Abstract:
Provided is a sheet stacking tray such that damage due to external force can be suppressed. The sheet stacking tray ( 30 ) is provided with a tray body ( 40 ), a first slide member ( 50 ), and a second slide member ( 60 ). When the first slide member and the second slide member are pulled out, the engagement between a first storage catch portion ( 44 ) of the tray body and a first latch portion ( 52 ) of the first slide member is released, and then the engagement between a second storage catch portion ( 54 ) of the first slide member and a second latch portion ( 62 ) of the second slide member is released.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a sheet placement tray (sheet stacking tray) configured as a pullout type such that its sheet placement surface on which sheets are placed is extendable, and to an image forming apparatus provided with such a sheet placement tray. 
       BACKGROUND ART 
       [0002]    Generally, in image forming apparatuses such as copiers, printers, and facsimile machines, there are widely used sheet feed trays and discharge trays on which sheet-form recording media are placed. It is preferable that sheet feed trays and discharge trays be small when not in use but be large enough to fit the size of sheets when in use. Thus, trays are known that are configured as a pullout type such that their sheet placement surface can be extended. 
         [0003]    For example, in Patent Document 1, there is disclosed a medium supporting tray that includes a base portion, a first pullout portion which is slidable with respect to the base portion, and a second pullout portion which is slidable with respect to the first pullout portion. In the medium supporting tray, a flat spring that is engaged with the first pullout portion is arranged in the base portion, and a flat spring that is engaged with the second pullout portion is arranged in the first pullout portion. Setting the spring force of the flat spring arranged in the base portion weaker than the spring force of the flat spring arranged in the first pullout portion allows the first pullout portion to be pulled out first when the first and second pullout portions are pulled out from a state where they are stored, and thus the second pullout portion, which is the weakest in strength due to its dimensions, can be prevented from being pulled out alone. 
       LIST OF CITATIONS 
     Patent Literature 
       [0004]    Patent Document 1: JP-A-2013-18581 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0005]    However, according to the above-described medium supporting tray of Patent Document 1, when the first and second pullout portions are stored from a state where they are pulled out, the first pullout portion is stored in the base portion before the second pullout portion is stored in the first pullout portion. Thus, the second pullout portion, which is the weakest in strength due to its dimensions, occasionally remains pulled out alone; this inconveniently makes the medium supporting tray likely to be damaged by an external force. 
         [0006]    Devised against the background discussed above, an object of the present invention is to provide a sheet placement tray that can be prevented from being damaged by an external force, and to provide an image forming apparatus provided with such a sheet placement tray. 
       Means for Solving the Problem 
       [0007]    According to one aspect of the present invention, a sheet placement tray (sheet stacking tray) includes a tray main body which has a sheet placement surface on which sheets are placed, a first slide member which is slidable with respect to the tray main body and which is arranged selectively either in a first stored position where it is stored in the tray main body or in a first pulled-out position where it is pulled out of the tray main body so as to extend the sheet placement surface, and a second slide member which is slidable with respect to the first slide member and which is arranged selectively either in a second stored position where it is stored in the first slide member or in a second pulled-out position where it is pulled out of the first slide member so as to extend the sheet placement surface. The tray main body includes a first storage engaged portion which is engaged with a first engaging portion of the first slide member in a state where the first slide member is stored in the first stored position, and a first pullout engaged portion which is engaged with the first engaging portion in a state where the first slide member is pulled out in the first pulled-out position. The first slide member includes the first engaging portion, a second storage engaged portion which is engaged with a second engaging portion of the second slide member in a state where the second slide member is stored in the second stored position, and a second pullout engaged portion which is engaged with the second engaging portion in a state where the second slide member is pulled out in the second pulled-out position. The second slide member includes the second engaging portion. When the first and second slide members are pulled out from a state where they are stored respectively in the first and second stored positions, the engagement of the first storage engaged portion with the first engaging portion is released, and thereafter the engagement of the second storage engaged portion with the second engaging portion is released. When the first and second slide members are stored from a state where they are pulled out respectively in the first and second pulled-out positions, the engagement of the second pullout engaged portion with the second engaging portion is released, and thereafter the engagement of the first pullout engaged portion with the first engaging portion is released. 
       Advantageous Effects of the Invention 
       [0008]    According to the sheet placement tray of the present invention, when the first and second slide members are pulled out from a state where they are stored respectively in the first and second stored positions, the engagement of the first storage engaged portion of the tray main body with the first engaging portion of the first slide member is released, and thereafter the engagement of the second storage engaged portion of the first slide member with the second engaging portion of the second slide member is released. In this way, when the first and second slide members are pulled out, the first slide member is pulled out first, and thus the second slide member, which is weak in strength due to its dimensions, can be prevented from being pulled out alone. 
         [0009]    When the first and second slide members are stored from a state where they are pulled out respectively in the first and second pulled-out positions, the engagement of the second pullout engaged portion of the first slide member with the second engaging portion of the second slide member is released, and thereafter the engagement of the first pullout engaged portion of the tray main body with the first engaging portion of the first slide member is released. In this way, when the first and second slide members are stored, the second slide member is stored first, and thus the second slide member, which is weak in strength due to its dimensions, can be prevented from being pulled out alone. 
         [0010]    Thus, both when the first and second slide members are pulled out and when they are stored, the second slide member, which is weak in strength due to its dimensions, can be prevented from being pulled out alone, and thereby the sheet placement tray can be prevented from being damaged by an external force. 
