Side position stapler for post-processing device

A sheet post-processing device receives a sheet from an image forming apparatus conveys a plurality of the sheets to a staple tray to form a sheet pile, and staples the sheet pile with a stapler. The stapler is arranged along a first side of the staple tray in a sheet width direction and has an opening for taking in a second side of the sheet pile when stapling the sheet pile at a staple position. The stapler unit is arranged at a position that a central portion of the second side of the sheet pile is situated inside the opening, and the staple position is located downstream of an alignment surface of an aligning member in a sheet conveying direction that aligns ends of the sheets in the sheet pile.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2008-189607 filed in Japan on Jul. 23, 2008 and Japanese Patent Application No. 2009-025702 filed in Japan on Feb. 6, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet post-processing device that processes sheets output from an image forming apparatus.

2. Description of the Related Art

Japanese Patent Application Laid-open No. 2007-31134 discloses a sheet post-processing device that receives a sheet from an image forming apparatus, temporarily piles sheets on a staple tray, staples an end of the sheet pile if required, and discharges the stapled sheet pile out of the sheet post-processing device. In this sheet post-processing device, a stapler that staples the sheet pile is arranged upstream of the staple tray in a sheet conveying direction.

However, arrangement of the stapler upstream of the staple tray in the sheet conveying direction disadvantageously leads to an increase in the length of the sheet post-processing device in the sheet conveying direction.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a sheet post-processing device that receives a sheet from an image forming apparatus and, directly discharges the sheet to outside when no post-processing is to be performed on the sheet, performs post-processing on the sheet and discharges post-processed sheet to outside when post-processing is to be performed on the sheet. The sheet post-processing unit includes a tray member configured to accumulate a plurality of the sheet as a sheet pile, the tray member having a first side that is parallel to a sheet width direction; an end aligning member having an end alignment surface configured to align trailing ends of the sheets in the sheet pile; and a stapler unit is configured to staple together the sheet pile at a second side thereof at a staple position, the stapler unit having an opening in which the second side of the sheet pile is inserted. The stapler unit is arranged near the first side of the tray member such that a central portion of the second side of the sheet pile is situated inside the opening of the stapler unit, and the staple position is located downstream of the alignment surface of the aligning member in a sheet conveying direction.

According to another aspect of the present invention, there is provided an image forming system that includes an image forming apparatus that forms an image onto a sheet based on image data; and the above sheet post-processing device. The sheet post-processing device receives the sheet with the image from the image forming apparatus and further processes the sheet if required.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. An image forming system1according to a first embodiment of the present invention includes, as illustrated inFIG. 16, a scanning unit (scanning device)3that scans an image from an original that is placed on an exposure glass2; an image forming unit (image forming apparatus)5that forms the image that is obtained by the scanning unit3on a sheet T; a sheet supply unit7that supplies the sheet T to the image forming unit5; and a sheet post-processing unit (sheet post-processing device)9that receives the sheet T on which the image is formed from the image forming unit5, post-processes (e.g., staples) the sheet T if required, and discharges the post-processed sheet T out of the sheet post-processing unit9. A platen40is provided onto the exposure glass2with a hinge in such a manner that the platen40can open and close.

The image forming system1includes an operation unit37that sends an operation signal, such as a paper-feed signal, to a later-described control unit27. The operation signal is sent to the control unit27in response to an instruction that is received via a control panel39that is arranged adjacent to the scanning unit3. A user can select a size of a sheet to be supplied to the image forming unit5and decide various settings including the number of copies via the control panel39.

The image forming unit5includes an image carrier on which an electrostatic latent image corresponding to the image obtained by the scanning unit3is formed; a developing unit that develops the electrostatic latent image on the image carrier with toner, thereby forming a toner image; a transferring unit that transfers the toner image onto the sheet T; and a fixing unit that fixes the transferred toner image onto the sheet T.

The scanning unit3includes an exposure lamp and a plurality of mirrors. The exposure lamp emits light to the original. The mirrors receive the light reflected from the original, and guide the light to the image carrier.

The sheet supply unit7includes sheet cassettes7a,7b, and7cthat are arranged in this order with the sheet cassette7abeing at the bottom. The sheet cassette7aaccommodates B5-sized sheets as the sheet T. The sheet cassette7baccommodates B4-sized sheets as the sheet T. The sheet cassette7caccommodates A4-sized sheets as the sheet T.

The sheet post-processing unit9is arranged between the scanning unit3that is located in an upper part of the image forming system1and the image forming unit5that is located in a lower part of the image forming system1.

