Abstract:
A conveyor device includes conveyor unit to convey a sheet along a path, a holder disposed at a downstream end of the path and holding sheets discharged from the conveyor unit in a stack, and a pressing unit. The pressing unit moves between a first position and a third position via a second position, contacts an uppermost sheet in the stack, and rises in an upward direction that approaches the third position as the sheets in the stack increase. The conveyor device also includes an urging member that does not apply an urging force to the pressing unit when the pressing unit is positioned between the first position and the second position; and applies an urging force to the pressing unit to urge the pressing unit toward the first position when the pressing unit is positioned between the second position and the third position.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2011-018684, filed on Jan. 31, 2011, the entire subject matter of which is incorporated herein by reference. 
     BACKGROUND 
     Aspects of the disclosure relate to a sheet conveyor device for conveying a sheet along a predetermined conveying path, an image reading device including the sheet conveyor device, and an image forming apparatus including the sheet conveyor device. 
     There is known an image forming apparatus which includes a sheet stacker for stacking sheets discharged after having been conveyed along a predetermined path, and which can avoid curling-up of the tailing ends of the stacked sheets, as viewed in a conveying direction, by pressing the stacked sheets on the sheet stacker with a sheet retaining member. 
     With the provision of the sheet pressing member, even when the sheet curling to some extent is discharged to the sheet stacker, the tailing end of the sheet may be kept from curling up. It is, therefore, possible to prevent or avoid collision of a sheet (specifically, its leading end), which is subsequently to the sheet stacker, against the sheet having been previously discharged and stacked in a curled-up state. 
     Further, because such collision may be avoided, it is also possible to prevent or avoid, for example, a drawback called a corner folding (i.e., folding of a corner at the leading end of a sheet) that is otherwise caused in the subsequently discharged sheet upon the collision against the previously discharged sheet. In addition, because such collision may be avoided, the already discharged sheet may be prevented or avoided from being pushed out of the sheet stacker upon the collision. 
     However, when the weight of the sheet pressing member is too heavy, or when an urging force acting on the sheet pressing member is too strong, the sheet pressing member may be not swung upwards even with the sheet striking against the sheet pressing member when the sheet is going to be discharged to the sheet stacker. 
     In that case, as illustrated in  FIG. 7A , a sheet  103  discharged to a sheet stacker  101  is abruptly bent downwards in its moving direction upon contacting with a sheet pressing member  105 . Therefore, the leading end of the sheet  103  collides against the sheet stacker  101 , thus possibly causing a drawback, such as the corner folding at the leading end of the sheet  103 . 
     On the other hand, when the weight of the sheet pressing member is light, or when the urging force acting on the sheet pressing member is weak, the sheet pressing member is swung upwards with the sheet, discharged to the sheet stacker, striking against the sheet pressing member. In that case, the sheet may be avoided from being abruptly bent downwards in its moving direction, and hence the occurrence of the above-described corner folding can also be avoided. 
     However, when the weight of the sheet pressing member is too light, or when the urging force acting on the sheet pressing member is too weak, the sheet pressing member cannot sufficiently hold down the already discharged sheets. In that case, as illustrated in  FIG. 7B , a position of the tailing end of an already discharged sheet  107  in the moving direction cannot be sufficiently displaced downwards, thus causing the problem that the subsequently-discharged sheet  103  is more liable to collide against the already discharged sheet  107 . 
     Stated another way, a pressing force applied from the sheet pressing member and acting on the sheet tends to cause the problem in any of the case where the pressing force is set excessively strong and the case where it is set excessively weak. Accordingly, optimizing the pressing force applied from the sheet pressing member and acting on the sheet is very difficult from the viewpoint of design. 
