Patent Publication Number: US-8109498-B2

Title: Sheet feeding device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2009-225786, filed on Sep. 30, 2009, the entire subject matter of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     An aspect of the present invention relates to a sheet feeding device to convey a sheet in a sheet feeding path. 
     2. Related Art 
     A sheet feeding device to be provided to, for example, an image forming apparatus such as a printer and a copier, having a base structure, one or more pairs of conveyer rollers arranged in positions along a feeding path, is known. 
     In the sheet feeding device, each of the conveyer rollers has a core shaft to be rotatably supported by the base structure and rollers which are fixed to the core shaft to be rotated along with the core shaft. The pair of conveyer rollers are thus rotated with the sheet in-between them so that the sheet is conveyed in the feeding path by the rotating force of the rollers. The sheet conveyed in the feeding path is led to an image forming unit of the image forming apparatus to have an image formed thereon. 
     When the conveyer rollers are rotated in the image forming apparatus by external driving force, the core shafts of the conveyer rollers may be subject to pressure of the driving force, and the conveyer rollers may be bowed by the pressure. When the conveyer rollers are bowed, the sheet may be conveyed in a skewed orientation with respect to the feeding path and may cause sheet feeding errors such as sheet jam. The error condition in the sheet may prevent the image forming unit from correctly forming the image on the sheet. Therefore, in order to restrict the deformation of the conveyer rollers, the feeding device may be provided with arm-pieces extending in a direction perpendicular to the core shafts and hooked to the core shafts at one end and fixed to the base structure at the other end so that the arm-pieces suppress the core shafts. 
     SUMMARY 
     Such an arm-piece is required for each conveyer roller and increases a quantity of pieces of components in the sheet feeding device. Moreover, if the sheet feeding device is equipped with a plurality of pairs of conveyer rollers, and each conveyer roller requires the arm-piece, the quantity of pieces of components in the sheet feeding device increases to be even larger. 
     In view of the above drawback, the present invention is advantageous in that a sheet feeding device, in which sheet feeding errors in the feeding path can be reduced in a less complicated configuration, is provided. 
     According to an aspect of the present invention, a sheet feeding device, having a sheet feeding mechanism to convey a sheet in a sheet feeding path, and an image processor to process an image formed on one of a first surface and a second surface of the sheet being conveyed in the sheet feeding path, is provided. The sheet feeding mechanism includes a base structure, a first roller arranged in a position along the feeding path, and a second roller arranged in a position along the feeding path on a downstream side with respect to the first roller. The first roller includes a first shaft, which is rotatably supported by the base structure at each axial end thereof, and a first roller body fixed to the first shaft. The second roller includes a second shaft, which is rotatably supported by the base structure at each axial end thereof, and a second roller body fixed to the second shaft. The first roller feeds the sheet to the sheet feeding path by rotating the first roller body being in contact with the sheet rotated along with the first shaft, and the second roller conveys the sheet in the sheet feeding path by rotating the second roller body being in contact with the sheet rotated along with the second shaft. The first roller and the second roller are connected with each other by a connector member, which rotatably supports the first shaft and the second shaft and maintains positional relation of the first shaft and the second shaft with respect to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  is an overall perspective view of an image processing apparatus with an ADF in a closed posture according to an embodiment of the present invention. 
         FIG. 2  is a top plan view of the image processing apparatus with the ADF according to the embodiment of the present invention. 
         FIG. 3  is a perspective view of the image processing apparatus with the ADF in an open posture according to the embodiment of the present invention. 
         FIG. 4  is a cross-sectional side view of the image processing apparatus according to the embodiment of the present invention taken from a line A-A in  FIG. 2 . 
         FIG. 5  is an enlarged partial view of the ADF according to the embodiment of the present invention. 
         FIG. 6  is a diagram to illustrate a feeding path, a feeding mechanism, a first image sensor, and a second image sensor in the ADF according to the embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of the image processing apparatus according to the embodiment of the present invention with a top cover being open. 
         FIG. 8  is a perspective partial view of the ADF according to the embodiment of the present invention with the top cover being removed. 
         FIG. 9  is a perspective partial view of the ADF according to the embodiment of the present invention with the top cover and an upper guide being removed. 
         FIG. 10  is a perspective view of the top cover being open in the ADF according to the embodiment of the present invention. 
         FIG. 11  is a cross-sectional partial view of the ADF according to the embodiment of the present invention taken from a line B-B in  FIG. 2 . 
         FIG. 12  is an enlarged perspective view of a first shaft, a second shaft, and a connector piece in the ADF according to the embodiment of the present invention. 
         FIG. 13A  illustrates bowed behaviors of the first and second shafts without the connector piece in the ADF according to the embodiment of the present invention.  FIG. 13B  illustrates restricted behaviors of the first and second shafts with the connector piece being attached in the ADF according to the embodiment of the present invention. 
         FIG. 14  is an enlarged cross-sectional view of the ADF according to the embodiment of the present invention taken from the line B-B in  FIG. 2 . 
         FIG. 15  is an enlarged cross-sectional view of the ADF without the connector piece according to the embodiment of the present invention taken from the line B-B in  FIG. 2 . 
         FIG. 16  is an enlarged top view of the ADF with the top cover removed according to the embodiment of the present invention. 
         FIG. 17  is an enlarged top view of the ADF with the top cover removed according to the embodiment of the present invention. 
         FIG. 18  is an enlarged cross-sectional view of the ADF according to the embodiment of the present invention taken from a line C-C in  FIG. 17 . 
         FIG. 19  is an enlarged cross-sectional view of the ADF taken from the line C-C in FIG.  17  but having no connector piece. 
         FIG. 20  is an enlarged perspective view of a modified connector piece in the ADF according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment according to the present invention will be described with reference to the accompanying drawings. 
     An automatic document feeder (ADF)  11  of an image processing apparatus  10  represents a sheet feeding device according to an embodiment of the present invention. In the present embodiment, directions concerning the image processing apparatus  10  will be referred to in accordance with the orientation of the image processing apparatus  10  shown in  FIG. 1 . That is, a nearer side in  FIG. 1 , on which an operation panel  3  is arranged, is referred to as front, and further side opposite from the operation panel  3  is referred to as rear. Further, a side which corresponds to a viewer&#39;s left-hand side is referred to as left, and an opposite side from the left is referred to as right. Furthermore, directions of the drawings in  FIGS. 2-20  are similarly based on the orientation of the image processing apparatus  10  as defined above and correspond to those with respect to the image processing apparatus  10  shown in  FIG. 1  even when the drawings are viewed from different aspects. 
