Patent Publication Number: US-7900909-B2

Title: Sheet feeding apparatus and image forming apparatus

Description:
This application is a divisional of U.S. patent application Ser. No. 12/102,349, filed Apr. 14, 2008, allowed Oct. 1, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet feeding apparatus and an image forming apparatus and, more particularly, to a construction of a separation feeding unit for separating and feeding sheets one by one to an image forming unit. 
     2. Description of the Related Art 
     Hitherto, an image forming apparatus such as copying apparatus, printer, or facsimile has a sheet feeding apparatus for feeding a sheet to an image forming unit, and the sheet feeding apparatus has a sheet separation feeding unit for separating and feeding the sheets one by one. 
     As such a sheet separation feeding unit, there is a sheet separation feeding unit having a feed roller and a retard roller (separating roller) which is come into pressure contact with the feed roller and to which a rotating force in the direction opposite to a sheet feeding direction is applied through a torque limiter. In the sheet separation feeding unit of such a retard separating system, the sheets are separated one by one by the operation of the torque limiter. 
       FIG. 10  is a diagram illustrating a construction of the sheet feeding apparatus in the related art having the sheet separation feeding unit of such a retard separating system.  FIG. 10  illustrates a cassette  200  in which sheets S are stored (supported), a side wall  203  on the downstream side in the sheet feeding direction of the cassette  200 , and a middle plate  201  provided for the cassette  200  so as to be movable in the vertical direction. The sheets S have been stacked on the middle plate  201 . 
     A pickup roller  129  feeds a top sheet Sa among the sheets S enclosed in the cassette  200 . A feed roller  130  is made of, for example, urethane. A retard roller  131  is made of, for example, EPDM and is come into pressure contact with the feed roller  130  by a spring (not shown). When the retard roller  131  is come into pressure contact with the feed roller  130 , a separation nip portion N is formed between the retard roller  131  and the feed roller  130  and a surface portion of the retard roller  131  which is in contact with the feed roller  130  is compressed. 
     The top sheet Sa fed out by the pickup roller  129  is conveyed to the separation nip portion N formed by the feed roller  130  and the retard roller  131 . 
     A sheet feeding frame  301  holds a spring (not shown) adapted to allow the retard roller  131  to be come into pressure contact with the feed roller  130 . A conveying path  303  is formed by a conveying guide  302  provided between the separation nip portion N and a pair of conveying rollers  305   a  and  305   b . A detecting sensor flag  304  detects a passage of the sheet S. 
     In the sheet feeding apparatus in the related art constructed as mentioned above, in the case of feeding the sheets, first, the pickup roller  129  rotates and the top sheet Sa supported in the cassette  200  is conveyed to the separation nip portion N. 
     As a sheet Sa fed to the separation nip portion N, in the case where only one sheet has been conveyed to the separation nip portion N, the retard roller  131  is driven by the sheet Sa by the operation of the torque limiter as illustrated in  FIG. 11 . Thus, the sheet Sa passes along the conveying path  303 . 
     If a plurality of sheets has been conveyed to the separation nip portion N, the retard roller  131  is rotated in the direction opposite to the sheet feeding direction of the feed roller  130  by the operation of the torque limiter as illustrated in  FIG. 12  without being driven by the feed roller  130 . Since the retard roller  131  is rotated in the direction opposite to the sheet feeding direction of the feed roller  130  as mentioned above, only one sheet Sa which is in contact with the feed roller  130  is conveyed and the other sheets are returned to the upstream side in the sheet feeding direction by the retard roller  131 . 
     In such a sheet feeding apparatus in the related art, there is a case where the surface of the retard roller  131  is scraped due to deterioration in durability or the surface of the retard roller  131  is charged by a slide friction between the retard roller  131  and the conveyed sheet S. When the surface is charged, a foreign matter (mainly, paper powder generated from the sheet) is deposited onto the surface of the retard roller  131  and a coefficient of friction of the surface of the retard roller  131  decreases. 
     Ordinarily, the retard roller  131  has halted by a friction caused by the pressure contact with the feed roller  130  when the feed roller  130  has been stopped. When the feed roller  130  starts to rotate, the retard roller  131  rotates in the sheet conveying direction synchronously with the rotation of the feed roller  130 . However, when the coefficient of friction of the surface decreases, the retard roller  131  starts to rotate in such a direction as to return the sheet in the direction opposite to the sheet feeding direction of the feed roller  130  irrespective of the stop/rotation of the feed roller  130 . 