A post-processing-unit conveyer path6is arranged inside a housing of the image forming system1. The sheet T on which the image is formed is conveyed from the image forming unit5to the sheet post-processing unit9through the post-processing-unit conveyer path6. A pair of conveyer rollers26is arranged upstream in the post-processing-unit conveyer path6. A pair of conveyer rollers28and a sheet leading-end sensor31are arranged in the middle of the post-processing-unit conveyer path6. The sheet leading-end sensor31detects an edge of the sheet.

A downstream end of the post-processing-unit conveyer path6in the sheet conveying direction is connected to a sheet entrance port4of the sheet post-processing unit9.

The sheet post-processing unit9includes a staple tray11and a discharge tray8. If the sheet T is to be post-processed, after conveyed from the image forming unit5, the sheet T is conveyed onto the staple tray11, and temporarily placed on the staple tray11. After post-processed (stapled), the sheet T is discharged onto the discharge tray8. If no post-processing is to be carried out, the sheet T is directly conveyed onto the discharge tray8.

A discharge path10extends downstream of the sheet entrance port4in a substantially horizontal manner. The discharge path10guides the sheet T from the sheet entrance port4to either the staple tray11or the discharge tray8.

A pair of entrance rollers12aand12bis arranged upstream in the discharge path10. A pair of staple-tray entrance rollers14aand14bis arranged in the discharge path10. A sheet trailing-end sensor33that detects a trailing end Tc of the sheet T is arranged near a nip between the entrance rollers12aand12b. The entrance roller12ais a driving roller while the entrance roller12bis a driven roller.

The staple-tray entrance roller14ais a driving roller. As illustrated inFIG. 1, the staple-tray entrance roller14ais a part of an assembly that includes a driving shaft extending in a sheet width direction and the staple-tray entrance roller14aand one more roller fixedly arranged on this driving shaft. The rollers in the staple-tray entrance roller assembly are arranged near the center of a width of the staple tray11in the sheet width direction, spaced from each other.

The staple-tray entrance roller14bis a driven roller. An assembly to which the staple-tray entrance roller14bbelongs is not visible inFIG. 1. The structure of this assembly is similar to the assembly to which the staple-tray entrance roller14abelongs. The structure of the entrance rollers12aand12bis similar to the structure of the staple-tray entrance roller14a.

The staple-tray entrance roller14ais rotated by a roller driving motor20. More particularly, a gear (not shown) that is fixed to a driving shaft of the roller driving motor20is engaged with a gear that is fixed to the driving shaft of the staple-tray entrance roller14a. Therefore, the staple-tray entrance roller14arotates when the roller driving motor20rotates. The driving shaft of the roller driving motor20and the driving shaft of the staple-tray entrance roller14aare arranged parallel to each other. Those driving shafts are supported by a single bearing rotatably in such a manner that the driving shafts cannot move in a shaft extending direction.

The staple-tray entrance roller14acan move together with the roller driving motor20in the sheet width direction away from a home position H by operation of a roller moving mechanism22. The roller moving mechanism22includes a pinion (not shown), a stepping motor (not shown) that rotates the pinion, and a rack (not shown) that engages with the pinion and is attached to the bearing. The rack can move in the sheet width direction. The roller moving mechanism22is controlled by the control unit27.

A tapping roller16is arranged downstream of the staple-tray entrance rollers14aand14b. The tapping roller16aligns the trailing end Tc of the sheet T that is conveyed onto the staple tray11. The tapping roller16is rotatably supported by an end of an arm the other end of which is swingably supported by the housing. The tapping roller16can move between a contact position where the tapping roller16is in contact with a sheet surface and a non-contact position where the tapping roller16is away from the sheet surface. Rotation of the tapping roller16and swing of the arm that supports the tapping roller16are controlled by the later-described control unit27.

A pair of discharge rollers18(18a,18b) discharges the sheet T onto the discharge tray8. The discharge roller18ais a driving roller while the discharge roller18bis a driven roller. The discharge roller18ais arranged downstream of the tapping roller16. The discharge roller18ais rotatably supported by an end of a discharge-roller supporting arm65the other end of which is swingably supported by the housing. The discharge roller18acan move between a discharge position where the discharge roller18ais in contact with the sheet surface and a non-discharge position where the discharge roller18ais away from the sheet surface. The discharge-roller supporting arm65and the arm that supports the tapping roller16do not interfere with each other, even when those arms are swinging. Rotation of the discharge roller18aand swinging of the discharge-roller supporting arm65are controlled by the later-described control unit27.

