34 B reaches the highest point together with the polyester detecting film  351 B and then the rotation shaft  29 B is further rotated, the polyester detecting film  351 B is rotatable around the rotation shaft  29 B and therefore is spaced from the polyester stirring film  34 B to start falling (free fall) onto the surface of the toner  28 B accumulated by its own weight. On the other hand, the polyester stirring film  34 B is connected with the rotation shaft  29 B and therefore follows the polyester detecting film  351 B to be gradually lowered while following the rotating operation of the rotation shaft  29 B. 
     Next, (a) to (d) of  FIG. 12  are sectional views each showing the state of the polyester stirring film  34 B in the case where the remaining amount of the toner  28 B is large and in the case where the remaining amount of the toner  28 B is small. Parts (a) and (b) of  FIG. 12  show an operation state of the polyester stirring film  34 B in the case where the remaining amount of the toner  28 B is relatively large, wherein (a) corresponds to the state of (b) of  FIG. 11  and (b) corresponds to the state of (a) of  FIG. 11 . In the state of (a) of  FIG. 12 , the polyester stirring film  34 B pushes upward the toner  28 B while contacting the polyester detecting film  351 B in synchronism with the rotation of the rotation shaft  29 B. Then, the toner  28 B has flowability and therefore as shown in (a) of  FIG. 12 , before the polyester stirring film  34 B reaches the highest point, the toner  28 B starts falling from the polyester stirring film  34 B onto the bottom of the toner container  23 B by its own weight, thus being gradually accumulated on the bottom of the toner container  23 B. Thereafter, when the rotation shaft  29 B is rotated and the polyester stirring film  34 B reaches the highest point, the polyester detecting film  351 B is rotatable around the rotation shaft  29 B and therefore starts falling by its own weight. Thus, the polyester detecting film  351 B falls after the toner  28 B is accumulated on the bottom of the toner container  23 B and stops on the surface of the toner  28 B. The state of the polyester detecting film  351 B at that time is shown in (b) of  FIG. 12 . In the case where the remaining amount of the toner  28  is large, a height from the bottom of the toner container  23  to the surface of the toner  28 B becomes high and therefore a stop position of the polyester detecting film  351 B is a position with a height  901 . 
     Next, (c) and (d) of  FIG. 12  show an operation state of the polyester stirring film  34 B in the case where the remaining amount of the toner  28 B is relatively small, wherein (c) corresponds to the state of (b) of  FIG. 11  and (d) corresponds to the state of (a) of  FIG. 11 . In the state of (c) of  FIG. 12  as described above, the polyester stirring film  34 B pushes upward the toner  28 B while contacting the polyester detecting film  351 B in synchronism with the rotation of the rotation shaft  29 B. In the case where the remaining amount of the toner  28 B is large, with later time, i.e., compared with the case where the remaining amount of the toner  28 B is large, at a higher position of the end portion of the polyester stirring film  34 B, the toner  28 B starts falling from the polyester stirring film  34 B onto the bottom of the toner container  23 B by its own weight, thus being gradually accumulated on the bottom of the toner container  23 B. Thereafter, when the rotation shaft  29 B is rotated and the polyester stirring film  34 B reaches the highest point, the polyester detecting film  351 B is rotatable around the rotation shaft  29 B and therefore starts falling by its own weight. Thus, the polyester detecting film  351 B falls after the toner  28 B is accumulated on the bottom of the toner container  23 B and stops on the surface of the toner  28 B. The state of the polyester detecting film  351 B at that time is shown in (d) of  FIG. 12 . In the case where the remaining amount of the toner  28  is small, a height from the bottom of the toner container  23  to the surface of the toner  28 B becomes low and therefore a stop position of the polyester detecting film  351 B is a position with a height  902 . 
     Depending on the remaining amount of the toner  28 B in the toner container  23 B, the surface height of the toner  28 B accumulated on the bottom of the toner container  23 B is changed and therefore there arises a difference in height of the position where the polyester detecting film  351 B] falls by its own eight and stops. As a result, there also arises a difference in electrostatic capacity between the electrostatic capacity sensor electrode  321 B and the electrode to be detected  361 B provided on the polyester detecting film  351 B. Then, the electrostatic capacity  33 B detect sensors the difference in electrostatic capacity, so that the CPU  40  can detect a distance between the polyester detecting film  351 B and the electrostatic capacity sensor electrode  321 B by the detection level from the electrostatic capacity sensor  33 B, with the result that the CPU  40  can calculate the remaining amount of the toner  28 B. 
     [Detection Characteristic of Remaining Toner Amount] 
     Next, with reference to (a) and (b) of  FIG. 10 , a detection characteristic of the remaining toner amount in this embodiment will be described. Incidentally, in this embodiment, the detection level of the electrostatic capacity sensor  33 B is outputted to the CPU  40 B as 8-bit data. In the following description, the detection level is represented by decimal number. 
     Part (a) of  FIG. 13  is a characteristic graph showing a relationship between the remaining amount of the toner  28 B in the toner container  23 B and the detection level of the electrostatic capacity sensor  33 B, wherein the ordinate represents the detection level and the abscissa represents the remaining toner amount (%). The sensitivity of the electrostatic capacity sensor  33 B in (a) of  FIG. 13  is set at 69 from the CPU  40  by using the serial communication. As shown in the characteristic graph of (a) of  FIG. 13 , in this embodiment, when the remaining amount of the toner  28 B in the toner container  23 B is 100%, the detection level of the electrostatic capacity sensor  33 B is  135 . On the other hands, when the remaining amount of the toner  28 B is 0%, the detection level of the electrostatic capacity sensor  33 B is  253 . 
     Part (b) of  FIG. 13  is a table T 1  obtained by tabulating a corresponding relation between the detection level of the electrostatic capacity sensor  33 B and the remaining toner amount (%) from the characteristic graph of (a) of  FIG. 13 . The remaining amount of the toner  28 B corresponding to the detection level which is not explicitly shown in the table T 1  can be obtained by linear interpolation of known remaining amounts of the toner  28 B shown in the table T 1 . Here, the measured detection levels are values in this embodiment and therefore vary when a measuring condition is changed. This is also true for the numerical values in the table T 1  for discriminating the remaining amount of the toner  28 B. The information of the table T 1  is written in advance in ROM of a storing portion or ROM provided in the process cartridge  5 B at a factory and then is shipped. Then, the information written in ROM provided in the process cartridge  5 B is read by the CPU  40 B when the process cartridge  5 B is mounted in the main assembly  101 , thus being stored in RAM of the storing portion of the control board  80 . Also in Embodiments 5 and 7 described later, the table information is stored (recorded) in ROM or RAM of the storing portion by these methods. Incidentally, the above method of recording the table information during the shipping is an example and therefore the present invention is not limited to the above-described methods. 
     [Processing Sequence of Remaining Toner Amount Detection] 
     Next, a processing sequence of the remaining toner amount detection in this embodiment will be described by using a flow chart of  FIG. 14 . The processing shown in  FIG. 14  is executed by the CPU  40 B on the basis of a control program stored in ROM of the storing portion and also in subsequent Embodiments, processing in each flow chart is similarly executed by the CPU  40 B. Incidentally, in the case where all the processing operations shown in the flow chart are not performed by the CPU  40 B but, e.g., an application-specific integrated circuit (ASIC) is mounted in the image forming apparatus, a function of executing any of the processing operations in the flow chart may also be performed by the ASIC. 
     In step  101 B (S 101 B), the CPU  40 B causes the polyester stirring film  34 B to perform the rotating operation. In this embodiment, a time required for the polyester stirring film  34 B to rotate one turn is about 1 sec. In S 102 B, the CPU  40 B makes the serial communication with the electrostatic capacity sensor  33 B to set the sensitivity of the electrostatic capacity sensor  33 B at 69. Then the CPU  40 B resets the timer and then starts the timer and at the same time starts reading of the detection level. 
     In S 103 B, the CPU  40 B receives reading data of the detection level from the electrostatic capacity sensor  33 B through the serial communication. In S 104 B, the CPU  40 B discriminates whether or not the polyester detecting film  351 B starts the free fall by its own weight from the detection level depending on the electrostatic capacity between the electrostatic capacity sensor electrode  321 B and the electrode to be detected  361 B provided on the polyester detecting film  351 B. Here, with reference to  FIG. 15 , a state in which the detection level of the electrostatic capacity sensor  33 B is changed by the free fall of the polyester detecting film  351 B by its own weight will be described.  FIG. 15  is a graph showing a state of progression of the detection level of the electrostatic capacity sensor  33 B with the lapse of time by the free fall of the polyester detecting film  351 B, wherein the ordinate represents the electrostatic capacity sensor detection level and the abscissa represents the time (sec). In  FIG. 15 , t 1  represents timing when the polyester stirring film  34 B is rotated to start a detecting operation by the electrostatic capacity sensor  33 B, and t 2  represents timing when the polyester detecting film  351 B raised to the highest point by the polyester stirring film  34 B starts the free fall by its own weight. Until t 2 , the electrode to be detected  361 B provided on the polyester detecting film  351 B is remote from the electrostatic capacity sensor electrode  321 B and therefore the detection level outputted from the electrostatic capacity sensor  33 B to the CPU  40 B is a low level (10 or less). However, when the polyester detecting film  351 B starts the free fall, the distance between the electrode to be detected  361 B and the electrostatic capacity sensor electrode  321 B is quickly shortened and therefore the detection level outputted from the electrostatic capacity sensor  33 B to the CPU  40 B is correspondingly increased. Then, when the polyester detecting film  351 B falls onto the toner  28 B and stops on the toner  28 B, the distance between the electrode to be detected  361 B and the electrostatic capacity sensor electrode  321 B becomes constant and therefore the detection level of the electrostatic capacity sensor  33 B is also stabilized at a certain value. In this embodiment, as shown at t 3  in  FIG. 15 , a rising threshold which indicates the start of the free fall of the polyester detecting film  351 B is set at 50 by the CPU  40 B. Further, from the low level (10 or less), by the detection of the timing (t 3 ) when the detection level exceeds the rising threshold, the CPU  40 B detects that the polyester detecting film  351 B starts the free fall by its own weight. 
