Patent Publication Number: US-9409742-B2

Title: Post-processing device controlling accumulation of sheet onto processing tray according to position of stack tray and image forming system including this post-processing device

Description:
INCORPORATION BY REFERENCE 
     This application is based on and claims the benefit of priority from Japanese Patent application No. 2013-250017 filed on Dec. 3, 2013, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a post-processing device performing post-processes to a sheet outputted from an image forming apparatus or the like, and an image forming system including this post-processing device. 
     A post-processing device is connected to an image forming apparatus, such as a copying machine or a printer, to carry-in a sheet outputted from the image forming apparatus after an image is formed on the sheet in the image forming apparatus and to perform post-processes, such as punching process, stapling process and others, to the sheet. The post-processing device temporarily accumulates the carried-in sheet on a process tray and aligns end parts of a predetermined number of the sheets by the process tray, and then, performs the post-processes, such as the stapling process, to these sheets and ejects the post-processed sheet onto a stack tray. There is also a post-processing device lowering the stack tray as the sheet is ejected onto the stack tray. 
     The post-processing device lowers the stack tray in accordance with the ejection of the sheet, not only when ejecting every the predetermined number of the sheets placed on the process tray to the stack tray, but also when ejecting every one sheet to the stack tray. Thereby, the sheet ejected from an ejection port of the post-processing device is stacked at a top face position of the stack tray or at an uppermost position of the sheets stacked on the stack tray. The stack tray is raised and returned to an original position when all the sheets on the stack tray are taken out. 
     However, for example, a time required for raising the stack tray from a lower side to an upper side in its movement path is lengthened compared with a time required for performing the post-processes of one sheet. In the above-mentioned post-processing device, in the middle of the post-processes of many sheets, if the entirety or a part of the sheets stacked on the stack tray are/is taken out, the following post-processed sheet is ejected even through the stack tray is not returned to the original position, i.e. located at the lower side. At this time, because the sheet is ejected in the air above the top face position of the stack tray or the uppermost position of the sheets stacked on the stack tray, the sheet is not suitably stacked and a trouble, such as dropping out from the stack tray, occurs. 
     By contrast, there is a finisher as the post-processing device temporarily accumulating a plurality of sheets outputted from an image forming apparatus on a post-process tray part, performing post-processes to a sheaf of the sheets, and stacking the post-processed sheet sheaf onto a stack tray part (a stack tray) lowering in accordance with carrying-in or stacking of the sheet sheaf. The finisher includes a sheet sheaf stack detecting sensor detecting the sheet on the stack tray part and an elevating function raising the stack tray part to an original position when the sheet sheaf stack detecting sensor detects that the sheet is taken out from the stack tray part. The finisher makes the sheet sheaf wait in the middle of conveyance to the stack tray part until the stack tray part is returned back to the original position after the sheet sheaf on the stack tray part is taken out. The finisher also resumes the conveyance of the sheet sheaf after the return of the stack tray part to the original position. 
     However, in the post-processing device as the above-mentioned finisher, the sheet sheaf stack detecting sensor detects whether or not the sheet is placed on the stack tray. According to this, when a part of the plurality of the sheets on the stack tray is taken out, the sheet sheaf stack detecting sensor cannot detect the taking-out of the part of the sheets. Therefore, in such a case, because the elevating function does not raise the stack tray, it is impossible to suitably stack the post-processed sheets on the stack tray. 
     In the above-mentioned post-processing device, when the entire sheets on the stack tray are taken out in the middle of the post-processes of many sheets, it is necessary to stop outputting the sheet from the image forming apparatus and to stop the post-processes of the post-processing device until the stack tray located at the lower side is raised to the original position. The stopping of works, such as the post processes, during the raising time of the stack tray causes waste of working time. 
