Patent Publication Number: US-8118301-B2

Title: Sheet discharging device and image forming apparatus including same

Description:
PRIORITY STATEMENT 
     The present patent application claims priority from Japanese Patent Application Nos. 2009-175032, filed on Jul. 28, 2009, and 2010-018271, filed on Jan. 29, 2010, both in the Japan Patent Office, each of which is hereby incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     Illustrative embodiments described in this patent specification generally relate to a sheet discharging device and an image forming apparatus, and more particularly to a sheet discharging device including a sheet discharging unit that discharges sheets and a sheet discharge tray that stacks the sheets discharged by the sheet discharging unit, and an image forming apparatus including the sheet discharging device. 
     2. Description of the Related Art 
     Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet of paper, etc.) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus. 
     Increasing demand for smaller installation space has required greater compactness of image forming apparatuses.  FIG. 1  is a vertical cross-sectional view illustrating a configuration of an image forming apparatus  110  of the related art. The image forming apparatus  110  includes a sheet feed tray  101  storing recording media such as sheets of paper, a sheet feed roller  102  provided downstream from the sheet feed tray  101  in a direction of conveyance of the sheet, a pair of conveyance rollers  103  provided downstream from the sheet feed roller  102  in the direction of conveyance of the sheet, image forming units  104 Y,  104 M,  104 C, and  104 K (hereinafter collectively referred to as image forming units  104 ) each forming a toner image of a specific color, that is, yellow, magenta, cyan, or black, on the sheet, conveyance belt  105  provided below the image forming units  104 , an irradiating device  106  that irradiates photoconductors included in the image forming units  104 , a fixing device  107  that fixes the toner image onto the sheet using heat, a sheet discharge tray  108  onto which the sheet having the fixed image thereon is discharged from the image forming apparatus  110 , a pair of discharging rollers  109  that conveys the sheet having the fixed image thereon to the sheet discharge tray  108 , and so forth. A sheet stored on the sheet feed tray  101  is fed forward by the sheet feed roller  102  and is conveyed to the conveyance belt  105  through the pair of conveyance rollers  103 . While the sheet is being conveyed by the conveyance belt  105 , toner images formed on the photoconductors included in the image forming units  104  are sequentially transferred onto the sheet and superimposed one atop the other so that a full-color toner image is formed on the sheet. The sheet having the full-color toner image thereon is then conveyed to the fixing device  107  to fix the full-color toner image onto the sheet with heat and pressure. Thereafter, the sheet having a fixed full-color image thereon is discharged from the image forming apparatus  110  through a discharging opening by the pair of discharging rollers  109  and is stacked on the sheet discharge tray  108 . 
     The sheet discharge tray  108  is hinged along one edge and attached to the image forming apparatus  110 . Accordingly, the sheet discharge tray  108  is opened to an extended position as illustrated by broken lines in  FIG. 1  to stack the sheet discharged from the image forming apparatus  110 . By contrast, with the sheet discharge tray  108  in a closed position as illustrated by solid lines in  FIG. 1  the sheet discharge tray  108  is flush with the exterior of the image forming apparatus  110 . In those image forming apparatuses in which a conveyance path of a sheet is almost straight from a sheet feed tray to a sheet discharge tray such as the image forming apparatus  110 , the sheet discharge tray is usually provided on either front or back side surfaces of the image forming apparatuses. For example, the image forming apparatus  110  shown in  FIG. 1  has the sheet discharge tray  108  provided on a front surface thereof. Consequently, an installation space required for the image forming apparatus  110  is increased to the front by the length of the sheet discharge tray  108 . 
     In addition, the sheet discharge tray  108  must have a size sufficient for stacking the sheet, which in turn increases the space required for the sheet discharge tray  108 . In order to reduce the space for the sheet discharge tray  108 , an opening may be provided at a portion of the sheet discharge tray  108  facing a main body of the image forming apparatus  110 , and the sheet is discharged from the image forming apparatus  110  through the opening and into the sheet discharge tray  108  while the sheet discharge tray  108  is closed. Such a configuration allows a user to use the image forming apparatus  110  without having to open the sheet discharge tray, thereby reducing the installation space for the image forming apparatus  110 . 
