Patent Publication Number: US-11036171-B2

Title: Image forming device, developer stirring method and non-transitory recording medium

Description:
The present invention claims priority under 35 U.S.C. § 119 to Japanese Application No. 2019-152012 filed on Aug. 22, 2019, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     Technological Field 
     The present invention relates to an image forming device, a developer stirring method and a non-transitory recording medium. One or more embodiments of the present invention more specifically relate to a technique for stirring developer filled in a developing unit attached to the image forming device. 
     Description of the Related Art 
     Developer containing toner and carrier is filled in a developing unit attached to an image forming device. The developer in the developing unit has a change of a bulk density influenced by a transit environment or a storage environment after factory shipment. To be more specific, an influence by surrounding environment of the developer in transit and/or in being stored may cause an aggregation of the toner so that the bulk density changes. The developer may have the bulk density changed compared to the bulk density in time of the factory shipment. When an image is formed using the developer that has the changed bulk density, a smoke may be caused and inside the device may get dirty, resulting in an occurrence of an image density defect. 
     As one of ways to solve this problem, an initial stirring operation is performed when a new developing unit is attached to the image forming device, for example. This known technique is introduced for example in Japanese Patent Application Laid-Open No. JP 2014-106344 A. According to the known technique, a screw in the developing unit is driven for a certain period of time set in advance at a setup at a customer site to stir the developer. 
     According to the known technique, however, the period of time to perform the initial stirring operation is fixed to the period of time set in advance. When the bulk density change is large, the stirring time is not sufficient. Even after the initial stirring operation, the developer may not be loosened sufficiently. In this case, when the image is formed after the initial stirring operation, it may still cause smoke and/or the image density defect. 
     In order to surely resolve the problem of smoke or the image density defect, it is required to set in advance a long initial stirring operation time. The longer initial stirring operation time, the longer setup time at the customer site. Thus, it will take the longer setup time to make the image forming device usable state. When the bulk density change is small, the developer is loosened sufficiently at a relatively early timing after start of the initial stirring operation. Even so, the initial stirring operation continues for a long time. The image forming device cannot be used for a long time. 
     SUMMARY 
     One or more embodiments provide an image forming device, a developer stirring method and a non-transitory recording medium that are enabled to determine if a developer is loosened to a condition almost equivalent to a condition in time of a factory shipment. 
     In one aspect, the present invention is directed to an image forming device to and from which a developing unit in which a developer containing toner is filled is detachable and removable. 
     According to an aspect of the present invention, the image forming device comprises a hardware processor that: enables the developing unit to perform a stir operation of the developer filled in the developing unit as an initial operation of the developing unit; obtains a reference value of a toner density set in advance in time of a factory shipment of the developing unit at time the stir operation is performed; and compares a toner density received from the developing unit during the stir operation with the reference value to determine a stir condition of the developer. 
     In another aspect, the present invention is directed to a developer stirring method. 
     According to an aspect of the present invention, the developer stirring method comprises: setting in advance a reference value of a toner density in time of a factory shipment of a developing unit in which a developer containing toner is filled; enabling the developing unit to perform a stir operation of the developer filled in the developing unit as an initial operation of the developing unit when the developing unit is attached to an image forming device and the developing unit becomes operative for the first time in the image forming device; obtaining the reference value at time the stir operation is performed; and comparing a toner density received from the developing unit during the stir operation with the reference value to determine a stir condition of the developer. 
     In another aspect, the present invention is directed to a non-transitory recording medium storing a computer readable program to be executed by a hardware processor in an image forming device to and from which a developing unit in which a developer containing toner is filled is detachable and removable. 
     According to an aspect of the present invention, the non-transitory recording medium storing a computer readable program to be executed by the hardware processor in the image forming device causing the hardware processor to perform: enable the developing unit to perform a stir operation of the developer filled in the developing unit as an initial operation of the developing unit; obtain a reference value of a toner density set in advance in time of a factory shipment of the developing unit at time the stir operation is performed; and compare a toner density received from the developing unit during the stir operation with the reference value to determine a stir condition of the developer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given herein below and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention. 
         FIG. 1  illustrates an exemplary structure of an image forming device; 
         FIG. 2  illustrates an example of a cross section of a developing unit; 
         FIG. 3  illustrates exemplary output characteristics of a toner density sensor; 
         FIG. 4  illustrates a flow diagram explaining an exemplary procedure of the process to set a reference value of a toner density performed prior to a factory shipment of the developing unit; 
         FIG. 5  illustrates a block diagram showing an example of a control mechanism of a controller of the image forming device; 
         FIG. 6  illustrates an example of types of a stir operation by a stir controller; 
         FIG. 7  illustrates an exemplary relation between an elapsed time of the stir operation performed as an initial operation of the developing unit and a value output by the toner density sensor; 
         FIG. 8  illustrates a flow diagram explaining an exemplary procedure of the process performed by the controller; 
         FIG. 9  illustrates a flow diagram explaining an exemplary procedure of a developer stir process in detail; and 
         FIG. 10  illustrates an exemplary conceptual configuration of an information forming system including the image forming device. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. 
     First Embodiment 
       FIG. 1  illustrates an exemplary structure of an image forming device  1  in which the first embodiment of the present invention may be practiced. The image forming device  1  is a printer that forms an image on a sheet material  9  such as a printing sheet and outputs in electrophotography. The image forming device  1  is capable of forming a color image in tandem system. The image forming device  1  includes a feeding unit  2 , an image forming unit  3  and a fixing unit  4  inside a device body  1   a . The image forming device  1  delivers the sheet material  9  stored in a sheet feeding cassette  8  one by one. The sheet feeding cassette  8  is provided in a lower part of the device body  1   a . The image forming device  1  forms a color image or a black and white image on the sheet material  9 , and delivers the sheet material  9  on a sheet delivery tray  6  through a sheet delivery port  5  provided in an upper part of the device body  1   a.  The image forming device  1  includes a controller  7  inside the device body  1   a . The controller  7  controls operations of each part such as the feeding unit  2 , the image forming unit  3  and the fixing unit  4 . The controller  7  controls a stiffing operation of a developer filled in a developing unit in advance as described later. 
     The feeding unit  2  includes the sheet feeding cassette  8 , a pick-up roller  10 , a sheet feeding unit  11 , a carrying path  12 , a resisting unit  13  and a secondary transfer roller  14 . The sheet feeding cassette  8  is a container in which a bundle of the sheet materials  9  are stored. The pick-up roller  10  takes the sheet material  9  from a top of the bundle of the sheet materials  9  stored in the sheet feeding cassette  8 , and feeds out toward the sheet feeding unit  11 . The pick-up roller  10  may feed the multiple sheet materials  9  toward the downstream side of the sheet feeding cassette  8 . The sheet feeding unit  11  picks up the single sheet material  9  on the top of one or more than one sheet material  9  fed by the pick-up roller  10 . 
