This application is based on Japanese Patent Application No. 2006-102847 filed on Apr. 4, 2006, the content of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a sheet feeding device used for an image forming apparatus such as a copier, a printer, a facsimile, and a multi-functional machine having the functions thereof and more particularly to a sheet feeding device having a cleaning member for removing foreign substances such as paper dust adhered to the outer peripheral surface of a conveying member and an image forming apparatus having the sheet feeding device. 
   Conventionally, a foreign substance removing device of the image forming apparatus makes a fixing type cleaning member (a flexible member such as a brush, felt, or a PET sheet) touch a roller member for conveying recording sheets, thereby removes foreign substances such as paper dust. Further, it makes a cleaning roller (a brush, felt, etc.) touch conveyed recording sheets, thereby removes foreign substances such as paper dust. 
   For example, Unexamined Japanese Patent Application Publication No. 11-52641 discloses a foreign substance removing device for making a fixed type cleaning member such as felt touch a conveying roller, thereby cleaning the surface of each recording sheet by the conveying roller. 
   Unexamined Japanese Patent Application Publication No. 11-208918 makes a brush touch a cleaning roller for cleaning conveyed recording sheets, thereby cleans the cleaning roller. 
   Unexamined Japanese Patent Application Publication No. 08-314344 is of a type of making a cleaning roller touch conveyed recording sheets. 
   Unexamined Japanese Patent Application Publication No. 2004-224451 makes a rotating brush roller touch a conveying roller, thereby cleans the conveying roller, makes a rotary roller touch the brush roller, thereby cleans the brush roller, and furthermore makes a flexible sheet touch the brush roller, thereby cleans the rotary roller. 
   Unexamined Japanese Patent Application Publication No. 2004-137076 (paragraph 0101, FIG. 9(a)), in a case that a conveying roller and a foreign substance removing member are rotated in the opposite direction and a case that they are rotated in the same direction, provides a speed difference between the moving speed of the tip of the foreign substance removing member and the moving speed of the peripheral surface of the conveying roller. 
   When feeding recorded sheets, particularly offset-printed sheets to the sheet feeding device arranged in the image forming apparatus or finisher, dusting powder or ink sludge adhered to a sheet and a coating agent on the sheet surface are adhered to the outer peripheral surfaces of the feed roller and conveying roller, thus the conveying force of the feed roller and conveying roller is lowered, and the sheet conveying performance becomes unstable. Therefore, it is necessary to clean the conveying roller. 
   However, in the foreign substance removing device for making a fixing type cleaning member touch the aforementioned feed roller and conveying roller, thereby removing foreign substances or making a cleaning roller such as a rotating brush touch a conveyed transfer material, thereby removing foreign substances and in the image forming apparatus using it, foreign substances such as paper dust cannot be stably removed over a long period of time, thus a problem arises that entering of foreign substances into the transfer area cannot be reduced for a long time. 
   Further, in the feed roller system of a reverse roller type, foreign substance stains such as paper dust adhered to the rotary rollers such as the pickup roller and feed roller are cleaned by pressing a flexible member such as a raising member like moquette, foamed polyurethane, or a PET sheet to the rollers. However, the raising member and flexible member cannot separate scraped foreign substances from the rollers, so that the cleaning effect is not continued, and it is necessary to periodically clean or exchange the cleaning member and rollers. 
   In the image forming apparatus disclosed in Unexamined Japanese Patent Application Publication No. 11-52641, foreign substances such as paper dust are collected immediately in the cleaning member, and unremovable foreign substances such as paper dust are conveyed into the transfer area, thus there is a problem imposed in the durability. 