     That is, inherently, the retard roller  131  rotates in the reverse direction in the case where a plurality of sheets has been conveyed to the separation nip portion N as mentioned above. However, when the coefficient of friction of the surface decreases, even in the case of feeding one sheet, the retard roller  131  rotates in the direction opposite to the rotating direction adapted to feed the sheet. 
     When the retard roller  131  rotates in the direction opposite to the rotating direction adapted to feed the sheet, the following problems occur. When the sheet Sa fed out by the pickup roller  129  collides with the retard roller  131  as illustrated in  FIG. 13 , a sheet front edge is rolled in by the retard roller  131  as illustrated in  FIG. 14  and there is a risk of occurrence of a defective feeding state where the front edge is bent. 
     Further, if the sheet S is curled toward the retard roller  131  side, the defective feeding of the bent front edge is more liable to occur. Since the sheet front edge collides with the surface of the retard roller  131 , a scratch occurs on the surface of the retard roller  131  and the defective feeding is further liable to occur. 
     To prevent such a drawback, in the sheet feeding apparatus having the sheet separation feeding unit of the retard separating system, a guide is provided at a front edge in the sheet feeding direction of the cassette. The sheet fed out by the feed roller  130  is guided to the separation nip portion N by the guide. By guiding the sheet toward the separation nip portion N by the guide, it is prevented that the sheet front edge is rolled in by the retard roller  131 . 
     As such a guide, for example, there is a guide arranged in such a manner that one end is supported to a fixing portion of a sheet conveying path and the other end is extended to a position near the separation nip portion from an almost tangential direction of an outer surface of the retard roller  131 . Such a construction has been disclosed in Japanese Patent Application Laid-Open No. H05-338837. 
       FIG. 15  is a diagram illustrating a construction of the sheet feeding apparatus in the related art having such a guide. A sheet guide  135  is made of a thin elastic member and is in elastically come into contact with the outer surface of the retard roller  131  from its almost tangential direction. 
     By allowing the sheet guide  135  to be come into contact with the outer surface of the retard roller, the sheet front edge can sufficiently reach the position near the separation nip portion N without colliding with the retard roller  131 . Thus, even when the retard roller  131  is rotated in the direction opposite to the sheet feeding direction, it is possible to prevent such an inconvenience that the sheet is rolled in by the retard roller  131  and the occurrence of the damage on the surface of the retard roller  131 . 
     In the sheet feeding apparatus in the related art, as already mentioned above, the surface of the retard roller  131  is scraped due to the deterioration in durability or the surface of the retard roller  131  is charged by the slide friction with the conveyed sheet S. 
     If the foreign substance such as a paper powder is deposited onto the surface of the retard roller  131  by a surface charging and the coefficient of friction of the surface of the retard roller  131  decreases, the rotation in the direction opposite to the sheet feeding direction of the retard roller  131  as mentioned above is caused. Particularly, in the case of using such a sheet that the paper powder is liable to be generated, the coefficient of friction decreases rapidly due to a large quantity of paper powder deposited on the surface and the rotation in the reverse direction of the retard roller  131  is caused early. Thus, the sheets cannot be stably separated and fed. 
     The sheet guide  135  illustrated in  FIG. 15  can be constructed in such a manner that even in the case where the retard roller  131  is rotated in the reverse direction, the front edge of the sheet is not come into contact with the retard roller  131  as much as possible. However, the rotation in the reverse direction of the retard roller  131  cannot be prevented. Therefore, even if the sheet guide  135  has been arranged, there is a large risk that the front edge of the sheet is come into contact with the retard roller  131  which is reversely rotated and the foregoing problem occurs. 
     SUMMARY OF THE INVENTION 
     The invention is, therefore, made in consideration of such a present situation and it is an object of the invention to provide a sheet feeding apparatus and an image forming apparatus in which sheets can be stably separated and fed. 