     In S 104 B, in the case where the CPU  40 B discriminates that the electrostatic capacity between the electrode to be detected  361 B and the electrostatic capacity sensor electrode  321 B is not a certain value or more and thus discriminates that the rising of the detection level is not detected, the sequence goes to S 108 B. In S 104 B, in the case where the CPU  40 B discriminates that the detection level rising is detected, the sequence goes to S 105 B. In S 105 B, the CPU  40 B discriminates whether or not the polyester detecting film  351 B which starts the free fall falls onto the toner  28 B and stops on the toner surface. In this embodiment, when a fluctuation of the detection level outputted from the electrostatic capacity sensor  33 B is 2 or less for 0.05 sec (50 milliseconds) or more, the CPU  40 B discriminates that the polyester detecting film  351 B stops on the toner surface. Incidentally, setting of a width and time of the fluctuation of the detection level of the electrostatic capacity sensor  33 B for detecting the timing when the polyester detecting film  351 B stops on the toner surface varies depending on the developing unit constitution, the electrostatic capacity sensor and the peripheral circuit and therefore is not limited to the above-described setting. In S 105 B, in the case where a state in which the fluctuation width, of the detection level outputted from the electrostatic capacity sensor  33 B to the CPU  40 B, of 2 or less is continued for 0.05 sec or more, the sequence by the CPU  40  goes to S 106 B, and in the case where the fluctuation width is not continued for 0.05 sec or more, the sequence goes to S 108 B. 
     In S 108 B, the CPU  40 B reads a timer value from the timer and discriminates whether or not 2 sec or more elapses from the start of the reading of the detection level by the electrostatic capacity sensor  33 B. When the lapse of time is less than 2 sec, the sequence returns to S 103 B. In the case where 2 sec or more elapses, the sequence by the CPU  40  goes to S 109 B. In S 109 B, from the fact that the detection level of the electrostatic capacity sensor  33 B does not exceed the rising threshold for 2 sec or more, the CPU  40 B discriminates that the electrostatic capacity sensor  33 B is abnormal, and then notifies the video controller  42  of the abnormality of the electrostatic capacity sensor  33 B. 
     In S 106 B, the CPU  40 B checks the detection level outputted from the electrostatic capacity sensor  33 B in S 103 B against the detection level of the table T 1  stored in ROM of the storing portion, thus calculating a corresponding remaining amount of the toner  28 B. In S 107 B, the CPU  40 B notifies the video controller  42  of the remaining amount of the toner  28 B calculated in S 106 B. 
     As described above, according to this embodiment, the remaining amount can be detected in real time with high accuracy and with a simple constitution irrespective of the magnitude of the toner amount. In this embodiment, by detecting the electrostatic capacity between the electrode to be detected of the polyester detecting film and the electrostatic capacity sensor electrode provided in the neighborhood of the bottom of the developing unit, the remaining toner amount corresponding to the electrostatic capacity can be calculated, with the result that the remaining amount can be detected from the full state of the toner to the empty state of the toner. 
     Embodiment 5 
     In Embodiment 4, the remaining toner amount was calculated by detecting the electrostatic capacity between the electrode to be detected of the polyester detecting film and the electrostatic capacity sensor electrode in the neighborhood of the bottom of the developing unit in a state in which the sensitivity of the electrostatic capacity sensor was constant. On the other hand, in this embodiment, an example in which the detection accuracy of the remaining toner amount is further improved more than Embodiment 4 by changing the sensitivity of the electrostatic capacity sensor depending on the remaining toner amount will be described. Incidentally, the constitution in  FIG. 1 , the constitutions in  FIGS. 9 and 10  described in Embodiment 4 and the detecting operation in  FIGS. 11 and 12  are also applied in this embodiment. Further, constituent elements identical to those in Embodiment 4 are represented by the same reference numerals or symbols and will be omitted from description since detailed description thereof is made in Embodiment 4. 
     [Detection Characteristic of Remaining Toner Amount] 
     Part (a) of  FIG. 16  is a characteristic graph showing a relationship between the remaining amount of the toner  28 B and the detection level of the electrostatic capacity sensor  33 B for each of values of the sensitivity set for the electrostatic capacity sensor  33 B, wherein the ordinate represents the detection level and the abscissa represents the remaining toner amount (%). In (a) of  FIG. 16 , plotted curves indicated by a solid line, a chain double-dashed line and a broken line show characteristics, between the remaining amount of the toner  28 B and the detection level of the electrostatic capacity sensor  33 B, at sensitivity values of 46, 69 and 92, respectively. 
     When the characteristic graph in the case of the sensitivity of 69 in (a) of  FIG. 16  is viewed, it is understood that in a region where the remaining amount of the toner  28 B is 25% or less and in a region where the remaining amount of the toner  28 B is 60% or more, a proportion of a change in detection level of the electrostatic capacity sensor  33 B to a change in remaining toner amount becomes small and thus it is difficult to discriminate the remaining toner amount with high accuracy. 
     When the characteristic graph in the case of the sensitivity of 92 is viewed, compared with the characteristic graph of the sensitivity of 69, in a region  903  where the remaining amount of the toner  28 B is large (60% to 100%), the proportion of the change in detection level of the electrostatic capacity sensor  33 B to the change in remaining toner amount is large. On the other hand, when the characteristic graph in the case of the sensitivity of 46, compared with the characteristic graph of the sensitivity of 69, in a region  904  where the remaining amount of the toner  28 B is small (0% to 25%), the proportion of the change in detection level of the electrostatic capacity sensor  33 B to the change in remaining toner amount is large. Therefore, when the electrostatic capacity is detected by setting the sensitivity so that large sensitivity is set for the electrostatic capacity sensor  33 B in the region  903  and so that smaller sensitivity is set for the electrostatic capacity sensor  33 B in the region  904 , it is possible to improve the detection accuracy of the remaining amount of the toner  28 B more than the case of Embodiment 4. 
     Part (b) of  FIG. 16  is a characteristic graph obtained by dividing the region of the characteristic graph of (a) of  FIG. 16  into three regions depending on the sensitivity set during the electrostatic capacity detection. In this embodiment, the sensitivity set for the electrostatic capacity sensor  33 B is set so that the sensitivity in a region  905  where the remaining toner amount is less than 25% is 46, the sensitivity in a region  906  where the remaining toner amount is 25% or more and less than 60% is 69 and the sensitivity in a region  907  where the remaining toner amount is 60% or more is 92. Incidentally, the sensitivity set depending on the remaining toner amount varies depending on the developing unit constitution, the electrostatic capacity sensor  33 B and the peripheral circuit and therefore is not limited to the numerical values set in this embodiment. 
     Each of tables T 1  to T 3  of (a) to (c) of  FIG. 17  is a table obtained by tabulating a corresponding relation between the detection level of the electrostatic capacity sensor  33 B and the remaining toner amount (%) from the characteristic graph of (a) of  FIG. 16 . The tables T 1 , T 2  and T 3  of (a), (b) and (c) of  FIG. 17 , respectively are obtained by tabulating the characteristic graphs of the sensitivity values of 69, 46 and 92, respectively. The remaining amount of the toner  28 B corresponding to the detection level which is not explicitly shown in each table can be obtained by linear interpolation of known remaining amounts of the toner  28 B shown in the table. Here, the measured detection levels are values in this embodiment and therefore vary when a measuring condition is changed. This is also true for the numerical values in each table for discriminating the remaining amount of the toner  28 B. 
     [Processing Sequence of Remaining Toner Amount Detection] 
     Next, a processing sequence of the remaining toner amount detection in this embodiment will be described by using a flow chart of  FIG. 18 . The processing operations in S 201 B to S 205 B, S 212 B and S 213 B in  FIG. 18  are the same as S 101 B to S 105 B, S 108 B and S 109 B in  FIG. 14  in Embodiment 4 and therefore will be omitted from description. 
