Patent Publication Number: US-8529423-B2

Title: Sheet folding and image formation apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a sheet folding apparatus for folding a sheet fed from an image formation apparatus to feed to a post-processing apparatus, and more particularly, to improvements in the jam handling mechanism to remove a sheet jam. 
     2. Description of the Related Art 
     Generally, this type of sheet folding apparatus has been known as an apparatus for folding a sheet with an image formed thereon by an image formation apparatus such as a printing press, printer apparatus and copier in a predetermined fold position to perform finish processing. 
     For example, Japanese Patent Application Publication No. 2009-018494 proposes an apparatus in which a sheet folding apparatus is coupled to a sheet discharge outlet of an image formation apparatus, folds a sheet with an image formed for filing, and carries the sheet out to a subsequent binding processing apparatus (post-processing apparatus). In the document, the sheet folding apparatus is coupled to the sheet discharge outlet of the image formation apparatus, and a bookbinding processing apparatus is disposed on the downstream side of the sheet folding apparatus. 
     Not only such a system configuration in Japanese Patent Application Publication No. 2009-018494, it is known widely that part of an apparatus casing is configured to be openable and closable to open and close the path when a paper jam occurs in the transport path of sheets in the sheet folding apparatus. Such a structure is generally configured by hinge-coupling part of a casing to an apparatus frame to be openable and closable and exposing the sheet transport path to the outside with the casing opened. 
     Japanese Patent Application Publication No. S61-002637 discloses a post-processing apparatus and proposes a jam open/close mechanism for hinge-coupling one side end edge (for example, the apparatus left side end portion) orthogonal to the sheet transport direction in an apparatus for collating and collecting sheets fed from an image formation apparatus to perform binding processing. 
     More specifically, first, such a sheet folding apparatus as described above is known in Japanese Patent Application Publication No. 2009-018494, etc. The sheet folding apparatus is disposed between the image formation apparatus and the post-processing apparatus, and folds an image-formed sheet to feed to the post-processing apparatus. The sheet folding apparatus is provided with a transport path for carrying a sheet from a carry-in entrance to a carrying-out exit without performing folding processing on the sheet, and a folding processing path for performing the folding processing on a sheet to feed to the carrying-out exit. 
     Then, in the sheet folding apparatus disposed between the image formation apparatus and the prost-processing apparatus, an apparatus configuration is required which is small and compact as possible, and particularly, slim in the sheet feed direction. It is natural because the installation space of the entire system is reduced (narrowed). 
     Therefore, previously, the applicant of the invention conceived slimming the folding processing mechanism by placing a folding processing path for performing folding processing on a sheet fed from the carry-in entrance in the direction for crossing a transport path (through-pass path) for carrying a sheet from the carry-in entrance to the carrying-out exit without performing the folding processing, and filed the patent application (Japanese Patent Application No. 2009-291375). When a sheet jam occurs in such an apparatus configuration, the need arises for opening the transport path to remove the jam. 
     The inventor of the invention arrived at the idea that it is possible to retrieve jam sheets occurring in both paths, by dividing the configuration into two upper and lower portions with the through-pass path as a boundary and opening and closing the upper unit in the path configuration in which the folding processing path is disposed in the direction for crossing the through-pass path. Concurrently therewith, the inventor arrived at the idea that it is possible to reduce the size of the entire system without the image formation apparatus and the post-processing apparatus located at the front and back and the open/close space interfering with one another, by providing the upper unit with open/close motion around the hinge in the side end portion (apparatus rear side end portion) parallel with the sheet transport direction with respect to the lower unit. 
     Further, second, in Japanese Patent Application Publication No. S61-002637, when a sheet is jammed in a press-contact portion in a pair of folding rollers, the sheet transport mechanism is opened, and the sheet is pulled out with the sheet nipped between the rollers. Therefore, in a thin sheet or a sheet becoming wrinkled by the jam, part of the sheet may be broken and remain inside the apparatus. Alternately, in pulling out the sheet nipped between the rollers inside the apparatus, the operator may be injured. 
     Then, the inventor of the invention arrived at the idea that it is possible to release a plurality of press-contact portions by withdrawing a roller positioned in the center, and at the same time, restore to the original engagement relationship reliably in a folding roller mechanism in which a plurality of press-contact rollers is disposed around the roller positioned in the center. 
     OBJECT OF THE INVENTION 
     It is a principal object of the invention to provide a sheet folding apparatus that permits a jammed sheet to be removed with ease when the jam occurs in the sheet folding apparatus which is disposed between an image formation apparatus and a post-processing apparatus to perform folding processing on an image-formed sheet. 
     In other words, first, it is an object of the invention to provide a sheet folding apparatus which permits a jammed sheet to be removed with ease in a transport path for carrying a sheet to a folding processing position, without the open/close space to open and close part of the casing for the removal interfering with the apparatuses disposed on the upstream side and the downstream side, and which enables the apparatus to be made small and compact. 
     Further, second, it is another object to provide the sheet folding apparatus which enables a sheet jammed in a lower portion of the sheet folding apparatus for performing folding processing on a sheet to be reliably removed by simplified operation. 
     BRIEF SUMMARY OF THE INVENTION 
     To attain the aforementioned objects, in the invention, a casing having a carry-in entrance and a carrying-out exit is divided into an upper unit and a lower unit via a first transport path for carrying a sheet from the carry-in entrance to the carrying-out exit, a second transport path for performing folding processing on a sheet is disposed in the direction for crossing the first transport path, and in the upper unit are disposed a sheet front end switchback path for reversing and carrying the sheet toward a folding roller pair and sheet deflecting means for guiding the sheet to the folding roller pair. Then, the upper unit is coupled to the lower unit to be openable and closable by a hinge shaft rotating around one side end portion orthogonal to the sheet transport direction of the first transport path. 
     The upper unit is coupled to the lower unit to be openable and closable, in the upper unit are disposed an upper sheet guide of the first transport path and the sheet front end switchback path constituting part of the second transport path, and therefore, by opening the upper unit, it is possible to retrieve a jam sheet in each of the first and second transport paths. Accordingly, it is possible to retrieve a jam sheet arising in the path by simplified structure. 
     Further, the upper unit is coupled to the lower unit to rotate by the hinge shaft around one side end portion orthogonal to the sheet transport direction of the first transport path for guiding a sheet from the carry-in entrance to the carrying-out exit, and therefore, without the image formation apparatus and the post-processing apparatus respectively positioned on the upstream side and the downstream side in the sheet transport direction and open/close area of the upper unit interfering (overlapping) with one another, it is possible to reduce the size of the installation space of the entire system. 
     Furthermore, to attain the above-mentioned objects, in the invention, a plurality of rolls is brought into press-contact with a first roll positioned in the center in the order of the second, third and fourth rolls, and a guide member is provided which guides a folded sheet along the periphery of the first roll in between the third roll and the fourth roll. 
     Then, the first roll is provided in a first bracket member that swings in the direction separating from the second and third rolls, and the fourth roll and the guide member are provided in a second bracket member that swings in the direction separating from the first roll. Then, the first bracket member and the second bracket member are interlocked to swing in the separation direction by operating means provided in one of the members. 
     By separating the first roll positioned in the center from the second and third rolls, it is possible to concurrently release press-contact in the first folding press-contact portion and the second folding press-contact portion, and it is thereby possible to remove a jam sheet by simplified structure and operation. Concurrently therewith, it is possible to withdraw the fourth roll in press-contact with the first roll and the guide member at the same time in the separation direction. Accordingly, it is possible to withdraw the folding enhancement press-contact portion and the guide member therefor in conjunction with each other concurrently with the folding press-contact portions, and therefore, the jam handling is extremely simplified. 
     Further, the structure for the handling is that the first roll, and the fourth roll and guide member are respectively attached to the first bracket member and the second bracket member to be swingable in the separation direction, and that the first bracket member and the second bracket member are interlocked to swing in the separation direction by the operating means provided in one of the members, and it is thereby possible to release a plurality of press-contact portions by simplified structure and simplified operation. 
     By this means, in the sheet folding apparatus, when a jam occurs, it is possible to remove a jammed sheet with ease. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an explanatory view of an entire configuration of an image formation system provided with a sheet folding apparatus according to the invention; 
         FIG. 2  is an enlarged explanatory view of principal part of a post-processing apparatus in the system of  FIG. 1 ; 
         FIG. 3  is an explanatory view of an entire configuration of the sheet folding apparatus in the system of  FIG. 1 ; 
         FIG. 4  is a perspective explanatory view showing a casing of the sheet folding apparatus; 
         FIG. 5  is an explanatory view of a state in which an upper unit is opened in the sheet folding apparatus; 
         FIG. 6A  and  FIG. 6B  contain explanatory views of a state in which the upper unit is opened and closed in the sheet folding apparatus, where  FIG. 6A  is an explanatory view of principal part with the upper unit opened, and  FIG. 6B  is an explanatory view of a guide mechanism for open/close operation; 
         FIG. 7  is an explanatory view showing a layout configuration of folding rollers of  FIG. 3  and second folding deflecting means; 
         FIG. 8A  shows a configuration explanatory view of a folding processing section;  FIG. 8B  is an enlarged explanatory view of a cam engagement portion of a bracket member; 
         FIG. 9  is a conceptual view showing press-contact and separation states of folding roller means; 
         FIG. 10  is an explanatory view of a release state in the folding processing section; 
         FIG. 11A  is a configuration view of operating means;  FIG. 11B  is a detailed explanatory view of a cover member; 
         FIG. 12  is an explanatory view of a driving mechanism according to sheet transport in the apparatus of  FIG. 3 ; 
         FIG. 13A  and  FIG. 13B  contain explanatory views of a sheet carry-in mechanism in the apparatus of  FIG. 3 , where  FIG. 13A  is an explanatory view of a gate stopper mechanism, and  FIG. 13B  is an explanatory view of a pinch roller moving up/down mechanism of sheet transport means; 
         FIG. 14  is a detailed explanatory view of an engagement state of path switching means; 
         FIG. 15  is an explanatory view of a driving system in the apparatus of  FIG. 3 , and shows a closed state of the upper unit; 
         FIG. 16  is another explanatory view of the driving system in the apparatus of  FIG. 3 , and shows an open state of the upper unit; 
         FIG. 17  is an explanatory view of the driving system in the apparatus of  FIG. 2 , and shows a semi-open state of the upper unit; 
         FIG. 18A  and  FIG. 18B  contain explanatory views of a driving mechanism of first folding deflecting means and second folding deflecting means in the apparatus of  FIG. 3 , where  FIG. 18A  shows a state in a waiting position, and  FIG. 18B  shows a state in an actuation position; 
         FIG. 19A  and  FIG. 19B  contain explanatory views of an operating state of the apparatus of  FIG. 3 , where  FIG. 19A  shows a state in which a sheet is registered, and  FIG. 19B  shows a state in which a sheet is carried from a first path to a second path; 
         FIG. 20A  and  FIG. 20B  contain explanatory views of the operating state of the apparatus of  FIG. 3 , where  FIG. 20A  shows a state in which a fold position of the sheet is inserted in a first nip portion, and  FIG. 20B  shows a state in which the first-folded sheet is fed to a second switchback path; 
         FIG. 21A  and  FIG. 21B  contain explanatory views of the operating state of the apparatus of  FIG. 3 , where  FIG. 21A  shows an initial state in which the sheet undergoes second folding in a second nip portion, and  FIG. 21B  shows a state in which the sheet that is folded in the second nip portion is carried out in a sheet discharge direction; 
         FIG. 22A ,  FIG. 22B ,  FIG. 22C ,  FIG. 22D  and  FIG. 22E  contain explanatory views of sheet folding forms in the sheet folding apparatus of the invention, where  FIG. 22A  shows an aspect for performing inward three-folding on the sheet in a ⅓ position,  FIG. 22B  shows an aspect for performing outward three-folding on the sheet in a ⅓ position,  FIG. 22C  shows an aspect for performing Z-folding on the sheet in a ¼ position,  FIG. 22D  shows an inward three-folding aspect with the margin provided, and  FIG. 22E  shows an outward three-folding aspect with the margin provided; 
         FIG. 23  is an explanatory view of a control configuration in the system of  FIG. 1 ; and 
         FIG. 24  is a flowchart illustrating processing operation in the control configuration of  FIG. 23 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will specifically be described below based on Embodiments shown in the figures.  FIG. 1  shows an image formation system provided with a sheet folding apparatus B according to the invention. This system is comprised of an image formation apparatus A and a post-processing apparatus C, and the post-processing apparatus C is installed with the sheet folding apparatus B as a unit. 
