Patent Publication Number: US-2020301343-A1

Title: Sheet transport device, image reading device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-049726 filed Mar. 18, 2019. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to sheet transport devices, image reading devices, and image forming apparatuses. 
     (ii) Related Art 
     Japanese Unexamined Patent Application Publication No. 2010-1091 discloses a known sheet feeding device including a vertically ascendable-descendible sheet load plate on which sheets are loaded, a feeder that comes into pressure contact with the upper surface of the sheets loaded on the sheet load plate and moves the pressure-contacted surface in a predetermined direction so as to sequentially feed the sheets, an ascend-descend unit that causes the sheet load plate to ascend and descend, a controller that controls driving of the ascend-descend unit, and an upper-surface detector that detects the upper surface of the sheets loaded on the sheet load plate. When the controller uses the ascend-descend unit to cause the sheet load plate to ascend to a reference feed position, the controller calculates a displacement amount from the reference feed position based on a timing at which the upper-surface detector detects the upper surface of the sheets and a timing at which the ascend-descend unit stops, and causes the sheet load plate to descend by the calculated displacement amount. 
     Japanese Unexamined Patent Application Publication No. 2004-106995 discloses a known sheet feeding device that includes a sheet feed tray on which sheets are loaded, a sheet feeder that separates the sheets loaded on the sheet feed tray from each other and feeds each sheet, and a registration unit that aligns the leading edges of the sheets fed by the sheet feeder by causing the leading edges of the sheets to abut on the registration unit by a predetermined abutment amount. The sheet feeding device further includes a receiver that receives a mixed mode signal for feeding sheets of various widths loaded on the sheet feed tray, and a controller that controls driving of the sheet feeder when the receiver receives the mixed mode signal, such that the abutment amount of the sheets on the registration unit is larger than the predetermined abutment amount. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to a sheet transport device, an image reading device, and an image forming apparatus that are capable of correcting a skew of a sheet loaded on a load section before the sheet is fed, as compared with a case where ascending-descending operation of the load section is not performed. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a sheet transport device including a sheet load tray on which a sheet is loaded, a detector that detects whether or not the sheet exists on the sheet load tray, a feeder that feeds the sheet one-by-one from the sheet load tray, and a sheet-load-tray ascend-descend unit that moves the sheet in a sheet loading direction to set an uppermost sheet at a sheet feed position of the feeder, and a controller. In a case where the sheet is detected by the detector, the controller causes the sheet load tray to ascend or descend before the feeder starts to feed the sheet so that ascending-descending operation for moving the sheet load tray between the sheet feed position and a descent position located below the sheet feed position is performed at least once. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a cross-sectional view schematically illustrating the internal configuration of an image forming apparatus; 
         FIG. 2  is a cross-sectional view illustrating the internal configuration of an image reading device; 
         FIG. 3  is a block diagram illustrating an example of a functional configuration of the image forming apparatus; 
         FIGS. 4A and 4B  are cross-sectional views schematically illustrating the configuration of a sheet load section,  FIG. 4A  illustrating a state where an ascendable-descendible plate has ascended to a sheet feed position,  FIG. 4B  illustrating a state where the ascendable-descendible plate has descended; 
         FIG. 5  is a flowchart illustrating the flow of the operation of the sheet load section; 
         FIGS. 6A to 6C  are cross-sectional views schematically illustrating the operation of the ascendable-descendible plate having sheets placed thereon,  FIG. 6A  illustrating a state where the sheets are placed on the ascendable-descendible plate,  FIG. 6B  illustrating a state where the ascendable-descendible plate is descending,  FIG. 6C  illustrating a state where the ascendable-descendible plate has descended and the sheets have been aligned; 
         FIGS. 7A and 7B  are cross-sectional views schematically illustrating the configuration of a sheet load section according to a first modification; 
         FIG. 8  is a plan view schematically illustrating the arrangement of protrusions in the sheet load section according to the first modification; 
         FIGS. 9A and 9B  are cross-sectional views schematically illustrating the state of a sheet bundle placed on the ascendable-descendible plate; 
         FIG. 10  is a cross-sectional view schematically illustrating the configuration of a sheet load section according to a second modification; and 
         FIGS. 11A and 11B  are cross-sectional views schematically illustrating the state of a sheet bundle placed on the ascendable-descendible plate. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described in further detail below with reference to exemplary embodiments and specific examples. However, the present disclosure is not to be limited to these exemplary embodiments and specific examples. 