     The S 206 B, as described above, in order to set the sensitivity of the electrostatic capacity sensor  33 B depending on the remaining amount of the toner  28 B, the CPU  40 B discriminate the remaining toner amount at the sensitivity of 69 from the detection level outputted from the electrostatic capacity sensor  33 B in S 203 B. In the case where the CPU  40 B discriminates that the detection level is more than 225 and thus the remaining amount of the toner  28 B at the sensitivity of 69 is less than 25%, the sequence by the CPU  40 B goes to S  207 B. In S 207 B, the sensitivity of the electrostatic capacity sensor  33 B is switched to 46 and then the sequence goes to S 210 B. In S 206 B, in the case where the CPU  40 B discriminates that the detection level is 225 or less, the sequence by the CPU  40 B goes to S 208 B. In S 208 B, the CPU  40 B discriminates whether or not the detection level is larger than 155. In the case where the detection level is larger than 155, the remaining amount of the toner  28 B is 25% or more and less than 60% and therefore the CPU  40 B does not perform the sensitivity switching operation while keeping the sensitivity of the electrostatic capacity sensor  33 B at 69, so that the sequence goes to S 210 B. In the case where the detection level is 155 or less, the CPU  40 B discriminates that the remaining amount of the toner  28 B is 60% or more, and the sequence by the CPU  40 B goes to S 209 B. In S 209 B, the sensitivity of the electrostatic capacity sensor  33 B is switched to 92, and the sequence goes to S 210 B. 
     In S 210 B, by using the sensitivity depending on the remaining amount of the toner  28 B determined by the processing operations from S 206 B to S 209 B, the CPU  40 B reads again the detection level from the electrostatic capacity sensor  33 B. 
     Then, the CPU  40 B checks the read detection level against the detection level of the table corresponding to the sensitivity stored in ROM of the storing portion, thus calculating a corresponding remaining amount of the toner  28 B. In S 211 B, the CPU  40 B notifies the video controller  42  of the remaining amount of the toner  28 B calculated in S 210 B. 
     As described above, according to this embodiment, the remaining amount can be detected in real time with high accuracy and with a simple constitution irrespective of the magnitude of the toner amount. That is, the sensitivity of the electrostatic capacity sensor is switched depending on the remaining toner amount and then the remaining toner amount is calculated from the table depending on the sensitivity and from the detection level of the electrostatic capacity sensor, so that the remaining toner amount detection accuracy can be further improved more than the case of Embodiment 4. 
     Embodiment 6 
     In Embodiment 4, the remaining toner amount was calculated by detecting the electrostatic capacity between the electrode to be detected of the polyester detecting film and the electrostatic capacity sensor electrode in the neighborhood of the bottom of the developing unit in a state in which the sensitivity of the electrostatic capacity sensor was constant. Further, in Embodiment 5, the detection accuracy of the remaining toner amount was improved more than Embodiment 4 by changing the sensitivity of the electrostatic capacity sensor depending on the remaining toner amount. In this embodiment, an example wherein in a state in which the polyester detecting film stops on the toner surface, the sensitivity of the electrostatic capacity sensor is swept and then the remaining toner amount is calculated from a value of the sensitivity when a target value of the detection level coincides with a measure value of the detection value, thus further improving the remaining toner amount detection accuracy will be described. Further, in Embodiments 4 and 5, in the state in which the polyester detecting film performed the rotating operation, the remaining toner amount detection was performed in real time. However, in this embodiment, it takes much time to sweep the sensitivity of the electrostatic capacity sensor and therefore in the state in which the polyester detecting film stops on the toner surface, the rotating operation of the polyester detecting film is stopped and then the remaining amount detection is performed. Incidentally, the constitution in  FIG. 1 , the constitutions in  FIGS. 9 and 10  described in Embodiment 4 and the detecting operation in  FIGS. 11 and 12  are also applied in this embodiment. Further, constituent elements identical to those in Embodiment 4 are represented by the same reference numerals or symbols and will be omitted from description. 
     [Detection Characteristic of Remaining Toner Amount] 
     Part (a) of  FIG. 19  is a characteristic graph showing a relationship between the sensitivity of the electrostatic capacity sensor and the remaining amount of the toner  28 B for which the target value and the measured value of the detection level of the electrostatic capacity sensor  33 B coincide with each other when the sensitivity is swept, wherein the ordinate represents the sensitivity and the abscissa represents the remaining toner amount (%). In this embodiment, the detection level target value of the electrostatic capacity sensor  33 B is set at 150. For example, a point  908  in (a) of  FIG. 19  shows that the sensitivity of the electrostatic capacity sensor  33 B is swept when the remaining amount of the toner  28 B is 66%, and the sensitivity of the electrostatic capacity sensor  33 B is 69 when the electrostatic capacity sensor detection level is the target value of 150. Also points  909  and  910  show similar results. The point  909  shows that the sensitivity of the electrostatic capacity sensor  33 B is 46 when the remaining amount of the toner  28 B is 35%, and the point  910  shows that the sensitivity of the electrostatic capacity sensor  33 B is 92 when the remaining amount of the toner  28 B is 100%. As a result, when the relationship between the remaining toner amount and the electrostatic capacity sensor sensitivity when the detection level of the electrostatic capacity sensor  33 B is  150  is plotted depending on the respective remaining amounts of the toner  28 B, the characteristic graph of (a) of  FIG. 19  is obtained. This characteristic graph shows linearity with respect to the relationship between the remaining amount of the toner  28 B and the detected sensitivity of the electrostatic capacity sensor  33 B and therefore it becomes possible to detect the remaining toner amount in real time with accuracy higher than those in Embodiments 4 and 5 from the full state of the toner to the empty state of the toner. Incidentally, the used detection level target value of the electrostatic capacity sensor  33 B and the used relationship between the remaining toner amount and the sensitivity in this embodiment vary depending on the developing unit constitution, the electrostatic capacity sensor and the peripheral circuit and therefore are not limited to the above-described numerical values and the characteristic graphs. 
     Part (b) of  FIG. 19  is a table T 4  obtained by tabulating a corresponding relation between the sensitivity level of the electrostatic capacity sensor  33 B and the remaining toner amount (%) from the characteristic graph of (a) of  FIG. 19 . The remaining amount of the toner  28 B corresponding to the sensitivity which is not explicitly shown in each table T 4  can be obtained by linear interpolation of known remaining amounts of the toner  28 B shown in the table T 4 . Here, the measured values of the sensitivity of the electrostatic capacity sensor  33 B are values in this embodiment and therefore vary when a condition of the electrostatic capacity sensor  33 B, the peripheral circuit or the like is changed. This is also true for the numerical values in the table T 4  for discriminating the remaining amount of the toner  28 B. 
     [Processing Sequence of Remaining Toner Amount Detection] 
     Next, a processing sequence of the remaining toner amount detection in this embodiment will be described by using a flow chart of  FIG. 20 . The processing operations in S 301 B to S 304 B, S 314 B and S 316 B in  FIG. 20  are the same as S 101 B to S 104 B, S 108 B and S 109 B in  FIG. 14  in Embodiment 4 and therefore will be omitted from description. 
     In S 304 B, in the case where the CPU  40 B discriminates that the detection level rising is detected, the sequence goes to S 305 B. In S 305 B, the CPU  40 B stops the rotation of the polyester stirring film  34 B before the polyester stirring film  34 B rotates and contacts the polyester detecting film  351 B. The reason why the rotation of the polyester stirring film  34 B is stopped in that a time is required for the CPU  40 B to sweep the sensitivity of the electrostatic capacity sensor  33 B from 1 to 92 thereby to read the detection level in the state in which the polyester detecting film  351 B stops on the toner surface in the toner container  23 B. Incidentally, in the case where the time required for the CPU  40 B to sweep the sensitivity of the electrostatic capacity sensor  33 B thereby to read the detection level is shorter than a time for which the polyester detecting film  351 B stops on the toner surface, the remaining amount detection may also be effected while rotating the polyester stirring film  34 B. In S 396 B, the CPU  40 B discriminates whether or not the polyester detecting film  351 B which starts the free fall falls onto the toner  28 B and stops on the toner surface. Also in this embodiment, similarly as in Embodiments 4 and 5, when a fluctuation of the detection level outputted from the electrostatic capacity sensor  33 B is 2 or less for 0.05 sec (50 milliseconds) or more, the CPU  40 B discriminates that the polyester detecting film  351 B stops on the toner surface. Incidentally, setting of a width and time of the fluctuation of the detection level of the electrostatic capacity sensor  33 B for detecting the timing when the polyester detecting film  351 B stops on the toner surface varies depending on the developing unit constitution, the electrostatic capacity sensor and the peripheral circuit and therefore is not limited to the above-described setting. In the case where a state in which the fluctuation width, of the detection level outputted from the electrostatic capacity sensor  33 B to the CPU  40 B, of 2 or less is continued for 0.05 sec or more, the sequence by the CPU  40  goes to S 307 B, and in the case where the fluctuation width is not continued for 0.05 sec or more, the sequence goes to S 315 B. In S 315 B, the CPU  40 B reads a timer value from the timer and discriminates whether or not 2 sec or more elapses from the start of the reading of the detection level by the electrostatic capacity sensor  33 B. When the lapse of time is less than 2 sec, the sequence returns to S 306 B. In the case where 2 sec or more elapses, the sequence by the CPU  40  goes to S 316 B. In S 316 B, from the fact that the detection level of the electrostatic capacity sensor  33 B does not exceed the rising threshold for 2 sec or more, the CPU  40 B discriminates that the electrostatic capacity sensor  33 B is abnormal, and then notifies the video controller  42  of the abnormality of the electrostatic capacity sensor  33 B. 
     In S 307 B, in order to continuously read the electrostatic capacity sensor detection level by sweeping the sensitivity of the electrostatic capacity sensor  33 B, the CPU  140 B makes the serial communication with the electrostatic capacity sensor  33 B, thus setting the electrostatic capacity sensor sensitivity at 1 as an initial value. 
