Patent Publication Number: US-10331058-B2

Title: Image forming apparatus configured to detect toner quality

Description:
INCORPORATION BY REFERENCE 
     This application is based upon, and claims the benefit of priority from, corresponding Japanese Patent Application No. 2017-119283 filed in the Japan Patent Office on Jun. 19, 2017, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section. 
     In an image forming apparatus typified by a multi-functional peripheral, a light is irradiated to a photoreceptor to form an electrostatic latent image on the photoreceptor based on image data. Then, a charged toner is supplied on the formed electrostatic latent image to make a visible image, and subsequently, the visible image is transferred to be fixed on a paper sheet and output outside the apparatus. 
     A typical image forming apparatus includes a developing device that uses a developer such as a toner to perform development. The developing device rotates a developer by a rotator or similar unit to charge the developer, and electrically attaches the developer on an electrostatic latent image, thus executing the development. The developing device is appropriately supplied with the toner consumed by the development by a toner container removably attachable to the image forming apparatus. A technique regarding toner supply has been proposed. 
     There has been proposed an image forming apparatus that includes a toner container, a developing unit, a magnetic flow rate sensor, and a controller. The developing unit is replenished with a toner from the toner container. The magnetic flow rate sensor measures a replenishment amount of the toner replenished from the toner container to the developing unit. The controller controls the toner replenishment from the toner container to the developing unit based on the toner replenishment amount measured by the magnetic flow rate sensor. 
     The following toner end detector included in an electrophotographic apparatus has been proposed. This toner end detector includes a toner housing chamber, an agitator, and a toner sensor. The toner housing chamber houses a toner. The agitator is rotationally driven in this toner housing chamber, and replenishes the toner in this toner housing chamber to the developing unit. The toner sensor is installed in the toner housing chamber, and detects a thickness of the toner in this toner housing chamber. The toner end detector uses an analog output voltage of this toner sensor that varies in accordance with the rotation of the agitator in the toner housing chamber, thus detecting the toner end based on the variation of this analog output voltage. 
     SUMMARY 
     An image forming apparatus according to one aspect of the disclosure forms image. The image forming apparatus includes a developer unit, a toner container, a capacitance sensor, a toner amount detector, and a determining unit. The developer unit forms a toner image. The toner container is located to be removably attachable to the image forming apparatus. The toner container supplies a toner to the developer unit. The capacitance sensor is located on a supply passage for the toner from the toner container to the developer unit. The capacitance sensor detects an electric charge amount and a relative dielectric constant of the toner. The electric charge amount is an electric charge amount when the toner passes through the supply passage. The toner amount detector detects an amount of the toner passing through the supply passage based on the electric charge amount detected by the capacitance sensor. The determining unit determines whether the relative dielectric constant of the toner detected by the capacitance sensor is in a predetermined range. 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description with reference where appropriate to the accompanying drawings. Further, it should be understood that the description provided in this summary section and elsewhere in this document is intended to illustrate the claimed subject matter by way of example and not by way of limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates an external appearance of a multi-functional peripheral when an image forming apparatus according to one embodiment of the disclosure is applied to the multi-functional peripheral. 
         FIG. 2  illustrates a configuration of the multi-functional peripheral according to the one embodiment. 
         FIG. 3  illustrates a configuration of a periphery of an image forming unit. 
         FIG. 4  illustrates an operation when an image is formed in the multi-functional peripheral. 
         FIG. 5  illustrates a cross section of a part of a configuration of a capacitance sensor. 
         FIG. 6  illustrates a cross section of a part of the configuration of the capacitance sensor. 
         FIG. 7  illustrates an exemplary display screen displaying an indication of a non-genuine toner. 
         FIG. 8  illustrates a periphery of an image forming unit included in a multi-functional peripheral according to another embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Example apparatuses are described herein. Other example embodiments or features may further be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. In the following detailed description, reference is made to the accompanying drawings, which form a part thereof. 
     The example embodiments described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the drawings, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     The following describes embodiments of the disclosure.  FIG. 1  schematically illustrates an external appearance of a multi-functional peripheral  11  when an image forming apparatus according to one embodiment of the disclosure is applied to the multi-functional peripheral.  FIG. 2  is a block diagram illustrating a configuration of the multi-functional peripheral  11  illustrated in  FIG. 1 . In the following drawings, like reference numerals are designated to the configuration similar to or corresponding to those in  FIGS. 1 and 2 , and their descriptions will not be further elaborated here. 