     Furthermore, in the following description with reference to the drawings, it should be noted that the drawings are schematic and that the dimensional ratios are different from the actual dimensional ratios. For providing an easier understanding, components other than those necessary for the description are omitted, where necessary. 
     1. Overall Configuration and Operation of Image Forming Apparatus 
       FIG. 1  is a cross-sectional view schematically illustrating the internal configuration of an image forming apparatus  1  according to an exemplary embodiment.  FIG. 2  is a cross-sectional view illustrating the internal configuration of an image reading device  2 .  FIG. 3  is a block diagram illustrating an example of a functional configuration of the image forming apparatus  1 . The overall configuration and the operation of the image forming apparatus  1  will be described below with reference to the drawings. 
     1.1. Overall Configuration 
     The image forming apparatus  1  includes an image reading device  2  as a reader that reads an image from a sheet S, such as a document, and converts it into image data, an image forming unit  3  as an image recorder that prints the read image data onto paper as a recording medium, an operational information unit  4  as a user interface, and an image processor  5 . 
     The image reading device  2  includes a sheet load section  21 , an automatic sheet feeder  22 , and an image reader  23  as an example of an imaging unit. The automatic sheet feeder  22  transports the sheet S placed on the sheet load section  21  to a read position of the image reader  23 . An image read by an image sensor (not shown), such as a charge-coupled device (CCD) line sensor, of the image reader  23  is converted into image data as an electric signal. 
     The image forming unit  3  includes a paper feeding device  32 , exposure devices  33 , photoconductor units  34 , developing devices  35 , a transfer device  36 , and a fixing device  37 , and forms image information received from the image processor  5  as a toner image onto paper P fed from the paper feeding device  32 . 
     The operational information unit  4  as a user interface is disposed on the front surface of the image reading device  2 . The operational information unit  4  is constituted of a combination of, for example, a liquid crystal display panel, various control buttons, and a touchscreen. A user of the image forming apparatus  1  may input various settings and a command via the operational information unit  4 . Moreover, various types of information are displayed to the user of the image forming apparatus  1  via the liquid crystal display panel. 
     The image processor  5  generates image data from the image read by the image reading device  2  and from print information transmitted from an external apparatus (such as a personal computer). 
     1.2. Image Forming Unit 
     Paper P designated in a print job for each printing process is fed from the paper feeding device  32  to the image forming unit  3  in accordance with an image formation timing of the image forming unit  3 . 
     The photoconductor units  34  individually include photoconductor drums  341  that are provided parallel to one another above the paper feeding device  32  and that are rotationally driven. The developing devices  35  form yellow (Y), magenta (M), cyan (C), and black (K) toner images on the corresponding photoconductor drums  341  having electrostatic latent images formed thereon by the exposure devices  33 . 
     The toner images formed on the photoconductor drums  341  of the respective photoconductor units  34  are sequentially electrostatically transferred (first-transferred) onto an intermediate transfer belt  361  of the transfer device  36 , so that a superposed toner image constituted of toners of the respective colors is formed. The superposed toner image on the intermediate transfer belt  361  is collectively transferred by a second-transfer roller  362  onto the paper P transported from a pair of registration rollers  321  and guided by a transport guide. 
     In the fixing device  37 , a fixation nip FN (fixation region) is formed by a pressure contact area of a pair of heating module  371  and pressing module  372 . 
     The paper P having the toner image collectively transferred thereon by the transfer device  36  is transported to the fixation nip FN of the fixing device  37  via a transport guide  363  in a state where the toner image is not fixed on the paper P yet. Then, the pair of heating module  371  and pressing module  372  fixes the toner image onto the paper P in accordance with heating and pressing functions. 