     In S 308 B, the CPU  40 B discriminates whether or not the sensitivity set for the electrostatic capacity sensor  33 B through the serial communication is 92 or less. In the case where the set sensitivity of the electrostatic capacity sensor  33 B is larger than 92, the sequence goes to S 316 B, in which the CPU  40 B notifies the video controller  42  of the abnormality of the electrostatic capacity sensor  33 B. In the case where the sensitivity is 92 or less, the sequence goes to S 309 B, in which the CPU  40 B reads again the detection level and in S 310 B, comparison with the detection level target value of 150 is made. Here, in the case where the measured value and the target value of the detection level of the electrostatic capacity sensor  33 B coincide with each other, the sequence by the CPU  40 B goes to S 312 B. In S 310 B, the detection level measured value and target value do not coincide, the sequence by the CPU  40 B goes to S 311 B, in which the CPU  40 B makes the serial communication with the electrostatic capacity sensor  33 B and increments the sensitivity of the electrostatic capacity sensor  33 B by 1 and then the sequence returns to S 308 B. 
     In S 312 B, the CPU  40 B checks the value of the sensitivity of the electrostatic capacity sensor  33 B set at that time against the sensitivity of the table T 1  stored in ROM of the storing portion, thus calculating a corresponding remaining amount of the toner  28 B. In S 313 B, the CPU  40 B notifies the video controller  42  of the remaining amount of the toner  28 B calculated in S 312 B. 
     As described above, according to this embodiment, the remaining amount can be detected in real time with high accuracy and with a simple constitution irrespective of the magnitude of the toner amount. That is, in the state in which the polyester detecting film stops on the toner surface, the electrostatic capacity sensor sensitivity is swept and then the remaining toner amount is detected from the sensitivity when the detection level target value and measured value coincide with each other, so that the remaining toner amount detection accuracy can be improved more than Embodiments 4 and 5. 
     Incidentally, in Embodiments 4 to 6, for easy understanding, description such that the electrostatic capacity sensor detection level obtained by a single detecting operation was checked against the table was made. However, by effecting control such that data for plural times of the detection is averaged and thereafter reference to an associated table is made, further enhancement of the detection accuracy can be expected. 
     Further, in Embodiments 4 to 6, an example in which the developing unit was integrally constituted was described. However, in a toner container of a supply type in which the developing roller and the toner container is separately provided, by providing the electrode to be detected and the polyester detecting film, the present invention is applicable. 
     Embodiment 7 
     A constitution of an image forming apparatus in this embodiment is the same as that described in Embodiment 1 and therefore will be omitted from description. 
     [Constitution of Developing Unit and Electrostatic Capacity Sensor] 
     Part (a) of  FIG. 21  is a sectional view of a developing unit and an electrostatic capacity sensor substrate  331 B which constitute a process cartridge  5 C. Inside the process cartridge  5 C shown in (a) of  FIG. 21 , a toner container  23 C, a toner  28 C of an associated color and a polyester stirring film  34 C for stirring the toner  28 C in the toner container  23 C are provided. The polyester stirring film  34 C (stirring) is provided on a rotation shaft  29 C in the toner container  23 C and performs a circulation rotation (circulation operation). The rotation shaft  29 C is also provided with a polyester detecting film  351 C (first member), having flexibility, for detecting a remaining amount of the toner  28 B, and a polyester detecting film  352 C (second member). The polyester detecting film  352 C is provided 90 degrees (predetermined angle) behind the polyester detecting film  351 C with respect to the rotational direction. Incidentally, this angle is not limited to 90 degrees. That is, the angle may only be required to cause a difference between a time difference between detection times of the polyester detecting film  351 C and  352 C by an electrostatic capacity sensor IC  33 C described later and a time difference between detection times of the polyester detecting films  352 C and  351 C by the electrostatic capacity sensor IC  33 C. Details will be described in processing along a flow chart of  FIG. 25  described later. Further, the angle may be an angle at which the polyester detecting films  351 C and  352 C do not contact each other. 
     As the polyester detecting films  351 C and  352 C, a general-purpose Mylar film is used. In this embodiment, thickness of the polyester detecting films  351 C and  352 C are 150 μm and 75 μm, respectively. A difference in warp degree is realized by changing the thicknesses of the polyester detecting films  351 C and  352 C and therefore the polyester detecting film  352 C has a larger warp degree than the polyester detecting film  351 C. Incidentally, such a constitution that the warp degree of the polyester detecting film  352 C is made larger than the warp degree of the polyester detecting film  351 C by, e.g., changing the material for the polyester detecting films  351 C and  352 C so that the warp degree of the polyester detecting film  352 C is larger than that of the polyester detecting film  351 C may be employed. Further, the polyester detecting films  351 C and  352 C are provided with an electroconductive electrode to be detected  361 C (first electrode) and an electroconductive electrode to be detected  361 C (second electrode), respectively, in the neighborhood of their ends with respect to their circumferential directions (perpendicular to their rotational axis directions). 
     Further, the electrostatic capacity sensor substrate  331 C shown in (a) of  FIG. 21  is provided with the following members. 
     On the electrostatic capacity sensor substrate  331 C provided in the main assembly  101 , the electrostatic capacity sensor IC  33 C (output means) and its peripheral circuit parts (not shown) are mounted. The electrostatic capacity sensor IC  33 C in this embodiment, e.g., detects a change in electrostatic capacity by an electrostatic capacity sensor electrode by using a difference between the electrostatic capacity by the electrostatic capacity sensor electrode and the electrostatic capacity by a reference electrode. On the electrostatic capacity sensor substrate  331 C, the electrostatic capacity sensor electrode  321 C (third electrode) and the reference electrode  320 C are formed in a copper foil pattern. The bottom of an outer casing of the developing unit approaches the electrostatic capacity sensor electrode  321 C when the process cartridge  5 C is mounted in the main assembly  101 . The electrostatic capacity sensor IC  33 C detects, in this state, a change in electrostatic capacity generated by the approach of the electrodes to be detected  361 C and  362 C, provided on the polyester detecting films  351 C and  352 C, toward the electrostatic capacity sensor electrode  321 C. 
     Incidentally, the electrostatic capacity sensor IC  33 C and its peripheral circuit parts may also be required to be capable of detecting the electrostatic capacity and thus can be replaced with analog integrated circuit parts. Further, in this embodiment, the electrostatic capacity sensor electrode  321 C is formed on the electrostatic capacity sensor substrate  331 C provided in the main assembly  101  but may only be required to be provided in the neighborhood of a wall surface of the developing unit and may also be directly molded on, e.g., the wall surface of the developing unit. In that case, it is preferable that electrical contacts are provided on the electrostatic capacity sensor substrate  331 C and the electrostatic capacity sensor electrode  321 C so as to be electrically connected when the process cartridge  5 C is mounted in the main assembly  101 . 
     Part (b) of  FIG. 21  is a perspective view showing a positional relationship between the polyester detecting film  351 C and the electrode to be detected  361 C. A similar constitution is also employed for the polyester detecting film  352 C and the electrode to be detected  362 C. A length of each of the electrodes to be detected  361 C and  362 C in the circumferential direction (perpendicular to the rotation shaft  29 C) is 30 mm. A length of each of the polyester detecting films  351 C and  352 C and the electrodes to be detected  361 C and  362 C in the axial direction (longitudinal direction) of the rotation shaft  29 C may be at least a length in which the detection surface of the electrostatic capacity sensor IC  33 C is covered. Incidentally, with respect to the length in the circumferential direction, in this embodiment, the polyester detecting film  352 C is longer than the polyester detecting film  351 C. The circumferential length of the polyester detecting film  351 C is set at a length to the extent that the polyester detecting film  351 C contacts the side wall surface of the toner container  23 C and on the other hand, the circumferential length of the polyester detecting film  352 C is set at a length in which the polyester detecting film  352 C contacts the bottom of the process cartridge  5 C. However, the lengths of the polyester detecting films  351 C and  352 C are set so that the polyester detecting films do not contact each other during stirring of the toner. A length of the polyester stirring film  34 C is set so as to sufficiently stir the toner in the process cartridge  5 C. Further, the polyester stirring film  34 C and the polyester detecting film  352 C are disposed at an angle of about 180 degrees in (a) of  FIG. 21  and are constituted so that after the toner is stirred by the polyester stirring film  34 C, the polyester detecting film  352 C is detected after the state of the toner is stabilized to some extent. That is, their arrangement may only be required that the detection of the electrode to be detected  362 C of the polyester detecting film  352 C can be effected in a state in which the toner is stabilized to some extent after the toner stirring by the polyester stirring film  34 C, and the angle is not limited to 180 degrees. The polyester detecting film  352 C is disposed 90 degrees behind the polyester detecting film  351 C with respect to the rotational direction and is formed with a member softer than that for the polyester detecting film  351 C but the present invention is not limited to this arrangement, material and thickness. 
