Patent Publication Number: US-6702279-B2

Title: Sheet treating apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a sheet treating apparatus in a copier, a laser beam printer or the like, and an image forming apparatus provided with the same, and more particularly to a sheet treating apparatus improved so that during the alignment and stitching process of sheets on the surfaces of which images have been formed by an image forming apparatus and which are delivered, particularly the processing operation of aligning the sheets, the grouping of the sheets by aligning means can be effected and also the alignment of the grouped sheet bundle can be effectively effected, and an image forming apparatus provided with such sheet treating apparatus. 
     2. Related Background Art 
     Generally, as sheet treating apparatuses, there have already been proposed and put into practice numerous apparatuses comprising a combination of first treating means for aligning and grouping sheets on which images have been formed and stapling a part of the bundle sheet as required, and second treating means for receiving and containing each aligned sheet bundle or stapled sheet bundle, including apparatuses disclosed, for example, in Japanese Patent Application Laid-Open No. 11-199123. 
     The construction of the aligning portion of a conventional sheet treating apparatus of this type is schematically shown in FIG. 33 of the accompanying drawings. In FIG. 33, the conventional sheet treating apparatus is comprised of a pair of carrying-out rollers  701  comprising a lower carrying-out roller  701   a  and a carrying-out roller  701   b  for carrying out sheets P from a sort path  700 , a treating unit  800  having first treating means for receiving, aligning and grouping the sheets P carried out, and stapling a part of the sheet bundle as required, and a stack tray  900  for containing and stacking therein each sheet bundle bundle-delivered after treatment. 
     Knurled belts  702  are wound on several axial locations between the lower carrying-out roller  701   a  and the carrying-out roller  701   b  of the pair of carrying-out rollers  701 , and sheet guides  703  are disposed at appropriate locations among the knurled belts  702 . 
     The treating unit  800  has a treating tray  801  inclined by the downstream side (the left upper portion as viewed in FIG. 33) thereof with respect to the direction of delivery of the sheets P being positioned upwardly and the upstream side (the right lower side as viewed in FIG. 33) thereof being positioned downwardly, a trailing end stopper portion  802  at the upstream side end portion, a pair of right and left aligning members  803  in the widthwise direction of the sheet, a pair of bundle delivery rollers  804  comprising a set of lower and upper bundle delivery rollers  804   a  and  804   b  disposed downstream of the treating tray  801 , a swingable guide  805  having an upper bundle delivery roller  804   b  on the underside of the leading end thereof, and supporting the upper bundle delivery roller  804   b  for movement toward and away from the lower bundle delivery roller  804   a , and a pull-in paddle  806  disposed above the intermediate portion. 
     In this case, the lower and upper bundle delivery rollers  804   a  and  804   b  of the pair of bundle delivery rollers  804  receive the sheet P from the pair of carrying-out rollers  701  onto the treating tray  801  with the upper bundle delivery roller  804   b  brought into its open state in which it is spaced apart from the lower bundle delivery roller  804   a  by the swinging control of the swingable guide  805 , and the upper bundle delivery roller  804   b  is brought into its closed state in which it is in contact with the lower bundle delivery roller  804   a  in synchronism with the termination of the reception, and also the lower bundle delivery roller  804   a  is rotatively driven in a clockwise direction to thereby bias the received sheet P so as to pull it back to the upstream trailing end stopper portion  802  side, i.e., the upstream side, on the treating tray  801 , and then the upper bundle delivery roller  804   b  is again spaced apart from the lower bundle delivery roller  804   a.    
     Also, the sheet P biased to the upstream side is continuedly subjected to the pulling-back action by the rotative driving of the pull-in paddle  806  and also is aligned by the operation of the aligning members  803 , and the feeding-in action for the end portion of the sheet by the rotation of the knurled belts  702  is applied thereto, and the sheet P is dashed against the trailing end stopper portion  802  via the sheet guides  703 , and the aligning operation is terminated in this manner. 
     The knurled belts  702 , as shown in FIG. 33, are wound on the lower delivery roller  701   a  adjacent to the lower portion between the pair of carrying-out rollers  701 , i.e., adjacent to the treating tray  801  and are made rotatable and also, there is provided an idle runner  791  idly rotated in contact with the lower inner peripheral surface of the knurled belts  702 , and during the paddling and aligning operations which will be described below, and particularly at the start of the aligning operation performed subsequently to the paddling operation, the idle runner  791  is pulled and operated toward the rearward side (the right side) as viewed in FIG. 33, and further to the supporting surface side of the trailing end stopper portion  802  by a solenoid  792  through a link  793 , whereby the knurled belts are pulled toward the inner side of the sheet guide  703  above them and are deformed (as indicated by the broken line in FIG. 33) so as not to hamper the sheet P from being dashed against the trailing end stopper portion  802 . 
     The sheet P delivered from the pair of carrying-out rollers  701  slides on the treating tray  801  until it is dashed against the dashing support surface  802   a  of the trailing end stopper portion  802  by its own gravity and the action of the pull-in paddle  806  which will be described later and the feeding action by the underside of the knurled belts  702  while the trailing end edge of the sheet P is downwardly guided by the sheet guides  703 . 
     The sheet P having dashed is aligned widthwisely of the sheet by the aligning members  803  to thereby form a sheet bundle. 
     The sheet bundle aligned on the treating tray  801  is subjected to the stitching process and so on at the aligning position, whereafter the upper bundle delivery roller  804   b  is brought into contact with the lower bundle delivery roller  804   a , and the lower bundle delivery roller  804   a  is now rotatively driven in a counter-clockwise direction, whereby the sheet bundle having been subjected to the treatment is bundle-delivered onto the stack tray  900 . 
     In the above-described example of the conventional art, however, the knurled belts have been driven at two positions, i.e., a position in which they contact with the sheet shown in FIG.  33  and feed the end portion of the sheet to the trailing end stopper portion  802  and a retracted position in which they are completely spaced apart from the sheet and are hidden behind the sheet guides  703 . 
     Therefore, when as shown in FIG. 32 of the accompanying drawings, the number of sheet bundles is great (the height of the bundles is great), the area of contact between the sheet P and the knurled belts  702  becomes large and therefore, the feeding-in force for the sheet P becomes greater than necessary and the sheet P might run upon the trailing end stopper portion  802  or might be buckled. On the other hand, if the height of the knurled belt  702  at the feeding-in position is made great in accordance with the case where the height of sheet bundles is great, when the number of sheet bundles stacked in the treating tray  801  is small, the area of contact between the sheet P and the knurled belt  702  will become small or they will not come into contact with each other, and the feeding-in force for the sheet will become small and it may become impossible to feed the sheet P to the trailing end stopper portion  802 . 
     SUMMARY OF THE INVENTION 
     So, it is the object of the present invention to provide a sheet treating apparatus which always makes the feeding force of an endless belt member substantially constant irrespective of the number of sheets stacked on a treating tray, and can effect more stable stacking and alignment of sheets, and an image forming apparatus provided with the same. 
     A typical construction according to the present invention for achieving the above object comprises stacking tray means having a stacking surface for receiving and stacking sheets thereon and a stopper portion for regulating the end portions of the sheets, a delivery rotary member for delivering the sheets to the stacking tray means, an endless belt member contacting with and acting on the upper surface of the sheets on the stacking tray means, and feeding the sheet to be delivered so as to pull the end portion thereof into the stopper portion, and traction means for pulling one end of the endless belt member in a predetermined direction, and during the sheet feeding by the endless belt member, the traction means is operated in conformity with the height of the sheets stacked on the stacking tray means to thereby control the contact pressure of the endless belt member against the sheets stacked on the stacking tray means so as to become substantially constant. 
