Abstract:
A sheet feeder includes a sheet stacking unit that stacks sheets, a sheet feeding unit that sequentially feeds the uppermost sheet of a stack of sheets stacked in the sheet stacking unit, an airflow supply unit that supplies an airflow to a side surface of the stack of sheets from an opening, a shield member that is disposed between the opening and the stack of sheets and a mechanism that changes the airflow from the airflow supply unit with respect to a stacking direction of the sheets by changing a relative position between the opening and the shield member in a direction other than the stacking direction of the sheets.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2010-144438 filed on Jun. 25, 2010. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to a sheet feeder and an image forming apparatus using the same. 
       SUMMARY 
       [0003]    According to an aspect of the invention, there is provided a sheet feeder including: 
         [0004]    a sheet stacking unit that stacks sheets; 
         [0005]    a sheet feeding unit that sequentially feeds the uppermost sheet of a stack of sheets stacked in the sheet stacking unit; 
         [0006]    an airflow supply unit that supplies an airflow to a side surface of the stack of sheets from an opening; 
         [0007]    a shield member that is disposed between the opening and the stack of sheets; and 
         [0008]    a mechanism that changes the airflow from the airflow supply unit with respect to a stacking direction of the sheets by changing a relative position between the opening and the shield member in a direction other than the stacking direction of the sheets. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Exemplary embodiments of the present invention will be described in detail based on the following figures. 
           [0010]      FIG. 1  is a diagram schematically illustrating a configuration of an image forming apparatus according to an exemplary embodiment of the invention; 
           [0011]      FIG. 2  is a schematic front view of a sheet feeder according to the exemplary embodiment of the invention; 
           [0012]      FIG. 3  is a schematic top view of the sheet feeder according to the exemplary embodiment of the invention; 
           [0013]      FIG. 4  is a schematic top view of a blower and an air adjusting unit according to the exemplary embodiment of the invention; 
           [0014]      FIGS. 5A and 5B  are schematic diagrams of the air adjusting unit according to the exemplary embodiment of the invention, where  FIG. 5A  is a diagram schematically illustrating the configuration of the periphery of a shield member as viewed in the direction of V in  FIG. 4  and  FIG. 5B  is a diagram illustrating the shield member; 
           [0015]      FIG. 6  is a diagram schematically illustrating the configuration of the periphery of the shield member when an air blowing port is opened; and 
           [0016]      FIGS. 7A to 7C  are front views illustrating other examples of the shield member according to the exemplary embodiment of the invention, where  FIG. 7A  is a diagram illustrating an example where the shield member includes a curve,  FIG. 7B  is a diagram illustrating an example where the shield member includes a step shape, and  FIG. 7C  is a diagram illustrating an example where the shield member is provided with slits. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the accompanying figures. 
       &lt;Image Forming Apparatus  1 &gt; 
       [0018]    An image forming apparatus  1  will be described with reference to  FIG. 1 .  FIG. 1  is a diagram schematically illustrating a configuration of the image forming apparatus  1  according to an exemplary embodiment of the invention. 
         [0019]    The image forming apparatus  1  shown in  FIG. 1  includes an image reading device  2  such as a scanner reading an image, an external device  3  such as a personal computer (PC), a receiver  5  connected to the image reading device  2 , the external device  3  and the like via a communication line  4 , and an image recording controller  7  receiving image information from the receiver  5  and controlling the image forming apparatus  1  as a whole. The image recording controller  7  outputs, for example, a feeding start signal, details of which will be described later. 
         [0020]    The image forming apparatus  1  further includes an image writing device  6  writing an image on the basis of the image information received by the image recording controller  7 , a cylindrical image holder  8  to which an electrostatic latent image is written by the image writing device  6 , a charging device  9  disposed in a circumferential direction of the image holder  8 , and an image developing device  10  developing the electrostatic latent image written to the image holder  8  using toner. The image forming apparatus  1  further includes a cleaner  11  removing toner remaining on the image holder  8 , a transfer roller  12  transferring an image formed on the image holder  8  to a sheet S, a fixing device  13  fixing the image transferred to the sheet S, a discharge roller  14  discharging the sheet S from the fixing device  13  and a discharging sheet stacking unit  15  on which the sheet S discharged by the discharge roller  14  are stacked. 
