Patent Publication Number: US-6908078-B2

Title: Sheet processing with sheet inserting device

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet processing device that performs processing such as the sorting and binding of sheets and, more particularly, to sheet conveying sections for conveying sheets to a sheet processing section. Still more particularly, the present invention relates to a sheet processing device capable of keeping large amounts of sheets on standby, irrespective of the size and material of the sheets and without the need to upsize the device itself. 
   2. Description of the Related Art 
   In recent years, some image forming apparatuses such as copy machines, printers, facsimiles, and the like, have a sheet processing device that selectively applies processing such as stapling or saddle stitch bookbinding to sheets having an image formed thereon. 
   In such processing devices, a buffer is provided upstream of the processing section, for keeping a plurality of sheets on standby, whereby processing can be performed without reducing productivity of the image forming apparatus. 
     FIG. 10  shows an image forming apparatus capable of high-speed, large-capacity image formation and having a conventional sheet processing device. Sheets S discharged from an image forming apparatus  100  are conveyed to a sheet processing device  102 , and then aligned by a processing tray  103  provided in the sheet processing device  102 . Thereafter, the sheets are stapled by a stapler  104 , and discharged to a stack tray  105 . 
   While the sheet bundle is being stapled in this manner, subsequent sheets cannot be delivered to the processing tray  103 . In such a case, therefore, after a conveying path has been switched by a flapper  102   a , the sheets are stacked one on top of another, with the front ends thereof aligned, and they are wound around a buffer roller  106 . In this state, the sheets are kept on standby in buffer path Pa. 
   After the above-described sheets having been stapled are discharged to the stack tray  105 , the sheets in buffer path Pa are conveyed to the processing tray section  103  in a stacked state. By repeating this operation, the stapling treatment can be performed without reduction in productivity of the image forming apparatus  100 . 
   In  FIG. 10 , reference numeral  114  denotes an inserter for setting sheets that are not to be printed on, references  107   a  and  107   b  are accommodating sections provided in the inserter  114 , and reference numeral  115  denotes a feed section for feeding sheets S accommodated in the accommodating sections  107   a  and  107   b.    
   Here, the inserter  114  is for accommodating sheets S 1  to be inserted in the accommodating sections  107   a  and  107   b , and conveying them to the sheet processing device  102 , while merging therewith the sheets S from the image forming section  100 A. For example, the merging occurs when the present image forming apparatus  100  is dedicated to a black-and-white printer, and color print sheets are to be inserted into a bound book, or when sheets to be inserted are specific sheets (e.g., heat-sensitive sheets) that cannot be passed through the image forming section  100 A of the present image forming apparatus  100 . 
   In  FIG. 10 , reference numeral  108  denotes a saddle stitching section that performs processing from stapling to bundle folding on-line. The sheet processing device  102  connected to the above-described high-speed, large-capacity image forming apparatus  100  includes, besides the saddle stitching section  108 , a “perfect binding” bookbinder that binds a book by pasting a spine to an aligned sheet bundle, and an offset stacker that performs only sorting and alignment on-line, with the bookbinding operation being conducted off-line. These may be connected to the system for use, depending on the purpose for using. 
   However, such a conventional sheet processing device has involved a problem in that the device itself increases in size because it has therein a buffer path Pa. 
   Specifically, under the size condition of the buffer roller  106  shown in  FIG. 10 , large-sized sheets such as A 3  or B 4  cannot be wound around the buffer roller  106 . When attempting to keep large-sized sheets on standby, a larger buffer roller is required. 
   Also, when attempting to wind thick sheets around the buffer roller  106 , high stiffness of the thick sheets increases the conveyance resistance, thereby causing skewing or jamming of the sheets. Furthermore, when the buffer path Pa is formed by the buffer roller  106 , there is a limit to the number of sheets to be stacked, because sheets are stacked while being conveyed in the buffer path Pa with a curvature. This might reduce the productivity of the image forming apparatus when performing time-consuming processing such as “perfect binding” book-binding. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a sheet processing device capable of keeping large amounts of sheets on standby, irrespective of the size and material of the sheets and without the need to upsize the device itself. 