   In the image forming apparatus disclosed in Unexamined Japanese Patent Application Publication No. 11-208918, a speed difference is provided between the cleaning roller and the transfer material, so that a problem arises that an unstable element is given to conveyance of the transfer material. 
   In the image forming apparatus disclosed in Unexamined Japanese Patent Application Publication No. 08-314344, at the point of time when foreign substances such as paper dust are collected on the surface of the cleaning roller, the effect is lost and there is a problem imposed in the durability. 
   In the image forming apparatus disclosed in Unexamined Japanese Patent Application Publication No. 2004-224451, unless the rubber of the conveying roller and the material of the cleaning member are set appropriately, stable sheet conveyability and a high effect cannot be obtained. 
   In the foreign substance removing apparatus disclosed in Unexamined Japanese Patent Application Publication No. 2004-137076, when the conveying roller and brush of the foreign substance removing member are rotated in the opposite direction, it is described to make the brush touch the peripheral surface of the conveying roller so as to move relatively. However, the relationship between the moving speed of the sliding section of the front end of the brush and the moving speed of the outer peripheral surface of the conveying roller is not described. 
   Further, the pickup roller of the sheet feeding device must send surely sheets to the feed roller and the pressurizing force of the pickup roller to sheets must be set to an appropriate load. To give a stable and appropriate load, a system of applying pressurizing force by the own weights of the pickup roller and holder is effective. However, in this case, when the cleaning mechanism for cleaning the pickup roller is made larger, a problem arises that an appropriate load cannot be given. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a sheet feeding device for eliminating the aforementioned faults, enabling removal of foreign substances such as paper dust over a long period of time, reducing entry of foreign substances into the transfer area, realizing miniaturization of the cleaning mechanism, and obtaining a good image quality and an image forming apparatus using the concerned device. 
   The above object can be accomplished by the structures indicated below. 
   1. A sheet feeding device having a cleaning member for cleaning the outer peripheral surface of a conveying member of a conveying unit for conveying sheets in sliding contact with it, wherein the conveying member and cleaning member are rotated in the same tangential direction at the sliding contact position, and assuming the linear speed of the outer peripheral surface of the conveying member during rotation as V 1  and the linear speed of the sliding portion of the cleaning member during rotation as V 2 , so as to satisfy the relationship of V 1 &gt;V 2 , the conveying member and cleaning member are controlled in driving. 
   2. An image forming apparatus comprising the sheet feeding device described in the above structure 1 and an image forming section for forming an image on a sheet fed from the sheet feeding device. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of the image forming apparatus composed of the image forming apparatus main body, finisher, large capacity sheet feeding device, and automatic document feeder. 
       FIG. 2  is a cross sectional view of the second sheet feeding unit of the image forming apparatus main body. 
       FIGS. 3(   a ) and  3 ( b ) are plane cross sectional views of the sheet feeding device. 
       FIGS. 4(   a ) and  4 ( b ) are a plane cross sectional view and a front view showing the rotation driving mechanism of the cleaning brush. 
       FIG. 5  is a cross sectional view of the cleaning unit of a comparative example having a fixed brush. 
       FIG. 6  is a characteristic diagram of the measured results of changes in the coefficient of friction of the outer peripheral surface of the feed roller. 
   