     With reference to  FIGS. 1 and 2 , the multi-functional peripheral  11  includes a control unit  12 , an operation unit  13 , an image reading unit  14 , an image forming unit  15 , a sheet feed cassette  16 , a hard disk  17  as a storage unit, a network interface unit  18 , a toner container  23 , an intermediate hopper  24 , and a capacitance sensor  25 . The network interface unit  18  is connected to a network. The toner container  23  includes a toner supply roller and similar unit. The intermediate hopper  24  temporarily stores toners in the multi-functional peripheral  11 . 
     The control unit  12  controls the entire multi-functional peripheral  11 . The control unit  12  is constituted of a central processing unit (CPU) and similar unit, and includes a main storage memory  19  that temporarily stores data. The operation unit  13  includes a display screen  21  as a touch panel type display that displays information transmitted from the multi-functional peripheral  11  side and contents input by a user. The operation unit  13  accepts inputs from the user relating to the image formation including conditions on an image formation such as the number of print copies and a tone. The image reading unit  14  includes an auto-document feeder (ADF)  22  as a document feeder that feeds a document set on a set position to a reading position. The image reading unit  14  reads an image of the document set on the ADF  22  or a placement table. Three sheet feed cassettes  16  are located to each internally house a plurality of paper sheets. The image forming unit  15  forms the image on the paper sheet fed from any of the sheet feed cassettes  16  based on image data of the document read by the image reading unit  14  and image data transmitted via the network. The hard disk  17  stores data on the image formation such as the transmitted image data, the input image formation condition, and similar data. 
     Next, a configuration of a periphery of the image forming unit  15  will be described.  FIG. 3  illustrates the configuration of the periphery of the image forming unit  15 . With reference to  FIG. 3 , the image forming unit  15  includes a photoreceptor  32 , a charger  33 , an exposure device  34 , a developer unit  31 , a transfer unit  37 , a cleaning unit  38 , a destaticizing lamp  42 , and a fixing unit  43 . The charger  33  charges the photoreceptor  32 . The exposure device  34  exposes a surface of the photoreceptor  32  based on the image data. The developer unit  31  supplies a toner  29  to the surface of the photoreceptor  32 . The transfer unit  37  transfers a toner image formed on the photoreceptor  32  to the paper sheet side. The cleaning unit  38  performs a cleaning by removing the toner  29  remaining on the photoreceptor  32  and similar cleaning after the transferring to the paper sheet. The destaticizing lamp  42  removes the electric charge remaining on the photoreceptor  32 . The fixing unit  43  includes a pair of fixing rollers and fixes the toner image on the paper sheet. 
     The photoreceptor  32  rotates in a direction indicated by an arrow R 1  in  FIG. 3 . A supply direction of the toner  29  and a conveyance direction of the paper sheet onto which the toner image is transferred are indicated by an arrow D 1 . The charger  33  charges the photoreceptor  32 . Then, the exposure device  34  exposes the surface of the photoreceptor  32  based on the image data read by the image reading unit  14  and similar data. Thus, an electrostatic latent image is formed on the surface of the photoreceptor  32 . The developer unit  31  includes a developing container  35  that houses the toner  29 , and a developing roller  36  that rotates to charge the toner  29  and supplies the toner  29  to the photoreceptor  32 . The toner  29  charged by the developer unit  31  is supplied to the surface of the photoreceptor  32 , thus forming a visible image by the toner, namely the toner image on the surface of the photoreceptor  32 . The formed toner image is transferred to the paper sheet side by the transfer unit  37 . The paper sheet onto which the toner image is transferred is fed to the fixing unit  43  side, and the fixing unit  43  fixes the toner image on the paper sheet. The cleaning unit  38  includes a cleaning roller  39  and a cleaning blade  41 . The cleaning roller  39  rotates to remove the toner  29  remaining on the photoreceptor  32 . The cleaning blade  41  is made of rubber and plate-shaped, and abuts on the surface of the photoreceptor  32 . The toner  29  remaining on the photoreceptor  32  without being transferred to the paper sheet side by the transfer unit  37  is removed by the cleaning roller  39  and the cleaning blade  41 . The electric charge remaining on the photoreceptor  32  is removed by the destaticizing lamp  42 . 
