Sheet processing apparatus and image forming apparatus

There are provided a sheet processing apparatus which can perform a punching process while suppressing decrease in productivity, and an image forming apparatus including the sheet processing apparatus. In a third carry-in route R3 branching from a first carry-in route, a discharge roller and a buffer roller convey a sheet for which the punching process has been performed by a punching unit, so that an upstream end in a sheet conveyance direction of the sheet for which the punching process has been performed precedes an upstream end in the sheet conveyance direction of a succeeding sheet following the sheet for which the punching process has been performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet processing apparatus and an image forming apparatus, and more particularly, to a sheet processing apparatus and an image forming apparatus which include a punching apparatus that performs a punching process for forming a punch hole on a sheet.

2. Description of the Related Art

Some conventional image forming apparatuses, such as duplicating machines, laser beam printers, ink-jet printers, facsimile machines and multifunction peripherals thereof, include a sheet processing apparatus which performs a binding process or a punching process for forming a punch hole, for a sheet on which an image has been formed. In such a sheet processing apparatus, for example, if the punching process is performed for the sheet, a sheet to be conveyed is caused to pass through a punch hole forming position for a punching apparatus once, and then is conveyed in the opposite direction to be returned to the punch hole forming position for the punching apparatus. Then, after the sheet is returned to the punch hole forming position in this way, the punch hole is formed at a central portion in a width direction, which is orthogonal to a sheet conveyance direction, of the sheet, by the punching apparatus (see Japanese Patent Application Laid-Open No. 2006-347678).

Incidentally, in the conventional sheet processing apparatus, and the conventional image forming apparatus including the sheet processing apparatus, there is one sheet conveyance route. Thus, if the sheet is reversed to form the punch hole, a succeeding sheet needs to wait on an upstream side in the sheet conveyance direction in the punching apparatus. Here, if the succeeding sheet is caused to wait at such a position, a waiting space, in which the succeeding sheet is caused to wait, needs to be provided on the upstream side in the sheet conveyance direction. If the waiting space is provided in this way, the size of the sheet processing apparatus is increased.

Moreover, if the waiting space is not provided, in order to secure a punching operation time for the punching apparatus, the image forming apparatus temporarily stops an image forming operation so that the succeeding sheet may not be conveyed to the sheet processing apparatus. Therefore, productivity of the image forming apparatus decreases.

Consequently, the present invention has been made in view of such a current situation, and it is an object of the present invention to provide a sheet processing apparatus which can perform the punching process while suppressing the decrease in the productivity, and an image forming apparatus including the sheet processing apparatus.

SUMMARY OF THE INVENTION

The present invention is a sheet processing apparatus which performs a punching process for a sheet, including a sheet conveyance route in which the sheet is conveyed; a branched conveyance route which branches from the sheet conveyance route; a sheet conveyance section provided on a downstream side in a conveyance direction of a branch point at which the branched conveyance route branches, in the sheet conveyance route, the sheet conveyance section being able to convey the sheet in the conveyance direction and in a direction opposite to the conveyance direction, the sheet conveyance section conveying the sheet which has passed through the branch point, in the opposite direction, and carrying the sheet into the branched conveyance route; a punching apparatus which performs the punching process for the sheet carried into the branched conveyance route; and a control section which controls the sheet conveyance section and the punching apparatus, wherein, after the control section causes the punching apparatus to perform the punching process for the sheet, the control section causes the sheet conveyance section to convey the sheet for which the punching process has been performed, in the conveyance direction, so that an upstream end in the sheet conveyance direction of the sheet for which the punching process has been performed precedes an upstream end in the sheet conveyance direction of a succeeding sheet following the sheet for which the punching process has been performed.

As in the present invention, the sheet for which the punching process has been performed is conveyed so that a downstream end in the sheet conveyance direction of the sheet for which the punching process has been performed precedes a downstream end in the sheet conveyance direction of a succeeding sheet following the sheet for which the punching process has been performed. Thereby, the punching process can be performed while decrease in productivity is suppressed.