     The carrying path  12  is a path to carry the sheet material  9  toward an arrow F 2  direction. The resisting unit  13  corrects the skew of the sheet material  9  carried along the carrying path  12 . The resisting unit  13  includes a pair of rollers. The resisting unit  13  drives the pair of rollers in accordance with a timing a toner image formed by the image forming unit  3  moves to a position of the secondary transfer roller  14  to carry the sheet material  9 , the skew of which is corrected, to a position of the secondary transfer roller  14 . The toner image formed by the image forming unit  3  is transferred to the sheet material  9  when the sheet material  9  passes through the secondary transfer roller  14 . The toner image transferred to a surface of the sheet is then fixed when the sheet material  9  passes through the fixing unit  4 . The fixing unit  4  conducts a heating process and a pressing process on the carried sheet material  9  to fix the toner image to the sheet material  9 . The sheet  9  is then delivered on the paper delivery tray  6  through the delivery port  5 . 
     The image forming unit  3  forms toner images of four colors, Y (yellow), M (magenta), C (cyan) and K (black), and transfers the toner images of the four colors at the same time to the sheet material  9  passing through the position of the secondary transfer roller  14 . The image forming unit  3  includes multiple toner bottles  19  ( 19 Y,  19 M,  19 C and  19 K) of the respective colors, multiple image forming units  20  ( 20 Y,  20 M,  20 C and  20 K) of the respective colors, multiple exposure units  25  ( 25 Y,  25 M,  25 C and  25 K) of the respective colors and a transfer unit  30 . 
     The transfer unit  30  is formed from a pair of rollers  31  and  32  and an endless belt. The pair of rollers  31  and  32  are arranged with a predetermined interval in between. The transfer unit  30  includes an intermediate transfer belt  33 , multiple primary transfer rollers  34  ( 34 Y,  34 M,  34 C and  34 K) and a cleaner  35 , and they are integrally assembled. The intermediate transfer belt  33  is crossed between the pair of rollers  31  and  32 . The multiple primary transfer rollers  34  are arranged at positions facing the respective image forming units  20  inner side of the intermediate transfer belt  33 . The cleaner  35  is to remove a toner remaining on a surface of the intermediate transfer belt  33 . 
     The roller  31  which is one of the pair of rollers  31  and  32  is a driving roller which is attached to a driving shaft arranged inner side of the device body  1   a  and rotates. The rotation of the driving shaft enables a circulating movement of the intermediate transfer belt  33  in an arrow F 1  direction. Another roller  32  is attached to a driven shaft arranged inside the device body  1   a . Another roller  32  rotates by the circulating movement of the intermediate transfer belt  33 . The pair of rollers  31  and  32  apply certain tension to the intermediate transfer belt  33  and they are arranged at positions separated from each other of a predetermined interval inside the device body  1   a . The roller  31  is attached to the driving shaft so that it is arranged at a position facing the secondary transfer roller  14 . The roller  31  sandwiches the intermediate transfer belt  33  between itself and the secondary transfer roller  14 , and applies a pressing force to the intermediate transfer belt  33 . The roller  31  sandwiches and presses the sheet material  9  fed from the resisting unit  13  between the intermediate transfer belt  33  and the secondary transfer roller  14  so that the toner image formed on the surface of the intermediate transfer belt  33  is secondarily transferred to the sheet material  9 . 
     The cleaner  35  is kept in a state that is in contact with the surface of the intermediate transfer belt  33  at a position that faces the roller  32 . The cleaner  35  removes a toner remaining on the surface of the intermediate transfer belt  33  that circularly moves in the arrow F 1  direction. 
     The image forming units  20 Y,  20 M,  20 C and  20 K corresponding to the respective colors are provided in a lower position of the transfer unit  30 . The exposure units  25 Y,  25 M,  25 C and  25 K corresponding to the respective colors are arranged in a further lower position of each of the image forming units  20 Y,  20 M,  20 C and  20 K. The toner bottles  19 Y,  19 M,  19 C and  19 K are provided in an upper position of the transfer unit  30  to supply a developer containing a toner of each color to the respective image forming units  20 Y,  20 M,  20 C and  20 K. 
     Each image forming unit  20 Y,  20 M,  20 C and  20 K has the similar structure but uses the different color of toner. To be more specific, each image forming unit  20 Y,  20 M,  20 C and  20 K includes an image carrier  21  formed as a photoreceptor drum, an electrifying unit  22  arranged around the image carrier  21 , a developing unit  23  and a cleaning blade  24 . If differentiation between each image forming unit  20 Y,  20 M,  20 C and  20 K is not necessary, the image units  20 Y,  20 M,  20 C and  20 K may be called as the image forming unit  20 . 
     The image carrier  21  has a photosensitive layer on a drum surface. The image carrier  21 , for instance, is in contact with the intermediate transfer belt  33  to which a transferring force by the primary transfer roller  34  of the transfer unit  30  is applied, and rotates in a clockwise direction. Along the rotation direction, the cleaning blade  24 , the electrifying unit  22  and the developing unit  23  are arranged around the image carrier  21 . The electrifying unit  22  includes an electrifying roller that is in contact with the surface of the image carrier  21 , and charges the surface of the image carrier  21  at a predetermined charge amount. The exposure unit  25  exposures the photosensitive layer charged by the electrifying unit  22  based on the image data to form a latent image on the surface of the image carrier  21 . The developing unit  23  is filled with a developer containing the toner and a carrier. The developer is supplied to the surface of the image carrier  21  and the latent image is enabled to be visible with the toner. The toner image is then formed on the surface of the image carrier  21 . The toner image formed on the image carrier  21  is primarily transferred to the intermediate transfer belt  33  at a position at which the toner image gets in contact with the intermediate transfer belt  33 . A bias voltage which is a reverse polarity from the charged toner image formed on the surface of the image carrier  21  is applied to the primary transfer roller  34 . The primary transfer roller  34  is enabled to primarily transfer the toner image formed on the surface of the image carrier  21  to the intermediate transfer belt  33  by an electrostatic power. 
     Each image forming unit  20 Y,  20 M,  20 C and  20 K works together with the corresponding primary transfer roller  34 Y,  34 M,  34 C and  34 K to superpose the toner image of each color one after another on the intermediate transfer belt  33  which is circulated and moved in the arrow direction F 1  and enable primary transfer. When the intermediate transfer belt  33  passes through the position of the image forming unit  20 K which is at downstream end, a color image which is superposing the toner images of four colors is formed on the surface of the intermediate transfer belt  33 . In order to form a black and white image on the sheet material  9 , the image forming units  20 Y,  20 M and  20 C are not brought into operation. Only the image forming unit  20 K corresponding to K (black) becomes operative to form the black and white image on the intermediate transfer belt  33  with the toner of K. 
