Patent Publication Number: US-10317836-B2

Title: Sheet stacking apparatus and an image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet stacking apparatus in which a sheet is stacked and to an image forming apparatus having the sheet stacking apparatus. 
     Description of the Related Art 
     The maximum length of a sheet which a user uses in a sheet conveying direction was previously about 19 inches. However, the demand for a sheet which is called “a long sheet” with a length of 26 to 30 inches (=660.4 to 762 mm) has been increasing as diversification progresses. In a case where such a sheet is used, when the length of a stacking tray is much less than the length of the sheet, the sheet may fall from the stacking tray. Thus, in order to stack a long sheet with the length of 30 inches, it is necessary for the stacking tray to have the length of about 30 inches. 
     On the other hand, since a user of a long sheet does not always use a long sheet, it is wasteful that the tray with the length of 30 inches occupies a user area. Thus, it is desirable that an extension tray for a long sheet has such a configuration that the extension tray can be detached or stored by a user and the extension tray can be used only when necessary. 
     For this reason, an extension tray for stacking discharged sheets that is provided in a detachably attachable manner has been proposed. In the configuration of such an extension tray, a leg portion for attachment is provided on a paper supporter made of a wire member and is configured to be inserted into a sheet discharging portion of an electronic device (Japanese Patent Laid-Open Application No. H9-278259). 
     When the extension tray is configured to be detachably attachable, it is desirable for the extension tray to be easily attached or detached. However, when the extension tray is configured to be easily attached or detached, a problem occurs in which the extension tray may unexpectedly come off. 
     On the other hand, when the extension tray is configured not to unexpectedly come off after having been attached, the operability of attaching and detaching of the extension tray becomes low. 
     SUMMARY OF THE INVENTION 
     The present invention provides a sheet stacking apparatus in which a sheet stacking portion is easily attached and detached and the sheet stacking portion is hard to come off during operation, and an image forming apparatus therewith. 
     A sheet stacking apparatus of the present invention, comprises: 
     a first stacking portion on which a sheet is stacked; 
     a second stacking portion on which a sheet is stacked, the second stacking portion being movable with respect to the first stacking portion; 
     a third stacking portion on which a sheet is stacked, the third stacking portion being detachably attachable to the first stacking portion or the second stacking portion; and 
     a restricting portion which restricts disengagement of the third stacking portion which has been attached, 
     wherein the second stacking portion is movable such that the second stacking portion is located at a first position and a second position; and 
     wherein the restricting portion does not restrict disengagement of the third stacking portion when the second stacking portion is located at the first position and the restricting portion restricts disengagement of the third stacking portion which has been attached when the second stacking portion is located at the second position. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic explanatory diagram of an image forming apparatus having a sheet processing apparatus according to an embodiment of the present invention. 
         FIG. 2  is an explanatory diagram showing the state in which a side tray is stored in an upper stacking tray according to the first embodiment. 
         FIGS. 3A and 3B  are explanatory diagrams showing the state in which the slide tray is drawn a little from the upper stacking tray according to the first embodiment. 
         FIGS. 4A and 4B  are explanatory diagrams of an extension tray according to the first embodiment. 
         FIG. 5  is an explanatory diagram showing the attaching of the extension tray according to the first embodiment. 
         FIGS. 6A and 6B  are explanatory diagrams showing the state in which the extension tray according to the first embodiment is attached. 
         FIG. 7  is an explanatory diagram showing a restricting portion which restricts the detaching of the extension tray according to the first embodiment. 
         FIGS. 8A and 8B  are diagrams for explaining a comparative example. 
         FIGS. 9A, 9B and 9C  are diagrams for explaining another comparative example. 
         FIGS. 10A and 10B  are explanatory diagrams showing a case where an extension tray according to the second embodiment is attached. 
         FIG. 11  is an explanatory diagram showing the state in which an extension tray according to the second embodiment is attached. 
         FIG. 12  is an explanatory diagram showing the attaching of a slide tray and the extension tray according to the second embodiment. 
         FIG. 13  is an explanatory diagram showing the attaching of the extension tray according to the second embodiment. 
         FIG. 14  is an explanatory diagram showing the attaching of the extension tray according to the second embodiment. 
