Patent Publication Number: US-11640132-B2

Title: Imaging system with polishing control

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is filed under 35 U.S.C. § 371 as a National Stage of PCT International Application No. PCT/US2019/048565, filed on Aug. 28, 2019, in the U.S. Patent and Trademark Office, which claims the priority benefit of Japanese Patent Application No. 2018-167844, filed on Sep. 7, 2018, in the Japanese Patent Office. The disclosures of PCT International Application No. PCT/US2019/048565 and Japanese Patent Application No. 2018-167844 are incorporated by reference herein in their entireties. 
     BACKGROUND 
     In an image forming apparatus, a surface of an image carrier is uniformly charged, the surface is exposed to form an electrostatic latent image, and the electrostatic latent image is developed by toner to form a toner image on the surface of the image carrier. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram of an example imaging apparatus. 
         FIG.  2    is a graph illustrating an example relationship between the number of rotation cycles of an example image carrier and rotational torque of the image carrier. 
         FIG.  3    is a graph illustrating an example relationship between relative humidity and image flow rank of the example imaging apparatus. 
         FIG.  4    is a schematic cross-sectional view illustrating a part of the example image carrier. 
         FIG.  5    is a schematic diagram illustrating a part of the example imaging apparatus. 
         FIG.  6    is a schematic cross-sectional view of an example polishing roller. 
         FIG.  7    is a schematic cross-sectional view of an example polishing roller. 
         FIG.  8    is a block diagram of an example image carrier polishing system. 
         FIG.  9    is a schematic diagram illustrating an example polishing motion control. 
         FIG.  10    is a schematic diagram illustrating another example polishing motion control. 
         FIG.  11    is a schematic diagram illustrating yet another example polishing motion control. 
         FIG.  12    is a flowchart illustrating an example polishing operation control process. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. An imaging system may include an imaging apparatus such as a printer, an image carrier polishing system or the like mounted on the imaging apparatus, or an imaging component. 
       FIG.  1    is a diagram illustrating a schematic configuration of an example imaging apparatus. An imaging apparatus  1  illustrated in  FIG.  1    may include, for example, an apparatus which forms a color image by using magenta, yellow, cyan, and black. The imaging apparatus  1  includes, for example, a conveying device  10  which conveys a sheet P corresponding to a recording medium, a developing device  20  which develops an electrostatic latent image, a transfer device  30  which secondarily transfers a toner image to the sheet P, an image carrier  40  in which an electrostatic latent image is formed on a surface (a peripheral surface), a fixing device  50  which fixes a toner image to the sheet P, and a discharging device  60  which discharges the sheet P. 
     The conveying device  10  may convey the sheet P corresponding to a recording medium having an image formed thereon on a conveying route R 1 . The sheet P is stacked and accommodated on, for example, a cassette K and is picked up and conveyed by a feeding roller  11 . The conveying device  10  allows the sheet P to reach a transfer nip portion R 2  through the conveying route R 1 , at a timing in which the toner image transferred to the sheet P reaches a transfer nip portion R 2 . 
     The developing device  20  may be provided for each of four colors. Each developing device  20  may include a developing agent carrier  24  which carries toner on the image carrier  40 . In some examples, a two-component developing agent including toner and carrier is used as a developing agent. For example, in the developing device  20 , the toner and the carrier are adjusted to a predetermined or particular mixing ratio and the toner and the carrier are mixed and stirred to uniformly disperse the toner. Accordingly, the developing agent is adjusted to have an optimal charge amount. The developing agent is carried by the developing agent carrier  24 . The developing agent carrier  24  rotates to carry the developing agent to a region facing the image carrier  40 . Then, the toner in the developing agent carried on the developing agent carrier  24  moves to the electrostatic latent image formed on the peripheral surface of the image carrier  40  so that the electrostatic latent image is developed. 
     The sheet P may be conveyed to the transfer nip portion R 2  in which the transfer device  30  secondarily transfers the toner image formed by the developing device  20  to the sheet P. The transfer device  30  includes, for example, a transfer belt  31  to which the toner image is initially transferred from the image carrier  40 , suspension rollers  34 ,  35 ,  36 , and  37  on which the transfer belt  31  are suspended, a primary transfer roller  32  which sandwiches the transfer belt  31  along with the image carrier  40 , and a secondary transfer roller  33  which sandwiches the transfer belt  31  along with the suspension roller  37 . 
