Patent Publication Number: US-2012046154-A1

Title: Sheet folding device, sheet processing device, image forming apparatus, and sheet folding method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2010-182350 filed in Japan on Aug. 17, 2010. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet folding device performing a folding process on a sheet member (hereinafter, simply referred to as a “sheet”) such as paper, transfer paper, and film, a sheet processing device including the sheet folding device, an image forming apparatus such as a copying machine, a printer, a facsimile, and a digital multi-functional peripheral (MFP) including the sheet processing device, and a sheet folding method performed in the sheet folding device. 
     2. Description of the Related Art 
     In a so-called post-processing peripheral device performing a predetermined process on a sheet discharged from an image forming apparatus such as a copying machine, a plurality of sheets are saddle-stitched by a staple and then pressed by pressing rollers or pressing plates to be folded into two (hereinafter, referred to as a “saddle-stitching and folding”). This technique is already known as disclosed in, for example, Japanese Patent Application Laid-open No. 2009-1417 and Japanese Patent Application Laid-open No. 2010-6602. 
     Among them, Japanese Patent Application Laid-open No. 2009-1417 discloses a technique in which a gap between folding rollers and a gap between guide plates are made to be variable to prevent occurrence of wrinkles or a deviation in a folded position caused when a nip portion of the folding rollers is deviated from a center of a folded position of a sheet bundle. More specifically, Japanese Patent Application Laid-open No. 2009-1417 discloses a sheet post-processing device including: a first roller; a second roller that is biased to be movable close to and away from the first roller and forms a nip portion together with the first roller; a stacking unit that stacks a sheet bundle; a folding plate of which the front end butts the sheet bundle stacked on the stacking unit to move the sheet bundle toward the nip portion so that the sheet bundle is pushed into the nip portion; a first guide member that is fixed relative to the first roller, is located between the nip portion and a position, at which the folding plate butts the sheet bundle, and nearer to the first roller than a common tangent line of the first and second rollers at the nip portion, and guides the sheet bundle butted and pressed by the folding plate toward the nip portion; and a second guide member that is disposed between the nip portion and the position at which the folding plate butts the sheet bundle and nearer the second roller than the common tangent line, follows the movement of the second roller, and guides the sheet bundle butted and pressed by the folding plate toward the nip portion together with the first guide member. 
     Further, Japanese Patent Application Laid-open No. 2010-6602 discloses a saddle-stitching and folding device in which a pressing unit stops a sheet bundle folded into two at a predetermined position and presses a fold line of the stopped sheet bundle from the front and rear surfaces between pressing surfaces facing each other for the purpose of providing a saddle-stitching and folding device capable of making a booklet that is saddle-stitched and folded and is strongly creased in a short time. More specifically, Japanese Patent Application Laid-open No. 2010-6602 discloses a saddle-stitching and folding device including: an aligning and saddle-stitching unit that aligns a conveyed sheet bundle and saddle-stitches the center thereof in the conveying direction; a folding unit that is provided downstream of the aligning and saddle-stitching unit and folds the sheet bundle into two; a pressing unit that stops the sheet bundle folded into two at a predetermined position and applies a pressure to a fold line of the stopped sheet bundle from the front and rear surfaces between pressing surfaces facing each other; and a pressing times control unit that determines pressing times that is number of applying a pressure to the fold line of the sheet bundle in the pressing unit and controls the pressing unit such that the pressing process is performed as many as the determined number of times. 
     However, as disclosed in Japanese Patent Application Laid-open No. 2009-1417, even when the sheet bundle butted and pressed by the folding plate is guided to the nip portion by the second guide member, which follows the movement of the second roller, together with the first guide member, occurrence of deflection cannot be suppressed. For this reason, when the deflection occurs immediately before the sheet bundle is introduced into the nip portion of the folding roller (the first and second rollers), a position of the folding plate is deviated from a position at which the sheet bundle is saddle-stitched, so that the sheet bundle may not be folded at a correct position. Further, wrinkles may be generated due to this reason. Furthermore, since the pressure applied to the sheet bundle decreases compared to a case other than a case where the folding roller is movable to widen a gap of the nip portion of the folding rollers, an adequate pressure may not be applied to the sheet bundle. As a result, the sheet bundle may not be correctly creased. When the sheet bundle is not correctly creased, a height of the folded saddle-stitched booklet increases, so that the appearance of the booklet is spoiled and stack performance of the booklet on a stacking tray is decreased. 
     On the other hand, in the invention disclosed in Japanese Patent Application Laid-open No. 2010-6602, since the sheet bundle folded into two in the folding unit is folded again in the pressing unit, if a fold line first formed in the folding unit is deviated from a fold line formed in the pressing unit, folding into a box-like configuration or a folding error may occur. conveying roller 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially solve the problems in the conventional technology. 
     According to an aspect of the present invention, there is provided a sheet folding device including: a guide unit that bends a sheet or a sheet bundle in a direction perpendicular to a conveying direction and guides a bent portion into between two members facing each other; a press-folding unit that presses to fold the bent portion; and a change controlling unit that performs control of changing a gap between the two members depending on a thickness of the sheet or the sheet bundle when the sheet or the sheet bundle is guided into between the two members. 