     1. Overall Configuration of the Image Processing Apparatus 
     The image processing apparatus  10  in the present embodiment has known image processing functions, such as a function to read an image formed on a sheet and generate image data representing the read image, and a data transmission function to transmit the generated image data to an external device. As shown in  FIGS. 1-3 , the image processing apparatus  10  includes an image processing unit  20  and the ADF  11 . The ADF  11  is arranged on top of the image processing unit  20 . Although not specifically shown in  FIG. 1 , a lower rear edge of the ADF  11  is supported rotatably to rotate about a shaft (not shown), which extends in the right-left direction along an upper rear edge of the image processing unit  20 . Therefore, the ADF  11  can shift postures thereof between a closed position (see  FIG. 1 ) and an open position (see  FIG. 3 ) when a front part of the ADF  11  is uplifted and lowered. As shown in  FIG. 3 , when the ADF  11  is in the open position, a top surface of the image processing unit  20  is exposed. 
     2. Image Processing Unit 
     The image processing unit  20  is provided with the operation panel  3  at a front part thereof. The operation panel  3  is a user interface device to display information concerning operations conducted in the image processing apparatus  10  and can be operated by a user to input information concerning the operations. Further, the image processing unit  20  includes a controller (not shown) to control the ADF  11  and the operation panel  3  and power unit (not shown) inside a chassis thereof. 
     As shown in  FIGS. 3-5 , the image processing unit  20  is provided with a contact glass  22  at a top surface thereof. The contact glass  22  includes two pieces of glasses, which are a fixed-reading glass  79  arranged on the left and a movable-reading glass  80  arranged on the right. A document separator  81 , which will be described later in detail, is arranged in a position between the fixed-reading glass  79  and the movable-reading glass  80 . 
     The image processing unit  20  includes a first and a second image sensors  24 ,  25 , which are image processors to read images formed on a sheet  9 . The second image sensor  25  is in a position below the contact glass  22  within the chassis. The second image sensor  25  is a known image reading sensor such as, for example, a contact image sensor (CIS) or a charge coupled device (CCD). The second image sensor  25  is slidably set on a slider shaft  78 , which extends in the right-left direction in the image processing unit  20 . The second image sensor  25  can be therefore slid on the slider shaft  78  in the right-left direction along the slider shaft  78  when driven by a driving mechanism (not shown) such as a pulley-and-belt mechanism. Description of the first image sensor  24  will be provided later. 
     When an original image formed on an original document such as a sheet of paper or an open-paged book is read by the second image sensor  25 , the ADF  11  is not necessarily used. In other words, for example, when the user places the document on the movable-reading glass  80  with the ADF  11  in the open position, the ADF  11  is not used. The second image sensor  25  is moved underneath the fixed-reading glass  79  along the slider shaft  78  from left to right so that the image on the document is sequentially read by the moving second image sensor  25 . The read image is converted into data representing the image in a control unit (not shown). 
     Alternatively, as described below, the second image sensor  25  may be activated in an image reading position  18  below the fixed-reading glass  79  when the ADF  11  is used. 
     3. ADF 
     As shown in  FIGS. 1-5 , the ADF  11  includes a sheet-feed tray  12 , on which a plurality of sheets  9  (e.g., paper and OHP films) of original documents can be stacked, and a sheet-discharge tray  14 , on which sheets discharged out of a feeding path  16  can be stacked. The sheet-feed tray  12  and the sheet-discharge tray  14  are arranged in vertically overlapping positions. In the present embodiment, the sheet-feed tray  12  is in an upper position above the sheet-discharge tray  14  and on an uppermost stream side of the feeding path  16 . Each sheet  9  includes a first surface  9 A being a top surface which faces upward and a second surface  9 B being a lower surface which faces downward when the sheet is in the sheet-feed tray  12 . 
     As shown in  FIGS. 4-6 , the ADF  11  picks up the sheets  9  stacked in the sheet-feed tray  12  one-by-one continuously and carries in the feeding path  16 . The feeding path  16  is illustrated in a double-dotted line in  FIG. 6 . The sheets  9  carried in the feeding path  16  are discharged out of the ADF  11  and led to the sheet-discharge tray  14 . The ADF  11  has the first image sensor  24 , which reads an image formed on the second surface  9 B. Further, ADF  11  includes the second image sensor  25 , which reads an image formed on the first surface  9 A. 
     3.1 Feeding Mechanism 
     The feeding mechanism in the ADF  11  of the present embodiment includes a sheet-feed unit  50 , conveyer unit  60 , and a sheet-discharge unit  70 . As shown in  FIGS. 4-6 , the feeding path  16  in the ADF  11  includes a first feeding path  26 , which extends from the sheet-feed tray  12  to the left, a curved feeding path  27 , which is continuous from the first feeding path and curved downward, and a second feeding path  28 , which is continuous from the curved feeding path  27  and extends to the upper right toward the sheet-discharge tray  14 . 
     The feeding mechanism in the ADF  11  has a base structure including a main frame  30 , an upper guide  34 , and a lower guide  36 . The main frame  30  has two sides defining front and rear ends of the ADF  11  and a bottom surface defining a bottom of the ADF  11  (see also  FIGS. 8-10 ). The upper guide  34 , extending from the sheet-feed tray  12  to an area in vicinity of a main roller  64 , holds the sheets  9  in the sheet-feed tray  12  from below and defines the first feeding path  26  to be partitioned from lower space. The lower guide  36  is a plate defining the second feeding path  28  and extends from an area below the main roller  64  toward an area in vicinity of the sheet-discharge unit  70 , which will be described later in detail. 
     The feeding mechanism in the ADF  11  further includes a top cover  32 , which is arranged to cover a left-side part of the ADF  11  with respect to the upper guide  24 . A left-side edge of the top cover  32  is swingably supported by a left-side edge of the main frame  30 . When a right-hand end of the top cover  32  is uplifted to rotate about the left-side edge, the top cover  32  in a closed position (see  FIG. 4 ) is shifted in an open position (see  FIG. 7 ). 