     SUMMARY 
     Aspects of the disclosure include a sheet conveyor device, which can prevent the leading end of a discharged sheet from being folded, and which can also avoid a subsequently discharged sheet from colliding against an already discharged sheet. Further, the disclosure provides an image reading device and an image forming apparatus, each including the sheet conveyor device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an example multifunction peripheral; 
         FIGS. 2A and 2B  illustrate an image scanner unit included in the multifunction peripheral shown in  FIG. 1 ; specifically,  FIG. 2A  is a vertical sectional view illustrating a state where a document supply tray is closed, and  FIG. 2B  is a vertical sectional view illustrating a state where the document supply tray is opened; 
         FIG. 3  is an enlarged view of example a stack lever and thereabout (i.e., a portion A denoted in  FIG. 2A ) in a first illustrative embodiment; 
         FIGS. 4A to 4C  are explanatory views of example to explain behaviors of the stack lever in the first embodiment; 
         FIG. 5  is an enlarged view of example a stack lever and thereabout in a second illustrative embodiment; 
         FIGS. 6A to 6C  are explanatory views of examples to explain behaviors of the stack lever in the second illustrative embodiment; and 
         FIG. 7A  is an explanatory view of example to explain a problem caused when a pressing force of a stack lever is too strong, and  FIG. 7B  is an explanatory view to explain a problem caused when the pressing force of the stack lever is too weak. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative embodiment will be described in detail with reference to the accompanying drawings. A sheet conveyor according to illustrative aspects of invention disclosure may for example, apply to a multifunction peripheral  1  as shown in  FIG. 1 . 
     First Embodiment 
     A multifunction peripheral  1 , shown in  FIG. 1 , includes not only a function (scan function) of an image reading device, but also other functions (e.g., a print function, a copy function, and a facsimile receiving and transmitting function). It is to be noted that the following description is made by employing up and down directions, left and right directions, and front and rear directions, which are denoted in  FIG. 1 , for easier understanding of relative positional relationships among various components of the multifunction peripheral  1 . 
     The multifunction peripheral  1  includes a printer unit  2 , a scanner unit  3  mounted at a top of the printer unit  2 , and an operating unit  4  disposed above the printer unit  2  and forward of the scanner unit  3 . The printer unit  2  includes an image forming mechanism capable of forming an image on a recording medium in accordance with electrophotography. Further, a paper feed cassette  6  capable of being withdrawn in a forward direction is disposed in a lower portion of the printer unit  2 , and a recording medium discharge section  7  to which the recording medium having been subjected to image formation is discharged is disposed in an upper portion of the printer unit  2 . 
     The scanner unit  3  has a structure that an ADF (Auto Document Feeder) is added to an image scanner of the flat bed (FB) type. The scanner unit  3  includes an FB main body  3 A and an ADF unit  3 B covering the upper surface side of the FB main body  3 A. The ADF unit  3 B is rotatable about its rear end in a direction in which its front end is displaced up and down. Thus, the ADF unit  3 B has a structure allowing it to be selectively displaced to a position where the ADF unit  3 B covers a document placement surface that is provided by an upper surface of the FB main body  3 A, and to a position where the document placement surface is exposed. 
     As shown in  FIGS. 2A and 2B , the ADF unit  3 B includes a supply roller  11 , a separation roller  12 , a main conveying roller  13 , a discharge roller  14 , etc., as rollers that are driven by power transmitted from a power source. A document placed on a document tray  16  can be conveyed to a document discharge section  18  by a group of those rollers along a conveying path in a substantially U-shape that is denoted by a two-dot-chain line in  FIG. 2B . 
     The document tray  16  is pivotable to a closed position shown in  FIG. 2A  and to an open position shown in  FIG. 2B . When the document tray  16  is moved to the closed position, it serves as a cover that covers a part of a top portion of the ADF unit  3 B, and when the document tray  16  is moved to the open position, it can be utilized as the document tray  16 . 
     A first document holder  21  is disposed at a position along one of opposed portions of the conveying path in the substantially U-shape. The first document holder  21  serves as a member for pressing the document, which is conveyed along the conveying path, against a first ADF glass (not shown) disposed in the FB main body  3 A. 