     The transfer belt  31  may include an endless belt which moves in a circulating manner by the suspension rollers  34 ,  35 ,  36 , and  37 . Each of the suspension rollers  34 ,  35 ,  36 , and  37  is a roller which is rotatable about each axis. The suspension roller  37  may include a driving roller which rotates about the axis. Each of the suspension rollers  34 ,  35 , and  36  may include a driven roller which is rotated by the rotation of the suspension roller  37 . In some examples, the primary transfer roller  32  is provided to press the image carrier  40  from the inner peripheral side of the transfer belt  31 . The secondary transfer roller  33  is disposed in parallel to the suspension roller  37  with, for example, the transfer belt  31  interposed therebetween and is provided to press the suspension roller  37  from the outer peripheral side of the transfer belt  31 . Accordingly, the secondary transfer roller  33  forms the transfer nip portion R 2  between the transfer belt  31  and the secondary transfer roller. 
     The image carrier  40  may be referred to as an electrostatic latent image carrier, a photosensitive drum, or the like. The image carrier  40  may be provided for each of four colors. Each image carrier  40  may be provided along the movement direction of the transfer belt  31 . In some examples, the developing device  20 , a charging roller  41 , an exposure device  42 , and a cleaning device  43  are provided on the periphery of the image carrier  40 . 
     The charging roller  41  may include a charging member that uniformly charges the surface of the image carrier  40  to a predetermined potential. The charging roller  41  moves, for example, to follow the rotation of the image carrier  40 . The exposure device  42  may be configured to expose the surface of the image carrier  40  charged by the charging roller  41  in response to an image formed on the sheet P. Accordingly, a potential of a portion exposed by the exposure device  42  in the surface of the image carrier  40  changes so that the electrostatic latent image is formed. In some examples, four developing devices  20  form the toner images by developing the electrostatic latent image formed on the image carriers  40  using the toners supplied from toner tanks N respectively facing the developing devices  20 . The toner tanks N are respectively filled with, for example, magenta, yellow, cyan, and black toners. The cleaning device  43  collects the toner remaining on the image carrier  40  after the toner image formed on the image carrier  40  is initially transferred to the transfer belt  31 . 
     The fixing device  50  may be configured to allow the sheet P to pass through a fixing nip portion R 3  for heating and pressing the sheet so that the toner image secondarily transferred from the transfer belt  31  to the sheet P is adhered and fixed to the sheet P. The fixing device  50  may include a heating roller  52  which heats the sheet P and a pressing roller  54  which presses and rotates the heating roller  52 . Each of the heating roller  52  and the pressing roller  54  is formed in, for example, a cylindrical shape and the heating roller  52  includes a heat source such as a halogen lamp. The fixing nip portion R 3  which is a contact region is provided between the heating roller  52  and the pressing roller  54  and the toner image is heated and fixed (e.g., fused) to the sheet P when the sheet P passes through the fixing nip portion R 3 . 
     The discharging device  60  may include discharging rollers  62  and  64  which discharge the sheet P having the toner image fixed thereto by the fixing device  50  to the outside of the apparatus. 
     An example printing process that may be performed by the imaging apparatus  1  will now be described. When an image signal of a recording target image is input to the imaging apparatus  1 , a control device of the imaging apparatus  1  rotates the feeding roller  11  so that the sheet P stacked in the cassette K is picked up and conveyed. Then, the surface of the image carrier  40  is uniformly charged to a predetermined potential by the charging roller  41  (a charging operation). Then, a laser beam is irradiated to the surface of the image carrier  40  by the exposure device  42  based on the received image signal to form an electrostatic latent image (an exposing operation). 
     In the developing device  20 , the electrostatic latent image is developed and a toner image is formed (a developing operation). The toner image which is formed in this way is initially transferred from the image carrier  40  to the transfer belt  31  in a region in which the image carrier  40  and the transfer belt  31  face each other (a transferring operation). The toner images formed on four image carriers  40  are sequentially superimposed on the transfer belt  31  so that one composite toner image is formed. Then, the composite toner image is secondarily transferred to the sheet P conveyed from the conveying device  10  in the transfer nip portion R 2  in which the suspension roller  37  and the secondary transfer roller  33  face each other. 