     The stacking tray means is inclined so that the downstream side thereof with respect to the delivery direction may become higher, and the sheet to be delivered is switched back to return with the direction thereof changed over, and the stopper portion may preferably be provided on the downstream side with respect to the direction of return of the sheet. 
     The endless belt member may preferably be supported with a portion of its inner peripheral surface twined around the delivery rotary member and be rotated with the delivery rotary member. 
     The construction may have height detecting means for detecting the height of the sheets stacked on the stacking tray means, and the traction means may be operated in conformity with the height of the sheets detected by the height detecting means. 
     The number of the sheets stacked on the stacking tray means may be counted to find the height of the sheets, and the traction means may be operated in conformity with the value thereof. 
     In the above-described construction, the endless belt member tries to feed the sheet with a substantially constant force irrespective of the stack height of the sheet bundle and therefore, the inconvenience during stacking that the sheet does not arrive at the stopper portion of the stacking tray means or is buckled or runs upon the stopper portion can be eliminated. 
     Accordingly, during the sheet aligning process by aligning means for effecting such treatment as a stitching process on the stacking tray means, the endless belt member can be deformed so as not to contact with the sheet by the pulling operation for the endless belt member by the traction means, whereby the smoothness of the alignment movement of the sheet in the widthwise direction thereof can be achieved, and irrespective of the stack height of the sheet bundle, the endless belt member tries to feed the sheet with a substantially constant force and therefore, the inconvenience during stacking that the sheet does not arrive the stopper portion at the rear end of the stacking tray means or is buckled or runs upon the stopper can be eliminated. 
     Also, the traction means is made to perform an upwardly pulling operation relative to the stacking surface of the stacking tray, whereby at a smaller movement stroke, the endless belt member can be retracted from the sheet, and the time required for control becomes short and productivity is improved, or the size of the apparatus can be made small. 
     Further, provision is made of height detecting means for detecting the height of the sheet bundle stacked on the stacking tray means, and the amount of traction is determined on the basis of information detected by the height detecting means, whereby it becomes possible to more accurately uniformize the amount of contact between the sheet bundle and the endless belt member and further, the feeding force of the endless belt member, and the inconvenience during stacking can be eliminated. 
     The present invention is constructed as previously described and therefore, the endless belt member tries to feed the sheet with a substantially constant force irrespective of the stack height of the sheet bundle and therefore, the inconvenience during stacking that the sheet does not arrive at the stopper portion at the rear end of the stacking tray means or is buckled or runs upon the stopper portion can be eliminated. 
     Accordingly, during the sheet aligning process by the aligning means for effecting such treatment as a stitching process on the stacking tray means, the endless belt member can be deformed so as not to contact with the sheet by the pulling operation for the endless belt member by the traction means, whereby the smoothness of the alignment movement of the sheet in the widthwise direction thereof can be achieved, and irrespective of the stack height of the sheet bundle, the endless belt member tries to feed the sheet with a substantially constant force and therefore, the inconvenience during stacking that the sheet does not arrive at the stopper portion at the rear end of the stacking tray means or is buckled or runs upon the stopper can be eliminated. 
     Also, the traction means is made to perform an upwardly pulling operation relative to the stacking surface of the stacking tray, whereby at a smaller movement stroke, the endless belt member can be retracted from the sheet, and the time required for control becomes short and productivity is improved or the size of the apparatus can be made small. 
     Further, provision is made of height detecting means for detecting the height of the sheet bundle stacked on the stacking tray means, and the amount of traction is determined on the basis of information detected by the height detecting means, whereby it becomes possible to more accurately uniformize the amount of contact between the sheet bundle and the endless belt member and further, the feeding force of the endless belt member, and the inconvenience during stacking can be eliminated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general cross-sectional illustration schematically showing the construction of a sheet treating apparatus according to an embodiment of the present invention. 
     FIG. 2 is a main section side cross-sectional illustration of a staple unit. 
     FIG. 3 is a plan illustration as viewed along the direction indicated by the arrow III in FIG.  2 . 
     FIG. 4 is a back illustration as viewed along the direction indicated by the arrow IV in FIG.  2 . 
     FIG. 5 is a vertical cross-sectional side illustration of a swingable guide and a treating tray. 
     FIGS. 6A and 6B are side illustrations showing a knurled belt and a belt moving mechanism. 
     FIG. 7 is a plan illustration as viewed along the direction indicated by the arrow VII in FIG.  5  and showing the treating tray and an aligning member moving mechanism. 
     FIG. 8 is a plan illustration of a stacking tray moving mechanism. 
     FIG. 9 is an illustration of a sensor arrangement around the stacking tray. 
     FIG. 10 is a side illustration of a punch unit. 
     FIG. 11 is a side illustration showing the operative state of the punch unit. 
     FIG. 12 is a front illustration of the punch unit. 
     FIG. 13 is an illustration of the lateral registration sensor moving mechanism of the punch unit. 
     FIG. 14 is an illustration of the lateral registration sensor moving mechanism of the punch unit. 
     FIG. 15 shows the operation of a sheet treating apparatus portion during a nonsort mode. 
     FIG. 16 shows the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIG. 17 shows the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIG. 18 shows the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIG. 19 shows the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIG. 20 shows the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIG. 21 shows the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIG. 22 shows the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIGS. 23A and 23B show the operation of the sheet treating apparatus portion during the staple sort mode. 
     FIG. 24 shows the operation of the sheet treating apparatus portion during the sort mode. 
     FIG. 25 shows the operation of the sheet treating apparatus portion during the sort mode. 
     FIG. 26 shows the operation of the sheet treating apparatus portion during the sort mode. 
     FIG. 27 is a plan view of the treating tray showing the sheet bundle aligning operation. 
     FIG. 28 is a plan view of the treating tray showing the sheet bundle aligning operation. 
     FIG. 29 is a plan view of the treating tray showing the sheet bundle aligning operation. 
     FIG. 30 is a plan view of the treating tray showing the sheet bundle aligning operation. 
     FIG. 31 is a cross-sectional illustration schematically showing the construction of an image forming apparatus provided with a sheet treating apparatus to which an embodiment of the present invention is applied. 
     FIG. 32 is a cross-sectional illustration schematically showing the construction of a sheet aligning portion in a sheet treating apparatus according to the conventional art. 
     FIG. 33 is a cross-sectional illustration schematically showing the construction when a number of sheets are stacked on a sheet aligning portion in the sheet treating apparatus according to the conventional art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A sheet treating apparatus according to an embodiment of the present invention and an image forming apparatus provided with the same will hereinafter be described in detail with reference to FIGS. 1 to  31 . 
     General Construction of Image Forming Apparatus 
     A description will first be made of an image forming apparatus according to the present invention, wherein the image forming apparatus is provided with a sheet treating apparatus. 
     FIG. 31 is a general cross-sectional illustration schematically showing the construction of an example of an image forming apparatus (copying apparatus) system provided with a sheet treating apparatus according to the present embodiment. 
     In the apparatus construction shown in FIG. 31, the image forming apparatus (copying apparatus)  300  is provided with an original reading portion  400  comprising an original placement stand  401  such as a platen glass plate for reading an automatically fed original D to be copied, a light source  402  and a lens system  403 , a feeding portion  500  for a sheet P for forming an image thereon, an image forming portion  600 , a sheet treating apparatus  1  for treating and stacking thereon the sheet P having an image formed thereon and delivered from a pair of delivery rollers  302  after image formation. 
