Patent Publication Number: US-9885994-B2

Title: Sheet conveyance apparatus, image forming apparatus, and image forming system

Description:
The entire disclosure of Japanese Patent Application No. 2015-143576 filed on Jul. 21, 2015 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet conveyance apparatus, an image forming apparatus, and an image forming system. 
     Description of the Related Art 
     There has been used an interleaf inserting apparatus which inserts interleaves, such as thick paper or colored paper (including a front cover sheet and a back cover sheet) into sheets on which an image is formed by an image forming apparatus. Sheet-feeding in the interleaf inserting apparatus includes two steps of primary sheet-feeding conveyance in which interleaves loaded on a loading unit are picked up and conveyed to a resist part, and secondary sheet-feeding conveyance in which the interleaves are conveyed from the resist part to a merging point with image-formed sheets. In the primary sheet-feeding conveyance, the interleaves on the loading unit need to be separated one by one by a separating roller or the like, and the time required for the primary sheet-feeding conveyance greatly varies according to the loading amount of the interleaves, the abrasion degree of the separating roller, and the like. Thus, the primary sheet-feeding conveyance is temporally unstable. The timing to start the primary sheet-feeding conveyance has been gradually advanced in order to ensure the productivity during the interleaves are inserted, and the primary sheet-feeding conveyance is controlled to be started before the actual insertion timing at the point when the insertion of the next interleaf is determined. In other words, in order to merge the interleaves with the image-formed sheets in a stable state, it is desired to complete the primary sheet-feeding conveyance as soon as possible. For example, the primary sheet-feeding conveyance can be advanced crossing jobs by completing the primary sheet-feeding conveyance of the interleaf to be used in the next job although the preceding job has not been terminated. 
     Furthermore, normally, when interleaves are inserted to a discharging path of the image-formed sheets from another path and a jam occurs during feeding an interleaf, the operation of the image forming apparatus has been forcibly stopped. Thus, the remaining sheets in the image forming apparatus need to be removed, and the operability has been poor. Accordingly, in order to reduce the remaining sheets in the image forming apparatus, there has been proposed an image forming apparatus which discharges the fed sheets in the apparatus after performing image forming processing without immediately stopping the apparatus when a jam occurs during feeding an interleaf (see JP 2003-280305 A). In other words, by continuing the operation to the sheets remaining inside the apparatus when the jam occurs, the efficiency of the operation at the time of recovery (recovery from the jam) is improved. 
     However, as described above, when primary sheet-feeding conveyance in an interleaf inserting apparatus is advanced and a jam occurs in the primary sheet-feeding conveyance, sheets before the order, in which the interleaf causing the jam is supposed to be inserted, have not been fed. In other words, the sheet-feeding and the conveyance of the sheets to be discharged before the uninserted interleaf have been suspended. In this case, the recovery needs to be performed from the sheets before the interleaf causing the jam in the order, and which has caused a problem that the productivity and the work efficiency when jobs are successively performed is reduced. 
       FIG. 17  illustrates an example of conventional sheet conveying control. In  FIG. 17 , an interleaf to be inserted as a front cover sheet of the k-th job (job k) is indicated as “Pk-front”. A sheet on which the m-th image of the k-th job is to be formed is indicated as “Qk-m”. An interleaf conveying path is a path to convey interleaves to be inserted, an image-forming-sheet conveying path is a path to convey sheets on which an image is to be formed, and a merged conveying path is a sheet conveying path after a merging point which is the sheets on which an image is to be formed and the interleaves are merged. The abscissa indicates time. 
     Here, it is assumed that it is instructed to discharge four sheets to form an image (image forming sheets), which sheets are to be discharged after a front cover sheet (interleaf) is discharged in the job  1 , and to discharge an image forming sheet which is a sheet to be discharged after a front cover sheet (interleaf) is discharged in the job  2 . When the sheets until the third image forming sheet of the job  1  have been fed at the point when a jam is detected during primary sheet-feeding conveyance of the front cover sheet of the job  2 , the fourth image forming sheet of the job  1  has not been fed but the sheet-feeding is stopped. As a result, at the point when the sheets until the third image forming sheet of the job  1  have been conveyed following the front cover sheet of the job  1 , the job is suspended. In other words, although the jam is caused by a sheet (interleaf) of the job  2 , the job  1  is suspended in the middle, and the recovery needs to be performed from the fourth image forming sheet of the job  1 . Thus, the productivity and work efficiency at recovery have been poor. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the problems in the above conventional technique, and an object thereof is to improve the productivity and work efficiency at the time of recovery from a jam which occurs in one of sheet feeding units when sheets fed from two or more sheet feeding units are to be discharged to a downstream side through a merging point. 
     To achieve the abovementioned object, according to an aspect, a sheet conveyance apparatus which conveys sheets fed from a first sheet feeding unit and sheets fed from a second sheet feeding unit to a merging point, inserts the sheets fed from the first sheet feeding unit into the sheets fed from the second sheet feeding unit in a predetermined order at the merging point, and discharges the sheets fed from the first sheet feeding unit and the sheets fed from the second sheet feeding unit to a downstream side through the merging point reflecting one aspect of the present invention comprises: a jam detecting unit configured to detect a jam of a sheet in the first sheet feeding unit; and a control unit configured to newly feed, when the jam is detected by the jam detecting unit, sheets which are before the predetermined order, in which a sheet causing the jam is supposed to be inserted, and have not been fed from the second sheet feeding unit, and convey the newly fed sheets to the downstream side through the merging point. 