     The sheet P to which the composite toner image is secondarily transferred is conveyed to the fixing device  50 . Then, the fixing device  50  fuses or otherwise fixes the composite toner image to the sheet P by heating and pressing the sheet P between the heating roller  52  and the pressing roller  54  when the sheet P passes through the fixing nip portion R 3  (a fixing operation). Next, the sheet P is discharged to the outside of the imaging apparatus  1  by the discharging rollers  62  and  64 . 
     Additionally, when the surface of the image carrier  40  is charged by the charging roller  41 , a discharge product (corona product) is generated on the surface of the image carrier  40 . The discharge product may include a substance generated by the activation of ozone, nitrogen oxide, or the like generated at the time of corona discharge or a substance generated by the reaction of these substances. The discharge product may include a nitrogen-based compound such as ammonium oxalate. Then, when the discharge product absorbs moisture, the electric resistance value of the surface of the image carrier  40  is largely decreased. As a result, since the latent image charge formed on the surface of the image carrier  40  flows in the direction of the latent image plane, an electrostatic latent image is not formed and an image flow occurs. The image flow may be understood to mean a phenomenon in which an image flows to be blurred or rubbed. 
       FIG.  2    illustrates a relationship between the number of rotation cycles (k cycle) of the image carrier  40  and the rotational torque (dynamic torque, N·m) of the image carrier  40 . As illustrated in  FIG.  2   , the rotational torque of the image carrier  40  tends to increase when the charging of the surface of the image carrier  40  is continued. Further, since the discharge product has viscosity, the rotational torque of the image carrier  40  increases as the amount of the discharge product generated on the surface of the image carrier  40  increases. For this reason, an increase in rotational torque of the image carrier  40  may be understood to mean that the amount of the discharge product generated on the surface of the image carrier  40  increases. 
       FIG.  3    illustrates a relationship between relative humidity (%) and an image flow rank of the imaging apparatus  1 . The image flow rank is evaluated as six values from 0 to 5, where 0 indicates a rank in which the smallest image flow occurs, and where 5 indicates a rank in which the largest image flow occurs. As illustrated in  FIG.  3   , the image flow rank or degree increases as the discharge product absorbs moisture. Furthermore, the tendency is the same even when absolute humidity is used as the humidity of the imaging apparatus  1 . 
     Since a member such as the transfer belt  31  and the charging roller  41  is in contact with the image carrier  40 , the discharge product generated on the surface of the image carrier  40  is gradually removed with the rotation of the image carrier  40 . However, when a surface  45  of the image carrier  40  includes a protection layer  46  as illustrated in  FIG.  4   , the discharge product generated on the surface of the image carrier  40  is not sufficiently removed. The protection layer  46  protects the surface  45  of the image carrier  40  in order to prolong the life of the image carrier  40 . The protection layer  46  is formed on the entire periphery of the surface  45  of the image carrier  40 . The material of the protection layer  46  includes, for example, a photocurable resin and a metal oxide surface treated with a phosphorus-containing compound. The above-described metal oxide includes one or more materials selected from a group including, for example, tin oxide, zinc oxide, and titanium oxide. The above-described phosphorus-containing compound may include a polymer having on its side chain a phosphorus oxo acid moiety capable of reacting with the metal oxide, a photoreactive moiety, and a lubricating moiety including one or more materials selected from the group including fluorine and silicon. The thickness of the protection layer  46  is, for example, 1.0 μm or more and 10.0 μm or less. 
     As illustrated in  FIG.  5   , the imaging apparatus  1  includes a polishing roller  47 . The polishing roller  47  may be disposed adjacent to the image carrier  40  and polishes the discharge product α formed on the surface  45  of the image carrier  40 . The polishing roller  47  includes, for example, a roller shaft  47   a  and a polishing portion  47   b . The roller shaft  47   a  is supported to be rotatable and is directly or indirectly connected to a rotational driving source such as a motor (not illustrated). The polishing portion  47   b  rotates to polish the discharge product α formed on the surface  45  of the image carrier  40 . 