The discharge roller18bis arranged opposed to the discharge roller18aand downstream of the staple tray11in the sheet conveying direction. A sheet discharge sensor35is arranged near a nip between the discharge rollers18aand18b.

The staple tray11is arranged under the staple-tray entrance rollers14aand14bon an inclined plane with an upstream end of the staple tray11being lower than a downstream end of the staple tray11.

A back-end fence13is attached to the staple tray11near the upstream end in the sheet conveying direction. The back-end fence13is used to align the trailing end Tc of the sheet T that is conveyed onto the staple tray11.

A cross section of the back-end fence13is shaped like a bracket. As illustrated inFIG. 1, the back-end fence13has a trailing-end receiving surface15that receives the trailing end Tc. The trailing-end receiving surface15is an inner surface of a longitudinal side of the bracket. The back-end fence13is arranged in such a manner that the longitudinal side extends in the sheet width direction and the bracket opens toward downstream in the sheet conveying direction.

A reverse roller24that aligns the trailing end Tc is arranged above the staple tray11immediately near the downstream side of the back-end fence13. The reverse roller24is controlled by the later-described control unit27.

A side fence17that is used to align the sheet sides is arranged on a first side of the staple tray11in the sheet width direction. A surface of the side fence17is arranged substantially perpendicular to the surface of the staple tray11. The side fence17is arranged in such a manner that a longitudinal side is perpendicular to the sheet width direction.

A jogger fence19that is used to align the sheet sides is arranged on a second side of the staple tray11in the sheet width direction. A surface of the jogger fence19is arranged substantially perpendicular to the surface of the staple tray11, and substantially parallel to the surface of the side fence17. That is, a longitudinal side of the jogger fence19is perpendicular to the sheet width direction. The jogger fence19can move in the sheet width direction by operation of a fence moving mechanism21. A home position of the jogger fence19is set away from the side fence17as far as possible.

The fence moving mechanism21includes a pinion, a rack that engages with the pinion and is attached to the jogger fence19, and a stepping motor that rotates the pinion. The rack can move in the sheet width direction.

A stapler23is arranged on the first side of the staple tray11near an upstream end of the side fence17in the sheet conveying direction. The stapler23staples an end of the sheet pile that is placed on the staple tray11.

The stapler23is arranged in such a manner that an opening25from which the sheets are inserted to the stapler23opens toward the center of the sheet width, and a staple position30as a target position to be stapled is set downstream of the trailing-end receiving surface15of the back-end fence13in the sheet conveying direction. The opening25is provided to a first stapler end23aof the stapler23.

The first stapler end23ais closer to the center of the sheet width of the staple tray11(closer to the jogger fence19) than a first side Ta of the sheet T is, if the sheet T is A3 size or B4 size. Assume that the sheet post-processing unit9cannot receive a sheet larger than the A3 sheet.

The discharge tray8includes a swinging member8athat forms a part of a surface of the discharge tray8. An end of the swinging member8ais supported by a shaft extending along a width of the discharge tray8in the sheet width direction, and the other end of the swinging member8ais positioned near an upstream end of the discharge tray8in the sheet conveying direction. When the swinging member8aswings in a direction indicated by an arrow P illustrated inFIG. 16, the sheet T that is placed on the discharge tray8moves toward the upstream end of the discharge tray8due to the weight of the sheet T. The swinging member8ais always pushed upward by a coil spring force, and is stopped by a later-described back-end stopper29directly or via the sheet T. The swinging member8aswings in the direction indicated by the arrow P, when a solenoid is ON. The swinging member8aswings in the direction reverse to the direction indicated by the arrow P, when the solenoid is OFF. The swinging member8ais controlled by the control unit27.

The back-end stopper29is swingably arranged under the discharge roller18b, opposed to the swinging member8a. The back-end stopper29stops the trailing end Tc of the sheet T that is placed on the discharge tray8. The back-end stopper29is always pushed by a coil spring force toward a stop position. The stop position is a position at which, if no sheet is placed on the discharge tray8, the swinging member8ais in contact with the back-end stopper29. The back-end stopper29swings away from the stop position to a release position, when a solenoid is ON. The back-end stopper29swings from the release position to the stop position, when the solenoid is OFF.

The configuration of the control unit27is described with reference toFIG. 15. A receiving unit38receives signals from the sheet leading-end sensor31, the sheet trailing-end sensor33, the sheet discharge sensor35, and the operation unit37. A determining unit41determines a current situation based on information that is received from the receiving unit38.