     The toner image formed on the intermediate transfer belt  33  gets in contact with the sheet material  9  carried by the feeding unit  2  and secondarily transferred on the surface of the sheet material  9  when passing through a position facing the secondary transfer roller  14 . To be more specific, the secondary transfer roller  14  is arranged at a position facing the roller  31  across the intermediate transfer belt  33 . The secondary transfer roller  14  applies the bias voltage which is a reverse polarity from the charged toner when the toner image primarily transferred to the intermediate transfer belt  33  is in contact with the sheet material  9  so that the toner image is secondarily transferred to the sheet material  9 . 
     Even after the secondary transfer of the toner image to the sheet material  9  at the secondary transfer roller  14 , some of the toner may remain on the surface of the intermediate transfer belt  33 . The remaining toner is attached to the surface of the intermediate transfer belt  33  and is circularly moved together with the intermediate transfer belt  33 . When the intermediate transfer belt  33  passes through the cleaner  35 , the remaining toner is removed from the surface of the intermediate transfer belt  33  by a cleaning blade or a cleaning brush provided with the cleaner  35 . 
     Even after the toner image formed on the image carrier  21  is primarily transferred to the intermediate transfer belt  33  in each image forming unit  20 Y,  20 M,  20 C and  20 K, some toner may remain on the surface of the image carrier  21 . The remaining toner proceeds toward the cleaning blade  24  in accordance with the rotation of the image carrier  21 , and removed from the surface of the image carrier  21  by the cleaning blade  24 . 
     The developing unit  23  is explained next.  FIG. 2  illustrates an example of a cross section of the developing unit  23 . The developer containing the toner and the carrier is filled inside a body  40  of the developing unit  23 . The developing unit  23  is detachable and removable to and from the image forming unit  20 . In other words, the developing unit  23  is detachable and removable to and from the device body  1   a  of the image forming device  1 . The body  40  of the developing unit  23  is provided with a toner supply port  40   a  at a predetermined position. The developer supplied from the toner bottle  19  is supplied inside through the toner supply port  40   a.  Once the developing unit  23  is attached to the device body  1   a , the developing unit  23  can be refilled with the developer supplied from the toner bottle  19  through the toner supply port  40   a.  For the new developing unit  23 , the developer is filled in advance in a filling space of the body  40  at the factory shipment. 
     As illustrated in  FIG. 2 , the developing unit  23  is provided with a developing sleeve  41 , a supply screw  42  and a stir screw  43  inside the body  40 . In addition, a partition  45  is arranged inside the body  40  of the developing unit  23 . The partition  45  separates an upper space and a lower space. In the upper space, the developing sleeve  41  and the supply screw  42  are arranged, and in the lower space, the stir screw  43  is arranged. The upper space and the lower space separated by the partition  45  communicate with each other through both ends of the supply screw  42  and the stir screw  43 , realizing transfer of the developer. 
     The developing sleeve  41  is arranged in the upper space separated by the partition  45 . A part of the developing sleeve  41  is exposed to outside from the body  40 . The exposed part of the developing sleeve  41  is arranged at a predetermined interval from the surface of the image carrier  21 . Once the developing unit  23  is attached to the device body  1   a , a rotation shaft  41   a  connects to a motor provided with the device body  1   a  so that the developing sleeve  41  rotates and is driven in a predetermined direction. The developing sleeve  41  rotates in the predetermined direction to supply the developer supplied from the supply screw  42  to the surface of the image carrier  21 . 
     The supply screw  42  is one of stir parts that have a function to stir the developer. The supply screw  42  is arranged in parallel with the developing sleeve  41 . The supply screw  42  includes a rotation shaft  42   a  that rotates and is driven by a motor of the device body  1   a . The rotation shaft  42   a  is driven to rotate in a predetermined direction so that the supply screw  42  transfers the developer supplied from the lower space along a longitudinal direction of the developing sleeve  41  and supplies the developer to the developing sleeve  41 . 
     The stir screw  43  is another part of stir parts to stir the developer. The stir screw  43  is arranged in parallel with the supply screw  42 . The stir screw  43  includes a rotation shaft  43   a  that rotates and is driven by a motor of the device body  1   a . The stir screw  43  may be driven by the same motor as that used for the supply screw  42 . In view of circulation of the developer inside the body  40 , the stir screw  43  and the supply screw  42  preferably rotate and are driven in the counter direction. 
     The stir screw  43  rotates in a predetermined direction to stir the developer and transfer the developer along a longitudinal direction of the screw. As a result, the toner contained in the developer can be friction charged. After stirring the developer in the lower space (stirring space) of the developing unit  23 , the stir screw  43  draws the developer to the upper space through the part communicated with the upper space in one end of the partition  45 . 
     The developing sleeve  41  includes a magnet member inside its inner periphery. The magnet member catches the charged toner on the surface of the sleeve. The developing sleeve  41  rotates, and supplies the toner caught on the surface of the sleeve to the surface of the image carrier  21 . A ratio of the toner and the carrier in the body  40  decreases, the less developer is caught on the surface of the sleeve, resulting in the density defect. In order to keep the ratio of the toner and the carrier at a certain value, the stir operation is performed by the supply screw  42  and the stir screw  43  in the developing unit  23 . 
     The developing unit  23  includes a toner density sensor  46 , a storage  47  and multiple vibration members  48  attached to an exterior-wall of the body  40 . 
     The toner density sensor  46  is arranged on the exterior-wall of the body  40  around the stir screw  43 , for example. The toner density sensor  46  detects toner density (ratio of the toner and the carrier) of the developer filled in the body  40 . The toner density sensor  46  is constructed by a Colpitts oscillator circuit, for instance. The Colpitts oscillator circuit is a LC tuning oscillator circuit formed from a coil and two capacitors. An oscillation frequency is determined based on a capacitance of the two capacitors and an inductance of the coil. Hence, the toner density sensor  46  constructed by the Colpitts oscillator circuit outputs a variation of the inductance of the coil due to a variation of the ratio of the toner and the carrier in the body  40  as a variation of the oscillation frequency. 
