Sheet processing apparatus and image forming system

Abstract

To disperse and carry sheets between a first sheet carrying path and a second sheet carrying path.SOLUTION: A sheet processing apparatus includes: a first sheet carrying path that carries a sheet to sheet supporting means; and a second sheet carrying path that branches from the first sheet carrying path at a branching part on the first sheet carrying path, and joins with the first sheet carrying path at a joining part upstream of a sheet outlet to the sheet supporting means in a sheet carrying direction. Control means controls guide means so that a first sheet which is first carried in a sheet bundle processed by sheet processing means is guided to the second sheet carrying path, and a second sheet following the first sheet is guided to the first sheet carrying path, and the first and second sheets join together at the joining part in an overlapping manner. The control means guides at least one sheet following the second sheet of a plurality of sheets forming the sheet bundle to the second sheet carrying path.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a sheet processing apparatus for processing sheets and an image forming system. [Background technology]

[0002] Conventionally, a sheet processing apparatus conveys sheets discharged from an image forming apparatus such as a printer or a copier onto a processing tray, and then performs edge alignment (hereinafter referred to as alignment) and binding (hereinafter referred to as stapling) of the sheet stack accumulated on the tray. Since subsequent sheets cannot be sent to the processing tray while a sheet is being processed on the processing tray, some sheet processing apparatuses are designed to temporarily accumulate the sheets discharged from the image forming apparatus in the sheet processing apparatus until the processing on the processing tray is completed, thereby preventing a decrease in the productivity of the entire system.

[0003] For example, according to the sheet processing device described in Patent Document 1, a normal conveying path and a second conveying path are provided as conveying paths following the processing tray. Then, while the preceding sheet is being processed on the processing tray, the following first sheet is conveyed to the second conveying path, and the conveying roller is stopped by an electromagnetic clutch to hold the following first sheet on the second conveying path. Also, the second sheet following the first sheet is conveyed to the normal path, and the conveying of the held first sheet is resumed in line with the second sheet, and the first and second sheets are sent to the sheet processing tray in an overlapping state, thereby delaying the arrival of the first sheet at the processing tray. As a result, even if the sheet is being processed in the sheet processing tray, the sheet can be sent from the image forming device to the sheet processing device, making it possible to perform a post-processing job for the sheet without reducing the productivity of the entire system.

[0004] In addition, when the processing time of the preceding sheet in the processing tray is longer, the subsequent sheets after the first sheet are also retained in the second transport path, making it possible to perform post-processing jobs without reducing the productivity of the entire system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 6-99070 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the example of Patent Document 1, while the preceding sheet is being processed in the processing tray, the following first sheet is transported to the second transport path, and the following second sheet and subsequent sheets are transported to the normal transport path. Even if the processing time of the preceding sheet in the processing tray is long, the following multiple sheets are transported to the second transport path while the preceding sheet is being processed in the processing tray, but when the processing tray is not being processed, the remaining sheets are all transported to the normal transport path. That is, among the sheets transported to the processing tray, only the first few pages of the post-processing unit are transported to the second transport path, so it is considered that the difference in the amount of paper passing between the normal transport path and the second transport path will become large as the cumulative number of sheets transported to the processing tray increases. This causes a problem that the influence of wear of the transport roller in the path and the accumulation of paper powder on the sheet transport performance is biased toward the normal transport path compared to the second transport path.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS In view of the above, an object of the present invention is to provide a sheet processing apparatus and an image forming system that distribute and transport a sheet between a first sheet transport path and a second sheet transport path. [Means for solving the problem]

[0008] One aspect of the present invention includes a sheet supporting means for supporting a sheet on which an image has been formed and which is sent from an image forming apparatus, a post-processing means for performing post-processing on a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting means, a first sheet transport path for guiding the sheet sent from the image forming apparatus to the sheet supporting means, a second sheet transport path for branching from the first sheet transport path at a branching portion on the first sheet transport path and merging with the first sheet transport path at a merging portion upstream in a sheet transport direction from an outlet to the sheet supporting means, a guide means for guiding the sheet at the branching portion to the first sheet transport path or the second sheet transport path, and a control means for controlling the guide means. a length of the second sheet transport path is longer than that of the first sheet transport path between the branching portion and the junction portion, and the control means controls the guiding means to guide a leading sheet of a plurality of sheets constituting a sheet stack to be post-processed by the post-processing means to the second sheet transport path and a final sheet to the first sheet transport path, and to selectively guide sheets other than the leading sheet and the final sheet to either the first sheet transport path or the second sheet transport path for each sheet, and causes a sheet transported on the second sheet transport path and a succeeding sheet transported on the first sheet transport path to merge in an overlapping manner at the junction portion. and the control means alternately switches, for each sheet bundle, whether to guide sheets other than the leading sheet and the last sheet of the plurality of sheets constituting the sheet bundle to the first sheet transport path or the second sheet transport path. The sheet processing apparatus is characterized in that One aspect of the present invention is a sheet transport device including: a sheet supporting means for supporting a sheet on which an image has been formed and which is sent from an image forming apparatus; a post-processing means for performing post-processing on a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting means; a first sheet transport path for guiding the sheet sent from the image forming apparatus to the sheet supporting means; a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a junction upstream in a sheet transport direction from an outlet to the sheet supporting means; a guide means for guiding the sheet to the first sheet transport path or the second sheet transport path at the branching portion; and a control means for controlling the guide means, wherein a length of the second sheet transport path is longer than that of the first sheet transport path between the branching portion and the junction portion, and the control means controls a sheet transport path on which the post-processing is performed by the post-processing means. the guiding means controls the guide means to guide the first sheet of a plurality of sheets constituting a sheet bundle to the second sheet transport path and the last sheet to the first sheet transport path, and selectively guides sheets other than the first and last sheet to either the first sheet transport path or the second sheet transport path for each sheet, and merges a sheet transported along the second sheet transport path and a subsequent sheet transported along the first sheet transport path in an overlapping manner at the junction, and the control means controls the guiding means to guide at least one of the sheets constituting the sheet bundle one behind the current sheet bundle, the leading edge of which reaches the branching portion, to the second sheet transport path when the post-processing means is in a non-processing state in which it is not processing the sheet bundle stacked on the sheet support means.

[0010] According to one aspect of the present invention, there is provided a method for manufacturing a sheet-printing apparatus, comprising: an image forming unit for forming an image on a sheet; a sheet supporting unit for supporting an image-formed sheet on which an image has been formed by the image forming unit; a post-processing unit for processing a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting unit; Growth done fruita first sheet transport path that guides the sheet to the sheet supporting means; a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a junction upstream in a sheet transport direction from an outlet to the sheet supporting means; a guide means that guides the sheet to the first sheet transport path or the second sheet transport path at the branching portion; and a control means that controls the guide means, wherein a length of the second sheet transport path is longer than that of the first sheet transport path between the branching portion and the junction portion, and the control means controls the second sheet transport path to guide a leading sheet of a plurality of sheets that constitute a sheet bundle to be post-processed by the post-processing means. the control means controls the guiding means to guide a first sheet to the first sheet transport path, and a final sheet to the first sheet transport path, and selectively guides sheets other than the first sheet and the final sheet to either the first sheet transport path or the second sheet transport path for each sheet, and merges a sheet transported through the second sheet transport path and a subsequent sheet transported through the first sheet transport path in an overlapping manner at the junction, and the control means alternately switches for each sheet bundle as to whether to guide the first sheet transport path or the second sheet transport path for sheets other than the first sheet and the final sheet among the multiple sheets constituting the sheet bundle. According to one aspect of the present invention, there is provided a method for manufacturing a sheet-printing apparatus, comprising: an image forming unit for forming an image on a sheet; a sheet supporting unit for supporting an image-formed sheet on which an image has been formed by the image forming unit; a post-processing unit for processing a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting unit; Growth done fruita first sheet transport path that guides the sheet to the sheet support means; a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a junction upstream in a sheet transport direction from an outlet to the sheet support means; a guide means that guides the sheet to the first sheet transport path or the second sheet transport path at the branching portion; and a control means that controls the guide means, wherein a length of the second sheet transport path is longer than that of the first sheet transport path between the branching portion and the junction portion, and the control means guides a leading sheet of a plurality of sheets that constitute a sheet stack to be post-processed by the post-processing means to the second sheet transport path. the guiding means is controlled so as to guide a final sheet to the first sheet transport path, and selectively guide sheets other than the leading sheet and the final sheet to either the first sheet transport path or the second sheet transport path for each sheet, and a sheet transported on the second sheet transport path and a sheet following the sheet transported on the first sheet transport path are merged in an overlapping manner at the junction, and the control means controls the guiding means to guide at least one sheet whose leading end reaches the branching portion, among sheets constituting a sheet stack one sheet behind the sheet stack, to the second sheet transport path when the post-processing means is in a non-processing state in which the post-processing means is not processing the sheet stack stacked on the sheet support means. The image forming system is characterized in that: Effect of the Invention

[0011] According to the present invention, the sheet can be transported in a distributed manner between the first sheet transport path and the second sheet transport path. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of an image forming system according to a first embodiment. [Diagram 2]FIG. 2 is a block diagram of a hardware configuration of a sheet processing apparatus controller according to the first embodiment. [Diagram 3] FIG. 2 is a functional block diagram of the sheet processing apparatus according to the first embodiment. [Figure 4] FIG. 4A is a diagram showing sheet conveyance, and FIG. 4B is a schematic diagram for explaining the positional relationship of sheets. [Diagram 5] FIG. 1A is a schematic diagram for explaining an alignment process in the sheet processing apparatus, and FIG. 1B is a schematic diagram showing a case where the alignment process is not performed on the first sheet. [Figure 6] FIG. 2A is a diagram showing sheet transport in a sheet processing apparatus according to a first embodiment, and FIG. 2B is a diagram showing sheet transport in a sheet processing apparatus according to a second embodiment. [Figure 7] 4 is a control flowchart in the sheet processing apparatus according to the first embodiment of the present invention. [Figure 8] 10 is a control flowchart in a sheet processing apparatus according to a second embodiment of the present invention. [Figure 9] FIG. 13 is a block diagram showing a hardware configuration of a sheet processing apparatus controller according to a third embodiment. [Figure 10] FIG. 13 is a functional block diagram of a sheet processing apparatus according to a third embodiment. [Figure 11] FIG. 13 is a control flowchart of sheet conveyance according to the third embodiment. [Figure 12] Schematic diagrams showing the positional relationship of the sheets, (a) showing the state where the leading edge of the third sheet has been transported to the branching point of the retreat transport path and the lower discharge transport path, (b) showing the state where the distance between the leading edge of the third sheet and the trailing edge of the first sheet is equal to or less than a predetermined distance, and (c) showing the state where the fourth sheet has been transported. [Figure 13] FIG. 13 is a control flowchart of sheet conveyance in the fourth embodiment. [Figure 14]Schematic diagrams showing the positional relationship of the sheets, (a) showing the state where the third sheet is guided to the shunt conveying path, (b) showing the state where the distance between the leading edge of the fourth sheet and the trailing edge of the second sheet is equal to or less than a predetermined distance, and (c) showing the state where the fifth sheet has been conveyed. [Figure 15] FIG. 13 is a functional block diagram illustrating another example of the sheet processing apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions, and the scope of the present invention is not limited to the following embodiment. In the present embodiment, the sheet includes not only plain paper, but also special paper such as coated paper, recording materials of special shapes such as envelopes and index paper, and plastic films and cloths for overhead projectors. Furthermore, a manuscript is also an example of a sheet, and the manuscript may be blank or may have an image formed on one or both sides.

[0014] <First embodiment> (Schematic configuration of an image forming system) 1, an image forming system 1000 according to the present embodiment includes an image forming apparatus 1 that forms an image on a sheet, and a sheet processing apparatus 100 that serves as a sheet processing apparatus mounted on the image forming apparatus 1. The image forming apparatus 1 is an image forming apparatus that includes a so-called intermediate transfer tandem type image forming section 10 including four image forming units 10Y, 10M, 10C, and 10K inside the main body of the apparatus. The image forming apparatus 1 forms an image on a sheet S based on image information read from an original or image information input from an external device, and outputs the image.

[0015] The image forming units 10Y, 10M, 10C, and 10K are electrophotographic units that form toner images of yellow (Y), magenta (M), cyan (C), and black (K). The configurations of the image forming units are basically the same except for the color of the toner they contain, so the image forming process will be described using the yellow image forming unit 10Y as an example.

[0016] When the image forming process starts, the photosensitive drum 5Y of the image forming unit 10Y, which is configured by coating the outer periphery of an aluminum cylinder with an organic photoconductive layer, is rotated. The surface of the photosensitive drum 5Y is uniformly charged by a charging device 7Y, and then exposed by an exposure device (e.g., a laser scanner) 9Y to form an electrostatic latent image. The electrostatic latent image is then visualized (developed) by toner supplied from a developing device 11Y to form a toner image.

[0017] Similarly, in the image forming units 10M, 10C, and 10K, toner images of corresponding colors are formed on the photosensitive drums. The toner images formed on the photosensitive drums are primarily transferred by the corresponding primary transfer rollers 6Y to 6K onto the intermediate transfer belt 12, which is an intermediate transfer body, in such a way that they are superimposed on each other.

[0018] In parallel with such an image forming process, the sheet feeding unit 4 executes a feeding operation to feed the sheet S toward the image forming unit 10. The sheet feeding unit 4 includes a sheet supporting device such as a cassette 2 or a manual feed tray 3 that supports the sheet S, and the sheet feeding unit 4 that feeds the sheet S supported by the sheet supporting device. The sheet feeding unit 4 is made up of a mechanism such as a retard separation type or a separation pad type, and separates the sheets S one by one and feeds them to the registration unit 23.

[0019] The registration unit 23 corrects the skew of the sheet S and conveys the sheet S toward the secondary transfer unit 25 in accordance with the progress of the image forming process in the image forming unit 10. In the secondary transfer unit 25, the secondary transfer outer roller 9 and the secondary transfer inner roller 18c are arranged to sandwich the intermediate transfer belt 12. Then, in the secondary transfer nip between the secondary transfer outer roller 9 and the intermediate transfer belt 12, the toner image carried on the intermediate transfer belt 12 is secondarily transferred to the sheet S. The transfer residual toner remaining on the intermediate transfer belt 12 is removed by the belt cleaning device 21. Note that the secondary transfer outer roller 9 abuts against the intermediate transfer belt 12 as shown by the solid line during secondary transfer, but is spaced from the intermediate transfer belt 12 at the position shown by the dotted line when secondary transfer is not being performed.

[0020] The sheet S onto which the unfixed toner image has been transferred is delivered to the fixing device 13, where it is sandwiched between a pair of heating rollers 14, 15 and heated and pressurized, thereby melting and fixing (fixing) the toner. The sheet S onto which the image has been fixed is delivered to the sheet processing device 100. In this embodiment, the sheet onto which the image has been fixed is directly discharged to the sheet processing device 100 by the pair of heating rollers 14, 15 of the fixing device 13. However, a pair of discharge rollers may be provided between the fixing device 13 and the discharge port of the image forming apparatus 1, and the sheet may be conveyed to the sheet receiving port of the sheet processing device 100 by the pair of discharge rollers.

[0021] The sheet processing apparatus 100 receives the image-formed sheets sent from the image forming apparatus through an acceptance path 112, and sorts and stacks them into the upper discharge tray 103 and the lower discharge tray 104. When sorting the sheets into the upper discharge tray 103 and the lower discharge tray 104, a switching flapper 101 is driven by a solenoid (not shown) to switch the conveying path. That is, when the sheet is discharged into the upper discharge tray 103, the sheet is conveyed to the upper discharge conveying path 109, and when the sheet is discharged into the lower discharge tray 104, the sheet is conveyed to the lower discharge conveying path 110. The retreat conveying path 111 is a path branched off at a branching portion 114 on the lower discharge conveying path 110, and merges with the lower discharge conveying path 110 again at a lower discharge junction 113 located immediately before the discharge outlet to the lower discharge tray 104. This junction constitutes a junction located upstream in the sheet conveying direction from the discharge outlet to the sheet supporting means 104 in this embodiment. The lower discharge conveying path 110 has lower discharge conveying upstream rollers 120 and lower discharge conveying downstream rollers 121, and the retreat conveying path 111 has retreat conveying upstream rollers 122 and retreat conveying downstream rollers 123, which are driven by a lower discharge motor (not shown). The conveying path is switched to the retreat conveying path 111 by a discharge conveying switching flapper 102. The use of the retreat conveying path 111 will be described later.

[0022] The lower discharge tray 104 includes a staple unit 105, a staple unit moving mechanism 115, and an alignment belt 106, and is capable of carrying out the following post-processing. When the trailing end of the sheet conveyed to the lower discharge tray 104 passes through the discharge rollers 107, the alignment belt 106 is lowered by a lifting motor (not shown) so as to come into contact with the sheet, and then rotated in a counterclockwise direction (in the direction of the arrow in the figure) by a driving motor (not shown). Then, the sheet is abutted against a stopper 108 to perform alignment processing in the discharge direction. When stapling is performed, after a predetermined number of sheets are stacked on the lower discharge tray 104 to form a stack, the staple unit moving mechanism 115 moves the staple unit 105 to a staple position, and the staple unit 105 performs stapling processing. During the above stapling processing, the lower discharge tray 104 cannot accept subsequent sheets.

[0023] (Hardware configuration of image forming system) Next, the hardware configuration of the image forming system 1000 around the sheet processing apparatus 100 will be described with reference to FIG. 2. Note that the configuration related to the conveyance to the upper discharge tray 103 will be omitted here. Reference numeral 301 denotes a controller that manages the image forming apparatus 1 and the sheet processing apparatus 100, 302 denotes an engine control unit that controls the image forming apparatus 1, and 303 denotes a sheet processing apparatus controller that controls the sheet processing apparatus 100. Reference numeral 304 denotes a serial command transmission signal line that transmits an instruction from the controller 301 to the engine control unit 302, and 305 denotes a serial command transmission signal line that transmits an instruction from the controller 301 to the sheet processing apparatus controller 303 by serial communication. Reference numeral 306 denotes a serial status transmission signal line that transmits status data from the engine control unit 302 to the controller 301 in response to the command, and 307 denotes a serial status transmission signal line that transmits status data from the sheet processing apparatus controller 303 to the controller 301 by serial communication. When performing a printing operation, the controller 301 transmits a serial command to the engine control unit 302 and the sheet processing apparatus controller 303. Also, control is performed by receiving status data from the engine control unit 302 and the sheet processing apparatus controller 303. In this way, when a plurality of devices are connected and operating, the controller 301 centrally manages the control and status of each device, and maintains consistency of operation between the devices.

[0024] The sheet processing apparatus controller 303 is a control IC and includes a CPU 231 for controlling various operations of the sheet processing apparatus, and a RAM 232 for temporarily storing control data required for the operation of the sheet processing apparatus. The sheet processing apparatus controller 303 also includes a ROM 233 for non-volatilely storing control tables required for the operation of the sheet processing apparatus, and a communication module 234 for performing communication processing with the controller 301 and the like. The sheet processing apparatus controller 303 further includes an I / O port 240 for inputting and outputting control signals to various units in the sheet processing apparatus 100. The staple unit drive circuit 201 and the staple unit movement motor drive circuit 202 receive control signals from the sheet processing apparatus controller 303 and drive the staple unit 105 and the staple unit movement mechanism 115 in the post-processing unit 211. The alignment belt motor drive circuit 203, the lower discharge motor drive circuit 204, and the discharge conveyance switching solenoid drive circuit 205 also receive control signals and drive the alignment belt 106, the lower discharge conveyance motor 330, and the discharge conveyance switching solenoid 331.

[0025] FIG. 3 is a control block diagram for explaining the transport control performed by the sheet processing apparatus controller 303. Note that, here, the configuration related to the transport to the upper discharge tray 103 is omitted. In FIG. 3, the sheet processing apparatus controller 303 has a transport control unit 308, a post-processing unit control unit 309, a lower discharge motor control unit 313, and a discharge transport switching solenoid control unit 314. The transport control unit 308 performs a discharge transport operation in response to a discharge control command from the controller, and instructs the post-processing unit control unit 309 to perform post-processing on the sheet and the bundle of sheets discharged from the image forming apparatus. The post-processing unit control unit 309 controls the staple unit 105, the staple unit moving mechanism 115, and the alignment belt 106 in the post-processing unit 211. When the sheet is discharged to the lower discharge tray 104, the transport control unit 308 drives the lower discharge transport motor 330 by the lower discharge motor control unit 313 to rotate the lower discharge transport upstream roller 120 and the lower discharge transport downstream roller 121 in the lower discharge transport path 110. Also, it rotates the shunt transport upstream rollers 122 and the shunt transport downstream rollers 123 in the shunt transport path 111. When the discharge destination of the sheet is the lower discharge tray 104, the discharge path switching control unit 320 of the transport control unit 308 determines whether to send the sheet to the shunt transport path 111 or to the lower discharge transport path 110. Then, the discharge transport switching solenoid control unit 314 drives the discharge transport switching solenoid 331, and the discharge transport switching flapper 102 switches the transport path.

[0026] (Configuration of evacuation transport path) Next, the relationship between the retreat conveying path 111 and the productivity of the entire apparatus when post-processing is performed in the lower discharge tray 104 will be described. FIG. 4(a) is a diagram showing the relationship between the sheet leading end position and time, with the vertical axis representing the position in the lower discharge conveying path 110 and the horizontal axis representing the elapsed time. The starting point of the vertical axis is the start position of the lower discharge conveying path 110, that is, the position where the discharge destination switching flapper 101 branches off from the receiving path 112. When post-processing is not performed on the preceding sheet stack, the sheet enters the lower discharge conveying path 110 (A in FIG. 4(a)), and then passes through the discharge conveying switching flapper 102 position (B in FIG. 4(a)), the lower discharge junction 113 position (C in FIG. 4(a)), and the discharge rollers 107. Then, discharge to the lower discharge tray 104 is completed (H in FIG. 4(a)). When the discharge of the last sheet of the first bundle to the lower discharge tray 104 is completed, that is, when the trailing edge of the third sheet passes the position of the discharge roller 107 (D in FIG. 4A), the three-sheet bundle is stapled on the lower discharge tray 104. In order to maximize the print productivity of the system, the sheet processing apparatus 100 needs to accept the sheets sent at the interval of the maximum productivity of the image forming apparatus. On the other hand, it takes a certain amount of time to staple the bundle of sheets, and the lower discharge tray 104 cannot accept subsequent sheets during this process. Here, the conveying path of the first sheet S11 of the subsequent bundle is switched by the discharge conveying switching flapper 102, and the sheet is conveyed to the evacuation conveying path 111 (E in FIG. 4A). The evacuation conveying path 111 has a longer path length to the lower discharge junction 113 than the lower discharge conveying path 110. That is, the path length of the second sheet transport path (111) between the branching portion 114 and the junction portion 113 is longer than the path length of the first sheet transport path (110). This makes it possible to delay the timing at which the first sheet S11 of the following stack arrives at the lower discharge junction 113 (F in FIG. 4A). In this figure, a section EF in which the sheet S11 proceeds along the retreat transport path 111 is indicated by a dotted line, and the sheet S11 arrives at the lower discharge junction 113 almost overlapping with the following sheet S12 transported to the lower discharge transport path 110.FIG. 4B shows the positional relationship of the sheets in the conveying path at the timing when the leading edge of the second sheet S12 and the leading edge of the first sheet S11 reach the lower discharge junction 113 and join together.

[0027] As described above, when post-processing is performed in the lower discharge tray 104, the first sheet of the following stack is detouring to the evacuation conveying path 111, so that the sheet processing device 100 can always receive sheets at a constant interval from the image forming device 1. The sheet S11 detouring to the evacuation conveying path 111 and the following sheet S12 conveyed to the lower discharge conveying path 110 need to be merged so as to overlap at the lower discharge junction 113 for the alignment process described later. For this purpose, it is necessary to configure the path length of the evacuation conveying path 111 to be longer than the path length of the lower discharge conveying path 110, or to configure the conveying speed of the sheet S11 in the evacuation conveying path to be slower than the conveying speed of the sheet S12 in the lower discharge conveying path 110. In this embodiment, the lower discharge conveying upstream rollers 120 and the lower discharge conveying downstream rollers 121 and the evacuation conveying upstream rollers 122 and the evacuation conveying downstream rollers 123 are driven at a constant speed by the same lower discharge conveying motor 330 (see FIG. 2). The speed is the same as the conveying speed of the upstream receiving path 112. Therefore, the path length of the shunt conveying path 111 is designed to be long enough so that the leading edge of the first sheet S11 reaches and merges with the lower discharge junction 113 at the same time that the leading edge of the second sheet S12 of the second bundle conveyed on the lower discharge conveying path 110 reaches the lower discharge junction 113. Therefore, the first sheet S11 and the second sheet S12 that have merged are discharged to the lower discharge tray 104 in a substantially overlapping state.

[0028] The time T_DG from when the trailing edge of the last sheet in a stack passes through discharge rollers 107 until the leading edge of the first sheet (first sheet S1) in the next stack reaches discharge rollers 107 is determined by the productivity of the image forming apparatus. In order to maximize the productivity of the system without any lost time due to the sheet processing apparatus 100 at the maximum throughput of the image forming apparatus, the time T_process required for the alignment and stapling of the stack must be designed to be shorter than the value of T_DG at the maximum throughput of the image forming apparatus. If T_process is longer than this, it is necessary to reduce the productivity of the image forming apparatus and increase the paper gap between stacks.

[0029] As can be seen from FIG. 4(a), among the sheets discharged to the lower discharge tray 104, only the first sheet of the stack to be post-processed passes through the evacuation conveying path 111. That is, the more sheets per stack to be post-processed, and the more copies (bundles) of stacks to be post-processed, the more the number of sheets passing through the lower discharge conveying path 110 becomes biased. In such a sheet processing device, a large number of sheets are usually passed through throughout the life of the device, and the characteristics of the sheet conveying performance may change due to the wear of the conveying rollers and the accumulation of paper dust in the path. In a configuration in which sheets that have passed through different conveying paths are merged and overlapped as in this example, if the amount of sheets passing through one path is biased, there is a risk that the degree of influence of roller wear and paper dust accumulation on the conveying performance may be greater than that of the other path. In such a case, the following problems may occur in the alignment process.

[0030] (Example of a problem in alignment processing due to uneven paper feed volume) Here, with reference to FIG. 5, the alignment process for two sheets that are joined at the lower discharge junction 113 and conveyed to the lower discharge tray 104 will be described. For these two overlapping sheets that are conveyed, the trailing end of the first sheet S11 of the stack is pulled back by the alignment belt 106 before the trailing end of the second sheet S12 of the stack, and strikes the stopper 108. Then, the second sheet S12 of the stack slides over the first sheet S11 of the stack and is similarly aligned by the stopper 108. For this purpose, as shown in FIG. 5(a), the second sheet S12 of the stack overlapping on the upper side needs to be discharged to the lower discharge tray 104 in a state where it has advanced beyond the first sheet S11 of the stack that is located below. Here, if the conveying performance changes significantly only in one path, there is a risk that the shift amount L_shift of the leading ends of the sheet S12 conveyed on the lower discharge conveying path 110 and the sheet S11 conveyed on the retreat conveying path 111 will not be as designed, and the desired alignment process will not be performed. In particular, if the transport performance of only the lower discharge transport path 110 is reduced, causing a delay in the transport of S12, and the second sheet S12 of the stack overlapping on the upper side is discharged to the lower discharge tray 104 behind the first sheet S11 of the stack below, as shown in Figure 5(b), no alignment process is performed on S11 at the bottom.

[0031] (Path switching control) As described above, in this embodiment, path switching control is executed so that the amount of paper passing through is not extremely biased between the lower discharge conveying path 110 and the retreat conveying path 111. That is, in this embodiment, the occurrence of lost time by the sheet processing apparatus 100 is avoided, the amount of paper passing through both paths is distributed, and the paths are switched so that the degree of influence on conveying performance due to roller wear and paper powder accumulation is not large only on one path.

[0032] Fig. 6(a) is a diagram showing the relationship between the sheet leading edge position and time when the sheet is transported on the lower discharge transport path by the path switching control according to the present embodiment, and shows an example in which staple processing is performed for multiple copies in groups of five sheets. The explanation of the sheet leading edge position on the vertical axis and the explanation of the retreat transport path shown by the dotted line are the same as those in Fig. 4(a). That is, the section in which the sheet S11 proceeds on the retreat transport path 111 from the position of the discharge transport switching flapper 102 to the position of the lower discharge junction 113 is shown by the dotted line, and the case where the sheet S11 proceeds on the lower discharge transport path 110 is shown by the solid line.

[0033] 6A, the last sheet of each stack is discharged to the lower discharge tray 104 through the lower discharge path 110, and while the sheet stack is being post-processed on the lower discharge tray 104, the first sheet of the following stack passes through the evacuation path 111. The transport path is switched so that stacks with a larger number of sheets passing through the lower discharge path 110 (first, third, fifth stack) and stacks with a larger number of sheets passing through the evacuation path 111 (second, fourth stack) are alternately repeated. It can be seen that the sheets sent at regular intervals from the image forming apparatus to the lower discharge path 110 are post-processed while maintaining productivity, and the number of sheets passing through the lower discharge path 110 and the evacuation path 111 are approximately the same.

[0034] 7 is a flowchart of path switching control performed by the discharge path switching control unit 320 when discharging the sheet S1 to the lower discharge tray 104 in order to realize the present invention. Note that this flowchart will be described on the assumption that the sheet S1 is the second or subsequent stack of sheets in a job, but in implementing the present invention, there is no problem in applying this to the first stack of sheets in a job in order to simplify the control program.

[0035] In step S101, it is determined whether sheet S1 is the first sheet of a stack to be subjected to sheet post-processing on the lower discharge tray 104. If it is the first sheet of the stack, the lower discharge tray 104 cannot accept the next sheet because the preceding stack is being post-processed. Therefore, in step S104, sheet S1 is sent to the shunt conveyance path 111.

[0036] Here, the discharge path switching control unit 320 stores a path selection mode, which is an internal control state, in the RAM 232, and alternates between two states, the evacuation conveying path paper passing mode and the lower discharge conveying path paper passing mode, for each post-processing bundle. That is, in step S106, if the current path selection mode is the evacuation conveying path paper passing mode, the path selection mode is switched to the lower discharge conveying path paper passing mode (step S107). On the other hand, if the current path selection mode is not the evacuation conveying path paper passing mode, the path selection mode is switched to the evacuation conveying path paper passing mode (step S108). In the path switching control for the second and subsequent sheets of the bundle, the path selection mode stored here is applied.

[0037] If the answer is No in step S101, that is, if the sheet S1 is not the first sheet of the stack of sheets to be post-processed on the lower discharge tray 104, it is determined in step S102 whether the sheet S1 is the last page of the stack of sheets to be post-processed on the lower discharge tray 104. If it is the last sheet of the stack of sheets to be post-processed (Yes in S102), it is sent to the lower discharge conveying path 110 in S105. That is, the last sheet of the multiple sheets that make up the sheet stack is guided to the lower discharge conveying path 110 as the first sheet conveying path. If the sheet S1 is not the first sheet of the stack of sheets to be post-processed or the last page of the stack of sheets to be post-processed (No in S102), the conveying destination of the sheet S1 is switched in step S103 according to the current path selection mode. That is, if the current path selection mode is the lower discharge conveying path paper passing mode (No in S103), it is sent to the lower discharge conveying path 110 in step S105. On the other hand, if the current path selection mode is the bypass transport path paper passing mode (Yes in S103), the sheet is sent to the bypass transport path 111 in S104.

[0038] As described above, according to this embodiment, the productivity of the system can be maintained in a configuration in which sheets that have passed through different transport paths are merged and overlapped. In addition, the transport paths are switched so that the paper feed volume of both paths is distributed, and it is possible to prevent the degree of influence of roller wear and paper dust accumulation on the transport performance from being biased toward one path. As a result, even if the cumulative amount of sheets fed to the post-processing tray increases, the positional relationship of the overlapped sheets is maintained as intended by the design, and post-processing such as alignment is performed correctly.

[0039] In addition, in this embodiment, the lower discharge tray 104 can be said to be a sheet support means for supporting discharged sheets, and the post-processing unit 211 can be said to be a sheet processing means for processing a sheet bundle consisting of a plurality of sheets discharged onto the sheet support means. Furthermore, the lower discharge transport path 110 can be said to be a first sheet transport path for transporting sheets to the sheet support means. Furthermore, the retreat transport path 111 can be said to be a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a merging portion upstream in the sheet transport direction from the discharge outlet to the sheet support means. Furthermore, the discharge transport switching flapper 102 can be said to be a guide means that selectively guides the sheet to the first sheet transport path or the second sheet transport path at the branching portion, and the sheet processing device controller 303 can be said to be a control means that controls the guide means. In addition, in this embodiment, the lower discharge transport path paper passing mode can be said to be a first mode that controls the guide means so that the number of sheets discharged to the sheet support means via the first sheet transport path increases. Furthermore, the shunt transport path sheet passing mode can be said to be a second mode in which the guiding means is controlled so that the number of sheets discharged to the sheet supporting means via the second sheet transport path increases among the multiple sheets constituting the sheet bundle. When the sheet processing means processes multiple sheet bundles continuously, the control means is capable of switching between the first mode and the second mode for each sheet bundle. More specifically, the first mode and the second mode are alternately switched for each sheet bundle. For this reason, the mode switching is executed so that the number of sheet bundles processed in the first mode and the number of sheet bundles processed in the second mode are approximately equal to each other among the total number of sheet bundles processed in the input sheet processing job (for example, the difference between the number of sheet bundles processed in the first mode and the number of sheet bundles processed in the second mode is 1 or less).

[0040] In this way, in the second mode, at least one sheet of the sheet bundle whose leading edge reaches the branching portion after the sheet processing means completes processing of the preceding sheet bundle discharged onto the sheet support means immediately before the sheet bundle is conveyed to the retreat conveying path 111. That is, in the second mode, the control means causes the guiding means to guide at least some of the sheets to the second sheet conveying path in a non-processing state in which the sheet processing means is not processing the sheet bundle on the sheet support means. Therefore, among the sheets following the first sheet of the sheet bundle, at least one sheet whose leading edge reaches the branching portion in the non-processing state is guided to the second sheet conveying path. This allows the sheets to be conveyed in a distributed manner between the first sheet conveying path and the second sheet conveying path, and the number of sheets to be sent to the first sheet conveying path and the number of sheets to be sent to the second sheet conveying path can be balanced among the total number of sheets conveyed during the input sheet processing job.

[0041] In the above-described embodiment, the lower discharge tray 104 is exemplified as a sheet supporting means, which serves both as an intermediate processing tray that temporarily supports sheets for processing the sheets and as a discharge tray to which the final product is discharged. However, the intermediate processing tray and the discharge tray may be provided separately, and the intermediate processing tray may serve as the sheet supporting means. In addition, although the post-processing unit 211 equipped with the staple unit 105 is exemplified as the sheet processing means, the sheet processing means may be configured to include, for example, a punching means for punching holes in the sheets.

[0042] In addition, in the present embodiment, the discharge path switching control unit 320 alternately switches the path selection mode for each bundle. In a job received by the sheet processing apparatus controller 303, when the total number of bundles (number of copies) to be post-processed is known in advance, the discharge path switching control unit 320 may schedule to switch the path selection mode for each number of copies so that the number of copies in each mode is half of the total number of copies. That is, similar to the case where the path selection mode is alternately switched for each conveyed sheet bundle, the discharge path switching control unit 320 may schedule to switch the path selection mode for each number of copies so that the difference between the number of sheet bundles processed in the first mode and the number of sheet bundles processed in the second mode is 1 or less. For example, when it is known that the total number of copies is a staple job of 10 copies, an embodiment is also possible in which the first 5 copies are conveyed in the lower discharge conveying path paper passing mode and the last 5 copies are conveyed in the evacuation conveying path paper passing mode.

[0043] <Second embodiment> Next, a second embodiment of the present invention will be described. In the above-mentioned first embodiment, a method for managing the distribution of the paper passing amount between the lower discharge conveying path 110 and the retreat conveying path 111 with the post-processing stack as one unit has been described. On the other hand, in the present embodiment, a difference is that path switching control is executed so as to distribute the distribution of the paper passing amount to both paths within one post-processing stack. In the following description, only the points different from the first embodiment will be described, and the other points will be omitted by assigning the same reference symbols as in the first embodiment.

[0044] FIG. 6B is a diagram showing the relationship between the position of the leading edge of a sheet and time when the sheet is conveyed along the lower discharge conveying path by the path switching control according to the present embodiment, and staple processing is performed for multiple copies, every five sheets, as in the first embodiment. As shown in FIG. 6B, the last sheet of each stack is discharged to the lower discharge tray 104 via the lower discharge conveying path 110, and while the sheet stack is being post-processed on the lower discharge tray 104, the first sheet of the following stack is passed through the evacuation conveying path 111. Then, the conveying path is switched so that the sheets passing through the lower discharge conveying path 110 and the evacuation conveying path 111 alternate in the stack to be post-processed. It can be seen that the sheets sent from the image forming device to the lower discharge conveying path 110 at regular intervals are post-processed without causing loss time in the sheet processing device, and the number of sheets passing through the lower discharge conveying path 110 and the evacuation conveying path 111 is almost the same.

[0045] 8 is a flowchart of path switching control in this embodiment performed by the discharge path switching control unit 320 when discharging sheets to the lower discharge tray 104. Note that, as in the first embodiment, this flowchart will be described on the assumption that the sheets are the second or subsequent stacks of sheets in a job, but in implementing the present invention, there is no problem if it is applied to the first stack of sheets in a job in order to simplify the control program.

[0046] In step S201, it is determined whether the sheet is the first sheet of the stack to be post-processed on the lower discharge tray 104. If it is the first sheet of the stack, the lower discharge tray 104 cannot accept the next sheet because the preceding stack is being post-processed. Therefore, in step S204, the sheet S1 is sent to the evacuation conveyance path 111. If the answer is No in step S201, that is, if the sheet S1 is not the first sheet of the stack to be post-processed on the lower discharge tray 104, it is determined in S202 whether the sheet is the last sheet of the post-processed stack. If the sheet is the last sheet of the post-processed stack (Yes in S202), it is sent to the lower discharge conveyance path 110 in S205. If the sheet is not the last sheet of the post-processed stack (No in S202), it is determined in step S203 whether the sheet S1 is the even-numbered sheet of the post-processed stack. If sheet S1 is an even-numbered sheet in the stack (Yes in S203), it is sent to the lower discharge conveying path 110 in S205. On the other hand, if sheet S1 is an odd-numbered sheet in the stack (No in S203), it is sent to the retreat conveying path 111 in S204.

[0047] In this manner, in the present embodiment, the control means (303) controls the guiding means to guide the first sheet (S1) of the sheet bundle processed by the sheet processing means to the second sheet transport path, and the second sheet (S2) following the first sheet to the first sheet transport path, so that the first and second sheets merge in a manner that they overlap at the junction. The control means then guides at least one sheet following the second sheet among the multiple sheets constituting the sheet bundle to the second sheet transport path. More specifically, the control means controls the guiding means so that the sheets following the second sheet among the multiple sheets constituting the sheet bundle are alternately guided to the first sheet transport path and the second sheet transport path for each unit number of sheets. By guiding at least one sheet following the second sheet to the second sheet transport path, the sheet is transported to the second sheet transport path during the sheet dischargeable period when the post-processing of the preceding sheet bundle is completed. That is, when the leading edge of the sheet following the second sheet and guided to the second sheet transport path reaches the branching portion, the sheet processing means is in a non-processing state in which the sheet stack on the sheet supporting means is not processed. This allows the sheets to be distributed and transported between the first sheet transport path and the second sheet transport path, and balance is achieved between the number of sheets sent to the first sheet transport path and the number of sheets sent to the second sheet transport path among the total number of sheets transported during the input sheet processing job. In this embodiment, the unit number is set to 1, but is not limited to this and may be set to a number such as 2 or 3.

[0048] <Third embodiment> Next, a third embodiment of the present invention will be described. In the first embodiment described above, the rollers 120 and 121 in the lower discharge conveying path 110 and the rollers 122 and 123 in the retreat conveying path 111 are driven in conjunction with each other by the lower discharge conveying motor 330. For this reason, the conveying speed of the sheet conveyed in the lower discharge conveying path 110 and the retreat conveying path 111 cannot be set individually. In this embodiment, the conveying speed of the sheet conveyed in these conveying paths 110 and 111 can be set independently, which is different from the first embodiment described above. In the following description, only the points different from the first embodiment will be described, and the description of the other points will be omitted by assigning the same reference numerals as those in the first embodiment.

[0049] Fig. 9 is a diagram showing a hardware configuration of an image forming system 1000 around the sheet processing apparatus 100 according to this embodiment. Fig. 10 is a control block diagram for explaining the transport control performed by the sheet processing apparatus controller 303 according to this embodiment. As shown in Figs. 9 and 10, in this embodiment, a lower discharge transport downstream clutch 332 is disposed on a power transmission path between the lower discharge transport motor 330 and the lower discharge transport downstream roller 121. Also, a shunt transport downstream clutch 333 is disposed on a power transmission path between the lower discharge transport motor 330 and the shunt transport downstream roller 123.

[0050] The lower discharge conveyance downstream clutch 332 is configured to be driven by the lower discharge conveyance downstream clutch drive circuit 206, and rotates and stops the lower discharge conveyance downstream roller 121. The shunt conveyance downstream clutch 333 is configured to be driven by the shunt conveyance downstream clutch drive circuit 207, and rotates and stops the shunt conveyance downstream roller 123. In addition, the sheet stop control unit 321 of the conveyance control unit 308 judges whether to stop the sheets in the lower discharge conveyance path 110 and the shunt conveyance path 111, or to release the stop of the stopped sheets. Based on the judgment result described later, the sheet stop control unit 321 rotates and stops the lower discharge conveyance downstream roller 121 by the lower discharge conveyance downstream clutch 332 using the clutch control unit 315. In addition, the shunt conveyance downstream clutch 333 rotates and stops the shunt conveyance downstream roller 123.

[0051] (Discharge and transport control) Next, the sheet discharge / conveyance control using the lower discharge / conveyance downstream clutch 332 and the shunting / conveyance downstream clutch 333 will be described with reference to Figures 11 and 12. Note that in the following description, the conveyance control of the second bundle of sheets will be described on the assumption that the preceding bundle of sheets has been discharged to the lower discharge tray 104. Also, in the following description, an example is shown in which stapling is performed on a bundle of three sheets.

[0052] FIG. 11 is a flowchart showing the control of the conveyance control unit 308 switching between the lower discharge conveyance path 110 and the retreat conveyance path 111 in the conveyance of the second bundle of sheets, and the control of the stop and restart of conveyance of the sheets in the two conveyance paths. First, the conveyance control of the first sheet S1 of the bundle will be described. In step S301, the conveyance control unit 308 judges whether the sheet is the first sheet of the bundle to be subjected to the sheet post-processing performed on the lower discharge tray 104. If it is judged to be the first sheet of the bundle, in step S302, the discharge path switching control unit 320 switches the discharge conveyance switching flapper 102 to send the sheet S1 to the retreat conveyance path 111. Then, in step S303, if the conveyance control unit 308 judges that the sheet S1 has reached the retreat conveyance downstream rollers 123, in step S304, the sheet stop control unit 321 operates the retreat conveyance downstream clutch 333. Then, the retreat conveyance downstream rollers 123 are stopped, and the sheet S1 is stopped in the retreat conveyance path 111.

[0053] Next, the conveyance control of the second sheet S2 of the stack will be described. In step S301, the conveyance control unit 308 determines that the sheet is not the first sheet of the stack, and then in step S305, the conveyance control unit 308 determines whether the sheet is the second sheet of the stack. If it is determined that the sheet is the second sheet of the stack, in step S306, the discharge path switching control unit 320 switches the discharge conveyance switching flapper 102 to send the sheet S2 to the lower discharge conveyance path 110. Then, in step S307, if the conveyance control unit 308 determines that the sheet S2 has reached the lower discharge conveyance downstream rollers 121, in step S308, the sheet stop control unit 321 operates the lower discharge conveyance downstream clutch 332. Then, the lower discharge conveyance downstream rollers 121 are stopped, and the sheet S2 is stopped in the lower discharge conveyance path 110.

[0054] Next, the conveyance control of the third sheet S3 of the stack will be described. In steps S301 and S305, the conveyance control unit 308 determines that the sheet S3 is neither the first nor the second sheet of the stack, and then in step S309, the conveyance control unit 308 determines whether the sheet S3 is the third sheet of the stack. If the sheet S3 is determined to be the third sheet of the stack, in step S310, the discharge path switching control unit 320 switches the discharge conveyance switching flapper 102 to send the sheet S3 to the evacuation conveyance path 111. FIG. 12A shows the sheet S1 stopped in the evacuation conveyance path 111, the sheet S2 stopped in the lower discharge conveyance path 110, and the sheet S3 conveyed to the evacuation conveyance path 111. In step S311, if the conveyance control unit 308 determines that the distance between the leading edge of the sheet S3 and the trailing edge of the sheet S1 is within a predetermined distance L, in step S312, the sheet stop control unit 321 releases the evacuation conveyance downstream clutch 333. Then, the shunting conveyance downstream roller 123 is rotated, and the conveyance of the sheet S1 is resumed so that the sheet S3 and the sheet S1 do not come into contact with each other. In this embodiment, in consideration of the response time of the shunting conveyance downstream clutch 333, it is determined that the distance between the leading edge of the sheet S3 and the trailing edge of the sheet S1 is within 20 mm, and the sheet S3 and the sheet S1 are within the predetermined distance L. Then, the lower discharge conveyance downstream clutch 332 is released in accordance with the release of the shunting conveyance downstream clutch 333 of the sheet S1 so that the sheets S1 and S2 overlap at the lower discharge junction 113. Then, the lower discharge conveyance downstream roller 121 is rotated, and the conveyance of the sheet S2 is resumed. FIG. 12(b) is a diagram showing the sheet S3 being conveyed to the shunting conveyance path 111, and the conveyance of the sheet S1 and the conveyance of the sheet S2 being resumed so that the sheets S3 and S1 do not come into contact with each other.

[0055] Next, the conveyance of the fourth sheet S4 of the stack will be described. When the conveyance control unit 308 determines in step S309 that it is the fourth sheet of the stack, in step S313 the discharge path switching control unit 320 switches the discharge / conveyance switching flapper 102 to send the sheet to the lower discharge conveyance path 110. Figure 12(c) shows the position of the fourth sheet S4 of the stack when it is being conveyed to the lower discharge conveyance path 110. The fifth and subsequent sheets are also sent to the lower discharge conveyance path 110 in the same manner as sheet S4.

[0056] By transporting in this manner, the time from when sheet S1 stops in the shunt transport path 111 until the leading edge of sheet S3 reaches the trailing edge of sheet S1 can be allocated to the post-processing time for the preceding bundle. When receiving post-processed sheets for a third bundle following the second bundle, each sheet is sent to the post-processing unit 211 according to the flowchart in FIG. 11 in the same way as for the second bundle.

[0057] As described above, according to the present invention, in a configuration in which sheets that have passed through different transport paths are merged and post-processed onto multiple overlapping sheets, it is possible to increase the time available for post-processing without reducing productivity.

[0058] In this embodiment, the lower discharge convey downstream roller 121 can be considered as a first sheet conveying means for conveying a sheet in the first sheet conveying path. The retreat convey downstream roller 123 can be considered as a second sheet conveying means for conveying a sheet in the second sheet conveying path and capable of being driven independently of the first sheet conveying means. The control means (303) temporarily stops the first sheet (S1) in the second sheet conveying path and temporarily stops the second sheet in the first sheet conveying path. It can also be said that the control means (303) controls the first and second sheet conveying means to release the stop of the first and second sheets before the leading edge of the third sheet (S3) following the second sheet reaches the trailing edge of the first sheet.

[0059] <Fourth embodiment> Next, a fourth embodiment of the present invention will be described. In the following description, only the points different from the third embodiment will be described, and the other points will be omitted by assigning the same reference symbols as in the first to third embodiments. The hardware configuration and control blocks for realizing this embodiment are the same as those in the third embodiment. Also, the length of the sheet to be conveyed is different from that in the third embodiment, and a case where two sheets enter the shunt conveying path 111 will be described. Also, the following description will be given by taking the conveying control of the second bundle of sheets as an example, as in the third embodiment.

[0060] 13 is a flowchart of the switching control between the lower discharge conveying path 110 and the retreat conveying path 111 by the conveying control unit 308 in conveying the second bundle of sheets, and the sheet stopping control in the conveying path. The sheet conveying control (S401 to S408) of the first and second sheets of the second bundle is similar to S301 to S308 in FIG. 11 described in the third embodiment, and a repeated description will be omitted.

[0061] The transport control of the third sheet S3 of the second bundle will be described. In steps S401 and S405, the transport control unit 308 determines that it is neither the first nor the second sheet of the bundle, and then in step S409, the transport control unit 308 determines whether it is the third sheet of the bundle. If it is determined that it is the third sheet of the bundle, in step S410, the discharge path switching control unit 320 switches the discharge / conveyor switching flapper 102 to send sheet S3 to the evacuation conveying path 111. FIG. 14(a) is a diagram showing that sheet S1 stops at the evacuation conveying path 111, sheet S2 stops at the lower discharge conveying path 110, and sheet S3 is conveyed to the evacuation conveying path 111.

[0062] Next, the transport control of the fourth sheet S4 of the second bundle will be described. In step S409, the transport control unit 308 determines that it is not the third sheet of the bundle, and then in step S411, the transport control unit 308 determines whether it is the fourth sheet of the bundle. If it is determined that it is the fourth sheet of the bundle, in step S412, the discharge path switching control unit 320 switches the discharge transport switching flapper 102 to send sheet S4 to the lower discharge transport path 110.

[0063] In step S413, when the conveyance control unit 308 determines that the distance between the leading edge of the sheet S4 and the trailing edge of the sheet S2 is within the predetermined distance L2, in step S414, the sheet stop control unit 321 releases the lower discharge conveyance downstream clutch 332. Then, the lower discharge conveyance downstream roller 121 is rotated to resume conveyance of the sheet S2 so that the sheet S4 and the sheet S2 do not come into contact with each other. In addition, the evacuation conveyance downstream clutch 333 is released in conjunction with the release of the lower discharge conveyance downstream clutch 332 so that the sheet S2 and the sheet S1 overlap at the lower discharge junction 113. In this embodiment, in consideration of the response time of the lower discharge conveyance downstream clutch 332, it is determined that the distance between the leading edge of the sheet S4 and the trailing edge of the sheet S2 is within 20 mm. FIG. 14B shows a state in which conveyance of the sheets S1 and S2 is resumed so that the sheets S4 and S2 do not come into contact with each other. Thereafter, the sheets S3 and S4 are conveyed so as to overlap each other at the lower discharge junction 113 and sent to the post-processing unit 211.

[0064] Next, the transport control of the fifth and subsequent sheets of a stack will be described. When the transport control unit 308 determines in step S411 that the sheet is the fifth or subsequent sheet of a stack, the discharge path switching control unit 320 switches the discharge transport switching flapper 102 to send the sheet to the lower discharge transport path 110 in step S415. The sheet is then sent to the post-processing unit without being stopped on the lower discharge transport path 110. Figure 14(c) shows the position of the fifth sheet S5 of the stack when it is transported to the lower discharge transport path 110. The sixth and subsequent sheets are also sent to the lower discharge transport path 110 in the same manner as sheet S5.

[0065] By transporting in this manner, the time from when sheet S1 stops in the retreat transport path 111 until the leading edge of sheet S4 reaches the trailing edge of sheet S2 present in the lower discharge transport path 110 can be allocated to the post-processing time for the preceding bundle. When accepting post-processed sheets for a third bundle following the second bundle, each sheet is sent to the post-processing unit 211 according to the flowchart in FIG. 13 in the same manner as for the second bundle.

[0066] As described above, according to the present invention, in a configuration in which sheets that have passed through different transport paths are merged and post-processing is performed on multiple overlapping sheets, it is possible to increase the time available for post-processing without reducing productivity.

[0067] In other words, in this embodiment, the control means (303) controls the first and second sheet conveying means to release the stop of the first and second sheets before the leading end of the fourth sheet (S4) reaches the trailing end of the second sheet.

[0068] In addition, in this embodiment, the case where the fourth sheet reaches the rear end of the second sheet has been described, but depending on the device configuration, the third sheet may reach the rear end of the first sheet first. In such a configuration, the same effect can be obtained by making S413 and S414 in the flow of Fig. 13 the processes following S410, and by subjecting the process of S413 to the first and third sheets.

[0069] In addition, in the above-mentioned embodiment, the lower discharge conveyance upstream roller 120, the lower discharge conveyance downstream roller 121, the shunt conveyance upstream roller 122, and the shunt conveyance downstream roller 123 are driven by the same driving source. However, the present invention is not limited to these configurations. For example, the lower discharge conveyance upstream roller 120 and the lower discharge conveyance downstream roller 121, and the shunt conveyance upstream roller 122 and the shunt conveyance downstream roller 123 may be driven by independent motors. Then, the two sheets may be overlapped by setting the respective speeds individually. A control block diagram in this case is shown in FIG. 15. In FIG. 15, a shunt conveyance section conveyance motor control section 413 and a shunt conveyance section conveyance motor 430 are provided, which drive the shunt conveyance upstream roller 122 and the shunt conveyance downstream roller 123. The other configurations are the same as those in FIG. 3. In this configuration, the speed of the shunting conveyance section conveyance motor 430 is controlled so that the sheet conveyance speed by the shunting conveyance upstream rollers 122 and the shunting conveyance downstream rollers 123 is slower than the sheet conveyance speed by the lower discharge conveyance upstream rollers 120 and the lower discharge conveyance downstream rollers 121. Therefore, two sheets overlap at the lower discharge junction 113.

[0070] Also, for example, in the case where all the rollers are driven by different driving sources, the sheet S1 may be stopped in the shunting conveyance path 111 by stopping the driving source of the shunting conveyance downstream roller 123 without using the shunting conveyance downstream clutch 333. The sheet S2 may be stopped in the lower discharge conveyance path 110 by stopping the driving source of the lower discharge conveyance downstream roller 121 without using the lower discharge conveyance downstream clutch 332. In the embodiment in which the sheet conveyance can be independently controlled in the lower discharge conveyance path 110 and the shunting conveyance path 111, the sheet conveyance speed in each of the conveyance paths 110, 111 may be changed according to the difference in the conveyance speed caused by wear in each of the conveyance paths 110, 111. In this case, the sheet does not need to be distributed to each of the conveyance paths 110, 111.

[0071] Furthermore, in the above-mentioned embodiment, the image forming system which forms an image by electrophotography has been described as an example, but the present invention may be applied to an image forming system which forms an image by inkjet. Also, the present invention has been described with an example in which the sheet processing apparatus 100 is controlled by the sheet processing apparatus controller 303, but it may be configured so that a part or the whole of the sheet processing apparatus 1 is controlled by a controller on the image forming apparatus 1 side. That is, in the present embodiment, the control means may be on the sheet processing apparatus 100 side or on the image forming apparatus 1 side, and the controllers on the sheet processing apparatus side and the image forming apparatus side may cooperate to constitute the control means. Furthermore, the above-mentioned embodiments may be combined in any manner. [Explanation of symbols]

[0072] 104: sheet support means (lower discharge tray), 110: first sheet transport path (lower discharge transport path), 111: second sheet transport path (shelter transport path), 113: junction (lower discharge junction), 114: branching section, 211: sheet processing means (post-processing unit), S1: first sheet, S2: second sheet

Claims

1. a sheet supporting means for supporting a sheet on which an image has been formed and which is sent from an image forming apparatus; a post-processing means for performing post-processing on a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting means; a first sheet transport path that guides a sheet sent from the image forming apparatus to the sheet support means; a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a merging portion upstream in a sheet transport direction from an outlet to the sheet support means; a guide means for guiding the sheet to the first sheet transport path or the second sheet transport path at the branching portion; A control means for controlling the guiding means, a length of the second sheet transport path is longer than a length of the first sheet transport path between the branching portion and the junction portion; the control means controls the guiding means to guide a leading sheet of a plurality of sheets constituting a sheet stack to be post-processed by the post-processing means to the second sheet transport path, guide a final sheet to the first sheet transport path, and selectively guide sheets other than the leading sheet and the final sheet to either the first sheet transport path or the second sheet transport path for each sheet, and merges a sheet transported on the second sheet transport path and a succeeding sheet transported on the first sheet transport path in an overlapping manner at the merging portion; the control means alternately switches, for each sheet bundle, whether to guide sheets other than the leading sheet and the last sheet of the plurality of sheets constituting the sheet bundle to the first sheet transport path or the second sheet transport path; A sheet processing apparatus comprising:

2. a sheet supporting means for supporting a sheet on which an image has been formed and which is sent from an image forming apparatus; a post-processing means for performing post-processing on a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting means; a first sheet transport path that guides a sheet sent from the image forming apparatus to the sheet support means; a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a merging portion upstream in a sheet transport direction from an outlet to the sheet support means; a guide means for guiding the sheet to the first sheet transport path or the second sheet transport path at the branching portion; A control means for controlling the guiding means, a length of the second sheet transport path is longer than a length of the first sheet transport path between the branching portion and the junction portion; the control means controls the guiding means to guide a leading sheet of a plurality of sheets constituting a sheet stack to be post-processed by the post-processing means to the second sheet transport path, guide a final sheet to the first sheet transport path, and selectively guide sheets other than the leading sheet and the final sheet to either the first sheet transport path or the second sheet transport path for each sheet, and merges a sheet transported on the second sheet transport path and a succeeding sheet transported on the first sheet transport path in an overlapping manner at the merging portion; the control means controls the guiding means to guide, when the post-processing means is in a non-processing state in which the post-processing means is not processing the sheet bundle stacked on the sheet supporting means, at least one sheet, the leading end of which reaches the branching portion, of the sheets constituting the sheet bundle immediately following the current sheet bundle, to the second sheet transport path. A sheet processing apparatus comprising:

3. the control means controls the guiding means so that sheets other than the leading sheet and the last sheet among the plurality of sheets constituting the sheet stack are alternately guided to the first sheet transport path and the second sheet transport path for each unit number of sheets.

3. The sheet processing apparatus according to claim 2, wherein the sheet processing apparatus is a sheet processing apparatus.

4. the control means controls the guiding means so as to balance the number of sheets to be sent to the first sheet transport path and the number of sheets to be sent to the second sheet transport path among the total number of sheets transported in the input sheet processing job.

4. The sheet processing apparatus according to claim 1, wherein the sheet processing apparatus is a sheet processing apparatus.

5. a first sheet transport means for transporting a sheet in the first sheet transport path; a second sheet transport means for transporting a sheet in the second sheet transport path and capable of being driven independently of the first sheet transport means; 5. The sheet processing apparatus according to claim 1, wherein the sheet processing apparatus is a sheet processing apparatus.

6. the control means controls the first and second sheet transport means so that a sheet transport speed in the second sheet transport path is slower than a sheet transport speed in the first sheet transport path.

6. The sheet processing apparatus according to claim 1, wherein the sheet processing apparatus is a sheet processing apparatus.

7. the control means controls the second sheet transport means to temporarily stop the sheet in the second sheet transport path.

6. The sheet processing apparatus according to claim 5,

8. The control means and controlling the guiding means so as to guide, when the post-processing means is in a non-processing state in which the post-processing means is not processing the sheet bundle stacked on the sheet supporting means, at least one sheet of the sheet constituting the sheet bundle following the current sheet bundle, the leading edge of which reaches the branching portion, to the second sheet transport path.

2. The sheet processing apparatus according to claim 1, wherein the sheet processing apparatus is a sheet processing apparatus.

9. an image forming unit that forms an image on a sheet; a sheet support means for supporting an image-formed sheet on which an image has been formed by the image forming unit; a post-processing means for processing a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting means; a first sheet transport path that guides the sheet on which the image has been formed to the sheet support means; a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a merging portion upstream in a sheet transport direction from an outlet to the sheet support means; a guide means for guiding the sheet to the first sheet transport path or the second sheet transport path at the branching portion; A control means for controlling the guiding means, a length of the second sheet transport path is longer than a length of the first sheet transport path between the branching portion and the junction portion; the control means controls the guiding means to guide a leading sheet of a plurality of sheets constituting a sheet stack to be post-processed by the post-processing means to the second sheet transport path, guide a final sheet to the first sheet transport path, and selectively guide sheets other than the leading sheet and the final sheet to either the first sheet transport path or the second sheet transport path for each sheet, and merges a sheet transported on the second sheet transport path and a succeeding sheet transported on the first sheet transport path in an overlapping manner at the merging portion; the control means alternately switches, for each sheet bundle, whether to guide sheets other than the leading sheet and the last sheet of the plurality of sheets constituting the sheet bundle to the first sheet transport path or the second sheet transport path; 1. An image forming system comprising:

10. an image forming unit that forms an image on a sheet; a sheet supporting means for supporting an image-formed sheet on which an image has been formed by the image forming unit; a post-processing means for processing a sheet stack consisting of a plurality of sheets discharged onto the sheet supporting means; a first sheet transport path that guides the sheet on which the image has been formed to the sheet support means; a second sheet transport path that branches off from the first sheet transport path at a branching portion on the first sheet transport path and merges with the first sheet transport path at a merging portion upstream in a sheet transport direction from an outlet to the sheet support means; a guide means for guiding the sheet to the first sheet transport path or the second sheet transport path at the branching portion; A control means for controlling the guiding means, a length of the second sheet transport path is longer than a length of the first sheet transport path between the branching portion and the junction portion; the control means controls the guiding means to guide a leading sheet of a plurality of sheets constituting a sheet stack to be post-processed by the post-processing means to the second sheet transport path, guide a final sheet to the first sheet transport path, and selectively guide sheets other than the leading sheet and the final sheet to either the first sheet transport path or the second sheet transport path for each sheet, and merges a sheet transported on the second sheet transport path and a succeeding sheet transported on the first sheet transport path in an overlapping manner at the merging portion; the control means controls the guiding means to guide, when the post-processing means is in a non-processing state in which the post-processing means is not processing the sheet bundle stacked on the sheet supporting means, at least one sheet, the leading end of which reaches the branching portion, of the sheets constituting the sheet bundle immediately following the current sheet bundle, to the second sheet transport path.

1. An image forming system comprising:

Images