         FIG. 15  is an explanatory diagram showing the attaching of the extension tray according to the second embodiment. 
         FIG. 16  is an explanatory diagram showing a configuration for restricting the detaching of the extension tray according to the second embodiment. 
         FIGS. 17A, 17B and 17C  are explanatory diagrams showing the state in which an extension tray according to the third embodiment is attached. 
         FIG. 18  is an explanatory diagram of the configuration for the restricting of the detaching of the extension tray according to the third embodiment. 
         FIG. 19  is an explanatory diagram of the configuration for the restricting of the detaching of the extension tray according to the third embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A sheet stacking apparatus according to embodiments of the present invention will be explained as an image forming apparatus including the sheet stacking apparatus with reference to the drawings. The image forming apparatus according to the embodiments of the present invention is a copying machine, a printer, a facsimile, or a multi-function machine thereof and has a sheet processing apparatus capable of aligning sheets discharged to a sheet stacking portion in the sheet discharging direction. 
     First Embodiment 
     &lt;Overall Configuration of the Image Forming Apparatus&gt; 
       FIG. 1  is a diagram of a cross-sectional view schematically showing the configuration of the image forming apparatus  200  according to an embodiment of the present invention. The configuration of the image forming apparatus will be described based the flow of a sheet. 
     As shown in  FIG. 1 , the image forming apparatus  200  includes the image forming apparatus main body  300  which forms an image on the sheet S, and the sheet processing apparatus  400 . The sheet processing apparatus  400  according to the present embodiment is configured to be detachably attachable to the image forming apparatus main body  300  and can be used as an option for the image forming apparatus main body  300  which can also be used alone. 
     The sheet cassette  301  is loaded in the lower portion of the image forming apparatus main body  300 , and the manual feed tray  302  is provided in the side portion of the image forming apparatus main body  300 . The sheet S set on the sheet cassette  301  or the manual feed tray  302  is conveyed to the image forming unit  304  by the sheet feeding unit  303  including conveying rollers. 
     The image forming unit  304  of the present embodiment employs an electro-photographic system in which toner images of respective colors of yellow, magenta, cyan, and black formed on a photosensitive drum are sequentially transferred onto a conveyed sheet where the transferred toner image is heated and fixed. 
     The sheet on which the toner image is transferred and fixed by the image forming unit  304  is conveyed to the sheet processing apparatus  400  by the discharging roller  305 . The sheet processing apparatus  400  is mounted on the downstream side in the sheet conveying direction of the image forming apparatus main body  300 . The sheet processing apparatus  400  conveys a plurality of sheets S fed from the image forming apparatus main body  300  to the stapler unit  402  by the conveying roller  401  where the sheets are stapled and they are discharged to the lower discharging portion  403 . 
     Further, the sheet processing apparatus  400  can discharge a conveyed sheet to the upper discharge portion  405  by the discharging roller  404  without diverting the conveyed sheet and performing the stapling process for the sheet. 
     &lt;Configuration of the Sheet Stacking Apparatus&gt; 
     Next, the sheet stacking apparatus which is a characterizing portion of the image forming apparatus of the present embodiment will be described. Here, an example will be explained in which the sheet stacking apparatus is applied to the upper discharging portion  405  for stacking sheets discharged from the sheet processing apparatus  400 . 
     As shown in  FIG. 1 , in the upper discharging portion  405  of the present embodiment, the upper stacking tray  150  is provided, which is fixed to a side surface of the sheet processing apparatus  400 . On the upper stacking tray  150 , the slide tray  151  which is slidably movable is provided. The slide tray  151  is configured to be slidable from the storage position hidden below the lower surface of the upper stacking tray  150  to the position where the slide tray  151  protrudes downstream in the sheet discharging direction. Normally, the slide tray  151  is stored on the lower surface of the upper stacking tray  150 . However, when a long sheet is discharged, the sheet stacking face is widened and a long sheet can be stacked by drawing out the slide tray  151  from the upper stacking tray  150 . 