     The feeding portion  500  is provided with cassettes  501  and  502  containing sheets P therein and detachably mounted on the main body of the apparatus, and a deck  504  disposed on a pedestal  503 . The image forming portion  600  is provided with a cylindrical photosensitive drum  601 , and a primary charger  602 , an exposing portion  603 , a developing device  604 , a transfer charger  605 , a separation charger  606 , a cleaner  607  and so on around the photosensitive drum  601 , and a fixing device  608  is disposed on the downstream side of the image forming portion  600  through a sheet transporting device  301 . 
     In the above-described image forming apparatus  300 , when a feed signal is outputted from a controller  310  in the main body of the apparatus, the feeding of the sheet P from the cassettes  501 ,  502  or the deck  504  of the feeding portion  500  is started. 
     On the other hand, the image of the original D placed on the original placement stand  401  is read by light from the light source  402  and is applied to the surface of the photosensitive drum  601  via the lens system  403 . The photosensitive drum  601  is charged in advance by a primary charger  602  and an electrostatic latent image is formed on the surface of the drum by the application of the reading light, and the electrostatic latent image is developed by the toner of the developing device  604 , whereby a corresponding toner image is formed. 
     The sheet P fed from the feeding portion  500  has its skew feed corrected by registration rollers  505  and is fed to the image forming portion  600  in timed relationship therewith. Then, in the image forming portion  600 , the toner image on the surface of the photosensitive drum  601  is transferred onto the sheet P by the transfer charger  605 , whereafter the sheet P onto which the toner image has been transferred is charged to the opposite polarity by the separation charger  606 , and is separated from the surface of the photosensitive drum  601 . 
     Thereafter, the sheet P is transported to the fixing device  608  by a sheet transporting device  301 , and the transferred image is permanently fixed by this fixing device  608 . The sheet P on which an image has been thus formed is delivered to the sheet treating apparatus  1  side by the pair of delivery rollers  302 . 
     General Construction of Sheet Treating Apparatus 
     The sheet treating apparatus according to the present invention will now be described. FIG. 1 is a general cross-sectional illustration schematically showing the construction of the sheet treating apparatus according to the present embodiment. 
     In FIG. 1, the reference numeral  2  designates a pair of inlet rollers for receiving the sheet P delivered from the pair of delivery rollers  302  of the image forming apparatus  300 , the reference numeral  3  denotes a pair of first transporting rollers for transporting the received sheet P, and the reference numeral  31  designates a sheet detecting sensor on the entrance side for detecting the passage of the sheet P. Also, the reference numeral  50  denotes a punch unit for forming perforations in the vicinity of the trailing end portion of the transported sheet. The reference numeral  5  designates a roller of a relatively large diameter (hereinafter referred to as the buffer roller) disposed on the way of transportation, and it transports the sheet P while pressing the sheet P against the surface of the roll by pressing runners  12 ,  13  and  14  disposed around the exterior of the roller  5 . 
     The reference numeral  11  denotes a first changeover flapper for selectively changing over between a nonsort path  21  and a sort path  22 . The reference numeral  10  designates a second changeover flapper for effecting the changeover of the sort path  22  and a buffer path  23  for temporarily storing the sheet P therein. The reference numeral  33  denotes a sensor for detecting the sheet P in the nonsort path  21 , and the reference numeral  32  designates a sensor for detecting the sheet P in the buffer path  23 . 
     The reference numeral  6  denotes a pair of second transporting rollers in the sort path  22 , and the reference numeral  129  designates a treating unit including a treating tray (stacking tray means)  130  which is a first stacking tray provided to temporarily accumulate the sheets P therein and align these accumulated sheets P and also to effect staple treatment by the stapler  101  of a stapler unit  100  (stitching means). One of a pair of bundle delivery rollers which are bundle transporting means, herein a lower delivery roller  180   a  as a fixed side, is disposed on the delivery end side of the treating tray  130 . The reference numeral  7  denotes a pair of first delivery rollers disposed in the sort path  22  for delivering the sheet P onto the treating tray  130 , and the reference numeral  9  designates a pair of second delivery rollers disposed in the nonsort path  21  for delivering the sheet P onto a sample tray  201 . 
     Further, the reference character  180   b  denotes an upper delivery roller supported on a swingable guide  150  and adapted to pressurizingly contact with the lower delivery roller  180   a  when the swingable guide  150  has come to its closed position, and bundle-deliver the sheets P on the treating tray  130  onto a stacking tray (second stacking tray)  200 . The reference numeral  40  designates a bundle stacking guide for supporting the edge of the trailing end (the trailing end with respect to the direction of bundle delivery) of the sheet bundles stacked on the stacking tray  200  and the sample tray  201 , and herein this bundle stacking guide  40  serves also as the outer packaging of the sheet treating apparatus  1 . 
     Construction of the Staple Unit 
     The staple unit (stitching means)  100  will now be described with reference to FIGS. 2 to  4 . FIG. 2 is a main section side cross-sectional illustration of the staple unit, FIG. 3 is a plan illustration as viewed along the direction indicated by the arrow III in FIG. 2, and FIG. 4 is a back illustration as viewed along the direction indicated by the arrow IV in FIG.  2 . 
     The stapler (stitching means)  101  is fixed onto a movable stand  103  with a holder  102  interposed therebetween. The movable stand  103  has a set of stud shafts  104  and  105  fixed in parallel with the trailing end edge of the sheets stacked on the treating tray  130 , and rolling runners  106  and  107  are rotatably assembled to the stud shafts  104  and  105 , respectively, and the rolling runners  106  and  107  are movably engaged in a series of aperture-shaped guide rails  108   a ,  108   b ,  108   c  formed likewise in parallel with a fixed stand  108 . 
     The rolling runners  106  and  107  have flanges  106   a  and  107   a  having a diameter larger than the aperture width of the series of aperture-shaped guide rails  108   a ,  108   b  and  108   c , while on the other hand, supporting runners  109  are provided at three locations on the lower surface side of the movable stand  103  holding the stapler  101 , and the movable stand  103  is moved on the fixed stand  108  along the series of aperture-shaped guide rails  108   a ,  108   b  and  108   c.    
     Here, the series of aperture-shaped guide rails  108   a ,  108   b  and  108   c , as shown in FIG. 3, is formed into a shape comprising a main guide rail aperture portion  108   a , a left end guide rail aperture portion  108   b  branching off from the left end portion side thereof and parallel therewith, and a right end guide rail aperture portion  108   c  branching off from the right end portion side thereof and parallel therewith. Accordingly, because of the rail shape of the respective portions, when the stapler  101  is positioned on the left end portion side, the rolling runner  106  is moved into the left end portion of the rail aperture portion  108   b  and the rolling runner  107  is moved into the left end portion of the rail aperture portion  108   a , and they are maintained in a rightwardly inclined posture in which they are inclined to the right side by a predetermined angle. When the stapler  101  is positioned on the intermediate portion, the rolling runners  106  and  107  are both in the rail aperture portion  108   a  and are maintained in a parallel posture in which they are not inclined. Further, when the stapler  101  is positioned on the right end portion side, the rolling runner  107  is moved into the right end portion of the rail aperture portion  108   c  and the rolling runner  106  is moved into the right end portion of the rail aperture portion  108   a , and the rolling runners are maintained in a leftwardly inclined posture in which they are inclined leftwardly by a predetermined angle, and the action of changing these postures is effected by an operating cam, not shown. 
     The staple unit  100  is provided with a position sensor, not shown, for detecting the home position of the stapler  101 , and usually the stapler  101  stands by at the home position on the left end side. 
