Patent Publication Number: US-7584950-B2

Title: Image forming apparatus and sheet feeding cassette

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2006-27293 filed Feb. 3, 2006. The entire content of this priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an image forming apparatus for printing an image on a sheet held in a sheet feeding tray. 
     BACKGROUND 
     In the conventional image forming apparatuses such as facsimile machines and printers, a sheet feeding tray for feeding a printing sheet and a sheet discharge tray for stocking a discharged sheet therein are separately provided. Japanese Unexamined Patent Application Publication No. 6-312551 discloses a recording device which feeds and discharges a sheet by the same conveyance roller. Japanese Unexamined Patent Application Publication No. 7-2345 discloses a document reader in which a sheet feeding tray is formed integrally with a sheet discharge tray. 
     SUMMARY 
     According to the recording device described in Japanese Unexamined Patent Application Publication No. 6-312551, the recording device is reduced in size by feeding and discharging the sheet using the same conveyance roller. Similarly, according to the document reader described in Japanese Unexamined Patent Application Publication No. 7-2345, the document reader is reduced in size by forming the sheet feeding tray and the sheet discharge tray in an integral fashion. However, with the configuration described in those publications, when a plurality of sheets to be fed are stacked, a discharged, printed sheet will possibly contact against the sheets to be fed and the printed sheet will possibly be wrongly fed to the print part again. As a result, paper jam can occur on a conveyance path or a desired image cannot be formed. 
     In view of the foregoing, it is an object of the invention to provide an image forming apparatus and a sheet feeding cassette which can smoothly discharge a sheet while using a tray that can serve as both of a sheet feeding tray and a sheet discharge tray. 
     In order to attain the above and other objects, the invention provides an image forming apparatus including: a print part; a feeding part; a first sheet feeding tray; and a second sheet feeding tray. The first sheet feeding tray is stores a sheet of a first size therein, the feeding part feeding the sheet of the first size from the first sheet feeding tray to the print part in a sheet feeding direction. The second sheet feeding tray is mounted on the first sheet feeding tray and stores a sheet of a second size smaller than the first size therein, the feeding part feeding the sheet of the second size from the second sheet feeding tray to the print part in the sheet feeding direction, the second sheet feeding tray receiving a sheet printed by the print part and discharged in a direction opposite to the sheet feeding direction. The second sheet feeding tray has a pair of side guides which are provided in parallel to the sheet feeding direction and which contact against side ends of the sheet of the second side to guide the sheet of the second side to the print part. At least one of the pair of side guides is provided with a plate part which extends from an upper edge of the side guide to the other side guide and which receives the printed sheet thereon. The plate part has a backward-feed prevention part which prevents the printed sheet from being fed to the print part again. 
     According to another aspect, the invention provides a sheet feeding cassette which can be attached to and detached from an image forming apparatus having a print part and a feeding part. The sheet feeding cassette includes: a first sheet feeding tray; and a second sheet feeding tray. The first sheet feeding tray stores a sheet of a first size therein, the feeding part feeding the sheet of the first size from the first sheet feeding tray to the print part in a sheet feeding direction. The second sheet feeding tray is mounted on the first sheet feeding tray and stores a sheet of a second size smaller than the first size therein, the feeding part feeding the sheet of the second size from the second sheet feeding tray to the print part in the sheet feeding direction, the second sheet feeding tray receiving a sheet printed by the print part and discharged in a direction opposite to the sheet feeding direction. The second sheet feeding tray has a pair of side guides which are provided in parallel to the sheet feeding direction and which contact against side ends of the sheet of the second side to guide the sheet of the second side to the print part. At least one of the pair of side guides is provided with a plate part which extends from an upper edge of the side guide to the other side guide and which receives the printed sheet thereon. The plate part has a backward-feed prevention part which prevents the printed sheet from being fed to the print part again. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing an outer appearance of an image forming apparatus according to an embodiment of the invention; 
         FIG. 2  is a perspective view of a sheet feeding cassette in the state where a second sheet feeding tray is closed; 
         FIG. 3  is a perspective view of the sheet feeding cassette in the state where the second sheet feeding tray is opened; 
         FIG. 4  is a perspective view showing the positional relationship between a print unit and the sheet feeding cassette when the sheet feeding cassette is mounted in the image forming apparatus and the second sheet feeding tray is slid rearward on the first sheet feeding tray; 
         FIG. 5  is a side sectional view showing the positional relationship between the print unit and the sheet feeding cassette when the sheet feeding cassette is mounted in the image forming apparatus and the second sheet feeding tray is slid rearward on the first sheet feeding tray; 
         FIG. 6  is a perspective view showing the positional relationship between the print unit and the sheet feeding cassette when the sheet feeding cassette is mounted in the image forming apparatus and the second sheet feeding tray is slid frontward on the first sheet feeding tray; and 
         FIG. 7  is a side sectional view showing the positional relationship between the print unit and the sheet feeding cassette when the sheet feeding cassette is mounted in the image forming apparatus and the second sheet feeding tray is slid frontward on the first sheet feeding tray. 