     The image formation apparatus A is configured as a printer, copier, printing press or the like for sequentially forming images on sheets. The apparatus as shown in  FIG. 1  is comprised of an image formation section  7 , original document reading section  20  and feeder section (original document feeding apparatus)  25  as a complex copying machine having the copier function and the printer function. 
     Further, the post-processing apparatus C is configured to perform post-processing such as folding processing, punching processing, sealing processing and binding processing on a sheet with an image formed in the image formation apparatus A. Then, the post-processing apparatus C is integrally provided with the sheet folding apparatus B for performing folding processing on a sheet with an image formed. The sheet folding apparatus B, image formation apparatus A and post-processing apparatus C will be described below in this order. 
     [Sheet Folding Apparatus] 
     The sheet folding apparatus B according to the invention is incorporated into the image formation apparatus A or the post-processing apparatus C, or is configured as an apparatus (stand-alone configuration) independent of the apparatuses. The apparatus as shown in the figure is disposed between the image formation apparatus A and the post-processing apparatus C as an optional unit. 
     In the sheet folding apparatus B, as shown in  FIG. 3  illustrating the entire configuration, a casing  29  is provided with a carry-in entrance  30  and a carrying-out exit  31 , the carry-in entrance  30  is arranged in a position continued to a main-body sheet discharge outlet  18  of the image formation apparatus A on the upstream side, and the carrying-out exit  31  is arranged in a position continued to a sheet receiving opening  69  of the post-processing apparatus C on the downstream side. In addition, in the invention, there are cases that the sheet folding apparatus B is not provided with an independent casing  29 , and for example, is incorporated into a casing of the post-processing apparatus C, and the cases do not require the carry-in entrance  30  and carrying-out exit  31 . 
     Accordingly, in the following description, the carry-in entrance  30  is synonymous with a carry-in portion, the carrying-out exit  31  is synonymous with a carrying-out portion, and for convenience in description, the description is given while assuming that the carry-in portion is the carry-in entrance  30  and that the carrying-out portion is the carrying-out exit  31 . 
     As shown in  FIG. 3 , the carry-in entrance  30  and carrying-out exit  31  are disposed opposite each other across the casing  29 . The carry-in entrance  30  and carrying-out exit  31  shown in the figure are disposed in opposite positions in the substantially horizontal direction. Then, in between the carry-in entrance  30  and the carrying-out exit  31  are disposed a first transport path  32  (sheet transport path; the same in the following description) for carrying out a sheet from the carry-in entrance  30  to the carrying-out exit  31  without performing folding processing, and a second transport path  33  (folding processing path; the same in the following description) for performing the folding processing on a sheet from the carry-in entrance  30  to carry out to the carrying-out exit  31 . A “sheet transport mechanism” for carrying a sheet in the predetermined direction (horizontal direction) is disposed in the first transport path  32 , and a “folding processing mechanism” for performing the folding processing on a sheet is disposed in the second transport path  33 . 
     [Casing Structure] 
     In the apparatus of  FIG. 3 , the casing  29  is comprised of an upper unit  29 A and a lower unit  29 B that are divided vertically via the first transport path  32  for guiding a sheet from the carry-in entrance  30  to the carrying-out exit  31  without performing folding processing. 
     Then, as shown in  FIG. 3 , in the upper unit  29 A are disposed an upper sheet guide  32   a  constituting the first transport path  32 , and a sheet front end switchback path  34  (first switchback path; the same in the following description) constituting the second transport path  33 . Concurrently therewith, the upper unit  29 A is provided with a carry-in roller  40   a , gate stopper  43 , pinch roller  42 , and carrying-out roller  62   a . The carry-in roller  40   a  and carrying-out roller  62   a  are supported by rotary shafts of the direction orthogonal to the sheet transport direction (the arrow direction in  FIG. 2 ) of the first transport path  32 . 
     The gate stopper  43  is configured to be swingable on a spindle  43   x  of the direction orthogonal to the sheet transport direction, as described later, and similarly, the pinch roller  42  is configured to be swingable on a spindle  42   x  of the direction orthogonal to the sheet transport direction. 
     Meanwhile, in the lower unit  29 B are disposed a lower sheet guide  32   b  constituting the first transport path  32 , folding roller pair ( 41 ,  49 ,  50 ), sheet discharge paths  36 ,  37 , storage stacker  65 , and sheet discharge roller  67 . 
     In addition, a first folding deflecting means  53  is provided in the lower unit  29 B (see  FIG. 5 ). Then, in the lower unit  29 B are disposed a shift motor MS for moving the first and second folding deflecting means  53 ,  54  up and down, and a feeding motor Mf. 
     In such a unit configuration, the upper unit  29 A is coupled to the lower unit  29 B to be openable and closable by the hinge shaft  28  around one side end portion orthogonal to the sheet transport direction of the first transport path  32 .  FIG. 4  shows a closed state, and  FIG. 5  shows an open state. In this closed state, as shown in  FIG. 3 , the upper sheet guide  32   a  and lower sheet guide  32   b  are opposed to each other with a predetermined spacing and form the first transport path  32 . Meanwhile, in the open state, the upper sheet guide  32   a  releases the path in the state of  FIG. 5  at a predetermined angle of θ around the hinge shaft  28  with respect to the lower sheet guide  32   b.    
       FIGS. 6A and 6B  show a mechanism for guiding the open/close operation of the unit in operating the upper unit  29 A to be opened and closed around the hinge shaft  28  with respect to the lower unit  29 B. As shown in  FIG. 6A , the upper unit  29 A is opened and closed around the hinge shaft  28  with respect to the lower unit  29 B. At this point, one of the upper unit  29 A and lower unit  29 B is provided with guide pins  27   p , while the other one is provided with guide grooves  27   g . Then, when open/close motion is performed around the hinge shaft  28 , the guide pin  27   p  is guided along the guide groove  27   g , and both of the units undergo the open/close motion in the correct position without rattling. In addition, in performing the open/close motion, it is necessary that the gate stopper mechanism and the driving system of the pinch roller mechanism are engaged and released, and the configuration will be described later. 
     Thus, the upper unit  29 A is coupled to the lower unit  29 B to be openable and closable, in the upper unit  29 A are disposed the upper sheet guide  32   a  of the first transport path  32  and the first switchback path  34 , and therefore, by opening the upper unit  29 A, it is possible to retrieve a jam sheet in each of the first and second transport paths  32 ,  33 . Accordingly, it is possible to retrieve a jam sheet arising in the path by simplified structure. 
     Further, the upper unit  29 A is coupled to the lower unit  29 B to rotate by the hinge shaft  28  around one side end portion orthogonal to the sheet transport direction of the first transport path  32 , and therefore, without the image formation apparatus A and the post-processing apparatus C respectively positioned on the upstream side and the downstream side in the sheet transport direction and open/close area of the upper unit  29 A interfering (overlapping) with one another, it is possible to reduce the size of the installation space of the entire system. 
     [Path Configuration] 
     As shown in  FIG. 3 , in the casing  29 , the first transport path  32  is disposed between the carry-in entrance  30  and the carrying-out exit  31 . This path may be a linear path disposed in the horizontal direction as shown in the figure, may be configured as a curved path, or may be disposed in the vertical direction, and it is possible to adopt any configuration. As described above, the first transport path  32  guides a sheet from the carry-in entrance  30  to the carrying-out exit  31  without performing the folding processing. 
     Further, the second transport path  33  is configured as a path for performing the folding processing on a sheet from the carry-in entrance  30 . Therefore, the second transport path  33  branches off from the first transport path  32 , and is configured to guide a sheet from the carry-in entrance  30  to sheet folding positions Np 1  and Np 2 . Concurrently therewith, as shown in  FIG. 3 , the second transport path  33  is disposed in a direction in which the path  33  crosses the first transport path  32 , and the first folding position Np 1  and the second folding position Np 2  are set in this path. 
     Then, the second transport path  33  is comprised of the first switchback path (first reverse path)  34  for guiding the sheet front end for first folding to the first folding position Np 1 , and a second switchback path (second reverse path)  35  for guiding the folded sheet front end to the second folding position Np 2  to perform second folding on the folding-processed sheet. 
     Thus, the second transport path  33  is disposed in the direction to cross the first transport path  32 , where the first switchback path  34  is disposed in the area above the first transport path  32 , the second switchback path  35  for carrying a sheet from the cross portion to the downstream side (the direction of the second folding position Np 2 ) is disposed in the area below the first transport path  32 , and the paths  34  and  35  are thus configured to be opposed vertically. 
     Then, each of the first switchback path  34  and second switchback path  35  is comprised of a curved path and formed substantially in the shape of an S-curve as shown in  FIG. 3 . In the second transport path (folding processing path)  33 , a folding processing section  48  described later is disposed in the first folding position Np 1  and second folding position Np 2 , and the path  33  is connected to a sheet discharge path  36  for carrying out the folded sheet from the second folding position Np 2  toward the carrying-out exit  31 . 
     In addition, the first transport path  32  and the second transport path  33  are disposed to cross each other, and the first switchback path  34  for guiding the sheet to the first folding position Np 1  may be disposed below the first transport path  32 , while the second switchback path  35  for guiding the folding-processed sheet to the downstream side may be disposed above the first transport path  32 . 
     Further, in the Embodiment of  FIG. 3 , the first transport path  32  is disposed in the horizontal direction, and when the first transport path  32  is disposed in the vertical direction in the casing  29 , it is possible to arrange the first switchback path  34  and second switchback path  35  to the left and right areas of the first transport path  32  to be opposite each other. 
     Further, in the Embodiment as shown in  FIG. 3 , in relation to the second switchback path  35  guiding the folded sheet to the second folding position Np 2  to perform second folding on the sheet, the path  35  is configured to reverse the feeding direction of the sheet, but when second folding is not performed on the sheet, the path  35  can be a path to extend straight, and in this case, the need is eliminated for providing the second switchback path as descried previously. 
     The second transport path  33  is connected to the sheet discharge path  36  for guiding the folding-processed sheet to the carrying-out exit  31 . The sheet discharge path  36  shown in the figure is provided in between the second folding position Np 2  for performing second folding on the sheet and the carrying-out exit  31 . In the sheet discharge path  36  is disposed a sheet discharge path  37  for guiding the folded sheet to a storage stacker  65  from a sheet discharge outlet  51  different from the carrying-out exit  31 . 
     Then, a path length (L 1 ) of the first switchback path  34  for guiding a sheet from the first transport path  32  to the first folding position (first nip portion) Np 1  and a path length (L 2 ) of the second switchback path  35  for guiding the folded sheet subjected to first folding to the second folding position (second nip portion) Np 2  are configured so that path length L 1 &gt;path length L 2 . 
