Patent Publication Number: US-10768564-B2

Title: Image forming apparatus and storage medium

Description:
BACKGROUND 
     Technological Field 
     The present invention relates to an image forming apparatus and a storage medium. 
     Description of the Related Art 
     Conventionally, in the image forming apparatus employing the electro-photographic method, there is a technique to slide a cleaning brush or a cleaning blade against a surface of an image carrier such as a photoconductor on which a toner image is formed to remove attached material such as residual toner attached to the surface of an image carrier. 
     When the image carrier is cleaned by the cleaning brush, in order to reduce the adhesion strength of the toner attached to the image carrier and to enhance the cleaning performance, there is a technique to apply lubricant to be attached to the image carrier. For example, a lubricant applying brush which rotates while coming into contact with the surface of the image carrier and a solid lubricant are used to apply the lubricant. The lubricant applying brush rotates so that the lubricant shaved from the solid lubricant is applied evenly to the surface of the image carrier. 
     The lubricant applying brush scrapes the surface of the image carrier to function as the cleaning brush. With this, the amount of the residual toner which reaches the cleaning blade positioned on the downstream side of the photoconductor in the rotating direction is decreased, and the cleaning performance by the cleaning blade is enhanced. 
     If the toner or the additive is attached to the surface of the cleaning brush or the lubricant applying brush, and the brush is stained, the cleaning performance of the stained portion decreases. Then, a stain due to the toner may appear on the image formed on the sheet or noise may occur in the image due to unevenness in applying the lubricant or unevenness in the polishing. 
     In view of the above problems, JP H11-237825 describes a technique to detect a change of an electric current value flowing in the cleaning brush and to determine whether there is attached material to the cleaning brush based on the above detection. If the stain in the cleaning brush is detected, influence to the image can be suppressed by performing cleaning. 
     When a portion of the cleaning brush or the lubricant applying brush is stained in the axis direction, noise occurs in only a portion of the sheet in the main scanning direction. For example, an image streak occurs. 
     According to the method described in JP H11-237825, the degree that the entire cleaning brush is stained can be determined but the stain in a portion of the cleaning brush in the axis direction cannot be determined. Even if the degree of the stain as a whole is small, the stain in a portion of the brush causes noise in the image. 
     SUMMARY 
     An object of the present invention is to provide an image forming apparatus and a storage medium to accurately detect a stain in an axis direction of a rotating member which comes into contact with a photoconductor while rotating. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present invention, an image forming apparatus reflecting one aspect of the present invention includes an image former which includes, an image carrier which carries a toner image transferred to a sheet; a developer which applies a developing bias and which develops the toner image on the image carrier; a conductive rotating member which rotates while coming into contact with the image carrier; and a voltage applier which applies a voltage to the rotating member, and a hardware processor which executes an attached material detection mode which detects material attached to a surface of the rotating member, wherein, in the attached material detection mode, the hardware processor controls the voltage applied by the developer and/or the voltage applier so that the developing bias is a value between a surface potential in a region on a surface of the image carrier in contact with a portion in which attached material exists on a surface of the rotating member if a reference voltage is applied by the voltage applier, and a surface potential in a region on the surface of the image carrier in contact with a portion in which the attached material does not exist on the surface of the rotating member if the reference voltage is applied, and the hardware processor controls the developer to develop a toner image on the image carrier. 
     According to another aspect of the present invention, a non-transitory computer-readable storage medium reflecting another aspect of the present invention has a program stored thereon for controlling a computer used in an image forming apparatus including an image former which includes, an image carrier which carries a toner image transferred to a sheet; a developer which applies a developing bias and which develops the toner image on the image carrier; a conductive rotating member which rotates while coming into contact with the image carrier; and a voltage applier which applies a voltage to the rotating member, wherein the program controls the computer to execute: an attached material detection mode which detects material attached to a surface of the rotating member, wherein, in the attached material detection mode, the voltage applied by the developer and/or the voltage applier are controlled so that the developing bias is a value between a surface potential in a region on a surface of the image carrier in contact with a portion in which attached material exists on a surface of the rotating member if a reference voltage is applied by the voltage applier, and a surface potential in a region on the surface of the image carrier in contact with a portion in which the attached material does not exist on the surface of the rotating member if the reference voltage is applied, and the developer is controlled to develop a toner image on the image carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinafter 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, and wherein: 
         FIG. 1  is a diagram showing a schematic configuration of an image forming apparatus; 
         FIG. 2  is a block diagram showing a configuration of main functions in the image forming apparatus according to a first embodiment; 
         FIG. 3  is a diagram showing a schematic configuration of an image former according to the first embodiment; 
         FIG. 4  is a diagram showing a schematic configuration of a cleaner; 
         FIG. 5A  to  FIG. 5C  are diagrams describing a mechanism of a toner development which occurs due to a stain in a lubricant applying brush; 
         FIG. 6A  to  FIG. 6C  are diagrams describing a relation between voltage applied to a lubricant applying brush and the toner development; 
         FIG. 7A  to  FIG. 7C  are diagrams describing a relation between a developing bias and the toner development; 
         FIG. 8  is a flowchart showing an operation of the image forming apparatus according to the first embodiment; 
         FIG. 9  is a flowchart showing an operation of the image forming apparatus according to a stain level calculating process; 
         FIG. 10  is a diagram describing a relation between a stain which occurs in a circumferential direction and toner development; 
         FIG. 11  is a block diagram showing a configuration of main functions in the image forming apparatus according to a second embodiment; 
         FIG. 12  is diagram showing a schematic configuration of an image former according to the second embodiment; and 
         FIG. 13  is a flowchart showing an operation of the image forming apparatus according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more 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 
     The first embodiment is described in detail with reference to the drawings. 