     The above-described arrangement can work well in a case in which images are formed on only several sheets of paper, because the sheet discharge tray  108  does not need to be opened. The sheets discharged from the image forming apparatus  110  through the opening may be manually received by the user and directly stacked on a desk positioned next to the image forming apparatus  110 , or the like. 
     One example of a related-art image forming apparatus includes a sheet discharge tray having an opening or a cutout therein with a width greater than the maximum width of a sheet of paper used in the image forming apparatus. The sheet discharge tray is rotatably provided near a discharging opening of the image forming apparatus from where the sheet is discharged to stack the sheet thus discharged. The opening or the cutout is positioned outside a conveyance path of the sheet discharged from the discharging opening of the image forming apparatus when the sheet discharge tray is in a first position protruding from the image forming apparatus to stack the sheet discharged from the image forming apparatus. By contrast, the opening or the cutout is positioned corresponding to the discharging opening when the sheet discharge tray is in a second position folded toward the image forming apparatus. 
     However, a problem with the above-described arrangement is that the sheet stacked on the sheet discharge tray in the first position may drop through the opening or the cutout. Further, a leading edge of the sheet discharged from the image forming apparatus may get stuck or jammed in the opening. 
     In another approach, to reduce the space required for the apparatus the sheet discharge tray is fixedly mounted at an angle to a substantially straight conveyance path of the sheets. The sheet discharge tray has an opening that can be covered or closed by a plate. The opening lies on a virtual line representing an extension of the conveyance path of the sheets. The sheets are discharged through the opening. 
     However, because the above-described sheet discharge tray is not rotatable but is fixed at an angle to the image forming apparatus, this configuration is not applicable to a sheet discharge tray having a shutter that is openably closed in conjunction with rotation or opening and closing of the sheet discharge tray. 
     SUMMARY 
     In view of the foregoing, illustrative embodiments described herein provide a sheet discharging device including a sheet discharge tray having an opening and a shutter disposed over the opening that opens and closes the opening. The opening does not prevent discharge of sheets to the sheet discharge tray in an extended or opened position, so that the sheets thus discharged are reliably stacked on the sheet discharge tray. Illustrative embodiments described herein also provide an image forming apparatus including the sheet discharging device. 
     At least one embodiment provides a sheet discharging device including a sheet discharging unit provided at one end of an image forming apparatus; a sheet discharge tray located adjacent to the sheet discharging unit, and a driving mechanism. The sheet discharging unit includes a pair of discharging rollers to discharge sheets from the image forming apparatus. The sheet discharge tray is rotatably provided at the end of the image forming apparatus in a stored position to cover the end of the image forming apparatus and in an extended position extended from the end of the image forming apparatus to stack the sheets discharged from the image forming apparatus. The sheet discharge tray includes an opening through which the sheets are discharged from the image forming apparatus. The opening is provided at a portion of the sheet discharge tray opposite the pair of discharging rollers. The sheet discharge tray further includes a shutter disposed over the opening to open and close the opening. The driving mechanism drives the shutter in conjunction with rotary movement of the sheet discharge tray to open the opening in the sheet discharge tray in the stored position and to close the opening in the sheet discharge tray in the extended position. 
     At least one embodiment provides an image forming apparatus including the sheet discharging device as described above and an image forming unit to form images on sheets based on image data. 
     Additional features and advantages of the illustrative embodiments will be more fully apparent from the following detailed description, the accompanying drawings, and the associated claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the illustrative embodiments described herein and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a vertical cross-sectional view illustrating a configuration of a related-art image forming apparatus; 
         FIG. 2  is a vertical cross-sectional view illustrating a configuration of an image forming apparatus according to illustrative embodiments; 
         FIG. 3  is a perspective view illustrating a configuration of a sheet discharging device according to a first illustrative embodiment; 
         FIGS. 4A and 4B  are vertical cross-sectional views respectively illustrating opened/closed states of a sheet discharge tray according to the first illustrative embodiment; 
         FIG. 5  is an enlarged view illustrating a part of the sheet discharge tray illustrated in  FIG. 4A ; 
         FIGS. 6A and 6B  are enlarged views respectively illustrating unpreferred and preferred examples of the configuration of the sheet discharging device according to the first illustrative embodiment; 
         FIG. 7A  is a vertical cross-sectional view illustrating a configuration of a sheet discharging device according to a second illustrative embodiment; 
         FIG. 7B  is a vertical cross-sectional view illustrating a configuration of a sheet discharging device according to a third illustrative embodiment; 
         FIG. 8  is a vertical cross-sectional view illustrating an example of operation of a shutter; 
         FIG. 9  is a vertical cross-sectional view illustrating a configuration of a sheet discharging device according to a fourth illustrative embodiment; 
         FIG. 10  is a vertical cross-sectional view illustrating a configuration of a sheet discharging device according to a fifth illustrative embodiment; and 
         FIGS. 11A to 11C  are vertical cross-sectional views respectively illustrating operations of the sheet discharging device illustrated in  FIG. 10 . 
