Patent Publication Number: US-9902580-B2

Title: Sheet feeding device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of International Application No. PCT/JP2014/076693, filed on Oct. 6, 2014, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a sheet feeding device. 
     BACKGROUND 
     More image scanners that read an image of a document and electrically process the read image, or more printers that print an image, have employed a sheet feeding device that feeds a sheet such as a document from which an image is read or a paper sheet on which an image is printed to an image reading unit or a printing unit. The sheet feeding device feeds a document downstream by rotating a pickup roller, which has a relatively large frictional coefficient, while coming in contact with the document. Since the pickup roller feeds a document downstream using a frictional force with the document, sheet feeding devices in which a contact state of a document with the pickup roller is adjusted to appropriately feed the document, are known (for example, Japanese Laid-open Patent Publication No. 10-35897 and Japanese Laid-open Patent Publication No. 2007-137526.) 
     However, when a document properly comes in contact with the pickup roller at the time of feeding but documents are not properly set on a document mounting board, a problem, in which a document cannot be fed downstream due to non-contact of the document with the pickup roller, may occur at the time of feeding a document using the pickup roller. For example, as described in JP 10-35897 A, when a guide is disposed upstream from the pickup roller and a document is separated apart upward from the pickup roller by the guide turning upward on standby, documents may stop in a part of the guide turning upward at the time of setting documents and the documents may not reach the position of the pickup roller. In this case, even when the guide is lowered at the time of feeding a document, no documents is present at the position of the pickup roller and thus no document can be forwarded downstream. Accordingly, there is room for improvement in a structure for feeding a document without causing non-feeding. 
     SUMMARY 
     According to an aspect of an embodiment, a sheet feeding device includes: a document mounting board configured to have documents mounted thereon; a feed mechanism configured to include a pickup roller rotating to forward the documents and to feed the documents mounted on the document mounting board to a downstream side in a feeding direction of the documents; and a base portion configured to support the feed mechanism, wherein a downstream end of the document mounting board in the feeding direction of the document in the feed mechanism, is connected to the base portion, so as to be rotatable about a first turning shaft that is parallel to a rotation shaft of the pickup roller, the first turning shaft is located downstream from the feed mechanism in the feeding direction of the document in the feed mechanism, a mounting surface of the document mounting board on which the documents are mounted, is located above the pickup roller, when the documents are mounted on the document mounting board, and the document mounting board turns about the first turning shaft such that the mounting surface moves downward and the mounting surface moves downward from a contact portion of the pickup roller with the document, when the documents mounted on the document mounting board are fed. 
     The object and advantages of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the disclosure, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram schematically illustrating a scanner including a sheet feeding device according to an embodiment; 
         FIG. 2  is a functional block diagram of the scanner including the sheet feeding device according to the embodiment; 
         FIG. 3  is a diagram illustrating a state in which the scanner illustrated in  FIG. 1  is not used; 
         FIG. 4  is a diagram illustrating a state in which documents are mounted on a document mounting board illustrated in  FIG. 1 ; 
         FIG. 5  is a diagram illustrating a state in which documents mounted on the document mounting board illustrated in  FIG. 1  are fed; 
         FIG. 6  is a detailed diagram illustrating a periphery of a pickup roller in  FIG. 4 ; 
         FIG. 7  is a detailed diagram illustrating a periphery of the pickup roller in  FIG. 5 ; 
         FIG. 8  is a diagram illustrating an angle between a first member and a second member and illustrating a document mounting state; 
         FIG. 9  is a diagram illustrating the angle between the first member and the second member and illustrating a document feeding state; 
         FIG. 10  is a flow diagram illustrating a processing sequence when an image of a document is read by the scanner including the sheet feeding device according to the embodiment; 
         FIG. 11  is a diagram illustrating a case in which protrusions are formed by a friction reducing process in a sheet feeding device according to a modified example of the embodiment; 
         FIG. 12  is a diagram illustrating a case in which rollers are used by a friction reducing process in a sheet feeding device according to a modified example of the embodiment; 
         FIG. 13  is a diagram illustrating a case in which a stepped portion is formed by a friction reducing process in a sheet feeding device according to a modified example of the embodiment; and 
         FIG. 14  is a diagram illustrating a case in which a vibration generating member is disposed by a friction reducing process in a sheet feeding device according to a modified example of the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a sheet feeding device according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. The present disclosure is not limited to the embodiment. Elements in the following embodiment include elements that can be easily replaced by those skilled in the art or elements that are substantially equal to each other. 