       FIG. 3  illustrates exemplary output characteristics of the toner density sensor  46 . As shown by an output characteristic G 1  of  FIG. 3 , the toner density sensor  46  outputs a frequency relative to the toner density in the developing unit  23 . The developer with a certain toner density D 1  (8%, for instance) is filled in the body  40  of the new developing unit  23 , for example. It is assumed, for example, the developer in the body  40  is sufficiently stirred at time of the factory shipment. In this case, a value output by the toner density sensor  46  is the frequency (output value) corresponding to the certain toner density D 1 . The toner density sensor  46  having the output characteristic G 1  of  FIG. 3 , for example, outputs an output value V 1  corresponding to the certain toner density D 1  when the developer in the body  40  is sufficiently stirred at time of the factory shipment. 
     There are individual variations in the toner density sensors  46 . The individual variations cause variations in the output characteristics. It is assumed, for example, the output characteristic of the toner density sensor  46  installed on the developing unit  23  is the output characteristic G 1  of  FIG. 3 . Even in this case, the output characteristic of the toner density sensor  46  installed on another developing unit  23  may be an output characteristic G 2  of  FIG. 3 , or an output characteristic G 3 . To be more specific, even when the certain toner density D 1  of the developer is filled in the body  40 , an output value output by the toner density sensor  46  may vary if the developing unit  23  is different. 
     In the first embodiment, when the developer in the body  40  is sufficiently stirred at time of the factory shipment, the toner density is measured by the toner density sensor  46  and the output value of the frequency output by the toner density sensor  46  is stored in the storage  47 . The stored output value is set in advance as a reference value of the toner density. The toner density of the developer in the body  40  which is sufficiently stirred does not always have to be actually measured by the toner density sensor  46  for setting the reference value of the toner density in time of the factory shipment. The output characteristic of the toner density sensor  46 , for instance, may be measured and the output value in a case where the developer with the certain toner density D 1  is measured may be calculated by an operation based on the output characteristic. The output value calculated by the operation may be set as the reference value of the toner density. 
     The storage  47  is a nonvolatile storage constructed by a semiconductor memory, for instance. The reference value of the toner density set in advance at the factory shipment of the developing unit  23  as described above is stored in the storage  47 . 
     Each of the multiple vibration members  48  is one of stirring parts that stir the developer. The multiple vibration members  48  are arranged on the exterior-wall around the stir screw  43  at predetermined intervals along a longitudinal direction of the stir screw  43 . Each vibration member  48  is constructed by a vibration motor, for instance. The vibration motor rotates an output shaft to which a vibrator is attached to generate vibration. The multiple vibration members  48  vibrate the exterior-wall to vibrate the developer in the body  40 . The developer is thus stirred. Hence, the developer is not only stirred by the supply screw  42  and the stir screw  43  but also vibrated by the vibration member  48  so that the developer is easily loosened. 
       FIG. 4  illustrates a flow diagram explaining an exemplary procedure of the process to set the reference value of the toner density performed prior to the factory shipment of the developing unit  23 . The process of  FIG. 4  should be performed prior to the shipment of the developing unit  23  and it may be performed during the manufacture. As illustrated in  FIG. 4 , the developer with the certain toner density D 1  is filled in the body  40  of the developing unit  23  (step S 1 ). After the developer is filled in the body  40 , the supply screw  42 , the stir screw  43  and the vibration members  48  are driven and the filled developer is stirred in the developing unit  23  (step S 2 ). Due to this stirring operation, the developer in the body  40  is sufficiently stirred. The developing unit  23  then obtains the output value received from the toner density sensor  46  while the developer has been sufficiently stirred as a reference value Vr of the toner density. The developing unit  23  stores the reference value Vr in the storage  47 . The above-described process is performed so that the reference value Vr obtained at time of the measurement of the certain toner density D 1  by the toner density sensor  46  installed on the developing unit  23  is set with the developing unit  23  shipped from the factory. 
     The developing unit  23  shipped from the factory is influenced by the surrounding environment in transit and/or in being stored. The influence may cause an aggregation of the toner so that the bulk density changes. To be more specific, the aggregation of the toner causes the higher bulk density of the developer in the body  40 . Higher bulk density of the developer, lower toner density measured by the toner density sensor  46 . More specifically, even when the developer with the certain toner density is filled in the body  40  of the developing unit  23 , the higher bulk density causes lower output value received from the toner density sensor  46 . 
     The controller  7  of the image forming device  1  stirs the developer filled in the body  40  of the developing unit  23  as an initial operation when putting the developing unit  23  attached to the device body  1   a  into operation for the first time. Due to the stir operation, the developer filled in the body  40  of the developing unit  23  is enabled to put the aggregation of the toner back to the condition (the developer is sufficiently loosened) equivalent to the condition in time of the factory shipment. The controller  7  determines the stirring condition of the developer filled in the body  40  based on the toner density (frequency) received from the toner density sensor  46  and the reference value Vr of the toner density set in advance at the factory shipment. The controller  7  is described in detail below. 
       FIG. 5  illustrates a block diagram showing an example of a control mechanism of the controller  7  of the image forming device  1 . The device body  1   a  of the image forming device  1  is provided with the controller  7 , an operational panel  53 , a communication interface  54  and a motor  58 . The controller  7  includes a CPU  50  and a memory  51 . The CPU  50  is a hardware processor that reads and executes a program  52  stored in the memory  51 . The memory  51  is a nonvolatile storage formed from a hard disk drive (HDD) or a solid-state drive (SSD), for example. The program  52  stored in the memory  51  is a developer stirring program. 
     The operational panel  53  is a user interface for a user to use the image forming device  1 . The operational panel  53  includes a display unit  53   a  and a manipulation unit  53   b.  The display unit  53   a  is constructed by a device such as a liquid crystal display, for instance. A variety of information is displayed on the display unit  53   a.  The manipulation unit  53   b  is constructed by a part such as a touch panel key and/or a push-button key. The manipulation unit  53   b  receives an input by the user. The communication interface  54  connects the image forming device  1  to a network such as LAN (Local Area Network) to enable communications with external devices. The image forming device  1 , for example, is enabled to receive a print job via the communication interface  54 . When the developing unit  23  is attached to the device body  1   a , the motor  58  is a driving resource that connects to at least the rotation shaft  43   a  of the stir screw  43  and rotates the stir screw  43 . The motor  58  may be connected to the rotation shaft  42   a  of the supply screw  42  via a link mechanism and rotate the supply screw  42  and the stir screw  43  at the same time. 