     [Circuit Diagram of Remaining Toner Amount Detection] 
       FIG. 22  is a circuit view of the remaining toner amount detection in this embodiment. A bypass capacitor  46   c  is used for removing noise of an analog power source terminal AVDD of the electrostatic capacity sensor IC  33 C. Further, a bypass capacitor  47 C is used for removing noise of a digital power source terminal DVDD of the electrostatic capacity sensor IC  33 C. To an SREF terminal of the electrostatic capacity sensor IC  33 C, the reference electrode  320 C is connected, and to an SIN  1  terminal, the electrostatic capacity sensor electrode  321 C is connected. The reference electrode  320 C is a copper foil pattern having the same area as that of the electrostatic capacity sensor electrode  321 C. The electrode sensor IC  33 C effects data transfer between itself and the CPU  40 C through the serial communication. The CPU  40 C outputs a clock signal, for communication synchronization, to an SCL terminal of the electrostatic capacity sensor IC  33 C. On the other hand, the electrostatic capacity sensor IC  33  outputs data (information on the electrostatic capacity) of 8 bit-detection level corresponding to a detected value of the electrostatic capacity, to the CPU  40 C via an SDA terminal. Incidentally, a detailed operation principle of the electrostatic capacity sensor IC  33  is a known art and therefore will be omitted. 
     [Operation of Polyester Detecting Film] 
     With reference to (a) and (b) of  FIG. 23 , operations of the polyester detecting films  351 C and  352 C in the case where the remaining toner amount is relatively large and in the case where the remaining toner amount is relatively small will be described. When the polyester detecting films  351 C and  352 C perform the rotating operation, as shown in (a) of  FIG. 23 , in the case where the remaining toner amount is relatively large, each of the polyester detecting films  351 C and  352 C is subjected to the resistance of the toner and is deformed toward a rear side with respect to the rotational direction which is an arrow direction in the figure, thus performing the rotating operation while being warped. In this case, the warp degree of the polyester detecting film  352 C is larger than that of the polyester detecting film  351 C, so that the polyester detecting film  352 C is largely deformed toward the rotational direction rear side. In this state a difference between a time when the polyester detecting film  351 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C and a time when the polyester detecting film  352 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C (hereinafter, the difference is referred to as a time difference) is long (large). On the other hand, as shown in (b) of  FIG. 23 , when the remaining toner amount is relatively small, compared with a decrease in warp degree of the polyester detecting film  351 C, a degree of a decrease in warp degree of the polyester detecting film  352 C is large. As a result, a time difference from the time when the polyester detecting film  351 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C until the time when the polyester detecting film  352 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C is short (small). By using this principle, the remaining toner amount is detected. 
     [Characteristic of Remaining Toner Amount Detection] 
     With reference to (a) to (c) of  FIG. 24 , a remaining toner amount detection characteristic will be described. As described above, the electrostatic capacity sensor IC  33 C outputs, to the CPU  40 , the 8 bit data corresponding to the detected value of the electrostatic capacity. In this embodiment, description will be made by representing the 8 bit data outputted from the electrostatic capacity sensor IC  33 C to the CPU  40 C as decimal number-detection levels. Part (a) of  FIG. 24  is a characteristic graph between the remaining toner amount (%) and the time difference (msec) between the polyester detecting films  351 C and  352 C detected by the electrostatic capacity sensor IC  33 C. As described above with reference to  FIG. 23 , the time difference is longer (larger) with a larger remaining toner amount, and the time difference is shorter (smaller) with a smaller remaining toner amount. As a result, the remaining toner amount can be detected by measuring the time difference. Part (b) of  FIG. 24  is waveform data when the remaining toner amount is 65%, wherein the abscissa represents the time (msec) and the ordinate represents the detection level of the electrostatic capacity sensor IC  33 C. It is understood that the time difference (msec) between the time when the polyester detecting film  351 C is detected and the time when the polyester detecting film  352 C is detected is 390 msec. 
     Part (c) of  FIG. 24  is a table T in which the time difference and the remaining toner amount are associated with each other. The remaining toner amount between numerical values in the table T can be obtained by linear interpolation of known remaining toner amounts. Here, the measured times are values in this embodiment and therefore vary when a measuring condition is changed. This is also true for the numerical values in the table T. The information of the table T is written in advance in ROM of a storing portion or ROM provided in the process cartridge  5 C at a factory and then is shipped. Then, the information written in ROM provided in the process cartridge  5 C is read by the CPU  40 C when the process cartridge  5 C is mounted in the main assembly  101 , thus being stored in RAM of the storing portion of the control board  80 . Also in Embodiments 8 and 9 described later, the table information is stored (recorded) in ROM or RAM of the storing portion by these methods. Incidentally, the above method of recording the table information during the shipping is an example and therefore the present invention is not limited to the above-described methods. 
     [Flow Chart of Remaining Toner Amount Detection] 
     Next, processing for detecting the remaining toner amount in this embodiment will be described by using a flow chart of  FIGS. 25A and 25B . Also in subsequent Embodiments, processing in each flow chart is similarly executed by the CPU  40 C. However, the present invention is not limited thereto but in the case where, e.g., an application-specific integrated circuit (ASIC) is mounted in the image forming apparatus, a function of any of steps may also be performed by the ASIC. 
     In step  101 C (S 101 C), the CPU  40 C causes the polyester detecting films  351 C and  352 C to perform the rotating operation. In this embodiment, a time required for each polyester detecting film to rotate one turn is about 1 sec. In S 102 C, the CPU  40 C serial-communicates with the electrostatic capacity sensor IC  33 C by using the circuit shown in  FIG. 22 , thus starting reading of the detection level of the electrostatic capacity sensor IC  33 C. Further, the CPU  40 C resets an unshown timer α together with the detection level reading and then starts measuring of a time from the start of the reading of the detection level of the electrostatic capacity sensor IC  33 C. 
     In S 103 C to S 105 C, the CPU  40 C calculates an initial value of the detection level of the electrostatic capacity sensor IC  33 C. First, in S 103 C, the CPU  40 C makes setting of a provisional (temporary) initial value of the detection level of the electrostatic capacity sensor IC  33 C (hereinafter referred to as a provisional initial value). The CPU  40 C measures plural points of the detection level from the start of the reading of the detection level of the electrostatic capacity sensor IC  33 C (hereinafter also referred to as monitoring), and then stores plural measured data values in, e.g., an unshown memory such as RAM. The CPU  40 C calculates an average of the detection level of the electrostatic capacity sensor IC  33 C from the plural data values stored in the memory, and takes this average as a provisional initial value. In this embodiment, the measurement is effected at, e.g., 10 points and the average thereof is calculated. However, the 10 point-measurement average is an example and therefore the average is not limited thereto. Further, the CPU  40 C resets an unshown timer β together with the provisional initial value calculation and then starts the measurement of the time with the timer β. 
     In S 104 C, the CPU  40 C discriminates whether or not the provisional initial value calculated in S 103 C is a relative value, i.e., whether or not the provisional initial value is a stable reference level and is qualified as an initial value. The CPU  40 C continues the monitoring of the detection level of the electrostatic capacity sensor IC  33 C in succession to S 103 C. For example, the CPU  40 C discriminates that the calculated provisional initial value is the stable reference level from the fact that the resultant detection level of the electrostatic capacity sensor IC  33 C falls within a certain range. In this embodiment, e.g., a discrimination criterion is such that the monitored detection level of the electrostatic capacity sensor IC  33 C falls within ±10% of the provisional initial value for 0.3 sec by making reference to the timer β. In S 104 C, in the case where the CPU  40 C discriminates that the monitored detection level of the electrostatic capacity sensor IC  33 C is within ±10% of the provisional initial value for 0.3 sec, the CPU  40 C sets, in S 105 C, the provisional initial value calculated in S 103 C as the initial value. The initial value set in S 105 C is used for calculating thresholds of other timers described hereinafter. 
     On the other hand, in the case where the CPU  40 C discriminates that the monitored detection level of the electrostatic capacity sensor IC  33 C is not within ±10% of the provisional initial value for 0.3 sec, the CPU  40 C discriminates in S 117 C that an error (abnormality) occurs. In this embodiment, the error discrimination is made based on whether or not 2.0 sec or more elapses from the start of the monitoring of the detection level of the electrostatic capacity sensor IC  33 C, i.e., from the start of the reading by making reference to the timer α. In S 117 C, in the case where the CPU  40 C discriminates that the lapse of the time from the start of the reading of the detection level of the electrostatic capacity sensor IC  33 C is less than 2.0 sec, the CPU  40 C resets the provisional initial value calculated in S 103 C and then effects the processing operations of S 103 C to S 105 C, thus calculating the provisional initial value again. On the other hand, in S 117 C, in the case where the CPU  40 C discriminates that, 2.0 sec or more elapses from the start of the reading of the detection level of the electrostatic capacity sensor IC  33 C, the CPU  40 C discriminates in S 118 C that any abnormality occurs, and then notifies the video controller  42  of the abnormality. 
     Next, in S 106 C to S 109 C, the CPU  40 C discriminates whether or not the polyester detecting film  351 C of the two polyester detecting films is detected. This is because the table T used for discriminating the remaining toner amount is based on the time (difference) from the time when the polyester detecting film  351 C is detected to the time when the polyester detecting film  352 C is detected. As a method of always detecting the polyester detecting film  351 C, in one period of the polyester detecting film, the time (difference) from the time when a first rising threshold is detected to the time when a second rising threshold is detected and the time (difference) from the time when the second rising threshold is detected to the time when a third rising threshold is detected are compared. In the constitution in this embodiment, a longer (larger) time difference corresponds to the time (difference) from the time when the polyester detecting film  352 C is detected to the time when the polyester detecting film  351 C is detected. The CPU  40 C measures the time (difference) between the detection times of the rising thresholds by using an unshown timer A and then compares the measured time differences as the whether or not they are a desired time (difference), so that it is possible to detect the polyester detecting film  351 C. 