A sheet-size comparing unit43compares a sheet size that is selected via the control panel39with a reference sheet size. Assume that the reference sheet size is B4 size.

A roller moving-direction deciding unit49decides a direction in which the staple-tray entrance rollers14aand14bare to be moved (hereinafter, “roller moving direction”) from a result of the comparison by the sheet-size comparing unit43. More particularly, if the selected sheet size is equal to or larger than the reference sheet size, the roller moving direction is decided as the sheet width direction toward the second side Tb of the staple tray11(i.e., toward the jogger fence19). If the selected sheet size is smaller than the reference sheet size, the roller moving direction is decided as the sheet width direction toward the first side Ta of the staple tray11(i.e., toward the side fence17).

A roller moving-distance calculating unit51calculates a moving distance U by which the staple-tray entrance rollers14aand14bare to be moved according to the sheet size that is selected via the control panel39. The moving distance U is decided in such a manner that a distance between the first side Ta and the first stapler end23aof the stapler23in the sheet width direction becomes M with the first side Ta being closer to the jogger fence19than the first stapler end23ais. The distance M is several millimeters. More particularly, if the sheet T is equal to or larger than the reference sheet size, the calculated moving distance U is a sum of the distance M and a distance between the first side Ta and the first stapler end23ain the sheet width direction that is measured before the sheet T is moved in the sheet width direction. If the sheet T is smaller than the reference sheet size, the calculated moving distance U is a difference between the distance M and the distance between the first side Ta and the first stapler end23ain the sheet width direction that is measured before the sheet T is moved in the sheet width direction.

A fence moving-distance calculating unit47calculates a moving distance V between the home position of the jogger fence19and a target position to which the jogger fence19is to be moved to receive the sheet T (hereinafter, “sheet receiving position”) from the sheet size that is selected via the control panel39, the roller moving direction, and the moving distance U. More particularly, the moving distance V is decided in such a manner that, after the sheet T is moved in the sheet width direction by the staple-tray entrance rollers14aand14b, a distance between a second side Tb, which is opposite to the first side Ta, and the jogger fence19in the sheet width direction becomes N. The distance N is several millimeters. If the sheet T is equal to or larger than the reference sheet size, the calculated moving distance V is a value that is obtained by subtracting a sum of the moving distance U and the distance N from a distance between the second side Tb and the home position of the jogger fence19that is measured before the sheet T is moved in the sheet width direction. If the sheet T is smaller than the reference sheet size, the moving distance V is a value that is obtained by subtracting the distance N from the sum of the moving distance U and the distance between the second side Tb and the home position of the jogger fence19that is measured before the sheet T is moved in the sheet width direction.

A processing unit55performs processes according to the determination made by the roller moving-direction deciding unit49, results of the calculation by the roller moving-distance calculating unit51and the fence moving-distance calculating unit47.

A sending unit57sends contents of the processes performed by the processing unit55to the fence moving mechanism21, the roller moving mechanism22, and the roller driving motor20. The control unit27includes a timer50.

The image forming system1has three modes including a direct discharge mode in which after the sheet T is conveyed from the image forming unit5, the sheet T is directly discharged without being subjected to any post-process; an alignment mode in which the sheet T is conveyed onto the staple tray11, the trailing end Tc and the sides are aligned on the staple tray11, and the aligned sheet pile is discharged; and a stapling mode in which the sheet pile is stapled on the staple tray11after the alignment, and the stapled sheet pile is discharged. The user selects one of the modes with the control panel39.

The operation of the image forming system1is described with four different cases. In a first case that is described below, the user selects the B4-sized sheet as the sheet T and the stapling mode with the control panel39.

The user opens the platen40, places the original on the exposure glass2, and closes the platen40. The user inputs various settings via the control panel39, more particularly, selects the B4-sized sheet as the sheet T and specifies the number of copies. After that, the user presses a paper feed button. When the image forming system1receives the paper-feed signal, the scanning unit3scans the image from the original, and the B4-sized sheet is conveyed as the sheet T from the sheet cassette7bto the image forming unit5. The image that is obtained by the scanning unit3from the original is formed on the sheet T. The sheet T on which the image is formed is conveyed to the sheet post-processing unit9via the post-processing-unit conveyer path6.

