Patent Publication Number: US-7905479-B2

Title: Feeder unit, sheet feeding device, and image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2008-100808 filed on Apr. 8, 2008, the entire subject matter of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     Aspects of the present invention relate to a feeder unit to feed sheets contained in a tray into a feeding path, a sheet feeding device having the feeder unit, and an image forming apparatus having the sheet feeding device. More specifically, a feeder unit having a main frame and a secondary frame, whilst the secondary frame is capable of being installed in a correct position of the main frame easily, is provided. Further, a sheet feeding device having the feeder unit and an image forming apparatus having the sheet feeding device are provided. 
     2. Related Art 
     Conventionally, a sheet feeding device to separate a sheet from a sheet stack contained in a tray and forward the separated sheet in a feeding path has been known. The sheet feeding device has a feed roller, which is in a position to be in contact with a topmost sheet in the sheet stack, so that the topmost sheet can be separated from the sheet stack by contact friction generated between the topmost sheet and the feed roller whilst the feed roller rotates. In Japanese Patent Provisional Publications No. 2002-60068 and No. 2005-247521, for example, a sheet feeding device having a frame with a swingable arm portion and a feed roller to rotate at the swingable end of the arm portion is disclosed. Rotation force (torque) from a motor is conveyed to the fed roller through gears which are rotatably supported by the frame. 
     The frame to rotatably support the gears can be molded out of rather inexpensive materials (e.g., resin) in consideration of manufacturing cost and convenience, weight saving, etc. However, the frame is often subject to distortional stress, which can be caused by feeding load in the feed roller and driving torques of the motor. Therefore, it is required that the frame is made of a material with rigidity. Further, the frame is required to be molded with dimensional accuracy in order to avoid irregular feeding and misalignment in a feeding path, and to feed the sheets smoothly and uniformly. 
     Furthermore, because the gears are rotatable in the frame, bearings to hold the gears are subject to wear away due to rotating friction. When the bearings are abraded and eroded, positions to hold the gears may be displaced, and the rotating force of the motor may not be effectively conveyed to the feed roller. Therefore, the frame is required to be molded out of a material with abrasion resistance. Often, the material with high rigidity, easy moldability, and high abrasion resistance can be rather costly. 
     In order to overcome the above difficulties, it is possible to form the bearings and the frame separately in different materials and to attach the bearings to the frame afterwards. In this configuration, the frame can be made of a material with higher rigidity and moldability but lower abrasion resistance whilst the bearings can be made of a material with higher abrasion resistance. Thus, the frame and the bearings can be made of different materials which are suitable to respective components; i.e., the frame can be made of a material which is inexpensive and suitable to the frame, and the bearings can be made of a material which is inexpensive and suitable to the bearings. 
     SUMMARY 
     Meanwhile, when the frame and the bearings are formed separately, it is required that the bearings are attached to the frame in specifically accurate positions with respect to the frame. When not in correct positions, the bearings can be deformed and/or displaced, and engagement accuracy of the gears is lowered; thus, the rotating force of the motor is not effectively transmitted to the feed roller. Instead, the gear teeth and the bearings are subject to excessive load and may be abraded to be corrupted. Moreover, the gears can be disengaged. Yet, placing the bearings accurately in correct positions is accompanied by difficulties. 
     In view of the above drawbacks, the present invention is advantageous in that a feeder unit, a sheet feeding device, and an image forming apparatus, having a detachable frame being attached to a main frame accurately and easily in a predetermined position so that transmission efficiency can be maintained and components can be prevented from being abraded even against intense rotation force, are provided. 
     According to an aspect of the present invention, a feeder unit to feed sheets, which are stacked in a tray, in a predetermined feeding direction, is provided. The feeder unit includes a main frame, having a pivotal end and a swingable end, being swingably supported at the pivotal end by a first shaft arranged substantially above the tray, having an upper surface and a lower surface, and arranged to extend from the first shaft toward an upper level of the tray with the lower surface facing the tray, a rotary member, which is arranged at the swingable end of the main frame, is rotatably supported by a second shaft extending in a same direction with the first shaft, and is arranged to come in contact with a topmost surface of the sheets stacked in the tray, a pair of opposing walls, which are formed in the main frame, and of which planes are perpendicular to the direction of the first shaft, a secondary frame, having a pair of supporting walls which come to face the opposing walls when the secondary frame is inserted in space partitioned by the opposing wall in the main frame through an opening, the opening formed on either surface of the main frame, a gear train including a plurality of gears to transmit predetermined rotation force to the rotary member, each of the gears being rotatable about a third shaft extending in the same direction with the first shaft and is rotatably supported by the pair of supporting walls, a positioning system to situate the secondary frame in a predetermined position in the partitioned space, and a detachment restricting system to restrict the secondary frame from being detached from the main frame. The secondary frame is situated in the predetermined position of the main frame when the rotary member rotates in a direction to feed the sheets. 
     According to another aspect of the present invention, a sheet feeding device is provided. The sheet feeding device includes a feeder unit to feed sheets in a sheet stack in a predetermined feeding direction, a transmission system to transmit rotating force from a drive source to the feeder unit, and a tray to contain the sheet stack. The feeder unit includes a main frame, having a pivotal end and a swingable end, being swingably supported at the pivotal end by a first shaft arranged substantially above the tray, having an upper surface and a lower surface, and arranged to extend from the first shaft toward an upper level of the tray with the lower surface facing the tray, a rotary member, which is arranged at the swingable end of the main frame, is rotatably supported by a second shaft extending in a same direction with the first shaft, and is arranged to come in contact with a topmost surface of the sheets stacked in the tray, a pair of opposing walls, which are formed in the main frame, and of which planes are perpendicular to the direction of the first shaft, a secondary frame, having a pair of supporting walls which come to face the opposing walls when the secondary frame is inserted in space partitioned by the opposing wall in the main frame through an opening, the opening formed on either surface of the main frame, a gear train including a plurality of gears to transmit predetermined rotation force to the rotary member, each of the gears being rotatable about a third shaft extending in the same direction with the first shaft and is rotatably supported by the pair of supporting walls, a positioning system to situate the secondary frame in a predetermined position in the partitioned space, and a detachment restricting system to restrict the secondary frame from being detached from the main frame. The secondary frame is situated in the predetermined position of the main frame when the rotary member rotates in a direction to feed the sheets. 