     In S 106 C, the CPU  40 C resets the timer A and then starts the timer A, thus starting the time measurement. In S 107 C, the CPU  40 C detects timing when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected (either one of the electrodes to be detected  361 C and  362 C) provided on the polyester detecting film (either one of the polyester detecting films  351 C and  352 C) starts a change to the extent that the detection level is not less than the rising threshold. However, at this stage, the CPU  40  cannot discriminate whether the detected timing is that for the polyester detecting film  351 C or that for the polyester detecting film  352 C. In this embodiment, the rising threshold of the detection level of the electrostatic capacity sensor IC  33 C is set at (initial value determined in S 105 C +30%). The CPU  40 C discriminates the timing when the detection level exceeds this rising threshold is timing when either one of the polyester detecting films reaches above the detection surface of the electrostatic capacity sensor IC  33 C. In S 107 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is the rising threshold (initial value +30%) or more, the CPU  40 C stops the timer A. 
     On the other hand, in S 107 C, in the case where the CPU  40 C discriminate that the detection level is less than the rising threshold, the CPU  40  discriminates in S 119 C whether or not the error occurs. In this embodiment, the discrimination of the error is made based on whether or not 2.0 sec or more elapses from the start of the timer A. In S 119 C, in the case where the CPU  40 C discriminates that 2.0 sec or more does not elapse from the start of the timer A, the sequence returns to the processing of S 107 C, in which the monitoring of the detection level of the electrostatic capacity sensor IC  33 C is continued. On the other hands, in S 119 B, in the case where the CPU  40 C discriminates that 2.0 sec or more elapses from the start of the timer A, the sequence goes to processing of S 120 C. In S 120 C, the CPU  40 C discriminates that some abnormality (error) such as non-detection of the electrode to be detected  361 C, failure of the electrostatic capacity sensor IC  33 C or communication abnormality between the CPU  40 C and the electrostatic capacity sensor IC  33 C, and then notifies the video controller  42  of the abnormality. 
     In S 108 C, the CPU  40 C discriminates whether or not the timing detected in S 107 C is the timing when the polyester detecting film  351 C reaches above the detection surface of the electric signal sensor electrode  321 C. The CPU  40 C reads a value of the stopped timer A and discriminate whether or not the value of the timer A falls within a specific range determined in advance. In this embodiment, the specific range (time) was 450 msec or more and 650 msec or less. For example, in the case where the timer A value is less than 450 msec, the CPU  40 C cannot discriminates whether the detection level by the electrostatic capacity sensor IC  33 C is that for the polyester detecting film  351 C or that for the polyester detecting film  352 C. The predetermined specific range (time) is required to be a value which is not less than a value obtained by dividing an arrangement distance from the polyester detecting film  351 C to the polyester detecting film  352  by a rotation speed for one turn and is also required to be a value which is not more than a value smaller than a time of one turn. In S 108 C, in the case where the CPU  40 C discriminates that the timer A value is within the specific range, the CPU discriminates that the polyester detecting film  351 C reaches the detection surface of the electrostatic capacity sensor electrode  321 C, i.e., that the polyester detecting film  351 C is detected. 
     On the other hand, in S 108 C, when the CPU  40 C discriminates that the timer A value is not within the specific range, the CPU  40 C discriminates that the polyester detecting film  351 C cannot be detected. In this case, the CPU  40  resets, after the sequence returns to the processing of S 106 C, the timer A and then starts the monitoring of the detection level of the electrostatic capacity sensor IC  33 C in order to detect the polyester detecting film  351  again. In S 109 C, the CPU  40 C starts a timer B from timing when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  361 C of the polyester detecting film  351 C changes to the extent that the detection level is not less than the rising threshold, thus starting the measurement of the time. The timer B is a timer for measuring the time difference between the timing when the polyester detecting film  351 C is detected and the timing when the polyester detecting film  352 C is detected. 
     Next, in S 110 C and S 11 C, the CPU  40  detects that the polyester detecting film  351 C passes. In S 110 C, the CPU  40 C detects timing when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected provided on the polyester detecting film changes to the extent that the detection level is not more than the falling threshold. In this embodiment, the falling threshold of the detection level is set at (initial value determined in S 105 C +20%). Further, the CPU  40 C discriminates the timing when the detection level is below this falling threshold is timing when either one of the polyester detecting films passes the detection surface of the electrostatic capacity sensor IC  33 C. In S 110 C, in the case where the CPU  40 C discriminate that the detection level of the electrostatic capacity sensor IC  33 C is not less than the falling threshold (initial value +20%), the CPU  40  discriminates in S 121 C whether or not the error occurs. In this embodiment, in S 121 C, in the case where the CPU  40 C discriminates that the lapse of the time from the start of the timer B is less than 2.0 sec, the sequence returns to the processing of S 110 C, in which the monitoring of the detection level of the electrostatic capacity sensor IC  33 C is continued. On the other hands, in S 121 C, in the case where the CPU  40 C discriminates that 2.0 sec or more elapses from the start of the timer B, the sequence goes to processing of S 122 C. In S 122 C, the CPU  40 C discriminates that some abnormality (error) such as failure of the electrode to be detected  361 C, failure of the electrostatic capacity sensor IC  33 C or communication abnormality between the CPU  40 C and the electrostatic capacity sensor IC  33 C, and then notifies the video controller  42  of the abnormality. Here, the reason why the rising threshold is (initial value +30%) and the falling threshold is (initial value +20%) is that hysteresis is provided and a malfunction due to noise is prevented. In S 111 C, the CPU  40 C detects that the polyester detecting film  351 C passes through above the detection surface of the electrostatic capacity sensor electrode  321 C. 
     Next, in S 112 C and S 113 , the CPU  40 C detects the timing when the polyester detecting film  351 C reaches above the detection surface of the polyester detecting film  351 C. In S 112 C, the CPU  40 C detects the timing when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C of the polyester detecting film  352 C changes to the extent that the detection level is not less than the rising threshold. 
     In this embodiment, the detection level rising threshold is (initial value +30%). The CPU  40 C discriminate that this timing when the detection level is not less than the rising threshold is the timing when the polyester detecting film  352 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C. In S 112 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is not less than the rising threshold, the sequence goes to processing of S 113 C. In S 112 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is less than the rising threshold, the CPU  40 C discriminates in S 123 C whether or not the error occurs. The processing operations in S 123 C and S 124 C are the same as those in S 121 C and S 122 C and therefore will be omitted from description. In S 113 C, the CPU  40 C stops the timer B with timing when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C of the polyester detecting film  352 C changes to the extent that the detection level is not less than the rising threshold. 
     IN S 114 C, the CPU  40 C reads the value of the timer B. In S 115 C, the CPU  40 C compares the timer B and the table T to check the value. The table T is, as shown in (c) of  FIG. 24 , such a table that pairs of the time differences (msec) and corresponding remaining toner amounts (%) are listed. For example, in the case of (b) of  FIG. 24 , the time difference is 390 msec, so that it is possible to detect that the remaining toner amount is 60% from the table T. The CPU  40 C discriminates, as described above, the remaining toner amount with respect to the value between numerical values in the table by checking the time difference against a value calculated by linear interpolation of the numerical values on the basis of the table T. In S 116 C, the CPU  40 C notifies the video controller  42  of the main assembly of the remaining toner amount (%) discriminated in S 115 C. 
     In this embodiment, the rotating operation of the polyester detecting film performed in the remaining toner amount detection sequence is described but if the polyester detecting film is rotated during the image forming operation or the like, the remaining amount can be detected. Further, the remaining toner amount detection may also be started from a state in which the rotation state of the polyester detecting film is stabilized by rotating the polyester detecting film several turns before the remaining toner amount detection. Further, in this embodiment, on the basis of a result of a single (one) measurement (the timer B value in S 114 C), the remaining toner amount is calculated but it is possible to further improve the accuracy by effecting the measurement plural times and then by discriminating the remaining toner amount from an average of the measured values. Here, the above-defined falling threshold and rising threshold, the timer A value and the error discrimination time are an example in the constitution in this embodiment. These constitutions are determined in total consideration of the arrangement of the polyester detecting films  351 C and  352 C, the rotation speed of the polyester detecting films, the circuit constant, the detection level of the electrostatic capacity sensor, and the like and therefore are not limited to those described above. 
     In this embodiment, in the processing operations of S 106 C to S 109 C, the sequence for detecting the polyester detecting film  351 C and then detecting the polyester detecting film  352 C was shown. 
     However, it is also possible to use the following method in place of the sequence. Three values of the timing when the detection level of the electrostatic capacity sensor IC  33 C changes to the extent that it is not less than the rising threshold are detected. A time difference from the image timing to the second timing and a time difference from the second timing to the third timing are calculated. In this case, it is possible to discriminate that a smaller value of the two time differences is a time difference from the detection of the polyester detecting film  351 C to the detection of the polyester detecting film  352 C. This time difference is checked against the table T to discriminate the remaining toner amount. As a result, the sequence can be simplified. 