     The paper P having the fixed toner image formed thereon is guided to a switch gate G 1  and is output from a first pair of output rollers  373  so as to be accommodated in a paper output tray TR 1  at the upper surface of the image forming apparatus  1 . If the paper P is to be inverted for duplex printing or is to be output with the image recorded face thereof facing upward, the transport direction of the paper P is switched toward a transport path  375  by the switch gate G 1 . 
     1.3. Image Reading Device 
     The image reading device  2  includes the sheet load section  21 , the automatic sheet feeder  22 , and the image reader  23 . The sheet load section  21  and the automatic sheet feeder  22  are connected to each other in an openable and closable manner above the image reader  23 . 
     The sheet load section  21  includes an ascendable-descendible plate  212  on which one or more sheets S having images recorded thereon are placed. The ascendable-descendible plate  212  is ascendable and descendible in accordance with the number of loaded sheets S and retains the sheets S at an ascent position where the upper surface of the sheets S is in contact with a nudger roller  221 . 
     The automatic sheet feeder  22  includes the nudger roller  221  that fetches the sheets S loaded on the ascendable-descendible plate  212  sequentially from the top, and also includes a separator  224  constituted of a feed roller  222  and a retardation roller  223  in pressure contact with the feed roller  222 . 
     In the separator  224 , the feed roller  222  and the retardation roller  223  form a pair that separates sheets S from each other, if multiple stacked sheets S are fed to a nip N, so as to transport the sheets S one-by-one to the image reader  23 . 
     In a transport path G, a transport roller  225  is disposed at a position downstream of the feed roller  222  in the transport direction of the sheet S. The transport roller  225  transports the sheet S fed by the feed roller  222  to a pre-registration roller  226 . 
     A registration roller  227  that adjusts the transport timing of the sheet S is disposed downstream of the pre-registration roller  226 . The pre-registration roller  226  corrects a skew of the sheet S by forming a loop in a state where the leading edge of the sheet S is in abutment with the registration roller  227  in a stopped state. The registration roller  227  is rotationally driven in accordance with a timing for starting a reading process. In a state where the loop of the sheet S is maintained by the transport roller  225  and the pre-registration roller  226 , the sheet S is pressed against a sheet passing surface PG 1  by a platen roller  228  so that the front face of the sheet S is read by the image reader  23 . 
     A sheet placement surface PG 2  that supports a sheet S placed thereon by an operator is disposed to the right of the sheet passing surface PG 1 . A sheet guide PG 3  is disposed between the sheet passing surface PG 1  and the sheet placement surface PG 2 . The sheet S passing over the sheet passing surface PG 1  is guided to the sheet guide PG 3  so as to be transported to a read sensor  232 . The sheet S whose front face is read by the image reader  23  is output by an output roller  229  to an output section  217  provided below the sheet load section  21 , while the rear face of the sheet S is read by the read sensor  232 . 
     An image reading sensor  231  that optically reads an image of a sheet S and converts it into an electric signal is provided below the sheet placement surface PG 2 . Specifically, the image reading sensor  231  reads an image from a sheet S passing over the sheet passing surface PG 1  or from a sheet S placed on the sheet placement surface PG 2 . The read image is converted into image data as an electric signal. 
     1.4. Block Configuration of Image Forming Apparatus 
     The image forming apparatus  1  includes a system control device  10  including an image output controller  11 , a read controller  12 , a power supply controller  13 , an exposure controller  14 , and a fixation temperature controller  15 , and executes a control program stored in a memory to control the operation of the entire image forming apparatus  1 . 
     The image output controller  11  gives operation control commands to, for example, the paper feeding device  32 , the exposure devices  33 , the photoconductor units  34 , the developing devices  35 , the transfer device  36 , and the fixing device  37  included in the image forming unit  3 . 
     Furthermore, the image output controller  11  gives operation control commands to the power supply controller  13 , the exposure controller  14 , and the fixation temperature controller  15  included in the system control device  10 . Specifically, the image output controller  11  determines whether or not, for example, the paper feeding device  32 , the exposure devices  33 , the photoconductor units  34 , the developing devices  35 , the transfer device  36 , and the fixing device  37  constituting the image forming unit  3  are to be driven by being supplied with power, and transmits commands to the respective controllers therefor in accordance with the determination results. 