     
    
    
     DETAILED DESCRIPTION 
     An image forming apparatus and a sheet feeding cassette according to an embodiment of the invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     First, with reference to  FIG. 1 , overall configuration of an image forming apparatus  1  in accordance with the embodiment will be described. 
       FIG. 1  is a perspective view showing an external appearance of the image forming apparatus  1 . In the following descriptions, the vertical direction is represented with reference to the normal use state of the image forming apparatus  1  (the state shown in  FIG. 1 ), the front-back direction is represented using the side on which an operation panel  10  described later as a near side (front) and the widthwise direction is represented when viewing the image forming apparatus  1  from the near side (front). 
     The image forming apparatus  1  is a so-called multifunction apparatus having scanning, color-copying and facsimile functions in addition to a printing function. The exterior of the image forming apparatus  1  is defined by a main body casing  2  that is made from a resin rectangular box-shaped member. 
     The operation panel  10  is provided on the front portion of an upper surface of the main body casing  2 . The operation panel  10  has an operation part  11 , on which various operation buttons for an input operation are formed, and a display part (for example, a liquid crystal display)  12 , on which an image such as a message is displayed. A scanner unit  20  for reading an image from a document is provided in the rear of the operation panel  10 . The scanner unit  20  is used to perform the scanning, color-copying and facsimile functions. 
     On the other hand, a sheet feeding cassette  3  is provided in a lower portion of the main body casing  2 . The sheet feeding cassette  3  can store therein a stack of a plurality of sheet-shaped recording media, such as papers and plastic sheets, so that each sheet-shaped recording medium extends substantially horizontally. Configuration of the sheet feeding cassette  3  will be described later in detail. 
     A U-shaped conveyance guide  90  is formed as shown in  FIG. 5  and V at the rear end of the main body casing  2  to guide the recording medium that has been conveyed rearward from the sheet feeding cassette  3  by a feeding unit  50  (to be described later) so that the recording medium will turn around upward and then move frontward as indicated by an arrow in the figures. As also shown in  FIGS. 5 and 7 , an image recording unit  80  is provided in the main casing  2  at a location in front of the U-shaped conveyance guide  90  and above the sheet feeding cassette  3  when the sheet feeding cassette  3  is attached to the main body casing  2 . The image recording unit  80  serves as a print part for forming (printing) an image on the recording medium. The recording medium on which the image is recorded is discharged in the forward direction toward a position near the front on the upper surface of the sheet feeding cassette  3  as also indicated by an arrow in the figures. 
     More specifically, as shown in  FIGS. 4 ,  5  and  7 , the print unit  80  has a PF (paper feed) roller  82  and a plurality of discharge rollers  84 . The discharge rollers  84  are provided in front of the PF roller  82 . In the print unit  80 , a sheet conveying path is defined to extend in the rear-to-front direction below the PF roller  82  and above the discharge rollers  84  as indicated by an arrow in  FIGS. 5  and  7 . As shown in  FIGS. 5 and 7 , a print head  86  is provided as being movable along a moving path that is located between the PF roller  82  and the discharge rollers  84  and that extends in the widthwise direction. The sheet is conveyed by the PF roller  82  in the forward direction, while being printed by the print head  86  that is moving above the sheet, and then is discharged by the discharge rollers  84  onto the sheet feeding cassette  3 . 
     Next, configuration of the sheet feeding cassette  3  will be described with reference to  FIG. 2  and  FIG. 3 . 
       FIG. 2  is a perspective view showing the sheet feeding cassette  3  in the state where a second sheet feeding tray  40  to be described later is closed.  FIG. 3  is a perspective view showing the sheet feeding cassette  3  in the state where the second sheet feeding tray  40  is opened. 