     [Configuration of Image Forming Apparatus] 
     The image forming apparatus  1  according to the present embodiment is a color image forming apparatus employing an intermediate transfer method which uses an electro-photographic process technique. As shown in  FIG. 1  to  FIG. 3 , the image forming apparatus  1  includes an automatic document conveyor  2 , a scanner  3 , an image former  4 , a sheet feeder  5 , a storage  6 , an operation/display unit  7 , a controller  10 , and an inline sensor S. 
     The automatic document conveyor  2  includes a placement tray to place a document D, a mechanism and conveying roller to convey the document D and the like to convey the document D to a predetermined conveying path. 
     The scanner  3  is provided with an optical system such as an optical source and a reflecting mirror, the optical source irradiates the document D conveyed on the predetermined conveying path or the document D placed on a platen glass and the scanner  3  receives the reflected light. The scanner  3  converts the received reflected light to an electric signal and outputs the electric signal to the controller  10 . 
     The image former  4  includes a yellow imager Y, a magenta imager M, a cyan imager C, a black imager K, an intermediate transfer belt T, and a fixer F. 
     Each imager YMCK forms a toner image in yellow, magenta, cyan, or black, respectively, on a photoconductor  41 , and the toner images in the colors YMCK formed on the photoconductor  41  are transferred by first transfer on the intermediate transfer belt T. 
       FIG. 3  is a diagram showing a schematic configuration of an image former  4 . Each imager includes the following, the drum shaped photoconductor  41  (image carrier) which is driven to rotate in a direction A as shown in the diagrams, a charging device  42  which uniformly charges the surface of the photoconductor  41 , an exposing device  43  which exposes the surface of the photoconductor  41  charged by the charging device  42  to form an electrostatic latent image, a developing device  44  (developer) which uses a developer including toner to visualize the electrostatic latent image formed on the exposing device  43 , a first transfer roller  45  which transfers the toner image formed on the photoconductor  41  onto a sheet, a cleaner  47  which removes toner on the photoconductor  41  which passed a transfer region, and an eraser  48  which erases the latent image on the photoconductor  41 . The toner image formed on the photoconductor  41  is transferred by first transfer onto an intermediate transfer belt T moving in the B direction as shown in the diagram. The toner image transferred onto the intermediate transfer belt T is transferred to the sheet by the second transfer roller  46 . Then, the sheet is conveyed to the fuser F, and the toner image is fused on the sheet. An inline sensor S is positioned for the imagers YMCK on a downstream side of the rotating direction B of the intermediate transfer belt T with relation to the transfer region between the first transfer roller  45  and the photoconductor drum so that an inline sensor S is able to read the toner image on the intermediate transfer belt T. 
     The configuration and the operation are the same for all images YMCK. Therefore, hereinbelow, the flow of the image forming operation performed by the image former  4  is described with reference to the yellow imager Y as the example. 
     The photoconductor  41  includes an organic photoconductor in which a photoconductor layer is formed including resin including an organic photoconductor on an outer circumferential surface of a drum-shaped metallic base. The photoconductor  41  rotates in the direction A shown in the diagrams. The resin included in the photoconductor layer may be polycarbonate resin, silicone resin, polystyrene resin, acrylic resin, methacrylic resin, epoxy resin, polyurethane resin, vinyl chloride resin, melamine resin, for example. The photoconductor  41  includes a layer structure in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are positioned in this order on a conductive original tube such as an aluminum tube. 
     The charging device  42  uses a charger to charge the photoconductor  41  to a certain electric potential in a minus polarity. 
     The exposing device  43  exposes a non-image region of the photoconductor  41  based on image data Dy from the controller  10  to remove charge of the exposed portion and forms the electrostatic latent image in the image region of the photoconductor  41 . 
     The developing device  44  includes a developing sleeve  44   a  positioned facing the photoconductor  41  with the developing region in between. For example, a developing bias with an AC voltage superimposed on a DC voltage with a same polarity as the charging polarity of the charging device  42 , that is, a minus polarity is applied to the developing sleeve  44   a . With this, the developer is supplied on the electrostatic latent image formed on the photoconductor  41 , and the yellow toner image is formed on the photoconductor  41 . The developer includes a toner and a carrier to charge the toner. The toner is not limited and well-known toner used widely can be used. For example, it is possible to use a binder resin which includes a colorant and as necessary, a charge controlling agent or a separating agent and which is processed with an external additive. The toner particle size is not limited, and preferably, the size is about 3 to 15 μm. 
