Patent Publication Number: US-11390482-B2

Title: Sheet processing apparatus and image forming system

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet processing apparatus that processes a sheet and an image forming system including the sheet processing apparatus. 
     Description of the Related Art 
     Conventionally, a finisher that is connected to an image forming apparatus such as a printer and performs a punching process on a sheet discharged from the image forming apparatus is proposed, for example, in Japanese Patent Laid-Open No. H10-279170. This finisher includes a sheet detection sensor that detects the sheet, a conveyance roller pair that conveys the sheet, and a punching device that punches a hole in the sheet conveyed by the conveyance roller pair. The punching device includes a puncher and a die that are each rotatably supported by a casing, and a puncher driving motor that drives the puncher and the die in synchronization. 
     In addition, in Japanese Patent Laid-Open No. H10-279170, after the leading end of the sheet is detected by the sheet detection sensor, an end portion position in a width direction of the sheet perpendicular to a sheet conveyance direction is detected by a sheet side end detection sensor at a predetermined timing, and the punching device is moved in the width direction on the basis of the detected information. 
     In recent years, for the image forming apparatus, there has been a demand that the interval between the trailing end of a preceding sheet and the leading end of a succeeding sheet be shortened to improve the productivity. This interval will be hereinafter referred to as a sheet interval. Here, Japanese Patent Laid-Open No. H10-279170 does not disclose how the punching device is controlled before and after the sheet interval. However, in the case where a punching position of the succeeding sheet is greatly displaced from a punching position of the preceding sheet or where the sheet is conveyed in a skewed state, the amount of movement of the punching device in the width direction for performing the punching process on the succeeding sheet after the punching process on the preceding sheet is finished is large. Therefore, in such a case, it is difficult to perform the punching process successively on a plurality of sheets with a short sheet interval. 
     SUMMARY OF THE INVENTION 
     The present invention provides a configuration that may improve the productivity in the case of successively performing a punching process on sheets. 
     According to a first aspect of the present invention, a sheet processing apparatus includes a sheet conveyance portion configured to convey a sheet in a conveyance direction, a punching member that is rotatably supported and configured to perform a punching process of punching a hole in the sheet conveyed by the conveyance portion in a predetermined position in the conveyance direction, a punching member moving portion configured to move the punching member in a sheet width direction perpendicular to the conveyance direction, a position detection portion disposed upstream of the predetermined position in the conveyance direction and configured to detect an end portion position of the sheet in the sheet width direction, and a controller configured to control the punching member moving portion to move the punching member to a position to punch the hole in the sheet. In a case of performing the punching process on a preceding sheet and a succeeding sheet successively conveyed to the predetermined position, the controller is configured to execute preliminary movement after the punching process on the preceding sheet is finished and before an end portion position of the succeeding sheet in the sheet width direction that coincides with a first punching position of the succeeding sheet in the conveyance direction reaches the position detection portion. In the preliminary movement, movement of the punching member in the sheet width direction is started for performing the punching process on the succeeding sheet. The first punching position is a position where the punching process is first performed on the succeeding sheet. 
     According to a second aspect of the present invention, a sheet processing apparatus includes a sheet conveyance portion configured to convey a sheet in a conveyance direction, a punching member that is rotatably supported and configured to perform a punching process of punching a hole in the sheet conveyed by the conveyance portion in a predetermined position in the conveyance direction, a punching member moving portion configured to move the punching member in a sheet width direction perpendicular to the conveyance direction, a position detection portion disposed upstream of the predetermined position in the conveyance direction and configured to detect an end portion position of the sheet in the sheet width direction, and a controller configured to control the punching member moving portion to move the punching member to a position to punch the hole in the sheet. In a case of performing the punching process on a preceding sheet and a succeeding sheet successively conveyed to the predetermined position, the controller starts moving the punching member in the sheet width direction to perform the punching process on the succeeding sheet, after the punching process on the preceding sheet is finished and before an end portion position of the succeeding sheet in the sheet width direction that coincides with a first punching position of the succeeding sheet in the conveyance direction reaches the position detection portion, in a case where a distance from a position of the punching member at an end of the punching process on the preceding sheet to the first punching position of the succeeding sheet in the sheet width direction is larger than a predetermined threshold value, the first punching position being a position where the punching process is first performed on the succeeding sheet, and starts moving the punching member in the sheet width direction to perform the punching process on the succeeding sheet, after the end portion position of the succeeding sheet in the sheet width direction that coincides with the first punching position of the succeeding sheet in the conveyance direction reaches the position detection portion, in a case where the distance from the position of the punching member at the end of the punching process on the preceding sheet to the first punching position of the succeeding sheet in the sheet width direction is equal to or smaller than the predetermined threshold value. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall schematic view of an image forming apparatus according to a first embodiment. 
         FIG. 2A  is a schematic view of a puncher and a die positioned in home positions. 
         FIG. 2B  is a schematic view of the puncher and the die positioned in punching starting positions. 
         FIG. 2C  is a schematic view of the puncher and the die positioned in engagement positions. 
         FIG. 2D  is a schematic view of the puncher and the die positioned in punching finishing positions. 
         FIG. 3  is a schematic diagram illustrating a mechanism of lateral movement of a punching device according to the first embodiment. 
         FIG. 4  is a block diagram illustrating a hardware configuration of an image forming system according to the first embodiment. 
         FIG. 5  is a block diagram illustrating a functional configuration of the image forming system according to the first embodiment. 
         FIG. 6  is a schematic diagram illustrating a state in which a preceding sheet and a succeeding sheet are conveyed in a state of being displaced from each other in the lateral direction. 
         FIG. 7A  is a first schematic diagram illustrating a motion of the punching device in the first embodiment in the case where the distance between punching positions of the preceding sheet and the succeeding sheet in the lateral direction is small. 
         FIG. 7B  is a second schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is small. 
         FIG. 7C  is a third schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is small. 
         FIG. 7D  is a fourth schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is small. 
         FIG. 7E  is a fifth schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is small. 
         FIG. 8  is a flowchart illustrating control of a punching process according to the first embodiment. 
         FIG. 9A  is a first schematic diagram illustrating a motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is large. 
         FIG. 9B  is a second schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is large. 
         FIG. 9C  is a third schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is large. 
         FIG. 9D  is a fourth schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is large. 
         FIG. 9E  is a fifth schematic diagram illustrating the motion of the punching device in the first embodiment in the case where the distance between the punching positions of the preceding sheet and the succeeding sheet in the lateral direction is large. 
         FIG. 10  is a block diagram illustrating a functional configuration of an image forming system according to a second embodiment. 
         FIG. 11  is a schematic diagram illustrating a state in which a preceding sheet and a succeeding sheet are conveyed in a skewed state. 
         FIG. 12  is a block diagram illustrating a functional configuration of an image forming system according to a third embodiment. 
         FIG. 13A  is a schematic diagram illustrating a state in which a succeeding sheet having a width different from the width of a preceding sheet is conveyed and the leading end of the succeeding sheet has not reached a line sensor yet. 
         FIG. 13B  is a schematic diagram illustrating a state in which a succeeding sheet having a width different from the width of a preceding sheet is conveyed and the leading end of the succeeding sheet has reached the line sensor. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     A first embodiment will be described with reference to  FIGS. 1 to 9E . First, an image forming system of the present embodiment will be described with reference to  FIG. 1 . 
     Image Forming System 
     As illustrated in  FIG. 1 , an image forming system  1 S according to the present embodiment is constituted by an image forming apparatus  1 , an image reading apparatus  2 , a document feeding apparatus  3 , and a sheet processing apparatus  4 . The image forming system  1 S forms an image on a sheet serving as a recording material, and outputs the sheet after processing the sheet by the sheet processing apparatus  4  if necessary. To be noted, examples of the sheet include paper sheets and plastic sheets. Hereinafter, the operation of each apparatus will be schematically described, and then the sheet processing apparatus  4  will be described in detail. 
     The document feeding apparatus  3  conveys a document placed on a document tray  18  to image reading portions  16  and  19 . The image reading portions  16  and  19  are each an image sensor that reads image information from a document surface, and both surfaces of the document are read in one time of document conveyance. The document whose image information has been read is discharged onto a document discharge portion  20 . In addition, the image reading apparatus  2  is capable of reading the image information from a still document set on a platen glass by reciprocating the image reading portion  16  by a driving device  17 . Examples of the still document include a document such as a booklet document to which the document feeding apparatus  3  is not applicable. 