     Further, the remaining toner amount was discriminated on the basis of the difference between the time when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  361 C provided on the polyester detecting film  351 C starts to change to the extent that the detection level is not less than the rising threshold and the time when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C provided on the polyester detecting film  352 C starts to change to the extent that the detection level is not less than the rising threshold. However, the remaining toner amount may also be discriminated on the basis of the difference between the time when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  361 C provided on the polyester detecting film  351 C starts to change to the extent that the detection level is not more than the falling threshold and the time when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C provided on the polyester detecting film  352 C starts to change to the extent that the detection level is not more than the falling threshold. Further, the remaining toner amount may also be discriminated on the basis of the difference between the time when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  361 C starts to change to the extent that the detection level is not less than the rising threshold and the time when the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C starts to change to the extent that the detection level is not more than the falling threshold. As a result, also the time when the polyester detecting film  352 C completely passes through over the electrostatic capacity sensor electrode  321 C can be considered and therefore the remaining toner amount can be detected with higher accuracy. 
     Further, in this embodiment, the electrode to be detected  361 C provided on the polyester detecting film  351 C was disposed in the neighborhood of the end of the polyester detecting film  351 C with respect to the circumferential direction. However, by disposing the electrode to be detected  361 C in the neighborhood of the rotation shaft  29 C (rotation shaft side), the polyester detecting film  351 C can be detected at a certain interval irrespective of the remaining toner amount while the polyester detecting film  351 C has flexibility. By calculating the difference from the time detected by the polyester detecting film  352 C, the warp degree of the polyester detecting film  352 C can be detected with high accuracy and therefore the remaining toner amount can be detected with higher accuracy. 
     Thus, the remaining toner amount is discriminated on the basis of the time difference from the timing when the polyester detecting film  351 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C to the timing when the polyester detecting film  352 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C. As a result, it is possible to detect the remaining toner amount in real time from the full state of the toner to the empty state of the toner. Further, the electrostatic capacity sensor changes its electrostatic capacity depending on the approach of the polyester detecting film and therefore speed-up of the detection time and the image forming operation can be performed simultaneously. Further, the warpage of the polyester detecting film is stable depending on the remaining toner amount even when the polyester detecting film is rotated at high speed and therefore the remaining toner amount can be detected in real time. 
     As described above, according to this embodiment, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detect with high accuracy. 
     Embodiment 8 
     In Embodiment 7, the polyester detecting film  351 C has flexibility and is warped by the resistance of the toner  28 C. In this embodiment, a stirring rod  261 C is provided. The stirring rod  261 C has high rigidity and also has a function of stirring the toner  28 C. Incidentally, the constitution of the image forming apparatus in this embodiment is the same as that described in Embodiment 7 except for the process cartridge  5 C and therefore will be omitted from detailed description. 
     A process cartridge in this embodiment will be described with reference to  FIG. 26 .  FIG. 26  is a sectional view of a process cartridge and an electrostatic capacity sensor  26  substrate in this embodiment. Inside the toner container  23 C of the process cartridge  5 C in this embodiment, the toner (not shown) of an associated color and a stirring rod  261 C for supplying the toner to a toner supply roller  121 C are provided. The stirring rod  261 C performs rotating motion around a rotation shaft  29 C, thus stirring the toner. Another rotation shaft  29 C is provided with the stirring rod  261 C for detecting the remaining toner amount, and a polyester detecting film  352 C. The stirring rod  261 C has high rigidity and performs a certain rotating operation irrespective of the resistance of the toner. The polyester detecting film  352 C is disposed 90 degrees behind the stirring rod  261 C with respect to the rotational direction and has flexibility. Further, as the stirring rod  261 C, a member having electroconductivity is used. In the neighborhood of the circumferential end of the polyester detecting film  352 C, an electroconductive electrode to be detected  362 C is provided. 
     The electrostatic capacity sensor substrate  331 C provided with the electrostatic capacity sensor IC  33 C, for detecting the remaining toner amount in the toner container  23 C, and the like is provided in the neighborhood of an outer wall of the developing unit with respect to the circumferential direction of the stirring rod and the polyester detecting film  352 C. The electrostatic capacity sensor electrode  321 C approaches the outer casing of the toner container  23 C when the process cartridge  5  is mounted in the main assembly  101 . In this state, the electrostatic capacity generated by the stirring rod  261 C or the electrode to be detected  362 C, which are provided in the developing unit, is detected by the electrostatic capacity sensor IC  33 C. The circuit diagram in this embodiment is the same as that of  FIG. 13  described in Embodiment 1 and will be omitted from detailed description in this embodiment. 
     The detection characteristic and the flow chart are similar to those of (a) to (c) of  FIG. 24  and  FIGS. 25A and 25B  in Embodiment 7. Incidentally, the stirring rod  261 C in this embodiment corresponds to the polyester detecting film  351 C and the electrode to be detected  361 C in Embodiment 7. For this reason, the  351 C in S 109 C in the flow chart of  FIG. 25A  is read as the stirring rod  261 C in this embodiment. The stirring rod  261 C has high rigidity and therefore rotates constantly irrespective of the resistance of the toner. For that reason, the stirring rod  261 C constantly rotates irrespective of the remaining toner amount and therefore the time detected by the electrostatic capacity sensor IC  33 C is always a certain interval. Therefore, by calculating the difference between the time detected by the stirring rod  261 C and the time detected by the polyester detecting film  352 C, i.e., the time difference, the warp degree of the polyester detecting film  352 C can be detected with high accuracy and therefore the remaining toner amount can be detected with higher accuracy. 
     As described above, according to this embodiment, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detected with high accuracy. 
     Embodiment 9 
     In Embodiment 7, the remaining toner amount is detected on the basis of the time difference between the values of timing when the electrostatic capacity sensor IC  33 C detects the two polyester detecting films. On the other hand, in this embodiment, the remaining toner amount is detected by detecting a change in electrostatic capacity detected by the electrostatic capacity sensor IC  33 C. First, a color laser printer in this embodiment will be described. The image forming apparatus, the process cartridge and the circuit diagram in this embodiment are the same as those described in Embodiment 7 with reference to  FIGS. 21 and 22  and thus will be omitted from detailed description in this embodiment. 
     [Characteristic of Remaining Toner Amount Detection] 
     With reference to (a) to (c) of  FIG. 27 , a remaining toner amount detection characteristic will be described. Part (a) of  FIG. 27  is a characteristic graph between the remaining toner amount (%) and the difference in detection level (detection level difference) between the polyester detecting films  351 C and  352 C detected by the electrostatic capacity sensor IC  33 C. The detection level difference is smaller with a larger remaining toner amount, and the detection level difference is larger with a smaller remaining toner amount. As a result, the remaining toner amount can be detected by calculating the detection level difference. Part (b) of  FIG. 27  is waveform data when the remaining toner amount is 10%. In this embodiment, the electrostatic capacity sensor IC  33 C calculates an average of each of the detection levels, detected thereby, of the electrode to be detected  361 C provided on the polyester detecting film  351 C and the electrode to be detected  362 C provided on the polyester detecting film  352 C. Then, by using a difference in average between the calculated detection (i.e., the detection level difference), the remaining toner amount is discriminated. In (b) of  FIG. 27 , it is understood that an average A of the detection level of the polyester detecting film  351 C is  195  and an average B of the detection level of the polyester detecting film  352 C is  210 , and thus the difference in average between the detection levels, i.e., the detection level difference is 15. 
     Part (c) of  FIG. 24  is a table N in which the detection level difference and the remaining toner amount are associated with each other. The remaining toner amount between numerical values in the table T can be obtained by linear interpolation of known remaining toner amounts. Here, the calculated detection level values are values in this embodiment and therefore vary when a measuring condition is changed. This is also true for the numerical values in the table T. 
     [Flow Chart of Remaining Toner Amount Detection] 
     Next, a sequence for detecting the remaining toner amount in this embodiment will be described by using a flow chart of  FIGS. 28A and 28B . Processing operations of S 201 C to S 205 C, S 215 C and S 216 C are the same as those of S 101 C to S 105 C, S 117 C and S 118 C of  FIGS. 25A and 25B  in Embodiment 7 and therefore will be omitted from description. In S 206 C, the CPU  40 C detects the polyester detecting film  351 C or  352 C. In S 206 C, the CPU  40 C detects timing when the electrostatic capacity detection level between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  361 C of the polyester detecting film  351 B or the electrode to be detected  362 C of the polyester detecting film  352 C states a change to the extent that the detection level is not less than the rising threshold. In this embodiment, the rising threshold of the detection level is set at (initial value determined in S 205 C +30%). The CPU  40 C discriminate that this timing when the polyester detecting film  351 C or the detection level is not less than the rising threshold is the timing when the polyester detecting film  352 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C. In S 206 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is not less than the rising threshold, the sequence goes to processing of S 207 C. On the other hand, in S 206 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is less than the rising threshold, the CPU  40 C discriminates in S 217 C whether or not the error occurs. The processing operations in S 217 C and S 218 C are the same as those in S 215 C and S 216 C and therefore will be omitted from description. 