     Embodiment 
       FIG. 1  is a schematic diagram illustrating a scanner including a sheet feeding device according to an embodiment. A sheet feeding device  5  of a scanner  1  illustrated in  FIG. 1  is configured as a device that separates documents S which are a plurality of feeding mediums stacked one by one and conveys the separated document S to an image reading unit  50  by which images of the document S are read. The sheet feeding device  5  includes a document mounting board  10  on which the documents S to be forwarded to the image reading unit  50  are mounted. The document mounting board  10  is attached to a scanner body  2  of the scanner  1  so as to be inclined from up to down from an upstream side to a downstream side in a conveyance direction of the document S when the scanner  1  is used. A top surface thereof serves as a mounting surface  15  on which the documents S are mounted. 
     The sheet feeding device  5  includes a feed mechanism  30  that feeds the document S mounted on the document mounting board  10  to the downstream side in the feeding direction of the document S, and the scanner body  2  also serves as a base portion that supports the feed mechanism  30 . That is, constituent members of the feed mechanism  30  are directly or indirectly attached to the scanner body  2  as the base portion. The feed mechanism  30  attached to the scanner body  2  in this way includes a pickup roller  31  that rotates to forward a document S and a separation member  35  that can separate the document S to be fed by the pickup roller  31  and feed only one document to the image reading unit  50 . 
     Among these, the pickup roller  31  is formed in a substantially columnar shape, an outer circumferential surface thereof is formed of a member such as rubber having a relatively high frictional coefficient, and a rotation shaft  33  thereof is perpendicular to a conveyance direction of the document S and is rotatable in a direction substantially parallel to a horizontal direction. An upper end of the outer circumferential surface of the pickup roller  31  is rotatable about the rotation shaft  33  toward the downstream side in the feeding direction of a document S by a driving force transmitted from a feed driving motor  45 . 
     The separation member  35  is disposed in the vicinity of the pickup roller  31  and at a position downstream from the vicinity of the upper end of the pickup roller  31 . The separation member  35  can forward only one document to the image reading unit  50  by regulating movement of the documents S other than the document S in contact with the pickup roller  31  among the documents S moving downstream in the conveyance direction by the rotating pickup roller  31 . 
     A downstream end of the document mounting board  10  in the feeding direction of the document S in the feed mechanism  30 , is connected to the scanner body  2  such that the document mounting board  10  attached to the scanner body  2  is rotatable about a first turning shaft  21 . The first turning shaft  21  is a turning shaft which is located downstream from the feed mechanism  30  in the feeding direction of the document S in the feed mechanism  30 , and the first turning shaft  21  is parallel to the rotation shaft  33  of the pickup roller  31 , and connects the document mounting board  10  to the scanner body  2 . 
     The document mounting board  10  connected to the scanner body  2  in this way, includes a first member  11  and a second member  12 , and the first member  11  is connected to the scanner body  2  so as to be rotatable about the first turning shaft  21 . The second member  12  is connected to an end of the first member  11  opposite to the end connected to the scanner body  2 , and the second member  12  is connected to the first member  11  so as to be rotatable about a second turning shaft  22  which is disposed parallel to the first turning shaft  21 . 
     In both of the first member  11  and the second member  12 , the top surfaces when the scanner  1  is normally used, serve as the mounting surface  15  on which the documents S are mounted. That is, a first mounting surface  16 , which is the mounting surface of the first member  11  on which the documents S are mounted, and a second mounting surface  17 , which is the mounting surface of the second member  12  on which the documents S are mounted, are both formed on the top surfaces of the first member  11  and the second member  12  when the scanner  1  is normally used. Among these, the first mounting surface  16  has a friction reducing processed portion for reducing frictional resistance against the document S moving in the feeding direction of the feed mechanism  30 . For example, the first mounting surface  16  is subjected to surface treatment using a material having a low frictional coefficient such as a fluorine-based material and thus the frictional coefficient of the first mounting surface  16  is lowered. 
     A pickup roller hole  13 , which is a hole through which the pickup roller  31  passes, is formed in the first member  11 . That is, the pickup roller  31  can forward the document S by rotating about the rotation shaft  33  and bringing the upper end of the outer circumferential surface thereof into contact with the document S when feeding the document S in the feed mechanism  30 . On the other hand, the first turning shaft  21 , which is a turning shaft for turning of the first member  11  and which is located downstream from the feed mechanism  30  in the feeding direction of the document S in the feed mechanism  30 , is located downstream from the pickup roller  31  in the feeding direction of the document S in the feed mechanism  30 . 