     A moving mechanism for the stapler  101  will now be described in detail. One rolling runner  106  of the movable stand  103  has a pinion gear  106   b  formed integrally therewith below the flange  106   a  and has a belt pulley  106   c  provided integrally therewith above it. The pinion gear  106   b  is connected through a driving belt looped around the output pulley of a driving motor M 100  on the surface of the stand and the belt pulley  106   c  and is in meshing engagement with a rack gear  110  fixed to the fixed stand  108  along the rail aperture, and the movable stand  103  is movable widthwisely of the sheet with the stapler  101  correspondingly to the forward or reverse rotation of the driving motor M 100 . 
     Also, a stopper bringing-down runner  112  is provided on a stud shaft  111  downwardly extending from the underside of the movable stand  103 , and this stopper bringing-down runner  112  plays the role of pivotally moving the trailing end stopper portion  131  of the treating tray  130  to avoid the collision of the trailing end stopper portion  131  with the stapler  101 , as will be described later. 
     Trailing End Stopper Portion 
     A description will now be made of the trailing end stopper portion  131  for striking against and supporting the trailing end edge of the sheet P on the treating tray  130 . 
     The trailing end stopper portion  131 , as shown in FIG. 2, has a striking and supporting surface  131   a  formed vertically upwardly relative to the stacking surface of the treating tray  130  for striking against and supporting the trailing end edge of the sheet P, and this striking and supporting surface  131   a  is pivotally movable downwardly about a pivot pin  131   b  as indicated by the arrow to the underside of the treating tray  130 . Also, a main link  132  provided with a cam surface  132   a  against which the stopper bringing-down runner  112  abuts and which is urged and actuated thereby is rammed against and positioned on a ramming plate  136  and is pivotally movable about a shaft  134  fixed to a frame or the like, not shown, against the force of a tension spring  135  and is connected to a pin  132   b  at the upper end portion for sliding movement in a slot in the other end portion of a connecting link  133  having one end portion thereof pivotally supported on the trailing end stopper portion  131  by a pin  131   c.    
     Accordingly, in this case, with regard to the trailing end stopper portion  131  which is brought into interfering relationship with the stapler  101  with the movement of the movable stand  103 , the stopper bringing-down runner  112  of the movable stand  103  urges the cam surface  132   a  of the main link  132 , whereby the trailing end stopper portion  131  is pivotally moved to a non-interfering position indicated by dots-and-dash line in FIG. 2, whereby the contact thereof with the stapler  101  is avoided. After the termination of staple treatment which will be described later, the movable stand  103  is returned to its home position, whereby the trailing end stopper portion  131  is also returned to its original state. Regarding the stopper bringing-down runner  112 , in order to hold the trailing end stopper portion  131  in its retracted position during the operation of the stapler  101 , a plurality of (herein three) such runners are disposed in the direction of movement of the movable stand  103 . 
     Also, a stapler stopper (indicated by the dots-and-dash line in FIG. 2)  113  having a supporting surface similar in shape to the striking and supporting surface  131   a  of the trailing end stopper portion  131  is attached to each side of a holder  102  holding the stapler  101 , and the supporting of the trailing end edge of the sheet is possible even if the trailing end stopper portion  131  is in its retracted position. 
     Epitome of the Treating Unit 
     The treating unit  129  including the treating tray  130  will now be described with reference to FIGS. 5,  6 A and  6 B. FIG. 5 is a longitudinal cross-sectional side illustration of a swingable guide and the treating tray, and FIGS. 6A and 6B are side illustrations showing a knurled belt and a belt moving mechanism. 
     The treating unit  129  constitutes the sheet treating apparatus, and is comprised of the treating tray  130 , the trailing end stopper portion  131 , aligning means  140 , a swingable guide  150 , a pull-in paddle (paddle means)  160 , a pair of bundle delivery rollers  180  and a knurled belt  190  as an endless belt member rotatively driven by the aforedescribed pair of first delivery rollers  7 . 
     The treating tray  130  is set in an inclined state by having its downstream side with respect to the direction of delivery of the sheet bundle (the left upper side as viewed in FIGS. 5,  6 A and  6 B) positioned upwardly and having its upstream side (the right lower side as viewed in FIGS. 5,  6 A and  6 B) positioned downwardly, and on the lower end portion thereof which is the upstream side, there are disposed sheet guides  130   c  disposed at predetermined intervals in the widthwise direction of the sheet, the knurled belt  190  and the trailing end stopper portion  131 , and stack height detecting means  195  is provided near the trailing end stopper portion  131 . Further, on the intermediate portion of the treating tray, the aligning means  140  is disposed occupying the external position corresponding to the left and right sides of the sheet P. Also, the swingable guide  150  including the pull-in paddle  160  and the pair of bundle delivery rollers  180  which will be described later is disposed in the upper portion which is also the downstream side, more particularly the upper area portion substantially constituting the treating unit. 
     The knurled belt  190  is an endless belt formed with a nonskid knurl on the entire outer peripheral surface thereof and molded to a required diameter, and having flexibility with which it is deformable in the direction of rotation thereof, and as shown in FIGS. 6A and 6B, and is rotatably twined on the delivery roller  7   a  adjacent to the lower portion between the pair of first delivery rollers  7 , i.e., adjacent to the treating tray  130  and also, a floating runner  191  floatingly rotated in contact with the lower inner peripheral surface of the knurled belt  190  is rotatably provided on a traction arm  196 . 
     The floating runner  191  is movable in a predetermined direction by moving means comprised of the traction arm  196  or the like. Traction means for the endless belt member is constituted by the floating runner and the moving means as described above. The traction arm  196  extends at a predetermined angle with respect to the treating tray  130  toward the trailing end stopper portion  131  of the treating tray below the pair of first delivery rollers  7 , and has a rack portion  196   a  formed integrally therewith. The rack portion  196   a  and a gear portion  192   a  provided on the driving shaft of a motor  192  for traction are in meshing engagement with each other. The motor  192  for traction is a pulse motor, and is designed such that the amount of rotation of the motor is determined by a pulse signal given to the motor and the floating runner  191  is pulled by an amount conforming to the amount of rotation of the motor, whereby the distance h between the knurled belt  190  and the treating tray  130  shown in FIG. 6A is changed. That is, when the floating runner  191  is traction-operated in the direction indicated by the arrow X in FIG. 6A by the motor  192  for traction, the knurled belt  190  separates from the treating tray and the sheet bundle and is deformed and retracted (indicated by the broken line in FIG. 6B) in a direction in which it is pulled toward the inside of the sheet guide  130   c  above it, and when it is retracted to maximum, it comes into the sheet guide  130   c . Conversely, when the floating runner  191  is moved in the direction indicated by the arrow Y in FIG. 6A, the knurled belt  190  and the treating tray  130  come close to each other, and when the floating runner  191  is moved to the fore end portion, the knurled belt  190  and the treating tray  130  assume a position in which they contact with each other. 
     When the sheet P is delivered onto the treating tray  130 , the knurled belt  190  is in a position in which it does not contact with the treating tray  130 . Immediately after the sheet P has been delivered onto the treating tray  130 , the knurled belt  190  is moved to its contacting position and feeds the sheet P toward the trailing end stopper portion  131 . At the start of the aligning operation performed subsequently to the paddle operation which will be described next, the floating runner  191  is traction-operated in the direction indicated by the arrow X in FIG. 6A by the motor  192  for traction, whereupon the knurled belt is spaced apart from the sheet P so as not to hamper the ramming of the sheet P against the supporting surface  131   a  during the aligning operation. 