     The CPU  50  of the controller  7  reads and executes the program  52  in the memory  51  to serve as a toner adjusting unit  55  and a job controller  56 . The toner adjusting unit  55  becomes operative when the developing unit  23  attached to the device body  1   a  is brought into operation for the first time. The toner adjusting unit  55  controls an operation to stir the developer filled in the body  40  as an initial operation of the developing unit  23 . The job controller  56  becomes operative after the initial operation of the developing unit  23  by the toner adjusting unit  55  is successfully completed. The job controller  56  controls a processing of a print job specified by the user. Upon receiving the print job via the communication interface  54 , for example, the job controller  56  drives each of the feeding unit  2 , the image forming unit  3  and the fixing unit  4  in a synchronized manner based on the print job. The job controller  56  controls to enable an image to print included in the print job to be formed correctly on the sheet material  9 . 
     The toner adjusting unit  55  includes a stir controller  61 , a reference value obtaining part  62  and a determining part  63 . The toner adjusting unit  55  brings each part into operation to enable the developing unit  23  to perform a stir operation as the initial operation. 
     The stir controller  61  enables the developing unit  23  to perform the stir operation of the developer filled in the body  40  of the developing unit  23  to be performed as the initial operation of the developing unit  23 . To be more specific, the stir controller  61  drives the motor  58  and rotates the stir screw  43  to stir the developer in the body  40 . The stir controller  61  also drives the vibration members  48  attached to the exterior-wall of the body  40  to cause the developer in the body  40  to vibrate and stir. 
     The stir controller  61  enables the developing unit  23  to perform the stir operation of the developer until a stir period set in advance elapses. The stir controller  61  switches the stir operation by each stir part such as the stir screw  43  or the vibration members  48  during the stir period. In the stir period, the stir operation is switched so that the developer is easily loosened. It is assumed, for example, the stir screw  43  rotates in one direction to stir the developer and that does not enable the developer to be loosened. Even in such a case, if the stir screw  43  rotates in an opposite direction, the developer may be loosened. It is assumed, for example, the stir screw  43  rotates at a predetermined speed doesn&#39;t enable the developer to be loosened. Even in such a case, the speed of the rotation of the stir screw  43  may be changed and the developer may be loosened. The stir controller  61  switches the manner of the stir operation by the stir part such as the stir screw  43  or the vibration members  48  in the stir period in order to loosen the developer sufficiently within the stir period. 
       FIG. 6  illustrates an example of types of the stir operation by the stir controller  61 . The stir controller  61 , for example, controls four types of stir operations, a first operation, a second operation, a third operation and a fourth operation, to be performed in the stir period. As the first operation, the stir controller  61  enables the stir screw  43  to rotate in the forward direction set in advance and the rotation speed is set at low speed. As the second pertain, the stir controller  61  enables the stir screw  43  to rotate in the reverse direction which is opposite from the forward direction and the rotation speed of the stir screw  43  is set at low speed. As the third operation, the stir controller  61  enables the stir screw  43  to rotate in the forward direction and the rotation speed of the stir screw  43  is set at high speed. As the fourth operation, the stir controller  61  enables the stir screw  43  to rotate in the reverse direction and the rotation speed of the stir screw  43  is set at high speed. In the example of  FIG. 6 , the vibration members  48  activate in every operation through the first to the fourth operations. However, this is given not for limitation. The activation of the vibration members  48  can be switched for each operation. 
     The stir controller  61  divides the stir period to enable the developing unit  23  to perform the stir operation, for example, into to four periods, a first period, a second period, a third period and a fourth period. The stir controller  61  allocates each of the four periods to the above-described four types of the stir operations, respectively. Every time the period elapses, the stir controller  61  switches the stir operation. As a result, the multiple types of stir operations are performed for the developer filled in the developing unit  23  in the stir period. The condition of the developer that has an aggregation of the toner and causing the higher bulk density can be back to the condition equivalent to the condition in time of the factory shipment. 
     The reference value obtaining part  62  obtains the reference value Vr of the toner density set in advance at the factory shipment of the developing unit  23  when the stir operation is performed by stir controller  61 . The developing unit  23  is attached to the device body  1   a  so that the developing unit  23  is electrically connected to the controller  7 . The reference value obtaining part  62  reads the reference value Vr set in advance at the factory shipment stored in the storage  47  provided with the developing unit  23  attached to the device body  1   a  to obtain the reference value Vr of the toner density. The reference value obtaining part  62  outputs the reference value Vr read from the storage  47  to the determining part  63 . 
     The determining part  63  compares the toner density received from the toner density sensor  46  of the developing unit  23  with the reference value Vr during the stir operation performed by the stir controller  61 . It is assumed that the toner density received from the toner density sensor  46  of the developing unit  23  reaches a value near the reference value Vr during the stir operation performed by the stir controller  61 . In this case, the developer in the body  40  of the developing unit  23  is loosened to the condition almost equivalent to the condition in time of factory shipment, and the determining part  63  determines the developer is sufficiently stirred. To be more specific, before the new developing unit  23  is being in use, the developer with the certain toner density D 1  is filled in the body  40  of the developer  23 . If the developer is sufficiently stirred at the initial operation of the developing unit  23 , the bulk density of the developer recovers to the condition equivalent to the condition in time of the factory shipment. The toner density detected by the toner density sensor  46  shows almost the same value as the reference value Vr set in advance at the factory shipment. Hence, when the toner density received from the toner density sensor  46  of the developing unit  23  shows the value near the reference value Vr, the determining part  63  determines that the developer is sufficiently stirred. 
     The determining part  63  determines that the value is near the reference value Vr when the toner density detected by the toner density sensor  46  is within a predetermined range of the reference value Vr. When the toner density detected by the toner density sensor  46  is within a range from about few percentages to below 20 percentages less or greater than the reference value Vr, the determining part  63 , for example, determines the toner density is the value near the reference value Vr. 
     The determining part  63  monitors the toner density received from the toner density sensor  46  constantly or every predetermined period of time during the stir period in which the stir operation is performed by the stir controller  61 . After detecting that the toner density reaches the value within the predetermined range of the reference value Vr during the stir period, the determining part  63  completes the stir operation by the stir controller  61 . Even when the stir period has not elapsed, the stir operation can be completed at earlier stage at the time of recovery if the developer filled in the developing unit  23  is recovered to the condition equivalent to the condition in time of factory shipment. Thus, the print job using the developing unit  23  can be started in the image forming device  1  earlier. 
     The toner density received from the toner density sensor  46  may not reach the value within the predetermined range of the reference value Vr at time of elapse of the stir period. In this case, the determining part  63  notifies an abnormality. The determining part  63 , for example, displays a notification on the display unit  53   a  of the operational panel  53 . The screen shows that the toner density is an abnormal value. By looking at the screen, the user or the maintenance operator is notified the abnormality. The notification of the abnormality does not have to be carried out through the screen displayed on the display unit  53   a.  The abnormality may be notified by a warning sound output from a speaker which is not illustrated in figures. 