   In one aspect of the invention, there is provided a sheet processing device that includes a sheet conveying section that conveys a sheet from an image forming apparatus; a sheet processing section that processes sheets conveyed from the sheet conveying section; and a sheet inserting device disposed between the image forming apparatus and the sheet processing section and including sheet accommodating sections for accommodating sheets that are not to be passed through the image forming apparatus, and paper feed means for feeding the sheets accommodated in the sheet accommodating section to the sheet conveying section in a predetermined order. The paper conveying section has a sheet standby unit including stacking means that stacks a predetermined number of sheets one on top of another, in a linear state with the ends thereof aligned, and bundle conveying means that conveys the stacked sheet bundle. 
   In the sheet processing device according to the present invention, it is preferable that the stacking means include an abutting section for aligning the ends of the sheets; abutting means for abutting a sheet against the abutting section; and hold-down means for holding down the end of the sheet abutted against the abutting section, opposite to the abutting section. It is also preferable that, after having held down the end of the sheet by the hold-down means, the stacking means superimpose a next sheet over the above-described sheet. 
   Preferably, the sheet processing device according to the present invention further includes a moving stage that supports the abutting section and the abutting means, and a reciprocating unit for reciprocal moving of the moving stage along the sheet conveying direction. 
   In the sheet processing device according to the present invention, it is preferable that the reciprocating unit move the moving stage an amount in accordance with a length of the sheet in the sheet conveying direction. 
   Preferably, the sheet processing device according to the present invention further includes a moving stage that supports the hold-down means, and a reciprocating unit for reciprocal moving of the moving stage along the sheet conveying direction. 
   In the sheet processing device according to the present invention, it is preferable that the reciprocating unit move the moving stage between a position where the hold-down means is away from the sheet and a position where the hold-down means holds down the end of the sheet. 
   In the sheet processing device according to the present invention, the sheet conveying section may comprise a sheet conveying path through which a sheet conveyed to the sheet processing section passes, and that the sheet standby unit be disposed in the sheet conveying path. 
   In the sheet processing device according to the present invention, the hold-down means may be a flapper that is turnable upward and downward, and that holds down the end of the sheet by turning downward. 
   In the sheet processing device according to the present invention, the sheet conveying section may comprise a sheet conveying path through which a sheet conveyed to the sheet processing section passes, and that the sheet standby unit be provided in an intermediate tray disposed above or below the sheet conveying path. 
   The sheet processing device according to the present invention further includes detecting means provided upstream of the sheet conveying path in the sheet conveying direction for detecting multi-feed, skewing of sheets, and/or image anomalies thereon, and preferably, the sheet processing device selectively introduces the sheets into the intermediate tray based on the detection results by the detecting means. 
   In the sheet processing device according to the present invention, the sheet processing section may be disposed either above or below the sheet standby unit. 
   In the sheet processing device according to the present invention, preferably, the sheet standby unit is disposed downstream of the sheet inserting device in the sheet conveying direction. 
   In the sheet processing device according to the present invention, it is preferable that the sheet conveying section be positioned to convey a sheet from the image forming apparatus to the sheet processing section. 
   In the sheet processing device according to the present invention, the sheet conveying section may be constituted of a plurality of sheet conveying sections so as to form a linear sheet conveying path. 
   In the sheet processing device according to the present invention, the abutting means may be formed of at least one paddle. 
   Thus, by providing the sheet standby unit in the sheet conveying section for conveying sheets to the sheet processing section, stacking a predetermined number of sheets in an aligned state, and thereafter conveying them to the sheet processing section, it is possible to keep large amounts of sheets on standby, irrespective of the size and material of the sheets and without the need to upsize the device itself. 
   Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view showing the construction of an image forming apparatus having a sheet processing device according to a first embodiment of the present invention. 
       FIGS. 2A and 2B  are a plan view and schematic diagram, respectively, of a sheet standby section provided in the sheet processing device shown in FIG.  1 . 
       FIGS. 3A  to  3 E are schematic diagrams illustrating a sheet stacking operation of the sheet standby section shown in  FIGS. 2A and 2B . 
       FIGS. 4A  to  4 C are schematic diagrams illustrating a bundle conveying operation of the sheet standby section. 
       FIGS. 5A and 5B  are schematic diagrams illustrating movements of a moving stage in the sheet standby section, in which the movement thereof changes depending on the sheet size. 
       FIGS. 6A  to  6 E are schematic diagrams illustrating a sheet stacking operation in the sheet standby section of a sheet processing device according to a second embodiment of the present invention. 