     A first image sensor (not shown) capable of reciprocally moving within the FB main body  3 A is disposed in the FB main body  3 A. When the first image sensor is moved to a position opposed to the first document holder  21  with the first ADF glass interposed therebetween, an image can be read by the first image sensor from a document being conveyed along the conveying path. 
     A second document holder  22  is disposed at another position along the conveying path in the substantially U-shape, i.e., at a position along a portion of the conveying path on the side (on the upstream side in the conveying direction) opposite to the position where the first document holder  21  is disposed. The second document holder  22  serves as a member for pressing the document, which is conveyed along the conveying path, against a second ADF glass  24 . 
     A second image sensor  26  is disposed inside the ADF unit  3 B at a position opposed to the second document holder  22  with the second ADF glass  24  interposed therebetween, and an image can also be read by the second image sensor  26  from a document being conveyed along the conveying path. Thus, in the multifunction peripheral  1 , images can be read by the first image sensor and the second image sensor from both front and rear surfaces of a document being conveyed along the conveying path. 
     As shown in  FIG. 3  in enlarged scale, a nip roller  31  is disposed under the discharge roller  14  for discharging the document to the document discharge section  18  in cooperation with the discharge roller  14 . Further, a stack lever  33  is disposed at a position where the leading end of the document in the conveying direction makes contact with the stack lever  33  when the document is discharged by the discharge roller  14  and the nip roller  31 . 
     The stack lever  33  is disposed such that its upper end is located at a position closer to the conveying path defined by the discharge roller  14  and the nip roller  31  than its lower end, and the stack lever  33  is constructed to be pivotable about the upper end thereof. Further, the stack lever  33  has a sloped surface  33 A extending obliquely downwards, and the document discharged by the discharge roller  14  and the nip roller  31  makes contact with the sloped surface  33 A. 
     A torsion coil spring  35  and a torsion coil spring  36  are disposed above the stack lever  33 . The torsion coil spring  35  has an arm  35 A that is always held in a state contacting with the stack lever  33 . The arm  35 A urges the stack lever  33  in a direction that causes the stack lever  33  to swing downwards (clockwise direction in  FIG. 3 ). 
     Further, when the stack lever  33  is swung upwards against an urging force of the torsion coil spring  35 , the torsion coil spring  35  is elastically deformed and the arm  35 A is displaced from a position denoted by solid lines in  FIG. 3  to a position denoted by broken lines. 
     On the other hand, the torsion coil spring  36  is held in a position away from the stack lever  33 , as denoted by solid lines in  FIG. 3 , in a state where the stack lever  33  is displaced to a lowermost position. The position of the stack lever  33  in that state will be referred to as a “first position” hereinafter. 
     When the stack lever  33  is pivoted and displaced upwards to some extent, an arm  36 A of the torsion coil spring  36  makes contact with the stack lever  33 . The position of the stack lever  33  in that state will be referred to as a “second position” hereinafter. 
     When the stack lever  33  is further pivoted upwards against the urging force of the torsion coil spring  36 , the torsion coil spring  36  is elastically deformed and the arm  36 A is displaced from a position denoted by the solid lines in  FIG. 3  to a position denoted by broken lines. The position of the stack lever  33  in that state will be referred to as a “third position” hereinafter. 
     Accordingly, the stack lever  33  is in a state urged by the torsion coil spring  35  within a range from the first position to the second position, and in a state urged by both the torsion coil spring  35  and the torsion coil spring  36  within a range from the second position to the third position. Further, an incline angle of the inclined surface  33 A of the stack lever  33  relative to a horizontal plane gradually reduces as the stack lever  33  is moved from the first position toward the third position. 
     In the multifunction peripheral  1  having the above-described construction, when the document is conveyed in the ADF unit  3 B, the stack lever  33  is in the state displaced to the first position, as illustrated in  FIG. 4A , in a stage where the number of documents having been already discharged to the document discharge section  18  is comparatively small. When the document is discharged by the discharge roller  14  and the nip roller  31  in that state, the leading end of the discharged document in the conveying direction makes contact with the stack lever  33 . 