     It is assumed that the toner density received from the toner density sensor  46  does not reach the value within the predetermined range of the reference value Vr during the stir period. In such a case, the determining part  63  restricts the job controller  56  to process the print job. As a result, problems like generation of smoke and/or the density defect can be avoided. 
       FIG. 7  illustrates an exemplary relation between the elapsed time of the stir operation performed as the initial operation of the developing unit  23  and the value output by the toner density sensor  46 . An area within the predetermined range of the reference value Vr is illustrated as a slanted line area in  FIG. 7 . The bulk density of the developer filled in the developing unit  23  may be higher than the value in time of the factory shipment. In this case, the value output by the toner density sensor  46  shows a value lower than the reference value Vr. The value is not in the predetermined range of the reference value Vr. The toner density sensor  46 , for example, outputs a value Vx. 
     The stir controller  61  enables the developing unit  23  to perform the stir operation during the stir period from a timing T 0  to a timing T 4 , for instance. The stir controller  61  enables the developing unit  23  to perform the first stir operation during the first period from the timing T 0  to the timing T 1 . The degree of change of the bulk density of the developer filled in the developing unit  23  may be small, for example, and the value output by the toner density sensor  46  may vary as shown by a curve C 1  of  FIG. 7  during the first period. In this case, the value output by the toner density sensor  46  reaches the value within the predetermined range of the reference value Vr during the first period. The stir controller  61  then completes the stir operation at a timing ta at which the determining part  63  determines that the value output by the toner density sensor  46  reaches the value within predetermined range of the reference value Vr. 
     When the value output by the toner density sensor  46  does not reach the value within the predetermined range of the reference value Vr during the first period, the stir controller  61  switches the stir operation from the first operation to the second operation at timing T 1 . The developer that was not sufficiently loosened with the first operation may be loosened gradually with the second operation so the stir operation is switched from the first operation to the second operation. The stir controller  61  enables the developing unit  23  to continue the second stir operation during the second period from timing T 1  to timing T 2 . The value output by the toner density sensor  46  may vary as shown by a curve C 2  of  FIG. 7  during the second period. The stir controller  61  then completes the stir operation at timing tb at which the determining part  63  determines that the value output by the toner density sensor  46  reaches the value within predetermined range of the reference value Vr. 
     When the value output by the toner density sensor  46  does not reach the value within the predetermined range of the reference value Vr during the second period, the stir controller  61  switches the stir operation from the second operation to the third operation at timing T 2 . The developer that was not sufficiently loosened with the second operation may be loosened gradually with the third operation so the stir operation is switched from the second operation to the third operation. The stir controller  61  enables the developing unit  23  to continue the third stir operation during the third period from the timing T 2  to timing T 3 . The value output by the toner density sensor  46  may vary as shown by a curve C 3  of  FIG. 7  during the third period. The stir controller  61  then completes the stir operation at timing tc at which the determining part  63  determines that the value output by the toner density sensor  46  reaches the value within predetermined range of the reference value Vr. 
     When the value output by the toner density sensor  46  does not reach the value within the predetermined range of the reference value Vr during the third period, the stir controller  61  switches the stir operation from the third operation to the fourth operation at timing T 3 . The developer that was not sufficiently loosened with the third operation may be loosened gradually with the fourth operation so the stir operation is switched from the third operation to the fourth operation. The stir controller  61  enables the developing unit  23  to continue the fourth stir operation during the fourth period from the timing T 3  to timing T 4 . The stir controller  61  then completes the stir operation when the value output by the toner density sensor  46  reaches the value within predetermined range of the reference value Vr. 
     In contrast, the value output by the toner density sensor  46  may vary as shown by a curve C 4  of  FIG. 7  during the fourth period. In this case, the value output by the toner density sensor  46  does not reach the value within the predetermined range of the reference value Vr, and the stir period elapses. The stir controller  61  then completes the stir operation at timing T 4  which is the end of the stir period. Even when the stir period elapses, the value output by the toner density sensor  46  may not reach the value within the predetermined range of the reference value Vr. In such a case, the abnormality is notified by the determining part  63 . 
     As described above, the stir controller  61  performs the multiple types of stir operations during the stir period set in advance to loosen the aggregated toner so that the stir controller  61  enables the bulk density of the developer to back to the condition almost equivalent to the condition in time of factory shipment. Before an elapse of the stir period, the stir controller  61  completes the stir operation at point of time the bulk density of the developer is back to the condition almost equivalent to the condition in time of the factory shipment. Thus, the image forming device  1  is enabled to be back to the state available for the user earlier than the ordinary way. 
     Even when the bulk density of the developer is not back to the condition almost equivalent to the condition in time of the factory shipment, the stir controller  61  completes the stir operation after the elapse of the stir period set in advance. This prevents the image forming device  1  from not being available for a long time. In this case, the determining part  63  notifies the abnormality and the processing of the print job by the job controller  56  is restricted. The prompt procedure can be taken by a maintenance operator, for instance. The generation of smoke or an occurrence of the density defect of the sheet material  9  on which the image is formed can be avoided. 
     A detailed process sequence performed in the above-described controller  7  is explained next.  FIGS. 8 and 9  illustrate examples of flow diagrams explaining exemplary procedures of the process performed by the controller  7 . This process illustrated in  FIGS. 8 and 9  is performed by the toner adjusting unit  55  of the controller  7 . Upon start of the process, the controller  7  determines if the developing unit  23  is attached to the device body  1   a  (step S 10 ). If the attachment of the developing unit  23  is not detected (when a result of step S 10  is NO), the process by the controller  7  completes. The attachment of the developing unit  23  may be detected (when a result of step S 10  is YES). In this case, the controller  7  determines if the attached developing unit  23  is new (step S 11 ). An electronic part such as a fuse is equipped in the developing unit  23 , for example. When the electricity is supplied to the developing unit  23  after the attachment of the developing unit  23 , the electronic part such as the fuse is cut. The controller  7  determines if the developing unit  23  is new by detecting the state of the electronic part upon the attachment of the developing unit  23 . The developing unit  23  attached to the device body  1   a  may not be new (when a result of step S 11  is NO). In this case, the process by the controller  7  completes. 
     When the developing unit  23  attached to the device body  1   a  is new (when a result of step S 11  is YES), the controller  7  determines to perform the stir operation of the developer as the initial operation of the developing unit  23  (step S 12 ). The controller  7  obtains the reference value Vr set in advance at the factory shipment of the developing unit  23  (step S 13 ). The controller  7 , for example, obtains the reference value Vr stored in advance in the storage  47  of the developing unit  23  attached to the device body  1   a . After obtaining the reference value Vr recorded in time of the measurement of the certain toner density D 1  by the toner density sensor  46  equipped with the developing unit  23 , the controller  7  starts a developer stir process (step S 14 ). 