       FIGS. 7A and 7B  are schematic diagrams illustrating movements of the moving stage in the sheet standby section, in which the movement thereof changes depending on the sheet size. 
       FIG. 8  is a schematic view showing the construction of an image forming apparatus having a sheet processing device according to a third embodiment of the present invention. 
       FIG. 9  is a schematic view showing the construction of an image forming apparatus having a sheet processing device according to a fourth embodiment of the present invention. 
       FIG. 10  is a schematic view showing the construction of a conventional image forming apparatus with a sheet processing device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, the embodiments according to the present invention will be described with reference to the accompanying drawings. 
     FIG. 1  is a schematic view showing the construction of an image forming apparatus having a sheet processing device according to a first embodiment of the present invention. 
   Referring to  FIG. 1 , reference numeral  1  denotes an image forming apparatus, reference numeral  1 A denotes the main body of the image forming apparatus, and reference numeral  14  denotes an inserter, which is a sheet inserting device provided adjacent to and downstream of the image forming apparatus  1 , and reference numerals  15  and  16 , respectively, denote a staple stacker and saddle stitch stacker, each of which constitutes a sheet processing device provided downstream of the inserter  14 . 
   Here, the image forming apparatus  1  includes an image forming section  1 B comprising a photosensitive drum  10 , fixing section  11  and so-on; and a sheet feeding section  1 C that feeds sheets S accommodated in cassettes  1   a  to the image forming section  1 B. 
   When forming an image, laser light is first applied on the photosensitive drum  10  to form an electrostatic latent image on the photosensitive drum  10 , and thereafter, the electrostatic latent image is visualized. Also, sheets S are fed from the cassettes  1   a  or from a double-sided conveying path  12  at a timing in synchronization with the start of application of the laser light. 
   Next, the sheet S is conveyed between the photosensitive drum  10  and a transfer roller  10   a , and when the sheet S passes therebetween, a developer image is transferred on the sheet by the transfer roller  10   a . Then, the sheet on which the developer image has been transferred is conveyed to the fixing section  11 , and the developer image is fixed on the sheet by applying heat and pressure at the fixing section  11 . 
   Thereafter, the sheet S on which the developer image has been fixed is discharged toward the inserter  14  through a flapper (not shown) and a discharge roller. When forming images on both sides of the sheet S, the sheet S is introduced into the double-sided conveying path  12  by a switching operation of the flapper, and thereafter the sheet S is again conveyed between the photosensitive drum  10  and the transfer roller  10   a  at the aforementioned timing. 
   In  FIG. 1 , reference numerals  13   a ,  13   b , and  13   c  denote plural (three, in this embodiment) sheet conveying sections provided downstream of the image forming apparatus  1 . The sheet conveying sections  13   a ,  13   b , and  13   c  forms a linear-shaped sheet conveying path Pc extending in substantially horizontal direction for conveying sheets S. 
   The portion below the sheet conveying section  13   a , which is the nearest to the image forming apparatus  1 , includes an inserter  14  comprising two sheet accommodating sections  14   a  and  14   b  where inserted sheets S 1  that are not to be printed, that is, ones that are not to be passed through the image forming apparatus  1 , are set, and a sheet feed section  14   c , which may serve as paper feed means for conveying sheets accommodated in the sheet accommodating sections  14   a  and  14   b  in a predetermined order. Here, the group of sheet accommodating sections  14   a  and  14   b  and the sheet feed section  14   c  in the inserter  14  have the same construction as that of the group of the cassettes  1   a  and the sheet feed section  1 C in the image forming apparatus  1 . The former and the latter groups maintain compatibility with each other. 
   The portion below the sheet conveying sections  13   b  and  13   c , which is located downstream of the sheet conveying section  13   a , includes a staple stacker  15  comprising a stapler  20 , container  21 , paddle device  19  and the like, which constitute the sheet processing section, for performing alignment and sorting of a sheet bundle and loading them; and a saddle stitch stacker  16  comprising a stapler  22  for stapling sheets at two portions at the center thereof, and a folding device  23  for folding the sheets at the central portion thereof and discharging the sheets to a folding stacker  24 , the stapler  22  and folding device  23  constituting the sheet processing section. 