     According to still another aspect of the present invention, an image forming apparatus is provided. The image forming apparatus includes a feeder unit to feed sheets in a sheet stack in a predetermined feeding direction, a transmission system to transmit rotating force from a drive source to the feeder unit, and a tray to contain the sheet stack, an image forming unit to form images on the sheets being fed. The feeder unit includes a main frame, having a pivotal end and a swingable end, being swingably supported at the pivotal end by a first shaft arranged substantially above the tray, having an upper surface and a lower surface, and arranged to extend from the first shaft toward an upper level of the tray with the lower surface facing the tray, a rotary member, which is arranged at the swingable end of the main frame, is rotatably supported by a second shaft extending in a same direction with the first shaft, and is arranged to come in contact with a topmost surface of the sheets stacked in the tray, a pair of opposing walls, which are formed in the main frame, and of which planes are perpendicular to the direction of the first shaft, a secondary frame, having a pair of supporting walls which come to face the opposing walls when the secondary frame is inserted in space partitioned by the opposing wall in the main frame through an opening, the opening formed on either surface of the main frame, a gear train including a plurality of gears to transmit predetermined rotation force to the rotary member, each of the gears being rotatable about a third shaft extending in the same direction with the first shaft and is rotatably supported by the pair of supporting walls, a positioning system to situate the secondary frame in a predetermined position in the partitioned space, and a detachment restricting system to restrict the secondary frame from being detached from the main frame. The secondary frame is situated in the predetermined position of the main frame when the rotary member rotates in a direction to feed the sheets. 
     According to the above configurations, the secondary frame can be effectively and securely settled in the predetermined position with respect to the main frame by utilizing the force acting on the gears which are supported by the secondary frame. Therefore, transmission efficiency can be maintained, and components of the feeder unit can be prevented from being abraded against intense rotation force. Further, the secondary frame and the gear train can be easily settled in the main frame. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  illustrates an external and perspective view of an MFD (multi-function device)  10  according to an embodiment of the present invention. 
         FIG. 2  illustrates a partial and cross-sectional side view of a printer unit  11  in the MFD  10  according to the embodiment of the present invention. 
         FIG. 3  illustrates a perspective top view of a feeding unit  60  in the MFD  10  according to the embodiment of the present invention. 
         FIG. 4  illustrates a perspective bottom view of the feeding unit  60  in the MFD  10  according to the embodiment of the present invention. 
         FIG. 5  illustrates a pathway of driving force from a motor  36  to feed rollers  25  in the MFD  10  according to the embodiment of the present invention. 
         FIG. 6  illustrates an enlarged perspective view of an encircled portion VI shown in  FIG. 3 . 
         FIG. 7  illustrates an enlarged perspective view of an encircled portion VII shown in  FIG. 4 . 
         FIG. 8  illustrates an exploded view of the feeding unit  60  of the MFD  10  according to the embodiment of the present invention. 
         FIG. 9  illustrates an exploded view of the feeding unit  60  of the MFD  10  according to the embodiment of the present invention. 
         FIG. 10  illustrates an enlarged partial view of a swingable arm  26  in the feeding unit  60  according to the embodiment of the present invention. 
         FIG. 11  illustrates an exploded view of a conveyer gear unit  64  in the feeding unit  60  according to the embodiment of the present invention. 
         FIG. 12  illustrates a perspective view of a frame  120  in the conveyer gear unit  64  according to the embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of the frame  120  taken from a line XIII-XIII shown in  FIG. 12 . 
         FIGS. 14A and 14B  are cross-sectional side views of the feeding unit  60  taken from a line XIV-XIV shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment according to an aspect of the present invention will be described with reference to the accompanying drawings. First, an overall configuration of an MFD  10  according to the embodiment of the present invention will be described.  FIG. 1  illustrates an external and perspective view of the MFD  10  according to the embodiment of the present invention. 
     The MFD  10  according to the present embodiment is configured integrally with a printer unit  11  and a scanner unit  12  and provided with functionalities for printing, scanning, and facsimile transmission. In the present embodiment, the printer unit  11  is configured to print an image in an inkjet printing method; however, the printer unit  1  may form images in a different printing method such as laser printing. Further, according to the present invention, the MFD  10  may be replaced with a printer device having solely a printing function. 
     A body of the MFD  10  according to the present invention has an approximate shape of a box with a width and a depth being respectively greater than a height. The scanner unit  12  being a flatbed scanner is provided at an upper portion of the MFD  10 , and a topmost portion includes a document cover  30 , which is openable/closable with respect to the body of the MFD  10 . The scanner unit  12  includes a contact glass and an image sensor (not shown) underneath the document cover  30 . When an original document with an image formed thereon is set on the contact glass and a scanning operation is started, the image is read by the image sensor. 
     The printer unit  11  is provided in a bottom portion of the MFD  10 . The printer unit  11  is configured to form an image on a recording sheet according to print data, which can be entered through the scanner unit  12  and from an external environment. The printer unit  11  includes a sheet cassette  70 , which stores recording sheets therein and is detachably attached to the MFD  10  through an opening  13 . The recording sheets stored in the sheet cassette  70  are fed by a feeder  16  along a sheet feeding path to a recording unit  24 , in which the image is formed. 
     The MFD  10  is provided with an operation panel  14  in an upper front portion thereof. (In the present embodiment, a near left side in  FIG. 2  corresponds to the front of the MFD  10 .) The operation panel  14  includes a liquid crystal display, which presents various information concerning operations, and keys, through which a user enters information. The MFD  10  operates according to the information and instructions entered through the operation panel  14  and transmitted from external devices. 