     The image forming apparatus  1  is an electrophotographic apparatus including an image forming portion  1 B of a direct transfer system. The image forming portion  1 B includes a cartridge  8  including a photosensitive drum  9 , and a laser scanner unit  15  disposed above the cartridge  8 . In the case of performing an image forming operation, the surface of the photosensitive drum  9  that is rotating is charged, the laser scanner unit  15  exposes the photosensitive drum  9  on the basis of the image information, and thus an electrostatic latent image is formed on the surface of the photosensitive drum  9 . The electrostatic latent image born on the photosensitive drum  9  is developed into a toner image with charged toner particles, and the toner image is conveyed to a transfer portion where the photosensitive drum  9  is opposed to a transfer roller  10 . A controller of the image forming apparatus  1  performs the image forming operation by the image forming portion  1 B on the basis of the image information read by the image reading portions  16  and  19  or image information received from an external computer via a network. 
     The image forming apparatus  1  includes a plurality of feeding apparatuses  6  that each feed sheets serving as recording media one by one at predetermined intervals. A sheet fed from a feeding apparatus  6  is conveyed to the transfer portion after the skew thereof is corrected by registration rollers  7 , and the toner image born on the photosensitive drum  9  is transferred thereto in the transfer portion. A fixing unit  11  is disposed downstream of the transfer portion in the sheet conveyance direction. The fixing unit  11  includes a rotary member pair that nips and conveys the sheet, and a heat generation member such as a halogen lamp for heating the toner image, and performs an image fixing process by heating and pressurizing the toner image on the sheet. 
     In the case of discharging the sheet on which an image has been formed to the outside of the image forming apparatus  1 , the sheet having passed through the fixing unit  11  is conveyed to the sheet processing apparatus  4  through a horizontal conveyance portion  14 . In the case of a sheet on a first surface of which an image has been formed in duplex printing, the sheet having passed through the fixing unit  11  is passed onto reverse conveyance rollers  12 , switched back and conveyed by the reverse conveyance rollers  12 , and conveyed again to the registration rollers  7  through a reconveyance portion  13 . Then, the sheet passes through the transfer portion and the fixing unit  11  again, thus an image is formed on a second surface of the sheet, and then the sheet is conveyed to the sheet processing apparatus  4  through the horizontal conveyance portion  14 . 
     The image forming portion  1 B described above is an example of an image forming portion that forms an image on a sheet, and an electrophotographic unit of an intermediate transfer system that transfers a toner image formed on a photosensitive member onto a sheet via an intermediate transfer member may be used. In addition, a printing unit of an inkjet system or an offset printing system may be used as the image forming portion. 
     Sheet Processing Apparatus 
     The sheet processing apparatus  4  includes a punching device  60  that performs a punching process on the sheet. The sheet processing apparatus  4  performs the punching process on sheets received from the image forming apparatus  1 , and discharges the sheets as a sheet bundle. In addition, the sheet processing apparatus  4  can also simply discharge the sheets received from the image forming apparatus  1  without performing the punching process. 
     The sheet processing apparatus  4  includes an inlet path  81 , an in-body discharge path  82 , a first discharge path  83 , and a second discharge path  84  as conveyance paths for conveying sheets, and includes an upper discharge tray  25  and a lower discharge tray  37  as discharge destinations to which the sheets are to be discharged. The inlet path  81  serving as a first conveyance path is a conveyance path for receiving and guiding a sheet from the image forming apparatus  1 , and the in-body discharge path  82  extending downward from the inlet path  81  and serving as a second conveyance path is a conveyance path for guiding the sheet toward an alignment portion  4 A. The first discharge path  83  is a conveyance path through which the sheet is discharged onto the upper discharge tray  25 , and the second discharge path  84  serving as a third conveyance path extends from an intermediate supporting portion  39  toward bundle discharge rollers  36  and guides the sheet toward the bundle discharge roller  36 . 
     The sheet discharged from the horizontal conveyance portion  14  of the image forming apparatus  1  is received by inlet rollers  21  disposed in the inlet path  81  and serving as a conveyance portion, and is conveyed in a sheet conveyance direction X toward pre-reverse conveyance rollers  22  through the inlet path  81 . A punching device  60  is disposed between the inlet rollers  21  and the pre-reverse conveyance rollers  22  in the sheet conveyance direction X, and the sheet conveyed in the inlet path  81  is subjected to a punching process by the punching device  60  that will be described later. In addition, an entrance sensor  27  changes the output value thereof on the basis of presence or absence of a sheet in a second detection position between the inlet rollers  21  and the pre-reverse conveyance rollers  22 . Examples of the output value include a voltage value and an output signal. The entrance sensor  27  serving as a second sensor is positioned upstream of a line sensor  68  and a pre-puncher sensor  63  that will be described later in the conveyance direction X. The pre-reverse conveyance rollers  22  convey the sheet received from the inlet rollers  21  toward the first discharge path  83 . 
     To be noted, the sheet conveyance speed of the inlet rollers  21  may be set to be higher than that in the horizontal conveyance portion  14  such that the sheet conveyance speed increases after the sheet is received by the inlet rollers  21 . In this case, it is preferable that a one-way clutch is disposed between a conveyance roller of the horizontal conveyance portion  14  and a motor that drives this conveyance roller such that the conveyance roller idles when the sheet is pulled by the inlet rollers  21 . 
     In the case where the discharge destination of the sheet is the upper discharge tray  25 , the reverse conveyance rollers  24  discharge the sheet received from the pre-reverse conveyance rollers  22  onto the upper discharge tray  25 . In the case where the discharge destination of the sheet is the lower discharge tray  37 , the reverse conveyance rollers  24  serving as a reverse conveyance portion perform switch-back conveyance of reversing the sheet received from the pre-reverse conveyance rollers  22 , and convey the sheet to the in-body discharge path  82 . A non-return flap  23  is disposed in a branching portion which is upstream of the reverse conveyance rollers  24  in the sheet discharge direction of the reverse conveyance rollers  24  and where the inlet path  81  and the in-body discharge path  82  branch from the first discharge path  83 . The non-return flap  23  has a function of suppressing the sheet switched back by the reverse conveyance rollers  24  returning to the inlet path  81 . 
     In-body discharge rollers  26 , intermediate conveyance rollers  28 , and kick-out rollers  29  that are disposed in the in-body discharge path  82  convey the sheet received from the reverse conveyance rollers  24  toward the alignment portion  4 A while sequentially passing the sheet onto one another. A pre-intermediate supporting sensor  38  detects the sheet at a position between the intermediate conveyance rollers  28  and the kick-out rollers  29 . As the entrance sensor  27 , the pre-puncher sensor  63 , and the pre-intermediate supporting sensor  38 , for example, optical sensors that detect the presence or absence of a sheet in a detection position by using light, or flag sensors that use a flag pressed by the sheet are used. 
     The alignment portion  4 A includes a bundle pressing flag  30 , an intermediate supporting portion  39  serving as a supporting portion, a bundle discharge guide  34 , and a driving belt  35 . The intermediate supporting portion  39  is constituted by an intermediate upper guide  31  and an intermediate lower guide  32 , and a plurality of sheets are supported thereon as a sheet bundle. The sheet bundle discharged toward the intermediate supporting portion  39  by the kick-out rollers  29  constituted by a roller pair is pressed against the intermediate lower guide  32  by the bundle pressing flag  30 . 
     Then, the sheet bundle discharged onto the intermediate supporting portion  39  is guided downward along the intermediate lower guide  32 , and is aligned by a longitudinal aligning plate provided at a downstream end portion of the intermediate supporting portion  39  in the sheet conveyance direction. In addition, the sheet bundle aligned by the longitudinal aligning plate in the sheet conveyance direction is aligned in a width direction perpendicular to the sheet conveyance direction by unillustrated lateral aligning plates. After such an alignment process is performed, the sheet bundle is pushed out by the bundle discharge guide  34  fixed to the driving belt  35 , and is passed onto the bundle discharge rollers  36  through the second discharge path  84 . The sheet bundle is discharged to the outside of the apparatus by the bundle discharge rollers  36  serving as a discharge portion, and is supported on the lower discharge tray  37 . 