The operation of the sheet post-processing unit9is described below. The sheet-size comparing unit43compares the sheet size (B4 size) that is selected via the control panel39with the reference sheet size (B4 size). Because the selected sheet size is equal to or larger than the reference sheet size, the roller moving-direction deciding unit49decides the roller moving direction in which the staple-tray entrance rollers14aand14bare to be moved as the sheet width direction toward the jogger fence19. The roller moving-distance calculating unit51calculates the moving distance U by which the staple-tray entrance rollers14aand14bare to be moved in such a manner that, after the sheet T is moved, the distance between the first side Ta and the first stapler end23ain the sheet width direction in the sheet width direction becomes M. The fence moving-distance calculating unit47calculates the moving distance V between the home position and the sheet receiving position of the jogger fence19in such a manner that, after the sheet T is moved, the distance between the second side Tb and the jogger fence19in the sheet width direction becomes N. With this configuration, a distance by which the jogger fence19is to be moved to align the sheet sides is fixed to a sum of M, N, and L, regardless of the sheet size, where L is distance between the sheet receiving surface of the side fence17and the first stapler end23ain the sheet width direction.

The operation of the sheet post-processing unit9is described with reference toFIG. 14. The determining unit41determines whether the sheet leading-end sensor31has turned to a detection state (Step S1). If the determining unit41determines that the sheet leading-end sensor31is still in non-detection state (No at Step S1), the process control repeats Step S1. If the determining unit41determines that the sheet leading-end sensor31has turned to the detection state (Yes at Step S1), the processing unit55moves the jogger fence19to the sheet receiving position (Step S2), and then rotates the entrance roller12aand the staple-tray entrance roller14a(Step S3). After passing through the sheet entrance port4, the sheet T, as illustrated inFIG. 2, is conveyed downstream, nipped by the entrance rollers12aand12band the staple-tray entrance rollers14aand14b. The determining unit41determines whether the sheet trailing-end sensor33has turned from the detection state to the non-detection state (Step S4). If the determining unit41determines that the sheet trailing-end sensor33is still in the detection state (No at Step S4), the process control repeats Step S4. If the determining unit41determines that the sheet trailing-end sensor33has turned from the detection state to the non-detection state (Yes at Step S4), the processing unit55moves the staple-tray entrance rollers14aand14bfrom the home position H toward the jogger fence19(Step S5). As illustrated inFIG. 3, the sheet T, which is nipped by the staple-tray entrance rollers14aand14b, is moved toward the jogger fence19by the movement of the staple-tray entrance rollers14aand14bwhile being conveyed downstream. When the trailing end Tc has passed through the nip between the staple-tray entrance rollers14aand14b, the sheet T falls onto the staple tray11. The determining unit41determines whether a staple-tray entrance sensor36has turned from the detection state to the non-detection state (whether the sheet T is placed on the staple tray11) (Step S6). If the determining unit41determined that the staple-tray entrance sensor36is still in the detection state (No at Step S6), the process control repeats Step S6. If the determining unit41determined that the staple-tray entrance sensor36is turned from the detection state to the non-detection tray (Yes at Step S6), the staple-tray entrance rollers14aand14bare moved to the home position H (Step S7) as illustrated inFIG. 4. After that, the tapping roller16and the reverse roller24are rotated (Step S8) as illustrated inFIG. 5, and thus the trailing end Tc of the sheet T that is conveyed onto the staple tray11comes abut against the back-end fence13for alignment. After the alignment of the trailing end Tc, as illustrate inFIG. 6, the jogger fence19is moved toward the side fence17by the fixed distance (M+N+L) (Step S9) to align the sheet sides. The determining unit41determines whether the alignment of the trailing end Tc and the sheet sides of the last one of the sheet pile has completed (Step S10). If the determining unit41that the alignment of the trailing end Tc and the sheet sides of the last sheet has not been completed (No at Step S10), the process control returns to Step S1. In other words, the trailing-end alignment and the sheet-side alignment have performed each time when the single sheet T is conveyed to the sheet post-processing unit9. If the determining unit41that the alignment of the trailing end Tc and the sheet sides of the last sheet has been completed (Yes at Step S10), the stapler23staples the end of the sheet pile (Step S11). After that, as illustrated inFIG. 7, the discharge roller18arotates, and the discharge-roller supporting arm65swings to a contact position (Step S12). Thus, the sheet pile is discharged, nipped by the discharge rollers18aand18b, onto the discharge tray8. The determining unit41determines whether the sheet discharge sensor35has turned from the detection state to the non-detection state (whether the sheet pile is discharged onto the discharge tray8) (Step S13). If the determining unit41determines that the sheet discharge sensor35is still in the detection state (No at Step S13), the process control repeats Step S13. If the determining unit41determines that the sheet discharge sensor35has turned from the detection state to the non-detection state (Yes at Step S13), the back-end stopper29is swung to the release position (Step S14), and then the swinging member8aof the discharge tray8is swung downward (Step S15). By this swing, the sheet pile that is placed on the discharge tray8moves downward toward the upstream end of the discharge tray8, sliding on the swinging member8a. The determining unit41determines whether a predetermined time (e.g., 3 seconds) has passed (Step S16). If the determining unit41determines that the predetermined time has not passed (No at Step S16), the process control repeats Step S16. If the determining unit41determines that the predetermined time has passed (Yes at Step S16), as illustrated inFIG. 9, the back-end stopper29is swung to the stop position (Step S17), and then the swinging member8aof the discharge tray8is swung upward (Step S18). Thus, the trailing end of the sheet pile is stopped by the back-end stopper29.