     According to an invention of Item. 2, in the sheet conveyance apparatus of Item. 1, the first sheet feeding unit preferably comprises a primary sheet-feeding conveyance unit configured to separate sheets one by one and convey the sheets to a resist part, and a secondary sheet-feeding conveyance unit configured to convey the sheets from the resist part to the merging point, and the jam detecting unit preferably detects a jam of a sheet in the primary sheet-feeding conveyance unit. 
     According to an invention of Item. 3, in the sheet conveyance apparatus of Item. 1 or 2, the sheets to be newly fed from the second sheet feeding unit are preferably until a sheet right before the predetermined order in which the sheet causing the jam is supposed to be inserted. 
     According to an invention of Item. 4, in the sheet conveyance apparatus of Item. 1 or 2, the sheets to be newly fed from the second sheet feeding unit are preferably until a sheet right before a top sheet in a job or a set including the sheet causing the jam. 
     To achieve the abovementioned object, according to an aspect, an image forming apparatus reflecting one aspect of the present invention comprises: a sheet conveyance apparatus of any one of Items. 1 to 4; and an image forming unit configured to form an image on a sheet, wherein the first sheet feeding unit is an interleaf inserting apparatus which inserts an interleaf into sheets on which the image is formed by the image forming unit. 
     According to an invention of Item. 6, in the image forming apparatus of Item. 5, the first sheet feeding unit is preferably positioned downstream of the image forming unit, and the second sheet feeding unit is preferably positioned upstream of the image forming unit. 
     According to an invention of Item. 7, in the image forming apparatus of Item. 5 or 6, at a point when the jam is detected by the jam detecting unit, when sheets after the predetermined order in which the sheet causing the jam is supposed to be inserted have been fed from the second sheet feeding unit, the control unit preferably stops or discharges the fed sheets after the predetermined order to a discharge destination different from a discharge destination of sheets before the predetermined order. 
     To achieve the abovementioned object, according to an aspect, an image forming system which conveys sheets fed from an interleaf inserting apparatus and sheets fed from an image forming apparatus to a merging point, inserts the sheets fed from the interleaf inserting apparatus into the sheets on which an image is formed by the image forming apparatus in a predetermined order at the merging point, and discharges the sheets fed from the interleaf inserting apparatus and the sheets fed from the image forming apparatus to a downstream side through the merging point reflecting one aspect of the present invention comprises: a jam detecting unit configured to detect a jam of a sheet in the interleaf inserting apparatus; and a control unit configured to newly feed, when the jam is detected by the jam detecting unit, sheets which are before the predetermined order, in which a sheet causing the jam is supposed to be inserted, and have not been fed from the image forming apparatus, and convey the newly fed sheets to the downstream side through the merging point. 
     To achieve the abovementioned object, according to an aspect, there is provided a non-transitory recording medium storing a computer readable control program to control a sheet conveyance apparatus, and the program reflecting one aspect of the present invention causes a computer to execute: conveying sheets fed from a first sheet feeding unit and sheets fed from a second sheet feeding unit to a merging point; inserting the sheets fed from the first sheet feeding unit into the sheets fed from the second sheet feeding unit in a predetermined order at the merging point; discharging the sheets fed from the first sheet feeding unit and the sheets fed from the second sheet feeding unit to a downstream side through the merging point; detecting a jam of a sheet in the first sheet feeding unit; newly feeding, when the jam is detected, sheets before the predetermined order, in which a sheet causing the jam is supposed to be inserted, and have not been fed from the second sheet feeding unit; and conveying the newly fed sheets to the downstream side through the merging point. 
     According to an invention of Item. 10, in the non-transitory recording medium storing the program of Item. 9, the sheets to be newly fed from the second sheet feeding unit are preferably until a sheet right before the predetermined order in which the sheet causing the jam is supposed to be inserted. 
     According to an invention of Item. 11, in the non-transitory recording medium storing the program of Item. 9, the sheets to be newly fed from the second sheet feeding unit are preferably until a sheet right before a top sheet in a job or a set including the sheet causing the jam. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
         FIG. 1  is a diagram schematically illustrating an image forming system according to an embodiment of the present invention; 
         FIG. 2  is an enlarged diagram schematically illustrating a sheet feeding part of an interleaf inserting apparatus; 
         FIG. 3  is a block diagram illustrating a functional configuration of an image forming apparatus; 
         FIG. 4  is a block diagram illustrating a functional configuration of a post-processing apparatus; 
         FIG. 5  is a block diagram illustrating a functional configuration of the interleaf inserting apparatus; 
         FIG. 6  is a flowchart illustrating interleaf feeding control processing to be performed in the interleaf inserting apparatus; 
         FIG. 7  is a flowchart illustrating sheet-feeding conveying control processing to be performed in the image forming apparatus; 
         FIG. 8  is a flowchart illustrating the sheet-feeding conveying control processing to be performed in the image forming apparatus; 
         FIG. 9  is a flowchart illustrating sheet conveying control processing to be performed in the post-processing apparatus; 
         FIG. 10  is a flowchart illustrating abnormal-sheet discharging destination determination processing to be performed in the post-processing apparatus; 
         FIG. 11  is a diagram illustrating an example of sheet conveying control in an operation example 1; 
         FIG. 12  is a diagram illustrating an example of sheet conveying control in an operation example 2; 
         FIG. 13  is a diagram illustrating an example of sheet conveying control in an operation example 3; 
         FIG. 14  is a diagram illustrating an example of sheet conveying control in an operation example 4; 
         FIG. 15  is a diagram illustrating an example of sheet conveying control in an operation example 5; 
         FIG. 16  is a diagram illustrating an example of sheet conveying control in an operation example 6; and 
         FIG. 17  is a diagram illustrating an example of conventional sheet conveying control. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of an image forming system according to the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. 