         [0011]    Further features and advantages of the present invention will become apparent from the description of embodiments given below. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    [ FIG. 1 ] is a sectional view showing a structure of an image forming apparatus provided with a second discharge tray (sheet placement tray) according to a first embodiment of the present invention; 
           [0013]    [ FIG. 2 ] is a perspective view showing a structure of a second discharge tray according to the first embodiment of the present invention; 
           [0014]    [ FIG. 3 ] is a bottom view showing a structure of a tray main body of the second discharge tray shown in  FIG. 2 ; 
           [0015]    [ FIG. 4 ] is a sectional view across line A-A′ in  FIG. 3 ; 
           [0016]    [ FIG. 5 ] is a bottom view showing a structure of a first slide member of the second discharge tray shown in  FIG. 2 ; 
           [0017]    [ FIG. 6 ] is a sectional view across line B-B′ in  FIG. 5 ; 
           [0018]    [ FIG. 7 ] is a bottom view showing a structure of a second slide member of the second discharge tray shown in  FIG. 2 ; 
           [0019]    [ FIG. 8 ] is a sectional view across line C-C′ in  FIG. 7 ; 
           [0020]    [ FIG. 9 ] is a bottom view showing a state where first and second slide members of the second discharge tray shown in  FIG. 2  are stored; 
           [0021]    [ FIG. 10 ] is a bottom view showing a state where a first slide member of the second discharge tray shown in  FIG. 2  is pulled out while a second slide member remains stored in the first slide member; 
           [0022]    [ FIG. 11 ] is a bottom view showing a state where first and second slide members of the second discharge tray shown in  FIG. 2  are pulled out; 
           [0023]    [ FIG. 12 ] is a diagram showing how an engaging portion has different degrees of ease in sliding over each engaged portion when a slide member of the second discharge tray shown in  FIG. 2  is pulled out; 
           [0024]    [ FIG. 13 ] is a diagram showing how an engaging portion has different degrees of ease in sliding over each engaged portion when a slide member of the second discharge tray shown in  FIG. 2  is stored; 
           [0025]    [ FIG. 14 ] is a bottom view showing a structure of and around first and second storage engaged portions in the state shown in  FIG. 9 ; 
           [0026]    [ FIG. 15 ] is a bottom view showing a state where a first engaging portion slides over a first storage engaged portion from the state shown in  FIG. 14 ; 
           [0027]    [ FIG. 16 ] is a bottom view showing a structure of and around a first pullout engaged portion and a second storage engaged portion in the state shown in  FIG. 10 ; 
           [0028]    [ FIG. 17 ] is a bottom view showing a structure of and around a first pullout engaged portion and a second storage engaged portion in the state shown in  FIG. 11 ; 
           [0029]    [ FIG. 18 ] is a bottom view showing a structure of and around a second pullout engaged portion in the state shown in  FIG. 11 ; 
           [0030]    [ FIG. 19 ] is a bottom view showing a state where a second engaging portion slides over a second pullout engaged portion from the state shown in  FIG. 18 ; 
           [0031]    [ FIG. 20 ] is a diagram illustrating inclination angles of inclined surfaces of engaged portions of a second discharge tray according to a second embodiment of the present invention; 
           [0032]    [ FIG. 21 ] is a diagram showing a structure of an engaged portion of a second discharge tray according to a modified example of the second embodiment of the present invention; 
           [0033]    [ FIG. 22 ] is a diagram illustrating a structure of first and second engaging protrusions of a second discharge tray according to a third embodiment of the present invention; and 
           [0034]    [ FIG. 23 ] is a diagram illustrating a structure of first and second engaging protrusions of a second discharge tray according to the third embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
       First Embodiment 
       [0036]    With reference to  FIGS. 1 to 19 , a description will be given of the structure of an image forming apparatus  100  that is provided with a second discharge tray (sheet placement tray)  30  according to a first embodiment of the present invention. In the image forming apparatus  100  shown in  FIG. 1  (here a digital multifunction peripheral is taken as an example), a copy operation proceeds as follows. In an image reading device  6 , document image data is read and converted into an image signal. On the other hand, in an image forming portion  3  inside a multifunction peripheral main body  2 , a photosensitive drum  5  that rotates in the clockwise direction in  FIG. 1  is electrostatically charged uniformly by a charging unit  4 , and an electrostatic latent image is formed on the photosensitive drum  5  by a laser beam from an exposure unit (such as a laser scanner unit)  7  based on the document image data read in the image reading device  6 . Then, developer (hereinafter referred to as toner) is attached to the electrostatic latent image by a developing unit  8 , and thereby a toner image is formed. Toner is fed to the developing unit  8  from a toner container  9 . 
         [0037]    Toward the photosensitive drum  5  having the toner image formed on it as described above, a sheet (recording medium) is transported from a sheet feeding mechanism  10  via a sheet transport passage  11  and a registration roller pair  12  to the image forming portion  3 . In the image forming portion  3 , the toner image on the surface of the photosensitive drum  5  is transferred to the sheet by a transfer roller  13  (image transfer portion). Then, the sheet to which the toner image has been transferred is separated from the photosensitive drum  5 , and is transported to a fixing portion  14 , where the toner image is fixed. The fixing portion  14  has a fixing roller pair  14   a.  The sheet which has passed through the fixing portion  14  is transported to a sheet transport passage  15  which branches into a plurality of directions, and the sheet is distributed among different transport directions by passage switching mechanisms  21  and  22  which has a plurality of passage switching guides arranged at branch points in the sheet transport passage  15 . The sheet is then, as it is (or after being transported to a sheet transport passage  16  and being subjected to two-sided copying), discharged via a discharge roller pair  20   a  or a discharge roller pair  20   b  onto a sheet discharge portion including a first discharge tray  17  and the second discharge tray (sheet placement tray)  30 . 