DESCRIPTION OF THE EMBODIMENTS

Next, an embodiment of the present invention will be described with reference to the drawings.FIG. 1is an overall configuration diagram of an image forming apparatus including a sheet processing apparatus according to an embodiment of the present invention.FIG. 1illustrates an image forming apparatus A and an image forming apparatus main body A1. A sheet processing apparatus B is connected to a side of the image forming apparatus main body A1. An image reading apparatus11is provided on an upper surface of the image forming apparatus main body A1.

Here, the image forming apparatus main body A1includes an image forming section2and a paper feeding section1. The image forming apparatus main body A1is adapted to send a sheet from the paper feeding section1to the image forming section2, perform printing on the sheet in the image forming section2, and then discharge the sheet via a paper discharge outlet3. It should be noted that, from sheets P of a plurality of sizes stored in paper feeding cassettes1aand1b, the paper feeding section1separates and feeds each designated one of the sheets P to the image forming section2. Moreover, the image forming section2includes, for example, a photosensitive drum4, a print head (laser light emitter)5arranged around the photosensitive drum4, a developing device6, a transfer charger7and a fixing device8.

The image reading apparatus11scans a document set on a platen12by a scan unit13, and electrically reads the document by a photoelectric conversion element (not illustrated). The image reading apparatus11includes a feeder apparatus15which feeds a document G received on a loading tray16to the platen12. In addition, if a document image is read, the feeder apparatus15conveys the document G to the platen12, and then, the scanning is performed by the scan unit13so as to read the document image. It should be noted that, for example, digital processing is performed for read image data in an image processing section, then the read image data is transferred to a data storage section14, and an image signal is transmitted to the laser light emitter5.

Then, in the image forming apparatus main body A1, depending on a received image signal, the laser light emitter5emits laser light depending on the image signal, onto the photosensitive drum so as to form an electrostatic latent image on the photosensitive drum. This electrostatic latent image is developed with toner by the developing device6so as to form a toner image. Subsequently, the toner image is transferred onto the sheet by the transfer charger7, and heating fixing is performed for the sheet P on which the toner image has been transferred, by the fixing device8. Thereby, the toner image is fixed on the sheet. The sheets P on which the toner image has been fixed in this way are sequentially carried out via the paper discharge outlet3to the sheet processing apparatus B.

It should be noted that, inFIG. 1, a circulation route9is a route for double sided printing in which, when images are formed on both sides of the sheet, the printing is performed on a front side of the sheet P by the fixing device8, two sides of the sheet P are reversed via a switchback route10, then the sheet P is fed to the image forming section2again, and the printing is performed on a reverse side of the sheet P. Then, the sheet P, which has been fed through this circulation route9to the image forming section2, and on which the double sided printing has been performed, is subsequently carried out via the paper discharge outlet3to the sheet processing apparatus B.

The sheet processing apparatus B takes in the sheets P carried out from the image forming apparatus main body A1, in order. Then, the sheet processing apparatus B performs a process for aligning and tying up a plurality of the sheets P which have been taken in, in a bundle, and a punching process for punching near back ends of the sheets P which have been taken in. Moreover, the sheet processing apparatus B performs processes such as a staple process (binding process) for stapling a back end side of the bundle of the sheets, and a bookbinding process.

It should be noted that, in the present embodiment, as illustrated inFIG. 2, a carry inlet23aof the sheet processing apparatus B is coupled to the paper discharge outlet3of the image forming apparatus main body A1. In addition, depending on a mode which is set, after the image forming performed in the image forming apparatus main body A1, the sheet processing apparatus B is adapted to directly receive the conveyed sheets on a sample tray21a, or to perform one of the punching process and a staple-binding process for the conveyed sheets and store the sheets on one of loading trays21band21c. Moreover, if a bookbinding mode is set, the sheet processing apparatus B is adapted to align the sheets in a bundle form for each copy, perform the staple process on the center of the bundle, then applies the bookbinding process for folding the bundle in a brochure form, and store the bundle in the brochure form on a saddle tray22.