         [0021]    The image forming apparatus  1  further includes plural sheet supply devices  17  supplying sheets S to the image holder  8  and the transfer roller  12  via a sheet transporting unit  16 . 
       &lt;Sheet Supply Device  17 &gt; 
       [0022]    The sheet supply device  17  will be described below with reference to  FIGS. 2 and 3 . Here,  FIG. 2  is a schematic front view of the sheet supply device  17  according to this exemplary embodiment of the invention and  FIG. 3  is a schematic top view of the sheet supply device  17  according to this exemplary embodiment of the invention. 
         [0023]    Each sheet supply device  17  includes a feeding sheet stacking unit  19  in which sheets S are stacked in good order and a sheet feeding unit  21  sequentially feeding the sheets S stacked in the feeding sheet stacking unit  19  from the uppermost to the image holder  8 . 
         [0024]    Here, the feeding sheet stacking unit  19  and the sheet feeding unit  21  will be described in more detail. The sheet feeding unit  21  will be first described and the feeding sheet stacking unit  19  will then be described. 
       &lt;Sheet Feeding Unit  21 &gt; 
       [0025]    The sheet feeding unit  21  includes a pickup roller  22  sequentially feeding the sheets S, a feed roller  29  and a retard roller  30  disposed downstream in a feeding direction (see arrow A) of the sheets of paper S relative to the pickup roller  22 , a pair of takeaway rollers  31  disposed downstream in the feeding direction of the sheets S relative to the feed roller  29  and the retard roller  30 , a feed motor (not shown) connected to the pickup roller  22 , the feed roller  29  and the retard roller  30  to supply driving power thereto, a level sensor  34  sensing height of the stack of the sheets S in the stacking direction, and a feedout sensor  28  sensing pass of the sheets S. 
         [0026]    The respective members will be described below. 
         [0027]    First, the pickup roller  22  is rotatably provided so as to feed the sheets S in the feeding direction (see arrow A). The pickup roller  22  is also disposed to be capable to swing (see arrow B) via a support arm  32  due to a solenoid (not shown). 
         [0028]    The level sensor  34  is disposed at a position facing a part of the pickup roller  22  and senses height of the stack of sheets S stacked on a bottom plate  20  by detecting a position of the pickup roller  22 . 
         [0029]    The feed roller  29  is disposed downstream in the feeding direction relative to the pickup roller  22  so as to be rotatable in the feeding direction (see arrow D), and feeds the sheet S from the pickup roller  22  to the downstream side in the feeding direction. 
         [0030]    The retard roller  30  is disposed downstream in the feeding direction relative to the pickup roller  22  so as to face the feed roller  29  and rotates in both the feeding direction and the anti-feeding direction opposite to the feeing direction. A torque having a predetermined limit is applied to the retard roller  30  from a torque limiter (not shown) in the anti-feeding direction. 
         [0031]    The pair of takeaway rollers  31  are disposed downstream in the feeding direction relative to the feed roller  29  and the retard roller  30  to face each other. The pair of takeaway rollers  31  are rotatable in the feeding direction (see arrow C) and transport the sheet S from the feed roller  29  to the downstream side. 
       &lt;Feeding Sheet Stacking Unit  19 &gt; 
       [0032]    The feeding sheet stacking unit  19  will be described below with reference to  FIGS. 2 to 5B .  FIG. 4  is a schematic top view illustrating the periphery of a blower  95  and an air adjusting unit  60  according to this exemplary embodiment of the invention.  FIGS. 5A and 5B  are schematic diagrams of the air adjusting unit  60  according to this exemplary embodiment of the invention, where  FIG. 5A  is obtained by rotating by 180° a schematic diagram illustrating a configuration of the periphery of a shield member  100  as viewed in the direction of arrow V in  FIG. 4  and  FIG. 5B  is a diagram illustrating the shield member  100 . In  FIGS. 5A and 5B , the blower  95  and a nozzle  97  are not shown for the purpose of simplicity and the sheets S other than the uppermost sheet S 1  are not shown. 