     Furthermore, in the present embodiment, the extension tray  152  can be attached on the slide tray  151  so that long sheets can be stacked without dropping from the stacking portion. Namely, the sheet stacking apparatus of the present embodiment has the upper stacking tray  150  which is the first stacking portion capable of stacking sheets, the slide tray  151  which is the second stacking portion and the extension tray  152  which is the third stacking portion. 
     The extension tray  152  is configured to be detachably attachable so as to be used only when discharging a long sheet. In the sheet stacking apparatus of the present embodiment, the extension tray  152  is configured to be easy to attach and detach and to be hard to fall off when attached. Hereinafter, the configuration for attaching the extension tray  152  will be described with reference to  FIGS. 2 to 7 . 
       FIG. 2  shows the state in which the slide tray  151  is completely stored in the stacking tray  150 . From this state, the slide tray  151  stored in the upper stacking tray  150  is drawn a little (about 25 mm) out so that the state shown in  FIG. 3A  is obtained. Before drawing out the slide tray  151 , as shown in  FIG. 3B , the abutting portion  151   a  for abutting in a vertical direction abuts against the rail portion  150   a  of the upper stacking tray  150  and the slide tray  151  is slidably supported. When the slide tray  151  is drawn out by about 25 mm, the slope  151   b  for holding the slide tray  151  shown in  FIG. 3B  abuts against the holding portion  150   b  of the upper stacking tray  150  due to its own weight thereby holding the slide tray  151 . 
     As shown in  FIGS. 4A and 4B , the extension tray  152  is formed by bending an elastically deformable wire rod member. When attaching the extension tray  152 , the leg portion  152   a  is bent in the direction shown by the arrow in  FIGS. 4A and 4B  from the state of  FIG. 4A  to the state of  FIG. 4B . Thereafter, the extension tray  152  is inserted into the gap H (refer to  FIG. 3B ) between the upper stacking tray  150  and the slide tray  151 . Thereafter, the bend of the extension tray  152  is released, and the posture for attachment of the extension tray  152  (the state of  FIG. 4A ) is achieved. Since the extension tray  152  is a wire-like member, it has a low elastic coefficient and is easily bent. 
       FIG. 5  is a diagram of a view showing the attaching portion of the extension tray  152  as viewed from the back side of the stacking surface. After the extension tray  152  is attached, the movement of the extension tray  152  in the vertical direction is restricted by the extension tray  152  being caught in the gap between the upper stacking tray  150  and the slide tray  151 . The movement of the extension tray  152  in the left and right directions is restricted by the engaging portion  152   b  of the extension tray  152  being caught between the first left and right direction restricting portion  150   c  and the second left and right direction restricting portion  150   d  of the upper stacking tray  150 . That is, as shown in  FIG. 5 , the first left and right direction restricting portion  150   c  and the second left and right direction restricting portion  150   d  are formed on the upper stacking tray  150 . When the extension tray  152  is inserted into the gap between the upper stacking tray  150  and the slide tray  151  and the bend of the leg portion  152   a  is released, the engaging portion  152   b  is engaged with the first left and right restricting portion  150   c  and the second left and right restricting portion  150   d  thereby restricting the movement in the right and left directions is restricted. Further, the movement in the front and rear directions is restricted by the extension tray  152  being caught between the thrust restricting portions  150   e  formed on the front side and the far side of the upper stacking tray  150 . In this state, the temporary fixation of the extension tray  152  is completed. 
     The extension tray  152  is bent inward as shown in  FIG. 4B  and then inserted in order to prevent interference with the outer wall portion  150   f  (refer to  FIG. 5 ) of the upper stacking tray  150 . 
     &lt;Restricting Portion&gt; 
     As described above, since the extension tray  152  is easy to bend, the extension tray  152  may disengage when a force that causes the bend depicted in  FIG. 4B  is applied in this state. Therefore, in the present embodiment, as described below, a restricting portion is provided at a predetermined position of the slide tray  151  for restricting the disengagement of the attached extension tray  152 . 
     As shown in  FIG. 6 , after attaching the extension tray  152 , the slide tray  151  is completely drawn out in the direction of the arrow in  FIG. 6B . When the slide tray  151  is completely drawn out, the protruding portion  151   c  as the restricting portion, which protrudes from the slide tray  151  is formed on the slide tray  151  so that the protruding portion  151   c  is positioned in the inside and vicinity of leg portion  152   a  of the extension tray  152  as shown in  FIG. 7 . 