     Next, the printer unit  11  will be described herein below with reference to  FIG. 2 .  FIG. 2  illustrates a partial and cross-sectional side view of the printer unit  11  in the MFD  10  according to the embodiment of the present invention. 
     The printer unit  11  includes the feeder  16 , the recording unit  24 , and a carrier unit  50 . Further, the feeder  16  includes the sheet cassette  70 , a feeding unit  60 , and a drive force conveyer system  27  (see  FIG. 5 ). In  FIG. 2 , the recording unit  24  is indicated in a double-dotted line. 
     The sheet cassette  70  in the feeder  16  is configured to be inserted into the printer unit  11  through the opening  13  (see  FIG. 1 ) in an inserting direction  90  and withdrawn from the printer unit  11  in a withdrawal direction  92 . The sheet cassette  70  includes a sheet tray  20  and a discharge tray  21  (see  FIG. 1 ), and the recording sheets in a stack are stored in the sheet tray  20 . The recording sheets which have been through the printing operation to be formed images thereon are discharged and received in the discharge tray  21 . In the present embodiment, the inserting direction  90  corresponds to a feeding direction  91 , in which the recording sheets stored in the sheet tray  20  are lead to a guide path  22 . 
     The feeding unit  60  feeds the recording sheets stored in the sheet tray  20  in the feeding direction  91  and includes a swingable arm  26 , feed rollers  25 , a conveyer gear unit  64 , and a planetary gear unit  65  (see  FIG. 3 ).  FIG. 3  illustrates a perspective top view of the feeding unit  60  in the MFD  10  according to the embodiment of the present invention.  FIG. 4  illustrates a perspective bottom view of the feeding unit  60  in the MFD  10  according to the embodiment of the present invention.  FIG. 5  illustrates a pathway of driving force from a motor  36  to the feed roller  36  in the MFD  10  according to the embodiment of the present invention. 
     The swingable arm  26  is arranged substantially above the sheet tray  20 . The feed rollers  25 , the conveyer gear unit  64 , and the planetary gear unit  65  are provided to the swingable arm  26 . The swingable arm  26  is swingably supported at a pivotal end thereof by a drive shaft  28 , which is provided above the sheet tray  20 . 
     The swingable arm  26  is molded out of synthetic resin with higher moldability and rigidity (e.g., ABS resin). As shown in  FIG. 2 , the swingable arm  26  is arranged in the feeding unit  60  to extend from the drive shaft  28  toward an upper level of the sheet tray  20  in an inclined attitude to orient a downstream side of the feeding direction  91  (i.e., toward a lower left-hand side in  FIG. 2 ). A pair of feed rollers  25  is arranged at a swingable end, which is an end further from the swing axis (i.e., the drive shaft  28 ), of the swingable arm  26 . An image of the swingable arm  26  is omitted from the feeding unit  60  shown in  FIG. 5 . 
     The feed rollers  25  are configured to come in contact with a topmost surface of the recording sheets stored in the sheet tray  20  and rotate about a roller shaft  62  to feed the recording sheets in the feeding direction  91 . The roller shaft  62  extends in parallel with an axial direction of the drive shaft  28  and is provided with one of the feed rollers  25  at each axial end thereof (see  FIG. 3 ). The roller shaft  62  is further provided with a conveyer gear  72 , which is engaged with a conveyer gear  117  in the conveyer unit  64 , which will be described later in detail. 
     The drive shaft  28  extends in parallel with a widthwise direction of the MFD  10  (i.e., perpendicularly to the cross-sectional plane in  FIG. 2 ) and is supported by a frame (not shown), which is a part of a chassis of the printer unit  11 , at each end thereof. At one end of the drive shaft  28 , as shown in  FIGS. 3-5 , a conveyer gear  67  is provided. When the conveyer gear  67  rotates, the drive shaft  28  rotates in a same direction accordingly. The conveyer gear  67  is coupled to a drive force conveyer system  27 , which includes conveyer gears  68 ,  69 . Specifically, the conveyer gear  68  in the drive force conveyer system  27  is engaged with the conveyer gear  67 . The conveyer gear  68  is engaged with the conveyer gear  69 , which is fixed to an output shaft  37  of the motor  36 . The motor  36  is controlled by a motor driver (not shown) to rotate in either direction. When the motor  36  is rotated by the motor driver, the rotation of the motor  36  is transmitted to a planetary gear unit  65 , which will be described later, and further through a transmission system, which includes the output shaft  37 , the drive force conveyer system  27 , the conveyer gear  67 , and the drive shaft  28 . Thus, the drive shaft  28  is rotated in a direction, depending on the rotating direction of the motor  36 . 
     The swingable arm  26  is provided with the conveyer gear unit  64  (see  FIG. 4 ) and a planetary gear unit  65  (see  FIG. 3 ). Thus, rotation of the drive shaft  28  is transmitted to the feed rollers  25  through the planetary gear unit  65 , the conveyer gear unit  64 , and the conveyer gear  72  so that the feed rollers  25  are rotated in a predetermined direction (i.e., a clockwise direction in  FIG. 2 ) to feed the recording sheets stored in the sheet tray  20  in the feeding direction  91 . The conveyer gear unit  64  and the planetary gear unit  65  will be described later in detail. 
     When the swingable arm  26  swings about the drive shaft  28 , the feed rollers  25  provided at the swingable end of the swingable arm  26  is moved accordingly in directions to become closer and further from the sheet tray  20 . The swingable arm  26  is pivoted to orient in a direction to droop downward by weights of the swingable arm  26  itself and the feed rollers  25  and/or expanding force of a resilient member such as a spring. 
     With the swingable arm  26  pivoted downward, the feed rollers  25  are pressed onto the topmost recording sheet in the sheet stack stored in the sheet tray  20 . When the feed rollers  25  are rotated on the sheet stack, the topmost recording sheet is forwarded in the feeding direction due to friction generated between the feed rollers  25  and the topmost recording sheet. The friction between the feed rollers  25  and the sheet stack, which is force in a direction opposite from the rotation direction of the motor  36 , affects each component included in between the motor  36  and the feed rollers  25 . 