     SUMMARY 
     In accordance with an embodiment of the present disclosure, a post-processing device includes a device main body, a processing tray, a placed sheet processing part, a stack tray, a detecting part, a stack tray driving part and a sheet conveying part. The device main body includes a sheet ejection port used for ejecting a sheet. The processing tray is arranged inside the device main body, on which the sheet is temporarily placed. The placed sheet processing part carries out post-process to the sheet in a state of being placed on the processing tray. The stack tray is arranged in the device main body to stack the sheet ejected from the sheet ejection port. The detecting part is arranged in the device main body to detect whether or not a top face of the stack tray or a top face of the sheet stacked on the stack tray is positioned at a detected position below the sheet ejection port. The stack tray driving part is configured so as to move downwardly the stack tray until the detecting part cannot detect the stack tray or the sheet stacked on the stack tray, when the sheet is ejected from the sheet ejection port, and then, to move upwardly the stack tray until the detecting part detects the top face of the stack tray or the top face of the sheet stacked on the stack tray. The stack tray driving part also moves upwardly the stack tray in a case where the detecting part does not detect the stack tray or the sheet stacked on the stack tray, when ejecting the sheet. The sheet conveying part is configured, when the sheet is ejected without the post-process by the placed sheet processing part, in a case where the detecting part detects the stack tray or the sheet stacked on the stack tray, so as to eject the sheet from the sheet ejection port without placing on the processing tray. The sheet conveying part also is configured, when the sheet is ejected without the post-process by the placed sheet processing part, in another case where the detecting part does not detect the stack tray or the sheet stacked on the stack tray, to stop the ejection of the sheet to the stack tray and to place the sheet on the processing tray until the detecting part detects the stack tray or the sheet stacked on the stack tray, and then, to eject the sheet placed on the processing tray from the sheet ejection port to the stack tray after the detecting part detects the stack tray or the sheet stacked on the stack tray. 
     In accordance with an embodiment of the present disclosure, an image forming system includes an image forming apparatus performing image forming process to a sheet and a post-processing device. the post-processing device includes a device main body, a processing tray, a placed sheet processing part, a stack tray, a detecting part, a stack tray driving part and a sheet conveying part. The device main body includes a sheet ejection port used for ejecting a sheet. The processing tray is arranged inside the device main body, on which the sheet is temporarily placed. The placed sheet processing part carries out post-process to the sheet in a state of being placed on the processing tray. The stack tray is arranged in the device main body to stack the sheet ejected from the sheet ejection port. The detecting part is arranged in the device main body to detect whether or not a top face of the stack tray or a top face of the sheet stacked on the stack tray is positioned at a detected position below the sheet ejection port. The stack tray driving part is configured so as to move downwardly the stack tray until the detecting part cannot detect the stack tray or the sheet stacked on the stack tray, when the sheet is ejected from the sheet ejection port, and then, to move upwardly the stack tray until the detecting part detects the top face of the stack tray or the top face of the sheet stacked on the stack tray. The stack tray driving part also moves upwardly the stack tray in a case where the detecting part does not detect the stack tray or the sheet stacked on the stack tray, when ejecting the sheet. The sheet conveying part is configured, when the sheet is ejected without the post-process by the placed sheet processing part, in a case where the detecting part detects the stack tray or the sheet stacked on the stack tray, so as to eject the sheet from the sheet ejection port without placing on the processing tray. The sheet conveying part also is configured, when the sheet is ejected without the post-process by the placed sheet processing part, in another case where the detecting part does not detect the stack tray or the sheet stacked on the stack tray, to stop the ejection of the sheet to the stack tray and to place the sheet on the processing tray until the detecting part detects the stack tray or the sheet stacked on the stack tray, and then, to eject the sheet placed on the processing tray from the sheet ejection port to the stack tray after the detecting part detects the stack tray or the sheet stacked on the stack tray. 
     The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present disclosure is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view schematically showing a post-processing device and a multifunction peripheral including this post-processing device according to an embodiment of the present disclosure. 
         FIG. 2  is a perspective view partially showing the post-processing device according to the embodiment of the present disclosure. 
         FIG. 3  is a sectional view schematically showing the post-processing device, in a situation where a stack tray is located at an original position, according to the embodiment of the present disclosure. 
         FIG. 4  is a sectional view schematically showing the post-processing device, in a situation where a plurality of sheets are stacked on the stack tray, according to the embodiment of the present disclosure. 