     The sheet feeding cassette  3  is configured from a first sheet feeding tray  30  and the second sheet feeding tray  40 . The first sheet feeding tray  30  is for storing a stack of standard sized sheets therein and for feeding the standard sized sheets to the print part  80  in a sheet feeding direction (rearward direction). The second sheet feeding tray  40  is mounted on the first sheet feeding tray  30 , and is for storing therein a stack of smaller-sized sheets whose size is smaller than the standard sized sheets, for feeding the smaller-sized sheets to the print part  80  in the sheet feeding direction (rearward direction), and further for serving as a sheet discharge tray for receiving a printed sheet that is discharged from the print part  80  in the direction opposite to the sheet feeding direction, that is, in the forward direction. As shown in  FIG. 1 , the sheet feeding cassette  3  is configured so as to be detachable from the main body casing  2 . That is, the sheet feeding cassette  3  can be horizontally pulled out forward from an opening  2   a  that is formed on the front surface of the main body casing  2 , and can be attached to the main body casing  2  by being horizontally inserted through the opening  2   a  into the main body casing  2 . 
     As shown in  FIGS. 2 ,  5 , and  7 , a feeding unit  50  is provided in the main casing  2  at a location below the print unit  80  and above the sheet feeding cassette  3  when the sheet feeding cassette  3  is mounted in the main body casing  2 . The feeding unit  50  has a support shaft  51  which is supported by a frame (not shown) provided in the main body casing  2  and which extends in the range from the center to the right end of the sheet feeding cassette  3  in the widthwise direction when the sheet feeding cassette  3  is mounted in the main body casing  2 . A large gear  53  is fixed at a right end of the support shaft  51  and a small gear (not shown) having the same diameter as the support shaft  51  is fixed in the vicinity of a left end of the support shaft  51 . The feeding unit  50  has an arm member  52  which is supported by the support shaft  51  and which is configured to be swingable around the support shaft  51  in the state where its tip end is lowered rearward. A feeding roller  60  is rotatably supported at the tip end (swinging end) of the arm member  52 . The rotational axis of the feeding roller  60  extends in the widthwise direction. The arm member  52  is swingable around its swinging axis. The swinging axis of the arm member  52  extends parallel to the rotational axis of the feeding roller  60 . The swinging axis of the arm member  52  is located above the sheets stored in the sheet feeding cassette  3 , and on the front side of the rotational axis of the feeding roller  60 , that is, on the upstream side of the rotational axis of the feeding roller  60  in the feeding direction of the recording medium by the feeding roller  60 . 
     As shown in  FIG. 2 , the first sheet feeding tray  30  is a resin-made rectangular tray-shaped member having a substantially A4 size when viewed from above. The first sheet feeding tray  30  has a bottom plate  33 , and can store a plurality of recording mediums in a stacked state on the bottom plate  33 . The first sheet feeding tray  30  can store standard-sized sheets (A4 size sheets, for example) on the bottom plate  33 . The first sheet feeding tray  30  further has a pair of side end guides (not shown), thereby positioning the center line of the recording mediums in the widthwise direction irrespective the size of the stored recording mediums. Thus, the recording mediums stored in the first sheet feeding tray  30  and positioned by the side end guides are prevented from moving or inclining in the widthwise direction (direction of the rotational axis of the feeding roller  60 ), while being fed by the feeding roller  60  in the feeding direction (rearward direction). 
     The first sheet feeding tray  30  has a guide plate  34  at its rear end. A metal separating member  34   a  is provided at the center of the guide plate  34  in the widthwise direction. The separating member  34   a  has a plurality of teeth which are arranged at regular intervals in the vertical direction and a front end of each tooth slightly protrudes from the front surface of the guide plate  34 . Thus, the plurality of recording mediums pushed by the feeding roller  60  of the feeding unit  50  contact against the front ends of the teeth, so that an uppermost recording medium is separated from remaining mediums and is supplied to the U-shaped conveyance guide  90  ( FIGS. 5 and 7 ). 
     The second sheet feeding tray  40  is attached to the first sheet feeding tray  30  so as to be slidable relative to the first sheet feeding tray  30  in the front-back direction. The second sheet feeding tray  40  can store thick and small-sized recording mediums, such as sheets for picture and postcards, in its central part in the widthwise direction. That is, the second sheet feeding tray  40  can store recording mediums with sizes smaller than the standard size of the sheets stored in the first sheet feeding tray  30 . As shown in  FIG. 3 , the second sheet feeding tray  40  can rotate around a shaft  47  so as to be opened upward. By opening the second sheet feeding tray  40 , sheets can be mounted on the first sheet feeding tray  30  and below the second sheet feeding tray  40 . 