     Accordingly, the pickup roller hole  13 , which is a hole through which an upper part of the pickup roller  31  of which the rotation shaft  33  is located below the first member  11  passes from the bottom surface of the first member  11  to the top surface thereof and which locates the upper part of the pickup roller  31  above the first mounting surface  16 , is formed in the first member  11 . When the scanner  1  is normally used, the upper part of the pickup roller  31  passes through the pickup roller hole  13  such that the upper part is located above the first mounting surface  16 . 
     In this way, by transmitting a driving force generated by a mounting board driving motor  25  to the document mounting board  10  including the first member  11  and the second member  12 , the document mounting board  10  can turn about the first turning shaft  21  or the second turning shaft  22 . That is, the document mounting board  10  includes a transmission mechanism (not illustrated) transmitting a driving force generated by the mounting board driving motor  25  and thus the first member  11  of the document mounting board  10  can turn about the first turning shaft  21  and the second member  12  can turn about the second turning shaft  22 . 
     In the scanner body  2 , a conveyance roller  41  is disposed downstream from the feed mechanism  30  in the feeding direction of the documents S in the feed mechanism  30 . On the downstream side of the conveyance roller  41  in the conveyance direction of the documents S in the conveyance roller  41 , a discharge roller  42  is disposed in the vicinity of a discharge port  3  of the documents S. The image reading unit  50  is disposed between the conveyance roller  41  and the discharge roller  42  in the conveyance direction of the documents S, that is, the image reading unit  50  is disposed downstream from the feed mechanism  30  in the feeding direction of the documents S in the feed mechanism  30 . Accordingly, the image reading unit  50  can read an image of the document S fed by the feed mechanism  30 . 
       FIG. 2  is a functional block diagram of a scanner including the sheet feeding device according to the embodiment. The hardware configuration of the control unit  70  includes a central processing unit (CPU), a graphic processing unit (GPU), a digital signal processor (DSP), a large scale integrated circuit (LSI), an application specific integrated circuit (ASIC), and/or a field-programming gate array (FPGA), functioning as the material controller that mainly performs operation process, or includes a control circuit. The control unit  70  includes a random access memory (RAM) and a read only memory (ROM) that sore programs or information, a fixed disk drive such as a hard disk drive, a solid state drive (SSD), and/or an optical disk, storing various kinds of information, and the like. In addition, The control unit  70  includes an input/output interface, and the hardware configuration of the control unit  70  is the same as a conventional personal computer or a scanner device and thus detailed description thereof will not be made. The mounting board driving motor  25  and the feed driving motor  45  are electrically connected to the control unit  70  and can be controlled by the control unit  70 . A conveyance driving motor  46  that generates a driving force for causing the conveyance roller  41  and the discharge roller  42  to rotate, is also electrically connected to the control unit  70  and can be controlled by the control unit  70 . The image reading unit  50  is also electrically connected to the control unit  70  and can be controlled by the control unit  70 , and image data read by the image reading unit  50  can be transmitted to the control unit  70 . 
     The scanner  1  includes a power supply button  61  that switches ON and OFF of a power supply, a scan button  62  that causes the scanner  1  to start scanning, and a document sensor  65  that detects presence of a document S mounted on the document mounting board  10 , and these are also electrically connected to the control unit  70 . Among these, the power supply button  61  and the scan button  62  are disposed on the surface of the scanner  1  and can be operated by a user of the scanner  1 . The document sensor  65  is disposed in the vicinity of the document mounting board  10  in the scanner body  2 , and the document sensor  65  can detect presence of a document S mounted on the document mounting board  10  using infrared rays or the like. 
     The sheet feeding device  5  according to this embodiment has the above-mentioned configuration and operations thereof will be described below.  FIG. 3  is a diagram illustrating a state in which the scanner illustrated in  FIG. 1  is not used. When the scanner  1  according to this embodiment is not used, the document mounting board  10  can be set to be parallel to the top surface of the scanner body  2  from the upper side of the top surface of the scanner body  2  and thus the document mounting board  10  can become a storage state. Specifically, when an image of a document S is not read by the image reading unit  50  and the document mounting board  10  is changed to the storage state, the first member  11  of the document mounting board  10  turns about the first turning shaft  21  to the image reading unit  50 . Accordingly, the first member  11  rises upward, and an end thereof opposite to an end close to the first turning shaft  21 , is located on the top surface of the scanner body  2 . 
     The second member  12  turns about the second turning shaft  22  to the image reading unit  50 . Accordingly, the second member  12  is located above the image reading unit  50  in the scanner body  2  and is disposed parallel to the top surface of the scanner body  2 . When the scanner  1  is not used, the second member  12  is changed to the storage state in which the second member  12  is parallel to the top surface of the scanner body  2  and thus the document mounting board  10  is stored. 