     [Configuration of Image Forming System] 
       FIG. 1  schematically illustrates a configuration of an image forming system  100 . As illustrated in  FIG. 1 , the image forming system  100  includes a sheet feeding apparatus  10 , an image forming apparatus  20 , a post-processing apparatus  30 , and an interleaf inserting apparatus  40 . In the image forming system  100 , the interleaf inserting apparatus  40  inserts interleaves into sheet conveyed from the image forming apparatus  20  by merging the interleaves (including front cover sheets and back cover sheets) with the sheets. 
     The sheet feeding apparatus  10  includes large-capacity sheet feeding trays T 11  to T 13 , and feeds sheets stored in the sheet feeding trays T 11  to T 13  to the image forming apparatus  20 . The sheet feeding trays T 11  to T 13  each store sheets of predetermined sheet types and sizes. 
     The image forming apparatus  20  includes an operation unit  22 , a display unit  23 , an image reading unit  24 , an image forming unit  25 , and sheet feeding trays T 14  and T 15 . The image forming apparatus  20  forms an image on a sheet fed from the sheet feeding apparatus  10  or a sheet fed from the sheet feeding trays T 14  and T 15 . The sheet feeding trays T 14  and T 15  each store sheets of predetermined sheet types and sizes. Hereinafter, the sheets fed from the sheet feeding trays T 11  to T 15  are also referred to as image forming sheets. The image forming sheets stored in the sheet feeding trays T 11  to T 15  are fed to the image forming unit  25 . In other words, the sheet feeding trays T 11  to T 15  are positioned upstream of the image forming unit  25 . 
     The operation unit  22  includes a touch panel formed so as to cover a display screen of the display unit  23  and various operation buttons, such as numeric buttons and a start button, and outputs operation signals based on a user&#39;s operation to the image-forming-apparatus control unit  21  (see  FIG. 3 ). 
     The display unit  23  is configured by a liquid crystal display (LCD), and displays various screens according to instructions of display signals input from the image-forming-apparatus control unit  21 . 
     The image reading unit  24  includes an automatic document feeder (ADF) and a scanner, and outputs image data obtained by reading document image to the image-forming-apparatus control unit  21 . 
     The image forming unit  25  forms an image on the image forming sheets based on the image data read by the image reading unit  24  or image data received from an external apparatus. 
     The post-processing apparatus  30  is configured by post-processing units  30 A,  30 B,  30 C, and  30 D, and performs, as needed, post-processing, such as folding processing, punching processing, binding processing, or cutting processing, to the image forming sheet conveyed from the image forming apparatus  20  and the interleaves inserted from the interleaf inserting apparatus  40 . The post-processing apparatus  30  includes sheet discharging trays T 31  to T 33 , and discharges sheet bundles or booklets generated by the image forming system  100  to the sheet discharging trays T 31  to T 33 . The sheet discharging trays T 31 , T 32  and T 33  are provided at the post-processing units  30 B,  30 C, and  30 D respectively. 
     The interleaf inserting apparatus  40  is positioned downstream of the image forming unit  25  of the image forming apparatus  20 . The interleaf inserting apparatus  40  includes loading trays T 41  and T 42  which loads interleaves, and inserts the interleaves into the image forming sheet conveyed inside the post-processing apparatus  30 . The interleaves are supplied to an image-forming-sheet conveying path at a merging point X, and inserted into the image forming sheets. 
       FIG. 2  is an enlarged diagram schematically illustrating a sheet feeding part of the interleaf inserting apparatus  40 . The interleaf inserting apparatus  40  includes the loading trays T 41  and T 42 , separating rollers  431  and  432 , resist parts  441  and  442 , and conveying rollers  443 ,  444 , and  445 . 
     The interleaves loaded on the loading trays T 41  and T 42  are separated and picked up one by one by the separating rollers  431  and  432 , and conveyed to the resist parts  441  and  442 . The conveyance of the leading edge of an interleaf in the conveying direction from the separating rollers  431  and  432  to the resist parts  441  and  442  is referred to as “primary sheet-feeding conveyance”. The time required for the primary sheet-feeding conveyance (pre-feeding time) greatly varies according to the kinds and the loaded number of interleaves, the abrasion degree of the separating rollers  431  and  432 , double-trying, or the like. 
     The resist parts  441  and  442  are configured by resist rollers which adjust the position of the leading edge of the sheet. The conveyance from the resist parts  441  and  442  to the merging point X with the image-forming-sheet conveying path is referred to as “secondary sheet-feeding conveyance”. The secondary sheet-feeding conveyance is stably performed by the resist parts  441  and  442 , and the nip parts of the conveying rollers  443  to  445 , and the time required for the secondary sheet-feeding conveyance (actual sheet-feeding time) hardly varies. 
     In other words, the interleaf-feeding in the interleaf inserting apparatus  40  includes two steps of the primary sheet-feeding conveyance which has an unstable factor in time and the secondary sheet-feeding conveyance which does not have an unstable factor in time. 