     In the developer unit  31 , a development, that is, a supply of the toner  29  to the photoreceptor  32  side, consumes the toner  29  in the developing container  35 . The toner  29  is supplied to the developing container  35  by the consumed amount. The toner container  23  is filled with the toner  29  to be supplied to the developer unit  31 . The toner  29  is supplied to the developing container  35  from the toner container  23  via the intermediate hopper  24  passing through a supply passage  28  through which the toner  29  passes. That is, the toner container  23  supplies the toner  29  to the developer unit  31 . The toner container  23  is located to be removably attachable to the multi-functional peripheral  11 . 
     The toner container  23  is filled with a genuine toner, namely the toner  29  provided by a developer of the multi-functional peripheral  11  as the toner  29  appropriate to the multi-functional peripheral  11 . On such a toner  29 , the developer and similar person of the multi-functional peripheral  11  preliminarily measure a relative dielectric constant of the toner  29 . However, among the commercially available toner containers  23  for replacement, there is a toner container  23  filled with a non-genuine toner, namely a toner not provided by the developer of the multi-functional peripheral  11  but having different components while the components are similar to the genuine toner. Such a non-genuine toner does not assure image quality, and continuous use of the non-genuine toner possibly adversely affects the multi-functional peripheral  11 . 
     The capacitance sensor  25  is located on the supply passage  28  for the toner  29  from the toner container  23  to the developer unit  31 , specifically, the developing container  35  included in the developer unit  31 . The capacitance sensor  25  detects an electric charge amount when the toner  29  passes through the supply passage  28  and the relative dielectric constant of the toner  29 . 
     Here, a configuration of the control unit  12  will be described. With reference to  FIG. 2  again, the control unit  12  includes a toner amount detector  26  and a determining unit  27 . The toner amount detector  26  detects an amount of the toner  29  passing through the supply passage  28  based on the electric charge amount detected by the capacitance sensor  25 . The determining unit  27  determines whether or not the relative dielectric constant of the toner  29  detected by the capacitance sensor  25  is within a predetermined range. Specifically, the determining unit  27  determines whether or not the relative dielectric constant of the toner  29  detected by the capacitance sensor  25  is equal to or more than a first value as an upper-limit value of the set predetermined range, and whether or not equal to or less than a lower-limit value of the set predetermined range. 
     Next, an image formation in the multi-functional peripheral  11  will be described.  FIG. 4  illustrates an operation when an image is formed in the multi-functional peripheral  11 . With reference to  FIG. 4 , when a request for an image formation from the user to the operation unit  13  is accepted, and then the image formation starts (in  FIG. 4 , Step S 11 , hereinafter “Step” will be omitted), the toner  29  is gradually consumed. Then, the supply of the toner  29  starts by the amount of the consumed toner  29  (S 12 ). That is, the toner  29  is replenished in the developing container  35  from the toner container  23  via the intermediate hopper  24  passing through the supply passage  28 . Here, the toner amount detector  26  uses the capacitance sensor  25  to detect the electric charge amount, and detects the toner amount (S 13 ). The capacitance sensor  25  detects the relative dielectric constant of the toner  29  (S 14 ). The determining unit  27  determines whether or not the relative dielectric constant of the toner  29  detected by the capacitance sensor  25  is in the predetermined range. Specifically the determining unit  27  determines whether or not the relative dielectric constant of the toner  29  is equal to or more than the first value and whether or not the relative dielectric constant of the toner  29  is equal to or less than a lower-limit value of the predetermined range (S 15 ). 
     Here, a description will be given of the detection of the relative dielectric constant of the toner  29  by the capacitance sensor  25 .  FIGS. 5 and 6  are cross sections of a part of a configuration of the capacitance sensor  25 . With reference to  FIGS. 5 and 6 , the capacitance sensor  25  includes a pair of electrodes  46   a  and  46   b . The electrode  46   a  on a positive side and the electrode  46   b  on a negative side are located across a distance d. The distance d is a distance between facing surfaces  47   a  and  47   b  of the electrodes  46   a  and  46   b  respectively. That is, in this configuration, the relative dielectric constant of the toner  29  is detected when the toner  29  passes between the pair of the electrodes  46   a  and  46   b  at a part of the supply passage  28 .  FIG. 5  illustrates a state where the toner  29  is included between the electrodes  46   a  and  46   b  by 50%.  FIG. 6  illustrates a state where the toner  29  is included between the electrodes  46   a  and  46   b  by 100%. 