     The upper guide  34  includes a right-side part and a left-side part. As shown in  FIG. 5  and in  FIG. 8 , in which the top cover  32  is omitted, the left-side part of the upper guide  34  is fixed to upper-left portions of the main frame  30 . Meanwhile, as shown in  FIG. 9 , in which the top cover  32  and the upper guide  34  are omitted, the lower guide  36  is fixed to lower-left portions of the main frame  30 . Thus, as shown in  FIG. 4 , the left-side part of the upper guide  34  and the lower guide  36  are arranged in positions which vertically overlap each other. 
     The right-side part of the upper guide  34  is a flat plate extending from an area in the vicinity of the right-side edge of the left-side part of the upper guide  34  toward upper-right in an inclined posture (see  FIG. 4 ). The right-side part of the upper guide  34  corresponds to the sheet-feed tray  12  to hold the sheets  9  from below. Meanwhile, the main frame  30  is formed to have a recessed portion on a right-hand side with respect to the lower guide  36 . The recessed portion corresponds to the sheet-feed tray  14  to store the discharged sheets  9  therein. 
     When the top cover  32  is in the open position (see  FIG. 7 ), the left-side part of the upper guide  34 , the sheet-feed unit  50 , and the conveyer unit  60 , which will be described later, are exposed. Therefore, when the sheet  9  is jammed in the ADF  11 , the top cover  32  in the open position allows the user to access the left-side part of the upper guide  34 , a sheet-feed unit  50 , and a conveyer unit  60  so that the jammed sheet  9  can be removed by the user therefrom. 
     The top cover  32  is formed to have a plurality of reinforcing ribs  131 ,  132  on an inner side thereof. The ribs  131 ,  132  project downwards, when the cover  32  is in the closed position, and extend between the right-side edge and the left-side edge of the top cover  32  along the first feeding path  26  and the curved feeding path  27 . 
     The ribs  131  are formed in a center portion with respect to the front-rear direction of the top cover  32  to extend between the right-side edge and the left-side edge of the top cover  32  along the first feeding path  26  and the curved feeding path  27 . However, the ribs  131  are partially omitted in a portion, which may otherwise interfere with components inside the top cover  32  being in the closed position. The ribs  132  are formed on each side of the ribs  131  along the front and rear edges of the top cover  32 . The ribs  132  are formed to have cutouts  132 A,  132 B to prevent interference with a first shaft  56  and a second shaft  66 , which will be described later in detail. 
     As shown in  FIGS. 4 and 5 , when the top cover  32  is in the closed position, the left-side part of the upper guide  34  is covered with the top cover  32 , and edges of the ribs  131 ,  132  formed on the top cover  32  and the upper guide  34  define the first feeding path  26 . In other words, the ribs  131 ,  132  on the top cover  32  serve as guiding edges to guide the sheets  9  in the first feeding path  26 . 
     The main roller  64  in the ADF  11  is arranged in a position between; the left-side edges of the main frame  30  and the ribs  131 ,  132  of the top cover  32 ; and the left-side edges of the upper guide  34  and the lower guide  36 . The main roller  64  is arranged to have an outer periphery thereof to be apart from the left-side edges of the main frame  30  and the ribs  131 ,  132  of the top cover  32  so that a clearance, i.e., the curved feeding path  27 , is formed in between the outer periphery of the main roller  64  and the left-side edges of the main frame  30  and the ribs  131 ,  132  of the top cover  32 . In other words, the left-side edge of the main frame  30 , the left-side edges of the ribs  131 ,  132 , and the outer periphery of the main roller  64  serve as guiding edges to guide the sheets  9  in the curved feeding path  27 . 
     The second feeding path  28  is formed in between the main frame  30  and the lower guide  36 . In other words, the lower guide  36  serves as a guiding edge to guide the sheets  9  in the second feeding path  28 . As shown in  FIGS. 3-5 , a bottom surface  31  of the ADF  11  has a linearly-formed opening  84 , extending in the front-rear direction when the ADF  11  is in the closes position, in vicinity of a bordering area between the curved feeding path  27  and the second feeding path  28 . The bordering area between the curved feeding path  27  and the second feeding path  28  is exposed to the bottom surface  31  through the opening  84 . 
     When the sheet  9  is conveyed in the curved feeding path  27  to the second feeding path  28 , the sheet  9  being conveyed is exposed to the fixed-reading glass  79  through the opening  84 . When the exposed sheet  9  is further conveyed in the second feeding path  28 , the document separator  81 , which is arranged in the vicinity of the position between the fixed-reading glass  79  and the movable-reading glass  80 , directs the sheet  9  securely in the second feeding path  28 . 
     3.1.1 Sheet-Feed Unit 
     As shown in  FIGS. 4-6 , the sheet-feed unit  50  is arranged on an upper-stream side of the first feeding path  26  closer to the sheet-feet tray  12  and picks up the sheets  9  stacked in the sheet-feed tray  12  one-by-one to feed in the first feeding path  26  toward a downstream side of the first feeding path  26 . The sheet-feed unit  50  includes a pickup roller  52 , a separator roller  54 , and a separator pad  57 , which are arranged above the upper guide  34  on the upper-stream side of the first feeding path  26 . 
     As shown in  FIG. 9 , the separator roller  54  includes a first shaft  56  and a separator  54 A being a body of the separator roller  54 . The first shaft  56  is rotatably supported by the main frame  30  at a front end  56 A and a rear end  56 B thereof. The separator  54 A is fixed to an axially midst portion of the first shaft  56 . The rear end  56 B of the first shaft  56  is connected to a motor (not shown) via a drive force conveyer  99  having a plurality of gears. Thus, the first shaft  56  is rotated by the motor in a predetermined rotational direction (i.e., clockwise in  FIG. 4 ), and the separator  54 A is rotated accordingly along with the first shaft  56 . The first shaft  56  is a steel round bar, and an outer diameter thereof may range from a few to a dozen millimeters. 