     The printer unit  11  includes a slope board  32 , which is provided at one end of the sheet tray  20  in the feeding direction (see  FIG. 2 ). The slope board  32  has a separator piece  34  on an inner surface thereof. When the feed rollers  25  feed the recording sheet in the feeding direction, and a front end of the recording sheet comes in contact with the slope board  23 , the recording sheet is guided upward by inclination of the slope board  32 . Further, when the topmost recording sheet being fed is accompanied by one or more succeeding recording sheets, the topmost recording sheet is separated from the succeeding recording sheets by the separator piece  34 . The topmost recording sheet guided by the slope board  32  is directed in the guide path  22 , which is provided above the slope board  32  and the feeder  16 . 
     The guide path  22  is formed to extend upward from the slope board  32  and curved to form an arc toward the front of the printer unit  11  (i.e., rightward in  FIG. 2 ) to lead the recording sheet therethrough, by the recording unit  24 , and to the discharge tray  21  (see  FIG. 1 ). Thus, the recording sheets stored in the sheet tray  20  are fed to the guide path  22  to be guided toward the upper portion of the printer unit  11 , pass by the recording unit  24 , which forms images on the recording sheets, and is discharged in the discharge tray  21 . 
     The recording unit  24  is to form an image on the recording sheet whilst the recording sheet is carried thereby in the guide path  22 . The recording unit  24  includes a carriage  40  and recording heads  41  being inkjet heads. The carriage  40  is driven by a carriage driving system (not shown) to be reciprocated in the widthwise direction of the recording sheet along guide rails  43 ,  44 . 
     In the printer unit  11 , a platen  42  to hold the recording sheet fed in the guide path  22  is provided along the guide path  22  in a position to oppose a lower surface of the recording unit  24 . Thus, the recording sheet is maintained substantially flat on the platen  24  to have the image recorded thereon by the recording unit  24  with a predetermined clearance from the lower surface of the recording unit  24 . The MFD  10  is provided with a plurality of ink cartridges (not shown), which are connected with the recording heads  41  through tubes (not shown). Colored inks contained in the ink cartridges are conveyed to the recording heads  41 , and fine ink drops are selectively ejected onto the recording sheet held by the platen  42  from the recording heads  41  whilst the carriage  40  is reciprocated. Thus, the recording sheet has the image recorded thereon by the recording unit  24  whilst being fed in the guide path  22 . 
     The printer unit  11  further includes a carrier unit  50  along the guide path  22 . The carrier unit  50  includes a carrier roller  51 , a discharge roller  52 , and pinch rollers to be pressed by the carrier roller  51  and the discharge roller  52  respectively. The carrier roller  51  is arranged on an upstream side in the feeding direction with respect to the recording unit  24 . Meanwhile, the discharge roller  52  is arranged on a downstream side in the feeding direction with respect to the recording unit  24 . The recording sheet fed by the feed rollers  25  is carried to the clearance between the platen  42  and the recording unit  24  to have the image formed thereon, and the recording sheet with the formed image is discharged by the discharge roller  52  in the discharge tray  21 . 
     Next, configurations and movements of the swingable arm  26 , the planetary gear unit  65 , and the conveyer gear unit  64  will be described.  FIG. 6  illustrates an enlarged perspective view of an encircled portion VI shown in  FIG. 3 .  FIG. 7  illustrates an enlarged perspective view of an encircled portion VII shown in  FIG. 4 .  FIG. 8  illustrates an exploded view of the feeding unit  60  of the MFD  10  according to the embodiment of the present invention.  FIG. 9  illustrates an exploded view of the feeding unit  60  of the MFD  10  according to the embodiment of the present invention.  FIG. 10  illustrates an enlarged partial view of a swingable arm  26  in the feeding unit  60  according to the embodiment of the present invention. 
     As shown in  FIGS. 3 and 4 , the swingable arm  26  includes an arm portion  75  and an extending portion  76 . The planetary gear unit  65  and the conveyer gear unit  64  are attached in the arm portion  75 . The extending portion  76  extends toward a widthwise center of the MFD  10  from a widthwise end, and the arm portion  75  is provided at the widthwise end of the extending portion  76 . The swingable arm  26  is provided with a plurality of (e.g., five) holder portions  79  at an upper end thereof (see  FIG. 8 ). More specifically, the extending portion  76  has three of the holder portions  79 , and the arm portion  75  has two of the holder portions  79 . Each of the holder portions  79  is formed to have a hole  78 , through which the drive shaft  28  is penetrated. The holder portions  79  are arranged in positions which are substantially evenly spaced from neighboring holder portions  79 . Thus, the drive shaft  28  penetrated through the holder portions  79  is held by a frame of the printer unit  11  at both ends thereof so that the swingable arm  26  is swingably supported by the frame. 
     The arm portion  75  is formed to extend from the drive shaft  28  in a direction perpendicular to a longer side (i.e., widthwise side) of the extending portion  76 . The arm portion  75  is further formed to have a casing portion  82 , in which the planetary gear unit  65  is set, at the upper end of the arm portion  75  in the vicinity of the drive shaft  28 . The casing portion  82  is recessed in a direction of a depth of the arm portion  75  from an upper surface level  83 . The planetary gear unit  65  is situated in the casing portion  82  through an aperture  85  of the upper surface level  83 . 
     The planetary gear unit  65  transmits rotation force of the drive shaft  28  to the conveyer gear unit  64 . The planetary gear unit  65  includes a planet gear  89 , an arm portion  88 , and a sun gear  87  (see  FIG. 5 ). The sun gear  87  is subject to the rotation force of the drive shaft  28  and rotates integrally with the drive shaft  28 . The sun gear  87  is arranged in the vicinity of an end opposite from the conveyer gear  67 . The sun gear  87  may be formed integrally with the drive shaft  28 . Alternatively, the sun gear  87  may be formed separately from the drive shaft  28  and fixed to the drive shaft  28  afterwards. 