     A path length L 3  of the sheet discharge path  37  for guiding the sheet further subjected to the folding processing to the storage stacker  65  from the second folding position Np 2  is configured so that L 3 &lt;L 2 &lt;L 1 . This is because when the first folding position (first nip portion) Np 1  is disposed near the first transport path  32 , the path lengths are L 3 &lt;L 2 &lt;L 1  as a result, and the path configuration is thereby made compact. 
     Accordingly, the first switchback path  34  with the long path length is disposed in the upper area of the first transport path  32 , the second switchback path  35  and the sheet discharge path  37  with the short path lengths are disposed in the lower area opposite the upper area, and further, the storage stacker  65  is disposed below the second switchback path  35  and the sheet discharge path  37 . By such a layout configuration, it is possible to make the inside space of the casing  29  compact. 
     [Path Switching Means] 
     The following path switching means  63  is disposed in the cross portion of the above-mentioned first transport path  32  and second transport path (folding processing path)  33 . As described previously, the second transport path  33  branches off from the first transport path  32  and guides a sheet fed from the carry-in entrance  30  to the first and second folding positions Np 1 , Np 2 . Therefore, the path switching means  63  is disposed in the cross portion of the first and second transport paths  32  and  33 . As shown in  FIG. 3 , a base end portion is axially supported by an apparatus frame (in the figure, spindle  62   x  of the carrying-out roller  62   a ) outside the path to be swingable. 
     Then, the path switching means  63  guides a sheet fed to the first transport path  32  to the first switchback path  34  of the second transport path  33  in the solid-line attitude in FIG.  3 , while guiding a sheet fed to the first transport path  32  to the carrying-out exit  31  from the carrying-roller pair  62  in the dashed-line attitude in  FIG. 3 . 
     A sheet guide  61  is provided in the cross portion of the first transport path  32  and second transport path  33  together with the path switching means  63 . The sheet guide  61  is disposed in between the second roller  41  and the carrying-out roller pair  62  in the first transport path  32 , guides a sheet fed from the carry-in roller pair  40  to the second transport path  33 , and concurrently therewith, guides a reversed sheet from the first switchback path  34  to the first folding position Np 1 . Further, the sheet guide  61  guides a sheet fed to the first transport path  32  to the carrying-out exit  31  from the carrying-out roller pair  62  without guiding the sheet to the second transport path  33 . 
     Therefore, the sheet guide  61  is disposed in the cross portion with a relatively long transport span, and guides the sheet to the second transport path  33  side or carrying-out exit  31  side in cooperation with the path switching means  63  as described previously. In the apparatus as shown in the figure, as shown in  FIG. 3 , the guide  61  comprised of a guide plate supported swingably in the spindle  61   x  by the apparatus frame. 
     As shown in  FIG. 14 , a link lever  60  is axially supported swingably by the path switching means  63 , and the link lever and path switching means  63  are integrally combined. Then, an electromagnetic solenoid  60 L is coupled to a front end portion of the link lever  60 , and a return spring  60   s  is extended in the direction in which the path switching means  63  guides a sheet to the second transport path  33  side. 
     Accordingly, when the electromagnetic solenoid  60 L is ON, the path switching means  63  is positioned in the first attitude (attitude for guiding a sheet to the second transport path  33 ). Further, when the electromagnetic solenoid  60 L is turned OFF, the link lever  60  rotates in a counterclockwise direction shown in the figure on the spindle  62   x  as the center by action of the return spring  60   s , and positions the path switching means  63  in the second attitude (attitude for guiding a sheet to the carrying-out exit  31 ). 
     Further, the path switching means  63  is disposed in the upper unit  29 A to be swingable between the first guide attitude facing the first transport path  32  and the second attitude shifted outside the path. The path switching shift means for swinging the path switching means  63  between the first guide attitude and the second guide attitude is comprised of a swing member (actuation lever)  63   y  integrally provided in the swing spindle, and the lever member  60  that engages in the swing member. Then, the lever member  60  has an engagement surface that engages in the swing member, and a guide surface  60   z  for guiding the engagement surface to the swing member  63   y  when the upper unit A rotates around the hinge shaft  28 . 
     [Configuration of Folding Rollers] 
     In the second transport path  33  are disposed the second roller  41 , first roller  49  and third roller  50  to come into press-contact with one another. The first nip portion (first folding position) Np 1  for first folding the sheet is formed in a press-contact point between the second roller  41  and first roller  49 , and the second nip portion (second folding position) Np 2  for second folding the sheet is formed in a press-contact point between the first roller  49  and the third roller  50 . 
     Meanwhile, in the roller diameter of each of the first, second and third rollers, the first roller diameter is the maximum, and for example, 30 mm, the second and third roller diameters are 20 mm, and the first roller  49  positioned in the center is configured to have the maximum diameter (for example, 1.5 time). This is because of configuring the folding portion front end to be compact by arranging the second roller  41  and third roller  50  around the periphery of the first roller  49  in the shape of satellites. In other words, with respect to the first roller  49  with the large diameter, the second roller  41  with the small diameter is brought into press-contact on the upstream side, the third roller  50  with the small diameter is brought into press-contact on the downstream side, and thereby, the first nip portion Np 1  for first folding and the second nip portion Np 2  for second folding are formed. 
     Further, the second roller  41  is disposed in the position such that part of the periphery faces the first transport path  32 , and the pinch roller  42  is brought into press-contact with the periphery of the roller  41 . By this means, the sheet in the first transport path  32  is fed to the downstream side by the second roller  41  and pinch roller  42 , and it is not necessary to provide the first transport path  32  with specific transport means and driving mechanism thereof. 
     [Configuration of the Folding Deflecting Means] 
     In the folding roller means comprised of three rollers ( 41 ,  49 ,  50 ) as described above, the first folding deflecting means  53  is disposed in the first nip portion Np 1 , and the second folding deflecting means  54  is disposed in the second nip portion Np 2 . The first folding deflecting means  53  and the second folding deflecting means  54  are formed of a mechanism that fold positions of the sheet fed to the second transport path  33  are inserted in the first nip portion Np 1  and the second nip portion Np 2 . 
     In the apparatus as shown in the figure, the first folding deflecting means  53  and the second folding deflecting means  54  are provided with the function of “inserting the fold position of the sheet in a roller nip portion” and the function of “feeding the front end and rear end of the sheet to the nip portion”. Therefore, the first and second folding deflecting means  53 ,  54  are respectively provided with driven rollers  53   a ,  54   a  and curved guides  53   b ,  54   b  and are configured to shift to positions from a withdrawal position outside the path to an actuation position inside the path. Then, by the operation of the driven roller and curved guide shifting from the withdrawal position to the actuation position, the fold position of the sheet is inserted in the nip portion, and then, the driven roller comes into press-contact with the periphery of the folding roller to rotate by being driven, and thereby acts to feed the front and rear ends of the sheet to the nip portion. 
     [Configuration of the First Folding Deflecting Means] 
     As shown in  FIG. 7 , to guide the fold of the sheet to the first nip portion (press-contact point) Np 1 , the first folding deflecting means  53  is comprised of the driven roller  53   a , curved guide  53   b  and up-and-down member  53   c.    
     As shown in  FIG. 7 , the first nip portion Np 1  for first folding the sheet is comprised of the second roller  41  and first roller  49 , the second roller  41  is disposed on the upstream side, and the first roller  49  is disposed on the downstream side. Thus, the driven roller  53   a  is disposed in a position for coming into contact with the periphery of the first roller  49 . Then, the curved guide  53   b  is configured to be a curved surface along the periphery of the second roller  41  positioned on the upstream side. 
     The driven roller  53   a  and the curved guide  53   b  are supported by the up-and-down member  53   c . The up-and-down member  53   c  is comprised of a bracket member (frame member) of an appropriate shape, the driven roller  53   c  is supported rotatably by the up-and-down member  53   c , and concurrently, the curved guide  53   b  is fixed to the member  53   c . Then, the up-and-down member  53   c  is supported by a guide rail (not shown) provided in the apparatus frame, and is configured to move up and down between an actuation position (dashed-line position in  FIG. 7 ) in which the driven roller  53   a  comes into contact with the periphery of the first roller  49 , and a waiting position (solid-line position in  FIG. 7 ) in which the driven roller  53   a  retracts out of the second transport path  33 . The up-and-down member  53   c  is coupled to a shift motor MS described later, and shifts positions of the driven roller  53   a  and curved guide  53   b  between the actuation position and the waiting position. 
     The above-mentioned driven roller  53   a  comes into press-contact with the first roller  49  positioned on the downstream side, and the press-contact point is shown by p 2  in  FIG. 7 . Then, when the fold position of the sheet is guided to the first nip portion Np 1 , the rear end side of the sheet is provided with the transport force in the press-contact point p 1 , and is guided to the first nip portion Np 1  along the periphery of the second roller  41 . Further, the front end side of the sheet is provided with the transport force in the press-contact point p 2 , and is guided to the first nip portion Np 1  along the periphery of the first roller  49 . 
     At this point, the transport length Lx between the press-contact point p 1  and the first nip portion Np 1  and the transport length Ly between the press-contact point p 2  and the first nip portion Np 1  are set at Lx&gt;Ly. The position of the driven roller  53   a  is set in such a transport length relationship. Then, the curved guide  53   b  forms the curved guide surface in the shape of a curve along the periphery of the second roller  41  with the longer transport length. 
     In other words, conventionally, the blade member for guiding a fold of the sheet to the nip portion (Np 1 , Np 2 ) has been provided separately from the sheet feeding means, and has become a cause of displacement of the fold or wrinkle occurring in the sheet when timing for acting on the sheet deviates. To solve the problem, in the apparatus as shown in the figure, the transport length Lx of the second roller  41  on the upstream side of the sheet fed to the first nip portion Np 1  and the transport length Ly of the first roller  49  on the downstream side are set at [Lx&gt;Ly], concurrently the curved guide surface of the curved guide  53   b  is configured in the shape for bringing the sheet along the periphery of the second roller  41  with the longer transport length, and the driven roller  53   a  and the curved guide  53   b  are concurrently shifted from the waiting position to the actuation position. 
     By thus configuring, it is possible to guide the fold of the sheet correctly to the first nip portion Np 1  without using particular folding blade means. 
     [Configuration of the Second Folding Deflecting Means] 
     The second folding deflecting means  54  will be described next. As shown in  FIG. 7 , the second folding deflecting means  54  is comprised of an up-and-down member  54   c , driven roller  54   a  attached to the member  54   c , and curved guide  54   b . The driven roller  54   a  is disposed in a position opposite the periphery of the third roller  50  positioned on the downstream side of the first roller  49 , and the curved guide  54   b  is disposed in a position opposite the periphery of the first roller  49  positioned on the upstream side. 
     Concurrently therewith, the driven roller  54   a  and the curved guide  54   b  are configured to shift to positions between a withdrawal position Wp withdrawn from the carrying path (hereinafter, referred to as a sheet path Sp; see  FIG. 7 ) of the sheet and an actuation position Ap entering inside the sheet path Sp by the up-and-down member  54   c.    
     The up-and-down member  54   c  is provided with a sleeve  54   s , and a support stem of the driven roller  54   a  is fitted with the sleeve  54   s  slidably. Thus, the driven roller  54   a  is fitted and supported by the up-and-down member  54   c  reciprocating in the predetermined stoke S, and shifts to positions between the withdrawal position Wp and the actuation position Ap by the up-and-down member  54   c  shifting. 
     Then, an adjuster spring  54   e  is provided between the driven roller  54   a  fitted with the sleeve  54   s  and the up-and-down member  54   c , and the driven roller  54   a  is biased in the direction of the third roller  50  by the adjuster spring  54   e . Concurrently therewith, an engagement protrusion  54   k  is integrally provided in the up-and-down member  54   c . The engagement protrusion  54   k  engages in a flange portion  54   n  of the support stem. 