   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Next, the image forming apparatus of the present invention will be explained with reference to the accompanying drawings. 
   [Image Forming Apparatus] 
     FIG. 1  is a schematic view of the image forming apparatus composed of an image forming apparatus main body A, a finisher FS, a large capacity sheet feeding device LT, and an automatic document feeder DF. 
   The image forming apparatus main body A includes an image forming section  1 , a fixing device  9 , and a sheet conveying system. The image forming section  1  is composed of a charging unit  3  arranged around an image carrier  2 , an image exposure unit  4 , a developing unit  5 , a transferring unit  6 , a discharging unit  7 A, a separation claw  7 B, and a cleaning unit  8 . 
   The sheet conveying system is constituted by a first conveying section composed of a sheet feeding cassette (sheet storing section)  10 , a first sheet feeding unit  11 , a second sheet feeding unit  12 , a conveying unit  13 , a sheet ejecting unit  14 , and a manual sheet feeding unit  15  and a sheet circulating and re-feeding section for circulating and re-feeding sheets S. 
   The sheet feeding cassette  10  and first sheet feeding unit  11  are formed by a plurality of sheet feeding units (three stories shown in  FIG. 1 ) and store and feed the sheets S of several kinds of sizes. 
   The sheets S sent from a sheet feeding device  20  of the large capacity sheet feeding device LT are sent to the second sheet unit  12 . 
   A document “d” loaded on the document table of the automatic document feeder DF is conveyed by a document feeding device  21  and the document image is read by the image reading device. 
   In the image forming section  1 , the processes of charging, exposing, developing, transferring, separating, and cleaning are performed. Each of the sheets S sent from the sheet feeding cassette  10 , manual sheet feeding unit  15 , and large capacity sheet feeding device LT is transferred an image by the transferring unit  6 . The sheet S carrying the image is fixed by the fixing unit  9 , is ejected from the sheet ejecting unit  14 , and is sent to the finisher FS. 
   The finisher FS is composed of an inlet conveying section  30 , a shifting unit  31 , a stacking unit  32 , a stapling unit  33 , a cover sheet feeding unit  34 , and a sheet ejecting unit  35 . 
   [Finisher] 
   Cover sheet K fed by the cover sheet feeding unit  34  is conveyed by the conveyance roller group and is stored in the stacking unit  32 . The cover sheet K is stacked on a plurality of sheets S stored in the stacking unit  32  and form a front cover sheet and a back cover sheet. Further, the cover sheet K can be used as an inserting sheet inserted between the plurality of sheets S. 
   When sheets S of a predetermined number are stacked and aligned in the stacking unit  32 , stapling needles are stuck at two locations of the sheets S or at one location in one corner of the sheets S by the stapling unit  33 , thus the sheets S are bound, and a booklet is prepared. 
   The sheets S bound are interposed and conveyed by the sheet ejecting unit  35  and are ejected and stacked on a main tray  36 . 
   [Sheet Feeding Device] 
   The sheet feeding device can be applied to the first sheet feeding unit  11  and manual sheet feeding unit  15  of the sheet feeding cassette (sheet storing section)  10  arranged in the image forming apparatus main body A, the sheet feeding device  20  of the large capacity sheet feeding device LT, the document feeding device  21  of the automatic document feeder DF, and the cover sheet feeding unit  34  of the finisher FS. 
     FIG. 2  is a cross sectional view of the second sheet feeding unit  12  of the image forming apparatus main body A shown in  FIG. 1 . 
   The second sheet feeding unit  12  includes a first cleaning member (hereinafter, referred to as a cleaning brush)  123  composed of a drive roller (conveying member)  121  for interposing and conveying the sheets S, a driven roller  122 , and a cleaning brush rotating in sliding contact with the drive roller  121 , a second cleaning member  124  for rotating in sliding contact with the cleaning brush  123 , and a third flexible cleaning member  125  in contact with the outer peripheral surface of the second cleaning member  124 . 
   The drive roller  121  is driven to rotate clockwise, and the cleaning brush  123  is driven to rotate counterclockwise by a drive unit not drawn, and the second cleaning member  124  is driven to rotate clockwise by a drive unit not drawn. The third cleaning member  125  is in pressure contact with the outer peripheral surface of the second cleaning member  124  counter to the rotation thereof. 
   The cleaning brush  123  is formed by a conductive brush. The specifications and characteristics of the conductive brush will be described later. The specifications and characteristics of the drive roller  121  will also be described later. 
     FIGS. 3(   a ) and  3 ( b ) are plane cross sectional views of the sheet feeding device, and  FIG. 3(   a ) shows the state before start of sheet feed, and  FIG. 3(   b ) shows the state at time of sheet feed. 