     The developing bias applied to the developing device  44  is controlled by the controller  10 . 
     First transfer is performed by using the first transfer roller  45  to transfer the yellow toner image formed on the photoconductor  41  onto the intermediate transfer belt T. Similarly for the imagers MCK, first transfer is performed to transfer the toner images in magenta, cyan, and black onto the intermediate transfer belt T. With this, the toner images with the colors YMCK are formed on the intermediate transfer belt T. 
     The intermediate transfer belt T is a semi-conductive endless belt hung around a plurality of rollers to be supported in a rotatable state. The intermediate transfer belt T is rotated in the direction B as shown in the diagrams with the rotation of the rollers. The intermediate transfer belt T is pressed against the opposing photoconductor  41  by the first transfer roller  45 . The transfer electric current according to the applied voltage flows in each first transfer roller  45 . With this, first transfer is performed and each of the toner images developed on the surface of each photoconductor  41  is successively transferred to the intermediate transfer belt T by the first transfer roller  45 . 
     The second transfer roller  46  is pressed by the intermediate transfer belt T and rotates in a manner following the intermediate transfer belt T. With this, the second transfer is performed and the toner images in the colors YMCK transferred and formed on the intermediate transfer belt T are transferred on a paper P conveyed from sheet feeding trays  51  to  53  of the sheet feeder  5 . In detail, the second transfer roller  46  is positioned in contact with the second transfer opposing roller  461  with the intermediate transfer belt T in between. When the paper P passes a transfer nip formed between the second transfer roller  46  and the second transfer opposing roller  461 , the second transfer is performed and the toner image on the intermediate transfer belt T is transferred onto the paper P. 
     The toner which is not transferred on the intermediate transfer belt T in the transfer region and which remains on the photoconductor  41  is transferred to the cleaner  47  and collected by the cleaner  47 . 
     The photoconductor  41  in which the toner on the surface is collected by the cleaner  47  is charged again by the charging device  42  and the next electrostatic latent image is formed to form the toner image. This process is repeated. 
       FIG. 4  is a schematic diagram showing a configuration of a cleaner  47 . 
     The cleaner  47  includes a cleaning blade  47   a , a collecting screw  47   b  provided substantially below the cleaning blade  47   a , a lubricant applying brush  47   c  provided on a downstream side in the rotating direction of the photoconductor  41  with relation to the cleaning blade  47   a , a voltage applier  47   d  which applies voltage to the lubricant applying brush  47   c  (see  FIG. 2 ), a solid lubricant  47   e  which supplies lubricant on the lubricant applying brush  47   c , a presser  47   f  which presses and holds the solid lubricant  47   e  against the lubricant applying brush  47   c , and a fixing blade  47   g  which is provided on the downstream side in the rotating direction of the photoconductor  41  with relation to the lubricant applying brush  47   c.    
     For example, the cleaning blade  47   a  is an elastic body such as polyurethane rubber processed in a plate shape. The cleaning blade  47   a  is positioned so that the tip slides against the photoconductor  41 . The cleaning blade  47   a  scrapes and removes the attached material such as toner which is not transferred and which remains on the surface of the photoconductor  41 . 
     The collecting screw  47   b  rotates in one direction and the collecting screw  47   b  conveys the toner scraped and dropped by the cleaning blade  47   a  to a waste toner box (not shown). 
     The lubricant applying brush  47   c  is a roll brush positioned in a position so that the tip is able to come into contact with the photoconductor  41 , and the lubricant applying brush  47   c  functions as the rotating member. The lubricant applying brush  47   c  includes on its surface brush hair including conductive members such as polyester and nylon. The lubricant applying brush  47   c  is provided so that the brush hair comes into contact with both the solid lubricant  47   e  and the photoconductor  41 . Under the control of the controller  10 , the lubricant applying brush  47   c  rotates in a counter rotation in which the surface advances in a direction opposite the advancing direction of the surface of the photoconductor  41  at the contact point with the photoconductor  41 , and the lubricant applying brush  47   c  rotates to be a linear speed slower than the photoconductor  41 . 
     The voltage applier  47   d  applies voltage to the lubricant applying brush  47   c . The applying voltage by the voltage applier  47   d  is controlled by the controller  10 . 
     For example, the solid lubricant  47   e  is a lubricant formed from metallic soap such as zinc stearate in a powder form from being melted, shaped and solidified. The solid lubricant  47   e  is positioned in a position in which the tip is able to come into contact with the lubricant applying brush  47   c . The solid lubricant  47   e  is scraped off from the tip by the rotation of the lubricant applying brush  47   c . The lubricant which is scraped off is conveyed to the photoconductor  41  and supplied to the surface of the photoconductor  41 . 
     The presser  47   f  includes a compression spring which biases the solid lubricant  47   e  toward the direction of the lubricant applying brush  47   c , and presses and holds the solid lubricant  47   e  toward the lubricant applying brush  47   c.    