     According to the invention, there is provided a sheet feeding apparatus comprising a sheet separation feeding unit which separates and feeds sheets supported in a sheet supporting unit, the sheet separation feeding unit comprises: a feed roller which feeds out the sheets in a sheet feeding direction; a separating roller which is rotatable in a direction opposite to the sheet feeding direction and separates the sheets one by one by a separation nip portion which is formed between the separating roller and the feed roller; and a charge eliminating mechanism which is provided on an upstream side in the sheet feeding direction in the separation nip portion and eliminates charges of the separating roller. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a printer as an example of an image forming apparatus having a sheet feeding apparatus according to an embodiment of the invention. 
         FIG. 2  is a diagram illustrating a schematic construction of the printer. 
         FIG. 3  is a diagram for describing a construction of the sheet feeding apparatus. 
         FIG. 4  is a first diagram illustrating a state at the time of executing a jam process of the sheet feeding apparatus. 
         FIG. 5  is a second diagram illustrating a state at the time of executing the jam process of the sheet feeding apparatus. 
         FIG. 6  is a first diagram for describing a construction of a retard roller charge eliminating unit provided for the sheet feeding apparatus. 
         FIG. 7  is a second diagram for describing the construction of the retard roller charge eliminating unit provided for the sheet feeding apparatus. 
         FIG. 8  is a first diagram for describing an attaching state of charge eliminating needles provided for the retard roller charge eliminating unit. 
         FIG. 9  is a second diagram for describing the attaching state of the charge eliminating needle provided for the retard roller charge eliminating unit. 
         FIG. 10  is a diagram illustrating a construction of a sheet feeding apparatus in the related art. 
         FIG. 11  is a first diagram for describing the sheet separation feeding operation of the sheet feeding apparatus in the related art. 
         FIG. 12  is a second diagram for describing the sheet separation feeding operation of the sheet feeding apparatus in the related art. 
         FIG. 13  is a third diagram for describing the sheet separation feeding operation of the sheet feeding apparatus in the related art. 
         FIG. 14  is a fourth diagram for describing the sheet separation feeding operation of the sheet feeding apparatus in the related art. 
         FIG. 15  is a diagram illustrating another sheet feeding apparatus in the related art. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An exemplary embodiment for embodying the invention will be described in detail hereinbelow with reference to the drawings. 
       FIG. 1  is a perspective view of a printer  100  as an example of an image forming apparatus having a sheet feeding apparatus according to the embodiment of the invention.  FIG. 2  is a diagram illustrating a schematic construction of the printer. 
     In  FIG. 1 , an image reading unit  41  having an image sensor and the like is provided over a printer main body  101 . The image reading unit  41  irradiates light to an original document put on platen glass serving as an original setting base plate and converts reflected light into a digital signal. An automatic document feeder (ADF)  41   a  conveys the original onto the platen glass in order to read an image of the original. 
     As illustrated in  FIG. 2 , an image forming unit  55  and sheet feeding apparatuses  51  to  54  each for feeding the sheets S to the image forming unit  55  are provided under the image reading unit  41 . 
     The image forming unit  55  has a scanner unit  42  and four process cartridges  55   a  for forming toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). The image forming unit  55  also has an intermediate transfer unit  63  arranged over the process cartridges  55   a.    
     Each of the process cartridges  55   a  has a photosensitive drum  55   b.    
     The intermediate transfer unit  63  has primary transfer rollers (not shown) which are provided inside of an intermediate transfer belt  63   a  and are come into contact with the intermediate transfer belt  63   a  at positions where it faces the photosensitive drums  55   b . By applying a transfer bias of a positive polarity to the intermediate transfer belt  63   a  by the primary transfer roller, the color toner images each having a negative polarity on the photosensitive drum are sequentially multiple-transferred onto the intermediate transfer belt  63   a . Thus, a full color image is formed on the intermediate transfer belt. 
     A secondary transfer unit  56  has a secondary transfer roller  56   a . The secondary transfer roller  56   a  is provided at a position where it faces the intermediate transfer belt  63   a  and transfers the full color image formed on the intermediate transfer belt onto the sheet S. A fixing unit  57  is arranged over the secondary transfer roller  56   a . The sheet feeding apparatuses  51  to  54  have: cassettes  51   a  to  54   a  serving as sheet supporting units each of which holds (encloses) the sheets S; and the pickup rollers  129  each serving as a sheet feeding member for feeding the sheets S enclosed in the cassettes  51   a  to  54   a.    