   Further, the manual sheet feeding unit  15 , the sheet feeding device  20  of the large capacity sheet feeding device LT, the document feeding device  21  of the automatic document feeder DF, and the cover sheet feeding unit  34  of the finisher FS have an almost similar structure as that of the first sheet feeding unit  11 , so that hereinafter, the first sheet feeding unit  11  will be explained as representation. 
   The sheets S loaded on a rise-and-fall plate  101  in the sheet feeding cassette  10  move up by a rise-and-fall member  102  moving up and down by a motor not drawn and when the top of the sheets S reaches a predetermined position where it makes contact with the outer peripheral surface of a pickup roller (first conveying member)  111 , the top of the sheets S is detected by a sensor not drawn, and the rise-and-fall plate  101  stops rising. 
   At the upper limit position of the sheets, a predetermined pressure P 1  is applied to the top of the sheets S by the own weights of the pickup roller  111  and a holder  114 . 
   By a sheet feed signal, the pickup roller  111  and a feed roller (second conveying member)  112  start rotation. The pickup roller  111  making pressure contact with the top of the sheets S at the predetermined pressure P 1  sends the sheets S to the nip position between the feed roller  112  and a multi-feed prevention roller (reverse roller)  113 , and then separates from the sheet surface. 
   The multi-feed prevention roller  113  is driven in the opposite direction of the conveying direction of the sheets S via a torque limiter not shown and makes pressure contact with the feed roller  112  at a predetermined pressure P 2  by a spring not drawn. 
   The multi-feed prevention roller  113 , when there exist no sheets S at the nip position and the feed roller  112  directly makes contact or when one sheet S is sent to the nip position, since the torque limiter slides at more than the limit torque, rotates by following the feed roller  112 , thereby conveys the one sheet S. 
   However, when two or more sheets S are sent to the nip position, the limit torque overcomes the frictional force between the sheets, rotates reversely the multi-feed prevention roller  113 , presses back the lower side sheets S, prevents feeding of a large number of sheets, thereby conveys one sheet S. 
   When the sheet feed start signal is input, the pickup roller  111  swings around the rotary shaft of the feed roller  112  and makes contact with the top of the sheets S by its own weight. Simultaneously, an electromagnetic clutch CL which will be described later is put into the connection state, and the feed roller  112  starts rotation, and furthermore, the pickup roller  111  starts rotation by a drive transmission unit which will be described later. 
   The sheets S are sent out by the rotation of the pickup roller  111 , are conveyed to the nip position where the feed roller  112  and multi-feed prevention roller  113  make pressure contact with each other, are handled one by one, and reach a conveyance roller pair  115  on the downstream side in the conveying direction. Incidentally, the first sheet feeding unit  11  and the conveyance roller pair  115  constitute a conveying unit. 
   When a sensor not drawn detects arrival of the sheets S at the conveyance roller pair  115 , the electromagnetic clutch CL enters the non-contact state, and the sheets S, by interposing and conveying by the conveyance roller pair  115 , are pulled out and conveyed from the nip position where the feed roller  112  and multi-feed prevention roller  113  make pressure contact with each other. 
   [Cleaning Member] 
   On the first document feeding unit  11 , above the space where the pickup roller  111  and feed roller  112  face each other, a first cleaning member (hereinafter, referred to as a cleaning brush)  116 , a second cleaning member  117 , a third cleaning member  118 , and a covering member  119  are arranged. 
   The cleaning brush  116  rotates in sliding contact with the outer peripheral surface of the pickup roller  111  and the outer peripheral surface of the feed roller  112 . The cleaning brush  116  is rotated by a driving unit, which will be described later and rotates counterclockwise as shown in the drawing. The cleaning brush  116  and pickup roller  111  rotate with a speed difference in the same direction at the sliding contact position. The cleaning brush  116  and feed roller  112  rotate with a speed difference in the same direction at the sliding contact position. 
   The cleaning brush  116  comes in sliding contact with the feed roller  112 , thereby removes paper dust and foreign substances adhered to them. 
   Specification of the cleaning brush  116 : 
   Brush of an electromagnetic acrylic material;
         Thickness of bristles of 6.25 deniers (One denier means a thickness of fibers with a weight of 50 mg per a length of 450 m.)   Density of bristles of 100000 pieces per (25.4 mm) 2      Outside diameter of 16 mm   Length of bristles of 4 mm       