     The image forming system  100  is a sheet conveyance apparatus which conveys sheets fed from the interleaf inserting apparatus  40  as a first sheet feeding unit and sheets fed from the sheet feeding trays T 11  to T 15  as a second sheet feeding unit to a merging point X, inserts the sheet fed from the interleaf inserting apparatus  40  into the sheets fed from the sheet feeding trays T 11  to T 15  in a predetermined order at the merging point X, and discharges the sheet fed from the interleaf inserting apparatus  40  and the sheets fed from the sheet feeding trays T 11  to T 15  to a downstream side through the merging point X. 
     [Configuration of Image Forming Apparatus] 
       FIG. 3  is a block diagram illustrating a functional configuration of the image forming apparatus  20 . As illustrated in  FIG. 3 , the image forming apparatus  20  includes an image-forming-apparatus control unit  21 , an operation unit  22 , a display unit  23 , an image reading unit  24 , an image forming unit  25 , a conveyance unit  26 , a communication unit  27 , and a storage unit  28 . Note that, a description for the functional unit which has been described will be omitted. 
     The image-forming-apparatus control unit  21  includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). The CPU reads various kinds of processing programs stored in the ROM, expands the programs in the RAM, and integrally controls the operations of the units of the image forming apparatus  20  according to the expanded programs. 
     The conveyance unit  26  includes a conveying roller to convey the sheets, and conveys the sheets inside the image forming apparatus  20 . Specifically, the conveyance unit  26  conveys the image forming sheets fed from the sheet feeding apparatus  10  or the sheet feeding trays T 14  and T 15  to the image forming unit  25 , and conveys the image forming sheets, on which an image is formed by the image forming unit  25 , to the post-processing apparatus  30 . 
     The communication unit  27  is an interface to transmit and receive data between external apparatuses, such as the post-processing apparatus  30  and the interleaf inserting apparatus  40  which are connected through a network. 
     The storage unit  28  is configured by a hard disk or a flash memory, and stores various kinds of data. For example, the storage unit  28  stores job information. The job information is to be input to the image forming apparatus  20  to form an image. The job information includes data for each page including image data, image forming conditions of the image data, and setting information, such as post-processing conditions. Furthermore, the job information includes information indicating predetermined orders to insert the interleaves into the image forming sheets. 
     The image-forming-apparatus control unit  21  transmits, through the communication unit  27 , the job information to the post-processing apparatus  30  and the interleaf inserting apparatus  40 . 
     When jam detection information indicating that a jam is detected is notified by the interleaf inserting apparatus  40 , the image-forming-apparatus control unit  21  newly feeds the sheets, which are before the predetermined order, in which the sheet causing the jam is supposed to be inserted, and have not been fed from the sheet feeding trays T 11  to T 15 , and conveys the newly fed sheet to the downstream side. Here, when a mode for performing the processing in units of sheets is selected, the sheets to be newly fed from the sheet feeding trays T 11  to T 15  are image forming sheets until the sheet right before the predetermined order in which the sheet causing the jam is supposed to be inserted. When a mode for performing in units of jobs, the sheets to be newly fed from the sheet feeding trays T 11  to T 15  are image forming sheets until the sheet right before the top sheet of the job including the sheet causing the jam. When a mode for performing in units of sets, the sheets to be newly fed from the sheet feeding trays T 11  to T 15  are image forming sheets until the sheet right before the top sheet of the set including the sheet causing the jam. 
     [Configuration of Post-Processing Apparatus] 
       FIG. 4  is a block diagram illustrating a functional configuration of the post-processing apparatus  30 . As illustrated in  FIG. 4 , the post-processing apparatus  30  includes a post-processing-apparatus control unit  31 , a post-processing unit  32 , a conveyance unit  33 , a communication unit  34 , and a storage unit  35 . 
     The post-processing-apparatus control unit  31  is configured by a CPU, a ROM, and a RAM. The CPU reads various kinds of processing programs stored in the ROM, expands the programs in the RAM, and integrally controls the operations of the units of the post-processing apparatus  30  according to the expanded programs. 
     The post-processing unit  32  performs post-processing, such as folding processing, punching processing, binding processing, or cutting processing, to the sheets. The conveyance unit  33  includes a conveying roller to convey the sheets, and conveys the sheets inside the post-processing apparatus  30 . The communication unit  34  is an interface to transmit and receive data between external apparatuses, such as the image forming apparatus  20  and the interleaf inserting apparatus  40  which are connected through a network. The storage unit  35  is configured by a hard disk or a flash memory, and stores various kinds of data. 
     When the sheets after the predetermined order in which the sheet causing a jam is supposed to be inserted have been fed from the sheet feeding trays T 11  to T 15  at the point when a jam detecting unit  47  (see  FIG. 5 ) detects the jam, the post-processing-apparatus control unit  31  discharges the fed sheet after the predetermined order to a discharge destination different from the discharge destination of the sheets before the predetermined order. When there is no discharge destination different from the discharge destination of the sheets before the predetermined order, the post-processing-apparatus control unit  31  stops the fed sheets after the predetermined order. 
     [Configuration of Interleaf Inserting Apparatus] 
       FIG. 5  is a block diagram illustrating a functional configuration of the interleaf inserting apparatus  40 . As illustrated in  FIG. 5 , the interleaf inserting apparatus  40  includes an interleaf-inserting-apparatus control unit  41 , a loading unit  42 , a primary sheet-feeding conveyance unit  43 , a secondary sheet-feeding conveyance unit  44 , a communication unit  45 , a storage unit  46 , and a jam detecting unit  47 . 