         FIG. 5  is a sectional view schematically showing the post-processing device, in a situation where the plurality of sheets are taken out from the stack tray, according to the embodiment of the present disclosure. 
         FIG. 6  is a sectional view schematically showing the post-processing device, in a situation in the middle of raising the stack tray to the original position, according to the embodiment of the present disclosure. 
         FIG. 7  is a sectional view schematically showing the post-processing device, in a situation where the stack tray has been returned to the original position, according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, with reference to the drawings, an embodiment of the present disclosure will be described. In the below-described embodiment, an image forming system includes an image forming apparatus performing image forming process to a sheet and a post-processing device according to the present disclosure. To a multifunction peripheral  1  as the image forming apparatus, the post-processing device  2  according to the present disclosure is applied. In the following, it will be described so that the front side of the plane of  FIGS. 1 and 3-7  correspond to the front side of the multifunction peripheral  1 . An arrow Fr in  FIG. 2  indicates the front side of the multifunction peripheral  1 .  FIG. 1  is a sectional view schematically showing the post-processing device and the multifunction peripheral including this post-processing device according to the embodiment of the present disclosure. The post-processing device  2  is located to a left side (another side) of the multifunction peripheral  1 . 
     First, the multifunction peripheral  1  will be described. As shown in  FIG. 1 , the multifunction peripheral  1  includes a roughly box-formed multifunction peripheral main body  3 . In a lower part of the multifunction peripheral main body  3 , a sheet feeding cassette  4  storing sheets (not shown) is installed. In an upper part of the multifunction peripheral main body  3 , an in-body sheet ejection space is arranged. In the in-body sheet ejection space, a relaying unit  5  constituting a conveying path of the sheet between the multifunction peripheral  1  and post-processing device  2 . On the multifunction peripheral main body  3 , an image reading device  6  including a reading part and a document feeding part is arranged to read a display object of a document as image data. 
     In a center part of the multifunction peripheral main body  3 , an intermediate transferring belt  7  is bridged over a plurality of rollers. Below the intermediate transferring belt  7 , an exposing part  8  composed of a laser scanning unit (LSU) and others is installed. Near the intermediate transferring belt  7 , four image forming parts  9  are installed for respective toner colors (for example, four colors of magenta, cyan, yellow and black) along a lower part of the intermediate transferring belt  7 . Each image forming part  9  is configured so that, around a photosensitive drum, a charging part, a developing part, a first transferring part, a cleaning part and a static eliminating part are located. Above each developing part, a toner container  10  containing a toner of the correspondent toner color is installed. 
     At one side (the right-hand side of the figure) in the multifunction peripheral main body  3 , a conveying path  11  of the sheet is arranged. At an upstream end of the conveying path  11 , the sheet feeding cassette  4  is positioned. At an intermediate stream part of the conveying path  11 , a second transferring part  12  including a part of the intermediate transferring belt  7  is positioned. At a downstream part of the conveying path  11 , a fixing part  13  is positioned. At a downstream end of the conveying path  11 , a multifunction peripheral sheet ejection port  14  is positioned. 
     Next, the relaying unit  5  will be described. The relaying unit  5  includes a relaying sheet feeding port  15 , a plurality of relaying feeding rollers  16  and a relaying sheet ejection port  17 . The relaying sheet feeding port  15  and relaying sheet ejection port  17  are formed so as to respectively open one end (a right side) and another end (the left side) of the relaying unit  5 . 
     The relaying sheet feeding port  15  is located at a position corresponding to the multifunction peripheral sheet ejection port  14  of the multifunction peripheral main body  3  when the relaying unit  5  is installed to the multifunction peripheral main body  3 . The plurality of the relaying feeding rollers  16  constitutes a relaying path  18  of the sheet from the relaying sheet feeding port  15  to the relaying sheet ejection port  17 . The relaying sheet ejection port  17  is located at a left lateral face of the multifunction peripheral main body  3  when the relaying unit  5  is installed to the multifunction peripheral main body  3 . 