     The upper discharge tray  25  and the lower discharge tray  37  are both movable in the up-down direction with respect to the casing of the sheet processing apparatus  4 . The sheet processing apparatus  4  includes sheet surface detection sensors that respectively detect the positions of the upper surface of the sheets on the upper discharge tray  25  and the lower discharge tray  37 , that is, the height of sheet stacks on the upper discharge tray  25  and the lower discharge tray  37 , and when either of the sensors detects a sheet, the corresponding tray is lowered in an A 2  direction or a B 2  direction. In addition, when a sheet surface detection sensor detects that sheets on the upper discharge tray  25  or the lower discharge tray  37  have been removed, the corresponding tray is lifted in an A 1  or B 1  direction. Therefore, the upper discharge tray  25  and the lower discharge tray  37  are controlled to ascend and descend so as to maintain the upper surface of the sheets supported thereon at a constant height. 
     Punching Device 
     Next, the punching device  60 , the line sensor  68 , and the pre-puncher sensor  63  will be described. The punching device  60  is a punching device of a rotary type that punches a hole in a sheet by a rotating puncher serving as a punching member. The punching device  60  includes a puncher  61  rotatably supported about a puncher shaft  65  and a die  62  that rotates about a die shaft  66  as illustrated in  FIG. 2A . The puncher  61  performs a punching process of punching a hole in the sheet conveyed by the inlet rollers  21  illustrated in  FIG. 1  at a predetermined position while rotating together with the die  62 . 
     The pre-puncher sensor  63  and the line sensor  68  are disposed upstream of the punching device  60  in the conveyance path, that is, upstream of the punching device  60  in the sheet conveyance direction X. The die  62  has a die hole  64  capable of engaging with the puncher  61 , and the puncher shaft  65  and the die shaft  66  are engaged with an unillustrated gear that is driven by a puncher driving motor  102  illustrated in  FIG. 4 . When the puncher driving motor  102  serving as a drive source drives, the puncher  61  rotates in a clockwise direction in  FIG. 2A  and the die  62  rotates in a counterclockwise direction in  FIG. 2A . 
     The pre-puncher sensor  63  serving as a first sensor and a sheet leading end detection portion detects the sheet at a first detection position upstream of the puncher  61  and the die  62  in the conveyance direction X. More specifically, the pre-puncher sensor  63  changes the output value thereof, for example, a voltage value or an output signal, on the basis of presence or absence of the sheet in the first detection position, and therefore the output value changes when the leading end or the trailing end of the sheet passes the detection position. 
     The line sensor  68  serving as a position detection portion is a sensor in which a plurality of image sensors such as charge coupled device sensors: CCD sensors or complementary metal oxide semiconductor sensors: CMOS sensors are arranged in line in a sheet width direction Y, that is, a lateral direction perpendicular to the conveyance direction X. Such a line sensor  68  is disposed upstream of a predetermined position in the conveyance direction X where the punching device  60  performs the punching process, and is capable of detecting the position of an end portion position of the sheet in the width direction Y. That is, the line sensor  68  detects the end portion position of the sheet by using the fact that the detection result of the sensor differs between a position where the sheet is present and a position where the sheet is not present. In addition, since a plurality of image sensors are arranged in the width direction Y in the line sensor  68 , the line sensor  68  is capable of detecting the end portion position of the sheet without moving in the width direction Y. 
       FIG. 2A  is a schematic diagram illustrating the puncher  61  and the die  62  positioned in home positions. The puncher  61  and the die  62  are positioned in the home positions at the start and end of an image formation job of forming an image on a sheet, and are still in the home positions also when a job is not input. The puncher  61  and the die  62  are disposed such that conveyance of the sheet is not hindered when the puncher  61  and the die  62  are in the home positions. In addition, the home position of the puncher  61  is a position upstream of an engagement position, where the puncher  61  and the die  62  engage with each other, by an angle θ in the rotation direction. 
       FIG. 2B  is a schematic view of the puncher  61  and the die  62  at positions to which the puncher  61  has rotated from the home position and in which the puncher  61  comes into contact with the sheet, and punching of the sheet starts at these positions. That is,  FIG. 2B  illustrates punching starting positions of the puncher  61  and the die  62 . At this time, the rotational position of the puncher  61  is a position upstream of the engagement position by an angle θ 1  in the rotation direction. 
       FIG. 2C  is a schematic view of the puncher  61  and the die  62  positioned at the engagement positions. When the puncher  61  and the die  62  are at the engagement positions, the puncher  61  engages with the die hole  64  of the die  62 , and thus a hole is punched in the sheet. 
       FIG. 2D  is a schematic view of the puncher  61  and the die  62  positioned at punching finishing positions. At these positions, the puncher  61  is separated from the sheet. The rotational position of the puncher  61  at this time is a position downstream of the engagement position by an angle θ 2  in the rotation direction. 
     As described above, the puncher  61  and the die  62  stand by in the home positions, and start being driven by the puncher driving motor  102  at a predetermined timing on the basis of detection of the leading end of the sheet by the pre-puncher sensor  63 . At this time, the puncher driving motor  102  is controlled such that the peripheral speed of the puncher  61  and the die  62  is equal to the sheet conveyance speed so as to suppress wrinkles and breakage in the sheet at the time of punching. The puncher  61  and the die  62  are separated from the punched sheet at the punching finishing positions. 
       FIG. 3  is a top view of the punching device  60 , the line sensor  68 , and the pre-puncher sensor  63  illustrating the layout thereof. A sheet  78  is conveyed in the conveyance direction X, that is, an arrow direction in  FIG. 3 , toward the punching device  60  by the inlet rollers  21 . The inlet rollers  21  are rollers that are rotationally driven to convey the sheet in the conveyance direction X. The pre-puncher sensor  63  is provided at the center in the width direction Y in the conveyance path of the sheet, and detects passage of the leading end and the trailing end of the sheet in the conveyance direction X in a center portion in the width direction Y. The detection result of each image sensor of the line sensor  68  changes in accordance with the presence or absence of the sheet when the sheet passes, and thus the line sensor  68  detects the left end position of the sheet, that is, the lower end position of the sheet in  FIG. 3 . To be noted, the width direction Y is approximately parallel to the rotation axis direction of the inlet rollers  21 . 
     The punching device  60  is coupled to a rack gear  70 . A pinion gear  75  transmits the rotational drive of a puncher lateral movement motor  74  to the rack gear  70 . A puncher moving device  70 A serving as a punching member moving portion includes the puncher lateral movement motor  74  serving as a drive source and a movement mechanism  70 B. In the present embodiment, the puncher lateral movement motor  74  is a stepping motor. The movement mechanism  70 B has a rack-and-pinion structure including the pinion gear  75  and the rack gear  70  as described above. Further, the movement mechanism  70 B is driven by the rotation of the puncher lateral movement motor  74 , and laterally moves the punching device  60  in the width direction Y while being guided by a guide shaft  77 . 
     A puncher lateral movement home position sensor: a lateral movement HP position sensor  71  is a photo interrupter constituted by a light emitting portion and a light receiving portion. A sensor flag  72  is integrally attached to the punching device  60 , and moves in accordance with the lateral movement of the punching device  60 . When the punching device  60  moves laterally toward the left end of the sheet, the sensor flag  72  enters the space between the light emitting portion and the light receiving portion of the puncher lateral movement home position sensor  71 . In contrast, when the punching device  60  laterally moves from the left end side of the sheet toward the center, the sensor flag  72  moves out of the space between the light emitting portion and the light receiving portion of the puncher lateral movement home position sensor  71 . As a result of this, the output of the puncher lateral movement home position sensor  71  changes, and the lateral movement position of the punching device  60  is specified. 
     The home position of the punching device  60  is set to a position to which the punching device  60  has moved outward, that is, toward the left end of the sheet, by a predetermined amount after the light in the puncher lateral movement home position sensor  71  is blocked. When the punching device  60  is in this home position, the puncher  61  does not collide with the sheet, that is, the puncher  61  is sufficiently retracted even in the case where a sheet of the maximum width that can be processed by the apparatus is conveyed. 