     The interleaf-inserting-apparatus control unit  41  is configured by a CPU, a ROM, and a RAM. The CPU reads various kinds of processing programs stored in the ROM, expands the programs in the RAM, and integrally controls the operations of the units of the interleaf inserting apparatus  40  according to the expanded programs. 
     The loading unit  42  includes the loading trays T 41  and T 42 . On the loading trays T 41  and T 42 , interleaves, such as thick paper or colored paper, are loaded. 
     The primary sheet-feeding conveyance unit  43  includes the separating rollers  431  and  432 , separates and picks up the interleaves loaded on the loading unit  42  one by one, and conveys the interleaves to the resist parts  441  and  442 . The secondary sheet-feeding conveyance unit  44  includes the conveying rollers  443  to  445 , and conveys the interleaves from the resist parts  441  and  442  to the merging point X with the image forming sheets. 
     The communication unit  45  is an interface to transmit and receive data between external apparatuses, such as the image forming apparatus  20  and the post-processing apparatus  30  which are connected through a network. The storage unit  46  is configured by a hard disk or a flash memory, and stores various kinds of data. 
     The jam detecting unit  47  is configured by multiple sensors provided at the conveying path in the primary sheet-feeding conveyance unit  43  of the interleaf inserting apparatus  40 . The sensors are to detect whether there is a sheet on the conveying path. The jam detecting unit  47  detects a jam (primary sheet-feeding jam) during the primary sheet-feeding conveyance unit  43  of the interleaf inserting apparatus  40  separates and picks up the sheets one by one, and outputs the detection result to the interleaf-inserting-apparatus control unit  41 . 
     When there is a next interleaf to be inserted, the interleaf-inserting-apparatus control unit  41  controls the primary sheet-feeding conveyance unit  43  to perform the primary sheet-feeding conveyance of the interleaf. Furthermore, when the timing to start the secondary sheet-feeding conveyance of the interleaf comes, the interleaf-inserting-apparatus control unit  41  controls the secondary sheet-feeding conveyance unit  44  to perform the secondary sheet-feeding conveyance of the interleaf. In other words, the interleaf-inserting-apparatus control unit  41  asynchronously (independently) controls the primary sheet-feeding conveyance unit  43  and the secondary sheet-feeding conveyance unit  44 . 
     When the jam detecting unit  47  detects the jam in the primary sheet-feeding conveyance unit  43 , the interleaf-inserting-apparatus control unit  41  notify the image-forming-apparatus control unit  21  through the communication unit  45  of the jam detection information indicating that the jam is detected. Furthermore, when the timing to start the secondary sheet-feeding conveyance of the interleaf causing a jam while the jam is being detected, the interleaf-inserting-apparatus control unit  41  notifies the image-forming-apparatus control unit  21  and the post-processing-apparatus control unit  31  through the communication unit  45  of the jam occurrence. 
     [Operation of Image Forming System] 
       FIG. 6  is a flowchart illustrating interleaf feeding control processing to be performed in the interleaf inserting apparatus  40 . This processing is to be performed at the timing when the primary sheet-feeding conveyance of the interleaf can be performed, that is, when the interleaf is to be inserted, and is implemented by software processing in cooperation of the CPU of the interleaf-inserting-apparatus control unit  41  and the programs stored in the ROM. 
     First, the interleaf-inserting-apparatus control unit  41  starts the primary sheet-feeding conveyance of the interleaf loaded on the loading unit  42  by controlling the primary sheet-feeding conveyance unit  43  (step S 1 ). Next, the interleaf-inserting-apparatus control unit  41  determines whether the primary sheet-feeding conveyance of the interleaf has been completed by the primary sheet-feeding conveyance unit  43  (step S 2 ). For example, a sensor to detect the presence of a sheet is provided near the resist parts  441  and  442 , and when the sensor detects that the leading edge of the interleaf in the conveying direction reaches the resist parts  441  and  442 , the interleaf-inserting-apparatus control unit  41  determines that the primary sheet-feeding conveyance of the interleaf has been completed by the primary sheet-feeding conveyance unit  43 . 
     When the primary sheet-feeding conveyance of the interleaf has not been completed (step S 2 ; NO), the interleaf-inserting-apparatus control unit  41  determines whether the jam detecting unit  47  has detected a jam in the primary sheet-feeding conveyance (step S 3 ). When the jam detecting unit  47  has not detected a jam in the primary sheet-feeding conveyance (step S 3 ; NO), the processing returns back to step S 2 . 
     In step S 3 , when the jam detecting unit  47  has detected a jam in the primary sheet-feeding conveyance (step S 3 ; YES), the interleaf-inserting-apparatus control unit  41  stops the primary sheet-feeding conveyance of the interleaf (step S 4 ), and stores, in the storage unit  46 , the jam detection information indicating that the jam in the primary sheet-feeding conveyance has been detected (step S 5 ) by controlling the primary sheet-feeding conveyance unit  43 . Furthermore, the interleaf-inserting-apparatus control unit  41  notifies the image-forming-apparatus control unit  21  through the communication unit  45  of the jam detection information (step S 6 ). 
     In step S 2 , when the primary sheet-feeding conveyance of the interleaf has been completed (step S 2 ; YES), or after step S 6 , the interleaf-inserting-apparatus control unit  41  determines, based on the job information, whether the timing to start the secondary sheet-feeding conveyance of the interleaf comes (step S 7 ). The job information includes a predetermined order to insert the interleaf (the insertion points of the interleaf), and although a jam is caused by the interleaf to be inserted, the interleaf-inserting-apparatus control unit  41  can grasp the timing to start the secondary sheet-feeding conveyance of the interleaf. When the timing to start the secondary sheet-feeding conveyance of the interleaf does not come (step S 7 ; NO), the processing returns back to step S 7  and waits until the timing to start the secondary sheet-feeding conveyance comes. 