     In the capacitance sensor  25 , the electric charge amount varies corresponding to a height h 1  from a bottom surface  48   a  to a top surface  48   b  of the loaded toner  29 , and the toner amount is detected based on the varying electric charge amount. Then, the replenishment amount of the toner  29  is calculated by, for example, integrating the supplied toner amount based on the detection result of the toner amount. The height h 1  is a height as 50% of an entire height of the electrode  46   a  and  46   b . A height h 2  is a height as 100% of the entire height of the electrode  46   a  and  46   b . Since respective areas of the surfaces  47   a  and  47   b  of the electrodes  46   a  and  46   b  and the distance d are constant, the relative dielectric constant of the toner  29  included between the electrodes  46   a  and  46   b  is detected corresponding to the heights h 1  and h 2  from the bottom surface  48   a  to the top surface  48   b  of the loaded toner  29 . 
     Here, assume that the relative dielectric constant of the genuine toner is three, the relative dielectric constant of a first non-genuine toner B 1  is five, the relative dielectric constant of a second non-genuine toner B 2  different from the first non-genuine toner B 1  is two, and the relative dielectric constant of atmosphere is one. Then, based on a value of the electric charge amount detected by the capacitance sensor  25 , the relative dielectric constant of the toner  29  is detected as follows. Note that: Q=CV (Q: electric charge amount (C), C: capacitance (F), V: inter-electrode voltage (V)), and C=ε r ·ε0·S/d (ε r : relative dielectric constant, ε 0 : dielectric constant (Fm −1 ), S: electrode size (m 2 ), d: inter-electrode distance (m)). The relative dielectric constant of the toner  29  is detected using the equations. The person who has developed the multi-functional peripheral  11  and provided the toner container  23  to the market is a person who knows the relative dielectric constant of the genuine toner. The above-described predetermined range can be a range configured considering a detection error added to 3 as the relative dielectric constant of the genuine toner, for example, a range of 2.5 to 3.5. 
     As illustrated in  FIG. 5 , when the toner amount between the electrodes is 50%, the toner  29  including only the genuine toner provides the relative dielectric constant between the electrodes as 3×0.5+1×0.5=2. The toner  29  including only the non-genuine toner B 1  provides the relative dielectric constant between the electrodes as 5×0.5+1×0.5=3. The toner  29  including only the non-genuine toner B 2  provides the relative dielectric constant between the electrodes as 2×0.5+1×0.5=1.5. As illustrated in  FIG. 6 , when the toner amount between the electrodes is 100%, the toner  29  including only the genuine toner provides the relative dielectric constant between the electrodes as 3×1+1×0=3. The toner  29  including only the non-genuine toner B 1  provides the relative dielectric constant between the electrodes as 5×1+1×0=5. The toner  29  including only the non-genuine toner B 2  provides the relative dielectric constant between the electrodes as 2×1+1×0=2. That is, when the non-genuine toner B 1  or the non-genuine toner B 2  is filled to the toner container  23  while the toner amount is 100%, the above-described values such as five as the relative dielectric constant and two as the relative dielectric constant are detected. 
     Here, assume that the toner amount is 100%. When the toner amount is 100% including the genuine toner by 75% and the non-genuine toner B 1  mixed by 25%, the relative dielectric constant is 3×0.75+5×0.25=3.5. At this time, when the first value is set to 3.5, the determining unit  27  determines the relative dielectric constant of the toner  29  to be equal to or more than the first value (YES at S 15 ). That is, when the relative dielectric constant of the toner  29  detected by the capacitance sensor  25  is equal to or more than the first value, the determining unit  27  determines that the non-genuine toner is mixed, not the detection error of the relative dielectric constant. The first value is a value on a level where the image formation is carried on while the mixture of the non-genuine toner is displayed for notification. For this determination, when the toner container  23  in which the genuine toner is filled is used at first, and the toner container  23  in which the non-genuine toner is filled is used from the middle of printing, the relative dielectric constant of the toner  29  gradually varies. That is, for example, when a few minutes or more has elapsed after the start of continuous printing by the multi-functional peripheral  11 , the relative dielectric constant of the toner  29  becomes outside of the predetermined range. 