     The protruding portion  151   c  has a restricting surface  151   c   1  which restricts the bending inward of the leg portion  152   a  of the extension tray  152  (in the direction of the arrow in  FIGS. 4A and 4B ). As a result, in the state in which the slide tray  151  is completely drawn out, even if it is attempted to deform and move the leg portion  152   a  of the attached extension tray  152  inward, the movement of the leg portion  152   a  is restricted by abutting against the restricting surface  151   c   1 . Therefore, in the state in which the slide tray  151  is fully drawn out, the attached extension tray  152  will not disengage. 
     The movement of the extension tray  152  in the vertical direction is restricted by the extension tray  152  being caught between the upper stacking tray  150  and the slide tray  151  and the movement of the extension tray  152  in the front and rear directions is restricted by the extension tray  152  being caught between the thrust restricting portions  150   e  of the upper stacking tray  150  even when the protruding portion  151   c  is provided. Therefore, the movement of the extension tray  152  is restricted against a force in all directions and the extension tray  152  will not come off due to an external force. 
     As described above, the attachment of the extension tray  152  is started by bending the leg portions  152   a  of the extension tray  152  in the state where the slide tray  151  is drawn a little (about 25 mm) as shown in  FIG. 3B . Then, the leg portions  152   a  of the extension tray  152  are inserted into the gap between the upper stacking tray  150  and the slide tray  151 . Thereafter, the attachment of the extension tray  152  is completed by drawing out the slide tray  151  completely. Thus, the extension tray  152  is easy to be attached. In the state in which the extension tray  152  is attached, the protruding portion  151   c  restricts the movement (bend) of the leg portions  152   a  of the extension tray  152  so that the extension tray  152  is not disengaged by an external force. When removing the extension tray  152 , it is possible to detach the extension tray  152  in the reverse order of the operations of the above-described attachment. Thus, the extension tray  152  can be easily detached. 
     When it is attempted that the extension tray  152  be attached after completely pulling out the slide tray  151  from the beginning, the leg portions  152   a  of the extension tray  152  interfere with the protruding portion  151   c  and cannot be attached. Conversely, if the slide tray  151  without the protruding portion  151   c  is to be used, there is a possibility that the slide tray  151  may come off when receiving a force in the direction of the arrow in  FIG. 4A  after the extension tray  152  has been attached. 
     In addition, as shown in  FIGS. 8A and 8B , the structure is conceivable in which the extension tray  503  made of a wire rod is inserted into the stacking tray  501  instead of the configuration in which the restricting portion is provided as in the present embodiment. In this structure, the extension tray  503  is attached by inserting the inserting portion  503   a  of the extension tray  503  into the hole  501   a  formed in the stacking tray  501 . As shown in  FIG. 8B , the inserting portion  503   a  has a stepped shape. Therefore, the movement of the extension tray  503  is restricted in the state where the extension tray  503  is attached. 
     In the above structure, the extension tray  503  can be attached by inserting the tip of the wire rod member into the hole portion  501   a , and the extension tray  503  can be detached by pulling it out from the hole  501   a.    
     However, in the configuration of  FIGS. 8A and 8B , when a force is applied at the time of use in the direction of the arrow in  FIG. 8B , which is opposed to the attaching direction, the extension tray  503  may easily disengage. When the gap between the brim of the hole  501   a  and the inserting portion  503   a  is made smaller in order to make the extension tray  503  hard to disengage, it becomes hard to attach the extension tray  503 . Also, if the extension tray  503  is secured with screws or the like after the attachment, the extension tray  503  will not disengage at the time of use, but the screws must be attached and detached at the time of attachment and detachment of the extension tray, which deteriorates the workability in the attachment and the detachment of the extension tray. 
     Further, as shown in  FIGS. 9A, 9B and 9C , a configuration in which the attachment is made by snap fit is conceivable.  FIG. 9A  is a diagram as viewed from the stacking surface side, and  FIG. 9B  is a diagram showing an enlarged cross sectional view of the snap-fit portion. 