   With these features, the inserted sheets S 1  accommodated in the sheet accommodating sections  14   a  and  14   b  of the inserter  14  are inserted between sheets S passed through the image forming apparatus  1  via the sheet conveying path Pc in a predetermined order, and these sheets including S 1  and S are conveyed to the staple stacker  15  or the saddle stitch stacker  16  according to a set mode, such as the stapling mode or the bookbinding mode. 
   The sheets S and S 1  conveyed to the staple stacker  15  are conveyed to a feed roller  17  and onto a processing tray  18 . Then, they are abutted against the stapler  20  by the paddle device  19  for alignment. Thereafter, the staple stacker  15  staples the sheets S and S 1  thus aligned by the stapler  20 . After the completion of this stapling treatment, the stapler  20  is moved, and the sheets S and S 1  are discharged onto the container  21 . As the loading goes on, the container  21  gradually descends. After the container is chock-full loaded with the sheets, it is pulled out toward the front, whereby the sheets can be conveyed in a next process. 
   On the other hand, the sheets conveyed to the saddle stitch stacker  16  are firstly stapled at two portions at the center thereof by the stapler  22 , and then, after having been folded by the folding device  23  at the center portion thereof, the sheets are discharged onto the stacker  24 . 
   In  FIG. 1 , reference  9  denotes a sheet standby section, which may serve as a sheet standby unit provided in the sheet conveying section  13   a . The sheet standby section  9  is configured to be able to keep a predetermined number of sheets S and S 1  conveyed from the image forming apparatus  1  and the inserter  14 , on standby in a stacked state, while the staple stacker  15  or saddle stitch stacker  16  (hereinafter, these are collectively referred to as the “staple stacker  15  or the like”) is performing processing. 
   As shown in  FIG. 2A and 2B , the sheet standby section  9  includes a swinging guide  28  that is supported so as to be turnable about a support shaft  38 ; a rear-end flapper  26 , which is hold-down means turned upward about a support shaft  37  by a solenoid  27 ; a delivery roller  25 ; shutters  32 , which form an abutting section turnably provided, a paddle  31 , which is abutting means for abutting the sheets S and S 1  delivered by the delivery roller  25  against the shutters  32 , and stacking means  9 A that stacks sheets S one on top of another, in a linear state and in a manner such as to keep the ends thereof aligned. 
   As shown in  FIG. 2A , the turning end of the swinging guides  28  is cut in into a comb shape, so that, when the rear-end flapper  26  turns, it is not hindered from turning by the swinging guide  28 . 
   The sheet standby section  9  is retained by an arm  35 , and includes a bundle conveying rollers  33  that turns about a fulcrum  35   a  in interlock with the shutters  32 , a discharge rollers  44  for discharging sheets, and bundle conveying means  9 B for conveying a stacked sheet bundle. 
   Next, stacking operation in the sheet standby section  9  with these features will be described. 
   First, for example, a sheet S delivered from the image forming apparatus  1  (image forming section  1 B) is conveyed by the delivery roller  25  and passes through the rear-end flapper  26 , as shown in FIG.  3 A. Thereafter, the sheet S is conveyed until the front end thereof is abutted against the shutters  32  by the paddle  31 , as shown in FIG.  3 B. 
   When a detection sensor (not shown) detects that the front end of the sheet S has been abutted against the shutters  32 , a control section (not shown) turns on the solenoid  27 , whereby the rear-end flapper  26  turns upward about the support shaft  37  and lifts the rear end of the sheet, as shown in FIG.  3 C. 
   Usually, the swinging guide  28  is locked by a stopper (not shown) under the self weight thereof, and is on standby at a position shown in FIG.  3 B. However, when the rear-end flapper  26  turns upward and consequently the sheet rear end is lifted, the rear-end flapper  26  is also lifted together with the sheet rear end, as shown in FIG.  3 C. 
   Thereafter, when the rear-end flapper  26  continues turning, and the front end thereof disengages from the sheet rear end, the sheet rear end is without support and descends, so that the swinging guide  28  also descends. As a result, the sheet S is regulated downward by the swinging guided  28 , as shown in FIG.  3 D. 
   When the solenoid is turned off after the sheet S has been regulated downward by the swinging guide  28 , the rear-end flapper  26  turns downward, and as shown in  FIG. 3E , it returns to its original position while holding down the sheet rear end from above. 
   Now, when a next sheet S 2  is conveyed after the rear-end flapper  26  has thus returned to the original position, the newly conveyed sheet S 2  passes over the top surface of the rear-end flapper  26 , and is delivered onto the previously conveyed sheet S. The sheet S 2  is superimposed over the sheet S with the front ends thereof kept aligned and in a linear state. 