     Meanwhile, the curved guide  54   b  is swingably supported by the apparatus frame. The guide as shown in the figure is integrally formed in a bracket  54   d  freely fitted with a rotary shaft  41   x  of the second roller  41 , and the guide surface of the curved guide  54   b  is disposed in a position opposite the periphery of the first roller  49 . Then, the curved guide  54   b  is engaged to shift to positions between the withdrawal position Wp withdrawn from the sheet path Sp and the actuation position Ap entering inside the path in conjunction with reciprocating motion of the up-and-down member  54   c.    
     Therefore, the bracket  54   d  is provided with a biasing spring  54   h  for biasing toward the withdrawal position Wp and an engagement piece  54   j . The engagement piece  54   j  engages with the up-and-down member  54   c , and is configured to shift from the withdrawal position Wp to the actuation position Ap in conjunction with the shift of the up-and-down member  54   c  (against the biasing spring  54   h ). 
     In the above-mentioned configuration, the up-and-down member  54   c  and the shift motor MS constitute the shift means for shifting the driven roller  54   a  and curved guide  54   b  to positions between the withdrawal position Wp and the actuation position Ap. Further, as a substitute for the configuration of the up-and-down member  54   c  reciprocating in a predetermined stroke, it is naturally possible to constitute the shift means using an actuator such as an actuation solenoid. In this case, the driven roller  54   a  and the curved guide  54   b  are coupled to a single actuation solenoid, or individual actuation solenoids. 
     [Sheet Transport Mechanism] 
     The sheet transport mechanism of the first transport path  32  ad second transport path  33  will be described according to  FIG. 3 . In the first transport path  32 , the carry-in roller pair  40  is disposed in the carry-in exit (carry-in portion)  30 , the carrying-out roller pair  62  is disposed in the carrying-out exit (carrying-out portion)  31 , and a register roller is disposed between the rollers. The register roller shown in the figure is comprised of the periphery of the second roller  41  described later and the pinch roller  42  in press-contact with the roller  41 . 
     Accordingly, in the first transport path  32  are disposed the carry-in roller pair  40 , carrying-out roller pair  62  and register roller (second roller)  41 . 
     Then, the carry-in roller pair  40  is comprised of a pair of rollers  40   a ,  40   b , and one of the rollers,  40   b , is coupled to the feeding motor Mf described later. Similarly, the carrying-out roller pair  62  is comprised of a pair of rollers  62   a ,  62   b , and one of the rollers,  62   b , is coupled to the feeding motor Mf. Further, the pinch roller  42  is disposed to, rotate in accordance with the second roller  41 , and the second roller  41  is also coupled to the feeding motor Mf. 
     In the second transport path (folding processing path)  33  are disposed the second roller  41 , first roller  49  and third roller  50  coming into press-contact with one another, and the sheet discharge roller pair  67  is disposed in the sheet discharge path  37 . Then, as shown in  FIG. 3 , the second transport path  33  (first switchback path  34  and second switchback path  35 ) is not provided with any sheet transport mechanism. 
     Then, to the second transport path  33 , the sheet is carried in the first switchback path  34  by the carry-in roller pair  40  and the register roller (second roller)  41  disposed in the first transport path  32 , and is fed to the downstream side by the first and second rollers  49 ,  41 . 
     The apparatus shown in the figure is characterized by simplifying the sheet transport mechanism disposed in the first and second transport paths  32 ,  33  and thereby reducing the size, noise and power consumption of the apparatus. Therefore, in the first transport path  32 , part of the periphery of the folding roller (second roller  41 ) disposed in the second transport path  33  is arranged to face the first transport path  32  in between the carry-in roller pair  40  and the carrying-out roller pair  62 . 
     Then, the pinch roller  42  is disposed around the periphery of the second roller  41  to carry the sheet fed from the carry-in roller pair  40  to the first switchback path  34 . By this means, it is not necessary to provide a specific transport roller in the first transport path  32 , and it is possible to achieve simplification of the transport mechanism. 
     Concurrently therewith, the second roller  41  is rotated in performing the folding processing on the sheet in a mode for carrying the sheet from the carry-in roller pair  40  to the first switchback path  34  by the carry-in roller pair  40  and the second roller  41 , while being halted so that the sheet is fed from the carry-in entrance  30  to the carrying-out exit  31  by the carry-in roller pair  40  and the carrying-out roller pair  62  in a mode for carrying a sheet from the carry-in entrance  30  to the carrying-out exit  31  without performing the folding processing on the sheet. By this means, it is possible to achieve reductions in power consumption and low-noise operation. 
     [Configuration of the Folding Processing Section] 
     As described previously, the folding processing section  48  is comprised of first, second, third and fourth rollers  49 ,  41 ,  50 ,  64  coming into press-contact with one another. Then, with the first roller  49  positioned in the center, the second roller  41 , third roller  50  and fourth roller  64  are disposed in this order along the rotation direction of the roller  49 . Further, between the third roller  50  and the fourth roller  64  is disposed a guide member  39  for guiding a folded sheet along the periphery of the first roller  49 . 
     Then, a sheet undergoes first folding in the press-contact portion Np 1  of the second roller  41  and the first roller  49 , the sheet undergoes second folding in the press-contact portion Np 2  of the first roller  49  and the third roller  50  on the downstream side, and then, the folded sheet undergoes folding enhancement in the press-contact portion Np 3  of the first roller  49  and the fourth roller  64 . 
     The apparatus configuration of the above-mentioned folding processing section  48  will be described below. “ 44 ” shown in  FIG. 8A  denotes the apparatus frame, and  FIG. 8A  shows the front side of mutually opposite front and back side frames (front and back in the sheet of  FIG. 8 ) of the apparatus housing. Each of the rollers  49 ,  41 ,  50  and  64  is rotatably supported between the front and back side frames (hereinafter, the pair of front and back side frames are simply referred to as the “apparatus frame”)  44 . 
     At this point, the first roller  49  is supported by the apparatus frame  44  via a first bracket member  45 , and concurrently therewith, the fourth roller  64  is supported by the apparatus frame  44  via a second bracket  46 . Further, the guide member  39  is supported by the second bracket member  46 . 
     This is because the first bracket member  45  separates the first roller  49  from the second and third rollers  41 ,  50 , and the second bracket member  46  separates the fourth roller  64  from the first roller  49 . 
     Therefore, as shown in  FIG. 9 , in the invention, the position relationship of the first to fourth rollers  49 ,  41 ,  50 ,  64  is configured as described below. On the periphery of the first roller  49 , the second and third rollers  41 ,  50  are brought into press-contact with the right hemisphere portion (angular interval within 180 degrees), and the fourth roller  64  is brought into press-contact with the left hemisphere portion (angular interval beyond 180 degrees). In  FIG. 9 , with reference to the vertical line z-z, the second and third rollers  41 ,  50  are brought into press-contact with the right side within 180 degrees, while the fourth roller  64  is brought into press-contact with the left side within 180 degrees. 
     From such an arrangement relationship, in other words, using the vertical line z-z passing through the circle center of the first roller  49  as a base point, the second roller  41  and third roller  50  are disposed around the periphery of the first roller at angular positions in the range of 0 to 180 degrees, and similarly, the fourth roller  64  is brought into press-contact at an angular position in the range of 180 degrees to 360 degrees. By this means, the second and third rollers  41 ,  50  are fixed to the apparatus frame, the first and fourth rollers  49 ,  64  are shifted in position, and it is thereby possible to release press-contact in three locations at the same time. Further, by placing the second and third rollers  41 ,  50  in the right hemisphere portion of the first roller  49 , and further placing the fourth roller  64  in the left hemisphere portion, it is possible to configure the roller mechanism to be small and compact. 
     Therefore, the second and third rollers  41 ,  50  are bearing-supported by the apparatus frame  44  at an angular interval of 180 degrees or less. In  FIG. 9 , the rotary shaft  41   x  of the second roller  41  is bearing-supported by the apparatus frame  44  to be rotatable, and similarly, a rotary shaft  50   x  of the third roller  50  is also bearing-supported. 
     Meanwhile, the first roller  49  is bearing-supported by the first bracket member  45 , and the bracket member  45  is supported at a spindle  45   r  by the apparatus frame  44 . The spindle  45   r  is set at the center position to swing the first roller  49  in the direction in which the roller  49  separates from the second and third rollers  41 ,  50 . 
     Then, the first bracket member  45  is acted upon by the spring force in the arrow direction shown in the figure from the biasing spring (biasing means)  47  fixed at its one end to the apparatus frame  44 , and brings the first roller  49  into press-contact with the second and third rollers  41 ,  50 . 
     Meanwhile, the fourth roller  64  is attached to the second bracket member  46 , and the second bracket member  46  is supported swingably at the spindle by the apparatus frame  44 . To the second bracket member  46  is fixed the guide member  39 , and the guide member  39  is formed in the shape of a curve for guiding the folded sheet along the periphery of the first roller  49  in between the third roller  50  and the fourth roller  64 . 
     In the second bracket member  64 , the position of the spindle is set in the apparatus frame  44  to be swingable in the direction in which the fourth roller  64  and the guide member  39  separate from the first roller  49 . In the bracket shown in the fig ure, the spindle is set at the rotary shaft  50   x  of the third roller  50 . The spindle may be set at the position other than the rotary shaft  50   x.    
     The fourth roller  64  is not directly attached to the second bracket member  46 , and is bearing-supported by the biasing lever  38  attached to the bracket. As shown in  FIG. 8A , in the biasing lever  38 , the front end axially supports the fourth roller  64 , the center portion is axially supported at the spindle  38   r  by the second bracket member  46  to be rotatable, and a biasing spring  52  engages in the base end portion. The biasing spring  52  is at its one end fixed and supported by the second bracket member  46 , and acts the spring force in the arrow direction on the biasing lever  38 . By this spring force, the fourth roller  64  is brought into press-contact with the first roller  49 . 
     Then, when the first bracket member  45  swings in a clockwise direction in  FIG. 9  on the spindle  45   r , the first roller  49  separates from the second and third rollers  41 ,  50 . Meanwhile, when the second bracket member  46  swings in a counterclockwise direction in  FIG. 9  on the rotary shaft  50   x , the fourth roller  64  and the guide member  39  separate from the first roller  49 . 
     In addition, in this case, after the second bracket  46  is shifted to the position in the direction in which the fourth roller  64  separates from the first roller  49 , it is necessary to shift the first bracket member  45  to the position in the direction in which the fourth roller  64  separates from the first roller  49 . This is because of preventing the fourth roller  64  from interfering with the movement of the first roller  49  when the first roller  49  shifts in the separation direction (see  FIG. 9 ). 
     By thus separating the first roller  49  positioned in the center from the second and third rollers  41 ,  50 , it is possible to concurrently release press-contact of the first folding press-contact portion Np 1  and the second folding press-contact portion Np 2 , and it is thus possible to remove a jam sheet by the simplified structure and operation. Concurrently therewith, it is possible to withdraw the fourth roller  64  and guide member  39  in press-contact with the first roller  49  at the same time in the separation direction. Accordingly, concurrently with the folding press-contact portions, it is possible to withdraw the folding enhancement press-contact portion Np 3  and the guide member  39  for the portion Np 3  in conjunction with each other, and therefore, jam handing is remarkably made ease. 
     The operating means  55  is provided in one of the first and second bracket members  45 ,  46 , and the members are interlocked so that when one of the members is swung, the other member also swings at the same time. In the members as shown in the figure, when the second bracket member  46  swings on the rotary shaft  50   x , a cam engagement portion  46   c  provided in the member  46  presses an interlocked engagement portion  45   z  of the first bracket member  45 , and swings the first bracket member  45  on the spindle  45   r  in the clockwise direction in  FIG. 9 . 