     As illustrated in  FIG. 3 , each of the sheet feeding apparatuses  51  to  54  has a sheet separation feeding unit  132  for separating the top sheet Sa fed out by the pickup roller  129 . 
     The sheet separation feeding unit  132  is constructed by: the feed roller  130  for feeding the sheet in the sheet feeding direction; and the retard roller  131  serving as a separating roller which can rotate in the direction opposite to the sheet feeding direction. When the retard roller  131  is come into pressure contact with the feed roller  130  by a spring (not shown), the separation nip portion N is formed between the retard roller  131  and the feed roller  130 . 
       FIG. 3  further illustrates the side wall  203  on the downstream side in the sheet feeding direction of the cassettes  51   a  to  54   a . The sheet feeding frame  301  holds the spring (not shown) adapted to allow the retard roller  131  to be come into pressure contact with the feed roller  130 . 
       FIG. 2  illustrates: a conveying path  103  for conveying the sheet S fed out of each of the cassettes  51   a  to  54   a  to the transfer unit  56 ; a conveying path  104  from the transfer unit  56  to the fixing unit  57 ; a conveying path  105  from the fixing unit  57  to a sheet discharging unit  58  through a flapper  61 ; and a conveying path  106  from the flapper  61  to a sheet discharging unit  59 . A re-conveying path  107  is a path for reversing the obverse and reverse sides of the sheet and guiding again the reversed sheet to the image forming unit in order to form an image onto the reverse surface of the sheet in which the image has been formed on one surface by the image forming unit  55 . In  FIG. 1 , side covers  1  and  11  form a part of the conveying paths  103  to  106 . By opening the side covers  1  and  11 , the user can remove the jammed sheet on each conveying path. 
     Subsequently, the image forming operation of the image forming apparatus  100  constructed as mentioned above will be described. 
     When the image forming operation is started, the scanner unit  42  irradiates a laser beam (not shown) onto the photosensitive drums  55   b  based on image information sent from a personal computer (not shown). The surfaces of the photosensitive drums  55   b  which have uniformly been charged so as to have a predetermined polarity and a predetermined electric potential are sequentially exposed and electrostatic latent images are formed on the photosensitive drums. After that, the electrostatic latent images are developed by the toner of yellow (Y), magenta (M), cyan (C), and black (Bk) and visualized as toner images of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. 
     By sequentially transferring the color toner images onto the intermediate transfer belt  63   a  by the primary transfer bias applied to the primary transfer rollers, a full color toner image is formed onto the intermediate transfer belt. 
     In parallel with the toner image forming operation, the pickup roller  129  conveys the top sheet Sa among the sheets S stored in each of the cassettes  51   a  to  54   a  to the separation nip portion N formed between the feed roller  130  and the retard roller  131 . The sheet Sa fed to the separation nip portion N is further conveyed by the feed roller  130  and the retard roller  131  which is driven by the feed roller  130 . 
     After that, the sheet Sa passes along the guide  302  and the conveying path  303 , is detected by the detecting sensor flag  304 , and reaches the pair of conveying rollers  305   a  and  305   b . Further, the sheet Sa sandwiched between the pair of conveying rollers  305   a  and  305   b  is conveyed to a conveying path  306  and is come into contact with a pair of registration rollers  62   a  and  62   b  in the stop state, so that a position of the front edge of the sheet is adjusted. 
     Subsequently, the pair of registration rollers  62   a  and  62   b  are driven at timing for making the full color toner image on the intermediate transfer belt coincide with the position of the sheet S in the secondary transfer unit  56 . Thus, the sheet Sa is conveyed to the secondary transfer unit  56 . In the secondary transfer unit  56 , the full color toner image is transferred onto the sheet Sa in a lump by a secondary transfer bias applied to the secondary transfer roller  56   a.    
     Subsequently, the sheet Sa on which the full color toner image has been transferred in this manner is conveyed to the fixing unit  57 . In the fixing unit  57 , the sheet receives a heat and a pressure and the toner of respective colors is melted, color-mixed, and fixed as a full color image onto the sheet Sa. After that, the sheet Sa on which the image has been fixed in this manner is discharged by the sheet discharging units  58  and  59  provided in the downstream of the fixing unit  57 . 