         [0033]    The feeding sheet stacking unit  19  includes a feeding container  26  in which a stack of sheets S is disposed, the bottom plate  20  disposed on the bottom of the feeding container  26  to stack the sheets S thereon, a wire (not shown) of which an end is connected to the bottom plate  20 , a bottom plate motor (not shown) connected to the other end of the wire, and an end guide  23 , a first side guide  24 , and a second side guide  25  limiting movement of the stack of sheets S stacked on the bottom plate  20 . The feeding sheet stacking unit  19  further includes the blower  95  blowing air to the side surface of the stack of sheets S and the air adjusting unit  60  adjusting the air blown from the blower  95 . 
         [0034]    The respective members will be described below. 
         [0035]    First, the end guide  23  will be described. The end guide  23  is disposed to come in contact with an end of the sheets S stacked on the bottom plate  20 , which is an end in the anti-feeding direction. The end guide  23  includes a surface along the stacking direction of the sheets of paper S so as to arrange the ends of the sheets S stacked on the bottom plate  20 . The end guide  23  may be movable depending on the size of the stacked sheets S. 
         [0036]    Next, the first side guide  24  and the second side guide  25  will be described. 
         [0037]    The first side guide  24  and the second side guide  25  are disposed to come in contact with ends of the sheets S stacked on the bottom plate  20 , which are two ends in the feeding direction of the sheets S. More specifically, the first side guide  24  and the second side guide  25  are opposed to each other with interposing the bottom plate  20  therebetween. For example, in  FIG. 2 , the first side guide  24  is disposed in a front side of the figure surface relative to the sheets S in  FIG. 2  (the first side guide  24  is not shown in  FIG. 2 ) and the second side guide  25  is disposed in a rear side of the figure surface relative to the sheets S in  FIG. 2 . 
         [0038]    The first side guide  24  and the second side guide  25  have a surface along the stacking direction of the sheets S so as to align the ends of the stack of sheets S stacked on the bottom plate  20 . Both or one of the first side guide  24  and the second side guide  25  may be movable in accordance with the size of the sheets S to be stacked. 
         [0039]    The second side guide  25  includes an air blowing port  51  formed to pass from the surface of the second side guide  25  coming into contact with the stack of sheets S to the surface opposite to the surface coming contact with the sheets S and opened to the side surface of the stack of sheets S. The air blowing port  51  is disposed to supply air to the uppermost sheet S 1  in the stack of sheets S. 
         [0040]    Next, the blower  95  will be described. 
         [0041]    The blower  95  is disposed at a position opposed to the second side guide  25  so as to blow air to the side surface of the stack of sheets S via the air blowing port  51 . 
         [0042]    More specifically, the blower  95  includes blades (not shown) disposed therein so as to generate air by rotation and a nozzle  97  discharging the air generated by the blades in a direction outside the blower  95 . An opening  99  opposed to the air blowing port  51  is formed in the nozzle  97 . By opposing the air blowing port  51  and the opening  99  to each other, an air flow path  62  from the blower  95  to the stack of sheets S is formed. 
         [0043]    In this example, the shape of the opening  99  of the nozzle  97  is equal to the shape of the air blowing port  51  and the opened portions thereof correspond to each other (see  FIG. 4 ). Accordingly, the air blown from the blower  95  can pass through the air blowing port  51  without any hindrance. 
         [0044]    Next, the air adjusting unit  60  will be described. 
         [0045]    The air adjusting unit  60  is disposed between the second side guide  25  and the blower  95 . 
         [0046]    The air adjusting unit  60  in this exemplary embodiment includes the shield member  100  disposed to be movable so as to intersect the air flow path  62 , a driving unit driving the shield member  100 , a photo sensor  107  sensing the movement of the shield member  100 , and a support member  109  supporting the air adjusting unit  60 . Here, the driving unit includes a driving motor  110  supplying power for moving the shield member  100 , a driving gear  112 , a first transmission gear  113  and a second transmission gear  114  transmitting the power generated by the driving motor  110  to the shield member  100 , and a guide pin  103  disposed in the second side guide  25  so as to guide the moving direction of the shield member  100 . 
         [0047]    The respective members will be described below. 