A second case where the user selects the A4-sized sheet as the sheet T and the stapling mode with the control panel39is described below. The sheet-size comparing unit43compares the sheet size (A4 size) that is selected via the control panel39with the reference sheet size (B4 size). Because the selected sheet size is smaller than the reference sheet size, the roller moving-direction deciding unit49decides the roller moving direction in which the staple-tray entrance rollers14aand14bare to be moved as the sheet width direction toward the side fence17. The roller moving-distance calculating unit51calculates the moving distance U of the staple-tray entrance rollers14aand14bin such a manner that, after the sheet T is moved, the distance between the first side Ta and the first stapler end23ain the sheet width direction becomes M. The fence moving-distance calculating unit47calculates the moving distance V between the home position and the sheet receiving position of the jogger fence19in such a manner that, after the sheet T is moved, the distance between the second side Tb and the jogger fence19in the sheet width direction becomes N.

The operation of the sheet post-processing unit9in the second case where the A4-sized sheet is selected as the sheet T is almost the same as the operation in the first case that is described with reference to the flowchart illustrated inFIG. 14where the B4-sized sheet is selected as the sheet T except for Step S5. More particularly, as illustrated inFIG. 10, after the sheet T is conveyed through the post-processing-unit conveyer path6, when the determining unit41determines that the sheet trailing-end sensor33is turned from the detection state to the non-detection state at Step S4, the processing unit55moves the staple-tray entrance rollers14aand14btoward the side fence17as illustrated inFIG. 11. By the movement of the staple-tray entrance rollers14aand14b, the sheet T is moved toward the side fence17while being conveyed downstream. The sheet T is moved to the position where the distance between the first side Ta and the first stapler end23ain the sheet width direction becomes M. After that, as illustrated inFIG. 12, the staple-tray entrance rollers14aand14bare moved to the home position H. The tapping roller16and the reverse roller24are driven, and the trailing end Tc is aligned by the movement of the tapping roller16and the reverse roller24. As illustrated inFIG. 13, the jogger fence19is moved by the fixed distance (M+N+L) toward the side fence17, and the sheet sides are aligned by the jogger fence19.

A third case where the user selects the B5 sheet as the sheet T and the alignment mode with the control panel39is described below. The sheet-size comparing unit43compares the sheet size (B5 size) that is selected via the control panel39with the reference sheet size (B4 size). Because the selected sheet size is smaller than the reference sheet size, the roller moving-direction deciding unit49decides the roller moving direction in which the staple-tray entrance rollers14aand14bare to be moved as the sheet width direction toward the side fence17. The roller moving-distance calculating unit51calculates the moving distance U of the staple-tray entrance rollers14aand14bin such a manner that, after the sheet T is moved, the distance between the first side Ta and the first stapler end23ain the sheet width direction becomes M. The fence moving-distance calculating unit47calculates the moving distance V between the home position and the sheet receiving position of the jogger fence19in such a manner that, after the sheet T is moved, the distance between the second side Tb and the jogger fence19in the sheet width direction becomes N.

The operation of the sheet post-processing unit9in the third case where the alignment mode is selected is almost the same as the operation in the second case that is described with reference to the flowchart illustrated inFIG. 14where the stapling mode is selected except that Step S11is skipped in the third case. More particularly, when the determining unit41that the alignment of the trailing end Tc and the sheet sides of the last sheet T has completed at Step S10, the processing unit55rotates the discharge roller18aand then swings the discharge-roller supporting arm65to the contact position (Step S12) without driving the stapler23. Thus, the unstapled sheet pile with the aligned trailing end Tc and the sheet sides is displayed onto the discharge tray8.