     Next, the post-processing device  2  will be described with reference to  FIGS. 1 and 2 .  FIG. 2  is a perspective view partially showing the post-processing device according to the embodiment of the present disclosure. The post-processing device  2  is attached to the left side of the multifunction peripheral main body  3 . 
     The post-processing device  2  includes a roughly box-formed device main body  20 . Below the device main body  20 , leg parts  21  are arranged. That is, the device main body  20  is supported by the leg parts  21 . 
     The device main body  20  includes a post-processing sheet feeding port  22  and a post-processing sheet ejection port (a sheet ejection port)  23 . The post-processing sheet feeding port  22  and post-processing sheet ejection port  23  are formed so as to respectively open one end (the right side) and another end (the left side) of the device main body  20 . 
     Inside the device main body  20 , a punching part  24 , a stapling part  25  and a shifting part  26  are arranged in this order along a conveying path of the sheet from the post-processing sheet feeding port  22  to the post-processing sheet ejection port  23 . The punching part  24  carries out punching process boring a punched hole in the sheet. The stapling part  25  carries out stapling process stapling every a predetermined number of the sheets. The shifting part  26  carries out shifting process shifting every one sheet or every one sheaf of the sheets in a width direction to adjust a position in the width direction of each sheet. The stapling part  25  and shifting part  26  works as a placed sheet processing part carrying out the stapling process and shifting process to the sheet in a state of being placed on a processing tray  28  mentioned below. The device main body  20  may include a sheet folding part carrying out folding process of the sheet or a mechanism having another post-processing function. 
     In addition, inside the device main body  20 , conveying rollers  27 , the processing tray  28  and sheet ejecting rollers  29  are arranged along the conveying path of the sheet and, above the processing tray  28 , an aligning member  30  is arranged. The conveying rollers  27  and sheet ejecting rollers  29  work as a sheet conveying part. The aligning member  30  is configured, for example, so as to come into contact with the sheet conveyed from the conveying rollers  27  and to move and align a rear end of the sheet to a side of the stapling part  25  on the processing tray  28 , when carrying out the stapling process or shifting process by the placed sheet processing part. 
     The conveying rollers  27  are positioned at a downstream side from the punching part  24  and at an upstream side from the stapling part  25  and shifting part in the conveying path of the sheet. The conveying rollers  27  convey the sheet conveyed directly from the post-processing sheet feeding port  22  (the sheet not processed by the punching part  24 ) or the sheet processed by the punching part  24  to the downstream side. 
     The processing tray  28  is positioned at the downstream side from the conveying rollers  27  in the conveying path of the sheet. On the processing tray  28 , the sheet to be processed by the placed sheet processing part composed of the stapling part  25 , shifting part  26  and others is temporarily placed. One end of the processing tray  28  is positioned at a side of the post-processing sheet ejection port  23  and another end of the processing tray  28  is positioned at a side of the stapling part  25 . The rear end of the sheet is put in contact with the other end of the processing tray  28 , and thereby, the rear end of the sheet is aligned. 
     The sheet ejecting rollers  29  are positioned at a side of the one end of the processing tray  28  and configured so as to eject every one sheet or every one sheaf composed of the predetermined number of the sheets placed on the processing tray  28 . The sheet ejecting rollers  29  are constructed, for example, as a pair of the sheet ejecting rollers  29  interposing the sheet placed on the processing tray  28  from an upper side and a lower side so that these sheet ejecting rollers  29  are rotated to eject the sheet. The pair of the sheet ejecting rollers  29  are configured so that one sheet ejecting roller  29  can be moved to be separated from and to come into pressure contact with the other sheet ejecting roller  29 . The one sheet ejecting roller  29  is separated from the other sheet ejecting roller  29 , when placing the sheet onto the processing tray  28 . The one sheet ejecting roller  29  comes into pressure contact with the other sheet ejecting roller  29 , when ejecting the sheet placed on the processing tray  28 , so as to interpose the sheet by an appropriate nip pressure according to the number of the sheets to be ejected. For example, the pair of the sheet ejecting rollers  29  also may come into pressure contact with the sheet and eject the sheet, in a case ejecting the sheet without carrying out the processes by the placed sheet processing part composed of the stapling part  25 , shifting part  26  and others. 