   This operation is repeated until processing of a preceding sheet bundle by the staple stacker  15  and the like disposed downstream of the inserter  14  in the conveying direction is completed, and a delivery of a subsequent sheet bundle to the staple stacker  15  and the like becomes possible. As a result, the sheet S can be kept on standby without stopping image forming operation. This prevents a reduction in productivity of the image forming apparatus  1 . 
   In this manner, by providing the sheet standby section  9  on the downstream side of the inserter  14 , it is possible to accommodate a front cover and slip sheets used when performing bookbinding treatment, in the sheet accommodating sections  14   a  and  14   b  of the inserter  14 , and also to keep these cover and slip sheets on standby. This increases efficiency in bookbinding treatment. 
   Now, a bundle conveying operation after the sheet bundle has thus been kept on standby, will be described with reference to  FIGS. 4A ,  4 B and  4 C. 
   When the processing of the preceding sheet bundle by the staple stacker  15  and the like has been completed, the delivery of the subsequent sheet bundle to the staple stacker  15  and the like becomes possible, and as shown in  FIG. 4A , the stacking of the sheets S has been completed, the shutters  32  turn about the support shaft  32   a , and retreats downward as shown in FIG.  4 B. 
   At this time, the bundle conveying rollers  33  retained by the arm  35  turns about the fulcrum  35   a  in interlock with shutters  32 , and is brought into pressure contact with the sheets S. Thereafter, the stacked sheet bundle is delivered to the staple stacker  15  and the like by the bundle conveying rollers  33  and discharge rollers  44 , as shown in FIG.  4 C. 
   In the present embodiment, the paddle  31 , shutters  32 , bundle conveying rollers  33 , and discharge rollers  44  are fixed to (held by) a moving stage  30  shown in FIG.  2 B. By a motor  34  and rack  30   a , the moving stage  30  is allowed to reciprocate according to the sheet size, along a guide plate  36  in the right and left direction, which is the sheet conveying direction. This makes it possible for the shutters  32  to move to the sheet front-end abutting position according to the sheet size. Here, the guide plate  36  has therein a slit  36   a  in order to prevent movements of the paddle  31 , rollers  33  and  44 , and shutters  32  from being hindered by the guide plate  36 . 
     FIGS. 5A and 5B  illustrates movements of the moving stage  30 .  FIG. 5A  shows a state in which the moving stage  30  has been moved to the left to accommodate large-sized sheets that have been stacked. On the other hand,  FIG. 5B  shows a state in which the moving stage  30  has been moved to the right by the motor  34  and small-sized sheets have been stacked. 
   In this manner, by providing the sheet standby section  9  in the sheet conveying section  13   a , stacking a predetermined number of sheets in a linear state, and then conveying them to the staple stacker  15  or the like, an increase in conveyance resistance can be inhibited even when the sheets has high stiffness. This prevents the occurrence of skewing or jamming of the sheets. 
   Also, since the number of sheets to be stacked can be increased, there is no risk of a reduction in productivity of the image forming apparatus  1  even when performing time-consuming processing, such as “perfect binding” bookbinding, in which binding is conducted using an adhesive without employing strings or wires. Furthermore, providing the sheet standby section  9  in an ordinary sheet conveying path, as in the present embodiment, enables the downsizing of the device. 
   Next, a second embodiment according to the present invention will be described. 
     FIGS. 6A  to  6 E are diagrams explaining the arrangement of a sheet standby section according to the second embodiment. In  FIGS. 6A  to  6 E, the same reference numerals denote the same or equivalent parts as those in  FIGS. 2A and 2B . 
   Referring to  FIGS. 6A  to  6 E, reference numeral  39  denotes a moving stage moveable in the right and left direction. The moving stage  39  has the rear-end flapper  26  and solenoid  27 . In this embodiment, the sheet rear end is held down by reciprocating, by the motor  40 , the rear-end flapper  26  together with the moving stage  39  in the right and left direction. 
   Now, sheet stacking operation in this embodiment will be described. 