     The second sheet feeding tray  40  is a resin-made rectangular tray-shaped member. The second sheet feeding tray  40  is almost the same as the first sheet feeding tray  30  in size in the widthwise direction and slightly smaller than the first sheet feeding tray  30  in size in the front-back direction. The second sheet feeding tray  40  is configured to store therein a stack of a plurality of recording mediums with each recording medium extending in the horizontal direction. 
     More specifically, although not shown in the drawings, a groove is formed on each of left and right side walls of the first sheet feeding tray  30  to extend in the front-to-rear direction. The left and right side ends of the shaft  47  are slidably engaged with the grooves on the left and right side walls of the first sheet feeding tray  30 . With this configuration, the second sheet feeding tray  40  can move in the front-to-rear direction relative to the first sheet feeding tray  30  by sliding the shaft  47  along the grooves.  FIG. 5  shows the case where the second sheet feeding tray  40  is positioned on the rear side of the first sheet feeding tray  30 , while  FIG. 7  shows the case where the second sheet feeding tray  40  is positioned on the front side of the first sheet feeding tray  30 . It is noted that the grooves are formed on the left and right side walls of the first sheet feeding tray  30  so as to be inclined downwardly toward the rear when the first sheet feeding tray  30  is oriented to extend horizontally. When the sheet feeding cassette  3  is mounted in the image forming apparatus  1 , the first sheet feeding tray  30  is oriented to extend horizontally in the image forming apparatus  1 . So, in the case where the sheet feeding cassette  3  is mounted in the image forming apparatus  1 , when the second sheet feeding tray  40  moves from the rear side ( FIG. 5 ) toward the front side ( FIG. 7 ) on the first sheet feeding tray  30 , the second sheet feeding tray  40  moves gradually upwardly in the image forming apparatus  1 . 
     As shown in  FIG. 2 , as in the first sheet feeding tray  30 , the second sheet feeding tray  40  has a pair of side end guides  41  and  42 . The side end guides  41  and  42  rise from the upper surface of the second sheet feeding tray  40 . The side end guides  41  and  42  are for positioning the center line of the recording mediums in the widthwise direction irrespective the size of the stored recording mediums. The sheets stored in the second sheet feeding tray  40  are smaller than the standard-sized sheets stored in the first sheet feeding tray  30 . The side end guides  41  and  42  extend in parallel to the sheet feeding direction (rearward direction), in which the feeding unit  50  feeds the sheet from the second sheet feeding tray  40 , and come into contact with side ends of the stored sheets to guide the sheets to the U-shaped conveyance guide  90 . 
     In the state where the second sheet feeding tray  40  is placed in the rear side on the first sheet feeding tray  30  (position shown in  FIGS. 2 ,  4 , and  5 ), the recording mediums stored in the second sheet feeding tray  40  prevent the feeding roller  60  from moving downward toward the first sheet feeding tray  30 . For this reason, the feeding roller  60  of the feeding unit  50  comes into contact with the recording mediums stored in the second sheet feeding tray  40 , not the recording mediums stored in the first sheet feeding tray  30 , thereby feeding the recording medium stored in the second sheet feeding tray  40  to the U-shaped conveyance guide  90 . 
     In the state where the second sheet feeding tray  40  is placed in the front side on the first sheet feeding tray  30  (position shown in  FIGS. 6 and 7 ), the feeding roller  60  moves downward toward the first sheet feeding tray  30 . For this reason, the feeding roller  60  of the feeding unit  50  comes into contact with the recording mediums stored in the first sheet feeding tray  30 , thereby feeding the recording medium stored in the first sheet feeding tray  30  to the U-shaped conveyance guide  90 . 
     As shown in  FIGS. 2 ,  6 , and  7 , a plate part  43  for receiving the printed sheet discharged from the print part  80  is formed at the side end guide  41 . The plate part  43  is a flat plate-shaped member which extends from an upper edge of the side end guide  41  in a direction perpendicularly to the plate-shaped side end guide  41  toward the side end guide  42 . That is, the plate part  43  extends horizontally parallel to the upper surface of the second sheet feeding tray  40 . The plate part  43  together with the upper surface of the second sheet feeding tray  40  function as the sheet discharge tray. That is, the plate part  43  can separately mount the pre-printed sheet stored therebelow and the printed sheet discharged thereon. In other words, the sheet printed by the print head  86  is discharged by the discharge rollers  84  onto the plate part  43 , while pre-printed sheets are mounted below the plate part  43 . 