     
    
    
     The accompanying drawings are intended to depict illustrative embodiments and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In describing illustrative embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result. 
     A description is now given of illustrative embodiments of the present invention with reference to drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views. 
       FIG. 2  is a vertical cross-sectional view illustrating a configuration of an image forming apparatus  100  according to illustrative embodiments. The image forming apparatus  100  according to illustrative embodiments has the same configuration as the related-art image forming apparatus  110  described previously, except for a configuration of a sheet discharging device included therein. 
     Specifically, the image forming apparatus  100  includes a sheet feed tray  1  that stores recording media such as sheets of paper, a sheet feed roller  2  provided downstream from the sheet feed tray  1  in a direction of conveyance of the sheet, a pair of conveyance rollers  3  provided downstream from the sheet feed roller  2  in the direction of conveyance of the sheet, image forming units  4 Y,  4 M,  4 C, and  4 K (hereinafter collectively referred to as image forming units  4 ) each forming a toner image of a specific color, that is, yellow, magenta, cyan, or black, on the sheet, a conveyance belt  5  provided below the image forming units  4 , an irradiating device  6  that irradiates photoconductors included in the image forming units  4 , a fixing device  7  that fixes the toner image onto the sheet using heat, a sheet discharging device  50 , and so forth. The sheet stored on the sheet feed tray  1  is fed by the sheet feed roller  2 , and is conveyed to the conveyance belt  5  through the pair of conveyance rollers  3 . While the sheet is being conveyed by the conveyance belt  5 , the toner images formed on the photoconductors included in the image forming units  4  are sequentially transferred onto the sheet and superimposed one atop the other so that a full-color toner image is formed on the sheet. The sheet having the full-color toner image thereon is then conveyed to the fixing device  7  to fix the full-color toner image onto the sheet with heat and pressure. Thereafter, the sheet having a fixed full-color image thereon is discharged from the image forming apparatus  100  through a discharging opening by a pair of discharging rollers  9   a  and  9   b  (hereinafter collectively referred to as a pair of discharging rollers  9 ) included in the sheet discharging device  50 . 
     A description is now given of the sheet discharging device  50  according to a first illustrative embodiment.  FIG. 3  is a perspective view illustrating a configuration of the sheet discharging device  50  according to the first illustrative embodiment.  FIG. 4A  is a vertical cross-sectional view illustrating a sheet discharge tray  8  in an opened state, and  FIG. 4B  is a vertical cross-sectional view illustrating the sheet discharge tray  8  in a closed state.  FIG. 5  is an enlarged view illustrating a part of the sheet discharge tray  8  in the opened state, circled by a broken line in  FIG. 4A . 
     Cylindrical protrusions  13  functioning as hinges and respectively provided at both ends of the sheet discharge tray  8  in the long direction thereof engage holes  25  respectively provided in the body of the image forming apparatus  100 , so that the sheet discharge tray  8  is rotatably supported by the image forming apparatus  100  and movable between an open position at an angle to the image forming apparatus  100  and a closed position substantially flush with the surface of the image forming apparatus  100 . The pair of discharging rollers  9  serving as a sheet discharging unit that discharges a sheet P having a fixed full-color image thereon from the image forming apparatus  100  is provided at the discharging opening of the image forming apparatus  100 . The cylindrical protrusions  13  of the sheet discharge tray  8  are positioned below the pair of discharging rollers  9 . A sheet P discharged from the image forming apparatus  100  while the sheet discharge tray  8  is opened is stacked on the sheet discharge tray  8 . 