     When the aligning operation is terminated and the next sheet is delivered onto the treating tray  130 , the floating runner  191  is again moved in the direction indicated by the arrow Y in FIG.  6 A and thus, the knurled belt  190  comes into contact with the sheet P. At this time, the height of the sheet bundle stacked on the treating tray  130  is roughly detected by the stack height detecting means  195  so that the amount of movement of the floating runner  191  may be controlled in conformity with the height of the sheet bundle. 
     Thereby, irrespective of the height of the sheet bundle stacked on the treating tray  130 , the amount of contact between the sheet P and the knurled belt  190  becomes constant. That is, as the stack height of a number of sheets stacked becomes greater, the position of the floating runner  191  when the knurled belt  190  contacts with the sheet deviates in the direction indicated by the arrow X in FIG.  6 A. 
     Thus, the sheet P delivered from the pair of first delivery rollers  7  slides on the treating tray  130  until the trailing end edge of the sheet P is rammed against the striking and supporting surface  131   a  of the trailing end stopper portion  131  while being downwardly guided by the sheet guides  130   c  due to the gravity of its own and the action of the pull-in paddle  160  and the feeding action of the portion of contact of the belt with the sheet by the rotation of the knurled belt  190 . 
     The amount of contact between the knurled belt  190  and the surface of the sheet becomes constant irrespective of the amount of stacked sheets and therefore, the sheet feeding force of the knurled belt  190  becomes substantially constant. 
     Further, as previously described, one lower delivery roller  180   a  constituting the pair of bundle delivery rollers  180  is disposed on the upper end portion of the treating tray  130 , and the other upper delivery roller  180   b  separably brought into contact with the lower delivery roller  180   a  is disposed on the front end portion of the underside of the swingable guide  150 , and these delivery rollers  180   a  and  180   b  are rotatable in forward and reverse directions by a driving motor M 180 . 
     While in the present embodiment, the height of the sheets stacked on the treating tray  130  is directly detected by the stack height detecting means to thereby determine the position of the floating runner  191  conforming thereto, i.e., the height position of the knurled belt  190 , the number of sheets delivered onto the treating tray  130  may be counted, and from the count value and the information of the stack height by the number of sheets obtained in advance by an experiment or the like, the stack height may be conjectured, and the floating runner  191  is moved so as to determine the height position of the knurled belt  190  so that the amount of contact between the sheet and the knurled belt  190  may become constant. 
     Also, design may be made such that the height position of the knurled belt  190  need not be changed for each sheet, but is changed for each plural sheets (e.g. each five sheets or each ten sheets). 
     Aligning Means 
     The aligning means  140  for aligning the sheet pulled into the trailing end stopper portion  131  in a direction orthogonal to the pull-in direction will now be described with reference to FIGS. 5 to  8 . FIG. 7 is a view as viewed along the direction indicated by the arrow VII in FIG. 5, and is a plan illustration of the treating tray and an aligning member moving mechanism, and FIG. 8 is a plan illustration of a stacking tray moving mechanism. 
     A set of aligning members  141  and  142  constituting the aligning means  140  are disposed on the surface of the treating tray  130  in opposed relationship with each other independently as a lower portion and an upper portion (corresponding to the opposite side edges of the sheet P) in FIG. 7, and one upper first aligning member  141  and the other lower second aligning member  142  have aligning surfaces  141   a  and  142   a  perpendicular to the surface of the treating tray  130  for urging and supporting the side edge of the sheet, and rack gear portions  141   b  and  142   b  for supporting the back of the sheet, and the rack gear portions  141   b  and  142   b  are disposed on the underside of the treating tray  130  through a set of guide grooves  130   a  and  130   b  parallel with the vertical direction (corresponding to the widthwise direction of the sheet P) and opened in the surface of the treating tray  130 . 
     That is, the aligning surfaces  141   a  and  142   a  are disposed in opposed relationship with each other on the upper surface side of the treating tray  130 , and the rack gear portions  141   b  and  142   b  are assembled to the underside thereof for movement in the alignment direction. 
     Individual pinion gears  143  and  144  driven for rotation in forward and reverse directions by respective driving motors M 141  and M 142  are in meshing engagement with the rack gear portions  141   b  and  142   b , respectively, whereby the first and second aligning members  141  and  142  are made movable in the alignment direction. For the first and second aligning members  141  and  142 , position sensors, not shown, for detecting their respective home positions are disposed, and in an ordinary case, the first aligning member  141  stands by at a home position set on the upper end portion thereof and the second aligning member  142  stands by at a home position set on the lower end portion thereof. 
     Swingable Guide 
     The swingable guide  150  will now be described. The swingable guide  150 , as previously described, pivotally supports the upper delivery roller  180   b  contacting with the lower delivery roller  180   a  of the pair of bundle delivery rollers  180  in the front end portion of the underside corresponding to the downstream side (the left side as viewed in FIG.  5 ), and is pivotally supported and swingably supported by a support shaft  151  on the rear end portion of the underside corresponding to the upstream side (the right side as viewed in FIG.  5 ), and is swingable by the controlled driving of a rotary cam  152  by a driving motor M 150 , and a closed state in which the upper delivery roller  180   b  is in contact with the lower delivery roller  180   a  is the home position thereof, and a position sensor, not shown, for detecting the home position is provided. 
     When in an ordinary case, each individual sheet P is delivered onto the treating tray  130 , the swingable guide  150  is moved to its opened state (the upper delivery roller  180   b  is spaced apart from the lower delivery roller  180   a  and the swingable guide  150  is upwardly swung) so as to enable the operations of delivery and alignment of the sheet P and the pull-in paddle operation which will be described next to be performed without hindrance, and when the sheet bundle treated on the treating tray  130  is delivered onto the stacking tray  200 , the swingable guide  150  is moved to its closed state (the upper delivery roller  180   b  is brought into contact with the lower delivery roller  180   a  and the swingable guide  150  is downwardly swung). 
     Pull-In Paddle 
     The pull-in paddle  160  will now be described. The pull-in paddle  160 , as shown in FIG. 5, is fixed to a driving shaft  161  above the treating tray  130 , and is adapted to be rotatively driven in a counter-clockwise direction as viewed in FIG. 5 at appropriate timing by a driving motor M 160 , and the length of each paddle is set to a length somewhat greater than the distance to the surface of the treating tray  130 , and the home position thereof is set to a position (a position indicated by the solid line in FIG. 5) which does not hinder the delivery of the sheet P from the pair of first delivery rollers  7  onto the treating tray  130 . 
     When in this state, the delivery of the sheet P onto the treating tray  130  is done, the pull-in paddle  160  is rotatively driven in a counter-clockwise direction, whereby the sheet P delivered onto the treating tray  130 , and further the trailing end edge of the sheet P is pulled in until it is rammed against the striking and supporting surface  131   a  of the trailing end stopper portion  131 , whereafter in a predetermined time, it is stopped at its home position detected by a position sensor, not shown, at good timing. 
     Stacking Tray and Sample Tray 
     The stacking tray  200  and a sample tray  201  will now be described with reference to FIGS. 8 and 9. FIG. 9 is an illustration of a sensor arrangement around the stacking tray. 
     The stacking tray  200  and the sample tray  201  are used properly in conformity with the situation, and the stacking tray  200  disposed below is selected when it receives the sheet bundle at a copy output, a printer output and so on, and the sample tray  201  is selected when it receives sheets at a sample output, an interruption output, an output during the overflow of the stacking tray, a function output, an output during job mixed stacking or the like. 