     Similar to the cleaning blade  47   a , an elastic body such as polyurethane rubber processed in a plate shape is used as the fixing blade  47   g . The fixing blade  47   g  is positioned so as to come into contact with the surface of the photoconductor  41  in a direction pulling the surface, and the tip of the fixing blade  47   g  slides against the photoconductor  41 . The fixing blade  47   g  extends the powder of the lubricant supplied to the surface of the photoconductor  41  to form a layer on the surface of the photoconductor  41 . The lubricant layer formed with zinc stearate has high separating performance and a small friction coefficient. Therefore, the quality in transfer and cleaning is good and the wearing of the photoconductor  41  can be suppressed to enable a long operating life. 
     The eraser  48  is an exposing unit such as the LED and is provided in the upstream side of the rotating direction of the photoconductor  41  with respect to the first transfer roller  45 . The eraser  48  removes electricity in the surface of the photoconductor  41  before the transferring. With this, the potential difference of the image portion and the non-image portion on the surface of the photoconductor  41  can be made smaller. 
     The image former  4  uses the fuser F to heat and pressure the paper P on which the toner images in the colors YMCK are transferred by second transfer and then passes the paper P through the predetermined conveying path to eject the paper P outside the apparatus. 
     The flow of processes described above is the image forming process performed by the image former  4 . 
     The inline sensor S is a sensor which can read the intermediate transfer belt T in a main scanning direction and the inline sensor S uses the image sensor such as a CCD to read the toner image formed on the intermediate transfer belt T while the paper passes. A total of four inline sensors S are provided near the imagers as described above, and the data read for each imager is transmitted sequentially to the controller  10 . 
     The inline sensor S functions as a detector. 
     The sheet feeder  5  includes a plurality of sheet feeding trays  51  to  53 , and a plurality of different types of paper P are stored in each sheet feeding tray  51  to  53 . The sheet feeder  5  feeds the stored paper P to the image former  4  through the predetermined conveying path. 
     The storage  6  includes a HDD (Hard Disk Drive), a semiconductor memory, and the like, and stores data such as the program data and various setting data in a rewritable state under the control of the controller  10 . 
     The operation/display unit  7  includes a liquid crystal display (LCD) with a touch panel and functions as a display  71  and an operation unit  72 . 
     The display  71  displays various operation screens and an operation status of various functions according to a display control signal input from the controller  10 . The display  71  receives touch operation by the user and outputs the operation signal to the controller  10 . 
     The operation unit  72  includes various operation keys such as numeric keys and a start key, and the operation unit  72  receives various input operation by the user and outputs the operation signal to the controller  10 . The user operates the operation/display unit  7  to be able to perform operation such as setting regarding the image forming including image quality setting, magnification setting, advanced setting, output setting, and paper setting, paper conveying instruction, and operation to stop the apparatus. 
     The controller  10  includes a CPU, a RAM, and a ROM. The CPU deploys various programs stored in the ROM to the RAM and in coordination with the various deployed programs, the controller  10  centrally controls the operation of various units in the image forming apparatus  1  such as the automatic document conveyor  2 , scanner  3 , image former  4 , sheet feeder  5 , storage  6 , operation/display unit  7 , and inline sensor S (see  FIG. 2 ). For example, the electric signals are input from the scanner  3  and the controller  10  performs various image processes. The controller  10  outputs the image data Dy, Dm, Dc, Dk of the colors YMCK generated by image processing to the image former  4 . The controller  10  controls the operation of the image former  4  to detect material attached to the lubricant applying brush  48   c  as described below. 
     [Attached Material Detection Mode] 
     The attached material detection mode according to the present embodiment is described with reference to the drawings. The attached material detection mode is the operation performed by the image forming apparatus  1  to detect the material attached to the surface of the lubricant applying brush  47   c.    
     In the description below, “stain” means attached material such as toner on the surface of the lubricant applying brush  47   c  and the lubricant which is not applied to the photoconductor  41  and which remains on the surface of the lubricant applying brush  47   c.    
       FIG. 5A  to  FIG. 5C  are diagrams describing the mechanism of toner developed due to stain in the lubricant applying brush  47   c.    
     As shown in  FIG. 5A , when the image is formed, a certain voltage (reference voltage) is applied to the lubricant applying brush  47   c  by the voltage applier  47   d . At this time, the charge of the lubricant applying brush  47   c  moves to the photoconductor  41 . For example, if the voltage of −500 V is applied by the voltage applier  47   d , minus charge moves from the lubricant applying brush  47   c  to the photoconductor  41 . 
     Here, as shown in  FIG. 5B , when there is a partial stain in a region r 2  of the lubricant applying brush  47   c , resistance of the region r 2  increases. With this, the charge moved to the photoconductor  41  reduces and the surface potential of the photoconductor  41  reduces. 
     When the photoconductor  41  comes into contact with the developing sleeve  44   a  in a state that the charge is moved from the lubricant applying brush  47   c  to the photoconductor  41 , if the surface potential of the photoconductor is V 0  and the developing bias is Vdc, the toner is not developed when V 0 &gt;Vdc but the toner is developed when V 0 &lt;Vdc. Therefore, as shown in  FIG. 5C , even if the potential is V 0 &gt;Vdc in the region R 1  of the surface of the photoconductor  41  in contact with the portion r 1  in which there is no stain in the lubricant applying brush  47   c , if the potential decreases and becomes V 0 &lt;Vdc in the region R 2  in contact with the portion r 2  in which there is the stain in the lubricant applying brush  47   c , the toner is developed. 