     Moreover, the image output controller  11  exchanges information with the read controller  12  and performs predetermined image read control if an image read command is received therefrom via the operational information unit  4 . 
     The read controller  12  controls the operation of the image reading device  2  to read an image from each sheet S by scanning while transporting the sheet S loaded on the sheet load section  21  to the image reader  23  via the automatic sheet feeder  22 , and receives the read image data. The received image data is accumulated in a storage unit (HDD). 
     2. Configuration and Operation of Sheet Load Section 
       FIGS. 4A and 4B  are cross-sectional views schematically illustrating the configuration of the sheet load section  21 . Specifically,  FIG. 4A  is a cross-sectional view illustrating a state where the ascendable-descendible plate  212  has ascended to a sheet feed position, and  FIG. 4B  is a cross-sectional view illustrating a state where the ascendable-descendible plate  212  has descended.  FIG. 5  is a flowchart illustrating the flow of the operation of the sheet load section  21 .  FIGS. 6A to 6C  are cross-sectional views schematically illustrating the operation of the ascendable-descendible plate  212  having sheets S placed thereon. Specifically,  FIG. 6A  is a cross-sectional view illustrating a state where sheets S are placed on the ascendable-descendible plate  212 ,  FIG. 6B  is a cross-sectional view illustrating a state where the ascendable-descendible plate  212  is descending, and  FIG. 6C  is a cross-sectional view illustrating a state where the ascendable-descendible plate  212  has descended and the sheets S have been aligned. The configuration and the operation of a sheet feeding unit constituted of the sheet load section  21  and the separator  224  will be described below with reference to the drawings. 
     2.1. Overall Configuration of Sheet Load Section 
     The sheet load section  21  supports the ascendable-descendible plate  212  as an example of a sheet load tray in an ascendable-descendible manner above a tray body  211 , and is capable of holding sheets of various sizes, that is, sheets S with different dimensions with respect to at least one of a sheet length corresponding to a distance in the sheet transport direction and a sheet width corresponding to a distance in the direction intersecting (orthogonal to) the sheet transport direction. 
     A sheet-edge aligning section  213  is provided at the sheet feed side of the tray body  211 . First edges (i.e., the leading edges in the sheet transport direction) of the sheets S loaded on the ascendable-descendible plate  212  come into contact with the sheet-edge aligning section  213  so that the leading edges of the sheets S are aligned. 
     Side guides  215  (see  FIG. 8 ) are disposed at the opposite edges in the direction intersecting (orthogonal to) the sheet transport direction, such that a center registration method is employed in which the opposite widthwise edges of the sheets S of various sizes are aligned in the width direction with reference to the side guides  215 . 
     The nudger roller  221  is disposed close to the feed roller  222  above the sheet-edge aligning section  213 . The nudger roller  221  is maintained at a retreated position during a standby mode by being lifted upward, and descends to a nip position (i.e. sheet feed position) during a sheet feeding mode so as to feed the uppermost sheet S on the ascendable-descendible plate  212 . 
     In  FIGS. 4A and 4B , the ascendable-descendible plate  212  is supported above the tray body  211  in a rotatable manner about a rotation axis  212   a . The upper surface of the ascendable-descendible plate  212  is provided with a load surface  212   b  for the sheets S. 
     An ascend-descend rod  214  that causes the ascendable-descendible plate  212  to ascend and descend between the sheet feed position and the descent position is in contact with the lower surface near a first end of the ascendable-descendible plate  212  in the sheet feeding direction. The ascend-descend rod  214  is capable of transmitting a driving force from a driving source (not shown), such as a stepping motor, to a rotation axis  214   a , such that the first end of the ascendable-descendible plate  212  ascends or descends in accordance with rotation of the ascend-descend rod  214  (see an arrow R in  FIG. 4A ). 
       FIG. 4A  illustrates a state where the ascendable-descendible plate  212  has ascended to the sheet feed position. When the ascendable-descendible plate  212  has ascended, the first edges (i.e. the leading edges in the sheet transport direction) of the sheets S placed on the load surface  212   b  may sometimes be misaligned (see  FIG. 6A ). 