       FIG. 4  is a diagram illustrating a state in which documents are mounted on the document mounting board illustrated in  FIG. 1 . When documents S are mounted on the document mounting board  10  to read images of the documents S using the scanner  1 , the first member  11  turns about the first turning shaft  21  in a direction in which the first member  11  is laid down, and the second member  12  turns about the second turning shaft  22  in a direction in which the second member  12  is separated apart from the scanner body  2 . Accordingly, the mounting surface  15  of the document mounting board  10  is inclined from up to down from upstream to the downstream in the feeding direction of the document S. In this case, an angle formed by the first mounting surface  16  of the first member  11  and the second mounting surface  17  of the second member  12 , is set to be less than 180°. 
     In this way, when the document mounting board  10  is changed to a document mounting state in which documents S are mounted on the document mounting board  10 , the document mounting board  10  turns about the first turning shaft  21  to a position at which the top end of the pickup roller  31  is not located above the first mounting surface  16  of the first member  11  by causing the pickup roller  31  to pass through the pickup roller hole  13 . Accordingly, when mounting documents S on the document mounting board  10 , the document mounting board  10  is inclined from up to down from an upstream end in the feeding direction of a document S to the end on the first turning shaft  21  side at an angle at which the mounting surface  15  for the documents S is located above the pickup roller  31 . Accordingly, when mounting documents S on the document mounting board  10 , the document mounting board  10  is changed to a state, in which the first mounting surface  16  of the first member  11  is located above the pickup roller  31 . 
       FIG. 5  is a diagram illustrating a state in which a document mounted on the document mounting board illustrated in  FIG. 1  is fed. When a document S mounted on the document mounting board  10  is fed by the feed mechanism  30  to read an image of the document S using the scanner  1 , the document mounting board  10  is changed to an document feeding state by turning about the first turning shaft  21  in a direction in which the mounting surface  15  moves downward. Accordingly, the pickup roller  31  passes through the pickup roller hole  13  of the first member  11  from the lower side of the first member  11  and the pickup roller  31  protrudes from the pickup roller hole  13  such that the top end thereof is located above the first mounting surface  16  of the first member  11 . 
     In other words, for change to the document feeding state, the document mounting board  10  turns about the first turning shaft  21  in a direction in which the mounting surface  15  moves downward such that the first mounting surface  16  is located below the top end of the pickup roller  31  passing through the pickup roller hole  13  from the lower side of the first member  11 . In this case, the document mounting board  10  is inclined from up to down from the upstream end in the feeding direction of a document S to the end on the first turning shaft  21  side, and the inclination angle thereof is smaller than the inclination angle in the state in which documents S are mounted on the document mounting board  10 . 
       FIG. 6  is a detailed diagram of a periphery of the pickup roller in  FIG. 4 . When the document mounting board  10  is changed to the document mounting state (see  FIG. 4 ) and documents S are mounted on the mounting surface  15 , the document mounting board  10  in the document mounting state is inclined from up to down from upstream to downstream in the feeding direction of a document S and thus the documents S move downstream in the feeding direction with their own weight. That is, the documents S mounted on the mounting surface  15  move from the second mounting surface  17  side to the first mounting surface  16  side. 
     In this case, since the document mounting board  10  in the document mounting state has a larger inclination angle than that of the document mounting board  10  in the document feeding state, the documents S can easily move to the first mounting surface  16  side. Since the first mounting surface  16  has a friction reducing processed portion and a frictional force between the document S coming in contact with the first mounting surface  16  and the first mounting surface  16  decreases, the document S coming in contact with the first mounting surface  16  can move more easily downstream in the feeding direction of a document S. 
     Here, the pickup roller  31  is disposed downstream from the document mounting board  10  in the feeding direction of a document S, but when the document mounting board  10  is in the document mounting state, the first mounting surface  16  of the first member  11  is located above the pickup roller  31 . That is, the pickup roller  31  does not protrude upward from the pickup roller hole  13 . Accordingly, the documents S, which is mounted on the mounting surface  15  of the document mounting board  10  and which is moved downstream in the feeding direction with their own weight, move to the position of the separation member  35  disposed downstream from the pickup roller  31  without coming in contact with the pickup roller  31 . 