       FIG. 6A  to  FIG. 6C  are diagrams describing the relation between the voltage applied to the lubricant applying brush  47   c  and the toner developing. 
     According to the attached material detection mode of the present embodiment, in the state in which the operation of the eraser  48  and the charging device  42  is stopped, the voltage Vbrush applied to the lubricant applying brush  47   c  is gradually raised from the low potential. When the value is raised to a predetermined value, the value is returned to the initial value. Such triangular wave control is repeated. For example, if the initial value of the Vbrush is −300 V, the surface potential of the photoconductor  41  follows and gradually increases from −100 V. 
     If the region on the surface of the photoconductor  41  which comes into contact with the portion in which there is no stain in the lubricant applying brush  47   c  is R 1  and the surface potential of R 1  is V 0 =V 1 , as shown in  FIG. 6A , the toner is developed if V 1  is lower than the developing bias Vdc. However, if the surface potential of the photoconductor  41  increases, at the timing when V 1  exceeds Vdc (t=t 1 ), the toner is not developed on the photoconductor  41 . 
     If the region on the surface of the photoconductor  41  which comes into contact with the portion in which there is the stain in the lubricant applying brush  47   c  is R 2  and the surface potential of R 2  is V 0 =V 2 , as shown in  FIG. 6B , the increase of V 2  is slower compared to the increase of V 1  in R 1 . Therefore, the timing that V 2  exceeds Vdc and that the toner is not developed (t=t 2 ) is later compared to t 1 . 
       FIG. 6C  is a diagram showing the toner image developed on the surface of the photoconductor  41 . If the toner is developed in the direction C in the diagrams, the toner is developed toward the downstream side in the region R 2  compared to the region R 1 . 
     The same result can be obtained by triangular wave control of the developing bias. 
       FIG. 7A  to  FIG. 7C  are diagrams describing the developing bias control in the attached material detection mode according to the present embodiment. Similarly, in a state with the operation of the eraser  48  and the charging device  42  stopped, the developing bias Vdc is gradually lowered from the high potential. When the value is lowered to a predetermined value, the value is returned to the initial value. Such triangular wave control is repeated. For example, if the initial value of Vdc is −700 V, and Vbrush is a constant voltage of −500 V, the surface potential of the photoconductor  41  is a value which follows Vbrush. 
     As shown in  FIG. 7A , if the surface potential of the region R 1  is V 0 =V 1 , in the region R 1 , if the developing bias Vdc exceeds the surface potential V 1  of the photoconductor  41 , the toner is developed. However, if the developing bias decreases, at the timing that the Vdc is lower than the V 1  (t=t 1 ), the toner is not developed on the photoconductor  41 . 
     As shown in  FIG. 7B , if the surface potential of the region R 2  is V 0 =V 2 , the surface potential V 2  of the photoconductor  41  becomes a lower potential than V 1  in the region R 2 . Therefore, the timing that the developing bias Vdc becomes lower than V 2  (t=t 2 ) is later than t 1 . 
     With this, as shown in  FIG. 7C , the toner is developed toward the downstream side in the direction C shown in the diagrams in the region R 2  compared to the region R 1 . 
     Therefore, in the attached material detection mode according to the present embodiment, the developing bias Vdc or the voltage Vbrush applied by the voltage applier  47   d  is controlled so that the developing bias Vdc is between the surface potential V 1  of the photoconductor  41  in the region R 1  when the reference voltage is applied to the lubricant applying brush  47   c  and the surface potential V 2  of the photoconductor  41  in the region R 2 . Also, the imaging device  44  develops the toner image. By analyzing the toner image developed here, the attached state of the stain on the lubricant applying brush  47   c  can be predicted. 
     According to the description below, only either one of the developing bias Vdc or the voltage Vbrush applied by the voltage applier  47   d  is controlled so that the value of the developing bias Vdc is within the above range. Alternatively, both the developing bias Vdc and the applied voltage Vbrush can be controlled. 
     The operation of the image forming apparatus  1  is described using the flowchart shown in  FIG. 8 . The process shown in  FIG. 8  is executed by the controller  10  in coordination with the program stored in the storage  6 . 
     The controller  10  determines whether it is the timing to perform the attached material detection mode (step S 101 ). The timing that the attached material detection mode is performed is timing such as when image forming is performed in a preset distance, for example. Such timing may also be the point in time when it is assumed that there is a stain in the lubricant applying brush  47   c  or at the end of the image forming operation. The attached material detection mode can be performed periodically. Alternatively, the attached material detection mode may be performed when it is assumed that there is a stain locally in the lubricant applying brush  47   c . Such occasion may be after continuous printing of partial coverage. 
     If it is determined that it is the timing to perform the attached material detection mode (step S 101 : YES), the controller  10  progresses to step S 102 . If it is determined that it is not such timing (step S 101 ; NO), the process in step S 101  is repeated. 