         [0048]    First, the shield member  100  serves as a shutter opening and closing the air blowing port  51  to open and close the air flow path  62  passing through the air blow port  51 . Specifically, the shield member  100  is formed of a plate-like member having a surface extending in the direction intersecting the air flow path  62 . The shield member  100  moves back and forth between the nozzle  97  of the blower  95  and the second side guide  25 . More specifically, the shield member  100  is disposed to be movable back and forth in the direction intersecting the air flow path  62 , that is, the direction (hereinafter, referred to as “sheet end direction”: see arrow E in  FIG. 4 ) along the end, which is close to the side guide, of the sheets S stacked on the bottom plate  20 . 
         [0049]    The shield member  100  is divided into three portions: a small-width portion  100   a , an inclined portion  100   b , and a large-width portion  100   c  in accordance with the width (the height in the vertical direction in  FIG. 5 ) in the stacking direction of the sheets S. That is, as shown in  FIG. 5B , the shield member  100  includes the small-width portion  100   a  which is one end portion of the shield member  100  in the sheet end direction and which has a small width in the stacking direction of the sheets S, the large-width portion  100   c  which is the other end portion of the shield member  100  in the sheet end direction and which has a large width in the stacking direction of the sheets S, and the inclined portion  100   b  which is disposed between the small-width portion  100   a  and the large-width portion  100   c  and in which the width in the stacking direction of the sheets S varies. As described later, as the shield member  100  moves in the sheet end direction, the large-width portion  100   c , the inclined portion  100   b  and the small-width portion  100   a  oppose to the air blowing port  51 . 
         [0050]    Here, as shown in  FIG. 5B , a lower end of the shield member  100  is straightly linear except for a light-blocking portion  115  to be described later. 
         [0051]    On the other hand, an upper end of the shield member  100  is not linear but becomes close to the lower end of the shield member  100  in the order of the large-width portion  100   c , the inclined portion  100   b  and the small-width portion  100   a . More specifically, the distance between the upper end of the shield member  100  and the lower end thereof is constant in the large-width portion  100   c  and the small-width portion  100   a . On the contrary, the distance therebetween varies in the inclined portion  100   b  and the inclined portion is formed by connecting the upper end of the small-width portion  100   a  in the stacking direction of the sheets S to the upper end of the large-width portion  100   c  with a straight line intersecting the stacking direction of the sheets S. 
         [0052]    The large-width portion  100   c  of the shield member  100  is disposed at the position opposed to the air blowing port  51  to block the air flow path  62 . The small-width portion  100   a  of the shield member  100  is disposed at the position opposed to the air blowing port  51  not to block the air flow path  62 . 
         [0053]    The shield member  100  is provided with a guide slit  105  at a position close to the bottom plate  20  in the stacking direction of the sheets S. The guide slit  105  extends in the sheet end direction. Two guide pins  103  formed in the second side guide  25  are located in the guide slit  105 , whereby a locus of the shield member  100  in the sheet end direction is regulated. 
         [0054]    The shield member  100  further includes a rack gear  102  at the end close to the bottom plate  20 . The rack gear  102  extends in the sheet end direction and converts the power supplied from the driving motor  110  into power for moving the shield member  100  in a linear direction as described later. 
         [0055]    The shield member  100  further includes a light-blocking portion  115  at an end close to the small-width portion  100   a  and at a position opposed to the photo sensor  107 . By causing the photo sensor  107  to sense the position of the light-blocking portion  115 , it is detected that the shield member  100  blocks the air flow path  62 . 
         [0056]    The driving motor  110  and the like will be described below. 
         [0057]    The driving motor  110  supplying power to cause the shield member  100  to move includes a driving shaft and the driving gear  112  is disposed at the same axis as the driving shaft. The first transmission gear  113  is disposed to engage with the driving gear  112  and the second transmission gear  114  is disposed to engage with the first transmission gear  113 . The second transmission gear  114  is disposed to engage with the rack gear  102  disposed in a lower surface of the shield member  100 . In this way, the driving power of the driving motor  110  is transmitted to the shield member  100 . 
       &lt;Operation of Sheet Feeder  17 &gt; 
       [0058]    Operations of a sheet feeding method in the sheet feeder  17  will be described with reference to  FIG. 6 .  FIG. 6  is a diagram schematically illustrating the configuration of the periphery of the shield member  100  in which the air blowing port  51  is opened. In  FIG. 6 , the sheets S other than the uppermost sheet S 1  among the sheets S is not shown for the purpose of simplification. 