       FIG. 4B  illustrates a state where the ascendable-descendible plate  212  has descended to the descent position. Because the ascendable-descendible plate  212  descends while rotating about the rotation axis  212   a  provided at an upstream position distant from the first end in the sheet transport direction, the ascendable-descendible plate  212  at the descent position is inclined so as to decrease in height toward the first end in the feeding direction (see reference sign H in  FIG. 4B ). Accordingly, the first edges (i.e. the leading edges in the sheet transport direction) of the sheets S placed on the load surface  212   b  are readily movable toward the sheet-edge aligning section  213  (see  FIG. 6C ). 
     2.2. Operation of Sheet Load Section 
     When images are to be read from sheets S, the user of the image forming apparatus  1  places the sheets S on the load surface  212   b  of the ascendable-descendible plate  212  and moves the side guides  215  so as to align and set the sheets S in the width direction. 
     When the sheets S are set on the ascendable-descendible plate  212  of the sheet load section  21  and a sheet detection sensor S 1  is turned on in step S 101 , the read controller  12  determines in step S 102  whether the reading mode for the sheets S is a correction priority mode for correcting a skew of the sheets S toward zero or a productivity priority mode for prioritizing productivity by increasing the number of feedable sheets S per unit time. The correction priority mode and the productivity priority mode may be set by the user via the operational information unit  4  when the sheets S are to be read, or may be set in the image forming apparatus  1  in advance. 
     In a case where the sheets S are detected by the sheet detection sensor S 1 , the image reading device  2  according to this exemplary embodiment may perform ascending-descending operation for moving the ascendable-descendible plate  212  between the sheet feed position and the descent position at least once before the automatic sheet feeder  22  starts feeding the sheets S, and may correct a skew of the sheets S before the sheets S loaded on the ascendable-descendible plate  212  are fed. 
     If the reading mode for the sheets S is the correction priority mode (A in step S 102 ), the number N 1  of ascents and descents of the ascendable-descendible plate  212  during the feeding of the sheets S is received in step S 103 . The number N 1  of ascents and descents may be set in the image forming apparatus  1  in advance, or may be set by the user via the operational information unit  4 . 
     Then, the ascending-descending operation of the ascendable-descendible plate  212  is performed at least once in step S 104  and step S 105 . As shown in  FIG. 6A , in the ascending-descending operation, the ascend-descend rod  214  is rotationally driven so that the ascendable-descendible plate  212  located at the feed position descends to the descent position, and then ascends again to the feed position. In this ascending-descending operation, as the ascendable-descendible plate  212  descends toward the descent position, the ascendable-descendible plate  212  becomes inclined so as to decrease in height toward the feeding direction, as schematically shown in  FIGS. 6B and 6C , and the sheets S move toward the sheet-edge aligning section  213  in accordance with an impact caused by the descent toward the descent position. 
     When the ascending-descending operation reaches the set number N 1  of ascents and descents (YES in step S 106 ), the ascendable-descendible plate  212  ascends to the feed position in step S 107 , so that the skew-corrected sheets S become in a feedable state. 
     If the reading mode for the sheets S is the productivity priority mode (B in step S 102 ), it is determined whether or not ascending-descending operation is set in step S 108 . If ascending-descending operation is set (YES in step S 108 ), the number N 2  of ascents and descents of the ascendable-descendible plate  212  is received in step S 109 . Then, the ascending-descending operation of the ascendable-descendible plate  212  is performed at least once in steps S 110  and S 111 . If the ascending-descending operation reaches the set number N 2  of ascents and descents (YES in step S 112 ), the ascendable-descendible plate  212  ascends to the feed position in step S 113 , so that the skew-corrected sheets S become in a feedable state. 