     As shown in  FIG. 8 , the arm portion  88  is provided with a cylinder-shaped guide portion  93 . The guide portion  93  guides the sun gear  87  to a position in which the sun gear  87  is engageable with the planet gear  89 . The guide portion  93  is formed to have a predetermined-sized inner circumference  94 , through which the drive shaft  28  can be penetrated and the sun gear  87  is suitably engaged with the planet gear  89  without loosening. The planetary gear unit  65  is situated in the casing portion  82  with the inner circumference  94  of the guide portion  93  aligned to the holes  78  of the holder portions  79 . When the drive shaft  28  is inserted through the inner periphery of the guide portion  93  and the openings  78  with the inner circumference  94  being aligned to the holes  78  of the holder portions  79 , the sun gear  87  and the planet gear  89  can be correctly engaged with each other. 
     When the drive shaft  28  rotates with the sun gear  87  engaged with the planet gear  89 , the planet gear  89  comes in engagement with and is disengaged from the conveyer gear unit  64 . In the present embodiment, when the drive shaft  28  in  FIG. 2  rotates in the counterclockwise direction, the planet gear  89  rotates around the sun gear  87  in the counterclockwise direction and comes in engagement with a conveyer gear  115  (see  FIG. 5 ) in the conveyer gear unit  64  so that the rotation of the drive shaft  28  is conveyed to the conveyer gear unit  64  through the planet gear  89 . Meanwhile, when the drive shaft  28  in  FIG. 2  rotates in the clockwise direction, the planet gear  89  rotates around the sun gear  87  in the clockwise direction to become apart and disengaged from the conveyer gear  115 . Therefore, the rotation of the drive shaft  28  is not conveyed to the conveyer gear unit  64 . 
     As shown in  FIGS. 7 ,  9 , and  10 , the arm portion  75  of the swingable arm  26  is formed to have a casing portion  100 , in which the conveyer gear unit  64  is situated. The casing portion  100  is formed in a position at an approximate center of the arm portion  75 , in which the casing portion  100  does not interfere with the casing portion  82 . An opening  102  of the casing portion  100  can be provided on either upper or lower surface of the arm portion  75 , but in the present embodiment, the opening  102  is formed on a lower surface level  84  closer to the sheet tray  20 . The casing portion  100  is formed to recess in the direction of the depth of the arm portion  75  from the lower surface level  84 . The conveyer gear unit  64  is situated in the casing portion  100  through the opening  102 . 
     The arm portion  75  is further formed to have a pair of partition walls  106 , which are opposing each other and define inner surfaces of the casing portion  100  in a widthwise direction  104  of the arm portion  75 . The planes of the partition walls  106  are in parallel with each other and perpendicular to an extending direction of the drive shaft  28 . Thus, partitioned space of the casing portion  100  is created in between the partition walls  106 . 
     As shown in  FIGS. 9 and 10 , the casing portion  100  includes a bottom surface  111 , which opposes to the opening  102  and recessed in the direction in which the conveyer gear unit  64  is inserted. The bottom surface  111  is formed to have apertures  112 ,  113 . When the conveyer gear unit  64  is situated in the casing portion  100 , an intermediate gear  116  and a conveyer gear  117  (see  FIGS. 3-7 ,  9 ) in the conveyer gear unit  64  are exposed through the aperture  112  and the aperture  113  respectively so that the gears  116 ,  117  do not interfere with the bottom surface  111 . When the conveyer gear unit  64  is situated in the casing  100  to the bottom surface  111 , a frame  120  (described later, see  FIG. 9 ) of the conveyer gear unit  64  becomes in contact with a contact portion  118  (see  FIGS. 9 ,  10 ), which is formed on the bottom surface  111  on a side closer to the casing portion  82 , at an arcuate projection  131  (see  FIGS. 11-13 ). At the same time, an arcuate projection  132  (see  FIGS. 11-13 ) of the frame  120  becomes in contact with a contact portion  119  (see  FIGS. 9 ,  10 ), which is formed on the bottom surface  111  on a side closer to the feed rollers  25 . According to the projections  131 ,  132  being in contact with the contact portions  118 ,  119  respectively, the conveyer gear unit  64  is situated in a correct position in the depth of the casing portion  100  in the direction from the opening  102  toward the bottom surface  111 . 
     Further, as shown in  FIGS. 9 and 10 , the casing portion  100  is formed to have a pair of U-shaped grooves  108 , each of which has a cross-sectional shape of U with a side closer to the opening  102  being open-ended, and a pair of V-shaped grooves  109 , each of which has a cross-sectional shape of V on the partition walls  106  with a side closer to the opening  102  being open-ended. The U-shaped grooves  108  and the V-shaped grooves  109  guide the conveyer gear unit  64  to be in a correct position in the casing portion  100  with respect to a lengthwise direction (i.e., a direction from the drive shaft  28  toward the feed rollers  25 ) of the arm portion  75 . When the conveyer gear unit  64  is situated in the casing portion  100 , bosses  143  and bosses  141 , which will be described later, come to fit in the U-shaped grooves  108  and in the V-shaped grooves  109  respectively. 
     Each of the U-shaped grooves  108  is formed on one of the partition walls  106  to oppose to each other. In the present embodiment, the U-shaped grooves  108  are arranged in the casing portion  100  on a side closer to the feed rollers  25 . Each of the V-shaped grooves  109  is formed on one of the partition walls  106  to oppose to each other. In the present embodiment, the V-shaped grooves  109  are arranged in the casing portion  100  on a side closer to the drive shaft  28 . 
     Furthermore, the casing portion  100  is formed to have a pair of claws  110  on the partition walls  106 . The claws  110  are engaged with bosses  142 , which will be described later, when the conveyer gear unit  64  is situated in the casing portion  100 . Thus, the conveyer gear unit  64  can be restricted from being unintentionally detached from the casing portion  100 . 