         [0059]    First, the operation states of the sheet feeder  17  include a standby state where the sheet feeder  17  is not driven, a driving state where the sheet feeder  17  is driving, and a sheet-out state where no sheet S is stacked in the sheet feeder  17 . The respective states will be described below. 
         [0060]    First, in the sheet-out state of the sheet feeder  17 , no sheet S is stacked in the feeding container  26 , and the pickup roller  22  pressed down by a solenoid (not shown) is lowered and is located at the position indicated by a dashed line in  FIG. 2 . 
         [0061]    Next, the standby state will be described. The sheets S are fed so as to change the sheet feeder  17  from the sheet-out state to the standby state. Specifically, when the sheets S are stacked on the bottom plate  20  of the feeding container  26  taken out of the image forming apparatus  1  in order to feed the sheets S and the feeding container  26  is inserted into the image forming apparatus  1 , a bottom-plate motor (not shown) is driven. By winding a wire (not shown) on the driving shaft of the bottom-plate motor, the bottomplate  20  is raised. Then, the uppermost sheet S 1  in the stack of sheets S is disposed to come in contact with the pickup roller  22  pressed down by the solenoid (not shown). The pickup roller  22  is raised by bringing the sheets S into contact with the pickup roller  22 . The level sensor  34  sensing the rising of the pickup roller  22  outputs a detection signal so that the bottom-plate motor (not shown) and the solenoid (not shown) are turned off on the basis of the detection signal. This state is the standby state of the sheet feeder  17 . 
         [0062]    In the sheet-out state and the standby state, the members of the sheet feeder  17  operate as follows. That is, the blower  95  is turned off and the driving motor  10  is also turned off. The shield member  100  is disposed to oppose the large-width portion  100   c  to the air blowing port  51  to block the air blowing port  51 . That is, the air flow path  62  is blocked by the shield member  100  (see  FIG. 5A ). The light-blocking portion  115  blocks the optical axis of the photo sensor  107 . The reason that the shield member  100  blocks the air blowing port  51  in the sheet-out state and the standby state is to prevent from particles, wastes, and dust from entering the air blowing port  51 . 
         [0063]    The operation of the sheet feeder  17  in the driving state will be described below. 
         [0064]    Here, the operation of the shield member  100  of the sheet feeder  17  will be first described and then the entire operations of the sheet feeder  17  will be described. 
         [0065]    The operation of the shield member  100  is described. First, using a feed start signal output from the image recording controller  7  as a trigger, the driving motor  110  rotationally drives the driving gear  112  in the CCW (counter clock wise) direction in  FIGS. 5A and 5B . By the rotation of the driving motor  110 , the shield member  100  starts moving to the left side (see arrow G) in  FIGS. 5A and 5B . That is, the shield member  100  starts moving to cause the inclined portion  100   b  and the small-width portion  100   a  to oppose to the air blowing port  51 . As the shield member  100  moves, the closed air blowing port  51  is sequentially opened. 
         [0066]    Specifically, when the inclined portion  100   b  of the shield member  100  is located at the position a in  FIG. 6 , the air blowing port  51  is sequentially opened from an upper corner of the right end thereof. That is, the air blowing port  51  is opened from the opposite side (see arrow G) of the side to which the shield member  100  moves and from the upside in the stacking direction of the sheets S. 
         [0067]    As the shield member  100  moves to positions b and c in  FIG. 6 , the area for blowing air is widened from the upside in the stacking direction of the sheets S to the downside. As the shield member  100  moves, the air is blown widely to the upper sheets of the stacked sheets S in the sheet end direction. Accordingly, the sheets S in the stack can easily waft to be separated from the upside. 
         [0068]    When the shield member  100  moves to the position d, the air is blown through the entire opening of the air blowing port  51 . That is, the entire air flow path  62  is opened. 
         [0069]    The operation of the shield member  100  will be continuously described. When the shield member  100  reaches the position d, the driving motor  110  is temporarily stopped. 