     In this example, the plate part  43  is provided only on the side end guide  41 . However, the plate part  43  may be formed also on the side end guide  42 . Or, the plate part  43  is provided on each of the side end guide  41  and the side end guide  42 . 
     As shown in  FIGS. 2 ,  6 , and  7 , the portion on the upper surface at the rear end of the plate part  43  serves as a backward-feed prevention surface  43   a . The backward-feed prevention surface  43   a  extends horizontally and parallel to the upper surface of the second sheet feeding tray  40 . It is noted that when the second sheet feeding tray  40  is slid frontward (the state shown in  FIGS. 6 and 7 ), the rear end of the backward-feed prevention surface  43   a  of the plate part  43  is located in front of and in the vicinity of the lower front edge  81  of the print part  80 . The backward-feed prevention surface  43   a  is in such a vertical height slightly higher than the vertical height of the lower front edge  81  of the print part  80  in the state where the second sheet feeding tray  40  is slid frontward (the state shown in  FIGS. 6 and 7 ), thereby making minimum a gap between the second sheet feeding tray  40  and the lower front edge  81  of the print part  80 . Thus, the backward-feed prevention surface  43   a  serves as a backward-feed prevention part for preventing the printed sheet from being fed by the feeding unit  50  back to the print part  80  again. 
     As shown in  FIGS. 2 ,  6 , and  7 , a front side extension  44  is formed at the front side of the plate part  43 . That is, the front side extension  44  is a plate shape that extends forwardly from the front edge of the plate part  43 . The front side extension  44  includes a main part  44   a  and an inclined part  44   b  which are arranged in the front-to-rear direction. The inclined part  44   b  is connected to the plate part  43 . The main part  44   a  is located in front of the inclined part  44   b . Thus, the main part  44   a  is connected to the front edge of the plate part  43  via the inclined part  44   b . The upper surface of the main part  44   a  extends horizontally and parallel to the upper surface of the second sheet feeding tray  40 . The upper surface of the main part  44   a  is in such a vertical height higher than the upper surface of the plate part  43 . The inclined part  44   b  smoothly connects the main part  44   a  to the plate part  43 . 
     As shown in  FIG. 7 , the plate part  43  and the front side extension  44  cooperate to substantially cover the sheets stored in the second sheet feeding tray  40  in the front-back direction. That is, when the sheet feeding cassette  3  is pulled out the image forming apparatus  1 , pre-printed sheets are stored in the second sheet feeding tray  40  so that the sheets are located below the plate part  43  and the front side extension  44 . Then, the sheet feeding cassette  3  is mounted in the image forming apparatus  1 . In the state where the second sheet feeding tray  40  is slid rearward, the rear end of the plate part  43  reaches the vicinity of the feeding roller  60 . 
     It is noted that when the second sheet feeding tray  40  is slid rearward (the state shown in  FIGS. 2 ,  4 , and  5 ), the main part  44   a  of the front side extension  44  is located in front of and in the vicinity of the lower front edge  81  of the print part  80 . The upper surface of the main part  44   a  of the front side extension  44  is in such a vertical height slightly higher than the vertical height of the lower front edge  81  of the print part  80  in the state where the second sheet feeding tray  40  is slid rearward (the state shown in  FIGS. 2 ,  4 , and  5 ), thereby making minimum the gap between the second sheet feeding tray  40  and the lower front edge  81  of the print part  80 . So, the main part  44   a  of the front side extension  44  serves as another backward-feed prevention part for preventing the printed sheet from being fed by the feeding unit  50  back to the print part  80 . 
     It is noted that in the state where the second sheet feeding tray  40  is slid rearward (the state shown in  FIGS. 2 ,  4 , and  5 ), the backward-feed prevention surface  43   a  is located below the print part  80  because the second sheet feeding tray  40  moves gradually downwardly as the second sheet feeding tray  40  moves to the rear. 