     As shown in  FIG. 9B , the snap fit portion  501   b  having an elastically deformable entrance portion is provided at a predetermined position of the stacking tray  501  and the extension tray  503  is attached by fitting the extension tray  503  made of a wire rod in the snap fit portion  501   b.    
     In the configuration shown in  FIGS. 9A, 9B and 9C , since the attached extension tray  503  is fixed to the snap fit portion  501   b , the possibility that the extension tray  503  disengages at the time of use is little. However, since the portion of the arm that nips the wire rod member (the portion L shown in  FIG. 9B ) is short and the snap fit portion  501   b  has a little bend amount, the tip portion  501   c  of the snap fit portion  501   b  will be scraped off when the extension tray  503  is detached. As a result, when the extension tray  503  is detached several times, the tip portion  501   c  disappears, and the function of preventing the extension tray  503  from disengaging may be impaired. 
     When the sheet processing apparatus  400  is used with the extension tray  503  being detached, the snap fit portion  501   b  protrudes from the stacking surface as shown in  FIG. 9C . As a result, there is a possibility that conveyance failure or loading failure occurs since the leading end of a sheet collides with the snap fit portion  501   b.    
     In contrast to the configurations of the comparative examples shown in  FIGS. 8A, 8B, 9A, 9B and 9C , in the present embodiment, the attached extended tray  152  will not come off in the state in which the slide tray  151  is drawn out. 
     As described above, in the sheet stacking apparatus of the present embodiment, the slide tray  151  is made slidable such that the slide tray  151  is located at the non-restricting position (the position in  FIG. 3 ) where the protruding portion  151   c  does not restrict the attaching and detaching of the extension tray  152  and at the restricting position (the position shown in  FIGS. 6A, 6B , and  7 ) where the disengagement of the attached extension tray  152  is restricted. This makes it possible to achieve both ease of attaching and detaching of the extension tray  152  and the prevention of disengagement of the attached extension tray  152 . 
     When using long sheets, the extension tray  152  is attached as described above, and the long sheets discharged from the upper stacking tray  150  to the extension tray  152  by the discharge roller  404  are stacked. On the other hand, when not using a long sheet, the extension tray  152  is detached. By using the extension tray  152  in this way, the extension tray  152  can be used only when a long sheet is used, and it is possible to prevent the extension tray  152  from always wastefully occupying the installation area. 
     Since the protruding portion  151   c  is located inside the surface on which the sheet is stacked even at the position where the extension tray  152  is prevented from coming off, it does not cause troubles such as obstruction of sheet conveyance and marks on the sheets when they are stacked. 
     Further, as shown in the cross-sectional view of  FIG. 6B , the stacking surface of the upper stacking tray  150 , the stacking surface of the slide tray  151 , and the stacking surface of the extension tray  152  have different angles. 
     In the case where the angles of the sheet stacking surfaces are different, even when the sheet is in state in which the sheet is bent along the front-back directions (hereinafter referred to as gutter-shaped curl), the gutter-shaped curl can be corrected by bending the sheet in the upstream/downstream direction of conveyance. Therefore, the gutter-shaped curl can be corrected also for a long sheet since the respective stacking surface angles of the upper stacking tray  150 , the slide tray  151 , and the extension tray  152  are different. For example, when the slide tray  151  and the extension tray  152  have the same angle, the gutter-shaped curl at the upstream side can be removed at the bent portion between the upper stacking tray  150  and the slide tray  151 , but the gutter-shaped curl at the downstream side of a long sheet cannot be removed. Therefore, as in the present embodiment, it is preferable that the stacking surface angles of the trays  151 ,  152  and  153  are different. 
     The sheet processing apparatus  400  is configured such that the gap between the upper stack tray  150  and the slide tray  151  is smaller when the slide tray  151  is in the stored position in which the slide tray  151  is completely stored in the upper stacking tray  150  than when the slide tray  151  is in the restricting position or the non-restricting position. Therefore, when attaching the extension tray  152 , after the slide tray  151  is slightly drawn out in the state shown in  FIGS. 3A and 3B , the extension tray  152  is attached. 