     The apparatus as shown in the figure indicates the case that the operating means  55  is provided in the second bracket member  46 , the second bracket member  46  is provided with a latch  56  for holding the member  46  in the press-contact position, and when the latch is released, the second bracket member  46  is able to swing on the rotary shaft  50   x  in the counterclockwise direction in  FIG. 9 . 
     The latch  56  is comprised of a cam lever  56   a  and a latch groove  46   w . The cam lever  56   a  is provided rotatably on the apparatus frame side, and is integrally provided with an operating lever (first operating lever)  56   b . Then, in a state of  FIG. 11A  in which the front end of the cam lever  56   a  engages in the latch groove  46   w , the second bracket member  46  is positioned in an actuation position (attitude). 
     Then, when the operating lever  56   b  is operated and the cam lever  56   a  rotates in a clockwise direction as shown in the figure, the cam lever front end is disengaged from the latch groove  46   w , and the second bracket member  46  rotates freely on the rotary shaft  50   x  (free state). 
     The second bracket member  46  is provided with a temporary latch  57 . For the temporary latch  57 , one of engagement hooks  57   a ,  57   b  that mutually engage is disposed on the apparatus frame side, while the other one is disposed on the second bracket member side. 
     The engagement hook  57   a  disposed on the second bracket member side is provided with an operating lever (second operating lever)  57   c  for releasing latch engagement. When the operating lever  57   c  is operated to rotate in a clockwise direction in the state as shown in  FIG. 11A , the temporary latch  57  is released, and the second bracket member  46  rotates freely on the rotary shaft  50   x.    
     Thus, the second bracket member  46  takes attitudes in three stages of engagement position (real latch position) Lp 1 , first release position (temporary latch position) Lp 2 , and second release position (free state) Lp 3 . Then, in the real latch position Lp 1 , the first to fourth rollers  49 ,  41 ,  50 ,  64  are set for the state in which the rollers are brought into press-contact with one another. In the temporary latch position Lp 2 , the first to fourth rollers are set for a loose fit state. In the free state Lp 3 , the second bracket member  46  can be swung in free angular positions. 
     Meanwhile, when the second bracket member  46  shifts in position on the rotary shaft  50   x  as the center from the engagement position Lp 1  to the second release position Lp 3 , the cam engagement portion  46   c  presses the interlocked engagement portion  45   z  of the first bracket member  45 . Then, the first bracket member  45  is interlocked in the clockwise direction in  FIG. 8A  on the spindle  45   r , and swings the bracket member  45  in the separation direction. By this swing, the first roller  49  separates from the second and third rollers  41 ,  50 , and the engagement of the press-contact portions Np 1 , Np 2  is released. 
     For the folding processing section  48 , in the casing  29  are disposed the sheet transport path (first transport path)  32 , folding roller means  49 ,  41 ,  50 ,  64 , and storage stocker  65  in this order from the top to the bottom. Then, the first roller  49 , second roller  41 , third roller  50  and fourth roller  64  for folding enhancement constituting the folding roller means are disposed above the storage stocker  65 . 
     Accordingly, when an operator pulls sheets out of the stacker  65 , there is a fear that the operator touches the roller press-contact portion. At the same time, when a sheet jam occurs in the roller press-contact portion, it is necessary to release the press-contact portion. Therefore, the second bracket member  46  is provided with a cover member  58  as described below. 
     [Configuration of the Cover Member] 
     The cover member  58  is to prevent the hand of an operator from being caught in the folding rollers when a jam occurs, and is attached in between the second switchback path  35  and the second bracket member  46 . The cover member  58  is comprised of a resin film member having flexibility, and its base end portion  58   a  is fixed to a guide member of the second switchback path  35  (see  FIG. 10 ), while its front end portion  58   b  is engaged and supported at slits  58   s  by pins  46   p  provided in the second bracket member  46 . 
     Then, a pair of second bracket members  46  are disposed at the opposite end portions in the shaft direction of the folding roller to be opposed to each other, and the cover member  58  is attached in between the pair of bracket members. 
     Accordingly, the cover member  58  covers the storage stocker  65  and the roller press-contact portions Np 2 , Np 3  positioned below when the second bracket member  46  is in the operating state. Meanwhile, when the second bracket member  46  is opened, it is configured that the operator is able to approach the roller press-contact portion from the storage stacker  65 . 
     [Configuration of a Full Detecting Sensor] 
     Further, in the second bracket member  46  is disposed a full detection lever  60  that detects an uppermost sheet of the storage stacker  65 . When the operator opens the second bracket member  46  to handle a jam, there is a fear that the detection lever is broken. Therefore, by integrally opening the detection lever  60  and second bracket member  46 , it is intended that the detection lever  60  withdraws from the work area of the jam handling. Sd shown in the figure denotes a sensor that detects the detection lever  60 . 
     [Driving Mechanism] 
     The driving mechanism of the apparatus as shown in  FIG. 3  will be described below according to  FIGS. 12 and 13 .  FIG. 12  shows the driving transfer system of the feeding motor Mf,  FIG. 13A  shows the state in which the gate stopper  43  is operated by the feeding motor Mf, and  FIG. 13B  shows the state in which the pinch roller  42  is operated by the feeding motor Mf. 
     In  FIG. 12 , a motor rotary shaft  100  of the feeding motor Mf conveys rotation in the forward direction (CW) and rotation in the backward direction to the rotary shaft  40   x  of the carry-in roller  40   b  via an intermediate shaft  101 . The rotary shaft  40   x  conveys to the rotary shaft  62   y  of the carrying-out roller  62   b  via a transmission belt V 1 . 
     By this means, the forward and backward rotation of the feeding motor Mf is conveyed to the carry-in roller pair  40   a ,  40   b  and carrying-out roller pair  62   a ,  62   b  as rotation in the sheet discharge direction. CW shown in the figure denotes a transmission system of rotation in the forward direction, and CCW denotes a transmission system of rotation in the backward direction. By gear transfer, the rotation directions of the carry-in roller pair  40   a ,  40   b  and the carrying-out roller pair  62   a ,  62   b  are set at one direction. 
     Further, the rotary shaft  100  of the feeding motor Mf conveys the rotation in the forward direction to the spindle  43   x  of the gate stopper  43  via an intermediate shaft  102 , while conveying the rotation to the spindle  42   x  of the pinch roller  42  via an intermediate shaft  103 . The transmission system is to shift in position the gate stopper  43  and the pinch roller  42  to the waiting position by the rotation in the forward direction (CW) of the feeding motor Mf, and will be described later including the clutch mechanism. 
     In rotation of the intermediate shaft  101 , the rotation in the forward direction (CW) is only conveyed to the folding rollers via a one-way clutch OWC. As shown in  FIG. 12 , the rotation in the forward direction of the intermediate shaft  101  is transferred to the first roller  49 , second roller  41 , third roller  50  and folding enhancement roller  64  by gears. In addition, the folding enhancement roller  64  is a roller in press-contact with the first roller  49  (described later). Further, the rotation in the forward direction (CW) and the rotation in the backward direction (CCW) of the feeding motor Mf are conveyed to the rotary shaft  67   x  of the sheet discharge roller  67 . 
     [Driving Mechanism of the Gate Stopper and Pinch Roller] 
     Driving of the gate stopper  43  and pinch roller  42  as shown in  FIG. 13A  and  FIG. 13B  will be described next.  FIG. 13A  shows the driving mechanism of the gate stopper  43 , the gate stopper  43  swings on the spindle  43   x , and a lock surface  43   s  at the front end shifts to positions between a lock position positioned in the first transport path  32  and a waiting position outside the path. 
     Therefore, the gate stopper  43  is always biased in the direction of an eccentric cam  43   b  by a spring  43   a , and shifts in position to the lock position (solid line in  FIG. 13A ) and the waiting position (dashed line in  FIG. 13A ) by the eccentric cam  43   b . Therefore, a cam follower  43   y  is formed at one end of the gate stopper  43 , and engages in the eccentric cam  43   b . Then, in the eccentric cam  43   b , a cam gear  43   c  rotating integrally with the cam  43   b  is coupled to a teeth-lacked gear  43   d  by gear. A transmission gear  43   g  of the feeding motor Mf is mated with the teeth-lacked gear  43   d . The teeth-lacked gear  43   d  and the transmission gear  43   g  mesh with each other so as not to convey driving in the teeth lacking portion. Then, the teeth-lacked gear  43   d  is integrally coupled to a control cam  43   e.    
     In the control cam  43   e  are engaged a biasing spring  43   h  and actuation solenoid  43 SL, the biasing spring  43   h  biases the teeth-lacked gear  43   d  in the transmission direction, and the actuation solenoid  43 SL is engaged to lock the control cam  43   e  to the non-transmission state by a lock hook  43   f . Accordingly, rotation of the feeding motor Mf is transferred to the teeth-lacked gear  43   d  by the transmission gear  43   g , and the eccentric cam  43   b  rotates by the rotation. Then, the actuation solenoid  43 SL is coupled to lock the transmission gear  43   g  and teeth-lacked gear  43   d  to the non-transmission state in the non-energized state, while conveying the rotation of the transmission gear  43   g  to the teeth-lacked gear  43   d  in the energized state. 
     In addition, in the eccentric cam  43   b  and the teeth-lacked gear  43   d , the gear coupling rate is set so that a single rotation of the teeth-lacked gear  43   d  rotates the eccentric cam  43   b  half rotation (½ rotation). Then, the gate stopper  43  swinging up and down by the eccentric cam  43   b  is provided with a flag  43   k  and position sensor S 4  (see  FIG. 13A ). Accordingly, the control cam  43   e  integrally formed in the teeth-lacked gear  43   d  shifts the gate stopper  43  to positions between the actuation position and the withdrawal position by two rotations. 
     Then, when the actuation solenoid  43 SL is controlled from the ON state to the OFF state after the teeth-lacked gear  43   d  rotates once, the gate stopper  43  is positioned in the withdrawal position, and rests in the position. Further, when the actuation solenoid  43 SL is controlled from the ON state to the OFF state after the teeth-lacked gear  43   d  rotates twice, the gate stopper  43  shifts from the actuation position to the withdrawal position by first one rotation, and returns from the withdrawal position to the actuation position by next one rotation. The position sensor S 4  is an abnormality detecting sensor that detects a state in which the gate stopper  43  is in the withdrawal position. 
     In such a configuration, the feeding motor Mf conveys the rotation of the motor to the eccentric cam  43   b  in the forward rotation. In the backward-direction rotation, the actuation solenoid  43 SL is maintained at the non-energized state (OFF state), and driving is not conveyed in the teeth lacking portion of the teeth-lacked gear  43   d.    
     The driving mechanism of the pinch roller  42  shown in  FIG. 13B  will be described next. As described previously, the pinch roller  42  is attached to an arm  42   b  (roller shift means; the same in the following), and the bracket  42   b  is configured to swing on the spindle  42   x  as the center. Therefore, the pinch roller  42  is kept always at the actuation position (solid line in  FIG. 13B ) by the biasing spring  42   a . A transmission gear  42   c  is coupled to the shaft portion of the arm  42   b  to rotate integrally, and a clutch gear  42   e  meshes with the transmission gear  42   c  via a transmission gear line  42   d . A transmission gear  42   g  of the feeding motor Mf is coupled to the clutch gear  42   e  via a torque limiter TLQ. 
     The clutch gear  42   e  is supported by a planetary lever  26  swinging on the intermediate shaft  103  as described previously as the center, and the spindle of the planetary lever is provided with the torque limiter TLQ. “ 42   f ” shown in the figure denotes a stopper for locking the clutch gear  42   e  to the non-transmission state. When the transmission gear  42   g  rotates by backward-direction rotation of the feeding motor Mf in the state of  FIG. 13B , the planetary lever  42   h  swings in a clockwise direction, and the clutch gear  42   e  attached to the lever  26  meshes with the transmission gear line  42   d  and conveys rotation of the transmission gear  42   g  to the transmission gear  42   c.    