     In step S 102 , the attached material detection mode is performed. 
       FIG. 9  is a flowchart showing an operation of the image forming apparatus in the attached material detection mode. The process shown in  FIG. 9  is executed by the controller  10  in coordination with the program stored in the storage  6 . 
     First, the controller  10  starts the triangular wave control of either the voltage Vbrush applied on the lubricant applying brush  47   c  or the developing bias Vdc (step S 1021 ). 
     Next, the controller  10  starts the rotation of the photoconductor  41  and the lubricant applying brush  47   c  (step S 1022 ). 
     Next, the controller  10  determines whether one cycle of the triangular wave of the Vbrush or Vdc passed (step S 1023 ). If it is determined that it is not passed (step S 1023 : NO), the controller  10  repeats the process of step S 1023 . If it is determined that it is passed (step S 1023 : YES), the process progresses to step S 1024 . 
     In step S 1024 , the controller  10  changes the rotation speed of the lubricant applying brush  47   c.    
     The above is described with reference to  FIG. 10 . When there is a stain in a portion in the circumferential direction of the lubricant applying brush  47   c , the region on the surface of the photoconductor  41  corresponding to the above is to be R 2 , and the other regions are to be R 1 . While the developing bias Vdc is controlled by triangular wave control, if the region R 1  is in contact with the developing sleeve  44   a  when the Vdc decreases and reaches the surface potential V 1  of the region R 1 , the toner is no longer developed at the timing of t 1  shown in  FIG. 10 . If the region R 2  is in contact, the toner continues to be developed until the timing t 2  in which Vdc reaches the surface potential V 2  of the region R 2 . That is, depending on whether the region R 2  comes into contact with the developing sleeve  44   a  during one cycle of the triangular wave, there is a shift in the timing that the toner is no longer developed. This makes it difficult to accurately calculate the level of the stain. Therefore, for every cycle of the triangular wave, the rotation speed of the lubricant applying brush  47   c  is changed at least once. The timing that the toner is no longer developed is specified in each rotation speed. By calculating the average value of the above, it is possible to suppress the influence in the variation of the level of the stain in the circumferential direction, and the accuracy of calculating the level of the stain can be enhanced. 
     Next, the controller  10  determines whether the photoconductor  41  rotated once (step S 1025 ). 
     Since the operation of the charging device  42  and the eraser  48  is stopped, when the photoconductor  41  starts the second cycle, there is influence of the potential remaining from the previous cycle. Therefore, the stain level of only one rotation of the photoconductor  41  is to be the target of calculation. If there is an apparatus which can erase or equalize the surface potential of the photoconductor  41  before cleaning with the eraser  48  or the pre-cleaning charger, such operation may be performed so as to be able to repeat the triangular wave control even after the second cycle of the photoconductor  41 . 
     If it is determined that the photoconductor  41  made one rotation (step S 1025 : YES), the controller  10  progresses the process to step S 1026 . If it is determined that one rotation is not made (step S 1025 ; NO), the process returns to step S 1023 . 
     In step S 1026 , the controller  10  controls the inline sensor S to read the toner on the intermediate transfer belt T in the main scanning direction. That is, the inline sensor S reads the toner image formed on the photoconductor  41  as shown in  FIG. 6C  or  FIG. 7C  transferred to the intermediate transfer belt T. 
     Next, the controller  10  calculates the stain level (step S 1027 ). Here, “stain level” means the degree that the stain is attached to the surface of the lubricant applying brush  47   c . Specifically, the stain level is calculated by the following method. 
     First, binarization image processing is performed on the image data read by the inline sensor S and the image data is converted to a solid/white image. 
     Next, if the local stain on the lubricant applying brush  47   c  is specified, in the direction of the arrow C shown in  FIG. 6C  or  FIG. 7C , the time (or distance) from the start of the triangular wave cycle to the change from solid to white in the specific position in the axis direction (direction orthogonal to the direction C shown in  FIG. 6C  or  FIG. 7C ) of the lubricant applying brush  47   c  is measured. By performing the above throughout the entire axis direction, the measured time or distance can be an index showing the state of the stain in each position in the axis direction, that is, the local stain level. 
     If the degree of the stain on the entire lubricant applying brush  47   c  is specified, the average value of the time (or distance) from the start of the triangular wave cycle to the change from solid to white measured in each position in the axis direction of the lubricant applying brush  47   c  is calculated. That is, if the average time or the average distance is large, it can be said that the entire surface potential of the photoconductor  41  decreased and the entire stain level of the lubricant applying brush  47   c  is high. Therefore, the measured time or distance can be an index showing the state of the entire stain due to use of the lubricant applying brush  47   c , that is, the entire stain level. 
     In step S 1027 , the stain level in each cycle of the triangular wave is calculated and the average is output as the stain level. 
     When the stain level is calculated, the attached material detection mode ends. The process returns to the flowchart shown in  FIG. 8 , and the controller  10  determines whether the stain level is equal to or larger than the predetermined value (step S 103 ). 