     In step S 7 , when the timing to start the secondary sheet-feeding conveyance of the interleaf comes (step S 7 ; YES), the interleaf-inserting-apparatus control unit  41  determines whether the jam detection information has been stored in the storage unit  46  (step S 8 ). When the storage unit  46  stores the jam detection information (step S 8 ; YES), the interleaf-inserting-apparatus control unit  41  notifies the image-forming-apparatus control unit  21  and the post-processing-apparatus control unit  31  through the communication unit  45  that the jam occurs (jam occurrence) (step S 9 ). 
     In step S 8 , when the jam detection information has not been stored in the storage unit  46  (step S 8 ; NO), the interleaf-inserting-apparatus control unit  41  starts the secondary sheet-feeding conveyance of the interleaf (step S 10 ) by controlling the secondary sheet-feeding conveyance unit  44 . In other words, the normal sheet conveyance is continued. After step S 9  or step S 10 , the interleaf feeding control processing in the interleaf inserting apparatus  40  is terminated. 
       FIGS. 7 and 8  are flowcharts illustrating sheet-feeding conveying control processing to be performed in the image forming apparatus  20 . The processing is implemented by software processing in cooperation of the CPU of the image-forming-apparatus control unit  21  and the programs stored in the ROM. Here, it is assumed that whether the processing is to be performed in units of jobs or in units of sheets has been selected. 
     First, the image-forming-apparatus control unit  21  determines whether a mode for performing the processing in units of jobs is selected (step S 11 ). Whether the processing is performed in units of jobs has been selected by a user, and the information indicating whether the processing is performed in units of jobs is stored in the storage unit  28  of the image forming apparatus  20 . 
     When the mode for performing the processing in units of jobs is not selected (step S 11 ; NO), that is, when a mode for performing the processing in units of sheets is selected, the image-forming-apparatus control unit  21  determines whether the jam detection information has been notified by the interleaf-inserting-apparatus control unit  41  (step S 12 ). 
     When the jam detection information has been notified (step S 12 ; YES), the image-forming-apparatus control unit  21  determines, based on the job information, whether the order to start the sheet-feeding of the image forming sheet is before the order in which the sheet causing the jam (hereinafter, referred to as a jam-detected interleaf) is supposed to be inserted (step S 13 ). When the order to start the sheet-feeding of the image forming sheet is before the jam-detected interleaf (step S 13 ; YES), the image-forming-apparatus control unit  21  continues the sheet-feeding and conveyance of new sheets from the sheet feeding trays T 14  and T 15  or the sheet feeding apparatus  10  by controlling the conveyance unit  26  (step S 14 ). The image-forming-apparatus control unit  21  controls the image forming unit  25  to form an image on the image forming sheet before the jam-detected interleaf (including the newly fed sheet). 
     In step S 13 , when the order to start the sheet-feeding of the image forming sheet is not before the jam-detected interleaf (step S 13 ; NO), that is, when the order to start the sheet-feeding of the image forming sheet is after the jam-detected interleaf, the image-forming-apparatus control unit  21  terminates the sheet-feeding and conveyance of the new sheets by controlling the conveyance unit  26  (step S 15 ). 
     In step S 12 , when the jam detection information has not been notified (step S 12 ; NO), after step S 14  or step S 15 , the image-forming-apparatus control unit  21  determines whether the jam occurrence has been notified by the interleaf-inserting-apparatus control unit  41  (step S 16 ). When the jam occurrence has been notified (step S 16 ; YES), the image-forming-apparatus control unit  21  determines whether an instant stop has been notified by the post-processing-apparatus control unit  31  (step S 17 ). When the instant stop has been notified (step S 17 ; YES), the image-forming-apparatus control unit  21  stops the conveyance of the image forming sheet by controlling the conveyance unit  26 , and terminates the conveyance of the image forming sheet (step S 18 ). 
     When the jam occurrence has not been notified in step S 16  (step S 16 ; NO), the instant stop has not been notified in step S 17  (step S 17 ; NO), or after step S 18 , the image-forming-apparatus control unit  21  determines whether the conveyance of all sheets has been terminated (step S 19 ). When there is a sheet which has not been conveyed (step S 19 ; NO), the processing returns back to step S 12  and is repeated. In step S 19 , when the conveyance of all sheets has been terminated (step S 19 ; YES), the sheet-feeding conveying control processing in the image forming apparatus  20  is terminated. 
     In step S 11 , when a mode for performing the processing in units of jobs is selected (step S 11 ; YES), the processing shifts to  FIG. 8 . The processing from steps S 20  to S 27  is the same as that from steps S 12  to S 19  except for that in step S 21 , and the different processing from that from steps S 12  to S 19  will be described. 
     When the jam detection information has been notified by the interleaf-inserting-apparatus control unit  41  (step S 20 ; YES), the image-forming-apparatus control unit  21  determines whether the order to start the sheet-feeding of the image forming sheet is before the top sheet of the job including the jam-detected interleaf (step S 21 ). When the order to start the sheet-feeding of the image forming sheet is before the top sheet of the job including the jam-detected interleaf (step S 21 ; YES), the image-forming-apparatus control unit  21  continues the sheet-feeding and conveyance of new sheets from the sheet feeding trays T 14  and T 15  or the sheet feeding apparatus  10  by controlling the conveyance unit  26  (step S 22 ). The image-forming-apparatus control unit  21  controls the image forming unit  25  to form an image on the image forming sheet before the top sheet of the job including the jam-detected interleaf (including the newly fed sheet). 