     The sheet discharge tray  8  includes an extendable auxiliary tray  10  therein. The auxiliary tray  10  is extended from the sheet discharge tray  8  to extend the sheet discharge tray  8  depending on a length of the sheet P. The sheet discharge tray  8  further includes an opening  14  at a lower portion therein, opposite the pair of discharging rollers  9 . The opening  14  is wider than the maximum width of the sheet P that can be conveyed by the image forming apparatus  100 , such that the sheet P discharged from the image forming apparatus  100  when the sheet discharge tray  8  is closed does not collide with the sheet discharge tray  8 . More specifically, the opening  14  is sized to accommodate the pair of discharging rollers  9  therewithin. Accordingly, when the sheet discharge tray  8  is closed, the pair of discharging rollers  9  is fitted into the opening  14 . As a result, a size of the image forming apparatus  100  in a direction of discharge of the sheet P when the sheet discharge tray  8  is closed can be reduced by the size of the pair of discharging rollers  9  compared to the related-art image forming apparatus  110  described previously. 
     The sheet discharge tray  8  is provided with a hinged shutter  11  over the opening  14 , and the shutter  11  is rotatably supported by protrusions  12  that engage holes  27  respectively provided in the sheet discharge tray  8  along opposite sides of the opening  14 . The shutter  11  moves with the sheet discharge tray  8 , that is, between an extended position (or the opened state) as illustrated in  FIG. 4A  and a stored position (or the closed state) as illustrated in  FIG. 4B . Accordingly, the shutter  11  is automatically opened and closed without requiring operation by a user. 
     The shutter  11  is constantly biased by a pair of torsion springs  24  respectively provided to the protrusions  12  toward a direction of closing the opening  14 . Accordingly, when the sheet discharge tray  8  is opened, the opening  14  is closed by the shutter  11  and is flush with the surface of the sheet discharge tray  8  as illustrated in  FIG. 4A , so that a sheet P discharged from the image forming apparatus  100  can be reliably stacked on the sheet discharge tray  8 . As illustrated in  FIG. 5 , the shutter  11  has a chamfered edge  23  opposite its hinged edge, such that the shutter  11 , biased by the torsion springs  24 , contacts a protruding lip or contact portion  19  along a lower upstream edge of the opening  14  to appropriately position the shutter  11 . 
     In addition, when the shutter  11  closes the opening  14  to form a flush surface with the sheet discharge tray  8 , an upper downstream edge  20  of the shutter  11  opposite the chamfered edge  23  in the direction of discharge of the sheet P rests above an upper downstream edge  14   a  of the opening  14  to which the sheet P is conveyed from the upper downstream edge  20 , forming a slight step thereat. This downward step enables a leading edge of the sheet P discharged from the image forming apparatus  100  to avoid getting stuck between the upper downstream edge  20  of the shutter  11  and the upper downstream edge  14   a  of the opening  14  in the sheet discharge tray  8 . 
     A description is now given of a driving mechanism that drives the shutter  11  in conjunction with opening and closing of the sheet discharge tray  8 . 
     As illustrated in  FIGS. 3 ,  4 A and  4 B, a pair of protrusions  15  each serving as the driving mechanism are provided near the pair of discharging rollers  9 . While the sheet discharge tray  8  is being moved to the closed position, the protrusions  15  contact a surface  26  of the shutter  11  to push the shutter  11  against the direction in which the shutter  11  is biased by the torsion springs  24  to open the shutter  11  and thus open the opening  14  as illustrated in  FIG. 4B . In the present embodiment, the protrusions  15  contact the shutter  11  at positions near the protrusions  12  of the shutter  11  to swing the shutter  11  out of the way of the opening  14 . The protrusions  15  and a cover  28  that is a component of the image forming apparatus  100  and which faces the sheet discharge tray  8  when the sheet discharge tray  8  is in the closed state may be formed together as a single integrated unit, thereby reducing a number of components. Alternatively, the protrusions  15  and a holding guide, not shown, for the pair of discharging rollers  9  may be formed together as a single integrated unit to accomplish the same end. 
     The two protrusions  15  are provided in a width direction of the image forming apparatus  100  so that the shutter  11  is reliably driven. In the first illustrative embodiment, the two protrusions  15  are provided at positions to contact right and left ends of the shutter  11 , thereby reliably driving the shutter  11 . 