     Then, the arm  42   b  integrated with the transmission gear  42   c  shifts to the withdrawal position as the dashed-line state in  FIG. 13B . Subsequently, the arm  42   b  engages in a stopper  42   k  and is locked in the position. At this point, the transmission gear line  42   d  and the clutch gear  42   e  idle by the torque limiter TLQ, are halted in rotation, and are locked in the state. 
     Then, when the feeding motor Mf rotates in the forward direction, the transmission gear  42   g  rotates in a clockwise direction, and the planetary lever  26  gear-coupled to the gear  42   g  rotates in a counterclockwise direction. In this state, the coupling between the clutch gear  42   e  and the transmission gear line  42   d  is released, and the clutch gear  42   e  and the transmission gear line  42   d  are locked in the state by the torque limiter TLQ. 
     Accordingly, in the forward-direction rotation of the feeding motor Mf, the rotation of the transmission gear  42   g  is not conveyed to the transmission gear  42   c  of the arm  42   b , and the pinch roller  42  is maintained at the state (the actuation position; solid line in  FIG. 13B ) in press-contact with the second roller  41  in the first transport path  32  by action of the biasing spring  42   a.    
     Meanwhile, when the feeding motor Mf rotates in the backward direction, the transmission gear  42   g  rotates in a counterclockwise direction, the clutch gear  42   e  of the planetary lever  26  engages in the transmission gear line  42   d  by the rotation, and the pinch roller  42  shifts in position to the withdrawal position (dashed line in  FIG. 13B ) withdrawn from the first transport path  32  and is locked in the state. 
     [Open/Close Operation of the Upper Unit] 
     The unit configuration of the gate stopper  43  will be described according to  FIG. 13A . The gate stopper  43 , spindle  43   x  and biasing spring  43   a  are attached to the upper unit  29 A, and to the lower unit  29 B are attached the eccentric cam  43   b  for moving the gate stopper  43  up and down, the cam gear  43   c  for driving and rotating the cam, the teeth-lacked gear  43   d , the transmission gear  43   g  and the feeding motor Mf for driving the cams and gears. 
     Then, in opening and closing the upper unit  29 A around the hinge shaft  28 , required is an engagement mechanism with the eccentric cam  43   b  on the lower unit  29 B side. The open/close mechanism will be described later according to  FIG. 15 . 
     Similarly, the unit configuration of the pinch roller  42  will be described according to  FIG. 13B . The pinch roller  42 , arm  42   b , spindle  42   x  of the arm, and biasing spring  42   a  are attached to the upper unit  29 A, and concurrently, the gear  42   c  provided in the spindle  42   x  and the transmission gear line  42   d  of the gear are also attached to the upper unit  29 A. Meanwhile, to the lower unit  29 B are attached the clutch gear  42   e  meshing with the transmission gear line  42   d , planetary lever  26 , torque limiter TLQ, transmission gear  42   g  and feeding motor Mf for driving them. 
     Then, in opening and closing the upper unit  29 A around the hinge shaft  28 , required is the engagement mechanism for the transmission gear line  42   d  attached to the upper unit  29 A and the clutch gear  42   e  attached on the lower unit  29 B side. The open/close mechanism will be described later according to  FIG. 15 . 
       FIGS. 15 to 17  are explanatory views of open/close operation of the upper unit  29 A.  FIG. 15  shows the operating state in which the upper unit  29 A is closed,  FIG. 16  shows an open state in which the upper unit  29 A is opened by a predetermined angle θ, and  FIG. 17  shows an intermediate state in opening/closing the upper unit  29 A. 
       FIG. 15  shows the unit closed state, and the cam follower  43   y  and eccentric cam  43   b  of the gate stopper  43  are engaged with each other so as to move the gate stopper  43  up and down by rotation of the cam. Further, the gear  42   c  for moving the pinch roller  43  up and down, and the transmission gear line  42   d  of the gear mesh with the clutch gear  42   e . In this state, each of the gate stopper  43  and pinch roller  42  moves up and down by the driving force conveyed from the feeding motor Mf. 
       FIG. 16  shows the unit open state. The cam follower  43   y  of the gate stopper  43  and the actuation lever  63   y  of the path switching means  63  are hinge-rotated the predetermined angle θ, and in this state, the cam follower  43   y  is in a position separate from the eccentric cam  43   b , while the actuation lever  63   y  is in a position separate from the link lever  60  (engagement release state). Further, the pinch roller  42  and the transmission gear line  42   d  for moving the roller up and down are hinge-rotated the predetermined angle θ, and in this state, the transmission gear line  42   d  is in a position separate from the clutch gear  42   e  (engagement release state). 
     Then, as shown in  FIG. 15 , in the eccentric cam  43   b  that engages in the cam follower  43   y  is formed a guide surface  43   z  for guiding the cam follower  43   y  to the cam surface. The guide surface  43   z  is formed in the shape of a cone with a slope for guiding the cam follower  43   y  to the cam surface during the process of shifting (close operation) to the closed state (the state in  FIG. 15 ) from the state in which the cam follower  43   y  engages in the guide surface  43   z  in the semi-open state of the upper unit  29 A as shown in  FIG. 17 . 
     In other words, in the eccentric cam  43   b  is formed the guide surface  43   z  for guiding the cam follower  43   y  to the cam surface, and the guide surface  43   z  is formed to guide the cam follower  43   y  to the cam surface when the upper unit  29 A swings and moves around the hinge shaft  28 . 
     Similarly, as shown in  FIG. 14 , in the link lever  60  that engages in the actuation lever  63   y  is formed a guide surface  60   z  in the shape of a cone for guiding the actuation lever  63   y  to the engagement surface, and the guide surface  60   z  is formed to guide the actuation lever  63   y  to the engagement surface when the upper unit  29 A swings and moves around the hinge shaft  28 . 
     Further, the clutch gear  42   e  for moving the pinch roller  42  up and down is attached to the planetary lever  26  as described previously, and the lever  26  swings on the rotary shaft  103  from the solid-line state to the dashed-line state in  FIG. 13B . In such a configuration, as shown in  FIG. 15 , the planetary lever  26  is provided in the rotary shaft  103  attached to the lower unit  29 B. The planetary lever  26  is provided with a sloped cam surface  26   z  that engages in a cam gear  42   i  attached to the upper unit  29 A. 
     Then, in opening and closing the upper unit  29 A around the hinge shaft  28 , the clutch gear  42   e  and the planetary lever  26  attached to the gear are shifted from the solid-line state to the dashed-line state in  FIG. 13B . 
     In other words, by the open/close operation of the upper unit  29 A, the clutch gear  42   e  attached to the lower unit  29 B is shifted from the transmission state to non-transmission state. By this means, the transmission gear  42   d  provided in the upper unit  29 A and the clutch gear  42   e  are engaged and released. Accordingly, when the sloped cam surface  26   z  of the planetary lever  26  is disposed in a position for engaging in the cam gear  42   i  of the upper unit A, the cam gear  42   i  constitutes an interlock member for actuating the planetary lever  26 . Alternately, other than the cam gear  42   i , an interlock member (cam actuator) may be provided in any component of the upper unit A or particularly in the upper unit A, and be configured to engage in the sloped cam surface  26   z.    
     Thus, the transport control means such as the gate stopper  43  and pinch roller  42  in the upper unit  29 A are coupled to the feeding motor Mf disposed in the lower unit  29 B by the transmission mechanism, engagement/release of the transmission mechanism is interlocked with the open/close operation of the upper unit  29 A, the motor is thereby shared as the driving motor of the folding roller pair of the lower unit  29 B, and it is thus possible to simplify the driving mechanism. 
     [Driving Mechanism of the Shift Motor] 
     Described next is the driving mechanism of the first folding deflecting means  53  and the second folding deflecting means  54  as described previously. As shown in  FIG. 18A  and  FIG. 18B , in the first folding deflecting means  53 , the driven roller  53   a  and the curved guide  53   b  are supported by the up-and-down member  53   c  moving up and down in a predetermined stroke. The up-and-down member  53   c  is provided with an actuation lever  85   a  swingable on a spindle  85   x  as the center to engage in the member  53   c . In other words, in the up-and-down member  53   c  supported by the apparatus frame in a guide rail (not shown) to be able to move up and down, a cam groove  53   d  is provided, and is disposed so that the front end of the actuation lever  85   a  engages in the cam groove  53   d.    
     Then, the actuation lever  85   a  is coupled to the spindle  85   x  via a spring clutch  85   d . Concurrently therewith, the spindle  85   x  is provided with a pulley  85   b , and rotation of the shift motor MS is conveyed to the pulley  85   b  via a transmission belt  85   c . Then, the spring clutch  85   d  is set to convey the rotation of the shift motor MS from the spindle  85   x  to the actuation lever  85   a . Concurrently therewith, when the load of predetermined torque or more is imposed, the spring clutch  85   d  idles with respect to the spindle  85   x , and is configured not to convey the rotation of the shift motor MS to the actuation lever  85   a.    
     Accordingly, when the shift motor MS rotates in the forward direction, the actuation lever  85   a  rotates from the state of  FIG. 18A  to the state of  FIG. 18B  in a clockwise direction shown in the figure, and after the driven roller  53   a  comes into contact with the periphery of the first roller  49 , the spring clutch  85   d  idles. Then, when the shift motor MS rotates in the backward direction, the actuation lever  85   a  rises from the state of  FIG. 18B  to the state of  FIG. 18A . After the up-and-down member  53   c  strikes the stopper  53   e , the spring clutch  85   d  idles and the state is locked as shown in the figure. In addition, a limit sensor Ls is disposed in the this position, and the rotation of the shift motor MS is halted by a state signal such that the up-and-down member  53   c  shifts to a predetermined stopper position. 
     Meanwhile, in the second folding deflecting means  54 , similarly, the up-and-down member  54   c  is supported by the apparatus frame to move up and down in a predetermined stroke, and is provided with the driven roller  54   a  and curved guide  54   b . As described previously, the up-and-down member  54   c  is provided with a rack  54   r  that meshes with a pinion  54   p . Then, the shift motor MS is coupled to the pinion  54   p  via a spring clutch  86   a . The spring clutch  86   a  is set to convey the rotation of the shift motor MS within predetermined torque, while idling at the predetermined torque or more. 
     In addition, in the first folding deflecting means  53  and the second folding deflecting means  54 , the up-and-down member  53   c  shifts in position from the withdrawal position to the actuation position by the forward-direction rotation of the shift motor MS, and by the rotation in this direction, the up-and-down member  54   c  of the second folding deflecting means shifts in position from the actuation position to the withdrawal position. Alternately, in the backward-direction rotation of the shift motor MS, the up-and-down member  54   c  of the second folding deflecting means  54  shifts in position from the withdrawal position to the actuation position, and by the rotation in this direction, the up-and-down member  53   c  of the first folding deflecting means  53  shifts in position from the actuation position to the withdrawal position. Thus, the first folding deflecting means  53  and second folding deflecting means  54  are configured to shift to positions between the actuation position and the withdrawal position in a relatively opposite manner by forward and backward rotation of the shift motor MS. 
     [Sheet Front End Detecting Sensor] 
     As shown in  FIG. 3 , a first sensor S 1  for detecting an end edge of a sheet is disposed in the first transport path  32 , and detects the end edge (front end and rear end) of the sheet carried in the first switchback path  34 . Further disposed is a second sensor S 2  for detecting the end edge of the sheet carried in the second switchback path  35 . The first sensor S 1  and second sensor S 2  detect the end edge of the sheet to calculate the fold position of the sheet, and the action of the sensors will be described later together with folding forms described later. 