     The stacking tray  200  and the sample tray  201  are held on tray base plates  202  and  203 , respectively, and can independently run in a vertical direction by the use of stepping motors M 200  and M 201  fixed to the respective base plates  202  and  203  with mounting frame plates  204  and  205  interposed therebetween. In this case, both of the trays  200  and  201  are constructed substantially in the same mode and therefore, herein, chiefly the stacking tray  200  side only will be described. 
     That is, a pair of frames  250  are vertically provided on the opposite end portions of the sheet treating apparatus  1 , and rack gear members  251  serving also as vertical guide rail portions are attached to the frames  250 , and use is made of a pair of guide runners  206  and  207  rotatably provided on a rear end portion extended from one end (corresponding to the left end with the widthwise direction of the sheet as the reference) of the tray base plate  202  and a rear end portion extended from the mounting frame plate  204  opposed thereto (likewise corresponding to the right end) to fit the guide runners  206  and  207  into the respective guide rail portions to thereby hold the stacking tray  200  for vertical movement, and a regulating member  208  is engaged with the turned-back end edge of one frame  250  to thereby restrain and regulate the backlash in the widthwise direction of the sheet. 
     On the other hand, the rotational output of the stepping motor M 200  is transmitted to a pulley  212  on a driving shaft  213  through a timing belt  211 . A ratchet wheel  215  biased by a spring  216  and only axially slidable is provided on the driving shaft  213 , and this ratchet wheel  215  is one-way-engaged with a driving gear  214  on the shaft. One of idler gears  218  disposed on the opposite end portions of a driven shaft  217  is in meshing engagement with the driving gear  214 , and the idler gears  218  are in meshing engagement with the rack gear members  251  through lift gear  219 . That is, the stacking tray  200  is made vertically movable through a driving system comprising these gear trains. 
     Also, the ratchet wheel  215  one-way-engaged with the driving gear  214  on the driving shaft  213  is provided so that during the downward movement of the stacking tray  200 , the driving system may not be damaged, for example, with foreign materials interposed, and herein, a required degree of biasing force is given to the spring  216  so that only during the upward movement of the stacking tray  200 , the ratchet wheel may idly rotate against the biasing force of the spring  216  correspondingly to preset conditions to thereby protect the driving system, and when such idle rotation, i.e., an abnormality, occurs, a clock slit or the like formed in the flange portion of the idler gear  218  may be immediately detected by a sensor S 201  to stop the driving of the stepping motor M 200 . The sensor S 201  is also used for the detection of a step out during the ordinary operation. 
     The disposition of sensors for the control of the upward and downward movement positions of the stacking tray  200  and the sample tray  201  will now be described. A sensor S 202  is a sensor for detecting the stacking area of the sample tray  201 , and detects that the sample tray  201  is positioned within a range from a sensor S 203   a  for detecting the upward movement limit position of the sample tray  201  to a sensor S 205  for detecting the surface of the sheets on the treating tray. 
     A sensor S 203   b  is a sensor for detecting that the sheets P delivered from the pair of second delivery rollers  9  onto the sample tray  201  have reached a predetermined number, and herein it is disposed at a position corresponding to the number of stacked sheets 1,000 from a nonsort sheet surface detecting sensor S 204 . 
     A sensor S 203   c  is a sensor for detecting that the sheets P delivered from the treating tray  130  onto the stacking tray  200  have reached a predetermined number, and is likewise disposed at a position corresponding to the number of stacked sheets 1,000 from the sheet surface detecting sensor S 205 . 
     A sensor S 203   d  is a sensor for limiting the height of stack when the stacking tray  200  receives the sheets P from the treating tray  130 , and is disposed at a position corresponding to the number of stacked sheets 2,000 from the sheet surface detecting sensor S 205 . 
     A sensor S 203   e  is a sensor for setting the downward movement limit position of the stacking tray  200 . 
     Also, sheet presence detecting sensors S 206   a  and S 206   b  are disposed on the stacking tray  200  and the sample tray  201 , respectively. 
     Among these sensors, only the sheet surface detecting sensors S 204  and S 205  are set to a light transmitting type for detecting the presence or absence of the sheet P by the transmission of light from one side edge to the other side edge of the sheet P, and herein, as the sheet surface detecting technique thereof, a state in which the trays  200  and  201  have been moved upwardly from below the respective sheet surface detecting sensors S 204  and S 205  to positions covering them is initial, and after the sheets have been stacked, the trays are moved downwardly until the sensor optical axis appears, whereafter the trays are moved upwardly until they cover the sensor optical axis, and this is repeated. 
     Punch Unit 
     The punch unit  50  will now be described with reference to FIGS. 10 to  14 . FIG. 10 is a side illustration of the punch unit, FIG. 11 is a side illustration showing the operative state of the punch unit, FIG. 12 is a front illustration of the punch unit, and FIGS. 13 and 14 are illustrations of the lateral registration sensor moving mechanism of the punch unit. 
     The punch unit  50 , as shown in FIG. 10, are comprised of punching means  60  and lateral registration detecting means  80 . 
     In the punching means  60 , a required number of sets, herein, a pair of right and left punch members  61  and die members  62  combined with the respective punch members  61  are disposed in a casing  63  at predetermined punch intervals in the left to right direction (corresponding to the widthwise direction of the sheet, and interlocking gears  64  and  65  (see FIG. 12) on the shaft thereof are in meshing engagement with each other, and are rotatable in synchronism with each other in the directions indicated by the arrows B and C in FIG. 10 by the driving of a punching motor  66 , and usually stand by at the home position of FIG.  10 . 
     After in this state, the sheet detecting sensor  31  (see FIGS. 13 and 14) has detected the trailing end of the sheet P introduced, the punching motor  66  is driven at predetermined timing, whereby the punch protruding pieces  61   a  of the punch members  61  and the die aperture portions  62   a  of the die member  62  come into meshing engagement with each other to thereby cut holes in the corresponding portions of the sheet P. In this case, the rotational speeds of the punch members  61  and the die members  62  are made coincident with the rotational speed of the pair of transporting rollers  3  (see FIG.  1 ), and further with the transportation speed of the sheet P in the direction indicated by the arrow A (see FIG.  10 ), whereby simultaneous punching in the course of transportation is possible. 
     On the other hand, the punch casing  63  supporting the punch members  61  and the die members  62  has guide runners  68  lying at upper and lower positions and rotatably supported by support shafts  69 , and the guide runners  68  are fitted onto each guide rails  67  parallel with the widthwise direction of the sheet P to thereby make the movement thereof in the widthwise direction possible and also, as shown in FIGS. 13 and 14, a pinion gear  70  rotatively driven by a punching means moving motor, not shown, is brought into meshing engagement with a rack gear  63   a  formed on the side of one end portion, and further, a punching means initial position detecting sensor  71  having a light receiving portion  71   a  is disposed on the aforementioned end surface. 
     Therefore, the punching means  60  is moved in a direction orthogonal to the direction of transportation of the sheet P, i.e., the directions indicated by the double-headed arrow D and E in FIGS. 13 and 14 (the widthwise direction of the sheet P), by the driving of the punching means moving motor, and with this movement, a punching means initial position defining portion  52  on the main body side of the apparatus can be detected by the punching means initial position detecting sensor  71 , and in this case, the punching means initial position is set to a side several millimeters short of a sheet reference position corresponding to the skew feed of the sheet P or the amount of deviation of the lateral registration. 