         [0038]    Moreover, although no illustration is given, a destaticizer that removes electrostatic charge remaining on the surface of the photosensitive drum  5  is arranged on the downstream side of a cleaning device  18 . Furthermore, the sheet feeding mechanism  10  is removably fitted to the multifunction peripheral main body  2 . The sheet feeding mechanism  10  includes a plurality of sheet feed cassettes  10   a  and  10   b  for storing sheets and a stack bypass (manual tray)  10   c  arranged over the sheet feed cassettes  10   a  and  10   b;  these are connected, via the sheet transport passage  11 , to the image forming portion  3  that includes the photosensitive drum  5 , the developing unit  8 , etc. 
         [0039]    In an upper part of the multifunction peripheral main body  2 , the image reading device  6  is arranged. Over the top surface of the multifunction peripheral main body  2 , a platen (document presser)  24  is openably/closably arranged that presses and thereby holds a document placed on a contact glass (unillustrated) in the image reading device  6 . On the platen  24 , a document transport device  27  is provided that automatically transports a document to the image reading device  6 . 
         [0040]    The sheet transport passage  15  is configured specifically as follows. The sheet transport passage  15  first branches into left and right passages on the downstream side of the fixing roller pair  14   a.  Of these passages, one (the passage that branches in the rightward direction in  FIG. 1 ) communicates with the first discharge tray  17 , and the other (the passage that branches in the leftward direction in  FIG. 1 ) then further branches into upper and lower passages via a transport roller pair  19 . Of these passages, one (the passage that branches in the leftward direction in  FIG. 1 ) communicates with the second discharge tray  30  while the other (the passage that branches in the down direction in  FIG. 1 ) communicates with the sheet transport passage  16 . 
         [0041]    The second discharge tray  30  is pivotably supported on a side surface of the main body of the image forming apparatus  100 . The second discharge tray  30  is arranged selectively either in an open position (the position in  FIG. 1 ) where it is open by a predetermined angle from the side surface of the main body or in a closed position where it is stored in a storage space (unillustrated) formed in the side surface of the main body to be a part of the side surface of the main body. 
         [0042]    As shown in  FIG. 2 , the second discharge tray  30  is formed to be a pullout type such that its sheet placement surface is extendable.  FIG. 2  shows a state as seen from the rear side in  FIG. 1 ; the left and right in  FIG. 2  are reversed as compared with those in  FIG. 1 . 
         [0043]    The second discharge tray  30  includes a tray main body  40  fitted to the side surface of the main body of the image forming apparatus  100 , a first slide member  50  which is slidable with respect to the tray main body  40 , and a second slide member  60  which is slidable with respect to the first slide member  50 . The tray main body  40 , the first slide member  50 , and the second slide member  60  are formed such that their lengths in the sheet width direction (the up/down direction in  FIG. 2 ) are increasingly smaller in the order named. 
         [0044]    The tray main body  40  includes a base portion  41 , and a sheet placement portion  42  which protrudes upward from the base portion  41  and which has the sheet placement surface on which sheets are placed. As a result of the sheet placement portion  42  protruding upward from the base portion  41 , a space is formed under the sheet placement portion  42 . In the space, the first and second slide members  50  and  60  are stored in a state stacked on each other. Moreover, in the right end of a central part of the sheet placement portion  42  in the sheet width direction (the up/down direction in  FIG. 2 ), a cutout portion  42   a  is formed so as to avoid contact with a holding portion  60   a,  which will be described later, of the second slide member  60  when the second slide member  60  is stored. 
         [0045]    The first slide member  50  is arranged selectively either in a first stored position where it is stored in the tray main body  40  or in a first pulled-out position (the position in  FIG. 2 ) where it is pulled out of the tray main body  40  so as to extend the sheet placement surface. Moreover, in the right end of a central part of the first slide member  50  in the sheet width direction (the up/down direction in  FIG. 2 ), a cutout portion  50   a  is formed so as to avoid contact with the holding portion  60   a,  which will be described later, of the second slide member  60  when the second slide member  60  is stored. 
         [0046]    The second slide member  60  is arranged selectively either in a second stored position where it is stored in the first slide member  50  or in a second pulled-out position (the position in  FIG. 2 ) where it is pulled out of the first slide member  50  so as to extend the sheet placement surface. Moreover, at the right end of a central part of the second slide member  60  in the sheet width direction (the up/down direction in  FIG. 2 ), the holding portion  60   a  is formed which is held by a user when the first and second slide members  50  and  60  are pulled out. 
         [0047]    On the reverse surface of the sheet placement portion  42  of the tray main body  40 , as shown in  FIGS. 3 and 4 , there is provided, erect therefrom, a pair of guide rails  43  that guides the side surface of the first slide member  50 . At a predetermined position on one side of the guide rails  43  (on the image forming apparatus  100 -side, the left side), there is arranged a first storage engaged portion  44  which is engaged with a first engaging portion  52 , which will be described later, of the first slide member  50  in a state (the state in  FIG. 9 ) where the first slide member  50  is stored in the first stored position. Moreover, at a predetermined position on the other side of the guide rails  43  (on the opposite side from the image forming apparatus  100 -side, the right side), there is arranged a first pullout engaged portion  45  which is engaged with the first engaging portion  52 , which will be described later, of the first slide member  50  in a state (the state in  FIGS. 10 and 11 ) where the first slide member  50  is pulled out in the first pulled-out position. The first storage engaged portion  44  and the first pullout engaged portion  45  are protruding portions that protrude from the bottom end of the guide rails  43  (the top end in  FIG. 4 ) into the tray main body  40  (inward with respect to the sheet width direction). 