Within a casing (outer cover)20of the sheet processing apparatus B, there are provided a first processing section BX1which aligns and accumulates the sheets from the carry inlet23afor each copy, and performs binding finishing for the sheets, on a processing tray29, and a second processing section BX2which aligns and accumulates the sheets for each copy, and performs brochure finishing for the sheets. A first carry-in route R1is provided between the first processing section BX1and the carry inlet23a. In addition, in this first carry-in route R1which is a sheet conveyance route, a second carry-in route R2is provided which branches from the first carry-in route R1so as to receive the conveyed sheets on the sample tray21a. Moreover, in this first carry-in route R1, a third carry-in route R3is provided which is a branched conveyance route that branches from the first carry-in route R1so as to convey the conveyed sheets to the second processing section BX2. It should be noted that a route switching member24sorts the sheets from the carry inlet23a, into any one of the first processing section BX1, the second carry-in route R2and the third carry-in route R3, depending on the mode which is set.

This third carry-in route R3is for carrying the sheets into the second processing section BX2when the brochure finishing is performed. In addition, this third carry-in route R3is also included in a waiting section in which a succeeding sheet that has been sent to the sheet carry inlet23ais caused to temporarily stay, during a process operation in which the process such as the staple-binding is applied to the bundle of sheets. It should be noted that, as will be described later, when a punch hole is formed on the sheet, the sheet is carried into this third carry-in route R3.

In addition, when an end-binding process is applied to the bundle of sheets which have been aligned and accumulated for each copy on the processing tray29, the succeeding sheet from the first carry-in route R1is switched back by a discharge roller25and a buffer roller27, and is caused to stay in this third carry-in route R3. It should be noted that, after the succeeding sheet is caused to temporarily stay, when processed sheets on the processing tray29are carried out, a plurality of the succeeding sheets within the third carry-in route is caused to overlap and is simultaneously conveyed to the processing tray29by the buffer roller27and the discharge roller25. It should be noted that this buffer roller27and the discharge roller25are included in a forward/reverse rotatable sheet conveyance section which conveys the sheet that has passed through a branch point BR, in the opposite direction, so as to carry the sheet into the third carry-in route R3, at a time of a punch hole forming operation to be described later.

Moreover, a paper discharge sensor S2is arranged at a paper discharge outlet25xof the first carry-in route R1. This paper discharge sensor S2detects the sheet passing through the first carry-in route R1so as to perform jam detection. In addition, at a downstream side of this paper discharge outlet25x, a vertical difference in level is formed to arrange the processing tray29. It should be noted that, in the first processing section BX1, there are provided the processing tray29, and an end-binding staple unit31which is a binding apparatus arranged on an upstream side in a sheet discharge direction of this processing tray29.

Moreover, the processing tray29is tilted so that the upstream side in the sheet discharge direction becomes lower. Furthermore, at an upstream end, which is on the upstream side in the sheet discharge direction, of the processing tray29, a sheet end regulation member32is provided which contacts with the back end, which is an upstream side end in the sheet discharge direction, of the discharged sheet, so as to regulate a position of the sheet in the sheet discharge direction. The sheet is discharged via the paper discharge outlet25x, and the back end of the sheet is caused to hit this sheet end regulation member32by a pair of switchback rollers26to be described later, and the tilt of the processing tray29. Thereby, the sheet is positioned at a binding position, which is a process position that has been previously set, in order to perform the binding process.

On the other hand, the pair of switchback rollers conveys the sheet discharged onto (carried into) the processing tray29, to the sheet end regulation member32. Here, this pair of switchback rollers26is forward/reverse rotatable so that this pair of switchback rollers26conveys the sheet discharged onto the processing tray29, in the discharge direction, and then conveys the sheet in a direction opposite to the discharge direction so as to direct the sheet to the sheet end regulation member32. Moreover, this pair of switchback rollers26includes a fixed roller26bprovided at a downstream side end portion of the processing tray29, and a movable roller26aprovided at a swinging guide133that is swingably provided over the processing tray29. In addition, the movable roller26acan connect and disconnect to the fixed roller26balong with swings of the swinging guide133.