     Also, the lateral registration detecting means  80  has a sensor arm  81  provided on one end portion of the punching means  60  and likewise movable in the directions indicated by the double-headed arrow D and E (the widthwise direction of the sheet P) orthogonal to the direction, indicated by the arrow A, of transportation of the sheet P by a pinion gear  82  rotatively driven by a lateral registration moving motor, not shown, being brought into meshing engagement with a rack gear  81   a  on the side edge, and on one end side of the sensor arm  81  which is close to the sheet P, there is provided a lateral registration detecting sensor  83  having a light receiving portion  83   a  for making one side edge of the sheet P movable in the directions indicated by the double-headed arrow D and E (the widthwise direction of the sheet P) orthogonal to the direction of transportation A and detecting one side edge of the sheet P, and on the other end side thereof, there is provided a lateral registration initial position detecting sensor  84  having a light receiving portion  84   a  parallel with the light receiving portion  83   a.    
     Therefore, the lateral registration detecting means  80 , as in the case of the punching means  60 , is moved in the directions indicated by the double-headed arrow D and E (the widthwise direction of the sheet P) orthogonal to the direction of transportation A of the sheet P by the driving of the lateral registration moving motor, and with this movement, the lateral registration initial position defining portion  63   b  corresponding to the pertinent end surface of the punch casing  63  can be detected by the lateral registration initial position detecting sensor  84 , and in this case, the lateral registration detecting sensor  83  can be set at a position corresponding to a selected sheet size. 
     When the side edge of the sheet P is to be detected, the sheet detecting sensor  31  detects the leading end of the sheet P, whereafter the punching means moving motor is driven at predetermined timing to thereby move the punching means  60  and the lateral registration detecting sensor  83 , and the light receiving portion  83   a  of the lateral registration detecting sensor  83  is interrupted by the side edge of the sheet P, whereby this is detected and the punching means and the lateral registration detecting sensor are stopped. That is, thereby, the punching positions for the sheet P can be made all present on the end portion of the sheet. 
     Flow of the Sheet During the Nonsort Mode 
     A description will now be made of the flow of the sheet P in the present sheet treating apparatus. 
     When the user designates the setting of the sheet delivery mode of the image forming apparatus as non-sort, as shown in FIG. 15, the first changeover flapper  11  of the sheet treating apparatus  1  is changed over to receive the sheet P to the nonsort path  21  side, and in this state, the pair of inlet rollers  2 , the pair of first transporting rollers  3  and the buffer roller  5  are rotatively driven to thereby introduce the sheet P delivered from the image forming apparatus  300  into the apparatus and transport it toward the nonsort path  21 . 
     When the trailing end of the sheet P is detected by the nonsort path sensor  33 , the pair of second delivery rollers  9  are rotatively driven at a speed suited for stacking to thereby deliver the sheet P onto the sample tray  201  and cause it to be stacked thereon. 
     When the user designates the setting of the sheet delivery mode of the image forming apparatus as staple sort, as shown in FIG. 16, the first changeover flapper  11  and second changeover flapper  10  of the sheet treating apparatus  1  are changed over to receive the sheet P to the sort path  22  side, and in this state, the pair of inlet rollers  2 , the pair of first transporting rollers  3  and the buffer roller  5  are rotatively driven to thereby introduce the sheet P delivered from the image forming apparatus  300  into the apparatus and transport it toward the sort path  22 . 
     When the trailing end of the sheet P has left the runner  14  at the last stage, the sheet P is delivered onto the treating tray  130  by the knurled belt  190  of the delivery roller  7   a  and the runner  7   b  constituting the aforedescribed pair of first delivery rollers  7 . In this case, the swingable guide  150  is upwardly opened, whereby the upper delivery roller  180   b  is spaced apart from the lower delivery roller  180   a  of the pair of bundle delivery rollers  180 , and a retractable tray  170  is protruded to a protruding position and therefore, even if the sheet P is thus delivered onto the treating tray  130  by the pair of first delivery rollers  7 , the suspension of the leading end portion of the sheet P and the bad return thereof which will be described next will not occur and the alignment of the sheet P on the treating tray  130  will be enhanced well. 
     The sheet P delivered onto the treating tray  130  begins to be returned to the trailing end stopper portion  131  side by its own gravity and in addition to this, the returning action is expedited with the counter-clockwise rotation of the paddle  160  stopped at the home position. When the trailing end of the sheet P is rammed against the trailing end stopper portion  131  and the sheet P is stopped, the rotation of the paddle  160  is also stopped, and then the alignment of the sheet P by the aligning members  141  and  142  is done, whereafter by the stitching of a sheet bundle by the staple operation and the delivering operation of the pair of bundle delivery rollers  180  in the closed state of the swingable guide  150 , the sheet bundle is stacked on the stacking tray  200 . 
     On the other hand, in the meantime, the sheet P delivered from the image forming apparatus  300 , as shown in FIG. 17, is twined around the buffer roller  5  by the changeover operation of the second changeover flapper  10  and is advanced by a predetermined distance from the buffer path sensor  32 , whereupon it stands by due to the stoppage of the buffer roller  5 , and at a point whereat the leading end of the next sheet P is advanced by a predetermined distance from the sheet detecting sensor  31 , the second sheet P 2  is superposed by a predetermined length earlier than the first sheet P 1  with the rotation of the buffer roller  5 , as shown in FIG. 18, and in this state, it is twined again around the buffer roller  5 , as shown in FIG. 19, and further the third sheet P 3  is likewise twined around the buffer roller  5 , whereafter the second changeover flapper  10  is again changed over, whereby the three sheets P 1 , P 2  and P 3  superposed one upon another with their leading ends shifted by predetermined lengths as shown in FIG. 20 are transported to the sort path  22 . 
     At this point of time, the bundle delivery operation for the preceding sheet bundle is terminated and herein, with the swingable guide  150  remaining closed as shown in FIG. 21, the pair of bundle delivery rollers  180   a  and  180   b  being forwardly rotated in the direction of delivery once receive the three sheets P 1 , P 2  and P 3  transported thereto. Then, at a point of time whereat as shown in FIG. 22, the trailing ends of the three sheets P have left the pair of first delivery rollers  7   a  and  7   b  and have contacted with the surface of the treating tray  130 , the pair of bundle delivery rollers  180   a  and  180   b  are reversely rotated so as to return the received three sheets P, and before the trailing ends of the three sheets P are rammed against the surface of the trailing end stopper portion  131 , for example, at a point of time whereat as shown in FIG. 23B, the three sheets P having deviation intervals “b” among them have become close to one another leading as interval “a” between their trailing ends and the surface of the trailing end stopper portion  131 , the swingable guide  150  is opened as shown in FIG. 23B to thereby space the pair of bundle delivery rollers  180   a  and  180   b  apart from each other. Then, the fourth and subsequent sheets P, as in the operation for the first sheet, pass the sort path  22  and are delivered onto the treating tray  130 . The third and subsequent sheets repeat the same operation as that for the second sheet, and a set number of sheets are stacked on the stacking tray  200 , thus terminating the treatment. 
     As previously described, in the superposition transportation of the plurality of sheets, each sheet P is offset in the direction of transportation. That is, the sheet P 2  is offset to the downstream side relative to the sheet P 1 , and the sheet P 3  is offset to the downstream side relative to the sheet P 2 . Here, the amount of offset between the sheets P and the roller pair spacing (elevating) start timing of the swingable guide  150  are concerned with the alignment time of the sheets P by the returning speed between the pair of bundle delivery rollers  180   a  and  180   b . That is, it is determined by the treating capacity of the image forming apparatus  300 , and in the present embodiment, at the transportation speed 750 mm/s of the sheet P, the amount of offset “b”=20 mm or so and the bundle delivery roller returning speed 500 mm/s, the spacing start position for the bundle delivery rollers has its timing set at a point of time whereat the trailing end of the sheet P 1  reaches about 40 mm (the value of the interval “a”) short of a point at which it is rammed against the surface of the trailing end stopper portion  131 . 