     In the printer  100 , there is a case where a jam occurs in the sheet feeding apparatuses  51  to  54 . In such a case, first, as illustrated in  FIGS. 4 and 5 , the retard roller  131  is moved downward and the pressure contact with the feed roller  130  is cancelled by a pressure canceling mechanism (not shown), thereby setting a jammed sheet S′ into a free state. After that, the side covers  1  and  11  (refer to  FIG. 1 ) are opened and the conveying guide  302  is rotated around a rotational center (not shown) as a center, thereby opening the conveying path  303  and processing the jammed sheet S′. 
     In  FIG. 3 , a guide member  411  for guiding the sheet toward the separation nip portion N between the feed roller  130  and the retard roller  131  is provided. The guide member  411  is formed by a conductive sheet having flexibility. As illustrated in  FIG. 6 , the guide member  411  is adhered to an SUS plate  413  by a conductive double-coated adhesive tape  412  and a front edge portion is bent toward the separation nip portion N. 
     The SUS plate  413  is adhered to the sheet feeding frame  301  by a double-coated adhesive tape  414 . The SUS plate  413  is conductive to the sheet feeding frame  301 . The sheet feeding frame  301  is connected to a frame body of a sheet metal of the printer main body  101  through an earth portion (not shown) formed by a sheet metal. By adhering the SUS plate  413  to the sheet feeding frame  301 , the guide member  411  is connected to the ground through the sheet feeding frame  301 . 
     The guide member  411  is bent from the halfway to an angle adapted to guide the sheet to a position near the separation nip portion and the front edge is extended to a position near the separation nip portion. However, since the guide member  411  is a thin elastic member, the bending angle is not stable. 
     In the embodiment, therefore, a backup portion  413   a  is provided for the SUS plate  413  at almost the same position as the portion of the guide member  411  which is bent to the separation nip portion side. By the backup portion  413   a , the guide member  411  can be pressed so as not to change the bending angle. 
     A charge eliminating unit  401  as a charge eliminating mechanism for eliminating the charges of the retard roller  131  is constructed by the guide member  411 , (the backup portion  413   a  of) the SUS plate  413  having the conductivity, the conductive double-coated adhesive tape  412 , the sheet feeding frame  301 , and the like. The charge eliminating mechanism is arranged on the upstream side in the sheet feeding direction in the separation nip portion N between the feed roller  130  and the retard roller  131 . In the embodiment, as illustrated in  FIG. 7 , the guide member  411  is in plane contact with the outer surface of the retard roller  131 , thereby improving charge eliminating performance. 
     Subsequently, the charge eliminating operation of the retard roller by the charge eliminating unit  401  will be described. 
     Upon sheet feeding, when the top sheet Sa is fed out by the pickup roller  129 , the sheet Sa is conveyed to the separation nip portion N by the guide member  411 . At this time, for example, even if the sheet Sa has been curled to the retard roller  131  side, the front edge of the sheet Sa is guided to the separation nip portion N by the guide member  411  without colliding with the retard roller  131 . 
     Since the bending portion of the guide member  411  is supported by the backup portion  413   a  of the SUS plate  413  and the bending angle is stable in this instance, the sheet Sa is certainly guided to the separation nip portion N. 
     As a sheet Sa fed to the separation nip portion N, if only one sheet has been conveyed to the separation nip portion N, the retard roller  131  is driven by the fed sheet Sa by the operation of the torque limiter as described in the related art. Thus, the sheet Sa passes along the conveying path  303 . 
     On the other hand, if a plurality of sheets has been conveyed to the separation nip portion N, the retard roller  131  is rotated in the direction opposite to the sheet feeding direction of the feed roller  130  by the operation of the torque limiter without being driven by the sheet Sa. Since the retard roller  131  is rotated in the direction opposite to the sheet feeding direction of the feed roller  130  as mentioned above, only one sheet Sa which is in contact with the feed roller  130  is conveyed and other sheets are returned to the upstream side in the sheet feeding direction by the retard roller  131 . 
     After that, the one separated sheet Sa passes along the conveying path  303  illustrated in  FIG. 3 , is detected by the detecting sensor flag  304 , and reaches the pair of conveying rollers  305   a  and  305   b.    