       FIG. 9  illustrates a flow diagram explaining an exemplary procedure of the developer stir process (step S 14 ) in detail. After starting the developer stir process as the initial operation of the developing unit  23 , the controller  7  starts the first operation to stir the developer at first (step S 20 ). To be more specific, the controller  7  enables the stir screw  43  to rotate in the forward direction at low speed and activates the vibration members  48  to vibrate the developer to stir the developer. Upon starting the first operation, the controller  7  obtains the value output by the toner density sensor  46  equipped with the developing unit  23  (step S 21 ), and determines if the value is close to the reference value Vr (step S 22 ). To be more specific, the controller  7  determines if the toner density detected by the toner density sensor  46  is the value within the predetermined range of the reference value Vr. The toner density detected by the toner density sensor  46  may be the value within the predetermined range of the reference value Vr as a result of the determination (when a result of step S 22  is YES). In this case, the process by the controller  7  proceeds to step S 36 . 
     Upon determining that the toner density detected by the toner density sensor  46  is not the value within the predetermined range of the reference value Vr as a result of the determination in step S 22  (when a result of step S 22  is NO), the controller  7  determines if the predetermined period of time (the first term from timing T 0  to timing T 1  illustrated in  FIG. 7 ) has elapsed after the stir operation has started (step S 23 ). The predetermined period of time may have not elapsed (when a result of step S 23  is NO). In this case, the process by the controller  7  returns to step S 21  to repeat the above-described process. The predetermined period of time may have elapsed (when a result of step S 23  is YES). In this case, the process by the controller  7  proceeds to step S 24 . 
     In step S 24 , the controller  7  switches the stir operation from the first operation to the second operation and starts stirring the developer with the second operation (step S 24 ). To be more specific, the controller  7  enables the stir screw  43  to rotate in the reverse direction at low speed and activates the vibration members  48  to vibrate the developer to stir the developer. The controller  7  obtains the value output by the toner density sensor  46  equipped with the developing unit  23  (step S 25 ), and determines if the obtained value is close to the reference value Vr (step S 26 ). The value output by the toner density sensor  46  may be within the predetermined range of the reference value Vr as a result of the determination (when a result of step S 26  is YES). In this case, the process by the controller  7  proceeds to step S 36 . 
     Upon determining that the value output by the toner density sensor  46  is not within the predetermined range of the reference value Vr as a result of the determination in step S 26  (when a result of step S 26  is NO), the controller  7  determines if the predetermined period of time (the second term from timing T 1  to timing T 2  illustrated in  FIG. 7 ) has elapsed after the stir operation has started (step S 27 ). The predetermined period of time may have not elapsed (when a result of step S 27  is NO). In this case, the process by the controller  7  returns to step S 25  to repeat the above-described process. The predetermined period of time may have elapsed (when a result of step S 27  is YES). In this case, the process by the controller  7  proceeds to step S 28 . 
     In step S 28 , the controller  7  switches the stir operation from the second operation to the third operation and starts stirring the developer with the third operation (step S 28 ). To be more specific, the controller  7  enables the stir screw  43  to rotate in the forward direction at high speed and activates the vibration members  48  to vibrate the developer to stir the developer. The controller  7  obtains the value output by the toner density sensor  46  equipped with the developing unit  23  (step S 29 ), and determines if the obtained value is close to the reference value Vr (step S 30 ). The value output by the toner density sensor  46  may be within the predetermined range of the reference value Vr as a result of the determination (when a result of step S 30  is YES). In this case, the process by the controller  7  proceeds to step S 36 . 
     Upon determining that the value output by the toner density sensor  46  is not within the predetermined range of the reference value Vr as a result of the determination in step S 30  (when a result of step S 30  is NO), the controller  7  determines if the predetermined period of time (the third term from timing T 2  to timing T 3  illustrated in  FIG. 7 ) has elapsed after the stir operation has started (step S 31 ). The predetermined period of time may have not elapsed (when a result of step S 31  is NO). In this case, the process by the controller  7  returns to step S 29  to repeat the above-described process. The predetermined period of time may have elapsed (when a result of step S 31  is YES). In this case, the process by the controller  7  proceeds to step S 32 . 
     In step S 32 , the controller  7  switches the stir operation from the third operation to the fourth operation and starts stirring the developer with the fourth operation (step S 32 ). To be more specific, the controller  7  enables the stir screw  43  to rotate in the reverse direction at high speed and activates the vibration members  48  to vibrate the developer to stir the developer. The controller  7  obtains the value output by the toner density sensor  46  equipped with the developing unit  23  (step S 33 ), and determines if the obtained value is close to the reference value Vr (step S 34 ). The value output by the toner density sensor  46  may be within the predetermined range of the reference value Vr as a result of the determination (when a result of step S 34  is YES). In this case, the process by the controller  7  proceeds to step S 36 . 
     In step S 36 , the controller  7  determines that the bulk density of the developer is back to the condition almost equivalent to the condition in time of the factory shipment, and determines the stir operation of the developer successfully completes (step S 36 ). More specifically, the controller  7  determines that the stir operation of the developer successfully completes at time the developer is sufficiently loosened during the stir period set in advance. 
     The controller  7  may determine that the value output by the toner density sensor  46  has not reached the value within the predetermined range of the reference value Vr as a result of the determination in step S 34  (when a result of step S 34  is NO). In this case, the controller  7  determines if the predetermined period of time (the fourth term from timing T 3  to timing T 4  illustrated in  FIG. 7 ) has elapsed after the stir operation has started (step S 35 ). The predetermined period of time may have not elapsed (when a result of step S 35  is NO). In this case, the process by the controller  7  returns to step S 33  to repeat the above-described process. The predetermined period of time may have elapsed (when a result of step S 35  is YES). The process by the controller  7  then determines that the bulk density of the developer could not be back to the condition almost equivalent to the condition in time of the factory shipment, and determines the stir operation of the developer completes unsuccessfully (step S 37 ). Thus, the developer stir process (step S 14 ) completes. 
     Referring back to the flow diagram of  FIG. 8 , after the developer stir process (step S 14 ), the controller  7  drives the stir screw  43  and the vibration members  48  to complete the stir operation (step S 15 ). The controller  7  then determines if the developer stir process (step S 14 ) is successfully complete (step S 16 ). Upon determining that the developer stir process (step S 14 ) is successfully complete (when a result of S 16  is YES), the toner adjustment performed by the controller  7  completes. 