     As shown in  FIG. 2 , on the front side of the side end guide  42 , a right-side extension  45  is formed to extend outwardly (rightwardly) from the upper edge of the front end of the side end guide  42 . The upper surface of the right-side extension  45  extends horizontally and parallel to the upper surface of the second sheet feeding tray  40 . The upper surface of the right-side extension  45  is in such a vertical height substantially the same as the upper surface of the main part  44   a  of the front side extension  44 . It is noted that when the second sheet feeding tray  40  is slid rearward (the state shown in  FIGS. 2 ,  4 , and  5 ), the right-side extension  45  is located in front of and in the vicinity of the lower front edge  81  of the print part  80 . The upper surface of the right-side extension  45  is in such a vertical height slightly higher than the vertical height of the lower front edge  81  of the print part  80  when the second sheet feeding tray  40  is slid rearward (the state shown in  FIGS. 2 ,  4 , and  5 ), thereby making minimum the gap between the second sheet feeding tray  40  and the lower front edge  81  of the print part  80 . So, the upper surface of the right-side extension  45  serves as another backward-feed prevention part for preventing the printed sheet from being fed back to the print part  80 . 
     A backward-feed prevention protrusion  70  is formed on the upper surface of the second sheet feeding tray  40  at a location on the outer side (left side) of the backward-feed prevention surface  43   a  of the plate part  43 . The backward-feed prevention protrusion  70  is for preventing the printed sheet from being fed to the print part  80  again. The backward-feed prevention protrusion  70  serves to mainly prevent rearward feeding of the relatively large standard sheet that has been fed from the first sheet feeding tray  30 . The backward-feed prevention protrusion  70  is of a substantially triangular shape when viewed from the side, and has a top  70   a  and a pair of gently-inclined surfaces  70   b  and  70   c . The pair of gently-inclined surfaces  70   b  and  70   c  extend downwardly from the top  70   a  to the front and to the rear, respectively. It is noted that when the second sheet feeding tray  40  is slid frontward (the state shown in  FIG. 6 ), the backward-feed prevention protrusion  70  is located in front of and in the vicinity of the lower front edge  81  of the print part  80 . The top  70   a  is configured to have a height substantially the same as the backward-feed prevention surface  43   a , thereby making minimum the gap between the second sheet feeding tray  40  and the lower front edge  81  of the print part  80  in the state where the second sheet feeding tray  40  is slid frontward (the state shown in  FIG. 6 ). 
     Next will be described, with referring to  FIG. 4  to  FIG. 7 , functions of the backward-feed prevention surface  43   a , the main part  44   a  of the front side extension  44 , the right-side extension  45 , and the backward-feed prevention protrusion  70  of the second sheet feeding tray  40 .  FIGS. 4 and 5  show the state where the second sheet feeding tray  40  is slid rearward.  FIGS. 6 and 7  show the state where the second sheet feeding tray  40  is slid frontward. 
     As shown in  FIG. 4  and  FIG. 5 , in the state where the second sheet feeding tray  40  is slid rearward, the main part  44   a  of the front side extension  44  and the right-side extension  45  are located in front of and in the vicinity of the lower front edge  81  of the print part  80 . The main part  44   a  of the front side extension  44  and the right-side extension  45  make minimum the gap between the second sheet feeding tray  40  and the lower front edge  81  of the print part  80 . Thus, when the small-sized sheet stored in the second sheet feeding tray  40  is fed by the feeding unit  50  to the print part  80  along the U-shaped conveyance guide  90  and then, discharged in the direction opposite to the sheet feeding direction and mounted on the plate part  43 , even if the user tries to take out the printed sheet and pushes the sheet toward the back side with mistake, since there is only a slight gap between the main part  44   a  of the front side extension  44  and the right side extension  45  and the print part  80 , the printed sheet is not fed to the print part  80  again. Therefore, there is no possibility that paper jam occurs on the conveyance path, and a desired image can be formed smoothly. 
     As shown in  FIG. 6  and  FIG. 7 , in the state where the second sheet feeding tray  40  is slid frontward, the backward-feed prevention surface  43   a  and the backward-feed prevention protrusion  70  are in front of and in the vicinity of the lower front edge  81  of the print part  80 . The backward-feed prevention surface  43   a  and the backward-feed prevention protrusion  70  make minimum the gap between the second sheet feeding tray  40  and the lower front edge  81  of the print part  80 . Thus, when the standard sheet stored in the first sheet feeding tray  30  is fed by the feeding unit  50  to the print part  80  and then, discharged in the direction opposite to the sheet feeding direction and mounted on the plate part  43 , even if the user tries to take out the printed sheet and pushes the sheet toward the back side with mistake, since there is only a slight gap between the backward-feed prevention surface  43   a  and the backward-feed prevention protrusion  70  and the print part  80 , the printed sheet is not fed to the print part  80  again. Therefore, there is no possibility that paper jam occurs on the conveyance path, and a desired image can be formed smoothly. 
     While the invention has been described in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.