     When punching a hole in the sheet, the punching device  60  is laterally moved from the home position to a punching position. The length from the position of the left end of the sheet to the punching position in the width direction Y is determined in advance. Therefore, the punching device  60  can be moved to a desired punching position on the basis of the width, that is, the length of the sheet in the width direction Y or the position of an end portion of the sheet. 
     That is, when the punching device  60  is in the home position, the puncher lateral movement motor  74  starts driving in such a direction as to move the punching device  60  toward the center of the sheet. Then, the punching device  60  moves and the sensor flag  72  moves out of the space between the light emitting portion and the light receiving portion of the puncher lateral movement home position sensor  71 . As a result of this, the signal of the puncher lateral movement home position sensor  71  changes, and by driving the puncher lateral movement motor  74  by a predetermined amount with this change timing as a starting point, the punching device  60  can be moved to a desired punching position corresponding to the sheet width. When the punching process on the sheet is finished, the punching device  60  is moved again to the home position. 
     Hardware Configuration 
       FIG. 4  is a block diagram illustrating a hardware configuration of the image forming system  1 S. To be noted, in  FIG. 4 , elements of the sheet processing apparatus  4  related to the control of the present embodiment are mainly illustrated, and illustration of the other elements is omitted. 
     The image forming system  1 S includes a main controller  101 , a video controller  119 , and an engine controller  301  as illustrated in  FIG. 4 , and the video controller  119  integrally controls the image forming apparatus  1  and the sheet processing apparatus  4 . The engine controller  301  controls the image forming apparatus  1 , and the main controller  101  controls the sheet processing apparatus  4 . 
     The video controller  119  is connected to the engine controller  301  and the main controller  101  respectively via serial command transmission signal lines  302  and  304 , and transmits commands to the engine controller  301  and the main controller  101  by serial communication. The engine controller  301  is connected to the video controller  119  via a serial status transmission signal line  303 , and transmits status data to the video controller  119  by serial communication. The main controller  101  serving as a controller is connected to the video controller  119  via a serial status transmission signal line  305 , and transmits status data to the video controller  119  by serial communication. 
     When performing an image forming operation, the video controller  119  performs control by transmitting serial commands to the engine controller  301  and the main controller  101  and receiving status data from the engine controller  301  and the main controller  101 . As described above, when a plurality of apparatuses are connected to each other and operated, the video controller  119  integrally manages the status and control of each apparatus to maintain cohesion between operations of the apparatuses. 
     The main controller  101  includes a central processing unit: CPU  306 , a random-access memory: RAM  307 , a read-only memory: ROM  308 , a system timer  111 , a communication portion  315 , an input/output port: I/O port  310 , and so forth. The CPU  306  is a central processing unit that controls various operations of the sheet processing apparatus  4 . The RAM  307  is a volatile memory that temporarily stores control data required for operation of the sheet processing apparatus  4 . The ROM  308  is a nonvolatile memory that stores a program and a control table required for operation of the sheet processing apparatus  4 . 
     The system timer  111  generates a timing required for various control, and the communication portion  315  performs communication with the video controller  119 . These CPU  306 , RAM  307 , ROM  308 , system timer  111 , and communication portion  315  are connected to the I/O port  310  via a bus  309 , and the I/O port  310  outputs and inputs control signals to and from various units of the sheet processing apparatus  4 . More specifically, the I/O port  310  is connected to the puncher lateral movement HP sensor  71  via a lateral movement HP sensor input circuit  318 . In addition, the I/O port  310  is connected to the line sensor  68  and the pre-puncher sensor  63  respectively via a line sensor input circuit  316  and a pre-puncher sensor input circuit  312 . Further, the I/O port  310  is connected to the puncher driving motor  102  and the puncher lateral movement motor  74  respectively via a puncher driving motor driving circuit  313  and a puncher lateral movement motor driving circuit  317 . 
     Functional Configuration 
       FIG. 5  is a block diagram illustrating a functional configuration of the image forming system  1 S. To be noted, in  FIG. 5 , mainly parts related to punching control on the sheet of the present embodiment are extracted and illustrated, and illustration of the other parts is omitted. 
     The main controller  101  includes the system timer  111 , a punching controller  112 , a sensor controller  116 , and a motor controller  117  as illustrated in  FIG. 5 , and controls conveyance of and punching on the sheet in the image forming system  1 S. Signals from the line sensor  68 , the pre-puncher sensor  63 , and the puncher lateral movement HP sensor  71  are input to the sensor controller  116 . Then, the sensor controller  116  outputs information about the presence or absence of a sheet at each sensor and information about the end portion position of the sheet to the punching controller  112 . The punching controller  112  drives the puncher driving motor  102  driving the puncher  61  and the die  62  and the puncher lateral movement motor  74  driving the punching device  60  by controlling the motor controller  117 . 
     The punching controller  112  includes an estimated movement amount calculation portion  113 , a preliminary movement execution determination portion  121 , a lateral movement confirmed position calculation portion  115 , and a lateral movement controller  114 . The punching controller  112  detects passage of the leading end of the sheet through the position of the pre-puncher sensor  63  from a signal change of the pre-puncher sensor  63  received via the sensor controller  116 . The end portion position of a succeeding sheet in the width direction Y that coincides, in the conveyance direction X, with the leading end thereof in the conveyance direction X is detected by the line sensor  68  on the basis of this detection timing. In the present embodiment, the end portion position is the position of a left end of the sheet. Hereinafter, an end portion position of a sheet in the width direction Y that coincides with a certain position in the conveyance direction X will be referred to as an end portion position of the sheet in the width direction Y at the certain position. 
     The estimated movement amount calculation portion  113  estimates and calculates a lateral movement amount, which is the distance between the final punching position of a preceding sheet and the first punching position of a succeeding sheet in the width direction Y, from the detection result of the line sensor  68 . The final punching position of the preceding sheet is a current lateral movement position of the puncher, and the puncher is laterally moved by the estimated lateral movement amount before the start of punching on the succeeding sheet. The preliminary movement execution determination portion  121  determines whether or not to execute the lateral movement of the puncher on the basis of the estimated value of the lateral movement amount calculated by the estimated movement amount calculation portion  113 . 
     The lateral movement confirmed position calculation portion  115  determines, on the basis of the timing at which the leading end of the sheet has passed the pre-puncher sensor  63 , the timing at which the left end of the sheet at the punching position has reached the position of the line sensor  68 . Then, by detecting the left end position of the sheet at this timing by the line sensor  68 , the lateral movement confirmed position of the puncher is finally calculated. 
     The lateral movement controller  114  controls the timing at which the lateral movement of the puncher is started and transmits a drive instruction to the puncher lateral movement motor  74  through the motor controller  117 , after the lateral movement amount is calculated by the estimated movement amount calculation portion  113  or the lateral movement confirmed position calculation portion  115 . 
     Deviation Between Preceding Sheet and Succeeding Sheet in Width Direction 
     Next, among successively conveyed sheets, a sheet that is conveyed first will be referred to as a preceding sheet  200 , a sheet conveyed subsequently to the preceding sheet  200  will be referred to as a succeeding sheet  201  with reference to  FIG. 6 , and the punching process in the case where these sheets are conveyed in a state of being displaced with each other in the width direction Y will be described. 
     The conveyance of the sheet can differ due to various factors such as the configuration of the conveyance path in the sheet processing apparatus, the state of the sheet, and whether the conveyance rollers are brand-new or used, and successively conveyed sheets can be conveyed in a state of being laterally shifted as described above. The maximum amount of displacement between the sheets when all these conditions lean toward varying the conveyance of sheets is determined for each apparatus. In the present embodiment, this displacement amount will be referred to as a maximum displacement amount  205  as illustrated in  FIG. 6 . 