     In step S 21 , when the order to start the sheet-feeding of the image forming sheet is not before the top sheet of the job including the jam-detected interleaf (step S 21 ; NO), that is, when the order to start the sheet-feeding of the image forming sheet is after the top sheet of the job including the jam-detected interleaf, the image-forming-apparatus control unit  21  terminates the sheet-feeding and conveyance of the new sheets by controlling the conveyance unit  26  (step S 23 ). 
     In the image forming apparatus  20 , when the operation of the image forming apparatus  20  is stopped due to the jam occurrence, the image-forming-apparatus control unit  21  displays a warning of the jam occurrence on the display unit  23 . Note that, the processing from steps S 20  to S 27  is an example of the case in which the processing is performed in units of jobs, but may be performed in units of sets. 
       FIG. 9  is a flowchart illustrating sheet conveying control processing to be performed in the post-processing apparatus  30 . The processing is implemented by software processing in cooperation of the CPU of the post-processing-apparatus control unit  31  and the programs stored in the ROM. 
     The post-processing-apparatus control unit  31  determines whether the conveyance of all sheets has been terminated (step S 31 ). When there is a sheet which has not been conveyed (step S 31 ; NO), the post-processing-apparatus control unit  31  determines whether the jam occurrence has been notified by the interleaf-inserting-apparatus control unit  41  (step S 32 ). When the jam occurrence has been notified (step S 32 ; YES), the post-processing-apparatus control unit  31  performs abnormal-sheet discharging destination determination processing (step S 33 ). 
     In the interleaf inserting apparatus  40 , when the timing to start the secondary sheet-feeding conveyance of the interleaf comes (step S 7 ; YES) and the jam detection information has been stored in the storage unit  46  (step S 8 ; YES), the jam occurrence is notified (step S 9 ) (see  FIG. 6 ), and thus the image forming sheet right before a predetermined order, in which the interleaf is supposed to be inserted, has passed the merging point X when the jam occurrence is notified. In the post-processing apparatus  30 , that there is a sheet which has not been conveyed (step S 31 ; NO) and the jam occurrence has been notified (step S 32 ; YES) means that there is an image forming sheet after the predetermined order in which the interleaf causing the jam is supposed to be inserted (a sheet to be discharged as an abnormal sheet). In other words, the abnormal-sheet discharging destination determination processing is to be performed when the image forming sheet after the predetermined order, in which the interleaf causing the jam is supposed to be inserted, has been fed from the sheet feeding trays T 11  to T 15  at the point when the jam detecting unit  47  detects the jam. 
     Here, the abnormal-sheet discharging destination determination processing will be described with reference to  FIG. 10 . The post-processing-apparatus control unit  31  determines whether there is a sheet discharging tray positioned downstream of the merging point X (step S 41 ). In the example illustrated in  FIG. 1 , the sheet discharging trays T 32  and T 33  are positioned downstream of the merging point X. When there is a sheet discharging tray positioned downstream of the merging point X (step S 41 ; YES), the post-processing-apparatus control unit  31  determines whether the downstream sheet discharging tray is different from the discharge destination specified in the jobs until this point (step S 42 ). 
     When the downstream sheet discharging tray is different from the specified discharge destination (step S 42 ; YES), the post-processing-apparatus control unit  31  changes the discharge destination of the image forming sheet being conveyed upstream of the merging point X to the downstream sheet discharging tray different from the specified discharge destination by controlling the conveyance unit  33  (step S 43 ). 
     When there is no sheet discharging tray positioned downstream of the merging point X in step S 41  (step S 41 ; NO), or when the downstream sheet discharging tray is the same as the specified discharge destination in step S 42  (step S 42 ; NO), the post-processing-apparatus control unit  31  determines whether there is a sheet discharging tray positioned upstream of the merging point X (step S 44 ). In the example illustrated in  FIG. 1 , the sheet discharging tray T 31  is positioned upstream of the merging point X. When there is a sheet discharging tray positioned upstream of the merging point X (step S 44 ; YES), the post-processing-apparatus control unit  31  changes the discharge destination of the image forming sheet being conveyed upstream of the merging point X to the upstream sheet discharging tray by controlling the conveyance unit  33  (step S 45 ). 
     In step S 44 , when there is no sheet discharging tray positioned upstream of the merging point X (step S 44 ; NO), the post-processing-apparatus control unit  31  instantly stops the conveyance of the image forming sheet being conveyed upstream of the merging point X (step S 46 ), and notifies the image-forming-apparatus control unit  21  through the communication unit  34  of the instant stop (step S 47 ) by controlling the conveyance unit  33 . After step S 43 , step S 45 , or step S 47 , the abnormal-sheet discharging destination determination processing is terminated. 
     Returning back to  FIG. 9 , when the jam occurrence has not been notified in step S 32  (step S 32 ; NO), or after step S 33 , the processing returns back to step S 31  and is repeated. In step S 31 , when the conveyance of all sheets has been terminated (step S 31 ; YES), the sheet conveying control processing in the post-processing apparatus  30  is terminated. 