     Outside the device main body  20 , a stack tray  31  stacking the sheet ejected from the post-processing sheet ejection port  23  is arranged so as to protrude outwardly from a left lateral face of the device main body  20 . The stack tray  31  is attached movable in upward and downward directions by a stack tray driving part  33  (refer to  FIG. 2 ). A moving path of the stack tray  31  is arranged to extend in the upward and downward directions below the post-processing sheet ejection port  23 . The stack tray  31  is located, for example, at an original position when the post-processing device  2  is in an original state or in a state not yet stacking the sheet. A level of the original position may be equal to an upper end of the moving path of the stack tray  31 . 
     In addition, outside the device main body  20 , a detecting part  32  is arranged. The detecting part  32  detects whether or not a top face of the stack tray  31  or a top face of the sheet stacked on the stack tray  31  is positioned at a detected position near the post-processing sheet ejection port  23 . For example, a level of the detected position is set approximately equal to the level of the original position of the stack tray  31  and the detecting part  32  is arranged near the upper end of the moving path of the stack tray  31 . The detecting part  32  includes a light emitting part (not shown) emitting a detecting light and a light receiving part (not shown) receiving the detecting light. The light emitting part and light receiving part are arranged so as to face to each other across the detected position. 
     The stack tray driving part  33  is arranged, as shown in  FIG. 2 , in a rear part of the device main body  20 . The stack tray driving part  33  includes, for example, a drive source  34 , such as a motor, a gear box  35 , an upper side pulley  36 , a lower side pulley  37 , a driving belt  38 , a guide part  39  and an attachment part  40 . 
     The stack tray driving part  33  runs every time the predetermined number of the sheets or a sheet sheaf are/is ejected from the post-processing sheet ejection port  23  onto the stack tray  31 . Concretely, the stack tray driving part  33  temporarily moves downwardly (lowers) the stack tray  31  until the detecting part  32  cannot detect the stack tray  31  or the sheet stacked on the stack tray  31 , when the predetermined number of the sheets or a sheet sheaf are/is ejected onto the stack tray  31 . After the stack tray  31  is moved downwardly and stopped, the stack tray driving part  33  moves upwardly (raises) the stack tray  31  until the detecting part  32  can detect the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31 . The stack tray driving part repeats the above-mentioned lowering and raising operations of the stack tray  31  while the sheet or sheet sheaf is ejected onto the stack tray  31 . 
     The gear box  35  includes a plurality of gears (not shown) and is connected to the drive source  34  and upper side pulley  36 . The plurality of gears of the gear box  35  are meshed so as to convert drive force from the drive source  34  to rotation of the upper side pulley  36 . The plurality of gears of the gear box  35  have a speed reduction gear and are configured so as to adjust rotating speed of the upper side pulley  36 . 
     The upper side pulley  36  is arranged above an uppermost position of the moving path of the stack tray  31  and the lower side pulley  37  is arranged below a lowermost position of the moving path of the stack tray  31 . The driving belt  38  is wound around the upper side pulley  36  and lower side pulley  37  and rotated according to the rotation of the upper side pulley  36 . 
     The guide part  39  is formed so as to extend in the upward and downward direction along the driving belt  38 . To the attachment part  40 , the stack tray  31  is attached. The attachment part  40  is attached so as to be fixed to the driving belt  38  and to be engaged with the guide part  39 . The attachment part  40  is moved in the upward and downward direction along the guide part  39  in accordance with the rotation of the driving belt  38 . For example, the guide part  39  is configured as a guide rail with a concave formed section and the attachment part  40  is configured to have a projected shape inserting into the concave formed portion of the guide part  39 . 