     When the local stain level is calculated, if the difference between the maximum value and the minimum value of the time (or distance) measured in each position in the axis direction in step S 1027  is equal to or larger than a predetermined value set in advance, it is determined that there is a local stain. 
     When the entire stain level is calculated, the stain level measured in step S 1027  is compared with the initial value of the stain level measured in advance when the use of the lubricant applying brush  47   c  is started (average of time or distance up to the change from solid to white measured in each position in the axis direction of the lubricant applying brush  47   c  at the start of use), and if the difference from the initial value is equal to or larger than a predetermined value, it is possible to determine that there are stains throughout the entire lubricant applying brush  47   c.    
     If it is determined that the stain level is not equal to or larger than the predetermined value (step S 103 : NO), the controller  10  ends the control. If it is determined that the stain level is equal to or larger than the predetermined value (step S 103 : YES), the process progresses to any of step S 104 , step S 107 , step S 108  or step S 109 . 
     In step S 104 , the controller  10  functions as a changer, and the controller  10  changes the conditions of image forming. Specifically, the rotation speed of the lubricant applying brush  47   c  is increased (step S 105 ). If there is the stain in the lubricant applying brush  47   c , as a result of the lubricant scraped by the lubricant applying brush  47   c  decreasing, the applied amount decreases. Therefore, by increasing the rotation speed, the applied amount increases. Alternatively, the controller  10  raises the pressing force of the solid lubricant  47   e  (step S 106 ). With this, the applied amount of lubricant can be increased. 
     As the change in the image forming conditions, both step S 105  and step S 106  can be performed. 
     In step S 107 , the controller  10  performs the cleaning mode of the lubricant applying brush  47   c . Specifically, there is a method to scrape the stain by placing a blade to collect the stain in the surface of the lubricant applying brush  47   c  into contact, and rotating the lubricant applying brush  47   c  in a state separated from the photoconductor  41  and solid lubricant  47   e.    
     In step S 108 , the controller  10  performs the lubricant applying mode. Specifically, only the photoconductor  41  and the lubricant applying brush  47   c  are rotated, and the rest of the units in the apparatus are stopped. With this, the lubricant is applied to the photoconductor  41 . 
     In step S 109 , the controller  10  performs a call for service. Performing the call for service means, for example, displaying that there is a need to call for service on the display  71  to urge the user to call for service or using the image forming apparatus  1  to notify to a person in charge of maintenance through the network. 
     As described above, when the image forming apparatus  1  according to the present embodiment is in the attached material detection mode of the present embodiment, the developing bias Vdc and/or the voltage Vbrush applied by the voltage applier  47   d  is controlled so that the developing bias Vdc is between the surface potential V 1  of the photoconductor  41  in the region R 1  when the reference voltage is applied to the lubricant applying brush  47   c  and the surface potential V 2  of the photoconductor  41  in the region R 2 . Also, the developing device  44  develops the toner image. Therefore, by analyzing the toner image developed here, the state of the stain attached to the lubricant applying brush  47   c  can be predicted. Consequently, the stain in the lubricant applying brush  47   c  in the axis direction can be accurately detected. 
     In the attached material detection mode, the developing bias Vdc or the voltage Vbrush applied by the voltage applier  47   d  is changed and applied while the photoconductor  41  makes one rotation. Therefore, the surface potential V 1  of the photoconductor  41  in the region R 1  and the surface potential V 2  of the photoconductor  41  in the region R 2  do not have to be obtained in advance in order to perform the above control. 
     The triangular wave control is performed on the developing bias Vdc or the voltage Vbrush applied by the voltage applier  47   d . Therefore, it is possible to determine the attached state of the stain on the lubricant applying brush  47   c  using the average value of the stain level measured repeatedly, and the above is highly accurate. 
     Each time the cycle of the triangular wave changes, the rotation speed of the lubricant applying brush  47   c  is changed at least once. Therefore, it is possible to suppress noise caused by the variation in the stain in the lubricant applying brush  47   c  in the circumferential direction, and the level of the stain can be determined with high accuracy. 
     The inline sensor S detects the intensity of the toner image formed on the photoconductor  41  in the attached material detection mode. Therefore, the variation of the stain in the lubricant applying brush  47   c  in the axis direction can be accurately detected. 
     If the stain level is a predetermined value or more, one of the following is performed, change in the image forming condition, the cleaning mode, the lubricant applying mode, or the call for service. If there is the stain in the lubricant applying brush  47   c , the image noise can be prevented in advance. 
     Second Embodiment 
     The second embodiment of the image forming apparatus is described with reference to the drawings. The same reference numerals are applied to the configuration similar to the first embodiment and the detailed information is omitted. 
     In the first embodiment, the stain level of the lubricant applying brush  47   c  including the lubricant applying function and the cleaning function for the surface of the photoconductor  41  is determined. According to the second embodiment, the stain level of the cleaning brush including the cleaning function for the surface of the photoconductor  41  is described. 