According to such a configuration, the sheet P discharged from the discharge roller25slides down on one of a loading surface of the processing tray29and the sheet loaded on the processing tray29, due to the pair of switchback rollers26and the tilt of the processing tray29. Thereby, the back end (an upstream end in the discharge direction) of the sheet P is caused to hit the sheet end regulation member32. Moreover, at the processing tray29, a side alignment unit (not illustrated) is arranged which pushes and aligns the width of the sheet. For this side alignment unit, any one of center reference for positioning the sheet carried into the processing tray29from the paper discharge outlet25x, with reference to the center of the sheet, and side reference for positioning the sheet with reference to a left or right side edge of the sheet, is employed. In addition, after a width direction of the sheet is positioned by this side alignment unit, depending on a mode selected by a user, for example, the end-binding staple unit31performs the binding process, and subsequently, the sheets are loaded on one of the loading trays21band21c, by the pair of switchback rollers26.

It should be noted that, inFIG. 2, an inlet sensor S1senses the sheet discharged from the image forming apparatus main body A1, and counts the number of sheets passing through. A paper side sensing sensor S3senses an upper side of the sheet loaded on the loading tray. A loading tray-paper presence/absence sensor S4senses presence/absence of the sheet on the loading tray. Moreover, an inlet roller40conveys the sheet carried out from the image forming apparatus main body A1.

Incidentally, as illustrated inFIG. 3, in the third carry-in route R3, a punching unit60is provided as a punching apparatus which forms a punch hole (punches) on each one of the sheets P. It should be noted that this punching unit60can move in the width direction which is orthogonal to a sheet conveyance direction, depending on a side end position of the conveyed sheet. Thereby, even if the sheet is shifted in the width direction, the punch hole can be formed on a central portion of the sheet. It should be noted that, in this punching unit60, on the side of the second processing section BX2, a stopper61is provided so that the stopper61can freely appear and disappear in the third carry-in route R3. In addition, at a time of a sheet buffering process to be described later, this stopper61is caused to project into the third carry-in route R3so as to be able to cause the sheet to wait within the third carry-in route R3, without directing the sheet to the second processing section BX2. Moreover, at a time of a punch hole forming process, this stopper61is caused to project into the third carry-in route R3to lock the sheet so as to be able to retain the sheet at a punch hole forming position for the punching unit60.

Moreover, a lateral registration unit62which senses the side end position in the width direction of the sheet is provided on an upstream side in the sheet conveyance direction of the branch point BR which branches into the third carry-in route R3, in the first carry-in route R1. In addition, if the punch hole is formed on the sheet, a lateral shift, which is a shift of the sheet in the width direction, is sensed by the lateral registration unit62, and then, the buffer roller27and the discharge roller25, which are forward/reverse rotatable, are reversed, as well as the route switching member24is switched, so as to carry the sheet into the third carry-in route R3.

Here, as illustrated inFIGS. 4A, 4B and 5, the lateral registration unit62has a unit main body62aand a rack section62b, and includes a sliding section62cwhich is provided so as to be slidable in the width direction in the unit main body62a. Moreover, the lateral registration unit62includes, for example, a lateral registration motor M9which rotates a pinion gear62dthat engages with the rack section62b, as a moving unit which slides the sliding section62c. In addition, if a shift amount of a position in the width direction of the sheet which has been conveyed with reference to the center of the sheet is sensed, the lateral registration motor M9is rotated so as to slide the sliding section62cin the width direction as illustrated by an arrow inFIG. 4A. Moreover, after the punch hole forming operation is completed, the lateral registration motor M9which moves the sliding section62cis reversed so as to return the sliding section62cto a home position.

It should be noted that when the sliding section62creturns to the home position, a lateral registration home position (HP) sensor63is shaded by a flag63awhich is provided at the rack section62b, so as to sense that the sliding section62chas returned to the home position.

On the other hand, a lateral registration sensor unit64is a sensing section which is provided in the sliding section62cand senses the side end position in the width direction of the sheet. This lateral registration sensor unit64includes a plurality of (five in the present embodiment) transmission sensors, that is, first to fifth lateral registration sensors64ato64e, which are provided side by side in the width direction. Here, the first lateral registration sensor64ais for sensing a leading end of the sheet, and the second to fifth lateral registration sensors64bto64eare for sensing a side end of the sheet.