     According to another aspect of the present invention, there is provided a sheet folding method including: bending a sheet or a sheet bundle in a direction perpendicular to a conveying direction and guiding the bent portion into between two members facing each other; presses to fold the bent portion; and performing control of changing a gap between the two members depending on a thickness of the sheet or the sheet bundle in order to suppress deflection of the bent portion when the sheet or the sheet bundle is guided into between the two members. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a system configuration of an image forming apparatus according to an embodiment of the invention; 
         FIG. 2  is a perspective view illustrating a press-folding unit in  FIG. 1 ; 
         FIG. 3  is a front view when the press-folding unit of  FIG. 2  is seen from the front side of the apparatus; 
         FIG. 4  is a diagram illustrating a state of the press-folding unit in which a pressing plate driving cam, a folding blade driving cam, and a side plate are excluded from the state of  FIG. 2 ; 
         FIG. 5  is a front view when  FIG. 4  is seen from the front side of the apparatus; 
         FIG. 6  is a perspective view illustrating the press-folding unit in which the moving plate is excluded from the state of  FIG. 4 ; 
         FIG. 7  is a front view when a dotted line portion H of  FIG. 6  is enlarged and seen from the front side of the apparatus; 
         FIG. 8  is a diagram illustrating the inside of a pressing unit in  FIG. 4 ; 
         FIG. 9  is a front view when the pressing unit of  FIG. 8  is seen from the front side of the apparatus; 
         FIG. 10  is a diagram illustrating a series of press-folding process and occurrence of deflection of the sheet bundle, and illustrates a state immediately before the center-folding process is performed after the sheet bundle is located at a center-folding position in a fourth conveying path; 
         FIG. 11  is a diagram illustrating a series of press-folding process and occurrence of deflection of the sheet bundle, and illustrates a state where the sheet bundle is pushed in by a folding blade into a nip portion of a pair of conveying rollers in the direction perpendicular to the sheet bundle; 
         FIG. 12  is a diagram illustrating a series of press-folding process and occurrence of deflection of the sheet bundle, and illustrates a state where the sheet bundle is conveyed by the conveying roller so that the front end of the sheet bundle is located before a folding position of pressing plates; 
         FIG. 13  is a diagram illustrating a series of press-folding process and occurrence of deflection of the sheet bundle, and illustrates a state where the sheet bundle is pressed by the pressing plates so that the front end of the sheet bundle passes the folding position of the pressing plates; 
         FIG. 14  is a diagram illustrating a press-folding example according to a first embodiment, and illustrates a state where the sheet bundle is bent and extruded in the direction perpendicular to the conveying direction of the sheet bundle from an opening of a fourth conveying path; 
         FIG. 15  is a diagram illustrating a press-folding example according to the first embodiment, and illustrates a state where the front end of the sheet bundle is located before the folding position of the pressing plates from the state of  FIG. 14 ; 
         FIG. 16  is a diagram illustrating a press-folding example according to the first embodiment, and illustrates a state where the sheet bundle is pressed by the pressing plates for a folding process thereon; 
         FIG. 17  is a diagram illustrating a press-folding example according to the first embodiment, and illustrates a state where the folding process of  FIG. 16  is ended, the pressing plates move away from each other, and the sheet bundle is further conveyed downstream; 
         FIG. 18  is a diagram illustrating a press-folding example according to the first embodiment, and illustrates a state where an extracting bar is inserted into the sheet bundle and is conveyed by applying a conveying force from a backside of the front end; 
         FIG. 19  is a diagram illustrating a press-folding example according to a second embodiment, and illustrates a state where the sheet bundle is conveyed to a folding position by a pair of conveying rollers and a folding blade; 
         FIG. 20  is a diagram illustrating a press-folding example according to the second embodiment, and illustrates a state where the sheet bundle conveyed by the pair of conveying rollers and the folding blade is press-folded; 
         FIG. 21  is a diagram illustrating a press-folding example according to a third embodiment, and illustrates a state where the sheet bundle is conveyed to the folding position by the pair of conveying rollers and the folding blade; 
         FIG. 22  is a diagram illustrating a press-folding example according to a third embodiment, and illustrates a state where the sheet bundled conveyed by the pair of conveying rollers and the folding blade is press-folded; 
         FIG. 23  is a block diagram illustrating a control configuration of a sheet post-processing device that controls change of the gap between the pressing plates in the third embodiment; 
         FIG. 24  is a diagram illustrating a press-folding example according to a fourth embodiment, and illustrates a state immediately before a center-folding process is performed after the sheet bundle is located at a center-folding position in a fourth conveying path; 
         FIG. 25  is a diagram illustrating a press-folding example according to the fourth embodiment, and illustrates a state where the sheet bundle is pushed in by the folding blade between the pair of conveying rollers, which move away from each other, in the direction perpendicular to the sheet bundle; 
         FIG. 26  is a diagram illustrating a press-folding example according to the fourth embodiment, and illustrates a state where the front end of the sheet bundle is conveyed downstream of a nip position of the pair of conveying rollers and the pair of conveying rollers conveys the sheet bundle therebetween; 
         FIG. 27  is a diagram illustrating a press-folding example according to the fourth embodiment, and illustrates a state where the front end of the sheet bundle reaches the folding position of the pressing plates and is press-folded by the pressing plates; 
         FIG. 28  is a diagram illustrating a press-folding example according to the fourth embodiment, and illustrates a state where the press-folding process is ended and the pressing plates move away from each other; 
         FIG. 29  is a diagram illustrating a press-folding example according to a fifth embodiment, and illustrates a state where the sheet bundle is bent and extruded in the direction perpendicular to the conveying direction of the sheet bundle from the opening in the fourth conveying path so that it is located between the conveying rollers moving away from each other; 
         FIG. 30  is a diagram illustrating a press-folding example according to the fifth embodiment, and illustrates a state where the front end of the sheet bundle reaches downstream of the nip position of the pair of conveying rollers from the state of  FIG. 29  and the pair of conveying rollers conveys the sheet bundle therebetween; 
         FIG. 31  is a diagram illustrating a press-folding example according to the fifth embodiment, and illustrates a state where the front end of the sheet bundle reaches the folding position of the pressing plates from the state of  FIG. 30  and is press-folded; 
         FIG. 32  is a diagram illustrating a press-folding example according to the fifth embodiment, and illustrates a state where the press-folding process is ended and the pressing plates move away from each other; and 
         FIG. 33  is a block diagram illustrating a control configuration of a sheet post-processing device that controls change of a gap between a pair of conveying rollers in the fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the embodiments to described below, a sheet corresponds to a reference numeral P, a sheet bundle corresponds to a reference numeral PB, a deflection portion corresponds to deflection PB, a press-folding unit corresponds to a center-folding unit  102  including an upper pressing unit  217 , a lower pressing unit  218 , a pressing plate driving cam  201 , pressing guide rollers  211  and  212 , and pressure releasing cams  209  and  210 , a change controlling unit corresponds to a CPU  301 , a pressing plate gap change controlling unit  303 , and a conveying roller gap change controlling unit  305 , a pair of pressing plates corresponds to pressing plates  219  and  220 , a pair of conveying rollers corresponds to conveying rollers  206  and  207 , a folding blade corresponds to a reference numeral  203 , a folding position corresponds to a position where the pressing plates  219  and  220  come into contact with the sheet or the sheet bundle to apply a pressure thereto (corresponding to a moving range of pressing guide rollers  211  and  212 ), stoppers correspond to reference numerals  250  and  251 , a thickness detecting unit corresponds to a sheet thickness detecting sensor  304 , a counting unit corresponds to an entrance sensor  13  and a counter, an external apparatus corresponds to an image forming apparatus PR, a communication unit corresponds to a communication unit  301   a,  a sheet folding device corresponds to a reference numeral  100 , and an image forming apparatus corresponds to a reference numeral PR. 
     Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. In explanation below, the same reference numerals will be given to the same components or the equivalent components, and redundant explanation of such components will be suitably omitted. 
       FIG. 1  is a diagram illustrating a system configuration of an image forming apparatus according to the embodiment. The image forming apparatus according to the embodiment includes an image forming apparatus PR and a sheet post-processing device  100  that serves as a sheet processing device installed after the image forming apparatus PR. The image forming apparatus PR includes an image forming unit (not shown) that forms an image by, for example, an electrophotography process and a feed unit that supplies a sheet to the image forming unit, and the image forming apparatus has a function of printing or forming an image on the sheet based on information transmitted from a personal computer PC, information read by a scanner, and information stored on a hard disk inside the image forming apparatus PR. As the image forming unit, a known image forming unit other than the electrophotography process type including a liquid ejecting type such as an inkjet type or a thermal type may be used. 
     The sheet post-processing device  100  includes a first conveying path (an entrance conveying path)  1  to receive a sheet P having an image formed thereon and discharged from the image forming apparatus PR, a second conveying path  2  to stack the sheet P on a discharge tray  22 , a third conveying path  3  to intermediately stack the sheet P, and a fourth conveying path  4  to convey a sheet bundle, which is saddle-stitched at the center of the sheet in the longitudinal direction in the third conveying path  3 , to a sheet folding unit. 
     The first conveying path  1  is provided with an entrance roller  10  and an entrance sensor  13 , and the entrance sensor  13  detects whether the sheet P is conveyed into the sheet post-processing device  100 . A sheet punching unit  101  is installed downstream of the entrance roller  10 , first and second conveying rollers  11  and  12  are disposed in this order downstream of the sheet punching unit  101  along a conveying direction, and the sheet P is conveyed to the third conveying path  3  by the first and the second conveying rollers  11  and  12 . 
     The second conveying path  2  is a path to convey the sheet P to the discharge tray  22  and is branched upward from the first conveying path  1 , and a branching claw  20  is provided at a branching position. The sheet P, of which an advancing direction is changed from the first conveying path  1  by the branching claw  20 , is conveyed from the first conveying roller  11  to the discharge tray  22  through a discharging roller  21 . The discharge tray  22  is also referred to as a proof tray. 
     The third conveying path  3  is provided with a discharge driven roller  31 , a discharge driving roller  33  and a discharging sensor  35 . In a sorting mode, a second conveying roller  12  with a shifting mechanism is moved by a driving unit (not shown) by a predetermined amount in a direction perpendicular to a conveying direction during a conveying operation so that the sheet P is shifted by a predetermined amount, and the sheet P is discharged by a discharge driving roller  33  to a discharge tray  32  to be sequentially stacked thereon. At a discharge port to the discharge tray  32 , the sheet P or a sheet bundle is nipped by the discharge driving roller  33  and the discharge driven roller  31 , and is applied with a conveying force to be discharged. In this discharging operation, a closed state, in which the sheet P or the sheet bundle is nipped so that the sheet P or the sheet bundle can be discharged, or an opened state, in which the sheet P or the sheet bundle is not nipped can be selectively established by moving a discharge guide  31   a  with the discharge driven roller  31  close to or away from the discharge driving roller  33 . After the operation of shifting the sheet P is completed, the discharge guide  31   a  is operated to nip the sheet between the discharge driven roller  31  and the discharge driving roller  33 , so that the sheet P is discharged to the discharge tray  32 . 
     A feeler  34  is provided near and above the discharge port, and a base end of the feeler  34  is rotatably attached to the sheet post-processing device  100  so that a front end of the feeler  34  comes into contact with an approximate center of the sheet P when the sheet P is stacked on the discharge tray  32 . A top surface detecting sensor (not shown) is provided near the base end of the feeler  34  to detect a height position of the front end of the feeler  34 , whereby a height of the stacked sheet P is detected. 
     When the top surface detecting sensor is turned on as the height of sheets increases as a result of increase of number of sheets staked on the discharge tray  32 , a control unit (not shown) controls a driving unit (not shown) to move the discharge tray  32  up and down so that the discharge tray  32  moves down. When the tray moves down and the top surface detecting sensor is turned off, downward movement of the tray  32  is stopped. When the tray  32  reaches a predetermined tray full height by repeating this operation, a stop signal is output from the sheet post-processing device  100  to the image forming apparatus PR, so that image forming operation of the image forming apparatus PR is stopped. 
     The third conveying path  3  is provided with a stapling tray  36  and a tapping roller  30 , and is provided, at an end position of the third conveying path  3 , with a stapler  41  that is segmented into a driver and a clincher and that moves in a reciprocating manner in a direction perpendicular to the surface of  FIG. 1 . Furthermore, the third conveying path  3  is provided, at a position before the end position, with jogger fences  37  and  38  that move in a reciprocating manner in a direction perpendicular to a surface of  FIG. 1  to align the sheets P on the stapling tray  36 . The sheet conveyed to the conveying path  3  is discharged onto the stapling tray  36  and is aligned in a width direction by the jogger fences  37  and  38 . 
     Further, the tapping roller  30  moves in a pendulum motion to come into contact with a top surface of the sheet to switch back the sheet toward the stapler  41  to cause a rear end of the sheet to abut on reference fences  39  and  40  to align a position of the sheet bundle in a longitudinal direction thereof (a position in the conveying direction). In an end-stitching mode, the stapler  41  moves in a direction perpendicular to a surface of  FIG. 1  and staples the sheet bundle PB at appropriate positions of a lower edge the sheet bundle PB so that the sheet bundle PB aligned in this manner is stitched, and the sheet bundle PB is nipped and applied with a conveying force by the discharge driven roller  31  and the discharge driving roller  33 , and is discharged onto the discharge tray  32 . 