     [Folding Processing Form] 
     A sheet folding method by the above-mentioned folding processing means will be described next according to  FIG. 22A ,  FIG. 22B ,  FIG. 22C ,  FIG. 22D  and  FIG. 22E . In a normal sheet with the image formed, there are cases that the sheet is folded in two or three for a letter finish. Further, in folding in three, there are cases of outward three-folding and inward three-folding.  FIG. 22A  shows an aspect of inward three-folding,  FIG. 22B  shows an aspect of outward three-folding, and  FIG. 22C  shows an aspect of Z-folding. 
     Then, in the case of two-folding, the sheet fed to the second transport path  33  is folded in a ½ position of the sheet size or in a ½ position with a margin left in the sheet end portion by the first and second rollers  49 ,  41  (first folding). 
     Meanwhile, in the case of three-folding, the sheet fed to the second transport path  33  is folded in a ⅓ position of the sheet size by the first and second rollers  49 ,  41  (first folding). The first and third rollers  49 ,  50  fold the remaining sheet in a ⅓ position of the folded sheet (second folding) to feed to the third transport path  36 . 
     Further, in the case of three-folding, when inward three-folding is performed as shown in  FIG. 22A , the sheet fed to the second transport path  33  is folded in a ⅓ position on the sheet rear end side by the first and second rollers  49 ,  41  and next, is folded in a ⅓ position on the sheet front end side. Similarly, in the case of outward three-folding, the sheet fed to the second transport path  33  is folded in a ⅓ position on the sheet front end side by the first and second rollers  49 ,  41  and next, is folded in a ⅓ position on the sheet rear end side. 
     Furthermore, in the case of three-folding, when Z-folding as shown in  FIG. 22C  is performed, the sheet fed to the second transport path  33  is folded in a ¼ position on the sheet rear end side by the first and second rollers  49 ,  41  and next, is folded in a ½ position of the sheet. 
     Moreover, there is the case that the fold width of three-folding is widened according to the envelop size to leave the margin. In the case of performing inward three-folding as shown in  FIG. 22D , the sheet is folded in a position slightly closer to the rear end side than the ⅓ position of the sheet size (first folding), and next, is folded in a position of the substantially same width as the width of the first-folded sheet on the sheet front end side (second folding). Similarly, in outward three-folding as shown in  FIG. 22E , the sheet is folded in a position slightly closer to the front end side than the ⅓ position on the sheet front end side, and next, is folded in a position of the substantially same width as the width of the first-folded sheet on the sheet rear end side (second folding). In other words, in the case of leaving the margin in the three-folded sheet, the sheet is folded so that the side of the second-folded sheet is long. 
     [Control Means] 
     The control means  95  for above-mentioned sheet folding is configured as described below. The sheet folding apparatus B as described previously is mounted with a control CPU, or a control section  91  of the image formation apparatus A is provided with a folding processing control section. Then, the control section is configured to enable the following operation. 
     First, the first switchback path  34  and second switchback path  35  of the second transport path  33  are provided with stopper means (not shown) for regulating the position of the sheet front end or sensor means (S 1  and S 2  shown in the figure) for detecting the position of the sheet front end. In the apparatus as shown in the figure, the first sensor S 1  is disposed in the first switchback path  34 , and the second sensor S 2  is disposed in the second switchback path  35 . Then, the control means  95  is configured to calculate timing at which the fold position of the sheet arrives at a predetermined position from the sheet size information sent from the image formation apparatus A and a detection signal from the sensor S 1  (S 2 ). 
     Then, the operation will be described according to the control block diagram shown in  FIG. 23 . In the image formation apparatus A, a control CPU  91  is provided with a control panel  15  and mode setting means  92 . The control CPU  91  controls a paper feed section  3  and image formation section  7 , corresponding to image formation conditions set in the control panel  15 . Then, the control CPU  91  transfers data and commands such as “post-processing mode”, “job finish signal” and “sheet size information” required for post-processing to the control section  95  of the post-processing apparatus C. 
     The control section  95  of the post-processing apparatus C is a control CPU, and is provided with a post-processing operation control section  95   a . Then, detection signals of the first sensor S 1  and second sensor S 2  are conveyed to the control CPU  95 . Meanwhile, the control CPU  95  conveys “ON”/“OFF” control signals to the stopper driving means (solenoid  43 SL) provided in the gate stopper means  43  and the path switching means  63 . 
     Then, for the control CPU  95 , folding processing execution programs are stored in ROM  96  to control the feeding motor Mf (not shown), shift motor MS, stopper driving means (solenoid  43 SL) and path switching means  63  so as to execute the folding forms as described previously. Further, RAM  98  stores data to calculate the fold of the sheet in fold position calculating means  97 , and actuation timing time of the shift motor Ms as data. 
     The fold position calculating means  97  is comprised of a computing circuit for calculating a fold position (dimension) from the sheet front end (front end in the sheet discharge direction), from the “sheet length size”, “folding form” and “margin dimension”. For example, in the two-folding mode, the sheet is folded in a ½ position in the sheet discharge direction, or a ½ position with a beforehand set margin left. For example, calculation of the fold position is obtained by calculating [{(sheet length size)−(margin)}/2]. Further, in the three-folding mode, for example, the fold position is calculated corresponding to the folding form such as letter folding (inward three-folding, outward three-folding) and filing folding (Z-folding, outward three-folding). 
     [Folding Processing Operation] 
     The action in the configuration of the sheet folding apparatus B will be described.  FIG. 19A  shows a state in which a sheet entering the carry-in entrance  30  undergoes register correction, and  FIG. 19B  shows a state in which the sheet is carried in the first switchback path  34  for first folding.  FIG. 20A  shows a state in which the sheet is folded in the first folding position Np 1 ,  FIG. 20B  shows a state in which the folded sheet is carried in the second switchback path  35 ,  FIG. 21A  shows a state in which the sheet is folded in the second folding position Np 2 , and  FIG. 21B  shows is a state in which the folded sheet is carried out. 
     In  FIG. 19A , a sheet is guided to the carry-in entrance  30 , and fed to the downstream side by the carry-in roller pair  40 . Then, the sheet front end is locked by the gate stopper  43 , and the sheet is curved and deformed in the shape of a loop inside the register area, and is aligned in the front end. 
     In  FIG. 19B , when the gate stopper  43  withdraws from first transport path  32 , the sheet is fed to the downstream side in the first transport path  32  by the above-mentioned sheet transport mechanism. Then, the control means  95  controls the path switching means  63  so as to guide the sheet to the first switchback path  34  from the first transport path  32  as shown in  FIG. 19B . 
     Thus, the sheet is carried in the first switchback path  34  by the pinch roller  42  and the second roller  41 . In addition, in the first transport path  32 , the first sensor S 1  is disposed on the downstream side of the pinch roller  42  and the second roller  42 , and detects the sheet front end carried in the first switchback path  34 . 
     In  FIG. 20A , based on a signal such that the first sensor S 1  detects the sheet front end, the control means  95  shifts the up-and-down member  53   c  of the first folding deflecting means  53  from the waiting position to the actuation position at timing at which the fold position of the sheet is shifted to a predetermined position. Thus, the sheet in the first transport path  32  is deformed in the shape of a V toward the first nip portion Np 1 . Then, when the driven roller  53   a  attached to the up-and-down member  53   c  comes into press-contact with the periphery of the first roller  49 , the sheet front end side is fed in the opposite direction (rotation direction of the first roller). 
     Meanwhile, the sheet rear end side feeds the sheet toward the first nip portion Np 1  by transport force of the pinch roller  42  and the second roller  41 . At this point, the curved guide surface of the curved guide  53   b  regulates the sheet to follow the roller periphery of the second roller  41 . 
     Accordingly, the sheet is fed toward the first folding position Np 1  on the front end side by the driven roller  53   a  and on the rear end side by the pinch roller  42  and the second roller  41 , and up-and-down timing of the up-and-down member  53   c  is to calculate the fold position. Therefore, the control means  95  beforehand sets the velocity for shifting the sheet by the pinch roller  42  and the second roller  41  and the timing (particularly, timing at which the driven roller  53   c  comes into contact with the periphery of the first roller  49 ) for shifting the driven roller  53   a  to the actuation position from the waiting position at optimal values by experiments. 
     Then, the curved guide surface of the curved guide  53   b  guides the sheet to follow the periphery of the opposed second roller  41  in synchronization with the shift of the driven roller  53   a  from the waiting position to the actuation position, and therefore, there is no fear that the fold position of the sheet changes every time. 
     In  FIG. 20B , the sheet folded in the ½ position (two-folding), ⅓ position (three-folding) or ¼ position (three-folding) in the first nip portion Np 1  is provided with the transport force by the first nip portion Np 1  and fed to the downstream side. Then, the control means  95  positions the up-and-down member  54   c  of the second folding deflecting means  54  in the actuation position in the two-folding mode, or in the waiting position in the three-folding mode.  FIG. 20B  shows control of the three-folding mode. In two-folding, the up-and-down member  54   c  is positioned in the actuation position, and the folded sheet is guided to the second nip portion Np 2  beginning with the front end, and is fed to the carrying-out exit  31  on the downstream side. 
     Then, in the three-folding mode, the control means  95  positions the up-and-down member  54   c  of the second folding deflecting means  54  in the waiting position as shown in  FIG. 20B . Thus, the sheet fed from the first nip portion Np 1  is fed to the second switchback path  35  beginning with the front end. Then, the second sensor S 2  detects the sheet front end (fold position). 
     In  FIG. 21A , with reference to a detection signal of the second sensor S 2 , in a stage in which the fold position for second folding arrives at a predetermined position, the control means  95  shifts the up-and-down member  54   c  of the second folding deflecting means  54  from the waiting position to the actuation position. Then, the sheet inside the second switchback path  35  is fed in the opposite direction in a stage in which the driven roller  54   c  comes into contact with the periphery of the third roller  50 . 
     By this means, the sheet is guided to the second nip portion Np 2  by the front end side sending the sheet by the driven roller  54   a  and the rear end side sending the sheet by the first nip portion Np 1  in respective opposite directions. In addition, in this case, the shift timing of the up-and-down member  54   c  from the waiting position to the actuation position is the same as in the case of the first folding deflecting means  53  as described previously, and the action of the guide member  54   b  is also the same as in the case. 
     In  FIG. 21B , in the folded sheet fed to the second folding position (second nip portion) Np 2 , the fold is reliably folded by the folding enhancement roller  64  coming into press-contact with the first roller  49 , and the sheet is carried to the sheet discharge path  36 . Then, the control means  95  feeds the folded sheet to the sheet discharge path  37  or feeds the sheet back to the first transport path  32  corresponding to the beforehand set sorting form. In the apparatus as shown in the figure, in inward three-folding and outward three-folding of the letter folding form with no need of binding in the post-processing apparatus C, the control means  95  controls a path switching flapper  38  to guide the sheet from the sheet discharge path  37  to the storage stacker  65 . 
     Further, in the two-folding mode and three-folding mode of ¼ Z-folding or the like for filing or with the need of the post-processing such as bookbinding processing, the sheet is carried to the first transport path  32  from the sheet discharge path  36 , and fed to the post-processing apparatus C from the carrying-out exit  31 . 
     [Folding Operation in the Two-Folding Mode] 
     In the above-mentioned folding operation, in the mode for folding the sheet in two, as shown in  FIG. 24 , the control means  95  receives a mode instruction signal of whether or hot to perform folding processing concurrently with a sheet discharge instruction signal from the image formation apparatus A. Next, the control means  95  calculates the fold position in the fold position calculating means  97  (St 01 ). Then, in the two-folding mode (St 02 ), the first sensor S 1  detects the sheet front end (St 03 ). After a lapse of sheet feeding time corresponding to the sheet length calculated in the fold position calculating means  97  from the detection signal (St 04 ), the control means  95  shifts the first folding deflecting means  53  from the waiting position to the actuation position (St 05 ). This shift is controlled by rotation of the shift motor MS. 