A fourth case where the user selects the direct discharge mode with the control panel39is described below. The operation of the sheet post-processing unit9in the fourth case where the direct discharge mode is selected only includes Steps S1, S3, and S12to S18of the flowchart illustrated inFIG. 14. More particularly, when the determining unit41determines that the sheet leading-end sensor31has turned to the detection state at Step S1, the entrance roller12aand staple-tray entrance roller14aare rotated (Step S3). After that, the discharge roller18ais rotated, and the discharge-roller supporting arm65is swung to the contact position (Step S12). Thus, the sheet T that is received from the image forming unit5is discharged onto the discharge tray8without being subjected to any post-process. After the sheet T is discharged onto the discharge tray8, Steps S13to S18are performed.

Effects of the first embodiment are described below. In the first embodiment, the stapler23is arranged on the first side of the staple tray11in the sheet conveying direction without being out of the upstream end of the staple tray11. This arrangement of the stapler23makes it possible to reduce the length of the sheet post-processing unit9in the sheet conveying direction.

Because the stapler23is arranged to staple the staple position away from the trailing end Tc by the predetermined distance, it is unnecessary to move the stapler23in the sheet conveying direction or in the direction reverse to the sheet conveying direction when the stapler23staples the staple position. Moreover, because this configuration needs no mechanism for moving the stapler23, the manufacture costs will decrease.

The first stapler end23ais arranged closer to the center of the width of the staple tray11in the sheet width direction than the first side of the sheet T is, if the sheet T is A3 size (which is the largest size from among the receivable sizes). Therefore, a second stapler end23bof the stapler23is positioned away outside from but relatively close to the staple tray11in the sheet width direction. This arrangement of the stapler23makes it possible to reduce the width of the sheet post-processing unit9in the sheet width direction.

If the sheet T that is received from the image forming unit5is equal to or larger than the B4-sized sheet, i.e., the first side Ta is outside of the first stapler end23ain the sheet width direction toward the second stapler end23b, before the sheet T is placed on the staple tray11, the sheet T is moved under control of the control unit27to the position at which the first side Ta is inside of the first stapler end23ain the sheet width direction toward the center of the staple tray11. With this configuration, the sheet T is smoothly conveyed onto the staple tray11without overlapped with the stapler23.

The positions of the side fence17and the stapler23in the sheet width direction are decided in such a manner that after the sheet sides are aligned by movement of the jogger fence19toward the side fence17, the stapler23can staple an end of the aligned sheet pile. Therefore, the stapler23can staple the end of the sheet pile without moving in the sheet width direction. Because this configuration needs no mechanism for moving the stapler23, the manufacture costs will decrease.

Because the jogger fence19is the only member that is required to move in the mechanism for aligning the sheet sides, the configuration of the fence moving mechanism21is simple. The simple configuration will suppress the manufacture costs.

The roller moving direction, in which the staple-tray entrance rollers14aand14bare to be moved, and the moving distance, by which the staple-tray entrance rollers14aand14bare to be moved, are decided or calculated based on information about the sheet size that is received from the image forming unit5in such a manner that, after the sheet T is moved in the sheet width direction, the first side Ta is positioned away from the opening25inside by the distance M. The jogger fence19is moved to the sheet receiving position that is decided in such a manner that, when the sheet T is conveyed onto the staple tray11after the sheet T is moved in the decided roller moving direction by the calculated moving distance, the distance between the jogger fence19and the second side Tb becomes N, i.e., the fixed value, even if the sheet size of the sheet T is variable. With this configuration, the distance by which the jogger fence19is moved to align the sheet sides is fixed to the sum of M, N, and L. This simplifies the control over the sheet-side alignment.

Before the sheet T is conveyed onto the staple tray11, the staple-tray entrance roller14ais moved to the position at which the distance between the first side Ta and the first stapler end23abecomes M. Therefore, the sheet T is placed onto the staple tray11without overlapped with the stapler23. Moreover, the distance by which the jogger fence19is moved to align the sheet sides becomes as small as possible. With this configuration, the sheet T is conveyed onto the staple tray11without fail, and the time required for the sheet-side alignment is reduced.

Before the sheet T is conveyed onto the staple tray11, the jogger fence19is moved to the position away from the second side Tb by the distance N. Therefore, the sheet T is placed onto the staple tray11without overlapped with the jogger fence19. Moreover, the distance by which the jogger fence19is moved to align the sheet sides is as small as possible. With this configuration, the sheet T is conveyed onto the staple tray11without fail, and the time required for the sheet-side alignment is reduced.