     The first shaft  56  is provided with a swingable holder  58 , which covers an upper side of the separator  54 A and extends toward the upper-stream side of the first feeding path  26  (see  FIG. 5 ). The holder  58  rotatably holds the pickup roller  52  at the extending part thereof. The pickup roller  52  is coupled to the first shaft  56  through gears (not shown), which are arranged within the holder  58 . Accordingly, when the first shaft  56  rotates, the pickup roller  52  rotates in the clockwise direction as well as the separator  54 A. As the pickup roller  52  is rotated, the holder  58  is urged to swing toward the upper guide  34  by the rotation. In the present embodiment, the pickup roller  52  and the separator  54 A are configured to have equal circumferential velocities. 
     As shown in  FIGS. 4-6 , the separator pad  57  is arranged in a position opposite from the separator  54 A across the first feeding path  26 . The separator pad  57  is pressed upward to an outer peripheral surface of the separator  54 A. The separator pad  57  may be formed of, for example, cork chips and causes friction with the second surface  9 B of the sheet  9  which is carried on the separator pad  57 . 
     The pickup roller  52  is rotated in accordance with the rotation of the first shaft  56  of the separator roller  54  with the outer peripheral surface thereof being in contact with the first surface  9 A of the topmost sheet  9  amongst the sheets  9  stacked in the sheet-feed tray  12 . Thus, the rotation force of the pickup roller  52  is conveyed to the sheet  9 , and the sheet  9  is carried in the first feeding path  26 . When the topmost sheet  9  is picked up by the pickup roller  52 , however, one or more subsequent sheets  9  may be picked up along with the topmost sheet  9 . When such subsequent sheets  9  are carried to the separator  54 A and the separator pad  57 , the subsequent sheets  9  are separated from the topmost sheet  9  by the friction in the separator pad  57  so that solely the topmost sheet  9  is further carried in the first feeding path  26 . 
     3.1.2 Conveyer Unit 
     As shown in  FIGS. 4-6 , the conveyer unit  60  carries the sheet  9 , picked up from the sheet-feed tray  12  by the sheet-feed unit  50 , in the first feeding path  26 , the curved feeding path  27 , and the second feeding path  28 . The conveyer unit  60  includes a conveyer roller  61 , the main roller  64 , and pinch rollers  62 ,  65 . The conveyer roller  61  is arranged above the upper guide  34  on the left-hand side with respect to the separator roller  54  (i.e., the lower-stream side than the separator roller  54  in the first feeding path  26 ). The main roller  64  is arranged in the position to define the curved feeding path  27 . 
     As shown in  FIG. 9 , the conveyer roller  61  includes a second shaft  66  and a conveyer  61 A being a body of the conveyer roller  61 . The second shaft  61  is rotatably supported by the main frame  30  at a front end  66 A and a rear end  66 B thereof. The conveyer  61 A is fixed to an axially midst portion of the second shaft  66 . The rear end  66 B of the second shaft  66  is connected to a motor (not shown) via the drive force conveyer  99 . Thus, the second shaft  66  is rotated by the motor in the predetermined direction (i.e., clockwise in  FIG. 4 ), and the conveyer  61 A is rotated accordingly along with the second shaft  66 . The second shaft  66  is a steel round bar, and an outer diameter thereof may range from a few to a dozen millimeters. The first shaft  56  and the second shaft  66  tend to be formed to have smaller diameters for manufacturing cost reduction. 
     According to the present embodiment, the peripheral velocity of the conveyer  61 A is faster than that of the separator  54 A. Due to the speed difference, clearance between the sheets  9 , which are separated by the separator  54 A and the separator pad  57 , is maintained. Moreover, the separator roller  54  is provided with a buffer (not shown) in between the first shaft  56  and the separator  54 A to absorb the speed difference between the separator  54 A and the conveyer  56 A. Therefore, when the conveying force is applied to the sheet  9  in the first feeding path  26  with the conveyer  61 A and the separator  54 A in contact with the first surface  9 A of the sheet  9 , the speed difference is absorbed by the buffer so that the sheet  9  is not carried in different conveying speeds. More specifically, the separator  54 A is normally rotated by the motor except when the sheet  9  is in contact with the conveyer  61 A and the separator  54 A simultaneously. In other words, the separator  54 A is driven to rotate by the conveyer  61 A via the sheet  9  specifically when the first surface  9 A of the sheet  9  is in contact with the conveyer  61 A and the separator  54 A. 
     As shown in  FIGS. 4-6 , the pinch roller  65  is arranged a position opposite from the conveyer  61 A across the first feeding path  26 . The sheet  9  conveyed forward by the separator roller  54  is nipped with the conveyer  61 A and the pinch roller  65 . Therefore, the sheet  9  with the first surface  9 A thereof in contact with the conveyer  61 A is carried in the first feeding path  26  by the conveying force of the rotating conveyer roller  61 . The sheet  9  is thus carried to the curved feeding path  27 . 
     As shown in  FIG. 9 , the main roller  64  includes a third shaft  67  and three (3) roller bodies  64 A. The third shaft  67  is rotatably supported by the main frame  30  at a front end  67 A and a left end  67 B thereof. The roller bodies  64 A are fixed to an axially midst portion of the third shaft  67  with clearance in between them The third shaft  67  is provided with a pair of intermediate bearings at the axially midst portion to have the three roller bodies  64 A in between the intermediate bearings. The rear end  67 B of the third shaft  67  is connected to the motor (not shown) via the drive force conveyer  99 . Thus, the third shaft  67  is rotated by the motor in a predetermined direction (i.e., counterclockwise in  FIG. 4 ), and the roller bodies  64 A are rotated accordingly along with the third shaft  67 . According to the present embodiment, the peripheral velocity of the roller bodies  64 A is faster than that of the conveyer  61 A of the conveyer roller  61 . Due to the speed difference, the sheet  9  being conveyed is prevented from being loosened in between the main roller  64  and the conveyer roller  61 . 