     In this embodiment, the explanation has been made to the case where the extension tray  152  is attached to the upper stacking tray  150 . However, the extension tray  152  may be attached to the tray of the lower discharging portion  403  in the same manner or may be attached to both the upper and lower trays. Further, not only on a tray on which sheets on which images are formed are stacked but also on a tray on which sheets to be provided to the image forming portion  304  are stacked, for example, such as the manual feed tray  302  and the slide tray  151  may be slidably provided and the extension tray  152  may be attached in a detachably attachable manner. 
     The extension tray  162  may be attached to either the upper stacking tray  150  or the slide tray  151 . 
     Second Embodiment 
     Next, a sheet stacking apparatus according to the second embodiment of the present invention will be explained. In the first embodiment explained above, the extension tray  152  is made of an elastically deformable wire rod member, and the bend of the leg portions of the extension tray  152  is restricted by the restricting portion provided on the slide tray  151 . In this embodiment, an example in which the extension tray is made of a plate member will be explained with reference to  FIGS. 10 to 12 . 
     In the sheet stacking apparatus of this embodiment, as shown in  FIG. 10A , the slide tray  161  which is the second stacking portion is slidably attached to the stacking tray  160  which is the first stacking portion.  FIG. 10A  shows the state in which the slide tray  161  is stored in the stacking tray  160 .  FIG. 10B  shows the state in which the extension tray  162  which is the third stacking portion is attached. The extension tray  162  of the present embodiment is a molded plate-shaped tray and is attached by inserting the extension tray  162  into the gap between the stacking tray  160  and the slide tray  161 . 
       FIG. 11  is a diagram showing a view of the state where the extension tray  162  is attached as viewed from the stacking surface side, and  FIG. 12  is a diagram showing a cross-sectional view taken along the line B-B in  FIG. 11 . As shown in  FIG. 12 , the J-shaped rail portion  160   a  is oppositely arranged on the lower surface of the stacking tray  160  and the leg portions  161   a  formed at both sides of the slide tray  161  in the sheet width direction (the direction perpendicular to the sheet conveying direction) engage slidably with the rail portion  160   a . The extension tray  162  is attached by inserting the extension tray  162  into the gap between the stacking tray  160  and the slide tray  161 . 
     As a result, the movement of the slide tray  161  in the vertical direction and in the front-rear direction is restricted by the stacking tray  160 . Further, the extension tray  162  is nipped between the stacking tray  160  and the slide tray  161  so that the movement of the extension tray  162  in the vertical direction and the front-rear directions is restricted. 
       FIG. 13  is a diagram showing a cross-sectional view taken along line A-A in  FIG. 11 . As shown in the partially enlarged view of  FIG. 13 , the projection portion  160 T is formed to serve as an engaging portion, which protrudes downward at a predetermined position on the lower surface of the stacking tray  160 . On the other hand, the projection portion  162 T which protrudes upward and serves as an engaged portion which can be engaged with the projection portion  160 T is formed on the extension tray  162 . Further, a step portion is formed at a predetermined position on the slide tray  161  so that there are the escape portion  161   b  where a gap is formed between the extension tray  162  and the slide tray  161  and the abutting portion  161   c  where a gap is not formed. 
     When attaching the extension tray  162 , the extension tray  162  is inserted into the gap between the stacking tray  160  and the slide tray  161  with the slide tray  161  being stored in the stacking tray  160 . Then, as shown in  FIG. 13 , the projection portion  162 T of the extension tray  162  is inserted to a position where the projection portion  162 T goes over the projection portion  160 T of the stacking tray  160 . At this time, the projection portion  162 T of the extension tray  162  easily goes over the projection portion  160 T of the stacking tray  160  since the projection portion  162 T of the extension tray  162  is bent in the direction of the arrow in  FIG. 13  and the escape portion  161   b  of the slide tray  161  is positioned below the projection portion  160 T and the projection portion  162 T escapes in the escape portion  161   b  of the slide tray  161 . 
       FIG. 14  is a diagram showing members of the slide tray  161  and the extension tray  162  as viewed from the back side of the stacking surface. The slide tray  161  is a member that is slidable in the direction of the arrow, but in the state of  FIG. 14 , the slide tray  161  is stored in the stacking tray  160 . 