     In a saddle-stitching mode, after alignment and stapling of the sheet P or the sheet bundle PB (see  FIG. 10 ) is finished, the rear end of the sheet P or the sheet bundle PB is nipped by clamp moving fences  120  and  121 , and the reference fences  39  and  40  escape outward in a sheet width direction so as not to disturb operation of conveying the sheet bundle PB. The clamp moving fences  120  and  121  are attached to a clamp longitudinal shaft  106  disposed out of an apparatus side plate so that the clamp moving fences  120  and  121  moves in a longitudinal direction (a vertical direction) while moving in a lateral direction (a horizontal direction) along the curved fourth conveying path  4 . 
     The clamp moving fences  120  and  121  is moved in the longitudinal direction by the clamp longitudinal shaft  106 , and is moved in the lateral direction by being caused to follow a guide rail  110  located at the apparatus side plate and having the same track as a curved track of the fourth conveying path  4 , whereby the sheet P or the sheet bundle PB is conveyed along the fourth conveying path  4 . The sheet or the sheet bundle PB of which a rear end is nipped is conveyed along the track of the guide rail  110  to a predetermined position depending on size of the sheet so that an appropriate position of a center portion of the sheet bundle in the length direction thereof is stapled and thereby the sheet bundle is saddle-stitched. The predetermined position depending on the size of the sheet is a position at a time when a predetermined number of pulses are sent after the clamp moving fences  120 ,  121  start from a position of a clamp moving fence home position sensor  49 . 
     The sheet P or the saddle-stitched sheet bundle PB is further conveyed downward by the clamp moving fences  120  and  121 , and is stopped at a position where the center portion of the sheet bundle in the length direction reaches a position of a folding blade  203 . Then, a folding process is performed. The stop position is a position at a time when a predetermined number of pulses depending on the size of the sheet are sent after the rear end of the sheet is detected by a folding position sensor  50 . Subsequently, the center portion of the sheet bundle in the length direction thereof stopped at the position for folding is introduced into a press-folding unit  200  by the folding blade  203  and the conveying rollers  206  and  207 . 
     The press-folding unit  200  folds the center portion of the introduced sheet bundle in the length direction thereof by pressing the center portion from above and below by pressing plates  219  and  220 . The sheet P or sheet bundle PB that has been center-folded is discharged onto a saddle-stitching tray  62  by conveying rollers  206  and  207  and a discharging roller  58 . 
     The sheet P or the sheet bundle PB discharged onto the saddle-stitching tray  62  is pressed by a sheet pressing roller  61  attached to a sheet pressing member  60  so as not to disturb operation of discharging a sheet discharged next by swelling of the folded sheet. 
     The sheet punching unit  101  and a center-folding unit  102  with the fourth conveying path  4  are configured to be attachable and detachable, making it possible to provide a sheet post-processing device configured in accordance with a demand of a user. Incidentally, in the present embodiment, the center-folding unit  102  serves as a sheet folding device. 
       FIG. 2  is a perspective view illustrating the press-folding unit, and  FIG. 3  is a front view when the press-folding unit is seen from the front side of the apparatus. The press-folding unit  200  is provided in the center-folding unit  102 , and includes a pressing plate driving cam  201 , a folding blade driving cam  202 , a folding blade  203 , a folding blade support bar  204 , and front and rear side plates  205 . When the folding blade driving cam  202  rotates, the folding blade support bar  204  horizontally moves along a horizontal groove  205   a  due to a relation between rotation of the cam idly fitted into a groove  202   a  and the horizontal groove  205   a  of the side plate  205 , and the folding blade  203  moves in a direction depicted by an arrow Q. Accordingly, the sheet P or the center portion of the sheet P in the length direction thereof is guided to the folding unit. 
       FIG. 4  is a diagram illustrating a state where the pressing plate driving cam  201 , the folding blade driving cam  202 , and the side plate  205  are excluded from the state of  FIG. 2 , and  FIG. 5  is a front view when  FIG. 4  is seen from the front side of the apparatus. 
     The press-folding unit  200  includes conveying rollers  206  and  207 , a moving plate  208 , pressing guide rollers  211  and  212 , and pressure releasing cams  209  and  210 . The folded front end of the sheet bundle PB or the sheet P introduced into the folding unit by the folding blade  203  is conveyed to the pressing unit by the conveying rollers  206  and  207 . By movement of the moving plate  208 , the pressing guide rollers  211  and  212  and the pressure releasing cams  209  and  210  connected to the moving plate  208  can be moved in a reciprocating manner in the sheet conveying direction. 
       FIG. 6  is a perspective view illustrating a state where the moving plate  208  is excluded from the state of  FIG. 4 , and  FIG. 7  is a front view when the dotted line portion C of  FIG. 6  is enlarged and seen from the front side of the apparatus. 
     In  FIGS. 6 and 7 , in an upper pressing unit  217  and a lower pressing unit  218  respectively located at upper and lower positions with a sheet conveying path interposed therebetween, a pressure is applied to four corners of each unit by springs. In a standby state, the upper pressing unit  217  and the lower pressing unit  218  are moved away from each other by the pressure releasing cams  209  and  210  provided inside the press moving plate  208 , and are ready for receiving the folded front end of the sheet bundle PB in this state. 
     When the moving plate  208  moves in the direction depicted by the arrow Q ( FIG. 7 ), the pressure releasing cams  209  and  210  connected to the moving plate  208  move, and pressure releasing rollers  213  and  215  of the upper pressing unit  217  and pressure releasing rollers  214  and  216  of the lower pressing unit  218  move in directions depicted by arrows A and B due to slopes of the pressure releasing cams  209  and  210 , so that the folded portion of the sheet bundle PB is pressed. 
       FIG. 8  is a diagram illustrating the inside of the pressing unit of  FIG. 4 , and  FIG. 9  is a front view when  FIG. 8  is seen from the front side of the apparatus. 
     In  FIGS. 8 and 9 , an upper pressing plate  219  and a lower pressing plate  220  are respectively provided in the upper pressing unit  217  and the lower pressing unit  218  inside the pressing unit, and the upper pressing plate  219  moves in the direction depicted by the arrow A and the lower pressing plate  220  moves in the direction depicted by the arrow B together with the upper and lower pressing units  217  and  218  in accordance with movement of the pressure releasing cams  209  and  210 . Due to this movement, the sheet P or the sheet bundle PB is nipped between the upper and lower pressing plates  219  and  220  to subject the sheet P or the sheet bundle PB to folding. 