     Next, in S 207 C and S 208 C, the CPU  40 C calculates the average of the detection level of the polyester detecting film  351 C or the polyester detecting film  352 C and detects the passing of the polyester detecting film  351 C or the polyester detecting film  352 C. In S 207 C, the CPU  40 C measures the monitored detection level of the electrostatic capacity sensor IC  33 C at plural points and stores the measured detection levels in, e.g., a memory. At this time, the CPU  40 C stores also the resultant number of measured data in the memory and calculates the average A from the plurality of the measured data and the number of the measured data. In S 208 C, the CPU  40 C detects timing when the electrostatic capacity detection level between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  361 C of the polyester detecting film  351 C or the electrode to be detected  362 C of the polyester detecting film  352 C changes to the extent that the detection level is not more than the falling threshold. In this embodiment, the falling threshold of the detection level of the electrostatic capacity sensor IC  33 C is (initial value determined in S 205 C) +20%. The CPU  40 C discriminates that the timing when the detection level of the electrostatic capacity sensor IC  33 C is not more than the falling threshold is the timing when the polyester detecting film  351 C or the polyester detecting film  352 C passes through over the detection surface of the electrostatic capacity sensor electrode  321 C. In S 208 C, when the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is not more than the falling threshold, the monitoring is ended and the average A is decided, so that the sequence goes to processing of S 209 C. In S 208 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is not the falling threshold or less, the CPU  40 C discriminates in S 219 C whether or not the error occurs. The processing operations of S 219 C and S 220 C are the same as those of S 215 C and S 216 C and therefore will be omitted from description. Incidentally, setting of the rising threshold and the falling threshold is the same as that in Embodiment 7 and will be omitted from description. 
     In S 115 C, the CPU  40 C compares the timer B and the table T to check the value. The table T is, as shown in (c) of  FIG. 24 , such a table that pairs of the time differences (msec) and corresponding remaining toner amounts (%) are listed. For example, in the case of (b) of  FIG. 24 , the time difference is 390 msec, so that it is possible to detect that the remaining toner amount is 60% from the table T. The CPU  40 C discriminates, as described above, the remaining toner amount with respect to the value between numerical values in the table by checking the time difference. 
     Next, in S 209 C, the CPU  40 C detects the polyester detecting film  351 C or  352 C. If the polyester detecting film  351 C is detected in S 206 C, the polyester detecting film  352 C is detected in S 209 C, and if the polyester detecting film  352 C is detected in S 206 C, the polyester detecting film  351 C is detected in S 209 C. In S 209 C, the CPU  40 C discriminates whether or not the electrostatic capacity detection level between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C of the polyester detecting film  352 B or the electrode to be detected  361 C of the polyester detecting film  351 C is not less than the rising threshold. In this embodiment, the rising threshold of the detection level is set at (initial value determined in S 205 C +30%). The CPU  40 C discriminate that this timing when the polyester detecting film  352 C or the detection level exceeds the rising threshold is the timing when the polyester detecting film  351 C reaches above the detection surface of the electrostatic capacity sensor electrode  321 C. In S 209 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is not less than the rising threshold, the sequence goes to processing of S 210 C. On the other hand, in S 209 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C not the rising threshold or more, the sequence goes to processing of S 221 C. The processing operations in S 221 C and S 222 C are the same as those in S 217 C and S 218 C and therefore will be omitted from description. 
     Next, in S 210 C and S 211 C, the CPU  40 C calculates the average of the detection level of the polyester detecting film  352 C or the polyester detecting film  351 C and detects the passing of the polyester detecting film  352 C or the polyester detecting film  351 C. In S 210 C, the CPU  40 C measures the monitored detection level of the electrostatic capacity sensor IC  33 C at plural points and stores the measured detection levels in, e.g., a memory. At this time, the CPU  40 C stores also the resultant number of measured data in the memory and calculates the average B from the plurality of the measured data and the number of the measured data. In S 218 C, the CPU  40 C discriminates whether or not the electrostatic capacity detection level between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C of the polyester detecting film  352 C or the electrode to be detected  361 C of the polyester detecting film  351 C is not more than the falling threshold. In this embodiment, the falling threshold of the detection level of the electrostatic capacity sensor IC  33 C is (initial value +20%). The CPU  40 C discriminates that the timing when the detection level is less than the falling threshold is the timing when the polyester detecting film  352 C or the polyester detecting film  351 C passes through over the detection surface of the electrostatic capacity sensor electrode  321 C. In S 211 C, in the case were the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is not more than the falling threshold, the monitoring of the detection level of the electrostatic capacity sensor IC  33 C is ended and the average B is decided, so that the sequence goes to processing of S 212 C. In S 211 C, in the case where the CPU  40 C discriminates that the detection level of the electrostatic capacity sensor IC  33 C is not the falling threshold or less, the CPU  40 C discriminates in S 223 C whether or not the error occurs. The processing operations of S 223 C and S 224 C are the same as those of S 215 C and S 216 C and therefore will be omitted from description. Further, setting of the rising threshold and the falling threshold is the same as that in Embodiment 7 and will be omitted from description. 
     In S 212 C, the CPU  40 C calculates the detection level difference between the polyester detecting films from the average A calculated in S 207 C and the average B calculated in S 210 C. In this embodiment, an absolute value of the difference between the average A and the average B is calculated. For example, in the case of (b) of  FIG. 27 , (average A−average B)=195−210 and thus its absolute value is 15. 
     In S 213 C, the CPU  40 C checks the detection level difference calculated in S 212 C against the table N. The table N is such a table that pairs of the detection level difference and corresponding remaining toner amounts are listed, e.g., as shown in (c) of  FIG. 27 . The CPU  40 C discriminates the remaining toner amount by checking the value against the table N. For example, in the case of (b) of  FIG. 27 , the absolute value of the detection level difference is 15, so that it is understood that the remaining toner amount is 10% from the table N of (c) of  FIG. 27 . Incidentally, as described above, the value between numerical values in the table N is calculated by performing linear interpolation of the known numerical values in the table N. In S 214 C, the CPU  40 C notifies the video controller  42  of the discriminated remaining toner amount. 
     Thus, in this embodiment, the remaining toner amount is discriminated on the basis of the detection level difference between the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  361 C provided on the polyester detecting film  351 C and the electrostatic capacity between the electrostatic capacity sensor electrode  321 C and the electrode to be detected  362 C provided on the polyester detecting film  352 C. As a result, it is possible to detect the remaining toner amount in real time from the full state of the toner to the empty state of the toner. Further, the electrostatic capacity sensor IC changes its electrostatic capacity detection level depending on the approach of the polyester detecting film and therefore speed-up of the detection time and the image forming operation can be performed simultaneously. Further, the warpage of the polyester detecting film is stable depending on the remaining toner amount even when the polyester detecting film is rotated at high speed and therefore the remaining toner amount can be detected in real time. 
     As described above, according to this embodiment, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detect with high accuracy. 
     Embodiment 10 
     In Embodiment 9, the polyester detecting film  351 C has flexibility and is warped by the resistance of the toner  28 C. In this embodiment, a stirring rod  261 C is provided and corresponds to the polyester detecting film  351 C. The stirring rod  261 C has high rigidity and also has a function of stirring the toner  28 C. Incidentally, the constitution of the image forming apparatus in this embodiment is the same as that described in Embodiment 7 except for the process cartridge  5 C and therefore will be omitted from detailed description. The constitution in this embodiment uses, the process cartridge of  FIG. 26  described in Embodiment 8, and the sequence for detecting the remaining toner amount uses a flow chart shown in  FIGS. 28A and 28B . Incidentally, in the description of the flow chart of  FIGS. 28A and 28B , the polyester detecting film  351 C is read as the stirring rod  261 C. Further, the detection characteristic is also the same as that of  FIG. 27  described in Embodiment 9. The stirring rod  261 C has high rigidity and therefore rotates constantly irrespective of the resistance of the toner  28 C. For that reason, the stirring rod  261 C constantly rotates irrespective of the remaining toner amount and therefore the detection level detected by the electrostatic capacity sensor IC  33 C becomes constant. Therefore, by calculating the difference between the detection level detected by the stirring rod  261 C and the detection level detected by the polyester detecting film  352 C, the detection level difference due to warpage of the polyester detecting film  352 C can be detected with high accuracy and therefore the remaining toner amount can be detected with higher accuracy. 
     As described above, according to this embodiment, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detected with high accuracy. 
     Other Embodiments 
     In the above-described embodiment, for easy understanding, description such that the reference to the table is made in a single detection is made. However, it is possible to except further enhancement of the detection accuracy by effecting control such that data measured plural times are averaged and thereafter reference to the respective tables is made. 
     Further, in the above-described embodiments, the constitution in which the two polyester detecting films are disposed in the developing unit was described. However, by disposing three or more polyester detecting films, it is possible to detect the remaining toner amount with higher accuracy. 
     Further, in the above-described embodiments, an integral constitution of the developing unit was described. However, also in a supply type toner container which is separately provided from the developing roller, the present invention is applicable by providing the electrode to be detected and the polyester detecting film inside the toner container. 
     As described above, also in other embodiments, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detected with high accuracy. 
     INDUSTRIAL APPLICABILITY 
     As described above, according to the present invention, the remaining toner amount can be detected in real time from the full state of the toner to the empty state of the toner, and even when the stirring member is operated at high speed, the remaining toner amount can be detected with high accuracy. 
     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 purpose of the improvements or the scope of the following claims. 
     This application claims priority from Japanese Patent Applications Nos. 072275/2011 filed Mar. 29, 2011; 084508/2011 filed Apr. 6, 2011 and 093147/2011 filed Apr. 19, 2011 which are hereby incorporated by reference.