     The slide tray  161  is drawn out from the provisionally attached state.  FIG. 15  shows the state after the slide tray  161  is drawn out in the direction of the arrow.  FIG. 16  is a cross-sectional view taken along the line A-A in  FIG. 11A  when the slide tray  161  is drawn out. 
     As shown in  FIG. 16 , when the slide tray  161  is drawn out, the abutting portion  161   c  as a restricting portion formed on the slide tray  161  moves to the position where the abutting portion  161   c  is opposed to the projection portion  160 T of the stacking tray  160 . Therefore, the back portion of the projection portion  162 T of the extension tray  162  comes into contact with the abutting portion  161   c . When the abutting portion  161   c  is in contact with the back portion of the projection portion  162 T, the projection portion  162 T cannot be bent in the escaping direction (direction of the arrow in  FIG. 13 ). That is, when the slide tray is at the drawn-out position, the abutting portion  161   c  restricts the movement of the attached extension tray  162  in the direction of disengagement. Accordingly, even if the extension tray  162  is pulled in the drawing direction (the direction of the arrow in  FIG. 16 ), the release of the engagement of the projection portion  162 T from the projection portion  160 T of the stacking tray  160  is restricted so that the projection portion  162 T does not disengage from the projection portion  160 T. Even in this configuration, the movement of the extension tray  162  in the vertical direction and the front-rear directions is restricted by the extension tray  162  being caught between the stacking tray  160  and the slide tray  161  as shown in  FIG. 12 . 
     In removing the extension tray  162 , when the slide tray  161  is pushed into the stacking tray  160  to make it in the storage state, the escape portion  161   b  reaches the position of the projection portion  160 T as shown in  FIG. 13 . As a result, the engagement of the projection portions  160 T and  162 T can be released so that the extension tray  162  can be drawn out in the same manner as at the time of attachment. 
     The slide tray  161  is movable between the non-restricting position where the projection portion  161   c  does not restrict the attaching and detaching of the extension tray  162  and the restricting position where the disengaging of the attached extension tray  162  is restricted. Therefore, when the slide tray  161  is stored in the stacking tray  160  as shown in  FIG. 13 , the extension tray  162  can be freely inserted and removed, and when the slide tray  161  is drawn out as shown in  FIG. 16 , the movement of the extension tray  162  in every direction is restricted so that the extension tray  162  will not disengage. 
     Therefore, when a user wishes to change a state between the state where a long sheet is used and the state where a long sheet is not used, i.e. when a user wishes to attach or detach the extension tray  162 , the user moves the slide tray  161  to the storage position (the position in  FIG. 13 ). On the other hand, when a long sheet is discharged and stacked, i.e., when the extension tray  162  should not be disengaged, the slide tray  161  is moved to the drawn-out position (the position in  FIG. 16 ) after the extension tray  162  has been attached. In this manner, depending on the position of the slide tray  161 , it is possible to achieve both the state in which the extension tray  162  can be inserted or drawn out and the state in which the extension tray  162  cannot be disengaged. 
     Third Embodiment 
     Next, a sheet stacking apparatus according to the third embodiment of the present invention will be described with reference to  FIGS. 17A, 17B, 17C, 18 and 19 . In the sheet stacking apparatus of the present embodiment, a restricting portion for restricting the disengagement of the attached third stacking portion is provided on a stacking tray as the first stacking portion. 
       FIG. 17A  shows the state according to the third embodiment, in which the extension tray  172  which is the third stacking member is inserted between the stacking tray  170  which is the first stacking member and the slide tray  171  which is the second stacking member as viewed from the stacking surface.  FIG. 17B  is a diagram showing a bottom view thereof and  FIG. 17C  is a diagram showing a view of the extension tray  172  alone. Further,  FIG. 18  is a diagram showing a view of the state where the extension tray  172  is inserted as shown in  FIG. 17A  as viewed from the back side of the stacking surface. 
     As shown in  FIG. 17C , the inserting portion  172   b  is formed in a thin plate shape on the upstream side of the stacking portion  172   a  of the extension tray  172 . The extension tray  172  can be attached by inserting the inserting portion  172   b  in the gap between the stacking tray  170  and the slide tray  171 . 