       FIGS. 6A to 6C  schematically illustrate how a skew at the leading edges of the sheets S is corrected in accordance with the ascending-descending operation of the ascendable-descendible plate  212 . As shown in  FIG. 6A , in a state where the sheets S are placed on the load surface  212   b  of the ascendable-descendible plate  212 , the leading edges of the sheets S (in the sheet transport direction) may sometimes be misaligned. In particular, in the image reading device  2  of a so-called free registration type that is capable of identifying which position of the sheet load section  21  sheets S are placed on, the sheets S placed on the ascendable-descendible plate  212  are positionally misaligned in the feeding direction. 
     When the ascendable-descendible plate  212  descends toward the descent position from this state, the ascendable-descendible plate  212  becomes inclined so as to decrease in height toward the feeding direction, as shown in  FIG. 6B . Thus, the sheets S on the load surface  212   b  of the ascendable-descendible plate  212  slide and move toward the sheet-edge aligning section  213  (see an arrow R in  FIG. 6B ). 
     Then, as shown in  FIG. 6C , when the ascendable-descendible plate  212  descends to the descent position, the ascendable-descendible plate  212  receives an impact caused as it stops at the descent position, so that the sheets S on the load surface  212   b  abut on the sheet-edge aligning section  213 , whereby the leading edges of the sheets S become aligned. Consequently, the skew of the sheets S loaded on the sheet load section  21  may be corrected before the sheets S are fed, as compared with a configuration where ascending-descending operation of the ascendable-descendible plate  212  as a sheet load tray is not performed. 
     First Modification 
       FIGS. 7A and 7B  are cross-sectional views schematically illustrating the configuration of a sheet load section  21 A according to a first modification.  FIG. 8  is a plan view schematically illustrating the arrangement of protrusions  211 A in the sheet load section  21 A according to the first modification.  FIGS. 9A and 9B  schematically illustrate the state of a sheet bundle SB placed on the ascendable-descendible plate  212 . 
     As shown in  FIGS. 7A and 7B , the sheet load section  21 A according to the first modification includes the protrusions  211 A protruding toward the ascendable-descendible plate  212  from the upper surface of the tray body  211 . 
     As shown in  FIGS. 7A and 7B , the protruding height of each protrusion  211 A is set such that the protrusion  211 A does not protrude from the load surface  212   b  of the ascendable-descendible plate  212  (see  FIG. 7A ) in a state where the ascendable-descendible plate  212  having loaded thereon a maximum number of sheets S allowed to be loaded thereon has ascended to the sheet feed position, and protrudes from the load surface  212   b  of the ascendable-descendible plate  212  (see h in  FIG. 7B ) when the ascendable-descendible plate  212  descends to the descent position. 
     Furthermore, as schematically shown in  FIG. 8 , the protrusions  211 A are multiple protrusions provided in the width direction intersecting the feeding direction of the sheets S, and are disposed in the central area in the width direction of the sheets S and come into contact with sheets S of the smallest transportable size allowed. 
     The protrusions  211 A having this configuration are provided on the upper surface of the tray body  211  so that, in a case where the multiple sheets S are loaded as the sheet bundle SB on the load surface  212   b  of the ascendable-descendible plate  212 , as shown in  FIG. 9A , the protrusions  211 A come into contact with the lowermost surface of the sheets S and cause the sheet bundle SB to bend when the ascendable-descendible plate  212  descends to the descent position. When the protrusions  211 A come into contact with the sheet bundle SB from below and cause the sheet bundle SB to bend upward in a convex shape, air layers AL are formed between the sheets of the sheet bundle SB. 
     When the ascendable-descendible plate  212  descends to the descent position, the air layers AL are formed between the sheets in the sheet bundle SB constituted of a bundle of a large number of sheets S, so that the sheets S become readily movable toward the sheet-edge aligning section  213 . 
     Furthermore, since the protrusions  211 A are disposed in the central area in the width direction of the sheets S and come into contact with sheets S of the smallest transportable size allowed (e.g. size A5), air intervenes the sheet bundle SB of the smallest sheet size, whereby the sheets S become readily movable. 
     As shown in  FIG. 9B , since the protrusions  211 A are set at a height where they do not come into contact with the lowermost surface of the sheets S when the ascendable-descendible plate  212  having loaded thereon a maximum number of sheets S allowed to be loaded thereon has ascended to the feed position, the uppermost surface of the sheets S is prevented from bending during the feeding process of the sheets S. 