     The stir operation in the developer stir process (step S 14 ) may be determined to be unsuccessfully complete (when a result of S 16  is NO). In such a case, the controller  7  notifies the abnormality of toner (step S 17 ). As a result, the controller  7  is enabled to notify the user or the maintenance operator that the toner density shows an abnormal value. The controller  7  also restricts the processing of the print job by the job controller  56  (step S 18 ). As a result, the problem such as the generation of smoke and/or the density defect can be avoided. 
     As described above, the developing unit  23  filled with the developer containing the toner is detachable and removable to and from the device body  1   a  of the image forming device  1  of the first embodiment. As the initial operation of the developing unit  23  attached to the device body  1   a , the image forming device  1  of the first embodiment enables the developing unit  23  to perform the stir operation of the developer filed in the developing unit  23 . The image forming device  1  compares the toner density output from the developing unit  23  during the stir operation of the developer with the reference value Vr, and determines the stir condition of the developer. The image forming device  1  refers to the value set in advance as the reference value Vr at the factory shipment so that the image forming device  1  is enabled to precisely determine if the developer filled in the developing unit  23  has been loosened to the condition almost equivalent to the condition in time of the factory shipment during the stir operation of the developer. As a result, the image forming device  1  is enabled to complete the stir operation as the initial operation at timing the developer is sufficiently loosened. This can avoid the longer setup time at the customer site. 
     When the developer is not sufficiently loosened, the image forming device  1  is enabled to stop processing of the print job. This solves the problem such as the generation of smoke and/or the density defect. 
     Second Embodiment 
     The second embodiment of the present invention is explained next. In the above-described first embodiment, the reference value Vr of the toner density set in advance at the factory shipment is stored in the storage  47  installed in the developing unit  23 . In the second embodiment, the reference value Vr of the toner density set in advance at the factory shipment is stored in a server. The structure of the image forming device  1  of the second embodiment is the same as that explained in the first embodiment. 
       FIG. 10  illustrates an exemplary conceptual configuration of an information forming system  100  including the image forming device  1 . The image forming system  100  includes a reference value registration device  110  which is installed in a factory  101  that manufactures the developing unit  23 , a server  120  installed on a cloud  102  such as an internet and the image forming device  1  installed in a place such as an office  103  at a client site. 
     In the factory  101 , the reference value registration device  110  and the developing unit  23  are connected to each other prior to the shipment of the developing unit  23 , and the reference value registration device  110  is enabled to obtain the value output from the toner density sensor  46  equipped with the developing unit  23 . While it is available for the reference value registration device  110  to obtain the value output from the toner density sensor  46 , the developer filled in the body  40  of the developing unit  23  may be stirred sufficiently. In such a case, the reference value registration device  110  enables the toner density sensor  46  to measure the toner density and obtain the value output from the toner density sensor  46 . The reference value registration device  110  then sends the obtained value to the server  120  as the reference value Vr. The reference value registration device  110  sends identification information such as a serial number for identifying the developing unit  23  to the server  120  together with the reference value Vr. 
     The server  120  includes a storage device  121  formed from a hard disk drive (HDD) or a solid-state drive (SSD), for example. Upon receiving the reference value Vr from the reference value registration device  110  in the factory  101  and the identification information of the developing unit  23 , the server  120  associates the reference value Vr and the identification with each other and stores in the storage device  121 . More specifically, the image forming system  1  of the second embodiment stores the reference value Vr set in advance at the factory shipment of the developing unit  23  in the server  120 . 
     The developing unit  23 , the reference value Vr of which is stored in the server  120 , is shipped from the factory  101 . After a variety of transit process and storage process, the developing unit  23  is carried to the client&#39;s office  103  and attached to the device body  1   a  of the image forming device  1 . For bringing the developing unit  23  attached to the device body  1   a  into operation for the first time, the image forming device  1  performs the initial operation of the developing unit  23 . More specifically, the image forming device  1  performs the stir operation to stir the developer filled in the developing unit  23 . In performing the stir operation, the reference value obtaining part  62  of the image forming device  1  is brought into operation to obtain the reference value Vr set in advance at the factory shipment of the developing unit  23 . 
     The reference value obtaining part  62  of the second embodiment accesses the server  120  on the cloud  102  via the communication interface  54 , and obtains the reference value Vr corresponding to the developing unit  23  from the server  120 . The reference value obtaining part  62 , for example, displays a screen to ask for the input of the identification information of the developing unit  23  on the display unit  53   a  of the operational panel  53 , and receives the input operation of the identification information by the user or the maintenance operator. The reference value obtaining part  62  sends the identification information input by the user or the maintenance operator to the server  120 , and obtains the reference value Vr corresponding to the developing unit  23  attached to the device body  1   a  from the server  120 . When the identification information of the developing unit  23  is stored in the storage  47  of the developing unit  23 , the reference value obtaining part  62  may read the identification information in the storage  47  and send the read identification information to the server  120 . 
     After the reference value Vr is obtained from the server  120  by the reference value obtaining part  62 , the image forming device  1  can perform the similar operation as the operation explained in the first embodiment. 
     As described above, the image forming device  1  of the first embodiment stores the reference value Vr of the toner density set in advance in time of the factory shipment of the developing unit  23  in the server  120 , and obtains the reference value Vr from the server  120 . With this structure, the developing unit  23  does not have to be equipped with the storage  47  to store the reference value Vr. The inexpensive developing unit  23  can be provided. 
     Everything else except for the points described above in the second embodiment is the same as that explained in the first embodiment. The working-effect explained in the first embodiment can be also obtained in the second embodiment. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the amended claims. 
     Modifications 
     While the embodiment of the present invention has been described above, the present invention is not limited to the embodiment. Various modifications may be applied to the present invention. 
     In the above-described embodiments, for example, the developer which is sufficiently loosened is measured by the toner density sensor  46  in time of the factory shipment of the developing unit  23  and the reference value Vr of the toner density is set. The toner density does not actually have to be measured by the toner density sensor  46  in time of the factory shipment. If the output characteristic corresponding to the individual difference of the toner density sensor  46  is measured at the factory shipment of the developing unit  23 , for example, the reference value Vr can be set by operation based on the output characteristic. 
     The image forming device  1  of the above-described embodiments is constructed by a color device capable of producing a printed color outputs. However, this is given not for limitation. The image forming device  1  does not always have to be the color device. The image forming device  1  may be a black and white only device. 
     In the above-described embodiments, the program  52  is installed in advance in the controller  7  of the image forming device  1 . The program  52  may be installed in the controller  7  via the communication interface  54 , for example. In this case, the program  52  may be provided over internet in a manner that enables a user to download, or may be provided in a manner that is recorded on a computer readable recording medium such as a CD-ROM or a USB memory.