     The preceding sheet  200  and the succeeding sheet  201  are successively conveyed from the right to the left in the conveyance direction X in  FIG. 6  as indicated by an arrow in  FIG. 6 . A dot line  202  indicates a punching position in the width direction Y in the case where the sheets are conveyed in an ideal state in which there is no displacement. This punching position will be also referred to as an ideal position.  FIG. 6  illustrates a case where the preceding sheet  200  is conveyed in a manner displaced to the most left in the width direction Y, that is, to the lowermost position from the ideal position in  FIG. 6 , whereas the succeeding sheet  201  is conveyed in a manner displaced to the most right in the width direction Y, that is, to the uppermost position from the ideal position in  FIG. 6 . Therefore, the distance between a punching position  203  of the preceding sheet  200  and a punching position  204  of the succeeding sheet  201  in the width direction Y is equal to the maximum displacement amount  205 . To be noted, in the description below, the “left” and the “right” in the width direction Y are directions in the case of viewing the sheet from above and in the conveyance direction X. 
     The puncher  61  of the punching device  60  illustrated in  FIG. 2A  and so forth has to perform punching at the punching position  203  of the preceding sheet  200 , then laterally move to the right in the width direction Y by the maximum displacement amount  205 , and perform punching at the first punching position  204  of the succeeding sheet  201 . The first punching position is a punching position that is the most downstream in the conveyance direction X among a plurality of punching positions of the succeeding sheet  201 . Here, the punching position  204  of the succeeding sheet  201  can be determined when the left end of the succeeding sheet  201  at the punching position  204  is detected by the line sensor  68 . That is, the position of the punching position  204  is determined when the end portion position of the succeeding sheet  201  in the width direction Y at the punching position  204  is detected by the line sensor  68 . 
     Therefore, the lateral movement of the puncher  61  needs to be completed while the sheet is conveyed by a distance from the position of the line sensor  68  to a predetermined position  207  where a hole is punched in the punching position  204  of the succeeding sheet  201  by the puncher  61  of the punching device  60 . The distance from the line sensor  68  to the predetermined position  207  is just L indicated in  FIG. 2 . If this distance L is set to a large value, the apparatus becomes larger and the cost becomes higher. In addition, there is a problem that, if the left end position of the sheet detected by the line sensor  68  is displaced while the sheet is conveyed to the predetermined position  207 , the error of the punching position becomes large. Therefore, the distance L is preferably set to be small by disposing the line sensor  68  near the predetermined position  207 . 
     The puncher lateral movement motor  74  serving as a drive source for lateral movement of the punching device  60  is preferably a stepping motor suitable for position control. Therefore, in the present embodiment, a stepping motor is used as the puncher lateral movement motor  74 . The stepping motor has restrictions in the torque that can be output, the number of rotations that can be output, and so forth. The punching device  60  is a unit constituted by heavy parts, and the motor cannot be driven at a speed equal to or higher than a predetermined speed for moving this heavy unit. Therefore, the punching device  60  is configured to be laterally moved at a predetermined speed. This speed will be referred to as a lateral movement speed. 
     Time required for the punching device  60  to laterally move by the maximum displacement amount  205  is determined in advance in accordance with the maximum displacement amount  205  and the lateral movement speed. The rotary puncher  61  starts punching at the position upstream of the engagement position by the angle θ 1  in the rotation direction as illustrated in  FIG. 2B . Therefore, the lateral movement of the punching device  60  needs to be completed before the puncher  61  reaches the position upstream of the engagement position by the angle θ 1  in the rotation direction. 
     As described above, the time that can be used for lateral movement of the punching device  60  is obtained by subtracting the time in which the puncher  61  rotates by the angle θ 1  from the time in which the sheet is conveyed by the distance L. This time will be referred to as a time T 1 . That is, the time T 1  is a time from a time point when the end portion position, that is, the left end position of the succeeding sheet  201  in the width direction Y at the punching position  204  is detected by the line sensor  68  to the start of the punching process on the punching position  204  of the succeeding sheet  201 . The distance by which the punching device  60  can be laterally moved in the time T 1  will be referred to as a maximum movement amount of the punching device  60 . In the case where the maximum movement amount is smaller than the maximum displacement amount  205 , the lateral movement of the punching device  60  is not completed before the punching timing if the lateral movement of the puncher is started after detecting the left end of the succeeding sheet  201  at the punching position  204  by the line sensor  68 . 
     Therefore, in the present embodiment, the main controller  101  enables execution of preliminary movement for performing the punching process on the succeeding sheet  201 . The preliminary movement is an operation of starting the movement of the puncher  61  of the punching device  60  in the width direction Y after finishing the punching process on the preceding sheet  200  and before the end portion position, that is, the left end position of the succeeding sheet  201  in the width direction Y at the first punching position  204  reaches the line sensor  68 . Specifically, the first punching position  204  of the succeeding sheet  201  is estimated before the left end position of the succeeding sheet  201  at the punching position  204  is detected by the line sensor  68 , that is, before the position of the first punching position  204  of the succeeding sheet  201  is confirmed. Then, the lateral movement of the puncher toward the estimated punching position is started. 
     Therefore, in the preliminary movement, the movement of the punching device  60  is started at the timing at which the end portion position of the succeeding sheet  201  in the width direction Y at any position within a range from the leading end of the succeeding sheet  201  in the conveyance direction X to the first punching position  204  of the succeeding sheet reaches the line sensor  68 . In the present embodiment, the first punching position  204  of the succeeding sheet  201  is estimated by measuring the end portion position of the succeeding sheet  201  in the width direction Y at the leading end of the succeeding sheet  201  in the conveyance direction X by the line sensor  68 . In other words, the first punching position  204  of the succeeding sheet  201  is estimated from the end portion position of the succeeding sheet  201  in the width direction Y at the leading end of the succeeding sheet  201  in the conveyance direction X detected by the line sensor  68 . Then, the movement of the punching device  60  is started approximately at the same timing as the timing at which the end portion position of the succeeding sheet  201  in the width direction Y at the leading end thereof in the conveyance direction X reaches the line sensor  68 . 
     Preliminary Movement of Punching Device 
     The preliminary movement in which the first punching position  204  of the succeeding sheet  201  is estimated and the lateral movement of the puncher is started on the basis of the estimated position will be described below with reference to  FIGS. 7A to 7E .  FIGS. 7A to 7E  are diagrams sequentially illustrating the movement from punching on the preceding sheet  200  to punching on the succeeding sheet  201  in time series in the case where the preceding sheet  200  and the succeeding sheet  201  are conveyed in a state of being shifted from each other by the maximum displacement amount  205 . To be noted, the leading end of a sheet mentioned in the description below is the leading end of the sheet in the conveyance direction, that is, the downstream end of the sheet in the conveyance direction. 
       FIG. 7A  illustrates a moment when the leading end of the succeeding sheet  201  is detected by the pre-puncher sensor  63 . The timing when the leading end position or the punching position  204  of the succeeding sheet  201  reaches the line sensor  68  is detected with this timing as a starting point. 
       FIG. 7B  illustrates a moment when the left end position of the leading end of the succeeding sheet  201  is detected by the line sensor  68 . At this time, the punching device  60  is at a position in a distance L 1  from the left end of the preceding sheet  200  toward the center of the sheet. This is because the left end position of the preceding sheet  200  at the punching position  203  is measured by the line sensor  68  and the punching device  60  is moved such that the distance between the punching device  60  and the left end of the preceding sheet  200  becomes L 1 . The distance L 1  is determined as a standard. 
     In addition, at this time, the left end position of the leading end of the succeeding sheet  201  is detected by the line sensor  68 , and the position of the punching position  204  of the succeeding sheet  201  is estimated on the basis of this result. The estimated position is in a distance L 2  from the left end position of the leading end of the succeeding sheet  201  toward the center of the sheet. The distance L 2  is equal to the distance L 1 . The estimated lateral movement amount of the punching device  60  is calculated on the basis of this estimated value. This calculation is performed by the estimated movement amount calculation portion  113  illustrated in  FIG. 4 . In the example of  FIGS. 7A to 7E , the estimated movement amount is used as the maximum displacement amount  205 . 
       FIG. 7C  illustrates a time when the punching device  60  starts the preliminary movement toward the estimated punching position of the succeeding sheet  201 . The determination regarding the execution of the preliminary movement is made by the preliminary movement execution determination portion  121  illustrated in  FIG. 4 . The preliminary movement execution determination portion  121  determines whether or not to execute the preliminary movement in the case where the estimated movement amount is larger than an execution determination threshold value of the preliminary movement serving as a predetermined threshold value. 