     Then, the determining unit  27  determines whether or not the detected relative dielectric constant of the toner  29  is equal to or more than a second value higher than the first value (S 16 ). The second value is a value on a level where the image formation by the multi-functional peripheral  11  is to be promptly halted due to a considerably high content ratio of the non-genuine toner. When the second value is set to four, the determining unit  27  determines the relative dielectric constant of the toner  29  not to be equal to or more than the second value (NO at S 16 ). Then, the display screen  21  displays an indication of the non-genuine toner while the image formation is performed (S 17 ). This process is performed until the image formation terminates (S 18 ). The value four set as the second value corresponds to a case where the genuine toner is 50% and the non-genuine toner B 1  is mixed by 50%. 
       FIG. 7  illustrates an exemplary display screen  21  displaying the indication of the non-genuine toner. With reference to  FIG. 7 , the display screen  21  displays the character string  51 , “Mixture of non-genuine toner is detected.” and also “OK,” and displays a selection key  52  that detects a press to cause the display screen  21  to transition to the other screen. The containing of the non-genuine toner B 1  in the toner  29  is thus notified. 
     On the other hand, at S 16 , when the relative dielectric constant of the toner  29  is equal to or more than the second value (YES at S 16 ), the determining unit  27  aborts the image formation. That is, the operation of the image formation is halted. The display screen  21  displays an indication of the mixture of the non-genuine toner B 1  and prompting the change of the toner container  23  (S 19 ). In this case, for example, on the display screen  21  illustrated in  FIG. 7 , a character string of “This toner container is not supported. Please change to the supported one.” is displayed instead of the character string  51 . 
     At S 15 , when the detected relative dielectric constant is less than the first value (NO at S 15 ), the accepted image formation is carried on until the image formation terminates, and the electric charge amount and the relative dielectric constant of the toner  29  are monitored (S 20 , S 18 ). 
     According to the multi-functional peripheral  11  having such a configuration, the capacitance sensor  25  detects the electric charge amount to detect the toner amount. This ensures using the toner amount for calculating a toner replenishment amount based on the detection result. The determining unit  27  determines whether or not the detected relative dielectric constant of the toner is in the predetermined range. This ensures reflecting the determination result on the image formation. Accordingly, the influence of the mixture of the non-genuine toner on the image formation can be reduced. In this case, the above-described configuration of the multi-functional peripheral  11  including the capacitance sensor  25  and similar unit eliminates the need for locating the above-described sensor to each toner container  23  removably attachable to the multi-functional peripheral  11 . As a result, this multi-functional peripheral  11  can maintain the satisfactory image formation with an inexpensive configuration. 
     Since such a capacitance sensor  25  can perform the detection without contacting the toner  29 , there is no restriction on the installation position different from a pressure sensor and similar sensor required to be located to each of the toner containers  23  for detecting unexpected opening. In this case, contamination of the capacitance sensor  25  by the toner  29  can be prevented, thus preventing the degradation of the detection accuracy. Furthermore, the detection of the toner itself ensures dealing with a case where a mechanism for determining the genuine toner and the non-genuine toner is not located to the toner container  23 . 
     In this case, the determining unit  27  determines whether or not the relative dielectric constant of the toner  29  is equal to or more than the first value. Then, when the determining unit  27  has determined that the relative dielectric constant of the toner  29  is equal to or more than the first value, the display screen  21  displays the indication that the non-genuine toner is mixed. Accordingly, whether or not the non-genuine toner is mixed can be more appropriately visually grasped. 
     In this case, when the relative dielectric constant of the toner  29  is determined to be equal to or more than the second value, the determining unit  27  performs the control so as to halt the operation of the image formation. This ensures halting the operation of the image formation to prevent the operational failure and the damage of the multi-functional peripheral  11  when the content ratio of the non-genuine toner is high and the influence on the multi-functional peripheral  11  is large, for example, the multi-functional peripheral  11  possibly causes the operational failure. When the determining unit  27  determines that the relative dielectric constant of the toner  29  is equal to or more than the second value, the display screen  21  display the indication prompting the change of the toner container  23 , thus prompting the use of the genuine toner to ensure preventing the damage of the multi-functional peripheral  11  and maintaining the high image quality. 