     However, because the urging force of the torsion coil spring  35  is set comparatively weak, the stack lever  33  is pivoted and displaced upwards (e.g., to a position denoted by broken lines in  FIG. 4A ) upon the leading end of the document making contact with the stack lever  33 . Therefore, in contrast to the the case where the stack lever  33  is not raised upwards, the moving direction of the document is prevented from being abruptly bent downwards upon the document making contact with the stack lever  33 , and the leading end of the document is also prevented from making contact with the upper surface of the document discharge section  18  at a steep angle. Accordingly, the occurrence of, e.g., the corner folding at the leading end of the document can be more readily prevented than in the case where it is more difficult to move the stack lever  33  in an upward direction. 
     On the other hand, as the number of documents D having been discharged to the document discharge section  18  increases, a top of the already discharged documents D reaches a position where the top document contacts the lower end of the stack lever  33 . Thereafter, the stack lever  33  comes into the state holding down the discharged documents D. At that time, the stack lever  33  is still in the state lightly urged by the torsion coil spring  35 . As the number of the discharged documents D further increases, the stack lever  33  is caused to gradually pivot upwards and then reaches the second position as shown in  FIG. 4B . 
     At the time when the stack lever  33  reaches the second position, the stack lever  33  comes into the state contacting with the arm  36 A of the torsion coil spring  36 . As the number of the discharged documents D further increases, the stack lever  33  is caused to gradually swing upwards. During such a period, the stack lever  33  is in the state strongly urged by both the torsion coil springs  35  and  36 . 
     Thus, during the period in which the stack lever  33  is pivoted from the second position to the third position, as shown in  FIG. 4C , the stack lever  33  is in the state firmly holding down the discharged documents D from above. As such the discharged documents D may be prevented from curling up or being in a loose state at the trailing ends. As a result, a subsequently discharged document may be prevented from making contact with and colliding with the ends of the stacked discharged documents D. 
     Stated another way, in the multifunction peripheral  1 , the urging force exerted on the stack lever  33  can be changed step by step in the movable range of the stack lever  33  such that an appropriate urging force acts on the stack lever  33  depending on the number of discharged documents D stacked on the document discharge section  18 . 
     More specifically, in a stage where the number of the discharged documents D is small, the urging force exerted on the stack lever  33  is set relatively weak to avoid the corner folding at the leading end of the document. In a stage where the number of the discharged documents D reaches a threshold value, the urging force exerted on the stack lever  33  is set relatively strong to firmly hold down the discharged documents D stacked on the document discharge section  18 . 
     Unlike the case where the urging force exerted on the stack lever  33  is set relatively weak simply to avoid the corner folding at the leading end of the document, the first embodiment can eliminate the problem that a force acting to hold down the documents becomes insufficient when the number of the already discharged documents D on the document discharge section  18  increases. Also, unlike the case where the urging force exerted on the stack lever  33  is set relatively strong simply to firmly hold down the documents, the first embodiment can eliminate the problem that the stack lever  33  becomes harder to displace potentially causing the document to be folded. 
     Second Embodiment 
     A second embodiment will be described below. It is to be noted that, in the following explanation of the second embodiment, different points from the first embodiment are primarily described in detail and detailed explanation of common components to those in the first embodiment is omitted by assigning the common components with the same reference numerals as those in the first embodiment. 
     As shown in  FIG. 5 , the stack lever  33  in the second embodiment is urged by a single torsion coil spring  37 . The torsion coil spring  37  functions substantially in a similar manner to the torsion coil spring  36  in the first embodiment. 
     More specifically, when the stack lever  33  is in the range from the first position to the second position, the torsion coil spring  37  does not make contact with the stack lever  33 . When the stack lever  33  is in the range from the second position to the third position, the torsion coil spring  37  urges the stack lever  33  in a direction in which the stack lever  33  is caused to pivot downwards. 