     The execution determination threshold value serving as a predetermined threshold value is a value equal to or larger than the maximum movement amount by which the puncher  61  of the punching device  60  can be moved by the puncher moving device  70 A illustrated in  FIG. 3  in the time T 1 . To be noted, the execution determination threshold value is equal to or less than a half or equal to or less than a third of the length of the sheet in the width direction. The time T 1  is a time from a time point when the end portion position, that is, the left end position of the succeeding sheet  201  in the width direction Y at the punching position  204  is detected by the line sensor  68  to the start of the punching process at the punching position  204  of the succeeding sheet  201  as described above. In the present embodiment, an amount obtained by adding a margin to the maximum movement amount of the punching device  60  is employed as the execution determination threshold value of the preliminary movement. That is, a value larger than the maximum movement amount of the punching device  60  is used as the execution determination threshold value. 
     In the present embodiment, the preliminary movement is performed in the case where the preliminary movement amount is larger than the execution determination threshold value as described above. However, such a threshold value does not have to be set. For example, a configuration in which the preliminary movement is necessarily executed even in the case where the estimated movement amount is small may be employed. 
     In addition, at the time of the preliminary movement, an upper limit of the preliminary movement amount serving as a predetermined upper limit value is determined in advance. The preliminary movement amount is an amount by which the punching device  60  actually moves in the width direction Y when the preliminary movement is executed. In the present embodiment, a value equal to the estimated movement amount is set as the upper limit of the preliminary movement amount. That is, the preliminary movement is stopped in the case where the movement amount in the preliminary movement has reached the predetermined upper limit value before the punching position of the succeeding sheet  201  is confirmed after the start of the preliminary movement. In addition, in the case where the punching position of the succeeding sheet  201  is confirmed during the preliminary movement before the movement amount reaches the upper limit, confirmed movement is performed without continuing the preliminary movement to the upper limit. The estimated movement amount from the position of the puncher  61  of the punching device  60  at the end of the punching process on the preceding sheet  200  to the estimated punching position is used as this predetermined upper limit value. To be noted, the predetermined upper limit value may be a constant value not dependent on the estimated movement amount. 
       FIG. 7D  illustrates a timing when the left end position of the succeeding sheet  201  at the punching position  204  is detected by the line sensor  68 . As a result of this, the final position of the punching position  204  is confirmed. At this timing, the punching device  60  is already in the middle of the preliminary movement. The target position of the lateral movement is updated from the estimated position to the confirmed position. 
     That is, the main controller  101  confirms the punching position of the succeeding sheet  201  in the case where the end portion position of the succeeding sheet  201  in the width direction Y at the punching position  204  is detected by the line sensor  68  during the preliminary movement. Then, the main controller  101  moves the punching device  60  to the confirmed punching position  204  regardless of the estimated punching position. This confirmed position is a position obtained by finely adjusting the estimated position. The lateral movement can be completed before the punching process on the succeeding sheet  201  if the punching device  60  can be moved from the current position by a distance  206  to the confirmed punching position  204 . 
       FIG. 7E  illustrates a state in which the punching device  60  has laterally moved to the confirmed punching position  204  of the succeeding sheet  201  and the succeeding sheet  201  is yet to be punched. 
     In the present embodiment, the left end position of the leading end of the succeeding sheet  201  is measured by the line sensor  68 , and then the preliminary movement of the punching device  60  is started. Therefore, the lateral movement amount of the punching device  60  required while conveying the succeeding sheet  201  by the distance L can be set to the distance  206  smaller than the maximum displacement amount  205  by the amount of the preliminary movement. If the lateral movement amount is the distance  206 , the lateral movement of the punching device  60  to the punching position  204  of the succeeding sheet  201  can be completed. 
     Control of Punching Process 
     The operation of the preceding sheet  200  and the succeeding sheet  201  has been described above in time series with reference to  FIGS. 7A to 7E . Next, a control method for this operation will be described with reference to a flowchart of  FIG. 8 .  FIG. 8  is a flowchart illustrating control by the main controller  101  in  FIG. 5 . In  FIG. 8 , in step S 1 , the main controller  101  waits for information about whether to perform the punching process on the succeeding sheet  201 . This is performed on the basis of a result of communication of the main controller  101  with the video controller  119  illustrated in  FIG. 4  via the communication portion  315 . That is, the main controller  101  makes the determination by detecting whether or not an instruction for a print job from an external device such as a personal computer or an instruction for printing or copying input by a user operation on an unillustrated operation panel has been received by the main controller  101  via the communication portion  315 . 
     Then, in the case where the succeeding sheet  201  is to be punched, in step S 2 , the estimated movement amount calculation portion  113  in the main controller  101  monitors a signal from the pre-puncher sensor  63  via the sensor controller  116 , and waits for the leading end of the succeeding sheet  201  to be detected by the pre-puncher sensor  63 . In step S 3 , with the timing at which the leading end of the succeeding sheet  201  is detected by the pre-puncher sensor  63  as the starting point, the main controller  101  waits for the left end of the leading end of the succeeding sheet  201  to reach the line sensor  68 . Then, in step S 4 , the left end position of the leading end of the succeeding sheet  201  is measured by the line sensor  68 . In step S 5 , the estimated punching position of the succeeding sheet  201  is calculated from the measurement result of the line sensor  68 . In step S 6 , the estimated movement amount, which is the lateral movement amount from the current position of the punching device  60  to the estimated punching position of the succeeding sheet  201 , is calculated. 
     In step S 7 , whether or not the calculated estimated lateral movement amount is larger than the execution determination threshold value of the preliminary movement is determined. In the present embodiment, in the case where the estimated lateral movement amount is equal to or smaller than the execution determination threshold value of the preliminary movement, that is, in the case where the result of step S 7  is No, the preliminary movement is not performed. The execution determination threshold value is set as a value smaller than the movement amount by which the punching device  60  can laterally move in a time after the left end position of the succeeding sheet  201  at the punching position  204  is detected by the line sensor  68  and before the punching position  204  of the succeeding sheet  201  is conveyed to a predetermined position at which the punching process is performed. 
     In the case where the estimated movement amount is smaller than the execution determination threshold value, the lateral movement of the punching device  60  can be completed before the punching process on the succeeding sheet  201  even if the lateral movement is started after the left end position of the succeeding sheet  201  at the punching position  204  is detected by the line sensor  68 . According to such a configuration, the lateral movement does not have to be executed twice for the preliminary movement and the confirmed movement to the confirmed punching position of the succeeding sheet  201 . A configuration like the present embodiment may be employed in the case where noise of motor caused by increase in the number of times of the lateral movement is problematic. However, if there is no problem concerning the noise or the like, a configuration in which a threshold value for execution determination is not provided and the preliminary movement is necessarily performed regardless of the value of the estimated movement amount may be employed. 
     In the case where the estimated movement amount is larger than the execution determination threshold value, that is, in the case where the result of step S 7  is Yes, the preliminary movement of the punching device  60  is started in step S 8 . After the start of the preliminary movement, the punching position  204  of the succeeding sheet  201  is confirmed, and processing of calculating the movement amount of confirmed movement is performed. In step S 9 , the lateral movement confirmed position calculation portion  115  in the main controller  101  waits for the left end position of the succeeding sheet  201  at the punching position  204  to reach the line sensor  68  with the timing at which the leading end of the succeeding sheet  201  is detected by the pre-puncher sensor  63  as a starting point. Then, in step S 10 , the left end position of the succeeding sheet  201  is measured by the line sensor  68  when the left end position of the succeeding sheet  201  at the punching position  204  reaches the line sensor  68 . 
     In step S 11 , the confirmed punching position of the succeeding sheet  201  is calculated from the measurement result of the line sensor  68 . In step S 12 , confirmed movement amount, which is the lateral movement amount from the current position of the punching device  60  to the confirmed punching position of the succeeding sheet  201 , is calculated. Then, in step S 13 , the movement to the confirmed position, that is, the confirmed movement is started. The completion of the confirmed movement is waited for in step S 14 , and the confirmed movement is stopped in step S 15  when the confirmed movement is completed. 