         [0070]    The shield member  100  starts moving in the direction opposite to arrow G in  FIGS. 5A and 5B . More specifically, the driving motor  110  rotationally drives the driving gear  112  in the CW (clockwise) direction in  FIGS. 5A and 5B  so that the shield member  100  moves to the right side in  FIGS. 5A and 5B , whereby the inclined portion  100   b  sequentially blocks the air blowing port  51 . After moving to the positions c, b, and a in  FIG. 6 , the large-width portion  100   c  is opposed to the air blowing port  51  and the light-blocking portion  115  stops at the position where a signal from the photo sensor  107  is blocked. 
         [0071]    The sheet feeder  17  repeatedly performs the above-mentioned operation during the feeding operation, that is, the sheet feeder  17  moves back and forth along the sheet end direction, whereby the upper sheets S in the stack of sheets can be kept separated. 
         [0072]    The entire operation of the sheet feeder  17  will be described below. 
         [0073]    First, using the feed start signal output from the image recording controller  7  as a trigger, the blower  95  is driven and the sheet feeding unit  21  is driven. Accordingly, the uppermost sheet S 1  in the stack of sheets S is picked up to be separated, and then fed in the feeding direction. As described above, using the feed start signal output from the image recording controller  7  as a trigger, the shield member  100  also starts moving to the left side (see arrow G) in  FIGS. 5A and 5B . 
         [0074]    The operation of the sheet feeding unit  21  will be described in detail. 
         [0075]    First, using the feed start signal output from the image recording controller  7  as a trigger, the pickup roller  22 , the feed roller  29  and the retard roller  30  are rotated by the feed motor (not shown). Then, the uppermost sheet S 1  picked up by the pickup roller  22  is separated and transported by the feed roller  29  and the retard roller  30  disposed downstream in the feeding direction relative to the pickup roller  22 . That is, the feed roller  29  rotating in the feeding direction (see arrow D) and the retard roller  30  rotatable in both directions with application of a torque having a predetermined limit from the torque limiter (not shown) in the anti-feeding direction come in contact with each other with a predetermined pressure so that the sheets S are separated and transported by an interaction therebetween. The retard roller  30  rotates in the feeding direction when only one sheet S exists in the contact portion with the feed roller  29 , and rotates in the anti-feeding direction when two or more sheets exist therein. 
         [0076]    The sheet S fed in the feeding direction by the feed roller  29  and the retard roller  30  is further transported downstream by the takeaway roller  31 . The transportation of the sheet S is detected by the feedout sensor  28 . When the sheet S is being transported by the takeway roller  31 , the feed roller  29  is stopped driving so that the feed roller  29  rotates with a one-way clutch (not shown). 
         [0077]    When the sheets S in the stack are sequentially fed from the upside, the sheet feeder  17  moves back and forth in the sheet end direction as described above, whereby the upper sheets S in the stack can be kept separated. 
         [0078]    When the feeding operation is repeated, the height of the stack of sheets S is sequentially lowered and the height of the pickup roller  22  upon pressing is lowered. Accordingly, the level sensor  34  detects the support arm  32  of the pickup roller  22  (receives light), the bottom plate  20  is raised by the bottom-plate motor (not shown), and the feeding operation is continuously performed. 
         [0079]    By repeatedly performing the above-mentioned operations, all the sheets S on the bottom plate  20  are fed out and the sheet-out state is reach again. 
         [0080]    In the configuration according to this exemplary embodiment, it is possible to prevent the uppermost sheet S 1  in the stack of sheets S and one or more sheets S therebelow from being picked up together. The configuration according to this exemplary embodiment exhibits a remarkable effect, for example, when special sheets such as coated sheets are used, when the surface of the sheet S is viscous and the like. 
         [0081]    Since the shield member  100  according to this exemplary embodiment includes the inclined portion  100   b , the shield member  100  moves in a direction intersecting the stacking direction of the sheets S. Accordingly, compared with the case where the shield member  100  moves in the stacking direction of the sheets S, it is possible to lower the height of the sheet feeder  17 . In addition, since the shield member  100  is disposed at a side of the stack of sheets S, it is possible to reduce the size of the image forming apparatus  1  including the shield member  100 . 