         [0048]    The first storage engaged portion  44  has an engaging inclined surface  44   a  and a non-engaging inclined surface  44   b.  In a state (the state in  FIG. 9 ) where the first slide member  50  is stored in the first stored position, the engaging inclined surface  44   a  is in contact (is engaged) with the first engaging portion  52 , which will be described later, of the first slide member  50 , but the non-engaging inclined surface  44   b  is not in contact (is not engaged) therewith. 
         [0049]    The first pullout engaged portion  45  has an engaging protrusion  45   a  and a regulating protrusion  45   b.  In a state (the state in  FIGS. 10 and 11 ) where the first slide member  50  is pulled out in the first pulled-out position, the engaging protrusion  45   a  is engaged with the first engaging portion  52 , which will be described later, of the first slide member  50 , and the regulating protrusion  45   b  regulates (restricts) the movement of the first slide member  50  in the pulling-out direction (the rightward direction). The engaging protrusion  45   a  has a non-engaging inclined surface  45   c  and an engaging inclined surface  45   d.  In a state where the first slide member  50  is pulled out in the first pulled-out position, the non-engaging inclined surface  45   c  is not in contact (is not engaged) with the first engaging portion  52 , which will be described later, of the first slide member  50 , but the engaging inclined surface  45   d  is in contact (is engaged) therewith. The regulating protrusion  45   b  has a regulating surface  45   e  which extends in a direction orthogonal to the pulling-out direction (in the sheet width direction) and which makes contact with the first engaging portion  52 , which will be described later, of the first slide member  50  to regulate (restrict) its movement in the pulling-out direction (the rightward direction). 
         [0050]    In the side surface of the first slide member  50 , as shown in  FIGS. 5 and 6 , there is formed a pair of guided portions  51  that slides along the pair of the guide rails  43  of the tray main body  40 . Moreover, at a predetermined position on one side (the left side) of the side surface of the first slide member  50  is formed the first engaging portion  52  which is elastically deformable sideways (outward with respect to the sheet width direction) and which is engaged with the tray main body  40 . The first engaging portion  52  is an elastic piece having a first engaging protrusion  52   a  which protrudes sideways and which is thereby engaged with the first storage engaged portion  44  and the first pullout engaged portion  45  of the tray main body  40 . 
         [0051]    Moreover, on the reverse surface of the first slide member  50 , there is provided, erect therefrom, a pair of guide rails  53  that guides the side surface of the second slide member  60 . At a predetermined position on one side (the left side) of the guide rails  53 , there is arranged a second storage engaged portion  54  which is engaged with a second engaging portion  62 , which will be described later, of the second slide member  60  in a state (the state in  FIGS. 9 and 10 ) where the second slide member  60  is stored in the second stored position. Moreover, at a predetermined position on the other side (the right side) of the guide rails  53 , there is arranged a second pullout engaged portion  55  which is engaged with the second engaging portion  62 , which will be described later, of the second slide member  60  in a state (the state in  FIG. 11 ) where the second slide member  60  is pulled out in the second pulled-out position. The second storage engaged portion  54  and the second pullout engaged portion  55  are protruding portions that protrude from the bottom end of the guide rails  53  (the top end in  FIG. 6 ) into the first slide member  50  (inward with respect to the sheet width direction). 
         [0052]    The second storage engaged portion  54  has an engaging inclined surface  54   a  and a non-engaging inclined surface  54   b.  In a state (the state in  FIGS. 9 and 10 ) where the second slide member  60  is stored in the second stored position, the engaging inclined surface  54   a  is in contact (is engaged) with the second engaging portion  62 , which will be described later, of the second slide member  60 , but the non-engaging inclined surface  54   b  is not in contact (is not engaged) therewith. The second pullout engaged portion  55  has an engaging protrusion  55   a  and a regulating protrusion  55   b.  In a state (the state in  FIG. 11 ) where the second slide member  60  is pulled out in the second pulled-out position, the engaging protrusion  55   a  is engaged with the second engaging portion  62 , which will be described later, of the second slide member  60 , and the regulating protrusion  55   b  regulates (restricts) the movement of the second slide member  60  in the pulling-out direction (the rightward direction). The engaging protrusion  55   a  has a non-engaging inclined surface  55   c  and an engaging inclined surface  55   d.  In a state where the second slide member  60  is pulled out in the second pulled-out position, the non-engaging inclined surface  55   c  is not in contact (is not engaged) with the second engaging portion  62 , which will be described later, of the second slide member  60 , but the engaging inclined surface  55   d  is in contact (is engaged) therewith. The regulating protrusion  55   b  has a regulating surface  55   e  which extends in a direction orthogonal to the pulling-out direction (in the sheet width direction) and which makes contact with the second engaging portion  62 , which will be described later, of the second slide member  60  to regulate (restrict) its movement in the pulling-out direction (the rightward direction). 