     A pickup spring  36  serving as a buffer member when documents S come in contact with the separation member  35 , is disposed on an upstream surface of the separation member  35  in the feeding direction of a document S, and the documents S moving to the position of the separation member  35  with their own weight, are buffered by the pickup spring  36  and ends thereof come in contact with the separation member  35 . Since the documents S move to the position of the separation member  35  and come in contact with the separation member  35  in this way, the documents S mounted on the document mounting board  10  can be fed by the pickup roller  31  when the feed mechanism  30  feeds the documents S. 
     It is preferable that the first mounting surface  16  of the first member  11  located above the pickup roller  31  be separated from the pickup roller  31  by a predetermined distance a or more. That is, when the distance a between the first mounting surface  16  and the pickup roller  31  is too small, a case in which a part of a document S enters the pickup roller hole  13  and comes in contact with the pickup roller  31  having a high friction coefficient and movement of the document S is stopped, is considered. In this way, it is preferable that the distance a between the first mounting surface  16  and the pickup roller  31  be about 2 mm, such that the document S entering the pickup roller hole  13  does not come in contact with the pickup roller  31 . 
       FIG. 7  is a detailed diagram of the periphery of the pickup roller in  FIG. 5 . When the feed mechanism  30  feeds documents S mounted on the document mounting board  10 , the document mounting board  10  turns about the first turning shaft  21  in a direction in which the mounting surface  15  moves downward, whereby the document mounting board  10  is changed to the document feeding state (see  FIG. 5 ). Accordingly, the mounting surface  15  of the document mounting board  10  moves downward from a contact portion  32  of the pickup roller  31  with the document S. That is, when the documents S mounted on the document mounting board  10  are fed, the document mounting board  10  turns about the first turning shaft  21  such that the first mounting surface  16  moves downward from the contact portion  32  of the pickup roller  31  with the document S. Accordingly, the document S located at the lowermost among the documents S mounted on the document mounting board  10  comes in contact with the pickup roller  31 . 
     Since the outer circumferential surface of the pickup roller  31  has a high frictional coefficient, the lowermost document S among the documents S mounted on the document mounting board  10 , is fed in the rotating direction of the pickup roller  31  due to a frictional force with the pickup roller  31  by causing the pickup roller  31  to rotate in a state in which the document S comes in contact therewith. That is, since the pickup roller  31  rotates in a direction in which the top end of the outer circumferential surface moves downstream in the feeding direction of a document S, the document S coming in contact with the pickup roller  31  at the contact portion  32  among the documents S mounted on the document mounting board  10 , moves downstream in the feeding direction with the rotation of the pickup roller  31 . 
     At this time, the documents S other than the document S coming in contact with the pickup roller  31 , are drawn by the document S coming in contact with the pickup roller  31  and try to move downstream in the feeding direction, but movement of the documents S is regulated by the separation member  35  disposed downstream from the pickup roller  31 . Accordingly, when the pickup roller  31  rotates in a state in which the documents S mounted on the document mounting board  10  come in contact with the pickup roller  31 , only the lowermost document S coming in contact with the pickup roller  31  is fed downstream from the pickup roller  31 . That is, when a plurality of documents S are mounted on the document mounting board  10 , the feed mechanism  30  separates the documents S by using the separation member  35  and feeds only one document to the image reading unit  50 . 
     It is preferable that a distance b between the first mounting surface  16  and the contact portion  32  of the pickup roller  31  with the document S when the first mounting surface  16  moves downward from the contact portion  32  of the pickup roller  31  with the document S be equal to or greater than 3 mm. That is, it is preferable that the protruding distance b of the pickup roller  31  from the first mounting surface  16  be equal to or greater than 3 mm. When the protruding distance b of the pickup roller  31  from the first mounting surface  16  is too small at the time of feeding a document S, a pushed-up distance of the document S by the pickup roller  31  is small, and thus the weight of the documents S is not applied to the pickup roller  31 . In this case, a frictional force between the pickup roller  31  and the document S decreases and thus the document S cannot be appropriately conveyed. Accordingly, it is preferable that the protruding distance b of the pickup roller  31  from the first mounting surface  16  be equal to or greater than 3 mm so as to secure a frictional force between the pickup roller  31  and the document S. 
       FIG. 8  is a diagram illustrating an angle between the first member and the second member and is illustrating the document mounting state.  FIG. 9  is a diagram illustrating the angle between the first member and the second member and is illustrating the document feeding state. The document mounting board  10  can be switched between the document mounting state and the document feeding state by turning about the first turning shaft  21 , but the relative angle between the first member  11  and the second member  12  in the document mounting board  10  is also changed in the document mounting state and the document feeding state. Specifically, in the document mounting board  10 , the angle θ formed by the first mounting surface  16  and the second mounting surface  17 , when the documents S are mounted on the document mounting board  10 , is set to be smaller than that when the documents S are fed. 