     In the second embodiment, a member corresponding to the torsion coil spring  35  in the first embodiment is not provided, and the stack lever  33  is pivoted downwards by its own weight when the stack lever  33  is in the range from the first position to the second position. 
     Even with the construction described above, in the stage where the number of documents having been discharged to the document discharge section  18  is comparatively small, as illustrated in  FIG. 6A , the stack lever  33  is pivoted and displaced upwards (e.g., to a position denoted by broken lines in  FIG. 6A ) when the leading end of the document strikes against the stack lever  33 . 
     Unlike the case where the stack lever  33  is not raised upwards, therefore, the moving direction of the discharged document is prevented from being abruptly bent downwards upon the document making contact with the stack lever  33 , and the leading end of the document is also prevented from making contact with the upper surface of the document discharge section  18  at a steep angle. Accordingly, the occurrence of, e.g., the corner folding at the leading end of the document can be more readily be prevented than in the case where it is more difficult to move the stack lever  33  in an upward direction. 
     Further, as shown in  FIG. 6B , at the time when the stack lever  33  reaches the second position, the stack lever  33  comes into the state contacting with an arm  37 A of the torsion coil spring  37 . Thereafter, as the number of the discharged documents D increases, the stack lever  33  is caused to gradually pivot upwards, whereby the stack lever  33  comes into the state strongly urged by the torsion coil spring  37 . 
     Thus, during the period in which the stack lever  33  is pivoted from the second position to the third position, as illustrated in  FIG. 6C , the stack lever  33  is in the state firmly holding down the discharged documents D from above. As such, the discharged documents D may be prevented from curling up or being in a loose state at the trailing ends. 
     Stated another way, even when the single torsion coil spring  37  is employed as described above, the urging force exerted on the stack lever  33  can be changed step by step in the movable range of the stack lever  33  such that an appropriate urging force acts on the stack lever  33  depending on the number of discharged documents D stacked on the document discharge section  18 . 
     Modifications, etc. 
     While illustrative embodiments have been described above, the disclosure is not limited to the foregoing concrete embodiments and the present invention can be practiced in various forms other than the embodiments disclosed herein. 
     For example, while the illustrative embodiments have been described above in connection with the case where the document discharged to the document discharge section  18  in the ADF unit  3 B is held down by using the stack lever  33 , a recording medium discharged to recording medium discharge section  7  in the printer unit  2  may be held down with a similar structure to that of the stack lever  33 . 
     In that case, it is also possible to avoid the leading end of the discharged recording medium from being folded, and to avoid a subsequently discharged recording medium from colliding with previously discharged recording media. 
     Further, while the illustrative embodiments have been described above in connection with the multifunction peripheral  1  that includes both the function as the image reading apparatus (i.e., the scan function) and the function as the image forming apparatus (i.e., the print function), the disclosure can also be applied to, e.g., a single-function image scanner only functioning as an image reading apparatus and a single-function printer only functioning as an image forming apparatus. 
     In the illustrative embodiments described above, the supply roller  11 , the separation roller  12 , the main conveying roller  13 , and the discharge roller  14  correspond to one example of a conveyor though it will be appreciated that other configurations are possible and within the knowledge of one or ordinary skill in the art. The document discharge section  18  corresponds to one example of a stack member though it will be appreciated that other configurations are possible and within the knowledge of one or ordinary skill in the art. The stack lever  33  corresponds to one example of a sheet pressing member though it will be appreciated that other configurations are possible and within the knowledge of one or ordinary skill in the art. Further, each of the torsion coil springs  36  and  37  correspond to one example of an urging member and the torsion coil spring  35  corresponds to one example of a second urging member though it will be appreciated that other configurations are possible and within the knowledge of one or ordinary skill in the art. 
     While certain aspects of the disclosure have been shown and described with reference to certain illustrative embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.