As this side end sensing unit, for example, the second to fifth lateral registration sensors64bto64eare arranged at positions where the second to fifth lateral registration sensors64bto64ecan sense the side end of the sheet P, depending on the size (one of B5, B5R, A4 and A4R) of the sheet P discharged from the image forming apparatus main body A1. It should be noted that a conveyance guide62eguides the sheet to a position below the lateral registration sensor unit64, and a base frame62fslidably supports the sliding section62c.

If the lateral registration unit62as described above senses the side end position of the sheet, for example, if the lateral registration unit62senses the side end position of the sheet of B5 size, first, when the first lateral registration sensor64asenses the leading end of the sheet, the sliding section62cis slid from the home position into the width direction. Then, subsequently, the sliding section62cis slid until the second lateral registration sensor64bsenses the side end position of the sheet.

Here, sensing signals related to the side end position of the sheet, from these respective lateral registration sensors64ato64e, are input to, for example, a CPU90, which is a control unit illustrated inFIG. 6to be described later. When the sensing signal from the second lateral registration sensor64bis input, the CPU90calculates a position shift of the sheet in the width direction, based on an amount of movement of the sliding section62cuntil then. Furthermore, the CPU90moves the punching unit60in the width direction to a position where the punch hole can be formed in the center of the sheet, based on a result of the calculation, and then performs the punch hole forming operation.

In addition, since the punching unit60is moved in the width direction based on the shift amount of the sheet P in this way, even if the sheet P is conveyed in a state where the sheet P is shifted, the punch hole can be formed at an appropriate position. In other words, in the present embodiment, after a lateral shift amount is sensed by the lateral registration unit62, the punching unit60is previously moved to the punch hole forming position. Thereby, a time for starting the punch hole forming operation can be shortened, in comparison with a case where the lateral shift amount is sensed after the sheet reaches the punching unit, and subsequently, the punching unit is moved to the punch hole forming position.

FIG. 6is a control block diagram of the image forming apparatus A. The CPU90includes a ROM (not illustrated) in which control programs corresponding to flowcharts illustrated inFIGS. 7 and 9to be described later are stored, and a RAM (not illustrated) which is used as an area in which control data is temporarily retained, and as a work area for calculation associated with control. Here, the inlet sensor S1, the discharge sensor S2, the paper side sensing sensor S3, the loading tray-paper presence/absence sensor S4, the first to fifth lateral registration sensors64ato64e, the lateral registration home position sensor63, a punching unit home position sensor65and an operation section91are connected to the CPU90.

It should be noted that the operation section91sets image forming conditions, for example, printing conditions such as designation of the sheet size, designation of the number of copies to be printed, designation of single sided/double sided printing, and designation of enlarged/reduced printing. Moreover, simultaneously with the image forming conditions, the operation section91sets process conditions such as a punch hole forming mode, a printout mode, an offset mode, a binding finishing mode and a brochure finishing mode.

Moreover, an inlet conveyance motor M1which drives the inlet roller40, a solenoid SL1which actuates the route switching member24, and a forward/reverse rotatable discharge motor M2which drives the discharge roller25are connected to the CPU90. Furthermore, a forward/reverse rotatable paper discharge motor M3which drives the pair of switchback rollers26, a forward/reverse rotatable alignment motor M4which drives the side alignment unit, and a forward/reverse rotatable staple motor M5which drives the end-binding staple unit31are connected. Moreover, a staple moving motor M6which moves the end-binding staple unit31in the width direction, a forward/reverse rotatable loading tray motor M7which moves the loading tray up and down, and a punch motor M8which drives the punching unit60to form the punch hole are connected. Furthermore, the forward/reverse rotatable lateral registration motor M9which moves the lateral registration unit62in the width direction, and a forward/reverse rotatable punch slide motor M10which is included in a moving section that slides the punching unit in the width direction are connected. Moreover, a stopper solenoid SL2which actuates the stopper61, and a forward/reverse rotatable buffer motor M11which drives the buffer roller27are connected.