It is possible to provide an image forming system including the image forming unit5and the sheet post-processing unit9that brings the above-described effects.

The sheet post-processing unit9is arranged between the scanning unit3and the image forming unit5. This arrangement makes it possible to reduce a required space.

A second embodiment of the present invention is described below. In the following description, parts corresponding to those in the first embodiment are denoted with the same reference numerals, and the same description is not repeated. Parts different from the first embodiment are described below.

The second embodiment is described with reference toFIG. 17. The entrance roller12aof the second embodiment is rotatably supported by an end of an arm59the other end of which is swingably supported. The arm59is always pushed downward by a coil spring force. The arm59swings upward when a solenoid61is ON, and downward when the solenoid61is OFF. In other words, the entrance roller12acan move between a sheet conveying position Q and a release position R that is away from the sheet conveying position Q.

In the first embodiment, the staple-tray entrance rollers14aand14bcannot move to the target position while the sheet T is nipped by the entrance rollers12aand12b. Therefore, the staple-tray entrance rollers14aand14bstarts moving to the target position after the trailing end Tc has passed through the nip between the entrance rollers12aand12b. To move the staple-tray entrance rollers14aand14bto the target position within a period between when the trailing end Tc has passed through the nip between the entrance rollers12aand12band when the trailing end Tc has passed through the nip between the staple-tray entrance rollers14aand14b, a speed at which the staple-tray entrance rollers14aand14bare moved is disadvantageously set higher than recommended speeds.

In the second embodiment, in contrast, if the sheet T coming from the image forming unit5has the length in the sheet conveying direction longer than the distance between the nip between the conveyer rollers28, which is arranged in the middle of the post-processing-unit conveyer path6, and the nip between the staple-tray entrance rollers14aand14b(e.g., the sheet T is A4 size), the entrance roller12ais moved from the sheet conveying position Q to the release position R when the sheet leading-end sensor31detects the leading end of the sheet T. With this configuration, the staple-tray entrance rollers14aand14bcan start moving to the target position after the trailing end Tc has passed through the nip between the conveyer rollers28. Therefore, the sheet T is moved in the sheet width direction at a recommended speed.

According to the second embodiment, the entrance roller12ais moved to the release position when the sheet T is nipped by the staple-tray entrance rollers14aand14bwith the trailing end Tc having passed through the conveyer rollers28that are arranged immediately upstream of the entrance rollers12aand12bin the sheet conveying direction. With this configuration, the staple-tray entrance rollers14aand14bcan be moved in the sheet width direction before the trailing end Tc has passed through the entrance roller12b. Therefore, the speed at which the staple-tray entrance rollers14aand14bare moved can be set to a recommended speed by setting the timing at which the staple-tray entrance rollers14aand14bstart moving in the sheet width direction earlier. This improves accuracy of the positional control of the staple-tray entrance rollers14aand14b.

The present invention is not to be limited to the present embodiments, but is to be construed as embodying all modifications and alternative constructions within the scope of the present invention. For example, it is possible to use an inkjet image forming unit that ejects ink from an ejection head onto the recording medium instead of the image forming unit5that transfers the toner image onto the recording medium.

Although the reference sheet size with which the sheet-size comparing unit43compares the selected sheet size is B4 size in the above-described embodiments, the reference sheet size can be set to some other size, such as A3 size.

Moreover, although the sheet post-processing unit9includes the image forming unit5and the scanning unit3as a unit, the image forming unit5and the scanning unit3can be formed in a separated manner.

Furthermore, although the image forming system1includes the scanning unit3, the image forming system1can exclude the scanning unit3. For example, a multifunction product (MFP) including a printer (image forming unit) and a sheet post-processing unit can be used.

According to an aspect of the present invention, a stapler is arranged on one side of a staple tray in a sheet width direction in such a manner that the stapler is inside of a downstream end of the staple tray in a sheet conveying direction. This arrangement reduces a length of a sheet post-processing unit perpendicular to the sheet width direction.

Moreover, the stapler is arranged to staple a staple position on a side of a sheet pile away from a trailing end of the sheet pile by a predetermined distance. Therefore, the stapler can staple the staple position without moving in the sheet conveying direction or a direction reverse to the sheet conveying direction. Because this configuration needs no mechanism for moving the stapler, manufacture costs will decrease.

Furthermore, because an opening of the stapler from which the sheet pile is inserted opens toward the center in the sheet width direction, a part of the stapler outside of the staple tray in the sheet width direction is suppressed. This arrangement reduces a width of the sheet post-processing unit in the sheet width direction.