     Upper Limit of Preliminary Movement 
     In the present embodiment, an upper limit is set for the movement amount in the preliminary movement as described above, and this upper limit is set to a value equal to the estimated movement amount. In the case where the punching position  204  of the succeeding sheet  201  is confirmed during the preliminary movement before the movement amount reaches the upper limit, the confirmed movement is performed without continuing the preliminary movement to the upper limit.  FIGS. 7A to 7E  illustrate this example, that is, the motion of the punching device  60  in the case where the distance between the punching positions of the preceding sheet  200  and the succeeding sheet  201  in the lateral direction is small. 
     In contrast, in the case where the punching position  204  of the succeeding sheet  201  is not confirmed even when the movement amount of the preliminary movement has reached the upper limit, the preliminary movement is stopped, and the confirmed movement is started after waiting for the punching position  204  of the succeeding sheet  201  to be confirmed. That is, the main controller  101  stops the preliminary movement in the case where the movement amount of the preliminary movement has reached a predetermined upper limit value after the preliminary movement is started and before the punching position  204  of the succeeding sheet  201  is confirmed. The motion of the punching device  60  in this example, that is, the motion of the punching device  60  in the case where the distance between the punching positions of the preceding sheet  200  and the succeeding sheet  201  in the lateral direction is large will be described with reference to  FIGS. 9A to 9E . In  FIGS. 9A to 9E , the same elements as in  FIGS. 7A to 7E  will be denoted by the same reference numerals and description thereof will be omitted. 
       FIG. 9A  illustrates a moment when the leading end of the succeeding sheet  201  is detected by the pre-puncher sensor  63 .  FIG. 9B  illustrates a moment when the left end position of the leading end of the succeeding sheet  201  is detected by the line sensor  68 .  FIG. 9C  illustrates a state in the middle of the preliminary movement of the punching device  60 . 
       FIG. 9D  illustrates a state in which the preliminary movement amount of the punching device  60  has reached the upper limit serving as a predetermined upper limit value and the lateral movement of the punching device  60  has been stopped. The upper limit is equal to the estimated movement amount. At this time, the left end position of the succeeding sheet  201  at the punching position  204  has not been detected by the line sensor  68  yet. The lateral position of the punching device  60  is maintained at this position. 
       FIG. 9E  illustrates a timing when the left end position of the succeeding sheet  201  at the punching position  204  is detected by the line sensor  68 . At this timing, the position of the punching position  204  of the succeeding sheet  201  is confirmed, and the confirmed movement of the punching device  60  is started. Since the difference between the estimated punching position and the confirmed punching position is sufficiently smaller than the distance by which the punching device  60  can be laterally moved in the time in which the sheet is conveyed by the distance L, the confirmed movement is completed without a problem. 
     As described above, in the present embodiment, the left end position of the leading end of the succeeding sheet  201  is detected by the line sensor  68 , thus the punching position  204  of the succeeding sheet  201  is estimated, and the preliminary movement of the punching device  60  is started on the basis of the estimated value. As a result of this, the lateral movement of the punching device  60  between sheets can be completed even in the case where sheets displaced from each other by the maximum displacement amount are successively conveyed, and thus the punching can be performed with high accuracy. Therefore, the movement of the punching device can be completed even in the case where distance L between the line sensor and the predetermined position at which the punching is to be performed by the punching device is smaller than in the case where the movement of the punching device is started after detecting the end portion position of the succeeding sheet at a punching position by the line sensor. If the distance L can be reduced as described above, the productivity can be improved. That is, according to the present embodiment, the productivity can be improved in the case where a punching process is performed on sheets that are successively conveyed. 
     In addition, increase in the size of the apparatus can be avoided because the distance L between the line sensor  68  and a punching position can be reduced. Further, since the puncher lateral movement motor  74  serving as a drive source of the punching device  60  does not have to be driven at high speed, an expensive motor does not have to be used as this motor, and thus the cost can be reduced. 
     Second Embodiment 
     A second embodiment will be described with reference to  FIGS. 10 and 11 . In the first embodiment described above, a value equal to the estimated movement amount is set as the upper limit of the preliminary movement amount. Therefore, a special value does not have to be calculated as the upper limit of the preliminary movement amount. In contrast, in the present embodiment, the upper limit of the preliminary movement amount serving as a predetermined upper limit value can be set to an arbitrary value. The arbitrary value is not necessarily equal to the preliminary movement amount, and an appropriate amount is calculated for each apparatus. The other elements and effects are substantially the same as those of the first embodiment described above. Therefore, the substantially same elements will be denoted by the same reference signs, and illustration and description thereof will be simplified or omitted. Mainly points different from the first embodiment will be described below. 
       FIG. 10  is a block diagram illustrating a functional configuration of an image forming system of the present embodiment. This block diagram is different from the block diagram of the first embodiment illustrated in  FIG. 5  in that a preliminary movement amount calculation portion  120  is added. 
     First, a problem of the case where the upper limit of the preliminary movement amount is equal to the estimated movement amount in the first embodiment will be described.  FIG. 11  illustrates a case where a sheet is conveyed in a skewed state. A sheet can be conveyed in a skewed state depending on various factors such as the mechanical configuration of the apparatus, the use state of the rollers, and the state of the sheet. In this case, successively conveyed sheets are conveyed in similar skew angles. In  FIG. 11 , the value of the estimated movement amount calculated by measuring the left end position of the leading end of a succeeding sheet  212  with respect to a punching position  213  of a preceding sheet  210  by the line sensor  68  in the case where the succeeding sheet  212  is not conveyed in a skewed state is a distance  216 . Here, since the punching position of the succeeding sheet is estimated on the premise that the succeeding sheet is not conveyed in a skewed state, the calculation is performed assuming that the succeeding sheet  212  is conveyed in a state indicated by a dot line in  FIG. 11 . Therefore, the punching position of the succeeding sheet  212  is estimated as a punching position  215 . 
     However, in actuality, the succeeding sheet  211  is conveyed in a skewed state as indicated by a solid line. In the case where the punching position of the actual succeeding sheet  211  is confirmed by measuring the left end of the actual succeeding sheet  211  at the punching position thereof by the line sensor  68 , the punching position is a position indicated as a punching position  214 . If an amount equal to the estimated movement amount is set as the preliminary movement amount, in the case where inter-punching distance is large, the punching device  60  moves by the distance  216  in the preliminary movement, and the lateral movement thereof stops there. Then, if the punching position of the succeeding sheet  211  is confirmed by measuring the left end of the succeeding sheet  211  at the punching position by the line sensor  68 , the punching position is confirmed as the punching position  214 , and the movement amount from the punching position  213  of the preceding sheet  210  is a distance  217 . This amount is smaller than the distance  216  calculated as the estimated movement amount. 
     In this case, if the punching device  60  moves by the distance  216  in the preliminary movement, the punching device  60  laterally moves in a direction opposite to the preliminary movement in the confirmed movement. In the case where sheets are conveyed in a skewed state as described above, the sheets are often successively conveyed in similar skew angles, and therefore the operation described above is repeated. As a result, the lateral movement amount of the punching device  60  becomes large. This increases the noise caused by the lateral movement of the punching device  60 , and also increases the power consumption of the puncher lateral movement motor  74 , which is a drive source of the lateral movement. In addition, in the case where there are constituent parts having lifetime corresponding to the lateral movement distance, the lifetime of those constituent parts is shortened. 
     The present embodiment can be preferably applied to an apparatus for which it is known in advance that sheets are successively conveyed in such skew angles that the distance  217  of the confirmed movement amount is smaller than the distance  216  of the estimated movement amount as described above. Therefore, in the present embodiment, the preliminary movement amount calculation portion  120  sets the upper limit of the preliminary movement amount to a value smaller than the estimated movement amount of the state in which the succeeding sheet is not skewed. In this case, the upper limit of the preliminary movement amount is set so as to satisfy the following. That is, the upper limit of the preliminary movement amount is set such that the remaining movement amount to reach the estimated movement amount is such a value that the lateral movement of the punching device  60  can be completed before the start of punching on the succeeding sheet even in the case where the lateral movement of the punching device  60  is started after the left end of the succeeding sheet at the punching position thereof is measured by the line sensor  68 . 