     Sort Mode 
     The sort mode will now be described. The user sets an original on the original reading portion  400  of the image forming apparatus  300 , and thereafter designates the sort mode on an operating portion, not shown, and switches on a start key, not shown. Thereby, the pair of inlet rollers  2  and the pair of first transporting rollers  3 , as shown in FIG. 24, transport the sheets P and stack them on the treating tray  130  as in the case of the staple sort mode. The aligning means  140  stacks a few sheets on the treating tray  130  while aligning the sheet bundle on the treating tray  130 , whereafter as shown in FIG. 25, the swingable guide  150  lowers in the closing direction and bundle-transports a bundle of a few sheets. 
     The sheet P transported next is twined around the buffer roller  5  as in the case of the staple sort mode, and is delivered onto the treating tray  130  after the termination of the bundle delivery. It is desirable as the result of an experiment that the number of sheets in the bundle of a few sheets bundle-delivered be 20 sheets or less. This number of sheets is set so as to become a number which satisfies the relation that the number of originals≧the number of sheets bundle-delivered≦20 sheets. 
     Consequently, if the number of sheets to be bundle-delivered is set to 5 when the program is prepared, 4 sheets at a time are bundle-delivered when the number of originals is 4. Also, if the number of originals is 5 or more, e.g. 14, the originals are divided into 5 sheets+5 sheets+4 sheets, and these are respectively aligned and bundle-delivered. 
     When the bundle delivery of the first bundle is all completed, the aligning member  141  on the left side is moved with the aligning member  142  on the right side to thereby offset the aligned position of the second bundle relative to the aligned position of the first bundle. The second bundle is aligned at the aforementioned offset position, and is bundle-delivered by a few sheets at a time like the first bundle. When the bundle delivery of the second bundle is completed, the aligning members  141  and  142  are returned to their positions at which they aligned the preceding first bundle, and align the third bundle. In this manner, as shown in FIG. 26, the bundle delivery of all the set number of bundles is completed while the sheet bundles are shifted relative to one another. 
     Aligning and Stapling Operations 
     The operations of aligning and stapling the sheets will now be described. First, when there is no sheet P on the treating tray  130 , that is, when the first sheets P (three sheets) of that job are to be delivered, as shown in FIG. 27, the left (lower as viewed in FIG. 27) and right (upper as viewed in FIG. 27) aligning members  141  and  142  which have so far stood by at the home positions are moved in advance to positions PS 11  and PS 21 , respectively, somewhat outwardly escaped relative to the width of the sheets P delivered. 
     As described above, when the three sheets P have their trailing ends supported by the trailing end stopper portion  131  and their undersides supported by the supporting surfaces  141   c  and  142   c  (see FIG. 29) of the aligning members  141  and  142 , respectively, the aligning members  141  and  142  are moved to positions PS 12  and PS 22 , respectively, as shown in FIG. 28, and move and align the sheets P to a first aligning position P 190 . Thereafter, one aligning member  141  is returned to and stands by at the position PS 11  in preparation for a sheet P delivered subsequently, and when the sheet delivery is done, it is again moved to the position PS 12 , where it moves and align this delivered sheet P to the first aligning position P 190 . At this time, the other aligning member  142  continues to stop at the position PS 22  to thereby perform its role as the reference position. The above-described operation is continued until it reaches the last sheet P in that bundle. Accordingly, the aligning operation is done thus and therefore, it never happens that as shown, for example, in FIG. 29, the end portion of the moving sheet P collides against the end portion or the like of the supporting surface  142   c  and is buckled. 
     The first sheet bundle which has been aligned is stapled as required, and is bundle-delivered and transported to and stacked on the stacking tray  200 . 
     Subsequently, the sheets P (three sheets) of the second bundle are delivered to the treating tray  130 , and at this time, the aligning members  141  and  142  are standing by at the positions PS 11  and PS 21  as for the first bundle, but their aligning position shifts to a second aligning position P 191 . This second aligning position P 191 , as shown in FIG. 30, lies rightwardly (upwardly as viewed in FIG. 30) by a predetermined amount L relative to the first aligning position P 190 . 
     That is, thereafter, bundle stacking is effected on the stacking tray  200  while the aligning position is changed for each sheet bundle, and the sort stacking by an offset amount L becomes possible. 
     The offset amount L may be varied between the sort mode and the staple mode. For example, during the staple mode, the offset amount may be an amount L 1  (about 15 mm) which can prevent the overlapping of staples for adjacent bundles after the bundle stacking, and during the sort mode, it may be an amount L 2  (about 20 to 30 mm) by which the visibility of bundle discrimination is improved, whereby the alignment movement distance during the staple mode can be shortened to thereby achieve an improvement in the treating speed. 
     Next, during the staple mode, the stapler  101  stands by in advance at a desired clinch position for the aligned sheet bundle, and staples at a point of time whereat the delivery and alignment of the last sheet P in the bundle have been completed. As previously described, the aligning position for sheet bundles changes correspondingly to the offset amount L for each bundle, and in conformity therewith, the stapler  101  is also moved. 
     Also, the construction in which the stapler  101  is reoriented and moved correspondingly to the stitching mode (the oblique stitching of the left side edge portion, the oblique stitching of the right side edge portion and two-point stitching) has already been described. In this construction, however, the range in which the same staple posture (horizontal and each inclined state) can be maintained is limited and further, there are numerous sheet widths over which stapling is effected, and there are cases where for different binding modes, stapling cannot be effected at the same aligning position and therefore, the first and second aligning positions P 190  and P 191  may be changed correspondingly to each stitching mode. 
     In the present embodiment, the stitching treatment is effected to the sheets being stacked on the first stacking tray means and therefore description has been made of the movement of the aligning means in the direction perpendicular to the sheet feeding direction and the paddle means for more rapid alignment, but a similar effect can also be obtained in a simple system, that is, when use is not made of the stitching means, the aligning means and the paddle means. 
     Since the present invention is constructed as described above, the endless belt member tries to feed the sheets with a substantially constant force irrespective of the stack height of the sheet bundles and therefore, it is possible to eliminate the inconvenience during stacking that the sheet does not arrive at the trailing end stopper portion of the stacking tray means or is buckled or runs upon the stopper portion. 
     Accordingly, in case of the sheet aligning treatment by the aligning means for carrying out such treatment as a stitching process on the stacking tray means, the endless belt member can be deformed so as not to contact with the sheet by the pulling operation of the traction means for the endless belt member, whereby the smoothness of the widthwise alignment movement of the sheet can be achieved, and the endless belt member tries to feed the sheets with a substantially constant force irrespective of the stack height of the sheet bundles and therefore, it is possible to eliminate the inconvenience during stacking that the sheet does not arrive at the trailing end stopper portion of the stacking tray means or is buckled or runs upon the stopper portion. 
     Also, the traction means can be made to perform an upwardly pulling operation relative to the stacking surface of the stacking tray, whereby at a smaller movement stroke, the endless belt member can be retracted from the sheet, and the time required for control becomes short, and productivity can be improved or the size of the apparatus can be made small. 
     Further, provision is made of the height detecting means for detecting the height of the sheet bundles stacked on the stacking tray means, and on the basis of information detected by this height detecting means, the amount of traction is determined, whereby it becomes possible to more accurately uniformize the amount of contact between the sheet bundle and the endless belt member, and further the feeding force, and the inconvenience during stacking can be eliminated.