     The pressing guide rollers  211  and  212  connected to the moving plate  208  move on the pressing plates  219  and  220  together with movement of the moving plate  208  in the direction depicted by the arrow Q. By this movement, folding is proceeded toward the folded front end of the sheet bundle PB with a curved shape of the upper and lower pressing plates  219  and  220  rotatable or movable along grooves  221 ,  222 ,  223 , and  224  (refer to  FIG. 7 ) in side surfaces of the upper and lower pressing units  217  and  218 . 
     Incidentally, in the case of such a press-folding process, deflection may occur in the sheet bundle PB at a time of folding the sheet bundle.  FIGS. 10 to 13  are diagrams illustrating a series of press-folding process and deflection occurring in the sheet bundle. The sheet bundle PB conveyed to an entrance of the nip portion between the pair of conveying rollers  206  and  207  of the center-folding unit  102  through the fourth conveying path  4  by the clamp moving fences  120  and  121  stops at a position where a position to be folded of the sheet bundle PB faces the folding blade  203  ( FIG. 10 ), and the front end of the folding blade  203  comes into contact with the sheet bundle PB, so that the sheet bundle PB is pushed into a nip between the pair of conveying rollers  206  and  207  from a slit-like opening  4   a  of the fourth conveying path  4  ( FIG. 11 ). The sheet bundle PB is conveyed into between the pressing plates  219  and  220  by the pair of conveying rollers  206  and  207  ( FIGS. 12 and 13 ). At this time, since a front end PB 1  of the sheet bundle PB is not creased, deflection PB 2  occurs at the front end PB 1  of the sheet bundle PB. When the height H of the deflection PB 2  is large and deflection is not symmetrical in a vertical direction or the front end PB 1  is deviated from a conveying center line Z during the folding process, which connects the nip of the conveying rollers  206  and  207  and a center of a gap between the pressing plates  219  and  220 , the folded position at a time when folding the sheet bundle by the pressure applied from the pressing plates  219  and  220  may be deviated, which causes a deviation of the folded position or occurrence of a wrinkle. Furthermore, the opening  4   a  is formed at a position where the conveying center line Z is aligned with a center position of the opening  4   a.    
     Hereinafter, examples of a process in which the deviation of the folding position or the wrinkle is prevented will be described as embodiments in detail. 
     FIRST EMBODIMENT 
       FIGS. 14 to 17  are diagrams illustrating an example of a process according to a first embodiment in which a sheet is nipped between stoppers to perform press-folding. The example of the process according to the first embodiment is an example in which the conveying roller and the folding blade are not used as a conveying instrument to convey the sheet bundle PB into between the pressing plates  219  and  220 ; but the sheet bundle PB is pressed from above and bellow by an upstream stopper  250  and a downstream stopper  251  in the conveying direction, which interpose the sheet bundle PB, so that the sheet bundle PB is bent and guided into between the pressing plates  219  and  220 . That is, the rear end (corresponding to the rear end of the sheet when the sheet is conveyed into a creasing device) of the conveyed sheet bundle PB is brought into contact with the downstream stopper  251  in the conveying direction, and the position to be folded of the sheet bundle PB is positioned at the center of the gap between the pressing plates  219  and  220 . Subsequently, the upstream stopper  250  in the conveying direction is brought into contact with the front end of the sheet bundle PB, and both stoppers  250  and  251  are moved close to each other. 
     Then, the sheet bundle PB starts to be bent ( FIG. 14 ), and is gradually pushed in between the pressing plates  219  and  220  from the opening  4   a  of the fourth conveying path  4  ( FIG. 15 ). Therefore, when the gap between the pressing plates  219  and  220  is set to an appropriate gap depending on a thickness of the sheet bundle PB ( FIG. 16 ), swelling of the deflection PB is suppressed. As a result, even when the pressure applied from the pressing plates  219  and  220  is released or the gap therebetween is widened, the center of the sheet bundle PB can be folded without swelling ( FIG. 17 ). The press-folded sheet bundle PB is pushed from the backside of the sheet bundle PB by a push out bar  252  ( FIG. 17 ). Alternatively, as shown in  FIG. 18 , an extracting bar  253  is inserted between folds of the sheet bundle PB to convey the sheet bundle by applying a conveying force from the backside of the front end PB 1 . 
     SECOND EMBODIMENT 
       FIGS. 19 and 20  are diagrams illustrating an example of a process of a second embodiment in which the pair of conveying rollers  206  and  207 , the folding blade  203 , and the pressing plates  219  and  220  are used to perform press-folding process. 
     In the example shown in  FIG. 12 , the gap between the pressing plates  219  and  220  is set such that it is larger than the height of the deflection PB 2  when the sheet bundle PB enters between the pressing plates  219  and  220 , but is narrowed after the sheet bundle PB enters between the pressing plates  219  and  220  by applying pressure. On the other hand, in the present embodiment, as shown in  FIG. 19 , the gap between the pressing plates  219  and  220  is narrowed so as to limit (regulate) the height H of the deflection of the sheet bundle PB using the pressing plates  219  and  220  when the sheet bundle PB is conveyed into between the pressing plates  219  and  220  by the pair of conveying rollers  206  and  207 . Accordingly, the deflection of the sheet bundle PB becomes smaller. When the deflection becomes smaller, as shown in  FIG. 20 , vertical asymmetry of the deflection or the deviation of the front end of the sheet bundle from the center line Z becomes smaller, so that the deviation of the folded position or the wrinkle can be reduced. 
     THIRD EMBODIMENT 
       FIGS. 21 and 22  are diagrams illustrating an example of a process of a third embodiment in which the folding blade is inserted to the position of the pressing plates to perform a press-folding process. 