     In this case, the configuration including the display screen  21  that displays the determination result by the determining unit  27  ensures visually clearly notifying the determination result, for example, whether the non-genuine toner is mixed, to the outside. 
     The following configuration may be employed.  FIG. 8  illustrates a periphery of an image forming unit  15  included in a multi-functional peripheral according to another embodiment of the disclosure. With reference to  FIG. 8 , the multi-functional peripheral is configured to include a charging mechanism  56  and a diselectrifying mechanism  57 . On the periphery of the image forming unit  15  included in the multi-functional peripheral, the charging mechanism  56  that charges the toner supplied from the toner container  23  is located on an upstream side with respect to the capacitance sensor  25  in a toner supply direction on the supply passage  28 , and the diselectrifying mechanism  57  that diselectrifies the toner is located on a downstream side with respect to the capacitance sensor  25  in the toner supply direction on the supply passage  28 . 
     This configuration ensures the detection of the relative dielectric constant after sufficiently charging the toner by the charging mechanism  56  even when the difference in the relative dielectric constant is small between the genuine toner and the non-genuine toner. Accordingly, whether or not the non-genuine toner is included can be determined with more certainty. In this case, the diselectrifying mechanism  57  performs the diselectrifying before the toner is supplied to the developing container  35 , thus not giving the influence on the image quality. 
     In the charging mechanism  56 , for example, a plate-shaped blade may be used to rub the toner so as to charge the toner. For example, friction between the blade and a toner replenishment roller of the toner container  23  is used to charge the toner  29 . This ensures charging the toner with more physical certainty. For the toner  29  charged by the charging mechanism  56 , when the charging amount of the toner  29  is controllable or small, the toner  29  may be supplied to the developing container  35  as it is without especially performing the diselectrifying. 
     In the above-described embodiment, the first value and the second value are appropriately determined corresponding to a destination, a user, and similar factor. That is, a control where the image formation is halted even when the content ratio of the non-genuine toner is about 10% may be performed. The level of the notification of the fact that the non-genuine toner is mixed may be differed corresponding to the content ratio. For example, when the content ratio of the non-genuine toner reaches a third value between the first value and the second value, the display screen  21  may display “This toner is not supported.” while the image formation is continued. A configuration where the detection accuracy of the capacitance sensor  25  is adjustable by the control by the control unit  12  may be employed. 
     While the display screen  21  displays the determination result in the above-described embodiment, not limiting to this, the determination result by the determining unit  27  may be notified by audio. The determination result may be notified by audio with display. 
     While the determining unit  27  determines whether or not the relative dielectric constant of the toner  29  is equal to or more than the first value and the second value in the above-described embodiment, not limiting to this, the determining unit  27  may determine whether or not the relative dielectric constant of the toner  29  is in a predetermined range. This ensures the determination of the mixture of the non-genuine toner even when a non-genuine toner having a low relative dielectric constant is mixed, thus dealing with the image formation and similar operation. 
     In the above-described embodiment, the capacitance sensor  25  may be located to be removably attachable to the multi-functional peripheral  11 . This ensures installing the capacitance sensor  25  to the multi-functional peripheral  11  corresponding to the condition of using the multi-functional peripheral  11  so as to determine whether or not the non-genuine toner is included. 
     In the above-described embodiment, the multi-functional peripheral  11  is not necessary to include the intermediate hopper  24 . The capacitance sensor  25  may be located at the intermediate hopper  24  as a part of the supply passage  28  for the toner  29 . 
     The capacitance sensor  25  may additionally include a height measurement sensor that measures a height of the toner  29 . This ensures the measurement of the height of the toner  29  by the height measurement sensor. The capacitance sensor  25  may be configured to contact the toner  29  to detect the relative dielectric constant of the toner  29 . 
     The image forming apparatus according to the disclosure is especially effectively used when maintaining the satisfactory image formation is required with the inexpensive configuration. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.