         [0053]    In the side surface of the second slide member  60 , as shown in  FIGS. 7 and 8 , there is formed a pair of guided portions  61  that slides along the pair of the guide rails  53  of the first slide member  50 . Moreover, at a predetermined position on one side (the left side) of the side surface of the second slide member  60  is formed the second engaging portion  62  which is elastically deformable sideways (outward with respect to the sheet width direction) and which is engaged with the first slide member  50 . The second engaging portion  62  is an elastic piece having a second engaging protrusion  62   a  which protrudes sideways and which is thereby engaged with the second storage engaged portion  54  and the second pullout engaged portion  55  of the first slide member  50 . Moreover, on the reverse surface of the second slide member  60 , a reinforcement rib  63  is provided erect therefrom along the guided portions  61 . 
         [0054]    In this embodiment, when, with the holding portion  60   a  held, the first and second slide members  50  and  60  are pulled out from a state (the state in  FIG. 9 ) where they are stored respectively in the first and second stored positions, the engagement of the first storage engaged portion  44  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  is released, and thereafter the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  is released. That is, as shown in  FIG. 12 , the engaging portion (the first engaging portion  52 , the second engaging portion  62 ) slides over X 1  more easily than over X 3 . Although the strength of the engagement of the engaging portion (the first engaging portion  52 , the second engaging portion  62 ) with the engaged portion (the first storage engaged portion  44 , the second storage engaged portion  54 ) can be adjusted according to the elastic force (the resilient force) of the engaging portion, the protrusion amount of the engaged portion, the inclination angle of the engaging inclined surface of the engaged portion, etc., in this embodiment, the elastic force of the first engaging portion  52  is set substantially the same as the elastic force of the second engaging portion  62 , while the protrusion amount of the second storage engaged portion  54  is set larger than the protrusion amount of the first storage engaged portion  44 . 
         [0055]    On the other hand, when the first and second slide members  50  and  60  are stored from a state (the state in  FIG. 11 ) where they are pulled out respectively in the first and second pulled-out positions, the engagement of the second pullout engaged portion  55  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  is released, and thereafter the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  is released. That is, as shown in  FIG. 13 , the engaging portion (the second engaging portion  62 , the first engaging portion  52 ) slides over Y 1  more easily than over Y 3 . Although the strength of the engagement of the engaging portion (the second engaging portion  62 , the first engaging portion  52 ) with the engaged portion (the second pullout engaged portion  55 , the first pullout engaged portion  45 ) can be adjusted according to the elastic force (the resilient force) of the engaging portion, the protrusion amount of the engaged portion, the inclination angle of the engaging inclined surface of the engaged portion, etc., in this embodiment, the elastic force of the second engaging portion  62  is set substantially the same as the elastic force of the first engaging portion  52 , while the protrusion amount of the first pullout engaged portion  45  is set larger than the protrusion amount of the second pullout engaged portion  55 . 
         [0056]    Furthermore, in this embodiment, when the first and second slide members  50  and  60  are pulled out, the first pullout engaged portion  45  of the tray main body  40  is engaged with the first engaging portion  52  of the first slide member  50 , and thereafter the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  is released. That is, as shown in  FIG. 12 , the engaging portion (the first engaging portion  52 , the second engaging portion  62 ) slides over X 2  more easily than over X 3 . The magnitude of a force required to engage the engaging portion (the first engaging portion  52 ) with the engaged portion (the first pullout engaged portion  45 ) can be adjusted according to the elastic force (the resilient force) of the engaging portion, the protrusion amount of the engaged portion, the inclination angle of the engaging inclined surface of the engaged portion, etc. 
         [0057]    Moreover, when the first and second slide members  50  and  60  are stored, the second storage engaged portion  54  of the first slide member  50  is engaged with the second engaging portion  62  of the second slide member  60 , and thereafter the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  is released. That is, as shown in  FIG. 13 , the engaging portion (the second engaging portion  62 , the first engaging portion  52 ) slides over Y 2  more easily than over Y 3 . The magnitude of a force required to engage the engaging portion (the second engaging portion  62 ) with the engaged portion (the second storage engaged portion  54 ) can be adjusted according to the elastic force (the resilient force) of the engaging portion, the protrusion amount of the engaged portion, the inclination angle of the engaging inclined surface of the engaged portion, etc. 
         [0058]    Next, the pullout operation and storage operation of the first and second slide members  50  and  60  of the second discharge tray  30  will be described. 
         [0059]    The first and second slide members  50  and  60  are pulled out from a state (the state in  FIGS. 9 and 14 ) where they are stored in the first and second stored positions as follows. First, as shown in  FIG. 15 , the first engaging portion  52  of the first slide member  50  slides over the first storage engaged portion  44  of the tray main body  40 , and thereby the engagement of the first engaging portion  52  of the first slide member  50  with the first storage engaged portion  44  of the tray main body  40  is released. This permits the first slide member  50  to slide in the rightward direction with respect to the tray main body  40  while the second slide member  60  remains stored in the second stored position. 
         [0060]    Then, the first engaging portion  52  of the first slide member  50  slides further over the engaging protrusion  45   a  of the first pullout engaged portion  45  of the tray main body  40  to be engaged with the first pullout engaged portion  45  of the tray main body  40 , and thus the state shown in  FIGS. 10 and 16  is achieved. 