In addition, the CPU90controls driving of each motor and the like according to sensor input, the control programs stored in the ROM, and setting in the operation section91. It should be noted that, in the present embodiment, while the CPU90is provided in the image forming apparatus main body A1, the CPU90may be mounted in the sheet processing apparatus B. Moreover, if the CPU is provided in the sheet processing apparatus B, the sheet processing apparatus B may be controlled by the CPU90provided in the image forming apparatus main body A1, via the CPU on the sheet processing apparatus side.

Incidentally, when the punch hole is formed on the sheet, if there is one sheet conveyance route as described above, the succeeding sheet needs to wait at a waiting position, or the image forming on the succeeding sheet needs to be temporarily stopped. However, if the succeeding sheet is caused to wait in this way, a waiting space, in which the succeeding sheet is caused to wait, needs to be provided on the upstream side in the sheet conveyance direction of the punching unit60. If the waiting space is provided in this way, the size of the sheet processing apparatus B is increased. Moreover, if the image forming apparatus A temporarily stops an image forming operation, productivity of the image forming apparatus A decreases.

Consequently, in the present embodiment, the punching unit60is provided in the third carry-in route R3so that, when the punch hole is formed on the sheet, the punch hole is formed on the sheet in the third carry-in route R3. According to such a configuration, as will be described later, the sheets can be partially overlapped, and the punch hole can be continuously formed without stopping the succeeding sheet. Alternatively, even if the sheet is caused to wait, the sheet can be caused to wait at a position near a reverse portion side. As a result, the waiting space can be narrowed, and the increase in the size of the sheet processing apparatus B can be prevented.

Next, control of a punch forming operation by the CPU90according to the present embodiment will be described by using the flowchart illustrated inFIG. 7. First, based on a sheet size signal from the operation section91, the CPU90determines a sheet size sensing sensor which senses the side end position of the sheet (S100). For example, if the size of the sheet is B5 size, the second lateral registration sensor64bis determined as the sheet size sensing sensor. Next, after the sheet is carried in from the image forming apparatus main body A1, the CPU90waits until the leading end of the sheet conveyed by the inlet roller40is sensed by a sheet leading end sensing sensor64a(S101). Subsequently, when the sheet leading end sensing sensor64asenses the leading end of the sheet, the CPU90conveys the sheet by a predetermined distance, for example, a sheet length (a length of the sheet in the sheet conveyance direction)—100 mm (S102). Then, when such conveyance of the sheet is completed (Y in S102), the lateral registration motor M9is rotated forward (S103), and the sliding section62cof the lateral registration unit62is moved in the width direction.

Thereby, the second lateral registration sensor64bgradually approaches the side end of the sheet. Then, before the sliding section62creaches a maximum amount of movement, when the second lateral registration sensor64bsenses a side portion in the width direction of the sheet (N in S104, Y in S105), the lateral registration motor M9is stopped (S106). It should be noted that when the side portion of the sheet is sensed, the sensing signal from the second lateral registration sensor64bis input to the CPU90. Then, based on this sensing signal and an amount of slide movement of the sliding section62c, the CPU90calculates the lateral shift amount of the sheet, drives the punch slide motor M10depending on a result of this calculation, and moves the punching unit60to the central portion in the width direction (S106). It should be noted that the sheet processing apparatus B includes the punching unit home position sensor65, and the punching unit home position sensor65senses a home position of the punching unit60moving in the width direction. The calculation result provided by the CPU90is an amount of the movement of the punching unit60from the home position. Thereby, if the sheet is shifted, the punching unit60can be moved to an appropriate position where the punch hole can be formed at the central portion in the width direction of the sheet, before the sheet reaches the punching unit60.

It should be noted that when the sheet P reaches the discharge roller25as illustrated inFIG. 8A, and subsequently, the back end of the sheet passes through the branch point BR, the CPU90reverses the discharge roller and the buffer roller27, and also turns the route switching member24downward as illustrated inFIG. 8B. Thereby, the sheet P is carried into the third carry-in route R3. It should be noted that, at this time, the CPU90causes the stopper61to project into the third carry-in route R3, and causes the back end of the sheet P carried into the third carry-in route R3to contact with this stopper61so as to enable the sheet P to be stopped at the punch hole forming position as illustrated inFIG. 8C. Moreover, since the back end of the sheet P contacts with the stopper61in this way, skew of the sheet P is corrected.