   Both the overlap amount of the pickup roller  111  and cleaning brush  116  and the overlap amount of the feed roller  112  and cleaning brush  116  are set at 0.5 mm to 1.5 mm. 
   The second cleaning member  117  is a rotary roller rotated by the driving unit in sliding contact with the cleaning brush  116 . The second cleaning member  117  refreshes the cleaning brush  116  by removing paper dust and foreign substances adhered to it. 
   The third cleaning member  118  is formed by a flexible thin plate, for example, a PET (polyethylene terephthalate) sheet in contact with the outer peripheral surface of the second cleaning member  117 . The tip portion of the third cleaning member  118  makes pressure contact with the outer peripheral surface of the second cleaning member  117  counter to the rotation thereof. The third cleaning member  118  removes paper dust and foreign substances adhered to the second cleaning member  117  and shields the space above the pickup roller  111 . 
   The covering member  119  is arranged at the symmetrical position to the third cleaning member  118  and is formed by a flexible thin plate, for example, a PET (polyethylene terephthalate) or urethane sheet in contact with the outer peripheral surface of the second cleaning member  117 . The tip portion of the covering member  119  is in slight contact with the outer peripheral surface of the second cleaning member  117  with trailing the rotation thereof. The covering member  119  removes paper dust and foreign substances adhered to the second cleaning member  117  and shields the space above the feed roller  112 . 
   When taking out sheets S defective in conveyance in the first sheet feeding unit  11  and lifting up the pickup roller  111  and swinging upward around the feed roller shaft, the space above the cleaning brush  116  is covered with the third cleaning member  118  and covering member  119 , so that paper dust and foreign substances around the second cleaning member  117  are prevented from leaking out. 
   When the brush of the cleaning member for cleaning the surface of the conveying roller in sliding contact with the conveying rubber roller is not conductive, the rubber roller surface is charged, and problems arise that stains due to paper dust and foreign substances adhered to the surface of the conveying rubber roller are hardly removed and the sheet surfaces are charged, thus in the transfer section of the image forming apparatus main body A, defective image transfer is caused. Therefore, it is preferable to give conductivity to the cleaning brush. 
   Particularly, the cleaning brush  116  for cleaning the pickup roller  111  and feed roller  112  must be miniaturized. However, the miniaturization has its limit and the outside diameter of the core bar wound with a raising brush must be about 6 mm at its minimum from the viewpoint of strength, though to fulfill a stable cleaning function, the outside diameter is preferably about 8 mm. 
   The bristle length of the cleaning brush  116  must be 3 mm or more. Therefore, when the core bar and bristle length are joined, the outside diameter of the cleaning brush  116  must be 14 mm or more. 
   [Rotation Driving Mechanism of the Cleaning Brush] 
     FIG. 4(   a ) is a plane cross sectional view showing the rotation driving mechanism of the cleaning brush  116  and  FIG. 4(   b ) is a front view thereof. 
   A driving source not drawn is connected to a coupling  110  and rotates continuously a gear G 1 . The gear G 1  meshes with a gear G 2  and rotates a rotary shaft  110 A. The electromagnetic clutch CL installed at the shaft end of the rotary shaft  110 A turns on or off rotation drive of the rotary shaft  110 A. 
   When the electromagnetic clutch CL enters the connection state, the rotary shaft  110 A rotates and the feed roller  112  rotates clockwise as shown in the drawing. A gear G 3  fixed to the rotary shaft  110 A of the feed roller  112  rotates a gear G 5  fixed to the shaft end of a rotary shaft  110 C of the pickup roller  111  via a gear G 4 . Therefore, both the feed roller  112  and pickup roller  111 , as shown in  FIG. 4(   b ), rotate clockwise. 