     As shown in  FIG. 9 , the arm portion  75  is formed to have a pair of holder walls  97 , which are in positions to oppose to each other in the widthwise direction  104 , to hold the conveyer gear  72  at the swingable end thereof. Space  96  between the holder walls  97  communicates with the casing portion  100 . Each of the holder walls  97  is provided with a bearing  98 , which projects outward in the widthwise direction  104 . When the conveyer gear  72  is settled in the space  96  and the roller shaft  62  is rotatably inserted through openings of the bearings  98  and a shaft hole of the conveyer gear  72 , the conveyer gear  72  along with the roller shaft  62  is rotatably held by the arm portion  75 . The feed rollers  25  are fixed onto each end of the roller shaft  62 . 
     The conveyer gear unit  64  includes a train of gears, which include the conveyer gear  115 , the intermediate gear  116 , the conveyer gear  117 , and the frame  120  which supports the gears  115 ,  116 ,  117  rotatably. According to the present embodiment, the conveyer gear  115  is engaged with the intermediate gear  115 , and the intermediate gear  116  is engaged with the conveyer gear  117 . Therefore, driving force inputted to the conveyer gear unit  64  is transmitted to the conveyer gear  115 , the intermediate gear  116 , and the conveyer gear  117 , in the order given. 
       FIG. 11  illustrates an exploded view of the conveyer gear unit  64  according to the embodiment of the present invention.  FIG. 12  illustrates a perspective view of the frame  120  in the conveyer gear unit  64  according to the embodiment of the present invention. 
     As shown in  FIG. 11 , the frame  120  is a frame assembly including a first frame  121  and a second frame  122 . The first frame  121  and the second frame  122  are made of synthetic resin, which has higher slidability than the material of the swingable arm  26 , and are molded to have similar but symmetry shapes. In the present embodiment, whilst the swingable arm  26  is made of ABS resin, the first and the second frames  121 ,  122  are made of POM, which has specifically high slidability, although moldability of which is lower than ABS resin. Therefore, abrasion in bearings  125 ,  126 ,  127 , which will be described later in detail, can be reduced. 
     The first frame  121  has a supporting wall  123 , which comes to face one of the partition walls  106  when the conveyer gear unit  64  is situated in the casing portion  100 . Meanwhile, the second frame  122  has a supporting wall  124 , which comes to face the other of the partition walls  106  when the conveyer gear unit  64  is situated in the casing portion  100 . The supporting walls  123 ,  124  are formed to have a plurality of ribs  129 , which project perpendicularly with respect to the supporting walls  123 ,  124 . When the first frame  121  is assembled with the second frame  122  with the supporting walls  123 ,  124  facing each other, tip ends of the ribs of the supporting wall  123  come into contact with tip ends of the ribs of the supporting wall  124  (see  FIG. 12 ). Thus, clearance between the supporting walls  123 ,  124  is maintained steady. The conveyer gear  115 , the intermediate gear  116 , and the conveyer gear  117  are arranged in the clearance. 
     Although the first frame  121  and the second frame  122  are formed substantially symmetrically to each other, it is to be noted that one of the first frame  121  and the second frame  122  (i.e., the first frame  121  in the present embodiment) is formed to have pins  130  at tip ends of two ribs  129 , which are formed on a side closer to the drive shaft  28  when the conveyer gear unit  64  is situated in the casing portion  100  of the swingable arm  26 . On the other hand, the second frame  122  is formed to have bores (not shown) in tip-end portions of two ribs  129 , which are formed on the side closer to the drive shaft  28  and correspond to the ribs  129  of the first frame  121  having the pins  130 . The pins  130  are inserted into the bores when the first frame  121  and the second frame  122  are assembled; thus, the first frame  121  and the second frame  122  can be easily assembled. 
     Each of the first frame  121  and the second frame  122  is formed to have a plurality of bearings  125 ,  126 ,  127  on the supporting walls  123 ,  124  respectively. The bearings  125 ,  126 ,  127  rotatably support a shaft  135  of the conveyer gear  115 , a shaft  136  of the intermediate gear  116 , and a shaft  137  of the conveyer gear  137  respectively. 
     According to the present embodiment, the shafts  135 ,  136 ,  137  are formed to have staged cores. More specifically, the shaft  135  has a core  135 A, which projects outward in an axial direction from laterals of the conveyer gear  115 , and a core  135 B, which has a smaller diameter than a diameter of the core  135 A and projects further outwardly in the axial direction from laterals of the core  135 A. Similarly, the shafts  136 ,  137  have staged cores  136 A,  137 A, and cores  136 B,  137 B respectively. 
     In correspondence to the shafts  135 ,  136 ,  137 , the bearings  123 ,  126 ,  127  in the first and the second frames  121 ,  122  are formed to have staged structures. More specifically, the bearings  125  are formed to have bearer portions  125 A to hold the core  136 A and bearer portions  125 B to hold the core  136 B respectively. A diameter of the bearer portions  125 B is smaller than a diameter of the bearer portions  125 A. Similarly, the bearings  126 ,  127  are formed to have bearer portions  126 A,  127 A to hold the cores  136 A respectively and bearer portions  126 B,  127 B to hold the cores  137 B respectively. 
     The bearer portions  125 B,  126 B,  127 B are through-holes penetrating through the supporting walls  123 ,  124 . During a normal feeding operation to feed the recording sheets in the feeding direction, the shafts  135 ,  136 ,  137  are held by the bearer portions  125 B,  126 B,  127 B at the cores  135 B,  136 B,  137 B respectively. 
     The bearer portions  125 A,  126 A,  127 A are formed on inner surfaces of the supporting walls  123 ,  124 . The bearer portions  125 A,  126 A,  127 A are round-shaped (e.g., circular, semicircular, or arcuate) ribs which project inward. In the present embodiment, the bearer portions  125 A are substantially semicircular ribs. The bearer portions  126 A are circular ribs, and the bearer portions  127 A are arcuate ribs. During the normal feeding operation, the shaft  135  is held by the bearer portions  125 B at the core  135 B but not by the bearer portions  125 A at the core  135 A. Namely, when the core  135 B is held by the bearer portions  125 B, the core  135 A is arranged to have clearance between outer periphery of the core  135 A and inner periphery of the bearer portions  125 A. Therefore, when the core  135 B is subject to unexpected stress and/or excessive rotation torque, which may be caused by, for example, sheet jam in the guide path  22 , the core  135  may be deformed; however, the shaft  135  can be supported by the bearer portions  125 A at the core  135 A. Similarly, the shafts  136 ,  137  can be held by the bearer portions  126 A,  127 A at the cores  136 A,  137 A respectively. 