     Second Modification 
       FIG. 10  is a cross-sectional view schematically illustrating the configuration of a sheet load section  21 B according to a second modification.  FIGS. 11A and 11B  are cross-sectional views schematically illustrating the state of the sheet bundle SB placed on the ascendable-descendible plate  212 . 
     The sheet load section  21 B according to the second modification includes side guides  215 A as an example of stoppers that cause the sheet bundle SB to bend by coming into contact with the lateral edges of the sheets S in the direction intersecting the feeding direction of the sheets S when the ascendable-descendible plate  212  ascends to the feed position. 
     As schematically shown in  FIG. 10 , the opposite lateral sides of the ascendable-descendible plate  212  are integrally provided with rack teeth  212   c  extending together with the ascendable-descendible plate  212  in the ascending-descending direction of the ascendable-descendible plate  212 . 
     At the lower side of the ascendable-descendible plate  212 , the side guides  215 A integrally have rack teeth  215   a  with the ascendable-descendible plate  212  interposed therebetween. The rack teeth  215   a  extend together with the side guides  215 A in the moving direction (i.e. the direction intersecting the sheet feeding direction) of the side guides  215 A. 
     The tray body  211  rotatably supports missing-tooth gears  216 . As shown in  FIG. 10 , the missing-tooth gears  216  according to this exemplary embodiment each have three teeth  216   a  at equal intervals in the circumferential direction, and any of the teeth  216   a  engages with the rack teeth  212   c  provided in the ascendable-descendible plate  212  and the rack teeth  215   a  provided in the side guides  215 A. 
     In the sheet load section  21 B having the above-described configuration, when the ascendable-descendible plate  212  ascends from the descent position to the feed position, the rack teeth  212   c  integrally provided on the ascendable-descendible plate  212  engage with the teeth  216   a  of the missing-tooth gears  216 , so that the missing-tooth gears  216  rotate within the range in which the teeth  216   a  are provided as the ascendable-descendible plate  212  ascends. In this case, if the teeth  216   a  of the missing-tooth gears  216  have a chance to engage with the rack teeth  215   a  provided in the side guides  215 A, the side guides  215 A move in the width direction of the sheets S within the rotating range of the missing-tooth gears  216  (see an arrow R 1  in  FIG. 11A ) so as to come into contact with the opposite edges of the sheet bundle SB, thereby causing the sheet bundle SB to bend. 
     When the side guides  215 A that have moved to cause the sheet bundle SB to bend become disengaged from the rack teeth  215   a  with the rotation of the missing-tooth gears  216 , the side guides  215 A move in opposite directions from each other to increase the distance therebetween in accordance with the restoring force of the bent sheet bundle SB (see arrows R 2  in  FIG. 11B ). 
     Because each missing-tooth gear  216  has three teeth  216   a  in the circumferential direction, the missing-tooth gear  216  performs intermittent rotation (see arrows in  FIG. 11A ) during the ascending of the ascendable-descendible plate  212 . At the same time, the side guides  215 A having the rack teeth  215   a  engaged with the missing-tooth gears  216  also move intermittently (see arrows R 1  in  FIG. 11A ) so as to cause the sheet bundle SB to repeatedly bend. 
     Accordingly, as schematically shown in  FIG. 11A , the sheets S may become readily movable owing to the air layers AL interposed between the sheets S. Specifically, when the ascendable-descendible plate  212  ascends from the descent position to the feed position, the air layers AL are repeatedly formed between the sheets in the sheet bundle SB constituted of a bundle of a large number of sheets S, so that the opposite widthwise edges of the sheet bundle SB are aligned and that the sheets S become readily movable toward the sheet-edge aligning section  213 . 
     According to the sheet load section  21  according to this exemplary embodiment, the ascending-descending operation for moving the ascendable-descendible plate  212  between the sheet feed position and the descent position therebelow is performed at least once before the automatic sheet feeder  22  starts feeding the sheets S, so that a skew of the sheets S may be corrected before the sheets S loaded on the ascendable-descendible plate  212  are fed. 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.