   To a rotary shaft  110 B of the gear G 4 , the cleaning brush  116  is fixed and rotates counterclockwise together with the rotary shaft  110 B as shown in the drawing. 
   A gear G 6  fixed to the other end of the rotary shaft  110 B rotates a gear G 7  fixed to a rotary shaft  110 D of the second cleaning member  117 . By the rotation of the gear G 7 , the second cleaning member  117  rotates clockwise as shown in the  FIG. 2 . 
   A holder  114  of the first sheet feeding unit  11  bears rotatably the rotary shaft  110 A, rotary shaft  110 B, and second cleaning member  117  and fixes the third cleaning member  118  and one end of the covering member  119 . The tip portion of the third cleaning member  118  is in pressure contact with the outer peripheral surface of the second cleaning member  117  counter to the rotation thereof. The tip portion of the covering member  119  is in pressure contact with the outer peripheral surface of the second cleaning member  117  with trailing the rotation thereof. 
   The holder  114  of the first sheet feeding unit  11  is supported rotatably around the rotary shaft  110 A of the feed roller  112 . During sheet feed, the stop of the upper mechanism of the first sheet feeding unit  11  composed of the pickup roller  111 , cleaning brush  116 , second cleaning member  117 , third cleaning member  118 , covering member  119 , and holder  114  is canceled and the pickup roller  111  swings and pressurizes the top of the sheets S stored in the sheet feeding cassette  10  at the predetermined pressure P 1  by its own weight and sends out the sheets S. 
   The cleaning unit composed of the cleaning brush  116 , second cleaning member  117 , third cleaning member  118 , and covering member  119  is formed small and light, so that it holds the predetermined pressure P 1  and can send out surely a minimum number of sheets S. 
   Particularly, the cleaning brush  116  and second cleaning member  117  are installed compatibly with the pickup roller  111  and feed roller  112 , thus the first sheet feeding unit  11  can be made smaller and lighter. By doing this, the degree of freedom of design of the first sheet feeding unit  11  having a constitution of sending appropriately sheets at the pressure by its own weight is made wider. 
   Further, foreign substances adhered to the surface of the pickup roller  111  from each surface of the sheets S and foreign substances adhered to the surface of the feed roller  112  from each surface of the sheets S are cleaned surely by the cleaning unit composed of the cleaning brush  116 , second cleaning member  117 , third cleaning member  118 , and covering member  119 . 
   Further, foreign substances adhered to the surface of the multi-feed prevention roller  113  from each rear of the sheets S and furthermore transferred to the feed roller  112  are also cleaned surely by the cleaning unit composed of the cleaning brush  116 , second cleaning member  117 , third cleaning member  118 , and covering member  119 . 
     FIG. 5  is a cross sectional view of the cleaning unit of a comparative example having a fixed brush. Further, with respect to the numerals used in the drawing, to the same sheet feeding mechanism as that shown in  FIG. 3 , the same numerals are assigned. 
   On the upper part of the pickup roller  111 , a cleaning member (cleaning brush)  116 A fixed to the support plate is arranged. The cleaning member  116 A removes foreign substances adhered to the outer peripheral surface of the pickup roller  111  in sliding contact with the outer peripheral surface of the pickup roller  111 . 
   On the upper part of the feed roller  112 , a cleaning member (cleaning brush)  116 B fixed to the support plate is arranged. The cleaning member  116 B removes foreign substances adhered to the outer peripheral surface of the feed roller  112  in sliding contact with the outer peripheral surface of the feed roller  112 . 
   On the upper part of a drive roller  115 A of the conveyance roller pair  115 , a cleaning member (cleaning brush)  116  is arranged. The cleaning member  116 C removes foreign substances adhered to the outer peripheral surface of the drive roller  115 A in sliding contact with the outer peripheral surface of the drive roller  115 A. 
   