Next, after the sheet P is carried into the third carry-in route R3(S107), and is caused to contact with the stopper61in this way, the CPU90performs the punching process by the punching unit60(S108). Here, at this time, as described above, before the sheet reaches the punching unit60, the punching unit60has moved to the appropriate position where the punch hole can be formed at the central portion in the width direction of the sheet. Therefore, the punch hole forming operation can be immediately started.

On the other hand, when the sheet P is carried into the third carry-in route R3, the CPU90reverses the lateral registration motor M9(S109) so as to move the lateral registration unit62in a direction of the home position. Then, subsequently, if the lateral registration home position sensor63is shaded by the flag63aprovided at the rack section62b, so as to sense that the sliding section62chas reached the home position (Y in S110), the lateral registration motor M9is stopped (S111). Thereby, the sliding section62creturns to the home position, and prepares to sense the side end position of the next succeeding sheet. Then, the punching unit60, which has completed the punching process, is driven to move by the punch slide motor M10. When the home position of the punching unit60is sensed by the punching unit home position sensor65, the punching unit60stops (S111).

Incidentally,FIG. 9is a flowchart illustrating the control when the punch hole is formed on the succeeding sheet after the punch hole has been formed on the sheet in this way. Here, after the punch hole is formed at a back end portion of the sheet by the punching unit60, the CPU90rotates the discharge roller25and the buffer roller27forward (S200), and conveys the sheet on which the punch hole has been formed, toward the processing tray29. Furthermore, the route switching member24is turned upward (S201). It should be noted that when the sheet P is conveyed to the processing tray29in this way, the succeeding sheet P1does not stop and is conveyed by the inlet roller40at a timing when the succeeding sheet P1reaches a position before the branch point BR as illustrated inFIG. 10A.

Thereby, when a preceding sheet P is conveyed by the forward rotation of the discharge roller25and the buffer roller27, the succeeding sheet P1is continuously conveyed by the inlet roller40which is an upstream sheet conveyance section, and reaches the branch point BR as illustrated inFIG. 10B. As a result, subsequently, a leading end portion of the succeeding sheet P1is conveyed in a state where the leading end portion of the succeeding sheet P1partially overlaps the back end portion of the preceding sheet P, along with the sheet P, toward the processing tray29, as illustrated inFIG. 10C. In other words, the back end, which is an upstream end in the sheet conveyance direction, of the preceding sheet P is conveyed in a state where the back end of the preceding sheet P precedes the back end, which is the upstream end in the sheet conveyance direction, of the succeeding sheet P1. In other words, as a result, even after the preceding sheet P is discharged on the processing tray29, the succeeding sheet P1is in a state where the succeeding sheet P1can be conveyed by the discharge roller25. Subsequently, when the back end of the succeeding sheet P1passes through the branch point BR (Y in S202), the CPU90reverses the discharge roller25and the buffer roller27, and also turns the route switching member24downward as illustrated inFIG. 11A(S203). Thereby, the succeeding sheet P1is carried into the third carry-in route R3. It should be noted that the CPU90determines that the back end of the succeeding sheet passes through the branch point BR in this way, for example, according to a sheet sensing signal from the inlet sensor S1.

Here, when the succeeding sheet P1is conveyed to the position before the branch point BR, and the sheet P is conveyed toward the processing tray29in this way, the succeeding sheet P1and the sheet P are conveyed in the state where the succeeding sheet P1partially overlaps the sheet P. Therefore, a timing when the back end of the succeeding sheet P1passes through the branch point BR can be advanced. As a result, the productivity at a time of the punching process can be improved. Moreover, a timing when the punching process for the succeeding sheet P1is started can be advanced.

It should be noted that the sheet processing apparatus B of the present invention can also simultaneously carry two sheets, that is, the sheet P on which the punch hole has been formed and the succeeding sheet P1, into the third carry-in route R3, in a state where the two sheets overlap each other, as illustrated inFIG. 11B, without causing the sheet P to pass through from the discharge roller25. In addition, the succeeding sheet P1, which is carried into the third carry-in route R3in this way, subsequently contacts with the stopper61. Thereby, the punching process is performed for the succeeding sheet P1by the punching unit60, in a state where a position of the back end is regulated. It should be noted that when the punch hole is formed on the succeeding sheet P1in this way, the sheet P that is a sheet after the punching process, on which the punch hole has been previously formed, has not reached the punch hole forming position, and thus the punch hole is not formed on this sheet P. In other words, if the sheet P after the punching process, for which the punching process has been performed, and the succeeding sheet P1are simultaneously carried into the third carry-in route R3, the sheet P and the succeeding sheet P1are shifted from each other and carried into the third carry-in route R3so that the punching process is not performed for the sheet P.

Next, when the punch hole is formed on the succeeding sheet P1in this way (Y in S204), it is determined whether or not the succeeding sheet P1is the last sheet (S205). Then, if the succeeding sheet P1is not the last sheet (N in S205), S200to S204are repeated. Moreover, if the succeeding sheet P1is the last sheet (Y in S205), the discharge roller25and the buffer roller27are rotated forward (S206), and the sheet on which the punch hole has been formed, and the succeeding sheet P1are discharged on the processing tray29. It should be noted that, in a case of such a configuration, three or more sheets may also be simultaneously carried into the third carry-in route R3. In this case, the preceding sheets sequentially pass through the discharge roller25and are conveyed to the processing tray29by the forward rotation of the discharge roller25and the buffer roller27.

As described above, in the present embodiment, the lateral registration unit62is provided on the upstream side in the sheet conveyance direction of the branch point BR which branches into the third carry-in route R3, and the punching unit60is provided in the third carry-in route R3, which is on a downstream side in the sheet conveyance direction, lower than the lateral registration unit62. In addition, depending on the lateral shift amount of the sheet which has been sensed by the lateral registration unit62, the punching unit60is moved in the width direction before the sheet reaches the punching unit60. Thereby, the time for starting the punch hole forming operation can be shortened in comparison with the case where the lateral shift amount is sensed after the sheet reaches the punching unit, and subsequently, the punching unit is moved.

In other words, the side end position of the sheet is sensed by the lateral registration unit62, and the punching unit60is moved in the width direction, depending on the side end position of the sheet which has been sensed by the lateral registration unit62, before the sheet reaches the punching unit60. Thereby, the punch hole forming operation can be started in a short time. As a result, productivity associated with the punching process in the sheet processing apparatus B is improved.

Moreover, the lateral registration unit62is provided on the upstream side in the sheet conveyance direction of the branch point BR which branches into the third carry-in route R3, and the punching unit60is provided in the third carry-in route R3. Thereby, the timing when the punching process for the succeeding sheet P1is started can be advanced. As a result, the productivity associated with the punching process in the sheet processing apparatus B is improved.

It should be noted that, in the above description, the succeeding sheet P1is conveyed in the state where the succeeding sheet P1partially overlaps the sheet P, toward the processing tray29. However, the present invention is not limited thereto. For example, the sheet P can be conveyed to the processing tray29without contacting with the succeeding sheet P1, as illustrated inFIG. 11C, by accelerating circumferential speeds (conveyance speeds) of the discharge roller25and the buffer roller27higher than a circumferential speed of the inlet roller40after the punch hole is formed.

Moreover, in the above description, a case has been described where the lateral registration unit62is moved by the lateral registration motor M9, and the punching unit60is moved by the punch slide motor M10. However, the present invention is not limited thereto. For example, the lateral registration unit62and the punching unit60may be moved by the same driving source. Moreover, in the above description, the lateral registration sensors64ato64eare moved in the width direction so as to sense a side end portion of the sheet. However, the side end portion of the sheet may be sensed by using a two-dimensional line polarization sensor or the like, in a state where the sensor is fixed.

This application claims the benefit of Japanese Patent Application No. 2009-231018, filed Oct. 2, 2009, which is hereby incorporated by reference herein in its entirety.