         [0061]    Thereafter, the second engaging portion  62  of the second slide member  60  slides over the second storage engaged portion  54  of the first slide member  50 , and thereby the engagement of the second engaging portion  62  of the second slide member  60  with the second storage engaged portion  54  of the first slide member  50  is released. This permits the second slide member  60  to slide in the rightward direction with respect to the first slide member  50 . 
         [0062]    Then, the second engaging portion  62  of the second slide member  60  slides further over the engaging protrusion  55   a  of the second pullout engaged portion  55  of the first slide member  50  to be engaged with the second pullout engaged portion  55  of the first slide member  50 , and thus the state shown in  FIGS. 11, 17, and 18  is achieved. Now, the pulling-out of the first and second slide members  50  and  60  is complete. 
         [0063]    On the other hand, the first and second slide members  50  and  60  are stored from a state (the state in  FIGS. 11, 17, and 18 ) where they are pulled out in the first and second pulled-out positions as follows. First, as shown in  FIG. 19 , the second engaging portion  62  of the second slide member  60  slides over the engaging protrusion  55   a  of the second pullout engaged portion  55  of the first slide member  50 , and thereby the engagement of the second engaging portion  62  of the second slide member  60  with the second pullout engaged portion  55  of the first slide member  50  is released. This permits the second slide member  60  to slide in the leftward direction with respect to the first slide member  50  while the first slide member  50  remains pulled out in the first pulled-out position. 
         [0064]    Then, the second engaging portion  62  of the second slide member  60  slides further over the second storage engaged portion  54  of the first slide member  50  to be engaged therewith, and thus the state shown in  FIGS. 10 and 16  is achieved. Here, as a result of the left-side end surface of the guided portions  61  making contact with the right-side end surface of the first engaging portion  52  of the first slide member  50 , the movement of the second slide member  60  in the leftward direction is regulated (restricted). 
         [0065]    Thereafter, the first engaging portion  52  of the first slide member  50  slides over the engaging protrusion  45   a  of the first pullout engaged portion  45  of the tray main body  40 , and thereby the engagement of the first engaging portion  52  of the first slide member  50  with the first pullout engaged portion  45  of the tray main body  40  is released. This permits the first slide member  50  to slide in the leftward direction with respect to the tray main body  40  while the second slide member  60  remains stored in the second stored position. 
         [0066]    Then, the first engaging portion  52  of the first slide member  50  slides further over the first storage engaged portion  44  of the tray main body  40  to be engaged therewith, and thus the state shown in  FIGS. 9 and 14  is achieved. Here, as a result of the left-side end surface of the first slide member  50  making contact with a wall portion  40   a  provided erect from the left-side end part of the tray main body  40 , the movement of the first slide member  50  in the leftward direction is regulated (restricted). Now, the storing of the first and second slide members  50  and  60  is complete. 
         [0067]    In this embodiment, as described above, when the first and second slide members  50  and  60  are pulled out from a state where they are stored respectively in the first and second stored positions, the engagement of the first storage engaged portion  44  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  is released, and thereafter the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  is released. In this way, when the first and second slide members  50  and  60  are pulled out, the first slide member  50  is pulled out first, and thus the second slide member  60 , which is weak in strength due to its dimensions, can be prevented from being pulled out alone. 
         [0068]    When the first and second slide members  50  and  60  are stored from a state where they are pulled out respectively in the first and second pulled-out positions, the engagement of the second pullout engaged portion  55  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  is released, and thereafter the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  is released. In this way, when the first and second slide members  50  and  60  are stored, the second slide member  60  is stored first, and thus the second slide member  60 , which is weak in strength due to its dimensions, can be prevented from being pulled out alone. 
         [0069]    Thus, both when the first and second slide members  50  and  60  are pulled out and when they are stored, the second slide member  60 , which is weak in strength due to its dimensions, can be prevented from being pulled out alone, and thereby the second discharge tray  30  can be prevented from being damaged by an external force. 
         [0070]    Moreover, as described above, when the first and second slide members  50  and  60  are pulled out, the first pullout engaged portion  45  of the tray main body  40  is engaged with the first engaging portion  52  of the first slide member  50 , and thereafter the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  is released. In this way, until the first slide member  50  is pulled out completely with respect to the tray main body  40 , the second slide member  60  can be prevented from starting to be pulled out with respect to the first slide member  50 . 
         [0071]    When the first and second slide members  50  and  60  are stored, the second storage engaged portion  54  of the first slide member  50  is engaged with the second engaging portion  62  of the second slide member  60 , and thereafter the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  is released. In this way, until the second slide member  60  is stored completely with respect to the first slide member  50 , the first slide member  50  can be prevented from starting to be stored with respect to the tray main body  40 . 
         [0072]    Thus, both when the first and second slide members  50  and  60  are pulled out and when they are stored, the second slide member  60 , which is weak in strength due to its dimensions, can be prevented more effectively from being pulled out alone. 
         [0073]    Moreover, as described above, on the side surface of the first slide member  50  is provided the first engaging portion  52  which is elastically deformable and which has the first engaging protrusion  52   a  that protrudes sideways, and on the side surface of the second slide member  60  is provided the second engaging portion  62  which is elastically deformable and which has the second engaging protrusion  62   a  that protrudes sideways. Thus, it is possible to easily engage and disengage the tray main body  40  and the first slide member  50  with and from each other, and it is also possible to easily engage and disengage the first slide member  50  and the second slide member  60  with and from each other. 