     The polishing roller  47  may include, for example, a brush roller  47 A illustrated in  FIG.  6   , an elastic roller  47 B illustrated in  FIG.  7   , or other types of similar rollers. The brush roller  47 A may include a plurality of brush bristles  47 Ab which are bristled on a peripheral surface of a roller shaft  47 Aa. In the elastic roller  47 B, for example, a sponge-like elastic body  47 Bb is attached to a peripheral surface of a roller shaft  47 Ba. The elastic body  47 Bb may be made of, for example, urethane, ethylene-propylene-diene rubber (EPDM), and the like. 
     The polishing roller  47  may rotate in a rotational direction different from that of the image carrier  40  or may rotate in the same rotational direction as that of the image carrier  40 .  FIG.  5    illustrates a case in which the polishing roller  47  rotates in a rotational direction different from that of the image carrier  40  as an example. When the polishing roller  47  rotates in the same rotational direction as that of the image carrier  40 , the polishing roller  47  is rotated so that the circumferential speed of the polishing roller  47  is different from that of the image carrier  40 . 
     As illustrated in  FIG.  8   , the imaging apparatus  1  includes an image carrier polishing system  70 . The image carrier polishing system  70  may include a torque detection device  71 , a humidity detection device  72 , a control device  73 , and a memory  74 . 
     The torque detection device  71  detects the torque (rotational torque and dynamic torque) of the image carrier  40 . The torque detection device  71  may include, for example, a torque sensor connected to the rotation shaft of the image carrier  40 . 
     The humidity detection device  72  detects the humidity of the imaging apparatus  1 . The humidity of the imaging apparatus  1  can be set to the humidity inside the imaging apparatus  1  and can be set to the humidity in the vicinity of the image carrier  40 . The humidity of the imaging apparatus  1  may be relative humidity or absolute humidity. The humidity detection device  72  may include, for example, a temperature/humidity meter installed inside the imaging apparatus  1 . 
     The control device  73  may include an electronic control device (computer) for performing a polishing operation control process. The control device  73  is communicatively connected to the torque detection device  71  and the humidity detection device  72 . The memory  74  is a computer readable memory which can be read by the control device  73 . For example, the memory  74  stores a polishing operation control program  75  for performing the polishing operation control process and the control device  73  performs the polishing operation control process by reading the polishing operation control program  75  from the memory  74  and performing the program. In some examples, the polishing operation control program  75  realizes the polishing operation control process in the control device  73 . The control device  73  may be a single electronic control device or a plurality of electronic control devices. The control device  73  may be used to selectively or in some cases exclusively perform the polishing operation control process or may be used to perform other controls of the imaging apparatus  1 . 
     The control device  73  may include a torque acquiring device  76 , a humidity acquiring device  77 , and a polishing operation control device  78 . 
     The torque acquiring device  76  acquires torque detected by the torque detection device  71  from the torque detection device  71 . This acquired torque indicates a characteristic detected by the torque detection device  71 . The humidity acquiring device  77  acquires humidity detected by the humidity detection device  72  from the humidity detection device  72 . This acquired humidity is a characteristic detected by the humidity detection device  72 . 
     The polishing operation control device  78  controls the polishing operation of the polishing roller  47  in response to the detected characteristics. In some examples, the polishing operation control device  78  adjusts a polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  in response to the detected characteristics. 
     The detected characteristics include torque acquired by the torque acquiring device  76 , humidity acquired by the humidity acquiring device  77 , and the like. In some examples, the detected characteristics may be understood to mean the torque acquired by the torque acquiring device  76  and the humidity acquired by the humidity acquiring device  77 . 
     The polishing operation (e.g., the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40 ) can be adjusted by a plurality of adjustment operations, for example, (1) the adjustment of the rotation speed of the polishing roller  47 , (2) the adjustment of the pressure of the polishing roller  47  with respect to the surface  45  of the image carrier  40 , and (3) the adjustment of the abrasive supply amount with respect to the polishing roller  47 . 
     Regarding the adjustment of the rotation speed of the polishing roller  47  (adjustment operation  1 ), the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the rotation speed of the polishing roller  47  increases. Additionally, the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases as the rotation speed of the polishing roller  47  decreases. 