     Further, as shown in the partially enlarged view of  FIG. 18 , a restricting member  174  as a restricting portion for restricting the disengagement of the extension tray  172  is attached to the stacking tray  170  by the screw  175 . 
     The restricting member  174  is a plate-like elastically deformable member having spring-like property. As shown in  FIG. 18 , when the slide tray  171  is stored in the stacking tray  170 , the restricting member  174  is urged by the force F in the direction of the arrow as shown in  FIG. 18  and the tip portion  174   a  abuts against the side surface  171   a  of the slide tray  171 . Since the force F by the restricting member  174  is not strong, the slide tray  171  can slide between the storage position and the drawn-out position with the tip portion  174   a  being in contact with the side surface  171   a.    
     Further, the size of the extension tray  172  in the sheet width direction is substantially the same as that of the slide tray  171 , so the extension tray  172  does not protrude from the side of the slide tray  171 . Therefore, in the state in which the slide tray  171  is in the storage position as the non-restricting position and the tip portion  174   a  of the restricting member  174  is in contact with the side surface  171   a  of the slide tray  171 , the extension tray  172  can be inserted and drawn out without being in contact with the restricting member  174 . 
       FIG. 19  is a diagram showing a view of the slide tray  171  in the state where the slide tray  171  is drawn out as viewed from the back side of the stacking surface. As shown in  FIG. 19 , the holding portion  172   c  as a cut out engaging portion is formed at a position which is located on the side surface of the extension tray  172 , which is farther in the insertion direction with respect to the tip portion  174   a  of the restricting member  174  when the extension tray  172  is attached. The holding portion  172   c  is provided at the position where the holding portion  172   c  can be engaged with the tip portion  174   a  when the slide tray  171  is drawn out and the side surface  171   a  moves to a position where the side surface  171   a  is not in contact with the tip portion  174   a  of the restricting member  174  and the force F of the restricting member  174  is released and the tip portion  174   a  goes farther in the inside direction than the side surface  171   a.    
     That is, as shown in  FIG. 19 , when the slide tray  171  moves in the downstream direction, the tip portion  174   a  is not in contact with the side surface  171   a  since the slide tray  171  is not in a position where the slide tray  171  is in contact with the tip portion  174   a . When the side surface  171   a  is not at a position where the side surface  171   a  is in contact with the tip portion  174   a , the force F of the restricting member  174  is released and the tip portion  174   a  of the restricting member  174  goes farther in the inside direction and the tip portion  174   a  moves into the neighborhood of the holding portion  172   c  of the extension tray  172 . In this state, even when a force for disengaging the extension tray  172  (a force in the direction of the arrow in  FIG. 19 ) is applied, the extension tray  172  does not disengage since the tip portion  174   a  abuts against the holding portion  172   c.    
     That is, as shown in  FIG. 18 , when the slide tray  171  is in the non-restricting position, i.e., the position where the slide tray  171  is stored in the stacking tray  170 , the tip portion  174   a  is in contact with the side surface  171   a  and not in contact with the holding portion  172   c  of the extension tray  172  so that the extension tray  172  can be freely inserted and drawn out. On the other hand, as shown in  FIG. 19 , when the slide tray  171  is at the restricting position where the slide tray  171  is drawn out, the tip portion  174   a  is in the vicinity of the holding portion  172   c  of the extension tray  172  and even if such a force in the direction of the arrow is applied that the extension tray  172  is disengaged, the tip portion  174   a  restricts the movement of the holding portion  172   c  so that the extension tray  172  does not disengage. 
     As described above, when the slide tray  171  is stored, the extension tray  172  can be detached and when the extension tray  172  is drawn out, the extension tray  172  does not disengage. Accordingly, the extension tray  172  can be inserted or drawn out into or from the sheet stacking apparatus while the disengagement of the extension tray  172  can be avoided when the extension tray  172  is used. 
     Further, a user can use the extension tray for a long sheet only when the user wishes to use the extension tray and it is possible to prevent the long extension tray from unnecessarily occupying the place when the extension tray is not used. Furthermore, the extension tray does not disengage when it is used. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2016-038572, filed Mar. 1, 2016, which is hereby incorporated by reference herein in its entirety.