     In the process during which the up-and-down member  53   c  of the first folding deflecting means  53  shifts to the actuation position, as described in  FIG. 20A , the sheet in the first transport path  32  is distorted toward the first nip portion Np 1  with reference to the fold position. Then, when the driven roller  53   a  of the first folding deflecting means  53  comes into contact with the periphery of the first roller  49 , the sheet is drawn and inserted in the first nip portion Np 1  beginning with the fold position. 
     At this point, in the two-folding mode, after a lapse of predicted time that the fold of the sheet is inserted in the first nip portion Np 1  with reference to a detection signal from the first sensor S 1  (St 06 ), the control means  95  shifts the second folding deflecting means  54  to the actuation position (St 07 ). The predicted time is set at time elapsed before the front end of the folded sheet arrives at the curved guide  54   b  after the fold position of the sheet is inserted in the first nip portion Np 1 . Accordingly, the front end of the folded sheet is guided by the curved guide surface of the curved guide  54   b  and is brought along the second roller periphery. 
     Concurrently therewith, since the driven roller  54   a  positioned in the actuation position rotates according to rotation of the third roller  50 , even when the front end of the folded sheet is curled in the direction departing from the second nip portion Np 2 , the sheet is reliably guided to the second nip portion Np 2  by the rotation of the driven roller  54   a  and third roller  50 . 
     Then, the control means  95  carries the folded sheet, which is fed from the second nip portion Np 2  to the sheet discharge path  36 , to the first transport path  32  from the sheet discharge path  36 . Next, the control means  95  prepares for processing of a subsequent sheet in a state in which the second folding deflecting means  54  is positioned in the actuation position (St 08 ). In the apparatus as shown in the figure, in relation to the first folding deflecting means  53  positioned in the waiting position, the second folding deflecting means  54  shifting to positions in a relatively opposite manner is positioned in the actuation position, but it is also possible to configure so that the second folding deflecting means  54  shifts to the waiting position by a detection signal of a sheet discharge sensor S 3  disposed in the sheet discharge path  36 . 
     [Folding Operation in the Three-Folding Mode] 
     In the mode for folding the sheet in three, as described in  FIGS. 19 to 21 , the control means  95  receives a mode instruction signal of whether or not to perform folding processing concurrently with a sheet discharge instruction signal from the image formation apparatus A. Next, the control means  95  calculates the fold position in the fold position calculating means  97  (St 01 ). Then, in the three-folding mode (St 09 ), the first sensor S 1  detects the sheet front end (St 10 ). 
     After a lapse of sheet feeding time corresponding to the sheet length calculated in the fold position calculating means  97  from the detection signal (St 11 ), the control means  95  shifts the first folding deflecting means  53  from the waiting position to the actuation position (St 12 ). This shift is controlled by rotation of the shift motor MS. 
     In the process during which the up-and-down member  53   c  of the first folding deflecting means  53  shifts to the actuation position, as described in  FIG. 20A , the sheet in the first transport path  32  is distorted toward the first nip portion Np 1  with reference to the fold position. Then, when the driven roller  53   a  of the first folding deflecting means  53  comes into contact with the periphery of the first roller  49 , the sheet is drawn and inserted in the first nip portion Np 1  beginning with the fold position. At this point, in the three-folding mode, the control means  95  waits for the second sensor S 2  to detect the sheet front end (St 13 ). 
     After a lapse of predicted time that the second-folding fold position of the sheet arrives at a predetermined position with reference to a detection signal such that the second sensor S 2  detects the sheet front end (St 14 ), the control means  95  shifts the second folding deflecting means  54  to the actuation position (St 15 ). The predicted time is set at a calculation value of the fold position calculating means  97 . Then, the sheet is given the transport force from the driven roller  54   a  and is inserted in the second nip portion Np 2 . The sheet discharge sensor S 3  detects the sheet front end, and the sheet is carried out to the first transport path  32  from the sheet discharge path  36 , or carried out to the storage stacker  65  from the sheet discharge path  37  corresponding to the folding form (St 16 ). 
     In addition, when the post-processing mode without performing the sheet folding processing is set from the mode setting means  92  in the above-mentioned step St 01 , the sheet is fed toward the carrying-out roller pair  62 . Then, in the first transport path  32 , the sheet guide  61  feeds the sheet front end into the nip portion of the carrying-out roller pair  62 . Accordingly, the sheet is guided to the carrying-out exit (carrying-out portion)  31  smoothly without undergoing stress of the gate stopper  43 , pinch roller  42  and second roller  41 . 
     [Configuration of the Sheet Discharge Path] 
     The folded sheet that is folded in two or three as described above is fed to the sheet discharge path  36  from the press-contact point of the first and third rollers  49 ,  50 . Then, the sheet is further folded by the folding enhancement roller (fourth roller)  64  in press-contact with the first roller  49 , and guided to the sheet discharge path  36 . The sheet discharge path  36  merges with the first transport path  32  as described previously. The sheet discharge path  37  branches off from the sheet discharge path  36 , is provided via the path switching flapper  38 , and guides the folded sheet to the storage stacker  65  disposed below the second transport path  33 . 
     Accordingly, the sheet with no need of carrying to the post-processing apparatus C e.g. the sheet folded in the letter form such as inward three-folding and outward three-folding is stored in the storage stacker  65  without being carried to the carrying-out exit  31 . 
     Then, in the folded sheet fed to the sheet discharge path  36 , the sheet to feed to the post-processing apparatus C for post-processing is carried toward the carrying-out exit  31  by the carrying-out roller  62 . In addition, in this case, the determination whether or not to perform post-processing is configured to be made by setting the post-processing condition concurrently with the image formation conditions in the control panel  15 , for example. Then, it is configured that the sheet is carried out to the storage stacker  65  or carried to the post-processing apparatus C corresponding to the set finish condition. 
     [Image Formation Apparatus] 
     The image formation apparatus A is provided with the following configuration as shown in  FIG. 1 . In this apparatus, the paper feed section  3  feeds a sheet to the image formation section  7 , the image formation section  7  prints in the sheet, and the sheet is carried out of the main-body sheet discharge outlet  18 . The paper feed section  3  stores sheets of a plurality of sizes in paper cassettes  4   a ,  4   b , and separates designated sheets on a sheet-by-sheet basis to feed to the image formation section  7 . In the image formation section  7 , for example, an electrostatic drum  8 , and a printing head (laser emitting device)  9 , developing device  10 , transfer charger  11  and fuser  12  arranged around the drum  8  are disposed, the laser emitting device  9  forms an electrostatic latent image on the electrostatic drum  8 , the developing device  10  adds toner to the image, the transfer charger  11  transfers the image onto the sheet, and the fuser  12  heats and fuses the image. 
     The sheet with the image thus formed is sequentially carried out of the main-body sheet discharge outlet  18 . “ 13 ” shown in the figure denotes a circulating path, and is a path for two-side printing for reversing the side of the sheet printed on the front side from the fuser  12  via a main-body switchback path  14 , then feeding the sheet to the image formation section  7  again, and printing on the backside of the sheet. Thus two-side printed sheet is carried out of the main-body sheet discharge outlet  18  after the side of the sheet is reversed by the main-body switchback path  14 . 
     “ 20 ” shown in the figure denotes an image reading section, scans an original document sheet set on a platen  21  with a scan unit  22 , and electrically reads the sheet with a photoelectric conversion element not shown. For example, the image data is subjected to digital processing in an image processing section, and then, transferred to a data storing section  16 , and an image signal is sent to the laser emitting device  9 . Further, “ 25 ” shown in the figure denotes a feeder apparatus, and feeds original document sheets stored in a stacker  24  to the platen  21 . 
     The image formation apparatus A with the above-mentioned configuration is provided with a control section (controller) not shown, and image formation conditions such as, for example, sheet size designation and color/monochrome printing designation and printout conditions such as number-of-copy designation, one-side/two-side printing designation, and scaling printing designation are set from the control panel  15 . 
     Meanwhile, the image formation apparatus A is configured so that image data read by the scan unit  22  or image data transferred from an external network is stored in the data storing section  16 , the data storing section  16  transfers the image data to buffer memory  17 , and that the buffer memory  17  transfers a data signal to the printing head  9  sequentially. 
     Concurrently with the image formation conditions, a post-processing condition is also input and designated from the control panel  15 . As the post-processing condition, for example, selected is a “printout mode”, “staple binding mode”, “sheet-bunch folding mode” or the like. The post-processing condition is set for the folding form in the sheet folding apparatus B as described previously. 
     [Post-Processing Apparatus] 
     As shown in  FIG. 2 , the post-processing apparatus C is provided with the following configuration. This apparatus has a housing  68  provided with the sheet receiving opening  69 , sheet discharge stacker  70 , and post-processing path  71 . The sheet receiving opening  69  is coupled to the carrying-out exit  31  of the sheet folding apparatus B as described previously, and is configured to receive a sheet from the first transport path  32  or the sheet discharge path  36 . 
     The post-processing path  71  is configured to guide the sheet from the sheet receiving opening  69  to the sheet discharge stacker  70 , and a processing tray  72  is provided in the path. “ 73 ” shown in the figure denotes a sheet discharge outlet, and is to collect sheets from the post-processing path  71  in the processing tray  72  disposed on the downstream side. “ 74 ” shown in the figure denotes a punch unit, and is disposed in the post-processing path  71 . A sheet discharge roller  75  is disposed in the sheet discharge outlet  73  to collect a sheet from the sheet receiving opening  69  in the processing tray  72 . 
     On the processing tray  72 , sheets from the post-processing path  71  are switch-back transported (in the direction opposite to the transport direction), and collated and collected using a rear end regulating member (not shown) provided on the tray. Therefore, above the tray is provided a forward/backward rotation roller  75  for switching back the sheet from the sheet discharge outlet  73 . Further, the processing tray  72  continues to the sheet discharge stacker  70 , and the sheet from the sheet discharge outlet  73  is supported (bridge-supported) on the front end side by the sheet discharge stacker  70  and on the rear end side by the processing tray  72 . 
     On the processing tray  72  is disposed a stapler unit  77  for binding a sheet bunch positioned by the rear end regulating member. “ 78 ” shown in the figure denotes aligning means, and aligns the width of the sheet carried onto the processing tray in the direction orthogonal to the transport direction. “ 79 ” shown in the figure denotes a paddle rotating body, and is coupled to a rotary shaft of the sheet discharge roller  75  to be driven to carry the sheet from the sheet discharge roller  75  toward the rear end regulating member. 
     “ 80 ” shown in the figure denotes sheet bunch carrying-out means, and carries a sheet bunch bound by the stapler unit  77  to the sheet discharge stacker  70  on the downstream side. Therefore, the sheet bunch carrying-out means  80  shown in the figure is comprised of a lever member  81  axially supported at the base end portion to be swingable, and a sheet end engagement member  82 . 
     Then, the sheet end engagement member  82  is equipped in the processing tray to reciprocate in the sheet discharge direction along the processing tray  72 , and is coupled to the lever member  81 . “Mm” shown in the figure denotes a driving motor for causing the lever member  81  to perform swinging motion. In addition, the sheet discharge stacker  70  is provided with an elevator mechanism, not shown, which moves up and down corresponding to a load amount of sheets. 
     In addition, this application claims priority from Japanese Patent Application No. 2010-123210 and Japanese Patent Application No. 2010-225836 incorporated herein by reference.