     
       
             
             
           
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
           
           
             
                 
                 
             
             
                 
               Cleaning brush (116) 
             
           
        
         
             
                 
               Feed roller (112) 
                 
                 
               Relative 
             
           
        
         
             
                 
                 
                 
                 
               Linear 
                 
                 
                 
               Linear 
               linear 
             
             
                 
               Linear 
               Outside 
               Constant 
               speed 
               Overlap 
               Outside 
               Constant 
               speed 
               speed 
             
             
                 
               speed 
               diameter 
               of gear 
               ratio 
               amount 
               diameter 
               of gear 
               ratio 
               ratio 
             
             
                 
               relationship 
               (mm) 
               G3 
               (V1) 
               (mm) 
               (mm) 
               G4 
               (V2) 
               V2 − V1 
             
             
                 
                 
             
           
        
         
             
               Example 
               V1 &gt; V2 
               32 
               33 
               1 
               1.23 
               16 
               23 
               0.72 
               −0.28 
             
             
               Comp. 
               V1 &lt; V2 
               32 
               21 
               1 
               1.23 
               14 
               18 
               1.49 
               0.49 
             
             
                 
             
             
               Comp.: Comparative example 
             
           
        
       
     
   
   Table 1 shows an example of the feed roller  112  and cleaning brush  116 . 
   In  FIGS. 4(   a ) and  4 ( b ), the gear G 3  fixed to the rotary shaft  110 A of the feed roller  112  meshes with the gear G 4  fixed to the rotary shaft  110 B and rotates the cleaning brush  116 . 
   Example 
   Assuming the outside diameter of the feed roller  112  as 32 mm, the number of teeth of the gear G 3  as  33 , the outside diameter of the cleaning brush  116  as 16 mm, and the number of teeth of the gear G 4  as 23, for the linear speed V 1  of the feed roller  112 , the linear speed V 2  of the cleaning brush  116  is 0.72, and the relative linear speed (V 1 −V 2 ) is −0.28, and V 1 &gt;V 2  results. 
   Comparative Example 
   Assuming the outside diameter of the feed roller  112  as 32 mm, the number of teeth of the gear G 3  as 21, the outside diameter of the cleaning brush  116  as 14 mm, and the number of teeth of the gear G 4  as 18, for the linear speed V 1  of the feed roller  112 , the linear speed V 2  of the cleaning brush  116  is 1.49, and the relative linear speed (V 1 −V 2 ) is −0.49, and V 1 &lt;V 2  results. 
   Further, in the example and comparative example, the overlap amounts of the outside diameter of the cleaning brush  116  shifted into the outside diameter of the feed roller  112  are all 1.23 mm. 
     FIG. 6  is a characteristic diagram of the measured results of changes in the coefficient of friction of the outer peripheral surface of the feed roller  112 . 
   With respect to the cleaning system, the four systems indicated below are compared and investigated. 
   (a) Example 
   The rotary cleaning brush  116  is used, and the cleaning brush  116  and feed roller  112  are rotated in the same tangential forward direction at the sliding contact position, and assuming the linear speed of the outer peripheral surface of the feed roller  112  during rotation as V 1  and the linear speed of the sliding contact section at the tip of the cleaning brush  116  as V 2 , V 1 &gt;V 2  is set. 
   (b) Comparative Example 1 
   The rotary cleaning brush  116  is used, and the cleaning brush  116  and feed roller  112  are rotated in the same tangential forward direction at the sliding contact position, and assuming the linear speed of the outer peripheral surface of the feed roller  112  during rotation as V 1  and the linear speed of the sliding contact section at the tip of the cleaning brush  116  as V 2 , V 1 &lt;V 2  is set. 
   (c) Comparative Example 2 
   The rotary cleaning brush  116  is used and the cleaning brush  116  and feed roller  112  are rotated in the tangential opposite direction at the sliding contact position. 
   (d) Comparative Example 3 
   A sheet feeding device having an arranged fixed cleaning brush shown in  FIG. 5 . 
   When the roller surface is stained by dusting powder, paper dust, and ink sludge, in the surface states of the pickup roller  111  and feed roller  112 , as the surface roughness Rz (ten-point average roughness) gets worse, a higher coefficient of friction μ is obtained. 