         [0082]    Here, the shield member  100  according to this exemplary embodiment is not limited to the above-mentioned configuration. Other configurations will be described with reference to  FIGS. 7A to 7C .  FIGS. 7A to 7C  are front views illustrating other configurations of the shield member  100  according to the exemplary embodiment of the invention, where  FIG. 7A  is a diagram illustrating the inclined portion  100   b  with a curve,  FIG. 7B  is a diagram illustrating the inclined portion  100   b  has a step shape, and  FIG. 7C  is a diagram illustrating the shield member  100  provided with slits. 
         [0083]    First, as shown in  FIGS. 7A and 7B , the inclined portion  100   b  of the shield member  100  may have a curved shape or a step shape. That is, a connecting portion  101  of the shield member  100  has only to have such a shape to change the height of the opened portion of the air blowing port  51  in the stacking direction of the sheets S as the shield member  100  moves. 
         [0084]    More specifically, for example, as shown in  FIG. 7A , the connecting portion  101  of the shield member  100  may have a shape obtained by connecting the upper end of the small-width portion  100   a  in the stacking direction of the sheets S to the upper end of the large-width portion  100   c  in the stacking direction of the sheets S with a curve. Here, the connecting portion has a curve which is convex to the upside in  FIG. 7A . When the inclined portion  100   b  of the shield member  100  has a curve convex to the upside, the area for blowing air to the upper sheets S is widened and the reliability in separating the sheets S is improved. 
         [0085]    For example, as shown in  FIG. 7B , the connecting portion  101  of the shield member  100  may have a shape obtained by connecting the upper end of the small-width portion  100   a  in the stacking direction of the sheets S to the upper end of the large-width portion  100   c  in the stacking direction of the sheets S having the step shape. 
         [0086]    When the inclined portion  100   b  of the shield member  100  has the step shape, the opened portion of the air blowing port  51  discontinuously varies as the shield member  100  moves, whereby the reliability in separating the sheets S is further improved. 
         [0087]    As shown in  FIG. 7C , the inclined portion  100   b  of the shield member  100  may include plural linear portions. Specifically, the inclined portion  100   b  may be provided with plural air slits  116 . Here, the air slit  116  is the opening  99  passing from the sheets S to the blower  95  and the opening  99  has a linear portion inclined relative to the stacking direction of the sheets S. 
         [0088]    When the inclined portion  100   b  of the shield member  100  is provided with plural air slits  116 , a portion passing air and a portion blocking air alternately face the air blowing port  51  as the shield member  100  moves. Accordingly, the air blown to the sheets S can be changed, thereby further improving the reliability in separating the sheets S. 
         [0089]    Although it is described above that the shield member  100  moves relative to the blower  95 , the blower  95  may move relative to the shield member  100  or both the shield member  100  and the blower  95  may move. More specifically, the rack gear  102  may be disposed in the blower  95  so as to transmit the driving power of the driving motor  110 . 
         [0090]    Although the relation of the air blowing port  51  disposed in the second side guide  25  and the inclined portion  100   b  of the shield member  100  is described above, the relation of the opening  99  of the blower  95  and the inclined portion  100   b  of the shield member  100  is the same as described above. That is, as the inclined portion  100   b  of the shield member  100  moves, the height of the opened portion of the opening  99  of the blower  95  in the stacking direction of the sheets S varies. Since the opening  99  of the blower  95  and the air blowing port  51  of the second side guide  25  are provided, it is possible to surely switch the portion passing air and the portion blocking the air, compared with the case where one of the opening  99  of the blower  95  and the air blowing port  51  of the second side guide  25  is provided. 
         [0091]    In the invention, only one of the opening  99  of the blower  95  and the air blowing port  51  of the second side guide  25  may be provided. 
         [0092]    Although it is described above that the sheet feeder  17  is disposed in the lower portion of the image forming apparatus  1 , the invention is not limited to this configuration. For example, the sheet feeder  17  may be disposed on the side of the image forming apparatus  1 . Alternatively, for example, a manual sheet stacking unit may be disposed on the side of the image forming apparatus  1  and the sheet feeder  17  may be disposed in the manual sheet stacking unit. Alternatively, the sheet feeder  17  may be provided as a body separated from the image forming apparatus  1 . 
         [0093]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.