     When the sheet passes through the separation nip portion N, the surface of the retard roller  131  is charged by the scrape of the surface or the slide friction of the conveyed sheet Sa. However, even if the roller surface is charged as mentioned above, the static electricity is propagated to the sheet metal frame body of the printer main body  101  through the guide member  411  which is extended toward the separation nip portion N and is come into contact with the retard roller  131 , the conductive double-coated adhesive tape  412 , the SUS plate  413 , the sheet feeding frame  301 , and the earth portion (not shown) and is eliminated. 
     When one sheet is fed, since the retard roller  131  is driven, a charge amount is small. However, when the retard roller  131  is reversely rotated, the charge amount increases. This is because since a plurality of sheets is returned, the slide friction occurs between the sheets and charges are generated. Although the generated charges charge the retard roller  131 , since the retard roller  131  is reversely rotated, they are soon eliminated by the guide member  411 . In the separation nip portion N, since the charge removal can be performed immediately after the charging of the retard roller  131  as mentioned above, the deposition of the paper powder to the retard roller  131  can be efficiently prevented. By preventing the paper powder or the like of the sheet from being deposited, the sheet can be stably separated and fed. 
     As illustrated in  FIG. 7 , since the guide member  411  is in plane contact with the outer surface of the retard roller  131 , the charges charged to the sheet flow to the guide member  411  through the sheet or the retard roller  131 . 
     Further, although the feed roller  130  is also charged, the charged charges also flow to the guide member  411  through the sheet and the retard roller  131  and are eliminated. 
     Although the guide member  411  is in plane contact with the outer surface of the retard roller  131  in the embodiment, even if the guide member  411  is arranged with a gap of a predetermined amount (micro amount) from the outer surface, the charges can be eliminated. 
     Subsequently, experiment results of the charge removal of the retard roller  131  which has been executed by using the charge eliminating unit  401  according to the embodiment will be described. In the experiment, the charge removal amount of the retard roller  131  is measured under the following conditions in each of the case where there is no guide member, the case where an insulating sheet is used as a guide member, and the case where a conductive sheet is used as a guide member as in the embodiment. 
     (Conditions) 
     Conveying sheet: After 50 sheets of Chinese Furaion [FLYING] were allowed to pass 
     Measuring portion: Surface of the retard roller  131   
     Measuring instrument: AS-mini made by Achilles Corporation 
     (Measurement Values) 
     Guide member (none): 3.5 to 3.8 kV 
     Guide member (insulating sheet): 2.7 to 3.0 kV 
     Guide member (conductive sheet): 1.3 to 1.5 kV 
     It has been found that the charge amount is reduced into about ½ by using the conductive sheet as a guide member  411  instead of the insulating sheet. Since the charge amount is reduced in this manner, the paper powder is difficult to be adsorbed to the surface of the retard roller  131  and the rapid decrease in coefficient of friction of the surface of the retard roller can be prevented. 
     As described above, the guide member  411  is formed by the conductive member, the guide member  411  is arranged near the retard roller  131  or is come into contact therewith, and the charges of the retard roller  131  are eliminated, so that the paper powder can be made difficult to be deposited to the retard roller  131 . Therefore, the rapid decrease in coefficient of friction of the surface of the retard roller can be prevented. Consequently, the sheet can be stably separated and fed. 
     In the embodiment, in order to obtain a larger charge eliminating advantage, first and second charge eliminating needles  423   a  and  423   b  are provided as illustrated in  FIG. 6  mentioned above. 
     Each of the first and second charge eliminating needles  423   a  and  423   b  is formed by sandwiching aluminum foil  424  by conductive double-coated adhesive tapes  425 . The first charge eliminating needle  423   a  is adhered by the conductive double-coated adhesive tape  425  to an upper edge of a charge eliminating needle plate  402  formed by a sheet metal. The second charge eliminating needle  423   b  is adhered to a lower edge of the charge eliminating needle plate  402  by the conductive double-coated adhesive tape  425 . 