         [0074]    Moreover, as described above, the protrusion amount of the second storage engaged portion  54  is larger than that of the first storage engaged portion  44 . Thus, when the first and second slide members  50  and  60  are pulled out, it is possible to easily release the engagement of the first storage engaged portion  44  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  and thereafter the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60 . Moreover, the protrusion amount of the first pullout engaged portion  45  is larger than that of the second pullout engaged portion  55 . Thus, when the first and second slide members  50  and  60  are stored, it is possible to easily release the engagement of the second pullout engaged portion  55  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  and thereafter the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50 . 
       Second Embodiment 
       [0075]    As a second embodiment, a description will be given of how an order is introduced in the strength of the engagement of the engaging portions (the first engaging portion  52 , the second engaging portion  62 ) with the engaged portions (the first storage engaged portion  44 , the first pullout engaged portion  45 , the second storage engaged portion  54 , the second pullout engaged portion  55 ) by varying the inclination angle of the inclined surfaces of the engaged portions. 
         [0076]    As shown in  FIG. 20 , the inclination angle (the inclination angle with respect to the retracting/extracting direction (the leftward/rightward direction)) of the engaging inclined surface (a second engaging inclined surface)  54   a  of the second storage engaged portion  54  is made larger than the inclination angle of the engaging inclined surface (a first engaging inclined surface)  44   a  of the first storage engaged portion  44  and the inclination angle of the non-engaging inclined surface  45   c  of the first pullout engaged portion  45 . Moreover, the inclination angle of the engaging inclined surface (a third engaging inclined surface)  45   d  of the first pullout engaged portion  45  is made larger than the inclination angle of the engaging inclined surface (a fourth engaging inclined surface)  55   d  of the second pullout engaged portion  55  and the inclination angle of the non-engaging inclined surface  54   b  of the second storage engaged portion  54 . 
         [0077]    In this embodiment, the elastic force of the first engaging portion  52  is set substantially the same as the elastic force of the second engaging portion  62 , and the protrusion amount of the second storage engaged portion  54  is set substantially the same as the protrusion amount of the first storage engaged portion  44  and the protrusion amount of the engaging protrusion  45   a.    
         [0078]    Otherwise, the structure in the second embodiment is similar to that in the previously-described first embodiment. 
         [0079]    The engaging protrusion  55   a  of the second pullout engaged portion  55  has only to be engaged with the second engaging portion  62 , and thus, as in the modified example of the second embodiment shown in  FIG. 21 , the protrusion amount of the engaging protrusion  55   a  can be reduced. The same applies to other embodiments. 
         [0080]    In this embodiment, as described above, the inclination angle of the engaging inclined surface  54   a  of the second storage engaged portion  54  is made larger than the inclination angle of the engaging inclined surface  44   a  of the first storage engaged portion  44 . Thus, when the first and second slide members  50  and  60  are pulled out from a state where they are stored respectively in the first and second stored positions, it is possible to easily release the engagement of the first storage engaged portion  44  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  and thereafter the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60 . 
         [0081]    Moreover, the inclination angle of the engaging inclined surface  45   d  of the first pullout engaged portion  45  is made larger than the inclination angle of the engaging inclined surface  55   d  of the second pullout engaged portion  55 . Thus, when the first and second slide members  50  and  60  are stored from a state where they are pulled out respectively in the first and second pulled-out positions, it is possible to easily release the engagement of the second pullout engaged portion  55  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  and thereafter the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50 . 
         [0082]    Moreover, as described above, the inclination angle of the engaging inclined surface  54   a  of the second storage engaged portion  54  is made larger than the inclination angle of the non-engaging inclined surface  45   c  of the first pullout engaged portion  45 . Thus, when the first and second slide members  50  and  60  are pulled out, it is possible to easily engage the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  and thereafter release the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60 . 
         [0083]    Moreover, the inclination angle of the engaging inclined surface  45   d  of the first pullout engaged portion  45  is made larger than the inclination angle of the non-engaging inclined surface  54   b  of the second storage engaged portion  54 . Thus, when the first and second slide members  50  and  60  are stored, it is possible to easily engage the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  and thereafter release the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50 . 
         [0084]    As described above, in the second embodiment, as in the first embodiment, both when the first and second slide members  50  and  60  are pulled out and when they are stored, the second slide member  60 , which is weak in strength due to its dimensions, can be prevented from being pulled out alone, and thereby the second discharge tray  30  can be prevented from being damaged by an external force. 
         [0085]    Otherwise, the effects of the second embodiment are similar to those of the previously-described first embodiment. 
       Third Embodiment 
       [0086]    As a third embodiment, a description will be given of how an order is introduced in the strength of the engagement of the engaging portions (the first engaging portion  52 , the second engaging portion  62 ) with the engaged portions (the first storage engaged portion  44 , the first pullout engaged portion  45 , the second storage engaged portion  54 , the second pullout engaged portion  55 ) by varying the friction force of the engaging portions with respect to the engaged portions. 
         [0087]    The tray main body  40 , the first slide member  50 , and the second slide member  60  are made of polycarbonate, polyethylene, or the like, and are all formed of the same resin. 
         [0088]    As shown in  FIGS. 22 and 23 , a storing direction-side (left-side) part (a part that makes contact with the engaging inclined surface  45   d  of the engaging protrusion  45   a  of the first pullout engaged portion  45 ) of the first engaging protrusion  52   a  of the first engaging portion  52  is made of rubber or the like, and forms a high friction portion  52   b  having a comparatively high friction coefficient with respect to the tray main body  40 . Moreover, a pulling-out direction-side (right-side) part (a part that makes contact with the engaging inclined surface  44   a  of the first storage engaged portion  44 ) of the first engaging protrusion  52   a  is made of resin such as polycarbonate, polyethylene, or the like, and forms a low friction portion  52   c  having a lower friction coefficient than the high friction portion  52   b  with respect to the tray main body  40 . 