     The shutter  11  has convexities  21  that contact the protrusions  15 .  FIGS. 6A and 6B  are enlarged view respectively illustrating unpreferred and preferred examples of the configuration of the sheet discharging device  50 . Specifically,  FIG. 6A  shows an unpreferred example of the configuration of the sheet discharging device  50 , and  FIG. 6B  shows the configuration of the sheet discharging device  50  according to the first illustrative embodiment. When the protrusions  12  of the shutter  11  are positioned at an upper downstream portion of the opening  14  as illustrated in  FIG. 6A , the protrusions  15  must protrude farther than the discharging roller  9   a  in order to prevent the shutter  11  from first contacting the discharging roller  9   a  when the sheet discharge tray  8  is closed. Otherwise, a surface of the discharging roller  9   a  that conveys the sheet P may be damaged by the shutter  11 . However, the protrusions  15  having a length too long may be also easily damaged by the shutter  11 . To solve such problems, the shutter  11  has the convexities  21  at positions contacting the protrusions  15  so that the protrusions  15  contact the convexities  21  to open the shutter  11  before the discharging roller  9   a  contacts the shutter  11  as illustrated in  FIG. 6B . In order to prevent the convexities  21  from being an obstacle to discharge of the sheet P, it is preferable that the convexities  21  and the protrusions  15  be provided outside the width of the sheet P and be prevented from contacting the sheet P. 
     Although the protrusions  12  of the shutter  11  are provided at the upper downstream portion of the opening  14  as described above in the first illustrative embodiment, the configuration of the sheet discharging device  50  is not limited thereto. For example, the protrusions  12  of the shutter  11  may be provided at a lower upstream portion of the opening  14  as illustrated in  FIG. 7A .  FIG. 7A  is a vertical cross-sectional view illustrating a configuration of the sheet discharging device  50  according to a second illustrative embodiment. Provision of the protrusions  12  at the lower upstream portion of the opening  14  can move the shutter  11  in conjunction with opening and closing of the sheet discharge tray  8  in the same manner as the first illustrative embodiment, the only difference being the edge along which the shutter  11  is hinged and about which it swings relative to the image forming apparatus  100 . 
     Specifically, in the configuration illustrated in  FIG. 7A , the protrusions  12  of the shutter  11  are provided at lower upstream portions of the sheet discharge tray  8  on the inner walls of the opening  14 , and the shutter  11  also serves as an auxiliary tray for supporting the sheet P discharged from the image forming apparatus  100 . 
     However the configuration according to the first illustrative embodiment illustrated in  FIGS. 4A and 4B  is preferable to that described above, because in the configuration according to the first illustrative embodiment, the pair of discharging rollers  9  is covered from the top thereof with the shutter  11 , whereas in the second embodiment the pair of discharging rollers  9  and number of components provided in a discharge opening of the image forming apparatus  100  are exposed from above. 
     Alternatively, although incurring more costs compared to the first and second illustrative embodiments, the shutter  11  may be hinged at both upper and lower edges and configured to include an upper flap  11   a  and a lower flap  11   b  as illustrated in  FIG. 7B .  FIG. 7B  is a vertical cross-sectional view illustrating a configuration of the sheet discharging device  50  according to a third illustrative embodiment. 
     In the configuration according to the third illustrative embodiment, protrusions  12   a  and  12   b  of the upper and lower flaps  11   a  and  11   b  are rotatably provided respectively at the upper and lower portions of the sheet discharge tray  8  along the inner walls of the opening  14 . Further, upper protrusions  15   a  and lower protrusions  15   b  are provided to drive the upper and lower flaps  11   a  and  11   b , respectively. Accordingly, both advantages provided by the first and second illustrative embodiments can be obtained in the third illustrative embodiment. 
     A description is now given of a rotatable range of the shutter  11 . 
       FIG. 8  is a vertical cross-sectional view illustrating operation of the shutter  11  of the sheet discharging device  50  according to the first illustrative embodiment. The shutter  11  is rotatable at least between a position A to close the opening  14  and a position B by being pushed away by the protrusions  15 . The shutter  11  is rotatable to a position beyond a virtual line representing an extension of the sheet P discharged from the image forming apparatus  100 , thereby being prevented from contacting the sheet P. 