     Next, the operation of ejecting the sheet by the post-processing device  2  with such a configuration will be described with reference to  FIGS. 3-7 .  FIG. 3  is a schematic diagram illustrating a situation, where the stack tray is located at the original position, in the post-processing device according to the embodiment of the present disclosure.  FIG. 4  is a schematic diagram illustrating a situation, where the plurality of the sheets are stacked on the stack tray, in the post-processing device according to the embodiment of the present disclosure.  FIG. 5  is a schematic diagram illustrating a situation, where the plurality of sheets are taken out from the stack tray, in the post-processing device according to the embodiment of the present disclosure.  FIG. 6  is a schematic diagram illustrating a situation, where the stack tray is raising toward the original position, in the post-processing device according to the embodiment of the present disclosure.  FIG. 7  is a schematic diagram illustrating a situation, where the stack tray has been returned to the original position, in the post-processing device according to the embodiment of the present disclosure. 
     In the post-processing device  2  in the original state, as shown in  FIG. 3 , since the stack tray  31  is located in the original position (the detected position), the detecting part  32  is detecting the top face of the stack tray  31 . Therefore, the stack tray driving part  33  does not drive the stack tray  31  and the stack tray  31  is stopped at the original position. 
     When the post-processing device  2  runs, the post-processing device  2  performs the post-processes appropriately selected by a user to the sheet S 1  supplied from the multifunction peripheral  1  via the post-processing sheet feeding port  22 . First, the operation in a case of carrying out the stapling process and shifting process by the placed sheet processing part (a first post-processing operation) will be described. In this first post-processing operation, the sheet S 1  conveyed directly from the post-processing sheet feeding port  22  (the sheet S 1  not processed by the punching part  24 ) or the sheet S 1  punching-processed by the punching part  24  is conveyed by the conveying rollers  27 , and then, fed to the processing tray  28  (refer to  FIG. 3 ). At this time, the pair of the sheet ejecting rollers  29  are separated from each other and the sheet S 1  is placed on the processing tray  28  between pair of the sheet ejecting rollers  29 . One sheet S 1  or one sheaf of the sheets S 1  is/are shifted to the side of the stapling part  25  by the aligning member  30 , and then, the stapling process by the stapling part  25  and the shifting process by the shifting part  26  are carried out. After that, the pair of the sheet ejecting rollers  29  come into pressure contact with each other to interpose the sheet(s) S 1  and to eject the sheet(s) S 1  to the post-processing sheet ejection port  23 . The sheet(s) S 1  ejected to the post-processing sheet ejection port  23  is/are placed (stacked) on the stack tray  31  (refer to  FIG. 4 ). 
     When such ejection process is done, the stack tray driving part  33  moves downwardly the stack tray  31  until the detecting part  32  cannot detect the stack tray  31  or the sheet stacked on the stack tray  31 , every time the predetermined number of the sheets or a sheet sheaf are/is ejected onto the stack tray  31 . Subsequently, when the stack tray  31  or the sheet stacked on the stack tray  31  is moved to at a position not detected by the detecting part  32 , the stack tray driving part  33  moves upwardly the stack tray  31  until the detecting part  32  detects the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31 . Thus, it is possible to keep the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31  at the same position (the detected position) always. 
     Next, the operation in a case of not carrying out the stapling process and shifting process by the placed sheet processing part (a second post-processing operation) will be described. In this second post-processing operation, the sheet S 1  conveyed directly from the post-processing sheet feeding port  22  (the sheet S 1  not processed by the punching part  24 ) or the sheet S 1  punching-processed by the punching part  24  is conveyed on by one by the conveying rollers  27 , and then, advanced to the ejection by the post-processing sheet ejection port  23  without placing on the processing tray  28  (refer to  FIG. 3 ). At this time, since sheet S 1  is not placed on the processing tray  28 , the pair of the sheet ejecting rollers  29  come into pressure contact with each other so as to eject the sheet S 1 . The sheet S 1  ejected from the post-processing sheet ejection port  23  is stacked on the stack tray  31  (refer to  FIG. 4 ). 
     Subsequently, in a similar way to the first post-processing operation, according to the predetermined number of the sheets, the stack tray driving part  33  lowers the stack tray  31  until the detecting part  32  cannot detect the stack tray  31  or the sheet stacked on the stack tray  31 , and then, the stack tray driving part  33  raises the stack tray  31  until the detecting part  32  detects the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31 . 