     The charge eliminating needle plate  402  is adhered to the conveying guide  302  by a conductive double-coated adhesive tape  422 . The upper edge of the charge eliminating needle plate  402  is bent so that a front edge of the first charge eliminating needle  423   a  is vertically come into contact with the outer surface of the retard roller  131 . The lower edge of the charge eliminating needle plate  402  is bent so that a front edge of the second charge eliminating needle  423   b  is come into contact with the sheet feeding frame  301 . 
     That is, in the embodiment, the first charge eliminating needle  423   a  is attached to the charge eliminating needle plate  402  so as to be vertically come into contact with the outer surface of the retard roller  131 , and the second charge eliminating needle  423   b  is attached to the charge eliminating needle plate  402  so as to be come into contact with the sheet feeding frame  301 . 
     When the sheet is conveyed as mentioned above, in the separation nip portion N, the surface of the retard roller  131  is charged by the slide friction with the conveyed sheet S. However, the charged surface portion is come into contact with the first charge eliminating needle  423   a  in association with the rotation of the retard roller  131 . Thus, the charges are eliminated from the first charge eliminating needle  423   a  to the sheet metal frame body of the printer main body  101  through the conductive double-coated adhesive tape  425 , the charge eliminating needle plate  402 , the conductive double-coated adhesive tape  425 , the second charge eliminating needle  423   b , the sheet feeding frame  301 , and the earth portion (not shown). 
     If a plurality of sheets has been conveyed to the separation nip portion N, the retard roller  131  is rotated in the reverse direction as shown by a broken arrow. Therefore, as illustrated in  FIGS. 6 ,  8 , and  9 , the first charge eliminating needle  423   a  is attached to the charge eliminating needle plate  402  so that the front edge of the needle is come into contact with the outer surface of the retard roller  131  in the vertical direction. 
     Further, in the embodiment, the first charge eliminating needle  423   a  is attached in such a manner that when the retard roller  131  is rotating in the feeding direction, the front edge of the needle is bent as shown by a solid line in  FIG. 6  and, when the retard roller  131  is rotating in the reverse direction, the front edge is bent as shown by a broken line. 
     Thus, no damage is given to the first charge eliminating needle  423   a  irrespective of the rotating direction of the retard roller  131 . When the first charge eliminating needle  423   a  is come into contact with the outer surface of the retard roller  131 , the higher charge eliminating performance is obtained. However, even if the first charge eliminating needle  423   a  is arranged with a gap of a predetermined amount from the outer surface, the charges can be eliminated. 
     Subsequently, experiment results of the charge removal of the retard roller  131  which has been executed by using the charge eliminating unit  401  in the case of using such charge eliminating needles will be described. In the experiment, the charge removal amount of the retard roller  131  in the case of using the conductive sheet as a guide member is measured under the following conditions. 
     (Conditions) 
     Conveying sheet: After 50 sheets of Chinese Furaion [FLYING] were allowed to pass 
     Measuring portion: Surface of the retard roller  131   
     Measuring instrument: AS-mini made by Achilles Corporation 
     (Measurement Value) 
     Guide member (conductive sheet)+charge eliminating needles: 0.1 to 0.2 kV 
     By adding the charge eliminating needles as mentioned above, the charge amount is reduced into almost 0 kV. Since the charge amount is reduced in this manner, the paper powder is difficult to be adsorbed to the surface of the retard roller  131  and the rapid decrease in coefficient of friction of the surface of the retard roller can be prevented. 
     The invention is not limited to the foregoing embodiment. Although the embodiment has been shown with respect to the example in which the guide member is constructed by the conductive sheet having the flexibility, such a construction that a flexible member is coated with a conductive material can be also used. That is, as a guide member, an arbitrary guide member may be used so long as it has a structure with the conductivity. 
     Although the guide member as a feature of the invention has been applied to the construction in which the sheets are fed out of each of the cassettes  51   a  to  54   a  by the pickup roller  129  and the sheets are separated by the feed roller  130  and the retard roller  131  in the embodiment, the invention is not limited to such a construction. 
     For example, the guide member of the invention may be applied to a construction of a sheet separation feeding unit in which the sheets stacked and supported on a tray are fed out by a feed roller without using the pickup roller and, further, separated by the retard roller which is come into pressure contact with the feed roller. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2007-114870, filed Apr. 24, 2007, which is hereby incorporated by reference herein in its entirety.