     With the shafts  135 ,  136 ,  137  being set in the bearings  125 ,  126 ,  127 , the conveyer gear  115 , the intermediate gear  116 , and the conveyer gear  117  are rotatably supported by the supporting walls  123 ,  124  of the frame  120 . 
     Further, the first and the second frames  121 ,  122  are formed to have bosses  141 ,  142 ,  143 , in positions which correspond to the bearer portions  125 B,  126 B,  127 B respectively on outer surfaces  123 A,  124 A of the supporting walls  123 ,  124 . The bosses  141 ,  142 ,  143  are circular ribs, which substantially encircle the circumferences of the bearer portions  125 B,  126 B,  127 B respectively and project outward from the outer surfaces  123 A,  124 A. The bosses  143  are fitted in the U-shaped grooves  108  in the casing portion  100  when the conveyer gear unit  64  is situated in the casing portion  100  of the swingable arm  26 . The bosses  141  are fitted in the V-shaped grooves  109  in the casing portion  100 . The bosses  142  are engaged with the claws  110  formed on the partition walls  106  in the casing portion  100 . The bosses  142  are formed to have beveled portions  142 A so that the bosses  142  can be easily engaged with the claws  110 . 
       FIG. 13  is a cross-sectional side view of the frame  120  taken from a line XIII-XIII shown in  FIG. 12 . The supporting walls  123 ,  124  are formed to have arcuate projections  131 ,  132  on edges  133 , which is a side closer to the bottom surface  111  of the casing portion  100  when the conveyer gear unit  64  is situated in the casing portion  100 . More specifically, the projections  131  are provided on the edges  133  and on a side closer to the bearings  127 . Meanwhile, the projections  132  are provided on the edges  133  and on a side closer to the bearings  125 . The edges  133  are formed to be substantially flat in a center portion between the projections  131 ,  133  whilst the projections  131 ,  132  are projected downward from the flat portion. When the conveyer gear unit  64  is situated in the casing  100  to the bottom surface  111 , the projections  131 ,  132  become in contact with the contact portions  118 ,  119  respectively so that the conveyer gear unit  64  is situated in the correct position in the depth of the casing portion  100 . It is to be noted that the projections  131 ,  132  may be omitted, and the edges  133 ,  134  may be in contact with the contact portions  118 ,  119  in order to situate the conveyer gear unit  64  in the correct position of the casing portion  100 . 
     When the conveyer gear unit  64  is installed in the casing portion  10 , a side having the conveyer gear  117  of the conveyer gear unit  64  is inserted firstly in the casing portion  100  through the opening  102 , and the bosses  143  are fitted in the U-shaped grooves  108 .Thus, the conveyer gear unit  64  can be placed in an approximate position in the lengthwise direction of the arm portion  75 . Thereafter, a side having the conveyer gear  115  of the conveyer gear unit  64  is pressed into the casing portion  100 . In this regard, the beveled portions  142 A of the bosses  142  come into contact with the claws  110  so that the partition walls  106  are pressed outward by the bosses  142  to be apart from each other. When the conveyer gear unit  64  is pressed further into the casing portion, the bosses  141  are fitted in the V-shaped grooves  109 , the bosses  142  pass over the claws  110 , and the bosses  142  become engaged with the claws  110 . Therefore, the conveyer gear unit  64  is restricted from being displaced in the direction of depth of the casing portion  100 . Namely, the conveyer gear unit  64  can be prevented from being unintentionally detached from the casing portion  100  by the engagement of the bosses  142  and the claws  110 . In this position, the conveyer gear unit  64  may be movable in the direction in which the conveyer gear unit  64  is inserted toward the opening  102 , when the feed rollers  25  rotate in the feeding direction  91 , the conveyer gear unit  64  is pressed toward the bottom surface  111 . Therefore, the projections  131 ,  132  become in contact with the contact portions  118 ,  119  so that the conveyer gear unit  64  can be in the correct position within a predetermined allowable range. 
     Next, behaviors of the feeding unit  60  will be described with reference to  FIGS. 14A ,  14 B.  FIGS. 14A and 14B  are cross-sectional side views of the feeding unit  60  taken from a line XIV-XIV shown in  FIG. 6 . In  FIG. 14A , the feeding unit  60  with the drive shaft  28  being rotated in the counterclockwise direction is illustrated. In  FIG. 14B , the feeding unit  60  with the drive shaft  28  being rotated in the clockwise direction is illustrated. 
     When the motor  36  is rotated by the motor driver (not shown) in a predetermined direction, the rotation is conveyed to the drive shaft  28  through the output shaft  37 , the drive force conveyer system  27 , and the conveyer gear  67 . According to the gear arrangement in the present embodiment, the motor  36  is rotated in a direction to rotate the drive shaft in the counterclockwise direction. 
     As shown in  FIG. 14A , when the drive shaft  28  rotates in the counterclockwise direction, the sun gear  87  is rotated in the same direction accordingly. In this regard, the planet gear  89  revolves around the sun gear  87  in the counterclockwise direction to come engaged with the conveyer gear  115 . Thus, the rotation of the planet gear  89  can be conveyed to and further from the conveyer gear  115 . Because the planet gear  89  is rotated by the rotation of the sun gear  87  in the clockwise direction, the conveyer gear  115  is rotated in the counter clockwise direction. When the rotation of the conveyer gear  115  is transmitted to the conveyer gear  72  through the intermediate gear  116  and the conveyer gear  117 , the feed rollers  25  are rotated in the clockwise direction. Accordingly, the recording sheet being in contact with the outer peripheries of the feed rollers  25  is fed in the feeding direction  91 . Assuming that the motor  36  is activated to rotate the feed rollers  25  in the opposite direction from the feeding direction, due to the presence of the planetary gear unit  65  between the drive shaft  28  and the conveyer gear unit  64 , the planet gear  89  is disengaged from the conveyer gear  115 , as shown in  FIG. 14B ; therefore, transmission of the rotation to the conveyer gear unit  64  is shut off by the planetary gear unit  65 . Thus, the planetary gear unit switches transmission and blocking of the rotation to the conveyer gear unit  64  according to the direction of the inputted rotation. 