     In the example shown in  FIG. 12 , the folding blade  203  pushes the sheet bundle PB into a position before the nip of the pair of conveying rollers  206  and  207 , and after the sheet bundle PB is nipped between the pair of conveying rollers  206  and  207 , the sheet bundle PB is conveyed into between the pressing plates  219  and  220  by the conveying force of the pair of conveying rollers  206  and  207 . On the other hand, in the present embodiment, the front end PB 1  of the sheet bundle PB is inserted to a press position of the pressing plates  219  and  220  by the folding blade  203 . That is, a front end  203   a  of the folding blade  203  comes into contact with the back surface of the sheet bundle PB to push the front end PB 1  of the sheet bundle PB into the press position of the pressing plates  219  and  220 . 
     When being pushed into the above-described position in this manner, since the folding blade  203  is located on the center line Z, the front end of the sheet bundle PB can be prevented from being deviated from the center line Z, and precision of the folded position can be further improved. In a case of such an operation, the folding blade  203  passes between the pair of conveying rollers  206  and  207  together with the sheet bundle PB, and occurrence of deflection in the sheet bundle PB is caused when the rotating speed of the pair of conveying rollers  206  and  207  is faster than the inserting speed of the folding blade  203 . Therefore, in the present embodiment, in order to prevent such deflection, inserting speed of the folding blade  203  is set to be equal to rotating speed of the pair of conveying rollers  206  and  207 . Then, when the pressing plates  219  and  220  perform folding action, the folding blade  203  is extracted from the sheet bundle PB. This is because the creasing degree is weak due to thickness of the folding blade  203  when the sheet bundle PB is folded with the folding blade  203  inserted therein. 
     The gap between the pair of conveying rollers  206  and  207  is made to be changed depending on the thickness of the sheet bundle. That is, when the sheet bundle PB is pushed by the folding blade  203  into a position of the pressing plates  219  and  220 , the gap between the pair of conveying rollers  206  and  207  needs to be provided as much as an amount corresponding to the sum of the thickness of the folding blade  203  and the thickness of the sheet bundle. Although the sheet bundle PB is pushed downstream by the pair of conveying rollers  206  and  207  after the press-folding process is performed by the pressing plates  219  and  200 , the inner surface of the sheet bundle PB is rubbed by the outer surface of the folding blade  203  when the folding blade  203  is present between the pair of conveying rollers  206  and  207 , so that the inner surface of the sheet bundle PB gets dirty. For this reason, the folding blade  203  is returned upstream of the nip of the pair of conveying rollers  206  and  207  as shown in  FIG. 12  and the like. 
     However, when the gap between the pair of conveying rollers  206  and  207  is wide, conveying (nipping) pressure is not sufficient in a case of a thin sheet bundle PB, so that the thin sheet bundle may not be discharged. On the other hand, when the gap between the pair of conveying rollers  206  and  207  is narrow, the nip of the pair of conveying rollers  206  and  207  generates resistance when pushing a thick sheet bundle by the folding blade  203 , so that the sheet bundle PB may be broken or get dirty due to trace of the conveying rollers  206  and  207 . 
     Therefore, in the present embodiment, compressing spring  206   a  and  207   a  are used to allow change of the gap between the pair of conveying rollers  206  and  207 , and the pair of conveying rollers  206  and  207  are elastically biased in directions in which the conveying rollers  206  and  207  move close to each other with predetermined elastic force at all times. Accordingly, the pair of conveying rollers  206  and  207  moves close to or away from the center line Z depending on the thickness of the sheet bundle PB, and a predetermined nipping pressure can be maintained. As a result, the sheet bundle can be prevented from getting dirty due to the folding blade  203 , and conveying performance of the sheet bundle PB can be maintained. 
     The thickness of the sheet bundle PB changes depending on the number of sheets and the thickness of the sheet. The gap between the pressing plates  219  and  220  needs to be widened in order to handle a thick sheet bundle, but deflection becomes larger in a case of a thin sheet bundle. Conversely, when the gap between the pressing plates  219  and  220  is narrowed in order to handle the thin sheet bundle PB, the thick sheet bundle PB may not enter between the pressing plates  219  and  220 . Therefore, in the present embodiment, the gap between the pressing plates  219  and  220  is made to be changed depending on the thickness of the sheet bundle PB. 
       FIG. 23  is a block diagram illustrating a control configuration of the sheet post-processing device  100  that controls change of the gap between the pressing plates  219  and  220 . In the same drawing, a control unit of the sheet post-processing device  100  includes a CPU  301 , a memory  302 , a pressing plate gap change controlling unit  303 , and a sheet thickness detecting sensor  304 . The CPU  301  includes a ROM and a RAM which are not shown in the drawings, a program stored on the ROM is developed on the RAM, and the control defined by the program is executed while the RAM is used as a work area and a data buffer. Furthermore, the memory  302  may be used as the RAM. 
     In the embodiment, the gap between the pressing plates  219  and  220  is changed and controlled in any one of the following manners 1) to 3):
     1) A sheet thickness detecting sensor  304  is provided at an arbitrary position in the third conveying path  3  or the fourth conveying path  4  to detect the thickness of the sheet bundle PB. The CPU  301  reads out the gap between the pressing plates  219  and  220  corresponding to the thickness of the sheet bundle PB from the memory  302 , which stores therein a relation between the thickness of the sheet bundle PB and the gap between the pressing plates as a table, in accordance with the detected thickness. The CPU  301  then instructs the pressing plate gap change controlling unit  303  so that the pressing plate gap change controlling unit  303  changes the gap between the pressing plates by controlling drive of a motor (not shown) driving the pressing plate driving cam  201  and the pressure releasing cams  209  and  210 .   2) When the sheet P is conveyed to the sheet post-processing device  100 , the number of the conveyed sheets P detected by the entrance sensor  13  is counted by the counter, the thickness of the sheet bundle PB is figured out on the basis of the thickness of one sheet recognized by the image forming apparatus PR and the number of sheets of one sheet bundle PB to be saddle-stitched, and the gap between the pressing plates is changed in the same manner as in 1).   3) Information on the number of sheets of the sheet bundle PB or a type of the sheet thereof is acquired from the image forming apparatus PR connected to the sheet post-processing device  100 , and the gap between the pressing plates  219  and  220  is changed in accordance with the information in the same manner as in 1).   

     Furthermore, the control unit shown in  FIG. 23  may be applied to the first embodiment and the second embodiment. 