     As shown in  FIGS. 4-6 , the pinch rollers  62 ,  63  are arranged in positions opposite from the main roller  64 A across the curved feeding path  27 . The sheet  9  conveyed in the curved feeding path  27  is nipped with the roller bodies  64 A and the pinch rollers  62  at the upper stream side of the curved feeding path  27 , and with the roller bodies  64 A and the pinch rollers  63  at a lower-stream side of the curved feeding path  27 . Therefore, the sheet  9  with the second surface  9 B in contact with the roller bodies  64 A is carried in the curved feeding path  27  by the conveying force of the rotation of the main roller  64 . Thus, the sheet  9  is carried to the second feeding path  28 . 
     3.1.3 Sheet-Discharge Unit 
     As shown in  FIGS. 4-6 , the sheet-discharge unit  70  discharges the sheet  9  having been conveyed in the second feeding path  28  by the conveyer unit  60  out to the feed-discharge tray  14 . The sheet-discharge unit  70  includes a discharge roller  72  and pinch rollers  74 , which are arranged in vicinity of the right-side end of the lower guide  36  on a downstream side of the second feeding path  28 . As shown in  FIG. 9 , the discharge roller  72  includes a fourth shaft  71 . The fourth shaft  71  is rotatably supported by the main frame  30  at a front end  71 A and a rear end  71 B thereof. The rear end  71 B of the fourth shaft  71  is connected to the motor (not shown) via the drive force conveyer  99 . Thus, the fourth shaft  71  is rotated by the motor in a predetermined direction (i.e., counterclockwise in  FIG. 4 ), and the discharge roller  72  is rotated accordingly along with the fourth shaft  71 . 
     As shown in  FIGS. 4-6 , the sheet  9  carried in the second feeding path  28  is nipped with the discharge roller  72  and the pinch rollers  74  and discharged out of the second feeding path  28  to the sheet-discharge tray  14 . 
     3.2 First Image Sensor 
     The first image sensor  24 , shown in  FIGS. 4-6 , is a known image reading sensor such as, for example, a CIS or a CCD. The first image sensor  24  is embedded in a recessed portion on the left-hand side in the upper guide  34  with a top surface thereof being exposed. That is, the first image sensor  24  is arranged on a lower-stream side with respect to the conveyer roller  61  and an upper-stream side with respect to the main roller  64 . The sheet  9  being conveyed in the first feeding path  26  is transferred above the first image sensor  24  with the second surface  9 B being exposed to the first image sensor  24 . 
     In a position opposite from the first image sensor  24  across the first feeding path  26 , a first white piece  76  is provided. The first white piece  76  is resiliently pressed toward the first image sensor  24  by a coil spring  77  (see  FIG. 5 ). Thus, when the sheet  9  is conveyed in the first feeding path  26  between the first image sensor  24  and the first white piece  76 , the sheet  9  is pressed toward the first image sensor  24  by the first white piece  76 . Accordingly, the first image sensor  24  reads an image formed on the second surface  9 B of the sheet  9  pressed closer to the first image sensor  24 . The image read by the first image sensor  24  is transferred to the control unit of the image processing apparatus, in which image data representing the read image is created. 
     3.3 Second Image Sensor 
     As shown in  FIGS. 4-6 , the second image sensor  25  is moved to stop at a predetermined image reading position  18  when the ADF  11  is used. When the second image sensor  25  is in the image reading position  18 , an upper surface of the second image sensor  25  faces the opening  84  in the second feeding path  28  through the fixed-reading glass  79 . With the second image sensor  25  facing the opening  84 , when the sheet  9  is carried in the second feeding path  28  to the image reading position  18  by the conveyer unit  60 , the sheet  9  passes above the upper surface of the second image sensor  25 . When the sheet  9  is further conveyed in the second feeding path  28 , the document separator  81  directs the sheet  9  to be away from the fixed-reading glass  79 . 
     Further, in a position opposite from the second image sensor  25  in the image reading position  18  across the second feeding path  28 , a second white piece  82  is provided. The second white piece  82  is resiliently pressed toward the image sensor  25  at the image reading position  18  by a coil spring  83  (see  FIG. 5 ). Thus, when the sheet  9  is conveyed in the second feeding path  28  between the second image sensor  25  and the second white piece  83 , the sheet  9  is pressed toward the second image sensor  25  by the second white piece  83 . Accordingly, the second image sensor  25  reads an image formed on the first surface  9 A of the sheet  9  pressed closer to the second image sensor  25 . The image read by the second image sensor  25  is transferred to the control unit of the image processing apparatus, in which image data representing the read image is created. 
     3.4 Sheet Detectors 
     As shown in  FIG. 8 , the conveyer unit  60  includes four pieces of sheet detectors  151 ,  152 ,  153 ,  154 . The sheet detectors  151 - 153  are arranged in the vicinities of and below the first shaft  56  to detect a front end of the sheet  9  set in the sheet-feed unit  50 . The sheet detector  154  is arranged in the vicinity of and below the second shaft  66  and detects the front end of the sheet  9  reaching the vicinity of the second shaft  66 . The sheet detectors  151 - 154  are in similar configuration; therefore, explanation of the sheet detectors  152 - 154  is represented by that of the sheet detector  151  described below. In the description hereinbelow, in terms of the sheet  9  in the feeding path  16 , the “front end” refers to an edge of the sheet  9  proceeding in front in the feeding path  16 . 
     As shown in  FIGS. 8 and 11 , the sheet detector  151  is swingably supported by the upper guide  34  and is normally resiliently upraised by a biasing member (not shown) in an uprising position as illustrated in a solid line in  FIG. 11 . The upper guide  34  is formed to have an opening, through which the uprising sheet detector  151  penetrates to protrude upward from the upper surface of the upper guide  34 . Therefore, when no sheet is set in the sheet-feed unit  50 , the sheet detector  151  is not in contact with the sheet. When the sheet detector  151  is cleared from the sheet, the sheet detector  151  intersects the first feeding path  26 . 
     When sheets  9  are set on the sheet-feed tray  12 , and the front ends of the sheets  9  are inserted in the sheet-feed unit  50 , the sheet detector  151  is pressed by the front ends of the sheets  9  downward to a lower position, as indicated in a double-dotted line in  FIG. 11 , below the second surface  9 B of the sheet  9 . Accordingly, the sheet detector  151  is displaced out of the first feeding path  26  and no longer intersects the first feeding path  26 . Meanwhile, in the vicinity of the sheet detector  151  below the upper guide  34 , a displacement sensor (e.g., a photo-interrupter)  151 A is provided to detect the displacement of the sheet detector  151  out of the first feeding path  26 . Accordingly, the displacement sensor  151 A can inform the control unit of the presence of the sheet  9  in the sheet-feed unit  50 . 