     It is known that, in an image forming apparatus employing an electrophotographic method such as the image forming apparatus  100 , the sheet P tends to be curled by heat applied by the fixing device  7 . When the sheet P discharged from the image forming apparatus  100  is considerably curled toward the shutter  11 , the sheet P may contact the shutter  11  even when the shutter  11  is positioned at the position B, causing scratches at the leading edge of the sheet P or on an image on the sheet P. 
     To solve this problem, the shutter  11  is rotatable further above the position B, that is, to a position C in  FIG. 8 , upon contact with the sheet P. That is, the shutter  11  is pushed by the sheet P and is swung to the position C, thereby reducing damage to the leading edge of the sheet P. It is to be noted that contact of the curled portion of the sheet P with the shutter  11  flattens the curled portion of the sheet P. 
     A description is now given of a configuration of the sheet discharging device  50  that prevents damage to the sheet P. 
       FIG. 9  is a vertical cross-sectional view illustrating a configuration of the sheet discharging device  50  according to a fourth illustrative embodiment. In the fourth illustrative embodiment, a driven roller  16  is provided on the surface  26  of the shutter  11 . The driven roller  16  may be formed of an elastic material such as resin or rubber. It is preferable that the surface of the driven roller  16  be made of a soft material such as sponge or a material with a low surface frictional resistance in order to reduce damage to an image formed on the sheet P. 
     A description is now given of the sheet discharging device  50  according to a fifth illustrative embodiment.  FIG. 10  is a vertical cross-sectional view illustrating a configuration of the sheet discharging device  50  according to the fifth illustrative embodiment.  FIG. 11A  is a vertical cross-sectional view illustrating the sheet discharging device  50  illustrated in  FIG. 10  at the start of closing of the sheet discharge tray  8 .  FIG. 11B  is a vertical cross-sectional view illustrating the sheet discharging device  50  illustrated in  FIG. 10  in which the sheet discharge tray  8  is in the process of being closed.  FIG. 11C  is a vertical cross-sectional view illustrating the sheet discharging device  50  illustrated in  FIG. 10  after the sheet discharge tray  8  is closed. 
     In the sheet discharging device  50  according to the fifth illustrative embodiment, the shutter  11  slides in a direction parallel to the surface of the sheet discharge tray  8  in conjunction with opening and closing of the sheet discharge tray  8 . The sheet discharge tray  8  includes a guide member  29  serving as the driving mechanism to slide the shutter  11  in the direction parallel to the surface thereof, and a recessed portion  18  that accommodates the shutter  11  therewithin when the sheet discharge tray  8  is closed. 
     The shutter  11  is driven by an arm  22  provided between the shutter  11  and the main body of the image forming apparatus  100 . One end  22   a  of the arm  22  is supported by the shutter  11 , and another end  22   b  of the arm  22  is supported by a shaft of the discharging roller  9   a . Accordingly, when the sheet discharge tray  8  is opened to the extended position, the arm  22  slides the shutter  11  in the direction parallel to the surface of the sheet discharge tray  8  to close the opening  14 . An angle between the arm  22  and the shutter  11  is changed in conjunction with opening and closing of the sheet discharge tray  8 . Accordingly, the shutter  11  slides into the recessed portion  18  provided within the sheet discharge tray  8  while the sheet discharge tray  8  is being closed as illustrated in  FIGS. 11A and 11B . When the sheet discharge tray  8  is completely closed, slide movement of the shutter  11  is completed so that the opening  14  is opened as illustrated in  FIG. 11C . The opening  14  can be opened even when the auxiliary tray  10  is stored within the sheet discharge tray  8 . 
     As described above, the sheet discharging device  50  according to the foregoing illustrative embodiments includes the sheet discharge tray  8  having the opening  14  therein. Accordingly, the sheet P discharged from the image forming apparatus  100  can be reliably discharged from the opening  14  even when the sheet discharge tray  8  is closed. As a result, the image forming apparatus  100  requires less installation space. In addition, the shutter  11  provided in the sheet discharge tray  8  closes the opening  14  to form a flush interior surface of the sheet discharge tray  8  when the sheet discharge tray  8  is opened to the extended position, thereby preventing a paper jam at the opening  14 . The shutter  11  swings out of the way to uncover the opening  14  when the sheet discharge tray  8  is closed, thereby allowing the sheet P to be reliably discharged from the image forming apparatus  100  through the opening  14 . 