     In this manner, excessive lateral movement can be avoided even if the sheet is conveyed in a skewed state. In addition, although the punching device  60  does not move by the distance  216  in the preliminary movement also in the case where the sheet is not skewed, that is, also in the case where the distance  217  of the confirmed movement amount is equal to the distance  216  of the preliminary movement amount, the remaining movement amount to the distance  216  is set to the amount described above. Therefore, the lateral movement of the punching device  60  for punching the succeeding sheet can be completed without a problem. 
     To be noted, in the present embodiment, an example in which the upper limit of the preliminary movement amount is set to an arbitrary value smaller than the estimated movement amount in the case where sheets are successively conveyed in similar skew angles, that is, in the case where the confirmed movement amount is smaller than the estimated movement amount, has been described. 
     However, depending on the configuration of the apparatus, there can be a case where the skew angles of the successively conveyed sheets are not similar. In this case, the confirmed movement amount can be larger than the estimated movement amount. In the case of such an apparatus configuration, the upper limit of the preliminary movement amount may be set on the basis of an assumed confirmed movement amount such that the lateral movement of the punching device  60  in the confirmed movement is completed before the start of the punching on the succeeding sheet. As described above, how the conveyed sheets are skewed differ between apparatuses, and therefore an optimal upper limit of the preliminary movement amount may be determined for each apparatus. 
     Third Embodiment 
     A third embodiment will be described with reference to  FIGS. 12, 13A, and 13B . In each embodiment described above, the punching position of the succeeding sheet is estimated from the end portion of the succeeding sheet in the width direction at the leading end thereof detected by the line sensor  68 . In contrast, in the present embodiment, the punching position of the succeeding sheet is estimated on the basis of information of the length of the preceding sheet and the succeeding sheet in the width direction. This information will be also referred to as sheet width information. The other elements and effects are substantially the same as those of the first embodiment described above. Therefore, the substantially same elements will be denoted by the same reference signs, and illustration and description thereof will be simplified or omitted. Mainly points different from the first embodiment will be described below. 
       FIG. 12  is a block diagram illustrating a functional configuration of an image forming system of the present embodiment. Unlike in the block diagram of the first embodiment illustrated in  FIG. 5 , the estimated movement amount calculation portion  113  receives sheet width information from the communication portion  315 , and the estimated movement amount can be calculated on the basis of this sheet width information. To be noted, the estimated movement amount calculation portion  113  of the present embodiment also has the function of calculating the estimated movement amount by measuring the left end position of the succeeding sheet at the leading end thereof by the line sensor  68  similarly to the first and second embodiments. 
       FIGS. 13A and 13B  illustrate a case where a succeeding sheet  220  has a smaller width than the preceding sheet  200 , that is, has a smaller length than the preceding sheet  200  in the width direction, and the sheets of this combination are successively conveyed. 
     Conventionally, in most apparatuses, when successively printing sheets of different widths, to avoid heating of an end portion of the fixing unit, the interval between the successively conveyed sheets, that is, the so-called sheet interval is increased by a throughput down operation or the conveyance of sheets is temporarily stopped by a cycle down operation. However, according to recent technical advancement in fixing units and fixing control, apparatuses that successively convey sheets of different widths without increasing the sheet interval in successive printing of sheets of different widths have become more recognizable. 
     In the present embodiment, sheets are conveyed in a center-referenced manner, and therefore the punching position of a sheet is determined mainly in accordance with the sheet width thereof. To be noted, a “center-referenced” manner is a conveyance method in which conveyance is performed such that the center positions of successively conveyed sheets coincide. 
     In  FIG. 13A , a punching position  221  of the succeeding sheet  220  is laterally displaced from the punching position  203  of the preceding sheet  200  by a distance  222 . This distance  222  is calculated on the basis of the sheet widths of the preceding sheet  200  and the succeeding sheet  220 . In the case where this distance  222  is larger than the maximum movement amount by which the punching device  60  can be laterally moved in a time in which a sheet is conveyed by the distance L from the line sensor  68  to the punching position thereof, the lateral movement cannot be completed before the start of the punching process on the succeeding sheet  220 . 
     Therefore, in the present embodiment, the estimated movement amount calculation portion  113  obtains, via the communication portion  315 , the sheet width information input from an external device or designated by a user, and the estimated punching position is determined on the basis of this sheet width information. That is, the main controller  101  estimates the punching position of the succeeding sheet  220  from the relationship between the length in the width direction, that is, the sheet width of the preceding sheet  200 , and the sheet width of the succeeding sheet  220 . 
     In the case where the length of the preceding sheet  200  in the width direction is different from the length of the succeeding sheet  220  in the width direction, the preliminary movement of the punching device  60  can be started at the following timing. That is, as in the first and second embodiments described above, the movement of the punching device  60  can be started on the basis of the information of the sheet width before the end portion position of the succeeding sheet  220  in the width direction at the leading end thereof reaches the line sensor  68 . As a result of this, the lateral movement of the punching device can be completed by performing the preliminary movement without providing a large sheet interval even in the case of successive conveyance of sheets of different sheet widths. 
     To be noted, the estimated movement amount calculation portion  113  may update the estimated movement amount by measuring the left end position of the leading end of the succeeding sheet  220  by the line sensor  68  similarly to the first and second embodiments after calculating the estimated movement amount based on the sheet width information. 
     That is, the main controller  101  estimates the punching position of the succeeding sheet  220  from the relationship between the length of the preceding sheet  200  in the width direction and the length of the succeeding sheet  220  in the width direction. Then, a first estimated movement amount, which is a movement amount from the position of the punching device  60  at the end of the punching process on the preceding sheet  200  to the estimated punching position of the succeeding sheet  220 , is calculated. In addition, the main controller  101  estimates the punching position of the succeeding sheet  220  from the end portion position of the succeeding sheet  220  in the width direction Y at the leading end thereof in the conveyance direction detected by the line sensor  68 . Then, a second estimated movement amount, which is a movement amount from the position of the punching device  60  at the end of the punching process on the preceding sheet  200  to the estimated punching position of the succeeding sheet  220 , is calculated. The main controller  101  causes one or more of first preliminary movement in which the preliminary movement is performed on the basis of the first estimated movement amount and second preliminary movement in which the preliminary movement is performed on the basis of the second estimated movement amount. 
     For example, the main controller  101  starts the first preliminary movement after the punching process on the preceding sheet  200  is finished and before the end portion position of the succeeding sheet  220  in the width direction Y at the leading end thereof in the conveyance direction X reaches the line sensor  68 . Then, the second preliminary movement is performed after the end portion position of the succeeding sheet  220  in the width direction Y at the leading end thereof in the conveyance direction X reaches the line sensor  68 . 
     This state is illustrated in  FIG. 13B . The distance  222  is the estimated movement amount based on the sheet width information serving as the first estimated movement amount. Since there is a possibility that the actual conveyance position of the succeeding sheet  220  is displaced in the lateral direction, a punching position  223  is estimated by measuring the left end position of the leading end portion of the succeeding sheet  220  by the line sensor  68 . A distance  225  is the estimated movement amount obtained by measurement by the line sensor  68  serving as the second estimated movement amount. 
     Displacement of punching position derived from the sheet width itself is estimated by using the sheet width information, and displacement of punching position derived from sheet conveyance is estimated by using a measurement value of a line sensor. By sequentially performing the preliminary movement on the basis of each estimation, punching can be performed with high accuracy without increasing the sheet interval even in the case of successively conveying sheets of different sheet widths. 
     Other Embodiments 
     Although the preliminary movement is started at a timing at which the leading end of the succeeding sheet reaches the line sensor, the preliminary movement may be started at a timing at which any position between the leading end of the succeeding sheet and the punching position reaches the line sensor. In short, the preliminary movement may be started at any timing as long as the preliminary movement can be started before the end portion position of the succeeding sheet in the width direction at the punching position reaches the line sensor. As a result of this, the movement of the punching device can be completed even in the case where the distance L from the line sensor to a predetermined position at which punching is performed by the punching device is smaller than in the case where the movement of the punching device is started after the end portion position of the succeeding sheet at the punching position is detected by the line sensor. 
     Although a case where the main controller  101  serving as a controller is included in a sheet processing apparatus has been described, the controller may be included in an image forming apparatus instead of in the sheet processing apparatus. 
     Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2020-041338, filed Mar. 10, 2020 which is hereby incorporated by reference herein in its entirety.