     3.5 Automatic Document Reading Operation of ADF 
     When one or more sheets  9  are set on the sheet-feed tray  12 , and the front ends of the sheets  9  are inserted below the right-side end of the top cover  32  in the sheet-feed unit  50 , the sheet detectors  151 - 153  and the displacement sensors  151 A inform the control unit of the presence of the sheets  9 . When the user uses the operation panel  3  to enter an instruction to start reading the images on the sheets  9 , the control unit manipulates the ADF  11  to start an automatic reading operation. Thus, the sheets  9  in the sheet-feed tray  12  are picked up separately and carried in the first feeding path  26  one-by-one. When the sheet detector  154  detects the sheet  9  reaching the vicinity of the second shaft  66 , the sheet detector  154  informs the control unit of the presence of the sheet  9 , and the control unit maintains the automatic reading operation in response to the information. As the sheet  9  is carried further in the first feeding path  26  to pass by the first image sensor  24 , the image formed on the second surface  9 B of the sheet  9  is read by the first image sensor  24 . The sheet  9  is further carried to the curved feeding path  27  and turned over to have the first and second surfaces  9 A,  9 B reversed in the curved feeding path  27 . When the sheet  9  is carried to pass by the second sensor  25 , the image formed on the first surface  9 A of the sheet  9  is read by the second image sensor  25 . The sheet  9  is carried further in the second feeding path  28  and discharged in the sheet-discharge tray  14  with the first surface  9 A facing downward. The automatic reading operation is automatically repeated until all the sheets  9  in the sheet-feed tray  12  are processed in the feeding path  16  and no more sheet  9  remains in the sheet-feed tray  12 . 
     As mentioned above, in the present embodiment, the “front end” in terms of the sheet  9  refers to an edge of the sheet  9  proceeding in front in the feeding path  16 . In other words, when the sheet  9  is in the first feeding path  26 , the front end of the sheet  9  is the leftmost end in  FIGS. 4-6 . After the sheet  9  is reversed in the curved feeding path  27 , in the second feeding path  28 , the front end is the rightmost end in  FIG. 4-6 . 
     4. Connector Pieces 
     As shown in  FIGS. 8 and 12 , the conveyer unit  60  in the present embodiment includes connector pieces  100  attached to the first shaft  56  and the second shaft  66 . The connector pieces  100  will be described below. Prior to description of the connector pieces  100 , however, assumable behaviors of the first shaft  56  and the second shaft  66  without the connector pieces  100  will be described below. 
     As shown in  FIG. 6 , when the separator roller  54  and the conveyer roller  64 , rotatably supported at the axial ends thereof, are rotated to apply conveying force to the sheet  9 , reaction force of the conveying force is applied from the sheet  9  to the first and second shafts  56 ,  66  via the separator  54 A and the conveyer  61 A. 
     When the separator roller  54  and the separator pad  57  separates the sheets  9 , friction force generated in the separator pad  57  with the sheet  9  affects the first shaft  56  and the second shaft  66  via the separator  54 A and the conveyer  61 A. 
     When the main roller  64  is rotated to convey the sheet  9 , tensile force in the sheet  9  caused by the difference of the peripheral velocities between; the separator roller  54 A and the conveyer rollers  61 A; and the roller bodies  64 A affects the first and second shafts  56 ,  66  via the separator  54 A and the conveyer  61 A. 
     When the reaction force, the friction force, and the tensile force affect the first and second shafts  56 ,  66 , as shown in  FIG. 13A , at least one of the first and second shafts  56 ,  66  without the connector pieces  100  is bowed in either the sheet-conveying direction or in an opposite direction from the sheet-conveying direction.  FIG. 13A  illustrates an example of the bowing behaviors of the first and second shafts  56 ,  66 . A bowing range for the first shaft  56  and the second shaft  66  can be, for example, 1-2 millimeters. 
     With the bowing range, the separator  54 A and the conveyer  61 A fixed to the first shaft  56  and the second shaft  66  respectively may be displaced, and positional relation amongst the separator  54   a , the conveyer  61 A, and the sheet  9  may change. In the changed positional relation, the sheet  9  may be carried in a skewed or incorrect orientation with respect to the first feeding path  26 . 
     Further, as shown in  FIGS. 4-6 , whilst the sheet  9  is carried sequentially in the first feeding path  26 , the curved feeding path  27 , and the second feeding path  28 , relative positions of separator roller  54 , the conveyer roller  62 , the main roller  64 , and the sheet  9  vary; therefore, the degrees of bowing for the first and second shafts  56 ,  66  fluctuate. In particular, the reactive force of the conveying force, the friction force in the separator pad  57 , and the tensile force caused by the velocity difference may vary in the transitional positional relations, in which the sheet  9  is nipped with the separator roller  54  and the separator pad  57 , in which the sheet  9  is nipped with the conveyer roller  61  and the pinch roller  65 , and in which the sheet  9  is nipped with the main roller  64  and the pinch rollers  62 ,  63 . Thus, the bowing behaviors of the first and the second shafts  56 ,  66  are not steady and may produce unstable speed to feed the sheet  9 . 
     When the sheet  9  is carried in the skewed orientation and/or in unstable feeding speeds, the first and second image sensors  24 ,  25  may not read the images on the first and second surfaces  9 A,  9 B correctly, and errors in image reproduction may occur easily. In the present embodiment, points which define the above-mentioned transitional positional relations are referred to as significant points for image reading, and the errors in image reading tend to occur more frequently in the vicinities of the significant points. 