     FOURTH EMBODIMENT 
       FIGS. 24 to 28  are diagrams illustrating an example of a process of a fourth embodiment in which the sheet bundle PB is pushed out by the folding blade  203  in a state where the conveying rollers  206  and  207  are moved away from each other, and the sheet bundle PB is nipped between the conveying rollers  206  and  207  and conveyed to the press position of the pressing plates  219  and  220  to perform press-folded. 
     The sheet bundle PB conveyed by the clamp moving fences  120  and  121  to the entrance of the nip of the pair of conveying rollers  206  and  207  of the center-folding unit  102  is stopped at a position where the position to be folded of the sheet bundle PB faces the folding blade  203  ( FIG. 24 ), and the front end of the folding blade  203  comes into contact with the sheet bundle PB to push the sheet bundle PB from the opening  4   a  into between the pair of conveying rollers  206  and  207  ( FIG. 25 ). At this time, the conveying rollers  206  and  207  move away to a position in which the conveying rollers  206  and  207  do not interfere with or contact the sheet bundle PB pushed by the folding blade  203 . 
     The sheet bundle PB is further pushed by the folding blade  203  to be conveyed into between the pressing plates  219  and  220 . When the front end of the sheet bundle PB exits the pair of conveying rollers  206  and  207 , the sheet bundle PB is nipped and conveyed by a pair of conveying rollers  206  and  207  ( FIG. 26 ). Whether the front end of the sheet bundle PB exits the pair of conveying rollers  206  and  207  is detected by a sheet detecting sensor (not shown) provided between a position of the pressing plates  219  and  220  and a position of the conveying rollers  206  and  207 . Incidentally, instead of the sheet detecting sensor, for example, a method may be employed in which a moving amount of the folding blade  203  is detected or a rotating amount of the motor driving the folding blade  203  is measured, and the moving amount of the folding blade  203  or the rotating amount is converted into a moving amount of the sheet bundle PB. 
     When the front end of the sheet bundle PB reaches between the pressing plates  219  and  220 , rotation of the conveying rollers  206  and  207  is stopped and movement of the sheet bundle PB is stopped. Then, the sheet bundle PB is nipped and folded while a nip position of the pressing plates  219  and  220  is gradually changed from a position closer to the conveying rollers  206  and  207  to the front end of the sheet bundle PB ( FIG. 27 ). After the folding process is performed, the pressing plates  219  and  220  are opened, and the conveying rollers  206  and  207  and the discharging roller  58  are rotationally driven to discharge the sheet bundle PB ( FIG. 28 ). 
     FIFTH EMBODIMENT 
       FIGS. 29 to 32  are diagrams illustrating an example of a process of a fifth embodiment in which the sheet bundle is interposed between the stoppers to locate the sheet bundle between the pair of separated conveying rollers and is then press-folded in the same manner as in the fourth embodiment. 
     In the example of the process of the fifth embodiment, the folding blade is not used as a conveying instrument to convey the sheet bundle PB into between the pressing plates  219  and  220  and the sheet bundle PB is interposed between the upstream stopper  250  and the downstream stopper  251  in the conveying direction and is pressed from above and below so as to be bent to be guided into between the conveying rollers  206  and  207  from the opening  4   a.  The present embodiment is different from the first embodiment in that the conveying rollers  206  and  207  are provided and the sheet bundle is conveyed from a position of the conveying rollers  206  and  207  into between the pressing plates  219  and  220  using the conveying rollers  206  and  207 . 
     That is, as in the first embodiment, when press of the sheet bundle PB by the stoppers  250  and  251  proceeds, the sheet bundle PB starts to be folded at the center thereof. At this time, the positions of the stoppers  250  and  251  are controlled so as to be vertically symmetrical to each other with respect to the center of the sheet bundle PB. When the positions of the stoppers are not symmetrical to each other vertically, deflection is deviated from the center position of the sheet bundle PB (which is equal to the center line Z shown in  FIG. 19  and the like), so that the folding process may not be performed at a correct position when the sheet bundle is pressed by the pressing plates  219  and  220 . Further, also when the deflection becomes larger, the center position of the sheet bundle PB is easily deviated. Accordingly, the gap between the pressing plates  219  and  220  is set to an appropriate value so that the deflection does not increase. 
     When press of the sheet bundle PB by the stoppers  250  and  251  further proceeds, the sheet bundle is extruded from the opening  4   a  in the fourth conveying path  4  toward the conveying rollers  206  and  207  ( FIG. 29 ). The sheet bundle PB is extruded into between the pressing plates  219  and  220  by the stoppers  250  and  251 , and the sheet bundle P is nipped between the conveying rollers  206  and  207  and conveyed after the front end PB 1  of the sheet bundle passes between the conveying rollers  206  and  207  ( FIG. 30 ). 
     When the front end PB 1  of the sheet bundle PB reaches between the pressing plates  219  and  220 , rotation of the conveying rollers  206  and  207  is stopped so that movement of the sheet bundle PB is stopped. Then, the pressing guide rollers  211  and  212  facing back surfaces of the pressing plates  219  and  220 , respectively, are moved from a position closer to the conveying rollers  206  and  207  to the front end of the sheet bundle PB to press the sheet bundle PB between the pressing plates  219  and  220  to perform press-folding ( FIG. 31 ). After folding is performed, the pressing plates  219  and  220  are opened and the conveying rollers  206  and  207  and the discharging roller  58  are rotated to discharge the sheet bundle PB ( FIG. 32 ). 
     In the fifth embodiment, since the sheet bundle is conveyed by the conveying rollers  206  and  207 , the sheet bundle PB may be more reliably and stably sent into between the pressing plates  219  and  220  compared to the first embodiment. 
     The thickness of the sheet bundle PB changes depending on the number of sheets and the thickness of the sheet. The gap between the conveying rollers  206  and  207  needs to be widened when conveying the sheet bundle in order to handle the thick sheet bundle PB, but the thin sheet bundle PB may not be conveyed when the gap between the conveying rollers  206  and  207  is widened. Conversely, when the gap between the conveying rollers  206  and  207  is narrowed in order to handle the thin sheet bundle PB, the thick sheet bundle PB may not enter between the conveying rollers  206  and  207  or load of the conveying rollers  206  and  207  becomes larger, so that a problem that folding become impossible to perform, the sheet bundle is damaged, or the power consumption of the sheet bundle driving motor increases may be occur. Therefore, in the embodiment, the gap between the conveying rollers  206  and  207  is made to be changed depending on the thickness of the sheet bundle PB. 