     In some examples, as illustrated in  FIG.  9   , the polishing roller  47  rotates by obtaining a rotational driving force from a rotational driving source  81  such as a motor. Accordingly, the rotation speed of the polishing roller  47  may be selectively varied by adjusting the rotation speed of the rotational driving source  81 . Further, when a gear mechanism  82  is disposed between the rotational driving source  81  and the roller shaft  47   a  of the polishing roller  47 , the rotation speed of the polishing roller  47  may be adjusted by changing the gear ratio (speed reduction ratio) of the gear mechanism  82 . The adjustment of the rotation speed of the rotational driving source  81  can be performed by adjusting, for example, a current amount supplied to the rotational driving source  81 . Additionally, the change of the gear ratio can be performed by using a gear mechanism having a variable gear stage as the gear mechanism  82  and changing the gear stage of the gear mechanism  82 . 
     (Regarding the adjustment of the pressure of the polishing roller  47  with respect to the surface  45  of the image carrier  40  (adjustment operation  2 ), the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the pressure of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases. Additionally, the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases as the pressure of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases. 
     In some examples, with reference to  FIG.  10   , a pressing mechanism  83  presses the surface  45  of the image carrier  40  by the polishing roller  47 . The pressing mechanism  83  may include a support portion  84  and an urging member  85  such as a coil spring disposed between the roller shaft  47   a  of the polishing roller  47  and the support portion  84 . The pressing mechanism  83  presses the roller shaft  47   a  of the polishing roller  47  against the surface  45  of the image carrier  40  by the urging member  85  supported by the support portion  84 . In some examples, when the support portion  84  is moved in a direction moving close to and away from the roller shaft  47   a , the pressure of the polishing roller  47  with respect to the surface  45  of the image carrier  40  can be adjusted. For example, the movement of the support portion  84  can be performed by fitting the support portion  84  to a guide rail (not illustrated) extending in a direction moving close to and away from the roller shaft  47   a  and moving the support portion  84  along the guide rail by an electric motor (not illustrated) such as a motor. 
     Regarding the adjustment of the abrasive supply amount with respect to the polishing roller  47  (adjustment operation  3 ), the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the abrasive supply amount with respect to the polishing roller  47  increases. Additionally, the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases as the abrasive supply amount with respect to the polishing roller  47  decreases. 
     In some examples, with reference to  FIG.  11   , an abrasive supply device  86  may supply an abrasive such as toner to the polishing roller  47 . The abrasive supply device  86  increases the polishing force of the polishing roller  47  by supplying the abrasive to the polishing roller  47 . In some examples, when the abrasive supply amount from the abrasive supply device  86  to the polishing roller  47  is adjusted, the pressure of the polishing roller  47  with respect to the surface  45  of the image carrier  40  can be adjusted. When the toner is used as the abrasive, for example, the abrasive can be removed from the polishing roller  47  by adhering the abrasive to a flicker roller to which a voltage is applied and scraping off the abrasive adhered to the flicker roller with a scraper. Further, when the toner is used as the abrasive, the toner moved from the polishing roller  47  to the image carrier  40  can be collected by the cleaning device  43 . 
     The control device  73  may be configured to control the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the humidity of the imaging apparatus  1  increases. Additionally, the control device  73  may control the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases as the humidity of the imaging apparatus  1  decreases. The control of the polishing operation of the polishing roller  47  may be continuously or incrementally performed in response to the humidity of the imaging apparatus  1 . When the control of the polishing operation of the polishing roller  47  is performed incrementally (stepwise), the control device  73  adjusts, for example, the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases when the humidity of the imaging apparatus  1  becomes higher than the reference humidity. Additionally, the control device  73  may adjust the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases when the humidity of the imaging apparatus  1  becomes equal to or lower than the reference humidity. The reference humidity may be an arbitrary value that is set to, for example, the humidity determined by experiments or the like when the image flow occurs. 
     The control device  73  may be configured to control the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the torque of the image carrier  40  increases. Additionally, the control device  73  controls, for example, the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases as the torque of the image carrier  40  decreases. The control of the polishing operation of the polishing roller  47  may be performed either continuously or stepwise in response to the torque of the image carrier  40 . When the control of the polishing operation of the polishing roller  47  is performed stepwise, the control device  73  adjusts, for example, the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases when the torque of the image carrier  40  becomes larger than the reference torque. Additionally, the control device  73  may be configured to adjust the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases when the torque of the image carrier  40  becomes equal to or smaller than the reference torque. The reference torque may be an arbitrary value that is set to, for example, the torque obtained by experiments or the like when the thickness of the discharge product becomes a predetermined value. 