     Meanwhile, the ADF  11  in the present embodiment is provided with the connector pieces  100 , which connect the first shaft  56  and the second shaft  66  to restrict the bowing behaviors of the first and second shafts  56 ,  66 . As shown in  FIG. 12 , the connector piece  100  is formed to have a first ring portion  101 , a second ring portion  102 , a connector portion  103 , and a guiding edge  104 . The first ring portion  101  is an annular portion, through which the first shaft  56  penetrates. The second ring portion  102  is an annular portion, through which the second shaft  66  penetrates. The connector portion  103  is a plate to connect the first and the second ring portions  101 ,  102 . The guiding edge  104  is formed at a lower side of the connector portion  103 . In the present embodiment, the connector piece  100  is an injection-molded and integrally-formed piece of thermoplastic resin with higher slidability (e.g., polypropylene resin). However, a material and a forming method of the connector piece  100  are not limited. For example, the connector piece  100  may be an assembly of a plurality of separately formed parts. For another example, the connector piece  100  may have bearings (e.g., ball bearings) to hold the first and second shafts  56 ,  66 . 
     Each of the first ring portion  101  and the second ring portion  102  is formed to have a shape of a short cylinder with a small axial length and a substantial radial thickness. The first ring portion  101  and the second ring portion  102  are formed to have an inner diameter, which is substantially (e.g., 0.05-0.2 millimeters) larger than an outer diameter of the first shaft  56  and the second shaft  66 . Therefore, the first shaft  56  and the second shaft  66  are connected by the connector piece  100  and allowed to rotate within the inner diameters of the first ring portion  101  and the second ring portion  102  respectively and restricted from being rattled. 
     The connector portion  103  is an elongated plate, which extends along a plane perpendicular to rotation axes of the first and second shafts  56 ,  66  and connects the first ring portion  101  and the second ring portion  102  in a shortest distance. 
     As shown in  FIG. 14 , which illustrates the connector piece  100  when viewed from a line B-B appearing in  FIG. 2  in the axial direction of the first and the second shafts  56 ,  66 , the connector piece  100  is formed to have the guiding edge  104  along the lower side thereof, which opposes the upper surface of the upper guide  34  across the first feeding path  26  when the connector piece  100  is installed in a correct position to hold the first and second shafts  56 ,  66 . More specifically, the guiding edge  104  is a flat rim, of which cross section is similar to a shape of “T” together with a cross section of the connector portion  103 . The guiding edge  104  extends substantially horizontally in the right-left direction above the upper guide  34 . When the upper guide  34  is in the closed position, the guiding edge  104  is in a position lower than the cutouts  132 A,  132 B formed in the ribs  132  of the top cover  32 . In other words, the guiding edge  104  extends along the first feeding path  26  and can be in contact with the first surface  9 A of the sheet  9  being carried in the first feeding path  26 . 
     It is to be noted that, in the case where the ADF  11  lacks the connector pieces  100 , as shown in  FIG. 15 , the front end of the sheet  9  traveling underneath the separator roller  54  may be turned upward to interfere with the cutouts  132 A,  132 B. The interfering sheet  9  may not be correctly carried further in the first feeding path  26  and may cause sheet jam. Meanwhile, in the present embodiment, the first feeding path  26  is smoothed by the guiding edges  104  of the connector pieces  100  (see  FIG. 14 ). Accordingly, the front end of the sheet  9  is prevented from being interfered with the cutouts  132 A,  132 B, and the sheet  9  is securely carried in the first feeding path  26 . 
     As shown in  FIG. 14 , a left-side end of the connector piece  100 , which corresponds to the lower-stream side of the first feeding path  26 , is formed to have a lower-stream side curved edge  104 B. The curved edge  104 B is formed continuously from the guiding edge  104  and curved to have an open end thereof directed upward (i.e., toward the upper side in  FIG. 14 ) to be away from the first feeding path  26 . The curved edge  104 B horizontally laps over the ribs  131 ,  132 . On the other hand, a right-side end of the connector piece  100 , which corresponds to the upper-steam side of the first feeding path  26 , is formed to have an upper-stream side curved edge  104 A. The curved edge  104 A is formed continuously from the guiding edge  104  and curved to have an open end thereof directed upward (i.e., toward the upper side in  FIG. 14 ). The curved edge  104 A horizontally laps over the separator  54 A, which is indicated by a double-dotted line appearing in  FIG. 14 . It is to be noted that the separator  51 A is closer to a viewer of  FIG. 14  than the connector piece  100 . In other words, the open end of the curved edge  104 A does not extend further toward the upper-stream side than the circumference of the separator  54 A. 
     In the sheet-feeding operation, although infrequently, sheet jam may occur in the first feeding path  26  on the downstream side with respect to the conveyer roller  61 , and successive part of sheet  9  may slack to tangle around the conveyer roller  61 . Accordingly, the sheet  9  may be pulled backward in the direction opposite from the sheet feeding direction by the conveyer roller  61 . When the sheet  9  is pulled backward, due to the outline of the lower-stream side curved edge  104 B, the sheet  9  being pulled backward is not caught by the connector piece  100  or not interfered with by the connector piece  100 . Further, when the sheet  9  is correctly carried in the sheet feeding direction, and even when the sheet  9  becomes in contact with the curved edge  104 B, the sheet  9  is not interfered with by the connector piece  100  but guided smoothly by the outline of the curved edge  104 . Meanwhile, the outline of the upper-stream side curved edge  104 A prevents the front end of the sheet  9 , which is nipped with the separator roller  54 , from being caught by the right-side end of the connector piece  100 . Further, because the open end of the curved edge  104 A does not extend further toward the upper-stream side than the circumference of the separator  54 A, the separating behavior of the separator roller  54  is prevented from being interfered with by the curved edge  104 A. 
     As shown in  FIG. 16 , the connector pieces  100  are arranged in parallel with the sheet feeding direction in symmetry positions P 1 , P 2  with respect to a line S, which is a reference line connecting axial centers of the first shaft  56  and the second shaft P 2 . 
     5. Effectiveness 
     In the above ADF  11 , the first shaft  56  and the second shaft  66  are connected by the connector pieces  100 ; therefore, the bowing behaviors of the first shaft  56  and the second shaft  66 , which can be caused by the reaction force of the conveying force, the friction force in the separator pad  57 , and the tensile force due to the difference of peripheral velocities, can be restricted. In other words, when the first shaft  56  tends to bow, the second shaft  66  supports the first shaft  56  via the connector pieces  100  and restricts the first shaft  56  from being deformed, and vice versa. On the other hand, without the connector pieces  100 , as shown in  FIG. 13A , the first shaft  56  and the second shaft  66  can be bowed. According to the present embodiment, as shown in  FIG. 13B , the first shaft  56  and the second shaft  66  reinforce each other to prevent the bowing behaviors. Therefore, the skewed orientation of the sheet  9  being carried due to the deformation of the first shaft  56  and the second shaft  66  can be prevented, and the speed to convey the sheet  9  can be prevented from being fluctuated. 