     If such a second post-processing operation is continued to a plurality of the sheets S 2 , as shown in  FIG. 4 , the plurality of the sheets S 2  are stacked on the stack tray  31  and the stack tray  31  is moved lower than the original position by the stack tray driving part  33 . At this time, the detecting part  32  detects the top face of the sheets S 2  stacked on the stack tray  31 . 
     While this second post-processing operation is continued, if the plurality of the sheets S 2  are taken out from the stack tray  31  (refer to  FIG. 5 ), the detecting part  32  cannot detect either of the stack tray  31  and the sheet at the detected position (incidentally, depending on the number of the taken-out sheets, the detecting part  32  may continue to detect the stack tray  31  or sheet). In such a case where the detecting part  32  cannot detect either of the stack tray  31  and the sheet at the detected position, the stack tray driving part  33  raises the stack tray  31  until the detecting part  32  detects the stack tray  31  or the sheet at the detected position. 
     Even if the sheet is taken out from the stack tray  31  and the stack tray  31  is raised while the second post-processing operation is continued as mentioned above, the sheet S 1  supplied from the post-processing sheet feeding port  22  is conveyed via the conveying rollers  27  directly or after the punching process by the punching part  24 . The sheet S 1  conveyed from the conveying rollers  27  during the raising of the stack tray  31  is fed to the processing tray  28  before being ejected onto on the stack tray  31  via the post-processing sheet ejection port  23 . When the stack tray  31  is raised, the pair of the sheet ejecting rollers  29  are separated from each other. Therefore, the sheet S 1  fed to the processing tray  28  is placed on the processing tray  28  between the pair of the separated sheet ejecting rollers  29 . The sheet S 1  placed on the processing tray  28  is shifted to the side of the stapling part  25  by the aligning member  30 . Thus, until the detecting part  32  detects the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31 , a plurality of the sheets S 3  conveyed by the conveying rollers  27  are temporarily placed on the processing tray  28  (refer to  FIG. 6 ). 
     Subsequently, after the stack tray  31  or the sheet stacked on the stack tray  31  is moved to the detected position by raising the stack tray  31 , and then, the detecting part  32  detects the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31 , the stack tray driving part  33  stops the driving of the stack tray  31  (refer to  FIG. 7 ). 
     When the raising of the stack tray  31  is thus finished, the pair of the sheet ejecting rollers  29  come into pressure contact with each other to interpose the plurality of the sheets S 3  placed on the processing tray in a lump and to eject them to the post-processing sheet ejection port  23 . The sheets S 3  ejected from the post-processing sheet ejection port  23  are stacked on the stack tray  31 . The stack tray driving part  33  drives and lowers the stack tray  31  in accordance with the number (height) of the ejected sheets S 3 . Concretely, the stack tray driving part  33  temporarily lowers the stack tray  31  until the detecting part  32  cannot detect the sheets S 3  stacked on the stack tray  31 . The stack tray driving part  33  lowers and stops the stack tray  31 , and then, the stack tray driving part  33  raises the stack tray  31  until the detecting part  32  detects the top face of the sheets S 3  stacked on the stack tray  31 . 