   In the sheet feeding device of the present invention, when the electromagnetic clutch CL is connected, for the pickup roller  111  and feed roller  112 , the cleaning brush  116  rotates in the same direction in the linear speed relationship of V 1 &gt;V 2  and stains of foreign substances such as paper dust, dusting powder, and ink sludge are transferred from the pickup roller  111  and feed roller  112  to the cleaning brush  116 . Foreign substances adhered to the cleaning brush  116  are collected by the second cleaning member  117  and then is removed by the third cleaning member  118 . 
   When the electromagnetic clutch CL is disconnected, the feed roller  112  is drawn by the sheets S held and conveyed by the conveyance roller pair  115  and is rotated at the linear speed V 1 , though the cleaning brush  116  is stopped, and the linear speed V 2  of the tip of the cleaning brush  116  is zero. However, also in this state, the pickup roller  111  and feed roller  112  are driven to rotate at the linear speed V 1 , so that the relationship of linear speeds of V 1 &gt;V 2  is kept unchanged. While the cleaning brush  116  is stopped, foreign substances collected at a predetermined location of the cleaning brush  116  are collected by the second cleaning member  117  at feed start time of the succeeding sheets S and then are removed by the third cleaning member  118 . 
   Further, also in the second sheet feeding unit  12  shown in  FIG. 2 , the cleaning brush  123  rotating forward in the linear speed relationship of V 1 &gt;V 2  cleans the outer periphery surface of the conveying roller  121  in contact with it. Further, the cleaning brush  123  is refreshed by the second cleaning member  124  and is cleaned more surely by the third cleaning  125 . 
   Generally, the pickup roller  111  and feed roller  112  which are covered with EDPM rubber with a high coefficient of friction μ have high sheet conveying force at an early stage of print, while when feeding off-set printed sheets S, dusting powder, paper dust, and ink sludge adhered to the sheets S before feeding are transferred onto the roller surface and are hardly removed, thus the durability of sheet conveyance is lowered. The reason is that the EDPM rubber with a high coefficient of friction μ has a property of easily pulling in foreign substances such as dusting powder, paper dust, and ink sludge inside the rubber. 
   (a) In the rotation system of the cleaning brush  116  in the linear speed relationship of V 1 &gt;V 2  indicated in the example, the coefficient of friction μ is high in continuous feed of up to 9000 sheets and stable high conveying force is obtained. 
   (b) In the rotation system of the cleaning brush  116  in the linear speed relationship of V 1 &lt;V 2  indicated in Comparative Example 1, although the coefficient of friction μ is lower than that of the example aforementioned, an almost stable coefficient of friction μ is obtained in continuous feed of up to 9000 sheets. 
   (c) In the form of reversing the cleaning brush  116  indicated in Comparative Example 2, the coefficient of friction is lowered and the coefficient of friction μ is changed greatly. 
   (d) In the fixed brush form, the coefficient of friction μ is suddenly lowered in continuous feed of about 200 sheets from the early stage of continuous feed down to the lower limit of sheet feed performance and when the continuous feed of sheets is continued, the coefficient of friction μ is lowered under the lower limit of sheet feed performance, thus defective sheet feed is caused. 
   Further, in the embodiment of the present invention, as a finisher connected to the image forming apparatus main body A, the finisher having the flat binding function is explained. However, the finisher of the image forming apparatus of the present invention is not limited to it and can be applied to a sheet feeding device of a finisher such as a pasting bookbinding device, a small paper cutter, a cover-wrapping bookbinding device, and a sealing device. 
   Further, in the embodiment of the present invention, the finisher connected to a copier is explained. However, the finisher can be applied to an image forming system connected of an image forming apparatus such as a light printing machine, a printer, a facsimile, and a multi-functional machine. 
   The present invention can provide a foreign substance removing device for enabling removal of foreign substances such as paper dust over a long period of time, reducing entry of foreign substances into the transfer area, realizing miniaturization of the cleaning mechanism, and obtaining a good image quality and an image forming apparatus using the concerned device. 
   Furthermore, improvement of the cleaning effect and durability of the first sheet feeding member and second sheet feeding member, improvement of the conveyability of paper-dusty sheets, and improvement of the conveyability of offset-printed sheets, particularly offset-printed coated paper can be realized effectively.
A sheet feeding device includes: a conveying member of a conveying unit which conveys a sheet; and a cleaning member which is in sliding contact with a circumferential surface of the conveying member to clean the circumferential surface. The conveying member and the cleaning member rotate in the same tangential direction at a sliding contact position thereof, and drives of the conveyance member and the cleaning member are controlled so that the following expression is satisfied: V1>V2 where V 1 represents a line speed of the circumferential surface of the conveying member during a rotation thereof, and V 2 represents a line speed of a sliding contact portion of the cleaning member during a rotation thereof.