     During the feeding operation of the feed rollers  25 , the feed rollers  25  are subject to stress in the direction opposite from the feeding direction due to friction generated between the feed rollers  25  and the recording sheet. The stress to the feed rollers  25  causes the conveyer gear  117 , which is rotated by the rotation torque of the motor  36 , to move in the counterclockwise direction (as indicated by an arrow  145  in  FIG. 14A ) around the conveyer gear  72  about an axis of the conveyer gear  72 . In this regard, the shaft  137  of the conveyer gear  117  upthrusts the bearings  127  in the direction indicated by the arrow  145 . Therefore, a lower side of the frame  120  closer to the feed rollers  25  becomes in contact with the contact portion  119  on the bottom surface  111  with the projections  132 , and the frame  120  can be set in the correct position with respect to the casing portion  100  within the predetermined allowable range. The stress to the feed rollers  25  further affects the conveyer gear  116  through the conveyer gear  72  and the conveyer gear  117 . Therefore, the conveyer gear  115  is moved around the conveyer gear  116  about an axis of the conveyer gear  116  in the counterclockwise direction (as indicated by an arrow  146  in  FIG. 14A ). In this regard, the shaft  135  of the conveyer gear  115  upthrusts the bearings  125  in the direction indicated by the arrow  146 . Therefore, an upper side of the frame  120  closer to the planetary gear unit  65  becomes in contact with the contact portion  118  on the bottom surface  111  with the projections  131 , and the frame  120  can be set in the correct position with respect to the casing portion  100  within the predetermined allowable range. Thus, when the feed rollers  25  are rotated in the feeding direction, the shaft  137  of the conveyer gear  117  and the shaft  135  of the conveyer gear  115  press the frame  120  toward the bottom of the casing portion  100  so that the conveyer gear unit  64  can be situated in the correct position in the casing portion  100 . 
     Thus, the conveyer gear unit  64  can be settled easily in the correct position with the above-described simplified configuration according to the rotation of the feed rollers  25 . 
     In the above embodiment, the conveyer gear unit  64  includes three (i.e., an odd-number of) gears, which are the conveyer gear  115 , the intermediate gear  116 , and the conveyer gear  117 . Therefore, the gears at each end of the gear train are moved toward the substantially same direction when the feed rollers  25  are subject to the stress from the recording sheets. It is to be noted that the gears at each end of the train gear are moved toward the same direction when the conveyer gear unit  64  includes three or more and odd-numbered gears. Therefore, the conveyer gear unit  64  may include three or more and odd-numbered gears. It may be noted that, when the conveyer gear unit includes a single gear, the gear is pressed toward the bottom of the casing portion  100  according to the rotation of the feed rollers  25 . 
     When the conveyer gear unit  64  includes two or more and even-numbered gears, a gear directly engaged with the conveyer gear  72  at one end of the gear train is moved toward the bottom of the casing portion  100 , and a gear at the other end of the gear train is moved toward the opening  102 . Therefore, when the conveyer gear unit  64  includes two or more and even-numbered gears, a restricting structure to restrict the gear at the other end of the gear train from being moved toward the opening  102 . 
     In the above embodiment, the swingable arm  26  is made of ABS resin whilst the frame  120  is made of POM, which has higher slidability than ABS resin. Therefore, the swingable arm  26  provides higher dimensional accuracy and rigidity whilst the frame can prevent abrasion which may be caused by rotational friction. 
     In the above embodiment, the shafts  135 ,  135 ,  137  has staged cores; therefore, when the cores  135 B,  136 B,  137 B are distorted by large rotation torque, the gears  115 ,  116 ,  117  are supported by the cores  135 A,  136 A,  137 A, and the shafts  135 B,  136 B,  137 B can be prevented from being corrupted. 
     Further, in the above embodiment, the planetary gear unit  65  between the drive shaft  28  and the conveyer gear unit  64  can prevent the reverse rotation of the drive shaft  28  from being transmitted to the conveyer gear unit  64 . Therefore, when the motor  36  rotates in a direction opposite from the feeding direction, the rotation is absorbed by the planetary gear unit  65 . When, for example, the reverse rotation is not absorbed by the planetary gear unit  65  but transmitted to the conveyer gear unit  64 , the conveyer gears  115 ,  117  are moved toward the opening  102 , and the conveyer gear unit  64  may be detached from the casing portion  100 . However, in the above embodiment, the conveyer gear unit  64  is prevented from being unintentionally detached. 
     It is to be noted that, however, the planetary gear unit  65  may not necessarily be arranged between the drive shaft  28  and the conveyer gear unit  64 , but may be arranged, for example, in the drive force conveyer system  27  as long as it is arranged on the upstream side than the conveyer gear unit  64  in the sheet feeding path. Further, the planetary gear unit  65  may even be omitted when the motor  36  is controlled to rotate solely in the feeding direction. 
     Furthermore, in the above embodiment, the conveyer gear unit  64  is situated in the correct position in the direction to be inserted in the casing portion  100  by the projections  131 ,  132  being brought into contact with the contact portions  118 ,  119  respectively. However, the position of the conveyer gear unit  64  with respect to the arm portion  75  may be determined by having the bosses  143  in contact with bottom portions of the U-shaped grooves  108  and the bosses  141  in contact with bottom portions of the V-shaped grooves. 
     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 feeder unit, the sheet feeding device, and an image reading apparatus 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.