   First, a sheet S delivered from the image forming apparatus  1 B is conveyed by the delivery roller  25  and passes over the rear-end flapper  26 , as shown in FIG.  6 A. Next, the sheet S is abutted against the shutters  32  by two paddle devices  31 , as shown in FIG.  6 B. Then, the moving stage  39  is moved to the right by the motor  40  as shown in  FIG. 6C , and thereafter, when the sheet rear end passes the rear-end flapper  26 , the flapper  26  is turned upward by the solenoid  27 , as shown in FIG.  6 D. 
   With the rear-end flapper  26  turned upward, the moving stage  39  is moved to the left, and then, as shown in  FIG. 6E , the sheet rear end is held down from the top surface thereof by lowering the rear-end flapper  26 . In this state, the moving stage waits for the delivery of the next sheet. 
   After a predetermined number of sheets are stacked by repeating the above-described operation, the shutters  32  is opened by the same procedure as that of the above-described first embodiment, and the sheet bundle is conveyed to the staple stacker  15  and the like. 
     FIGS. 7A and 7B  illustrate movements of the moving stage  39  according to the sheet size.  FIG. 7A  shows a position of the moving stage  39  when large-sized sheets are loaded, while  FIG. 7B  shows a position thereof when small-sized sheets are loaded. 
   Next, a third embodiment according to the present invention will be described. 
     FIG. 8  is a schematic view showing the construction of an image forming apparatus having a sheet processing device according to the third embodiment. In  FIG. 8 , the same reference numerals denote the same or equivalent parts as those in FIGS.  1 . 
   Referring to  FIG. 8 , reference numeral  41  designates an intermediate tray disposed below the sheet conveying path PC. In this embodiment, the intermediate tray  41  has the sheet standby section  9 , and is arranged to stack sheets and be on standby. In  FIG. 8 , reference numeral  42  designates a plurality of path switching flappers provided in the sheet conveying path Pc. A sheet passing through the sheet conveying path Pc is delivered into the intermediate tray  41  by turning downward a predetermined path switching flapper  42  according to the size of sheet. 
   A plurality of sheets is stacked one on top of another by the switching of the path switching flapper  42 , in a linear state and so as to align the ends thereof, and thereafter, as in the case of the above-described first embodiment, the sheets are discharged to a sheet processing device  50  by the bundle conveying rollers  33  and discharge rollers  44 . 
   Furthermore, providing another intermediate tray  41  for sheet standby, disposed in parallel with the substantially horizontal sheet conveying path Pc, enables more sheets, or various sheets such as cardboards or the like to be kept on standby. 
   In this embodiment, the intermediate tray  41  has been disposed below the sheet conveying path Pc, but it may also be disposed above the sheet conveying path Pc. 
   If it is arranged that sheets are conveyed to the intermediate tray  41  when multi-feed, skewing of sheets, and/or image anomalies thereon are detected by a sensor (not shown) that is provided upstream of the sheet conveying section  13   b  in the conveying direction for detecting multi-feed, skewing of sheets and/or image anomalies thereon, it becomes possible to use the intermediate tray  41  as an anomalous sheet standby tray. 
   Next, a fourth embodiment according to the present invention will be described. 
     FIG. 9  is a schematic view showing the construction of an image forming apparatus having a sheet processing device according to the fourth embodiment. In  FIG. 9 , the same reference numerals denote the same or equivalent parts as those in FIGS.  1 . 
   In this embodiment, a paper feed port  14   d  of the inserter  14  is located on the left side of the inserter  14 , and a delivery port  14   e  to the staple stacker  15  is also located on the left side thereof. With these arrangements, when image forming is started from the top page, sheets each having an image formed on the top surface thereof in the image forming section  1 B are automatically loaded in a state collated by page with the image surfaces thereof placed face down in the staple stacker  15 . It is therefore unnecessary to reverse the sheet surfaces for each of the sheets. 
   Even when a printed sheet is set in the inserter  14 , the top surface side thereof can be set as a printed surface. This improves the operationality in sheet setting. In this embodiment, in order that a sheet from the inserter  14  can also be kept on standby as required, the sheet standby section  9  is disposed above the staple stacker  15  located upstream of the saddle stitch stacker  16 . 
   In this way, by providing the sheet standby section  9  on the downstream side of the inserter  14 , it is possible to accommodate a front cover and slip sheets used when performing bookbinding treatment, in the sheet accommodating sections  14   a  and  14   b  of the inserter  14 , and also to keep these cover and slip sheets on standby. This provides increased efficiency in bookbinding treatment. 
   While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.