     A example control process of the polishing operation which may be performed by the control device  73  will now be described with reference to  FIG.  12   . The process may be performed by the control device  73  by, for example, reading the polishing operation control program  75  from the memory  74  and performing the program. Furthermore, part of the operations shown below may be performed at the same time or may be performed in a different order from that shown. 
     As illustrated in  FIG.  12   , the control device  73  uniformly charges the surface  45  of the image carrier  40  to a predetermined potential by the charging roller  41  (operation S 1 ). Accordingly, the discharge product α is generated on the surface  45  of the image carrier  40 . 
     At operation S 2 , the control device  73  polishes the discharge product α generated on the surface  45  of the image carrier  40  by the charging of the image carrier  40  by the polishing roller. At this time, the control device  73  may perform the polishing operation of the polishing roller  47  in a condition set to an initial value. 
     At operation S 3 , the control device  73  acquires the torque acquired by the torque acquiring device  76  and the humidity acquired by the humidity acquiring device  77  as the detected characteristics. 
     Then, the control device  73  controls the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the torque acquired by operation S 3  increases. Further, the control device  73  controls the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the humidity acquired by operation S 3  increases. The control device  73  may control the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases as the torque acquired by operation S 3  increases. 
     In some examples, the control device  73  determines whether the torque acquired by operation S 3  is larger than the reference torque (operation S 4 ). When it is determined that the torque acquired by operation S 3  is larger than the reference torque (operation S 4 : YES), the control device  73  then determines whether the humidity acquired by operation S 3  is higher than the reference humidity (operation S 5 ). When it is determined that the humidity acquired by operation S 3  is higher than the reference humidity (operation S 5 : YES), the control device  73  controls the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  increases (operation S 6 ). Additionally, when it is determined that the torque acquired by operation S 3  is equal to or smaller than the reference torque (operation S 4 : NO) or the humidity acquired by operation S 3  is equal to or lower than the reference humidity (operation S 5 : NO), the control device  73  controls the polishing operation of the polishing roller  47  so that the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  decreases (operation S 7 ). 
     The control of the polishing operation of the polishing roller  47  is performed by a plurality of adjustment operations, for example, (1) the adjustment of the rotation speed of the polishing roller  47 , (2) the adjustment of the pressure of the polishing roller  47  with respect to the surface  45  of the image carrier  40 , and (3) the adjustment of the abrasive supply amount with respect to the polishing roller  47 . 
     In some examples, since the discharge product α is generated on the surface  45  of the image carrier  40  by the charging of the image carrier  40 , the discharge product α is polished by the polishing roller  47 . Additionally, the control device  73  can appropriately remove the discharge product α from the surface  45  of the image carrier  40  in order to control the polishing operation of the polishing roller  47  in response to the detected characteristics. Accordingly, the occurrence of the image flow may be prevented. 
     The control device  73  can readily adjust the polishing force of the polishing roller  47  with respect to the surface  45  of the image carrier  40  by adjusting the rotation speed of the polishing roller (adjustment operation  1 ), by adjusting the pressure of the polishing roller with respect to the surface of the image carrier (adjustment operation  2 ), or by adjusting the abrasive supply amount with respect to the polishing roller  47  as the polishing operation of the polishing roller  47  (adjustment operation  3 ). 
     The control device  73  can effectively prevent the occurrence of the image flow by controlling the polishing operation of the polishing roller  47  based on the humidity of the imaging apparatus  1  and the torque of the image carrier  40 . 
     When the polishing roller  47  and the image carrier  40  rotate in different rotational directions, a rotational friction is generated between the polishing roller  47  and the image carrier  40  regardless of the rotation speed of the polishing roller  47 . Accordingly, the discharge product α generated on the surface  45  of the image carrier  40  may be polished. Additionally, since the polishing roller  47  is rotated so that the circumferential speed of the polishing roller  47  is different from the circumferential speed of the image carrier  40  when the polishing roller  47  and the image carrier  40  rotate in the same rotational direction, a rotational friction is generated between the polishing roller  47  and the image carrier  40 . Accordingly, the discharge product α generated on the surface  45  of the image carrier  40  may be polished. 
     It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail.