Patent Publication Number: US-6991225-B2

Title: Sheet process device once stacking received sheets on first stack means and then transferring them to second stack means

Description:
This is a divisional application of U.S. patent application Ser. No. 09/178,481, filed on Oct. 26, 1998 now U.S. Pat. No. 6,517,065. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet process device which once stacks received sheets of paper (simply referred as “sheets” hereinafter) on a first stack means and then shifts the stacked sheets to a second stack means. 
   2. Related Background Art 
   Conventionally, a device consisting of a combination of a process tray and a stack tray has been known as a sheet process device used in an image formation apparatus such as a copy machine, a printer or the like. On the process tray, sheets are stapled according to necessity. On the stack tray, sheets are received and stacked each sheaf. 
   In this sheet process device, a stapler to staple the sheets and a jogger to adjust or align the sheets with movement in front and rear directions are provided on the periphery of the process tray. Sheaves of sheets are adjusted on the process tray, the adjusted sheaves are respectively stapled, and the stapled sheaves are then discharged to the stack tray by a pair of sheaf discharge rollers. 
   Then, the stack tray is moved in forward and reverse directions (i.e., sheet-width direction) for each sheaf to sort over the sheaves of sheets. Moreover, the stack tray can be moved in upward and downward directions to fit a sheet face to the discharge roller. 
   However, the conventional sheet process device has following problems, and thus solutions for these problems have been earnestly expected. That is, in case of discharging the sheaf of sheets (paper) not yet stapled, if such the sheaves stacked on the process tray in large quantities are discharge at a time, the sheaves of sheets on the stack tray are off the alignment, whereby it becomes difficult to sort the sheets. 
   Further, in order to avoid a situation that, while the sheaves of sheets not stapled yet and stacked on the process tray are discharged to the stack tray, next or following sheets are fed to the process tray, it is necessary to temporarily stop an operation of the image formation apparatus itself during the sheet discharge operation. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a sheet process device which can solve the above conventional drawbacks. 
   Another object of the present invention is to provide a sheet process device in which sheaves of sheets can be discharged without the sheaves stacked on the stack tray being off the alignment. 
   Still another object of the present invention is to provide a sheet process device in which sheaves of sheets stacked on a process tray can be discharged to a stack tray without next or following sheets being fed to the process tray while the current sheets on the process tray are discharged and without an image formation apparatus itself being stopped. 
   In one embodiment, the sheet process device of the present invention comprises first stack means for stacking thereon discharged sheets, second stack means for stacking thereon the sheets transferred from the first stack means, and a transfer unit for transferring the sheets from the first stack means to the second stack means. In addition, the device comprises transfer control means for driving, when a size of the sheet discharged to the first stacking means is equal to or smaller than a predetermined size, the transfer unit in accordance with stacking of the first predetermined number of sheets on the first stacking means, and for driving, when the sides of the sheet discharged to the first stacking means is larger than a predetermined size, the transfer unit in accordance with stacking of a predetermined number of sheets smaller than the predetermined number of sheets on the first stack means. 
   Other objects and features of the present invention will become apparent from the following detailed description and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view showing structures of an image formation apparatus and a sheet process device according to an embodiment of the present invention; 
       FIG. 2  is a sectional view showing a structure of a finisher  500  shown in  FIG. 1 ; 
       FIG. 3  is a block diagram showing a structure of a controller in the image formation apparatus shown in  FIG. 1 ; 
       FIG. 4  is a block diagram showing a structure of an image signal control unit  203  shown in  FIG. 3 ; 
       FIGS. 5A ,  5 B,  5 C and  5 D are views showing relation between a state that an original is set and a state that a sheet on which an original image has been formed is discharged; 
       FIG. 6  is a view showing a flow of the sheet in the finisher in a nonsort mode; 
       FIG. 7  is a view showing a flow of the sheet in the finisher in a staple-sort mode; 
       FIG. 8  is a view showing a flow of the sheet in the finisher in the staple-sort mode; 
       FIG. 9  is a view showing a flow of the sheet in the finisher in the staple-sort mode; 
       FIG. 10  is a view showing a flow of the sheet in the finisher in the staple-sort mode; 
       FIG. 11  is a view showing a flow of the sheet in the finisher in the staple-sort mode; 
       FIG. 12  is a view showing a state that the sheet is discharged onto a process tray; 
       FIG. 13  is a view showing a state that the sheet is discharged onto the process tray; 
       FIGS. 14A and 14B  are views showing a state that the sheet is discharged onto the process tray; 
       FIG. 15  is a view showing a flow of sheets in the finisher in a sort mode; 
       FIG. 16  is a view showing a flow of the sheets in the finisher in the sort mode; 
       FIG. 17  is a view showing a state that sheaves of sheets are stacked on a stack tray; 
       FIG. 18  is a view showing an adjustment operation; 
       FIG. 19  is a view showing the adjustment operation; 
       FIG. 20  is a view showing the adjustment operation; 
       FIG. 21  is a view showing an adjustment position in a two-point binding mode; 
       FIG. 22  is a view showing an adjustment position in a front-oblique binding mode; 
       FIG. 23  is a view showing an adjustment position in a rear-oblique binding mode; 
       FIG. 24  is a flow chart showing a procedure in an operation mode discrimination process; 
       FIG. 25  is a flow chart showing a procedure in a nonsort process; 
       FIG. 26  is a flow chart showing a procedure in a sort process; 
       FIG. 27  is a flow chart showing a procedure in a staple-sort process; 
       FIG. 28  is a flow chart showing a procedure in a sort sheet sequence process; 
       FIG. 29  is a flow chart showing a procedure in a paper attribute discrimination process; 
       FIG. 30  is a flow chart showing a procedure in the paper attribute discrimination process subsequent to the procedure shown in  FIG. 29 ; 
       FIG. 31  is a flow chart showing a procedure in a sheaf discharge operation discrimination process; 
       FIG. 32  is a flow chart showing a procedure in a staple process; and 
       FIGS. 33A ,  33 B and  33 C are views showing a concrete example of a sheaf discharge operation. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
   The embodiment of a sheet process device according to the present invention will be explained hereinafter. The sheet process device in the embodiment is installed to an image formation apparatus, and processes or handles sheets discharged from the image formation apparatus. 
   Initially, a body of the image formation apparatus will be explained.  FIG. 1  is a sectional view showing structures of the image formation apparatus and the sheet process device according to the embodiment. 
   As shown in  FIG. 1 , an image formation apparatus  100  mounts thereon an automatic original feed unit  101 . The unit  101  feeds a setting original leftward from its initial page one by one in due order, carries the fed original from left to right above a previously set running read position on a platen glass  102  through a curved path, and then carries the original outward. At a time when the original carried from left to right passes through the running read position on the glass  102 , an image on this original is read by a scanner unit  104  supported at a position corresponding to the running read position. Concretely, when the original passes through the running read position, a face of the original to be read (referred as read face hereinafter) is illuminated by light from a lamp  103  of the scanner unit  104 , and reflected light from the read face of the original is guided to a lens  108  through mirrors  105 ,  106  and  107 . The light passed through the lens  108  is color separated by an RGB color separation filter and then visualized as an image on an image pickup face of an image sensor unit  109 . 
   By carrying the original from left to right such that it passes through the running read position, an original reading scan is performed. In this scan, it should be noted that a direction perpendicular to an original carrying direction is considered as a main-scan direction and the original carrying direction itself is considered as a sub-scan direction. That is, at the time when the original passes through the running read position, the original image is read line by line in the main-scan direction by the image sensor unit  109 , and simultaneously the original is carried in the sub-scan direction, so that the whole original image is read. Further, the optically read image is converted into image data and outputted by the image sensor unit  109 . The image data outputted from the unit  109  is subjected to a predetermined process, and then the obtained data is inputted to an exposure control unit  110  as a video signal. 
   In a case where the original image is read without using the automatic original feed unit  101 , the scanner unit  104  is moved from left to right to scan the original in a state that the original mounted on the platen glass is at rest, thereby reading the original image (original fixation read). 
   The exposure control unit  110  modulates and outputs laser beam on the basis of the inputted video signal, and the laser beam is irradiated onto a photosensitive drum  111  in a scanning manner. Thus, an electrostatic latent image according to the laser beam is formed on the drum  111 . In this case, the unit  110  outputs the laser beam such that a correct image (i.e., not mirror image) is formed in case of the original fixation read. 
   The electrostatic latent image on the photosensitive drum  111  is visualized as a development-agent image by means of development agents respectively supplied from development units  112  and  113 . Further, the sheet is fed from a cassette  114 , a cassette  115  or a manual paper feed unit  125  at timing synchronous with start of laser beam irradiation, and the fed sheet is carried between the photosensitive drum  111  and a transfer unit  116 . Then, the development-agent image formed on the drum  111  is transferred onto the fed sheet by the transfer unit  116 . 
   The sheet onto which the development-agent image has been transferred is carried to a fixing unit  117 , and the unit  117  fixes the development-agent image to the sheet by heat pressing. The sheet passed through the unit  117  is discharged outward by discharge rollers  118 . In a case where double-face recording has been set, it is controlled that the sheet is guided to reverse paths  122  and  123  by a switching operation of a flapper  121 , carried to a paper refeed carry path  124 , and then again fed between the photosensitive drum  111  and the transfer unit  116  at the above timing. Further, in a case where a face of the sheet on which the image is formed (referred as image-formed face hereinafter) is reversed and discharged, it is controlled that the sheet is once guided into the reverse paths  122  and  123  by the switching operation of the flapper  121 , carried toward the discharge rollers  118  by the switching operation of the flapper  121 , and then discharged outward through the rollers  118 . Hereinafter, such the control is called as a reverse paper discharge control. By the reverse paper discharge control, the sheet can be discharged in such a state as its image-formed face is turned downward. 
   As shown in the drawing, in a case where a later-described sheet process device (referred as finisher hereinafter)  500  is installed to the image formation apparatus  100 , the apparatus is set to perform such the reverse paper discharge control. 
   Subsequently, a structure of a controller to control the entire apparatus will be explained with reference to  FIG. 3 .  FIG. 3  is the block diagram showing the structure of the controller in the image formation apparatus shown in  FIG. 1 . 
   As shown in  FIG. 3 , the controller has a CPU circuit unit  205  which contains therein a CPU (not shown), a ROM  206  and a RAM  207 . Thus, the controller entirely controls an original feeder control unit  201 , an image reader control unit  202 , an image signal control unit  203 , a printer control unit  204 , an operation unit  208  and a finisher control unit  501 , on the basis of control programs stored in the ROM  206 . The RAM  207  temporarily stores control data, and is used as a working area for a calculation process in the control. 
   The original feeder control unit  201  drives and controls the automatic original feed unit  101  on the basis of an instruction from the CPU circuit unit  205 . The image reader control unit  202  drives and controls the above scanner unit  104 , the image sensor unit  109  and the like, to transfer RGB analog image signals outputted from the unit  109  to the image signal control unit  203 . 
   The image signal control unit  203  converts each of the RGB analog image signals transferred from the unit  109  into a digital signal, performs a necessary process on the obtained digital signal, converts the processed digital signal into the video signal, and finally outputs the obtained video signal to the printer control unit  204 . Such the process operation by the unit  203  is controlled by the CPU circuit unit  205 . The printer control unit  204  drives the above exposure control unit  110  on the basis of the inputted video signal. 
   The operation unit  208  has plural keys for setting various functions concerning the image formation, a display unit for displaying information representing setting states, and the like. Thus, the unit  208  outputs a key signal corresponding to each key operation to the CPU circuit unit  205 , and also displays the corresponding information on the basis of a signal from the unit  205 . 
   The finisher control unit  501  which is installed in the finisher  500  drives and controls the finisher  500  as a whole by sending/receiving information to/from the CPU circuit unit  205  through a not-shown communication IC (IPC). The finisher control unit  501  has a CPU  401 . Various actuators such as an inlet motor M 1 , a buffer motor M 2 , a paper discharge motor M 3  and the like, and various sensors such as an inlet sensor  531 , a path sensor  532  and the like are connected to the CPU  401 . 
   Subsequently, a structure of the image signal control unit  203  will be explained with reference to  FIG. 4 .  FIG. 4  is the block diagram showing the structure of the image signal control unit  203  shown in  FIG. 3 . 
   As shown in  FIG. 4 , the image signal control unit  203  has an A/D converter  301  which converts the RGB analog image signals sent from the image reader control unit  202  into the RGB digital signals and outputs the obtained digital signals. The RGB digital signals are inputted to a black correction/white correction unit  302 , and the unit  302  performs shading correction on the inputted RGB digital signals. The shading-corrected RGB digital signals are then inputted to an ND signal generation unit  303 , and the unit  303  generates a luminance signal from these RGB digital signals. The generated luminance signal is then inputted to an image process unit  304 . The unit  304  performs various image processes such as a zooming process (i.e., reduction and enlargement process) on the inputted luminance signal, and the processed luminance signal is then inputted to a density correction unit  305 . The unit  305  performs luminance-density conversion on the inputted luminance signal, and further performs density correction at a printer. Then, the obtained signal is stored in a page memory  306  as the video data (or video signal). 
   The page memory  306  has a storage capacity corresponding to one page of the predetermined-size original. The video data is stored in the memory  306  in the image reading order of the above original image reading scan. At the time of original fixation read, the stored video data is read in the storing order. On the other hand, at the time of original running read, the stored video data is read in the reverse order as to the main-scan direction and in the storing order as to the sub-scan direction. That is, at the time of original running read, the image read in one direction along the main-scan direction is reversed toward a direction opposite to such one direction along the main-scan direction, whereby a mirror image process is performed. 
   It should be noted that the mirror image process can be achieved even in a manner that the main-scan direction is reversed at the time of storing the video data in the page memory  306 , and then the stored video data is read always in the determined direction. 
   The video data read from the page memory  306  is once stored in a hard disk drive (HDD)  307  if necessary, and the video data read from the HDD  307  is sent to the printer control unit  204  as the video signal. For example, in case of performing copy output for plural pages, the video data of the first page is directly outputted from the memory  306  to the unit  204 , but the video data of the second and following pages are once stored in the HDD  307  and then sent to the unit  204 . 
   Subsequently, an original setting state that the original is being set in the automatic original feed unit  101  and a paper discharge state that the sheet on which the original image has been formed is controlled to be inverted and then discharged will be explained with reference to  FIGS. 5A to 5D .  FIGS. 5A to 5D  are the views showing relation between the original setting state and the paper discharge state. 
   In the embodiment, as shown in  FIG. 5A , the original of which read face has been turned upward is set on the automatic original feed unit  101  such that the first page of the original is put on uppermost. 
   In such the original setting state, the automatic original feed unit  101  feeds and carries the original from its first page (i.e., uppermost page) in due order, to the platen glass  102 . On the glass  102 , as shown in  FIG. 5B , the original of which read face is opposite to an upper face of the glass  102  is carried in a Df direction. At the time when the original passes through the running read position, the image on the read face of the original is read in a main-scan direction Sm by the scanner unit  104  supported at the running read position. Thus, as the image on the read face of the original is read in the main-scan direction Sm, the original is carried in the Df direction (i.e., sub-scan direction Sb), whereby the original reading scan is performed for the entire read face. If the running-read image is formed as it is, this image becomes a mirror image. Therefore, to prevent this, the read image is subjected to the above mirror image process and then formed on the sheet in such an image formation process as above. As a result, as shown in  FIG. 5C , the image facing toward the same direction as that at the time of the original setting state is formed on the image formation face (i.e., upper face) of the sheet, and the sheet passes through the fixing unit  117 . This sheet is subjected to the above reverse paper discharge control, and the sheet of which image formation face has been turned downward is then discharged in a Do direction as shown in  FIG. 5D . 
   Subsequently, a structure of the finisher  500  will be explained with reference to  FIG. 2 .  FIG. 2  is the sectional view showing the structure of the finisher  500  shown in  FIG. 1 . 
   The finisher  500  performs various sheet postprocesses such as a process to sequentially take in the plural sheets discharged from the image formation apparatus  100 , adjust or align the took-in sheets and sheaf the adjusted sheets, a staple process to bind or staple a trailing edge of an obtained sheaf by a stapler, a punch process to punch holes in the trailing edge side of the sheaf, a sort process, a nonsort process and the like. When the finisher  500  is connected to the apparatus  100  and the original running read is performed, the image corrected through the mirror process is formed on the sheet in the apparatus  100 , and the sheet of which image formation face has been turned downward in the reverse paper discharge control is then discharged from the apparatus  100 . Subsequently, in the finisher  500 , the above various processes such as the staple process and the like are performed on the above discharged sheet. 
   As shown in  FIG. 2 , the finisher  500  takes in the sheet discharged from the image formation apparatus  100  by a pair of inlet rollers  502 , and the took-in sheet is then carried toward a buffer roller  505  by a pair of carrier rollers  503 . An inlet sensor  531  is provided at the halfway position on the carrier path between the rollers  502  and the rollers  503 , and a punch unit  550  is provided at the halfway position on the carrier path between the rollers  503  and the roller  505 . If necessary, the punch unit  550  operates to punch the holes in the trailing edge side of the carried sheet. 
   The buffer roller  505  can layer and wind thereon a predetermined number of sheets carried by the rollers  503 . That is, while the roller  505  is rotating, the sheet is wound around an outer periphery of the roller  505  by pressure rollers  512 ,  513  and  514 , and the wound sheet is then carried in a rotational direction of the roller  505 . 
   A switch flapper  511  is provided between the pressure rollers  513  and  514 , and a switch flapper  510  is provided at a downstream side of the roller  514 . The flapper  511  separates the wound sheet from the buffer roller  505  and guides the separated sheet to a nonsort path  521  or a sort path  522 . The flapper  510  separates the wound sheet from the roller  505  and guides the separated sheet to the sort path  522 , or guides the sheet wound around the roller  505  to a buffer path  523  as it is. 
   When the sheet wound around the roller  505  is guided to the nonsort path  521 , the wound sheet is separated from the roller  505  and guided to the path  521  by the switch flapper  511 . The sheet guided to the path  521  is then discharged onto a sample tray  701  through a pair of discharge rollers  509 . A paper discharge sensor  533  is provided at the halfway position on the nonsort path  521 . 
   When the sheet wound around the buffer roller  505  is guided to the buffer path  523 , both the switch flappers  510  and  511  do not operate. Thus, the sheet is carried to the path  523  in the state that the sheet is being wound around the roller  505 . A buffer path sensor  532  is provided at the halfway position on the path  523  to detect the sheet thereon. 
   When the sheet wound around the buffer roller  505  is guided to the sort path  522 , the switch flapper  511  does not operate but only the switch flapper  510  operates to separate the wound sheet from the roller  505 . The plural sheets separated are then guided to the sort path  522  and stacked or put on an intermediate tray (referred as process tray hereinafter)  630  through pairs of carrier rollers  506  and  507 . The sheets stacked on the process tray  630  in the form of sheaf are subjected to an adjustment process, a staple process and the like, if necessary. Then, the processed sheets are discharged onto a stack tray  700  by discharge rollers  680   a  and  680   b . The roller  680   b  is supported by a rock guide  650 , and the guide  650  rocks (or swings) the roller  680   b  by a rock motor (not shown) such that the roller  680   b  comes into contact with the uppermost sheet on the tray  630 . In the state that the roller  680   b  contacts with the uppermost sheet on the tray  630 , the roller  680   b  can cooperate with the roller  680   a  to discharge the sheaf of sheets on the tray  630  toward the stack tray  700 . 
   The above staple process is performed by a stapler  601 . The stapler  601  is arranged to be movable along one edge (outer edge) of the process tray  630 , and can bind or staple the sheaf of sheets stacked on the tray  630  at its endmost position (i.e., trailing edge) (see  FIGS. 21 to 23 ) of the sheet in a paper carrying direction (leftward direction in  FIG. 2 ). 
   Subsequently, an adjustment (or alignment) operation in the finisher  500  will be explained with reference to  FIGS. 18 to 20 .  FIGS. 18 to 20  are the views showing the adjustment operation to be performed on the process tray  630  of the finisher  500  shown in  FIG. 2 . 
   As shown in  FIG. 18 , when the initial sheet is discharged from the image formation apparatus  100  onto the process tray  630 , front-side and rear-side adjustment members  641  and  642  being on standby at home positions (indicated by alternate long and two short dashed lines) are previously moved to respective positions PS 11  and PS 21  slightly away from a width of the sheet to be discharged (i.e., distance between PS 11  and PS 21  is slightly wider than sheet width). As shown in  FIG. 19 , the sheet discharged on the tray  630  is dropped between the members  641  and  642  as its trailing edge is being supported by a stopper  631 , and then the member  641  is moved to a position PS 12  at the timing when the downward face of the discharged sheet comes into contact with a support face of the tray  630 . By such movement of the member  641 , the sheet is moved to a first adjustment position  690  and adjusted. 
   After adjusting the first sheet, as shown in  FIG. 19 , the front-side adjustment member  641  is returned to the position PS 11  and is on standby for the next sheet to be discharged onto the tray  630 . When the next sheet is discharged onto the tray  630 , the member  641  is again moved to the position PS 12  to adjust the next sheet at the first adjustment position  690 . During this operation, the rear-side adjustment member  642  is maintained to be at a position PS 22  to act as an adjustment standard. 
   The above operation is repeated until the final sheet in the sheaf is processed. When the discharge and adjustment of the first sheaf of sheets completes, later-described sheaf discharge is performed to move the sheaf to the stack tray  700 . 
   After the first sheaf is discharged onto the stack tray  700 , as shown in  FIGS. 19 and 20 , the front-side adjustment member  641  is moved from the position PS 12  to a position PS 13 , and also the rear-side adjustment member  642  is moved from the position PS 22  to a position PS 23 . Subsequently, when the first (initial) sheet in the second sheaf is discharged onto the process tray  630 , this sheet is similarly dropped between the members  641  and  642  as its trailing edge is being supported by the stopper  631 . Then, the member  642  is moved from the position PS 23  to a position PS 24  at the timing when the downward face of the discharged sheet comes into contact with the support face. By such movement of the member  642 , the sheet is moved to a second adjustment position  691  and adjusted. For the second and subsequent sheets, the member  642  is moved to the position PS 23  and on standby for the sheet next discharged onto the tray  630 . When the discharge of the next sheet onto the tray  630  completes, the member  642  is again moved to the position PS 24  to adjust the sheet at the second adjustment position  691 . During this operation, the front-side adjustment member  641  is maintained to be at the position PS 13  to act as the adjustment standard. The above operation is repeated until the final sheet in the sheaf is processed. When the discharge and adjustment of the second sheaf completes, the later-described sheaf is processed. When the discharge and adjustment of the second sheaf completes, the later-described sheaf discharge is performed to move the sheaf to the stack tray  700 . As shown in  FIG. 19 , the first adjustment position  690  is far from, in the rear of the tray  630 , the second adjustment position  691  by a predetermined amount (i.e., offset distance L). 
   After then, the adjustment is performed as the adjustment position of each sheaf is alternately changed or switched between the positions  690  and  691 . Thus, as shown in  FIG. 17 , the plural sheaves of which adjustment positions are alternately changed are stacked on the stack tray  700 . That is, by alternately changing the adjustment position for each sheaf, sorting is performed in the offset distance L for the respective sheaves. 
   The offset distance L is set to be different in each of the sort mode and the staple-sort mode. For example, in the staple-sort mode, the offset distance L is set to have an amount (i.e., distance) L 1  sufficient to prevent an overlap of staples (or styli) between the stacked sheaves adjacent to each other. On the other hand, in the sort mode, the offset distance L is set to be a distance L 2  sufficient to certainly distinguish the adjacent sheaves from each other. The offset distances L 1  and L 2  satisfy relation of L 1 &lt;L 2 , and process speed in the staple mode can be improved by such setting. 
   Subsequently, the staple operation will be explained with reference to  FIGS. 21 to 23 .  FIGS. 21 to 23  are the views for explaining operation states according to the binding modes (i.e., front-oblique binding mode, rear-oblique binding mode and two-point binding mode) of the stapler  601 . 
   In the staple mode, the stapler  601  is previously on standby at a desired clinch position for the adjusted sheets. Thus, when the discharge and adjustment of the final sheet in the final sheaf completes, the stapler  601  performs the staple operation. In this case, the stapler  601  is controlled to offset-move in synchronism with offset movement (movement amount L 1 ) of the sheaf. 
   Further, the stapler  601  changes its direction and moves according to the binding modes (i.e., front-oblique binding mode, rear-oblique binding mode and two-point binding mode). 
   For example, as shown in  FIG. 21 , in the two-point binding mode, the staple operation to staple the sheaf, at two points on its trailing edge side, adjusted at each of the adjustment positions  690  and  691  is performed. As shown in  FIG. 22 , in the rear-oblique binding mode, the staple operation to obliquely staple the sheaf, at its trailing-edge rear point, adjusted at each of the adjustment positions  690  and  691  is performed. As shown in  FIG. 23 , in the front-oblique binding mode, the staple operation to obliquely staple the sheaf, at its trailing-edge front point, adjusted at each of the adjustment positions  690  and  691  is performed. In each of  FIGS. 21 to 23 , an alternate long and two short dashed line represents the first adjustment position  600 , and a solid line represents the second adjustment position  691 . At this time, in a case where the adjustment position is in front of the discharge position, the rear-side adjustment member  642  reciprocates to carry the sheet to the front-side adjustment member  641  side being the adjustment standard. On the other hand, in a case where the adjustment position is in the rear of the discharge position, the front-side adjustment member  641  reciprocates to carry the sheet to the rear-side adjustment member  642  side. 
   Subsequently, the sheaf discharge operation in the staple mode will be explained. 
   In one-point staple sort mode, when the above adjustment operation terminates, the stapler  601  starts the staple operation. Further, during the adjustment operation or staple operation, the rock guide  650  starts descent. In this case, speed of the rock guide motor is controlled such that the paper discharge roller  680   b  is put on the sheaf about that time when the staple operation terminates. 
   Descent start timing of the rock guide  650  is variable according to the number of sheets of the sheaf stacked on the process tray  630 . That is, if such the number is small, since a movement distance up to putting of the roller  680   b  on the sheaf is long and an operation time of the stapler  601  is short, the rock guide  650  starts descent while the adjustment operation is being performed. On the other hand, if such the number is large, since the movement distance up to putting of the roller  680   b  on the sheaf is short and the operation time of the stapler  601  is long, the rock guide  650  starts descent substantially at the same time when the staple operation starts. 
   After elapsing a predetermined time from putting of the roller  680   b  on the sheaf to an end of a bound of the roller  680   b , it is judged whether or not the staple operation terminates. If the operation terminates, the sheaves are discharged onto the stack tray  700  by the rollers  680   a  and  680   b . On the other hand, if the operation does not terminate, a process waits for termination of the staple operation. In such a state waiting for the termination of the staple operation, sheaf discharge speed control is performed. In this control, the sheaf is carried at high speed after the sheaf carrying starts. However, the discharge speed is reduced before the trailing edge of the sheaf exceeds the trailing edge of the rollers  680   a  and  680   b , such that the discharge speed becomes suitable for stacking the sheaves onto the stack tray  700  in case of the sheaf discharging. 
   In the two-point staple sort mode, the rock guide starts decent when the staple operation at a first staple point terminated and thus the stapler moves to a second staple point. While the second point is being stapled, the rock guide  650  is on standby as it is being put on the sheaf. The paper discharge roller  680   b  starts the sheaf discharge operation at the same time when the staple operation terminates. The following operation is identical with that in the one-point staple sort mode. 
   Subsequently, a flow of the sheet in the finisher  500  will be explained for each of the nonsort mode, the staple-sort mode and the sort mode. 
   Initially, the flow of the sheet in the nonsort mode will be explained with reference to  FIG. 6 .  FIG. 6  is the view showing the flow of the sheet in the finisher  500  in the nonsort mode. 
   When a user designates, in the image formation apparatus  100 , the paper discharge mode as the nonsort mode, as shown in  FIG. 6 , then the inlet rollers  502 , the carrier rollers  503  and the buffer roller  505  are rotatively driven, whereby a sheet P discharged from the apparatus  100  is taken in the finisher  500  and then carried. The switch flapper  511  is rotatively driven by a solenoid (not shown) to a position shown in the drawing, whereby the sheet P is guided into the nonsort path  521 . Then, when the paper discharge sensor  533  detects a trailing edge of the sheet P, then the discharge rollers  509  rotate at a speed suitable for the stacking and discharge the sheet P onto the sample tray  701 . 
   Subsequently, the flow of the sheet in the staple-sort mode will be explained with reference to  FIGS. 7 to 13 ,  FIGS. 14A and 14B  and  FIG. 17 .  FIGS. 7 to 13 ,  FIGS. 14A and 14B  are the views showing the flow of the sheet in the staple-sort mode, and  FIG. 17  is the view showing a state that the plural sheaves of sheets are stacked on the stack tray  700  in the finisher  500 . 
   When the staple-sort mode is designated by the user, as shown in  FIG. 7 , then the inlet rollers  502 , the carrier rollers  503  and the buffer roller  505  are rotatively driven, whereby the sheet P discharged from the apparatus  100  is taken in the finisher  500  and then carried. The switch flappers  510  and  511  are stopped at positions shown in the drawing, whereby the sheet P is guided into the sort path  522 . Then, the sheet P guided in the path  522  is discharged onto the process tray  630  by the carrier rollers  507 . At this time, dangling, insufficient returning or the like of the sheet P discharged by the rollers  507  can be prevented by a projection tray  670  projected upward. Also, alignment of the sheets on the tray  630  can be improved by the tray  670 . 
   The sheet P discharged on the process tray  630  starts moving on the tray  630  toward the stopper  631 , by its own weight. Such movement of the sheet P is assisted by an assist member such as a paddle or the like (not shown). When the trailing edge of the sheet P hits against the stopper  631  and thus the sheet P stops, then the discharged sheets are adjusted by the adjustment members  641  and  642  as described above. When the predetermined number of sheets P are adjusted and stacked, then the above staple operation and the sheaf discharge operation are performed, whereby the sheaf of sheets P are discharged onto the stack tray  700 . As described above, since the sheet of which image-formed face was turned downward is discharged from the image formation apparatus  100 , the first page of which image-formed face was turned downward is at the lowermost position in the sheaf consisting of the predetermined number of adjusted sheets stacked upward in the page order. Further, the sheaf is bound at a position Ls (upper right position Lrs 1  or lower right position Lrs 2 ) shown in  FIGS. 5A to 5D . 
   Subsequently, the flow of the sheets constituting the next (i.e., second) sheaf will be explained. This flow occurs while the sheet P of the first sheaf is took in and then the first sheaf is discharged. 
   As shown in  FIG. 8 , a sheet P 1  of the first page in the next (i.e., second) sheaf discharged from the image formation apparatus  100  is wound around the buffer roller  505  by operating the switch flapper  510 . The roller  505  carries the sheet P 1  to a position far from the buffer path sensor  532  for a predetermined distance and then stops. As shown in  FIG. 9 , when a leading edge of a sheet P 2  of the next page advances from the inlet sensor  531  for a predetermined distance, then the buffer roller  505  starts rotating, whereby the next sheet P 2  is overlaid on the sheet P 1  such that the sheet P 2  is advanced from the sheet P 1  by a predetermined distance. As shown in  FIG. 10 , the sheet P 2  is wound around the buffer roller  505  in a state that the sheet P 2  is being overlaid on the sheet P 1 , and then carried to the buffer path sensor  532 . After then, the buffer roller  505  again carries the sheet P 2  to the position far from the sensor  532  for the predetermined distance and then stops. Further, as shown in  FIG. 10 , when a leading edge of a sheet P 3  of the next page advances from the inlet sensor  531  for the predetermined distance, then the buffer roller  503  again starts rotating. Thus, the sheet P 3  is overlaid on the sheaf of the sheets P 1  and P 2  such that the sheet P 3  is advanced from the sheaf for a predetermined distance. The sheets P 1 , P 2  and P 3  wound around the roller  505  are separated therefrom by the switch flapper  511  and carried to the sort path  522  as the sheaf P of the three sheets. At this time, the discharge operation of the sheaf P on the process tray  630  has terminated. Thus, as shown in  FIG. 12 , the rock guide  650  has been descended and its descended position is maintained, whereby the sheaf P of the three sheets is took in between the discharge rollers  680   a  and  680   b.    
   Subsequently, as shown in  FIG. 13 , when the trailing edge of the sheaf P exceeds the carrier rollers  507  and reaches the process tray  130 , then the discharge rollers  680   a  and  680   b  reverse-rotate to carry the sheaf P toward the stopper  631 . As shown in  FIG. 14A , before the trailing edge of the sheaf P hits against the stopper  631 , the rock guide  650  ascends to separate the roller  680   b  from the sheet face. As shown in  FIG. 14B , in case of carrying the sheaf P consisting of the plural sheets, each sheet is offset in the carrying direction. That is, the sheet P 2  is offset from the sheet P 1  toward the side opposite to the stopper  631  side, and also the sheet P 3  is similarly offset from the sheet P 2 . The fourth and subsequent sheets are discharged onto the process tray  630  through the sort path  522  in the same manner as in the discharge operation of the first sheaf. After the second sheaf is stacked on the stack tray  700 , the subsequent sheaves are processed by repeating the same operation, whereby the predetermined number of sheaves are stacked on the tray  700 . As shown in  FIG. 17 , the plural sheaves are stacked on the stack tray  700  such that the sheaves are alternately offset. Further, in each sheaf, the first-page sheet of which image-formed face was turned downward is at the lowermost position, and the subsequent sheets are stacked upward in the page order. 
   Subsequently, the flow of the sheets in the sort mode will be explained with reference to  FIGS. 15 and 16 .  FIGS. 15 and 16  are the views showing the flow of the sheets in the finisher in the sort mode. 
   As shown in  FIG. 15 , when the sort mode is set, then the inlet rollers  502  and the carrier rollers  503  are rotatively driven, whereby the sheets discharged from the image formation apparatus  100  are sequentially stacked on the stack tray  630 , in the same manner as in the staple-sort mode. Then, the above sheaf discharge operation is performed to discharge the sheaf P onto the stack tray  700 . On the other hand, during this operation, as shown in  FIG. 16 , the sheet P 1  discharged from the apparatus  100  is wound around the buffer roller  505  by operating the switch flapper  510 . The roller  505  carries the sheet P 1  to the position far from the buffer path sensor  532  for the predetermined distance and then stops. Subsequently, when the leading edge of the next sheet P 2  advances from the inlet sensor  531  for the predetermined distance, then the buffer roller  505  starts rotating, whereby the next sheet P 2  is overlaid on the sheet P 1  such that the sheet P 2  is advanced from the sheet P 1  by the predetermined distance. 
   As above, the same operation as in the staple-sort mode is performed in the sort mode, whereby the predetermined number of sheaves are stacked on the tray  700  in the state that the sheaves are alternately offset. Further, in each sheaf, the first-page sheet of which image-formed face was turned downward is at the lowermost position, and the subsequent sheets are stacked upward in the page order. 
   The control for each mode as above is performed by the finisher control unit  501 . The unit  501  discriminates the mode set based on the instruction from the CPU circuit unit  205  in the image formation unit  100 , and drives and controls each unit according to procedure determined for the set mode. 
   A control process for the sheaf discharge operation of such the sheet process device (i.e., finisher) as having the above structure will be explained hereinafter. 
   The CPU  401  in the finisher control unit  501  communicates with the image formation apparatus  100  through the communication IC (IPC) to exchange the data, and performs various controls according to various programs stored in a not-shown ROM. 
   (Operation Mode Discrimination Process) 
     FIG. 24  is a flow chart showing a procedure in the operation mode discrimination process. A program for the operation mode discrimination process has been stored in a ROM (not shown) in the finisher control unit  501  and executed by the CPU  401 . 
   Initially, it waits for the process until the finisher (i.e., sorter) starts (step S 1 ). When a copy start key on the operation unit in the image formation apparatus body is depressed and the signal for starting the operation of the finisher is inputted from the apparatus body to the CPU  401  in the finisher control unit  501  through the communication IC (IPC), the finisher starts the operation. Thus, the CPU  401  starts driving the inlet motor M 1 , the buffer motor M 2  and the paper discharge motor M 3  (step S 2 ). On the other hand, if the signal for starting the finisher is not inputted to the CPU  401 , the finisher is on standby. 
   Subsequently, the operation mode is discriminated (step S 3 ). If the operation mode is the nonsort mode, the nonsort process is executed (step S 4 ). If the operation mode is the sort mode, the sort mode is executed (step S 5 ). If the operation mode is the staple-sort mode, the staple-sort mode is executed (step S 6 ). 
   When either one of the processes in the steps S 4  to S 6  terminates, then the driving of the inlet motor M 1 , the buffer motor M 2  and the paper discharge motor M 3  is stopped (step S 7 ), and the flow returns to step S 1 . Thus, the finisher is on standby. 
   (Nonsort Process) 
     FIG. 25  is a flow chart showing a nonsort process procedure. The nonsort process is executed in the step S 4 , if it is discriminated in the step S 3  that the operation mode is the nonsort mode. In the nonsort process, since the sheet P is initially guided onto the sample tray  701 , the flapper  511  is driven to select the nonsort path  521  (step S 101 ). 
   Then, it is judged whether or not the finisher starts the operation, i.e., the finisher is “ON” (step S 102 ). If judged that the finisher is “ON”, the sheet P discharged from the image formation apparatus body is carried to the paper path in the finisher. Then, it waits for the process until the sheet P is carried by the inlet motor M 1 , its leading edge is detected by the path sensor  531  in the path, and thus the sensor  531  comes to be “ON” (step S 103 ). When the sensor  531  is “ON”, then it waits for the process until the trailing edge of the sheet P exceeds the sensor  531 , and thus the sensor  531  comes to be “OFF” (step S 104 ). 
   When the sensor  531  is “OFF”, then the flow returns to the step S 102 . Then, if the finisher is again “ON”, the same processes as above are repeated. On the other hand, if the finisher is “OFF”, it waits for the process until all the sheets are discharged onto the sample tray  701  (step S 105 ). When all the sheets are completely discharged, then the operation of the flapper  511  is released (step S 106 ), and the nonsort process terminates. 
   (Sort Process) 
     FIG. 26  is a flow chart showing a sort process procedure. The sort process is executed in the step S 5 , if it is discriminated in the step S 3  that the operation mode is the sort mode. 
   In the sort process, since the sheet P is guided onto the process tray  630 , the flapper  511  is initially driven to select the sort path  522  (step S 201 ). 
   Then, it is judged whether or not the finisher is “ON” (step S 202 ). If judged that the finisher is “ON”, the sheet P discharged from the apparatus body is carried to the paper path in the finisher. Then, it waits for the process until the sheet P is carried by the inlet motor M 1 , and its leading edge is detected by the path sensor  531  in the path (step S 203 ). 
   When the sensor  531  is “ON”, a sort sheet sequence starts (step S 204 ). Then, it waits for the process until the trailing edge of the sheet P exceeds the path sensor  531 , and thus the sensor  531  comes to be “OFF” (step S 205 ). 
   When the sensor  531  is “OFF”, then the flow returns to the step S 202 . Then, if the finisher is again “ON”, the same processes as above are repeated. On the other hand, if the finisher is “OFF”, it waits for the process until all the sheets are discharged onto the process tray  630  (step S 206 ). When all the sheets are completely discharged, then the operation of the flapper  511  is released (step S 207 ), and the sort process terminates. 
   (Staple-Sort Process) 
     FIG. 27  is a flow chart showing a staple-sort process procedure. The staple-sort process is executed in the step S 6 , if it is discriminated in the step S 3  that the operation mode is the staple-sort mode. 
   In the staple-sort process, since the sheet P is guided onto the process tray  630 , the flapper  511  is initially driven to select the sort path  522  (step S 301 ). Then, it is judged whether or not the finisher is “ON” (step S 302 ). If judged that the finisher is “ON”, the sheet P discharged from the apparatus body is carried to the paper path in the finisher. Then, it waits for the process until the sheet P is carried by the inlet motor M 1 , its leading edge is detected by the path sensor  531  in the path, and thus the sensor  531  comes to be “ON” (step S 303 ). When the sensor  531  is “ON”, the sort sheet sequence starts (step S 304 ). 
   Further, it waits for the process until the sheet P is carried, its trailing edge exceeds the sensor  531 , and thus the sensor  531  comes to be “OFF” (step S 305 ). When the sensor  531  is “OFF”, then the flow returns to the step S 302 . If the finisher is again “ON”, the same processes as above are repeated. On the other hand, if the finisher is “OFF”, it waits for the process until all the sheets are discharged onto the process tray  630  (step S 306 ). When all the sheets are completely discharged, then the operation of the flapper  511  is released (step S 307 ), and the staple-sort process terminates. 
   (Sort Sheet Sequence Process) 
     FIG. 28  is a flow chart showing a sort sheet sequence process procedure. The sort sheet sequence process is executed in the step S 204  in the above sort process and the step S 304  in the above staple-sort process, and allocated to every sheet carried. Further, a program for this process is a multitask program and executed by the CPU  401 . 
   In the sort sheet sequence process, initially, the sheet is carried for 50 mm (step S 401 ), and the buffer motor starts driving the buffer roller (step S 402 ). In this case, since the sort sheet sequence starts in response to “ON” of the path sensor  531 , the buffer motor starts the operation at the time when the leading edge of the sheet is carried for 50 mm toward the downstream side from the position at which the path sensor  531  was turned on. 
   Such start timing is necessary to carry the subsequent sheets, and also necessary to restart carrying “wind sheet” wound around the buffer roller and standing thereon. By this start timing, the sheet overlaid on the wind sheet can be carried together with the wind sheet. 
   Although “50 mm” is described as a condition to define the above timing in the embodiment, such the condition can be arbitrarily set. After then, the sheet is carried for 150 mm (step S 403 ), and a paper attribute discrimination process is performed (step S 404 ). Although the paper attribute discrimination process will be later explained in detail, roughly this process is to discriminate an attribute of the carried sheet between “whether the sheet is to be wound (i.e., wind sheet)” and “whether the sheet is to be used for the sheaf discharge after the sheaves are stacked on the process tray”. 
   As a result of the paper attribute discrimination process, it is judged whether or not the sheet is the wind sheet (step S 405 ). If judged that the sheet is designated as the wind sheet, the flapper  510  is driven to select the buffer path  523  (step S 406 ). Then, if the sheet is carried as it is, the sheet can be guided to the buffer path  523  for winding the sheet around the buffer roller. 
   Subsequently, buffer motor stop control starts at the time when the path sensor  532  on the buffer path  523  is turned on, and the sheet is wound around the buffer roller (steps S 407  and S 408 ). When the leading edge of the sheet exceeds the path sensor  532 , then the buffer roller is stopped. In this case, when sheet attachment control is performed, the buffer roller is stopped in consideration of an overrun amount. 
   After stopping the buffer roller, the wound sheet is on standby as it is until the buffer roller restarts the rotation to wind thereon the subsequent sheet. After the roller restarts, at a time when the sheet discharge onto the tray completes (step S 409 ), a value of a discharge counter for counting the number of sheets discharged onto the process tray is increased by “1”, and the process terminates (step S 410 ). 
   On the other hand, if judged in the step S 405  that the sheet is not the wind sheet, the flapper  510  is driven to select the sort path  522  (step S 411 ). By selecting the sort path  522 , the sheet is guided not to the buffer path  523  but to the path being the paper discharge path to the process tray. 
   Then, after the completion of the discharge onto the process tray is confirmed (step S 412 ), the value of the discharge counter is increased by “1” (step S 413 ), and the sheet is adjusted at the adjustment position defined for each sheet by the two adjustment members (step S 414 ). When the sheet is discharged onto the process tray, the sheet is adjusted or aligned in a direction substantially perpendicular to the sheet carrying direction and the paddle is rotated at the same time when the sheet is discharged, thereby adjusting the sheet in its carrying direction. 
   After then, a later-described sheaf discharge operation discrimination process is performed (step S 415 ), and the process terminates. 
   (Paper Attribute Discrimination Process) 
     FIGS. 29 and 30  are flow charts showing a procedure in the paper attribute discrimination process. The paper attribute discrimination process is executed in the step S 404  in the above sort sheet sequence process. 
   Initially, a value of a buffer passage counter for counting the number of sheets passed through the buffer roller is increased by “1” (step S 501 ). When the sheet is discharged onto the process tray, information representing which of the front side and the rear side the sheet is adjusted to sort the sheaf is set as information (representing sheet adjustment position) for each sheet (step S 501 A). 
   Subsequently, it is judged whether or not the sheet is final sheet in one sheaf (step S 502 ). In this case, one sheaf is a unit for the sort in the sort mode, or a unit for the stapling in the staple-sort mode. 
   If judged that the sheet is not the final sheet, it is further judged whether the sheet has a size (windable size) capable of being wound around the roller (step S 503 ). If judged that the sheet has the windable size, a wind counter for counting the number of windable sheets is referred. Thus, it is further judged whether or not a value of the wind counter is “0” (step S 504 ). 
   If judged that the value of the wind counter is not “0”, such the value is decreased by “1” (step S 505 ), and the sheet is designated as “wind sheet” (step S 506 ). Here the object to wind the sheet around the buffer roller is to temporarily stagnate the discharged sheet such that this sheet is discharged together with the subsequent sheet to give a sufficient time for the process at the downstream side. Namely, the object is to improve productivity. 
   If judged in the step S 504  that the value of the wind counter is “0”, it is further judged whether or not the operation mode is the sort mode (step S 507 ). If judged that the operation mode is not the sort mode, i.e., the operation mode is the staple-sort mode, the process terminates. On the other hand, if judged that the operation mode is the sort mode, it is further judged whether or not the value of the buffer passage counter is “4” (sep S 508 ). If judged that the value is “4”, it is further judged whether or not the carried sheet is the sheet two before the final sheet in the sheaf (step S 509 ). 
   If judged that the carried sheet is the sheet two before the final sheet in the sheaf, the value of the buffer passage counter is set to be “0” and the value of the wind counter is set to be “2” (step S 510 ), and “sheaf discharge sheet” representing that the sheaf discharge is performed from the process tray is designated on the carried sheet(step S 511 ). If judged that the value of the buffer passage counter is “5”, also “sheaf discharge sheet” is designated (step S 512 ). In other cases, the process terminates as it is. 
   Such the control has a following meaning for the operation in the sort mode and the windable size (A4, LTR, B5 in the embodiment). That is, the sheaf discharge operation is basically the operation “to discharge every five sheets from the process tray”. However, only in the case where “the fourth sheet on the process tray is also the sheet two before the final sheet in the sheaf”, i.e., only in the case where “every five sheets are discharged from the process tray” and the case where “final one of the sheets is the sheaf discharge sheet”, the sheaf discharge operation is the operation to perform the sheaf discharge from the process tray with four sheets. When the sheet discharge with four sheets is performed, the sheet one before the final sheet in the subsequent sheaf is the wind sheet, and this wind sheet is discharged together with the final sheet, whereby the sheet discharge is performed. 
   By performing such the control, in case of performing the sheet discharge operation from the process tray, it becomes possible to always wind the subsequent sheet. At this time, at least the process time (between leading edge of sheet and leading edge of next sheet) for one sheet can be secured extra. Therefore, high productivity can be realized in the sheaf discharge operation which requires the relatively longer operation time as compared with the case where each sheet is discharged. 
   Although the sheaf discharge operation is described in the embodiment, the present invention is not limited to this. For example, the present invention is applicable to a staple operation, exclusive control for sheets in a carrier driving system, and the like. In these cases, such high productivity as in the present invention can be also realized. 
   On the other hand, if judged in the step S 503  that the sheet does not have the windable size, it is further judged whether or not the operation mode is the sort mode (step S 513 ). 
   If the operation mode is not the sort mode but is the staple-sort mode, the process terminates. On the other hand, if the operation mode is the sort mode, it is judged whether or not the value of the buffer passage counter is “3” (step S 514 ). If the value is not “3”, the process terminates. On the other hand, if the value is “3”, the process in the above step S 510  is performed. 
   The processes in the above steps S 510  and S 511  are the process to designate the carried sheet as “sheaf discharge sheet” representing the sheet to be sheaf-discharged and the accompanied counter setting process (to clear buffer passage counter and set wind counter). In this case, to designate “sheaf discharge sheet” means that the sheaf discharge operation from the process tray to the stack tray starts when the carried sheets are discharged and stacked on the process tray, and such designation is used in a later-described sheaf discharge operation discrimination process. 
   On the other hand, if judged in the step S 502  that the carried sheet is the final sheet in the sheaf, the already-set adjustment position information is reversely set. The adjustment position information is set for each sheet. Therefore, for example, if it is assumed that the front-side position is an adjustment position A and the rear-side position is an adjustment position B, the currently set adjustment position information is discriminated (step S 515 ). If the information represents the position A, the adjustment position information is set to represent the position B (step S 516 ). On the other hand, if the information represents the position B, the information is set to represent the position A (step S 517 ). As above, by reversing the adjustment position information, it becomes possible to sort (or offset) each sheaf on the process tray and the stack tray. After then, the flow advances to the above step S 510 . 
   According to the processes as described above, the discrimination and setting processes for the attribute concerning the sheet (i.e., whether wind control is to be performed, whether sheaf discharge is to be performed) complete. 
   (Sheaf Discharge Operation Discrimination Process) 
     FIG. 31  is a flow chart showing a procedure in the sheaf discharge operation discrimination process. The sheaf discharge operation discrimination process is executed in the step S 415  in the above sort sheet sequence process. 
   In this process, initially it is judged whether or not the operation mode is the staple-sort mode (step S 601 ). If judged that the operation mode is not the staple-sort mode, it is further judged whether or not the sheet discharged onto the process tray  630  is the sheaf discharge sheet (step S 602 ). If judged that the discharged sheet is not the sheaf discharge sheet, the process terminates and the flow returns to the above sort sheet sequence process. 
   On the other hand, if judged in the step S 602  that the discharged sheet is the sheaf discharge sheet, the rock guide  650  is driven such that the discharge roller  680   a  comes into contact with the sheaf on the process tray  630  (step S 605 ). Then, after the bound of the discharge roller  680   b  ends, the roller  680   b  is driven for a predetermined amount, and as a speed of a sheaf discharge motor M 180  is controlled, the sheaf on the process tray  630  is discharged onto the stack tray  700  (step S 606 ). 
   Subsequently, the stack tray  700  is moved up and down to complete the sheaf stacking onto the tray  700  (step S 607 ). After then, the value of the discharge counter is set to be “0” (step S 608 ), and the process terminates. 
   On the other hand, if judged in the step S 601  that the operation mode is the staple-sort mode, it is further judged whether or not the sheet discharged on the process tray  630  is the sheaf discharge sheet (step S 603 ). If judged that the discharged sheet is not the sheaf discharge sheet, the process terminates, and the flow returns to the above sort sheet sequence process. On the other hand, if judged that the discharged sheet is the sheaf discharge sheet, the flow advances to a staple process sequence (step S 604 ). After the staple process for the sheaf on the process tray  630  terminates, the flow advances to the above step S 605  to move the rock guide  650  downward, thereby performing the above sheaf discharge operation (steps S 605  to S 608 ). After then, the process terminates and the flow returns to the sort sheet sequence. 
   (Staple Process) 
     FIG. 32  is a flow chart showing a procedure in the staple process. The staple process is executed in the step S 604  in the above sheaf discharge operation discrimination process. 
   In the staple process, initially the stapler  601  is moved for a predetermined amount up to a staple position (step S 701 ), the sheaf on the process tray  630  is then adjusted or aligned by an adjustment means  640  composed of the front-side and rear-side adjustment members  641  and  642  (step S 702 ), and the staple operation for a (first) staple point is performed (step S 703 ). 
   Then, it is judged whether or not the binding mode is the staple two-point binding mode (step S 704 ). If judged that the binding mode is not the two-point binding mode, the adjustment for the sheaf by the adjustment means  640  is released (step S 707 ), and the staple process terminates. 
   On the other hand, if judged in the step S 704  that the binding mode is the staple two-point binding mode, the stapler  601  is moved for a predetermined amount up to a second staple position (step S 705 ), and the staple operation for a second staple point is performed (step S 706 ). Then, the adjustment for the sheaf by the adjustment means  640  is released (step S 707 ), and the staple process terminates. 
   Subsequently, a concrete example of the sheaf discharge operation will be explained on the basis of the paper attribute discrimination process.  FIGS. 33A to 33C  are views showing the concrete example of the sheaf discharge operation. 
     FIG. 33A  shows a case where the sheaf discharge operation is performed on the original of eight pages (i.e., sheets). In this case, any sheet designation is not performed on the sheets (numbers 1 to 4) corresponding to first to fourth pages of the original, the value of the buffer passage counter is counted up to “4” (step S 501 ), and the sheets are stacked on the process tray as there are (step S 512 ). 
   The following sheet (number  5 ) corresponding to fifth page of the original is designated as the sheaf discharge sheet (steps S 512  and S 511 ). When this sheet is stacked on the process tray, then the sheaf discharge operation for the first to fifth pages of the original is performed. 
   The following sheets (numbers  6  and  7 ) corresponding to sixth and seventh pages of the original are designated as the wind sheets (step S 506 ), and these sheets are wound around the buffer roller. When the sixth and seventh sheets are stacked on the process tray together with the sheet which corresponds to eighth page of the original and is designated as the final sheet of the sheaf discharge sheet (steps S 502  and S 511 ), the sheaf discharge operation for the sixth to eighth page of the original is performed. 
   When the sheaf discharge operation of the final sheet is performed, then the value of the wind counter is set to be “2” (step S 510 ). Therefore, the sheets corresponding to first and second pages in the next original are designated as the wind sheets, and the similar sheaf discharge operation for these sheets is performed. 
     FIG. 33C  shows a case where the sheaf discharge operation is performed on the original of six pages (i.e., sheets). In this case, like the case of the eight-page original, any sheet designation is not performed on the sheets corresponding to first to third pages of the original, and these sheets are stacked on the process tray as there are (step S 512 ). Since the sheet corresponding to following fourth page of the original is the sheet two before the final sheet in the sheaf (step S 509 ), such the fourth sheet is designated as the sheaf discharge sheet (step S 511 ), and the sheaf discharge operation for the first to fourth pages of the original is performed. 
   In case of performing the designation operation for the sheaf discharge sheet, since the value of the wind counter is “2” (step S 510 ), the sheet corresponding to fifth page of the original is designated as the wind sheet (step S 506 ) and also designated as the final sheet of the sheaf discharge sheet (step S 511 ). When such the fifth sheet is stacked on the process tray together with the sheet corresponding to sixth page of the original, then the sheaf discharge operation is performed. The sheets corresponding to first and second pages of the following sheaf (i.e., original) are designated as the wind sheets. 
   As described above, by performing the sheaf discharge operation in which the wind sheet and the sheaf discharge sheet are designated, the next or following sheet is not discharged onto the process tray while the sheaf of sheets stacked on the process tray is being discharged onto the stack tray. Also, the sheaf discharge operation can be performed without stopping the body itself of the operation of the image formation apparatus. Moreover, since the sheaf discharge operation is performed according to the sheet two before the final sheet in the sheaf, it can be prevented that the sheaf discharge operation is performed as the final sheet in one sheaf and the first sheet in next sheaf overlap each other. 
   In the step S 509  (in case of six-page original), if the sheaf discharge is not performed according to the sheet two before the final sheet in the sheaf, as shown in  FIG. 33B , the final (i.e., sixth) sheet in the sheaf is wound around the buffer roller while the sheaf discharge operation for the first to fifth sheets is being performed, and such the sixth sheet is discharged onto the process tray together with the first sheet in the next sheaf, whereby the sort (offset) operation can not be normally performed. 
   In the embodiment, the two sheets are wound around the buffer roller, and the sheaf discharge operation is performed when the sheet two before the final sheet of the sheaf is discharged onto the process tray. However, in a case where B sheets of paper can be wound around the buffer roller, the sheaf discharge operation may be performed when any one of the sheets (B+1) to two before the final sheet of the sheaf is stacked on the process tray. That is, in case of the six-page original shown in  FIG. 33C , the sheaf discharge operation may be performed when the sheet of the number “ 3 ” is stacked on the process tray. If doing so, the sheets of the numbers “ 4 ” and “ 5 ” are wound around the buffer roller and then stacked on the tray together with the final sheet of the number “ 6 ”. 
   Further, in the embodiment, the two sheets are wound around the buffer roller and then stacked on the process tray together with the following third sheet. However, the number of sheets to be wound is not limited to two, but the single or the three or more sheets may be wound around the roller. That is, such the number may be appropriately set according to the carrying speed of the sheet sent from the image formation apparatus body to which a sheet postprocess device is installed, the sheaf discharge operation, and the like. 
   As explained above, in the mode not to perform the binding process, the sheaf discharge operation is performed according as the predetermined number of sheets are stacked on the process tray or according as final one of the sheets constituting a group is stacked on the process tray. Therefore, the sheaf discharge operation can be performed without breaking the sheaves of sheets stacked on the stack tray. 
   Further, in the case where the sheets on the process tray are adjusted or aligned at either the first adjustment position or the second adjustment position by the adjustment members, the adjustment position defined by the adjustment member is changed according as the final one of the sheets constituting the group is stacked on the stack tray. Therefore, the sheaf discharge operation can be performed in such the state as the sheets have been adjusted in each sheaf (i.e., group). 
   Furthermore, in the case where the sheet is once stagnated in the buffer path and then carried to the process tray, it is controlled that the sheet is stagnated in the buffer path according as the binding process starts or the sheaf discharge operation starts. Therefore, in case of performing the sheaf discharge operation, the next or following sheet is not discharged onto the process tray while the sheaf of sheets stacked on the process tray is being discharged onto the stack tray, and also the operation of the image formation apparatus body is not stopped during such the operation. 
   Furthermore, in the case where the sheaf is discharged from the process tray, such the sheaf discharge operation is performed according as a second predetermined number of sheets smaller than a first predetermined number of sheets are stacked on the process tray when the sheet size is larger than a predetermined size. Therefore, the sheaf discharge operation for the sheets of which size is large can be performed with the sheaf having the small number of sheets. Thus, the sorting can be easily performed without breaking the sheaves of sheets stacked on the stack tray.