     For example, when the document mounting board  10  is switched from the document feeding state ( FIG. 9 ) to the document mounting state ( FIG. 8 ), the angle θ formed by the first mounting surface  16  and the second mounting surface  17 , decreases by causing the second member  12  to turn about the second turning shaft  22  relative to the first member  11 . Accordingly, when the documents S are mounted on the document mounting board  10 , a contact area between the document S and the second member  12  decreases, and thus the frictional force between the document S and the second member  12  decreases. By decreasing the angle θ formed by the first mounting surface  16  and the second mounting surface  17 , the second member  12  is close to an upright state and thus a ratio of the weight of the documents S applied to the first member  11  increases. Since the frictional resistance of the first mounting surface  16  of the first member  11  decreases by the friction reducing process, the documents S mounted on the document mounting board  10 , can easily move downstream in the feeding direction and can easily reach the separation member  35  of the feed mechanism  30 . 
     On the other hand, when the document mounting board  10  is switched from the document mounting state ( FIG. 8 ) to the document feeding state ( FIG. 9 ), the angle θ formed by the first mounting surface  16  and the second mounting surface  17 , increases by causing the second member  12  to turn about the second turning shaft  22  relative to the first member  11 . Accordingly, since the contact area between the mounting surface  15  of the document mounting board  10  and the document S increases, the document S can be stably held while the document S is fed by the feed mechanism  30 . 
     In the sheet feeding device  5  according to this embodiment, the document S can be appropriately fed by switching the document mounting board  10  between the document mounting state and the document feeding state, which can be realized by setting the positional relationship of the first turning shaft  21 , the second turning shaft  22 , and a separation nip  38  (see  FIGS. 6 and 7 ) to an appropriate positional relationship. That is, in the sheet feeding device  5 , since the first turning shaft  21 , the second turning shaft  22 , and the separation nip  38  are arranged from upstream to downstream in the feeding direction of a document S in the order of the second turning shaft  22 , the separation nip  38 , and the first turning shaft  21 , the document S can be appropriately conveyed. The separation nip  38  mentioned herein is a contact portion between the separation member  35  and the pickup roller  31 . 
     That is, when the first turning shaft  21  is located upstream from the separation nip  38 , in order to cause the pickup roller  31  to pass through the pickup roller hole  13  and enable switching between the document mounting state and the document feeding state, a case in which the first turning shaft  21  has to be disposed at a position protruding into the feeding path of a document S, is considered. In this case, since the document S comes in contact with the first turning shaft  21  protruding into the feeding path of a document S or the first member  11 , the document S cannot be fed. When the second turning shaft  22  is located downstream from the separation nip  38 , the same result as when the document mounting board  10  is constituted by only one member, is obtained, and thus advantages that the document mounting board  10  is changed to the storage state or the document S can be easily brought into contact with the separation member  35  in the document mounting state, cannot be achieved. 
     On the contrary, since the first turning shaft  21 , the second turning shaft  22 , and the separation nip  38  are arranged in the order of the second turning shaft  22 , the separation nip  38 , and the first turning shaft  21  from upstream to downstream in the feeding direction of a document S, the document S can be satisfactorily fed and advantages based on the change of the angle between the first member  11  and the second member  12  of the document mounting board  10 , can be achieved. 
     A processing sequence when an image of a document S is read by using the scanner  1  performing the above-mentioned operations, will be described below.  FIG. 10  is a flow diagram illustrating a processing sequence when an image of a document is read by using the scanner including the sheet feeding device according to the embodiment. When an image of a document S is read by using the scanner  1  including the sheet feeding device  5  according to the embodiment, the power supply is turned on by operating the power supply button  61  (step ST 11 ). Then, the document mounting board  10  is opened (step ST 12 ). That is, the document mounting board  10  in the storage state is changed to the document mounting state. The operation of opening the document mounting board  10  in the storage state and changing to the document mounting state may be performed manually by allowing a user to grasp the document mounting board  10 , or the storage state may be changed to the document mounting state electrically using a driving force generated by the mounting board driving motor  25 . 
     Then, a user sets documents S to be read by mounting the documents S of which images will be read on the mounting surface  15  of the document mounting board  10  (step ST 13 ). When the documents S are mounted on the document mounting board  10 , the scan button  62  is pushed (step ST 14 ). Accordingly, an input instruction indicating start of scanning is input to the scanner  1 . 
     When the scan button  62  is pushed, it is first determined whether or not a document S is present on the document mounting board  10  (step ST 15 ). This determination is performed on the basis of the detection result of the document sensor  65  by the control unit  70 . When it is determined that no document S is present on the document mounting board  10  (No determination in step ST 15 ), pushing of the scan button  62  is waited for again in step ST 14 . 
     On the other hand, when it is determined that a document S is present on the document mounting board  10  (Yes determination in step ST 15 ), the document mounting board  10  is moved downward to the lower side of the pickup roller  31  (step ST 16 ). That is, the mounting board driving motor  25  is driven to switch the document mounting board  10  in the document mounting state to the document feeding state. At this time, the angle θ formed by the first mounting surface  16  and the second mounting surface  17  also increases. 
     By activating the feed driving motor  45  or the conveyance driving motor  46  in this state, the pickup roller  31  or the conveyance roller  41  starts its rotation (step ST 17 ). Accordingly, the documents S mounted on the document mounting board  10  are fed from the document mounting board  10  to the image reading unit  50  one by one. The image reading unit  50  reads an image of a document S that is forwarded in this way (step ST 18 ). The image read by the image reading unit  50  is transmitted to the control unit  70  and is stored in a storage unit (not illustrated) or the like of the scanner  1 . 
     Then, it is determined whether a document S is not present on the document mounting board  10  (step ST 19 ). This determination is also performed on the basis of the detection result of the document sensor  65  by the control unit  70 . When the control unit  70  determines that a document S is present on the document mounting board  10  (No determination in step ST 19 ), the document S mounted on the document mounting board  10  continues to be fed again in step ST 17 . 
     On the other hand, when it is determined that no document S is present on the document mounting board  10  (Yes determination in step ST 19 ), the pickup roller  31  and the conveyance roller  41  are stopped (step ST 20 ). That is, since there is no document S to be fed to the image reading unit  50  by the pickup roller  31  or the conveyance roller  41 , the pickup roller  31  and the conveyance roller  41  are stopped by stopping the feed driving motor  45  and the conveyance driving motor  46 . 
     Then, the document mounting board  10  is made to protrude upward from the pickup roller  31  (step ST 21 ). That is, the mounting board driving motor  25  is driven to switch the document mounting board  10  in the document feeding state to the document mounting state. When the document mounting board  10  is switched to the document mounting state, the scanning by using the scanner  1  ends (step ST 22 ). The scanner  1  ending the scanning waits for mounting documents S on the document mounting board  10  by switching the document mounting board  10  to the document mounting state and prepares for next scanning. 
     In the sheet feeding device  5  according to the above-mentioned embodiment, when documents S are mounted on the document mounting board  10 , the mounting surface  15  is located above the pickup roller  31  and thus the documents S on the mounting surface  15  can be more satisfactorily moved to the position of the separation member  35  and be brought into contact with the separation member  35 . When the documents S mounted on the document mounting board  10  are fed, the document S moving to the position of the separation member  35  can be fed by the pickup roller  31  by causing the document mounting board  10  to turn such that the mounting surface  15  moves downward from the contact portion  32  of the pickup roller  31  with the document S. As a result, it is possible to more satisfactorily prevent occurrence of non-feeding of a document S. 
     The document mounting board  10  includes the first member  11  and the second member  12 , the first mounting surface  16  is located above the pickup roller  31  when documents S are mounted on the document mounting board  10 , and the first mounting surface  16  moves downward from the pickup roller  31  when a document S is fed. Accordingly, the document S can be fed by the pickup roller  31 . In this way, by constituting the document mounting board  10  with the first member  11  and the second member  12 , the document mounting board  10  can be changed to be suitable for each use state of the scanner  1 . As a result, it is possible to more satisfactorily prevent occurrence of non-feeding of an document S and to achieve improvement in usability. 
     In the document mounting board  10 , when documents S are mounted on the document mounting board  10 , the angle formed by the first mounting surface  16  and the second mounting surface  17  is smaller than that when the document S is fed. Accordingly, the document S mounted on the document mounting board  10  can be easily moved to the position of the separation member  35 . As a result, it is possible to more satisfactorily prevent non-feeding of a document S from occurring. 
     When an image of an document S is not read, the document mounting board  10  is stored in a state in which the second member  12  is located above the image reading unit  50  and it is thus possible to achieve compactness of the scanner  1  in a non-used state. As a result, it is possible to improve usability of the scanner  1 . 
     Since the first mounting surface  16  has the friction reducing processed portion for reducing frictional resistance to the document S moving in the feeding direction, the document S on the mounting surface  15  can be more satisfactorily moved to the position of the separation member  35  when documents S are mounted on the document mounting board  10 . As a result, it is possible to more satisfactorily prevent occurrence of non-feeding of an document S. 
     Modified Example 
     In the sheet feeding device  5  according to the embodiment, surface treatment using a material having a low frictional coefficient is used as the friction reducing process which is performed on the first mounting surface  16 , but the friction reducing process is not limited thereto.  FIG. 11  is a diagram illustrating a modified example of the sheet feeding device according to the embodiment in which protrusions are formed by the friction reducing process. In the friction reducing process which is performed on the first mounting surface  16 , for example, as illustrated in  FIG. 11 , a plurality of protrusions  80  may be formed on the first mounting surface  16 . The protrusions  80  are formed on the first mounting surface  16  to have a constant height in the conveyance direction of a document S and form unevenness in the direction perpendicular to the conveyance direction of a document S. That is, the protrusions  80  are formed to protrude from the first mounting surface  16  when viewed from the conveyance direction of a document S. By forming the plurality of protrusions  80  on the first mounting surface  16  in this way, a contact area between the first mounting surface  16  and the document S can be decreased. Accordingly, it is possible to reduce a frictional force therebetween and to more satisfactorily move a document S to the position of the separation member  35 , when documents S are mounted on the document mounting board  10 . 
     Since the first member  11  moves downward from the top end of the pickup roller  31  at the time of feeding a document S, the protrusions  80  are not easily abraded by the fed document S. Accordingly, even when friction reduction is carried out using the protrusions  80 , it is possible to continuously decrease a frictional force between the first mounting surface  16  and a document S. 
       FIG. 12  is a diagram illustrating a modified example of the sheet feeding device according to the embodiment in which a roller is used by the friction reducing process. In the friction reducing process which is performed on the first mounting surface  16 , for example, as illustrated in  FIG. 12 , a plurality of rollers  85  may be disposed in the first mounting surface  16 . Each roller  85  is formed in a substantially columnar shape and is disposed to be rotatable about a rotation shaft parallel to the rotation shaft  33  of the pickup roller  31 . The roller  85  is buried in the first member  11  to have a positional relationship that the top end thereof slightly protrudes from the first mounting surface  16 . By disposing the plurality of rollers  85  in the first mounting surface  16  in this way, resistance acting when a document S moves on the first mounting surface  16 , can be reduced and thus the document S can be more satisfactorily moved to the position of the separation member  35  at the time of mounting documents S on the document mounting board  10 . 
       FIG. 13  is a diagram illustrating a modified example of the sheet feeding device according to the embodiment in which a stepped portion is formed by the friction reducing process. In the friction reducing process which is performed on the first mounting surface  16 , for example, as illustrated in  FIG. 13 , a stepped portion may be formed in the periphery of the pickup roller hole  13  and the other portion. That is, the periphery of the pickup roller hole  13  may be formed as a convex portion  91  protruding from the other portion and a portion separated from the pickup roller hole  13  may be formed as a concave portion  92  having a smaller height than the convex portion  91 . By forming the stepped portion including the convex portion  91  and the concave portion  92  in the first mounting surface  16 , a contact area between the first mounting surface  16  and a document S can be decreased. Accordingly, it is possible to reduce a frictional force therebetween and to more satisfactorily move a document S to the position of the separation member  35  at the time of mounting documents S on the document mounting board  10 . 
       FIG. 14  is a diagram illustrating a modified example of the sheet feeding device according to the embodiment in which a vibration generating member is disposed by the friction reducing process. In the friction reducing process which is performed on the first mounting surface  16 , for example, as illustrated in  FIG. 14 , a vibration generating member  95  may be disposed in the first member  11 . The vibration generating member  95  can electrically generate vibration in the first mounting surface  16 . In this way, by disposing the vibration generating member  95  in the first member  11  and generating vibration in the first mounting surface  16  by using the vibration generating member  95 , a contact time between the first mounting surface  16  and a document S is decreased and it is thus possible to reduce a frictional force therebetween. Accordingly, it is possible to more satisfactorily move a document S to the position of the separation member  35  at the time of mounting documents S on the document mounting board  10 . 
     It is preferable that the vibration generating member  95  be activated to generate vibration in the first mounting surface  16  after the document sensor  65  detects that a document S is mounted on the document mounting board  10  and before the document S is fed by the feed mechanism  30 . 
     The sheet feeding device according to the present disclosure can more satisfactorily prevent non-feeding of an document from occurring. 
     All examples and conditional language recited herein are intended for pedagogical purposes of aiding the reader in understanding the disclosure and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the disclosure. Although the embodiments of the present disclosure have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.