         [0089]    On the other hand, a storing direction-side (left-side) part (a part that makes contact with the engaging inclined surface  55   d  of the engaging protrusion  55   a  of the second pullout engaged portion  55 ) of the second engaging protrusion  62   a  of the second engaging portion  62  is made of resin such as polycarbonate, polyethylene, or the like, and forms a low friction portion  62   b  having a comparatively low friction coefficient with respect to the first slide member  50 . Moreover, a pulling-out direction-side (right-side) part (a part that makes contact with the engaging inclined surface  54   a  of the second storage engaged portion  54 ) of the second engaging protrusion  62   a  is made of the same material as the high friction portion  52   b,  such as rubber, and forms a high friction portion  62   c  having a higher friction coefficient than the low friction portion  62   b  with respect to the first slide member  50 . 
         [0090]    In this embodiment, the elastic force of the first engaging portion  52  is set substantially the same as the elastic force of the second engaging portion  62 , and the protrusion amount of the second storage engaged portion  54  is set substantially the same as the protrusion amount of the first storage engaged portion  44  and the protrusion amount of the engaging protrusion  45   a.  Moreover, the inclination angle of the engaging inclined surface of the first storage engaged portion  44  is set substantially the same as that of the second storage engaged portion  54 , and the inclination angle of the engaging inclined surface of the first pullout engaged portion  45  is set substantially the same as that of the second pullout engaged portion  55 . 
         [0091]    Otherwise, the structure in the second embodiment is similar to that in the previously-described first embodiment. 
         [0092]    In this embodiment, as described above, the low friction portion  52   c  is provided in a pulling-out direction-side (right-side) part of the first engaging protrusion  52   a,  and the high friction portion  62   c  is provided in a pulling-out direction-side (right-side) part of the second engaging protrusion  62   a.  Thus, when the first and second slide members  50  and  60  are pulled out from a state where they are stored respectively in the first and second stored positions, it is possible to easily release the engagement of the first storage engaged portion  44  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  and thereafter the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60 . It is also possible to easily engage the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50  and thereafter release the engagement of the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60 . 
         [0093]    Moreover, the high friction portion  52   b  is provided in a storing direction-side (left-side) part of the first engaging protrusion  52   a,  and the low friction portion  62   b  is provided in a storing direction-side (left-side) part of the second engaging protrusion  62   a.  Thus, when the first and second slide members  50  and  60  are stored from a state where they are pulled out respectively in the first and second pulled-out positions, it is possible to easily release the engagement of the second pullout engaged portion  55  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  and thereafter the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50 . It is also possible to easily engage the second storage engaged portion  54  of the first slide member  50  with the second engaging portion  62  of the second slide member  60  and thereafter release the engagement of the first pullout engaged portion  45  of the tray main body  40  with the first engaging portion  52  of the first slide member  50 . 
         [0094]    As described above, also in the third embodiment, as in the previously-described first and second embodiments, both when the first and second slide members  50  and  60  are pulled out and when they are stored, the second slide member  60 , which is weak in strength due to its dimensions, can be prevented from being pulled out alone, and thereby the second discharge tray  30  can be prevented from being damaged by an external force. 
         [0095]    Otherwise, the effects of the third embodiment are similar to those of the previously-described first embodiment. 
         [0096]    It should be understood that the embodiments disclosed herein are in every aspect illustrative and not restrictive. The scope of the present invention is defined not by the description of embodiments given above but by the appended claims, and encompasses many modifications and variations made in the sense and scope equivalent to those of the claims. 
         [0097]    For example, although the above-described embodiments deal with, as an example, an image forming apparatus exploiting electrophotography, this is in no way meant to limit the present invention. The present invention is applicable equally to image forming apparatuses adopting other image forming methods such as an inkjet method, a thermal transfer method, etc. The present invention is widely applicable also to devices which simply transport sheets, devices which post-process sheets having undergone image formation or the like, etc. 
         [0098]    Moreover, although the above-described embodiments deal with a case where the sheet placement tray is a discharge tray, this is in no way meant to limit the present invention. Instead, the sheet placement tray may be a sheet feed tray. 
         [0099]    Moreover, although the above-described embodiments deal with an example where the first and second engaging portions are formed in the side surfaces of the first and second slide members, this is in no way meant to limit the present invention. Instead, the first and second engaging portions may be formed in central parts of the first and second slide members in the sheet width direction. In this case, for example, the first engaging portion which is elastically deformable in the up/down direction may be formed in a central part of the first slide member in the sheet width direction, and the first storage engaged portion and the first pullout engaged portion may be formed in a central part of the reverse surface of the tray main body in the sheet width direction. Likewise, the second engaging portion which is elastically deformable in the up/down direction may be formed in a central part of the second slide member in the sheet width direction, and the second storage engaged portion and the second pullout engaged portion may be formed in a central part of the reverse surface of the first slide member in the sheet width direction. Moreover, the first and second engaging portions may be formed in both the side surfaces and the central parts of the first and second slide members in the sheet width direction. 
         [0100]    Moreover, the technical scope of the present invention encompasses any structure obtained by combining, as necessary, the structures of the above-described embodiments and modified examples.