       FIG. 11  shows a functional configuration of the image forming apparatus  1  according to the present embodiment.  FIG. 12  shows a schematic configuration near the image former  4  of the image forming apparatus  1  according to the present embodiment. As shown in  FIG. 11  and  FIG. 12 , the cleaner  47  includes a cleaning blade  47   a , a collecting screw  47   b , a cleaning brush  47   h , and a voltage applier  47   i.    
     The cleaning brush  47   h  is a roll brush positioned in a position in which the tip can come into contact with the photoconductor  41 . The cleaning brush  47   h  includes brush hair including conductive material such as polyester or nylon on the surface and the brush hair is positioned to come into contact with the photoconductor  41 . Under the control of the controller  10 , the cleaning brush  47   h  rotates in a counter rotation in which the surface rotates in the direction opposite to the progressing direction of the surface of the photoconductor  41  at the contact point with the photoconductor  41 . With this, the cleaning brush  47   h  removes the attached material such as the toner which is not transferred remaining on the photoconductor  41 . 
     The voltage is applied to the cleaning brush  47   h  by the voltage applier  47   i  (see  FIG. 11 ). The voltage applied by the voltage applier  47   i  is controlled by the controller  10 . 
     The cleaning brush  47   h  functions as the rotating member. 
     According to the second embodiment, a lubricant is externally added to the toner. Alternatively, a mechanism separate from the cleaning brush is provided to apply the lubricant to the photoconductor  41 . 
     The operation of the image forming apparatus  1  is described below with reference to the flowchart described in  FIG. 13 . The process shown in  FIG. 13  is executed by the controller  10  in coordination with the program stored in the storage  6 . 
     First, the controller  10  determines whether it is the timing to perform the attached material detection mode (step S 201 ). If it is determined that it is the timing to perform the attached material detection mode (step S 201 : YES), the controller  10  progresses the process to step S 202 . If it is determined that it is not such timing (step S 201 : NO), the process in step S 201  is repeated. 
     The attached material detection mode in step S 202  is similar to step S 102 , and therefore the description is omitted. 
     In step S 203 , the controller  10  determines whether the stain level is equal to or larger than a predetermined value, and when the controller  10  determines that the value is equal to or larger than a predetermined value (step S 203 : YES), the process progresses to step S 204 , S 206  or step S 207 . However, if it is determined that it is not the predetermined value or more (step S 203 : NO), the control ends. 
     In step S 204 , the controller  10  functions as a changer to change the image forming condition. Specifically, the controller  10  increases the rotation speed of the cleaning brush  47   h  (step S 205 ). With this, the cleaning properties by the cleaning brush  47   h  to clean the surface of the photoconductor  41  can be enhanced. 
     In step S 206 , the controller  10  performs the cleaning mode of the cleaning brush  47   h . Specifically, there is a method to scrape the stain by placing the blade to collect the stain in the surface of the cleaning brush  47   h  into contact, and rotating the cleaning brush  47   h  in a state separated from the photoconductor  41 . 
     In step S 207 , the controller  10  performs a call for service. 
     As described above, the image forming apparatus  1  according to the present embodiment is able to accurately detect the stain in the cleaning brush  47   h  in the axis direction. 
     If the stain level is equal to or larger than a predetermined value or more, any of the following is performed, the change in the image forming condition, the cleaning mode, or the call for service. With this, it is possible to prevent in advance noise in the image when there is the stain in the cleaning brush  47   h.    
     Other Embodiments 
     The embodiments are described specifically above, but the embodiments described above are merely preferable examples, and the embodiments are not limited to the above. 
     In the embodiments above, the voltage applied to the lubricant applying brush  47   c  or the cleaning brush  47   h  or the developing bias controlled by triangular wave control is described but the embodiments are not limited to the above. 
     For example, the surface potential V 1  of the photoconductor  41  in the region R 1  and the surface potential V 2  of the photoconductor  41  in the region R 2  are measured in advance, and the voltage applied to the lubricant applying brush  47   c  or the cleaning brush  47   h  or the developing bias can be controlled to a certain value so that the developing bias is a value between V 1  and V 2 . 
     According to the present embodiment, the inline sensor S as the detector reads the toner image on the intermediate transfer belt T in the main scanning direction, but the embodiments are not limited to the above. The toner image can be detected on the photoconductor  41  in the axis direction, and the toner image on the photoconductor  41  can be directly read. A post processing device connected downstream of the image forming apparatus  1  can read the image formed on the sheet. 
     Alternatively, the apparatus may not be provided with an inline sensor S, and the image formed on the output sheet may be confirmed by sight by the user. 
     According to the above description, as the computer readable medium including the program to implement the embodiment, examples using a nonvolatile memory or a hard disk are disclosed but the embodiments are not limited to the above. For example, a portable recording medium such as a CD-ROM can be applied as the computer readable medium. A carrier wave is also applied as the medium to provide data of the program according to the embodiments through the communication lines. 
     The detailed configuration and the detailed operation of the devices included in the image forming apparatus can be suitably changed without leaving the scope of the present invention. 
     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 appended claims. 
     The entire disclosure of Japanese Patent Application No. 2018-208518, filed on Nov. 6, 2018, including description, claims, drawings and abstract is incorporated herein by reference in its entirety.