       FIG. 33  is a block diagram illustrating a control configuration of the sheet post-processing device  100  that controls change of the gap between the conveying rollers  206  and  207 . This control configuration is different from the control configuration of changing the gap between the pressing plates  219  and  220  shown in  FIG. 23  in that the pressing plate gap change controlling unit  303  is replaced by a conveying roller gap change controlling unit  305 , and the other configurations are the same as those of the respective units of  FIG. 23 . 
     Incidentally, the mechanism moving the conveying rollers  206  and  207  close to or away from each other is not particularly shown, but a configuration may be adopted in which conveying roller shafts  206   a  and  207   a  shown in  FIG. 5  or  8  are supported to be movable close to or away from each other, a distance between the conveying roller shafts  206   a  and  207   a  is set by driving a cam mechanism using a motor controlled to be driven by the conveying roller gap change controlling unit  305 , and power to drive the conveying rollers  206  and  207  is transmitted from a motor (not shown) by a power transmitting mechanism. Since these mechanisms are generally used as a mechanism system of a conveying mechanism, explanation of the mechanisms is omitted herein. 
     In a case that the control system is configured as illustrated in  FIG. 33 , any one of the following processes 1) to 3) may be employed.
     1) The sheet thickness detecting sensor  304  is provided at an arbitrary position in the third conveying path  3  or the fourth conveying path  4  to detect the thickness of the sheet bundle PB, the CPU  301  reads out the gap between the conveying rollers  206  and  207  corresponding to the thickness of the sheet bundle PB from the memory  302 , which stores therein a relation between the thickness of the sheet bundle PB and the gap between the pressing plates as a table, in accordance with the detected thickness, and the CPU  301  instructs the conveying roller gap change controlling unit  305  so that the conveying roller gap change controlling unit  305  changes the gap between the conveying rollers  206  and  207  by controlling drive of a motor (not shown) driving a cam setting the gap between the conveying rollers  206  and  207 .   2) When the sheet P is conveyed to the sheet post-processing device  100 , the number of the conveyed sheets P detected by the entrance sensor  13  is counted by the counter, the thickness of the sheet bundle PB is figured out on the basis of the thickness of one sheet recognized by the image forming apparatus PR and the number of sheets of one sheet bundle PB to be stitched, and the gap between the conveying rollers  206  and  207  is changed in the same manner as in 1).   3) Information on the number of sheets of the sheet bundle PB or the type of the sheet thereof is acquired from the image forming apparatus PR connected to the sheet post-processing device  100 , and the gap between the conveying rollers  206  and  207  is changed in accordance with the information in the same manner as in 1).   

     Furthermore, the gap between the pressing plates  219  and  220  and the gap between the conveying rollers  206  and  207  may be controlled to be changed by a combination of the third embodiment and the fifth embodiment. 
     As described above, according to the embodiment, various advantageous effects including the following advantageous effects 1) to 8) can be obtained.
     1) In an aspect in which the gap between the pressing plates  219  and  220  is changed so as to regulate the deflection PB 2  of the sheet bundle from when the sheet bundle is conveyed between the pressing plates  219  and  220  until the sheet bundle is folded at the center thereof by the pressing plates  219  and  220 , the precision of the position folded by the pressing plates  219  and  220  can be improved, wrinkles can be prevented, and a height of the folded sheet or sheet bundle can be reduced by reliably creasing the sheet or sheet bundle.   2) In an aspect in which the gap of the conveying rollers  206  and  207  are widened until the front end PB 1  of the sheet bundle PB passes the gap, the sheet bundle is not creased by the conveying rollers  206  and  207  and occurrence of folding into a box-like configuration and a folding position error can be prevented. As a result, a deviation in folded position and occurrence of wrinkles can be prevented and a height of the folded sheet or sheet bundle can be reduced by reliably creasing the sheet or sheet bundle.   3) In an aspect in which the sheet bundle PB is pushed into between the conveying rollers  206  and  207  and/or the pressing plates  219  and  200  by the folding blade  203 , the precision of the folding position can be improved.   4) In an aspect in which the thickness of the sheet bundle PB is detected and the gap between the pressing plates  219  and  200  or the gap between the conveying rollers  206  and  207  is controlled depending on the thickness of the sheet bundle PB, deflection can be suppressed even when the thickness of the sheet bundle PB is different, so that the precision of the folded position can be improved, and occurrence of wrinkles can be prevented.   5) In an aspect in which the number of sheets of the sheet bundle PB is counted and the gap between the pressing plates  219  and  220  or the gap between the conveying rollers  206  and  207  is controlled depending on the number of sheets of the sheet bundle PB, deflection can be suppressed even when the thickness of the sheet bundle PB is different, so that the precision of the folded position can be improved, and occurrence of wrinkles can be prevented. At this time, since the detection sensor detecting the thickness of the sheet bundle PB is not needed, cost can be reduced.   6) In an aspect in which the gap between the pressing plates  219  and  220  or the gap between the conveying rollers  206  and  207  is controlled on the basis of information on the number of sheets and/or the type of the sheet received from an external apparatus, for example, an image forming apparatus, deflection can be suppressed even when the thickness of the sheet bundle PB is different, so that the precision of the folded position can be improved, and occurrence of wrinkles can be prevented. At this time, since the detection sensor detecting the thickness of the sheet bundle PB or the counter is not needed, cost can be reduced.   7) In an aspect in which the gap between the conveying rollers  206  and  207  is controlled on the basis of the thickness of the folding blade  203  and the sheet bundle, a conveying error can be prevented and the sheet bundle can be prevented from getting dirty during the center-folding process.   8) In an aspect in which the conveying speed of the conveying rollers  206  and  207  is set to be equal to the speed of the folding blade  203  during pushing, deflection caused by a difference in speed therebetween can be prevented and the sheet bundle can be prevented from getting dirty due to rubbing.   

     According to an aspect of the invention, since a gap between two members is controlled to be changed depending on the thickness of the sheet or the sheet bundle while the sheet or the sheet bundle is guided into between the two members, a deviation in folded position and occurrence of wrinkles can be prevented and the height of the folded sheet or sheet bundle can be reduced by reliably creasing the sheet or the sheet bundle. 
     Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.