     In accordance with the embodiment, as described above, the post-processing device  2  includes a device main body  20 , a processing tray  28 , a placed sheet processing part composed of the stapling part  25 , shifting part  26  and others, a stack tray  31 , a detecting part  32 , a stack tray driving part  33  and a sheet conveying part composed of the conveying rollers  27  and sheet ejecting rollers  29 . The device main body  20  includes the post-processing sheet ejection port  23  used for ejecting a sheet. The processing tray  28  is arranged inside the device main body  20 , on which the sheet is temporarily placed. The placed sheet processing part carries out post-process to the sheet in a state of being placed on the processing tray  28 . The stack tray  31  is arranged in the device main body  20  to stack the sheet ejected from the post-processing sheet ejection port  23 . The detecting part  32  is arranged in the device main body  20  to detect whether or not a top face of the stack tray  31  or a top face of the sheet stacked on the stack tray  31  is positioned at a detected position below the post-processing sheet ejection port  23 . The stack tray driving part  33  is configured so as to move downwardly the stack tray  31  until the detecting part  32  cannot detect the stack tray  31  or the sheet stacked on the stack tray  31 , when the sheet is ejected from the post-processing sheet ejection port  23 , and then, to move upwardly the stack tray  31  until the detecting part  32  detects the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31 . The stack tray driving part  33  also moves upwardly the stack tray  31  in a case where the detecting part  32  does not detect the stack tray  31  or the sheet stacked on the stack tray  31 , when ejecting the sheet. The sheet conveying part is configured, when the sheet is ejected without the post-process by the placed sheet processing part, in a case where the detecting part  32  detects the stack tray  31  or the sheet stacked on the stack tray  31 , so as to eject the sheet from the post-processing sheet ejection port  23  without placing on the processing tray  28 . The sheet conveying part also is configured, when the sheet is ejected without the post-process by the placed sheet processing part, in another case where the detecting part  32  does not detect the stack tray  31  or the sheet stacked on the stack tray  31 , to stop the ejection of the sheet to the stack tray  31  and to place the sheet on the processing tray  28  until the detecting part  32  detects the stack tray  31  or the sheet stacked on the stack tray  31 , and then, to eject the sheet placed on the processing tray  28  from the post-processing sheet ejection port  23  to the stack tray  31  after the detecting part  32  detects the stack tray  31  or the sheet stacked on the stack tray  31 . 
     By applying such a configuration, even if the sheet stacked on the stack tray  31  is taken out, the stack tray driving part  33  can locate the stack tray  31  so as to align the top face of the stack tray  31  or the top face of the sheet stacked on the stack tray  31  with the detected position near the post-processing sheet ejection port  23  always. Therefore, while the sheet conveyed directly from the post-processing sheet feeding port  22  (the sheet not processed by the punching part  24 ) or the sheet punching-processed by the punching part  24  is ejecting without the processes in the placed sheet processing part composed of the stapling part  25 , shifting part  26  and others, even if the sheet already ejected and stacked on the stack tray  31  is taken out, since the following sheets are temporarily accumulated on the processing tray  28 , it is possible to carry out the sheet ejection process after the stack tray  31  is located at an appropriate position, and then, to suitably stack the sheet on the stack tray  31 . 
     Further, the post-processing device  2  does not stop the conveying operation of the sheet from the multifunction peripheral  1  and post-processing works of the sheet in the raising time of the stack tray  31 . The post-processing device  2  also can immediately carry out the ejection of the sheet accumulated on the processing tray  28  after the raising of the stack tray  31 . Therefore, even if the sheet is taken out from the stack tray  31  in the middle of the ejection of the sheet, no waste of working time occurs. That is, the post-processing device  2  can eject the sheet at an appropriate position always to stack the sheet on the stack tray  31  without stopping the conveying operation and post-processing works of the sheet. 
     In the embodiment, the detecting part  32  is arranged near the upper end of the moving path of the stack tray  31 . Thereby, the detected position of the detecting part  32  is set near the upper end of the moving path of the stack tray  31  and the detecting part  32  can achieve the detection according to the movement of the stack tray  31 . 
     In the embodiment, the detecting part  32  includes the light emitting part emitting the detecting light and the light receiving part receiving the detecting light and the light emitting part and light receiving part are arranged so as to face to each other across the detected position. Thereby, the detecting part  32  can be applied to the post-processing device  2  without needing complicated structure. 
     Although, in the embodiment, the configuration of the post-processing device  2  independently provided from the multifunction peripheral  1  was described, in another embodiment, the post-processing device  2  is provided in the image forming apparatus, such as the multifunction peripheral  1 , or configured so as to be united with the multifunction peripheral  1  or another image forming apparatus. 
     The embodiment was described in a case of applying the configuration of the present disclosure to the post-processing device  2  connected to the multifunction peripheral  1  as the image forming apparatus. On the other hand, in another embodiment, the configuration of the disclosure may be applied to another the post-processing device  2  connected to any of various image reading devices, such as a printer, copying machine or a facsimile. 
     While the present disclosure has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present disclosure.