     The shutter  11  is rotatably provided at the opening  14 . In a case in which the protrusions  12  of the shutter  11  are provided at the upper portion of the opening  14 , the shutter  11  covers the opening  14  from the top thereof when the sheet discharge tray  8  is closed. This configuration prevents the user from touching an exit of the sheet P discharged from the image forming apparatus  100  where a number of components such as the pair of discharging rollers  9  are provided, achieving safety of the user. In addition, such a configuration hides the exit of the sheet P, enhancing design of the image forming apparatus  100 . 
     The shutter  11  is constantly biased by the torsion springs  24  toward the direction of closing the shutter  11 . Accordingly, the shutter  11  automatically closes the opening  14  when the sheet discharge tray  8  is opened, facilitating operation of the user. 
     The upper downstream edge  20  of the shutter  11  is higher than the upper downstream edge  14   a  of the opening  14  when the shutter  11  is closed. Accordingly, the sheet P discharged from the image forming apparatus  100  is prevented from getting stuck at a boundary between the shutter  11  and the opening  14 , thereby reliably discharging the sheet P onto the sheet discharge tray  8 . 
     The sheet discharging device  50  includes the protrusions  15  that contact the shutter  11  when the sheet discharge tray  8  is closed. Accordingly, the shutter  11  is pushed away and opened by the protrusions  15  to open the opening  14  when the sheet discharge tray  8  is closed. The shutter  11  is opened and closed in conjunction with opening and closing of the sheet discharge tray  8  as described above, thereby facilitating operation of the user. 
     The protrusions  15  may be formed together with components of the image forming apparatus  100  such as the holding guide for the pair of discharging rollers  9  as a single integrated unit, thereby reducing a number of components and costs. Further, provision of the multiple protrusions  15  can achieve smooth movement of the shutter  11 . 
     The shutter  11  includes the convexities  21  at the portions contacting the protrusions  15 . Accordingly, the shutter  11  contacts the protrusions  15  without contacting the pair of discharging rollers  9  when the sheet discharge tray  8  is closed, thereby preventing damage to the surfaces of the pair of discharging rollers  9 . 
     The shutter  11  has a wider rotation range so that the sheet P colliding with the shutter  11  moves the shutter  11  further downstream in the direction of conveyance of the sheet P, thereby reducing impact on the sheet P. 
     The shutter  11  is provided with the driven roller  16  rotated by conveyance of the sheet P colliding with the shutter  11 , thereby reducing impact on the sheet P. 
     The shutter  11  opens and closes the opening  14  of the sheet discharge tray  8  by sliding in the direction parallel to the surface of the sheet discharge tray  8 . Accordingly, the shutter  11  does not protrude from the sheet discharge tray  8 , thereby reducing the installation space compared with the configuration in which the shutter  11  is rotated to open and close the opening  14 . 
     The shutter  11  opens and closes the opening  14  of the sheet discharge tray  8  by sliding in the direction parallel to the surface of the sheet discharge tray  8  in conjunction with opening and closing of the sheet discharge tray  8 . As a result, operation of the user is facilitated, and the installation space for the image forming apparatus  100  is reduced. Further, the opening  14  can be closed by the shutter  11  without extending the auxiliary tray  10  from the sheet discharge tray  8  to reliably discharge the sheet P on the sheet discharge tray  8 . 
     The pair of discharging rollers  9  is fitted into the opening  14  of the sheet discharge tray  8  when the sheet discharge tray  8  is closed. Accordingly, the image forming apparatus  100  can be made more compact by an amount equivalent to a size of the pair of discharging rollers  9  compared to the configuration of the related art in which the sheet discharge tray is provided outside the pair of discharging rollers. 
     The sheet discharging device  50  according to the foregoing illustrative embodiments is applicable to image forming apparatuses such as copiers, printers, facsimile machines, inkjet recording devices, and multifunction devices having two or more of copying, printing, facsimile, and inkjet-recording functions. 
     It is to be noted that illustrative embodiments of the present invention are not limited to those described above, and various modifications and improvements are possible without departing from the scope of the present invention. It is therefore to be understood that, within the scope of the associated claims, illustrative embodiments may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the illustrative embodiments.