     According to the present embodiment, the ADF  11  does not require the conventional arm-pieces hooking the first shaft  56  and the second shaft  66  to the main frame  30  or intermediate bearings to hold the first shaft  56  and the second shaft  66  at the lengthwise centers thereof. Therefore, a framework and assembly of the entire ADF  11  can be simplified, and a quantity of pieces of components in the ADF  11  can be reduced. 
     In other words, in the ADF  11  according to the present embodiment, errors (e.g., distortion and/or displacement of images) in the image reading operation conducted in cooperation with the first and second image sensors  24 ,  25  can be prevented from being caused. Further, due to the simplified configuration and reduction of the quantity of components, the inner space of the ADF  11  can be effectively arranged, and the entire ADF  11  can be downsized. 
     In the ADF  11  in the present embodiment, the first image sensor  24  is arranged along the first feeding path  26  on the lower-stream side with respect to the conveyer roller  61  and on the upper-stream side with respect to the main roller  64 . Therefore, although the first image sensor  24  may be in a position to be affected by the significant points, the bowing behaviors of the first and second shafts  56 ,  66  are restricted, and image-reading errors can be reduced. 
     The ADF  11  in the present embodiment is provided with two connector pieces  100  in the symmetry positions P 1 , P 2  with respect to the line S, which is the lengthwise centers of the first and second shafts  56 ,  66 . Therefore, the connector pieces  100  can evenly restrict the lengthwise bowing behaviors of the first and second shafts  56 ,  66  so that the skewed orientation of the sheet  9  can be effectively prevented. 
     However, the ADF  11  may be provided with a single connector piece  100  instead of a pair of connector pieces  100 . In such configuration (not shown), the single connector piece  100  can be arranged on the line S so that the connector piece  100  can evenly restrict the lengthwise bowing behaviors of the first and second shafts  56 ,  66 . Further, each of the separator  54 A and the conveyer  61 A may be divided in two pieces so that the single connector piece  100  can be arranged in clearance between the two pieces of separators  54 A and the conveyers  61 A. 
     Alternatively, the ADF  11  may be provided with one or more pairs of connector pieces  100  in symmetry positions P 3 , P 4  (see  FIG. 16 ) with respect to the line S and in the vicinities of the axial ends of the separator  54 A and the conveyer  61 A, which are in the axial center of the separator roller  54  and the conveyer roller  61 A. With the connector pieces  100  in the positions P 3 , P 4 , arranged closer to the axial center of the first and second shafts  56 ,  66 , the first and second shafts  56 ,  66  are effectively restricted from being bowed and reinforced at the center portions thereof, which can be deformed in larger amounts than the other parts of the first and the second shafts  56 ,  66 . 
     Additionally or alternatively, the ADF  11  may be provided with one or more pairs of connector pieces  100  in symmetry positions P 5 , P 6  (see  FIG. 16 ) with respect to the line S and in the vicinities of the axial ends of the first and second shafts  56 ,  66  to have the guiding edges  104  of the connector pieces  100  to be in contact with the sheet  9  at the vicinities of the widthwise ends thereof. With the connector pieces  100  in the positions P 5 , P 6 , the guiding edges  104  of the connector pieces  100  can suppress the widthwise ends of the sheet  9  downward. Thus, the widthwise ends of the sheet  9  can be prevented from being curled in the first feeding path  26 , and sheet jam can be avoided. 
     Alternatively, the ADF  11  may be provided with at least one connector piece  100  in a position P 7  (see  FIG. 17 ), which is in adjacent to an outer or inner side of the sheet detector  154 . With the connector piece  100  in the position P 7 , even when the sheet  9  tends to be uplifted by reaction force of the sheet detector  154 , the connector piece  100  in adjacent to the detector piece  154  suppresses the sheet  9  downward and prevents the sheet  9  from floating away from the first feeding path  26  (see  FIG. 18 ). Accordingly, the sheet detector  154  is pressed securely downward by the sheet  9  to be shifted in the lower position below the second surface  9 B of the sheet  9  and detects the front end of the sheet  9  reaching the vicinity of the second shaft  66 . Thus, errors in detecting the sheet  9  can be prevented. If the connector piece  100  is not in adjacent to the sheet detector  154 , the sheet  9  may be uplifted due to the reaction force of the sheet detector  154  (see  FIG. 19 ), and the sheet detector  154  remains in the upraised position to intersect the first feeding path  26 . In such a case, the sheet  9  is not detected, and a detecting error occurs. Additionally, the connector pieces  100  may be arranged in positions adjacent to outer or inner sides of the sheet detectors  151 - 153  similarly to the sheet detector  154 . 
     Alternatively, the connector piece  100  may be formed to have an opening  105  in the first ring portion  101  (see  FIG. 20 ). With the opening  105 , when the connector piece  100  is attached to the first shaft  56 , the first shaft  56  may be inserted in the first ring portion  101  through the opening  105 , which may be circumferentially widened when the first shaft  56  passes through. In this configuration, the connector piece  100  can be more easily attached to the first shaft  56 . Additionally, the connector piece  100  may be formed to have an opening in the second ring portion  102 . 
     Although an example of carrying out the invention has been described, those skilled in the art will appreciate that there are numerous variations and permutations of the sheet feeding device that fall within the spirit and scope of the invention as set forth in the appended claims. It is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or act described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. 
     For example, the separator roller  54  and the conveyer roller  61  may not necessarily be adjacent to each other. More specifically, a third roller may be arranged in between the separator roller  54  and the conveyer roller  61 . In such configuration, for example, the connector piece  100  to connect the separator roller  54  and the conveyer roller  61  may be formed to have an opening, through which a shaft of the third roller penetrates without interfering with the connector piece  100 . For another example, the connector piece  100  may be formed to have a curved shape to avoid the third roller.