     [Operation Examples when an Interleaf Jam Occurs] 
     Operation examples when a jam occurs in the primary sheet-feeding conveyance of an interleaf will be described below. In  FIGS. 11 to 16 , an interleaf to be inserted as a front cover sheet of the k-th job (job k) is indicated as a “Pk-front”, and an interleaf to be inserted as a back cover sheet of the k-th job is indicated as a “Pk-back”. The m-th image forming sheet of the k-th job is indicated as “Qk-m”. The abscissa indicates time. 
     Operation Example 1 
       FIG. 11  illustrates an example of sheet conveying control of the interleaf conveying path in the interleaf inserting apparatus  40 , the image forming sheet conveying path in the image forming apparatus  20  and the sheet feeding apparatus  10 , and the merged conveying path after the merging point X of the post-processing apparatus  30  in an operation example 1. In the operation example 1, it is instructed to discharge five image forming sheets after a front cover sheet (interleaf) is discharged in the job  1 , and to discharge five image forming sheets after a front cover sheet (interleaf) is discharged in the job  2 . Furthermore, in the jobs  1  and  2 , it is instructed to discharge output objects to the sheet discharging tray T 33  of the post-processing unit  30 D. Moreover, in the operation example 1, it is selected that the processing is performed in units of jobs. 
     In the interleaf inserting apparatus  40 , when a jam is detected during the primary sheet-feeding conveyance of the front cover sheet of the job  2 , the primary sheet-feeding conveyance of the front cover sheet of the job  2  is stopped and the jam detection information is stored. At this time, in the image forming apparatus  20  and the sheet feeding apparatus  10 , the sheets until the third image forming sheet of the job  1  (Q 1 - 3 ) have been fed. In the image forming apparatus  20  and the sheet feeding apparatus  10 , the image forming sheets which are not fed included in the job  1  (Q 1 - 4  and Q 1 - 5 ) are newly fed and the image formation is performed to the sheets. In other words, the sheet-feeding of the image forming sheets included in the job  1  before the front cover sheet of the job  2  in the order is continued, but the image forming sheets included in the job  2  are not newly fed and the sheet-feeding thereof is stopped. At the merging point X of the post-processing apparatus  30 , the image forming sheets of the job  1  (Q 1 - 1  to Q 1 - 5 ) are conveyed following the front cover sheet of the job  1 , and the discharging in the job  1  is completed. At the timing when the front cover sheet of the job  2  is inserted, the conveyance is stopped due to the jam. The recovery is performed from the top sheet of the job  2  (P 2 -front). 
     Note that, in the operation example 1, the conveying control when the processing is performed in units of sheets is the same as that of  FIG. 11 . Furthermore, when the processing to be performed in units of sets is selected and a job in which multiple sets of a sheet bundle including a front cover sheet and five image forming sheets is performed, the sheet-feeding and image formation of the fourth and fifth image forming sheets in the first set are continued if a jam is caused by the front cover sheet in the second set while the sheets until the third image forming sheet in the first set have been fed. 
     Operation Example 2 
       FIG. 12  illustrates an example of sheet conveying control of the interleaf conveying path in the interleaf inserting apparatus  40 , the image forming sheet conveying path in the image forming apparatus  20  and the sheet feeding apparatus  10 , and the merged conveying path after the merging point X of the post-processing apparatus  30  in an operation example 2. In the operation example 2, it is instructed to discharge a back cover sheet (interleaf) after five image forming sheets are discharged in the job  1 , and to discharge a back cover sheet (interleaf) is discharged after five image forming sheets are discharged in the job  2 . Furthermore, in the jobs  1  and  2 , it is instructed to discharge output objects to the sheet discharging tray T 33  of the post-processing unit  30 D. Moreover, in the operation example 2, it is selected that the processing is performed in units of sheets. 
     In the interleaf inserting apparatus  40 , when a jam is detected during the primary sheet-feeding conveyance of the back cover sheet of the job  1 , the primary sheet-feeding conveyance of the back cover sheet of the job  1  is stopped and the jam detection information is stored. At this time, in the image forming apparatus  20  and the sheet feeding apparatus  10 , the sheets until the second image forming sheet of the job  1  (Q 1 - 2 ) have been fed. In the image forming apparatus  20  and the sheet feeding apparatus  10 , the image forming sheets before the back cover sheet of the job  1  (Q 1 - 3  to Q 1 - 5 ) in the order are newly fed, and the image formation is performed to the sheets. In other words, the sheet-feeding of the image forming sheets before the back cover sheet of the job  1  in the order is continued, but the image forming sheets included in the job  2  after the back cover sheet of the job  1  in the order are not newly fed and the sheet-feeding thereof is stopped. At the merging point X of the post-processing apparatus  30 , the image forming sheets of the job  1  (Q 1 - 1  to Q 1 - 5 ) are conveyed, and the conveyance is stopped due to the jam at the timing when the back cover sheet of the job  1  is inserted. The recovery is performed from the back cover sheet of the job  1  (P 1 -back). 
     Operation Example 3 
       FIG. 13  illustrates an example of sheet conveying control of the interleaf conveying path in the interleaf inserting apparatus  40 , the image forming sheet conveying path in the image forming apparatus  20  and the sheet feeding apparatus  10 , and the merged conveying path after the merging point X of the post-processing apparatus  30  in an operation example 3. In the operation example 3, it is instructed to discharge three image forming sheets in the job  1 , and to discharge a back cover sheet (interleaf) is discharged after two image forming sheets are discharged in the job  2 . Furthermore, in the jobs  1  and  2 , it is instructed to discharge output objects to the sheet discharging tray T 33  of the post-processing unit  30 D. Moreover, in the operation example 3, it is selected that the processing is performed in units of sheets. 
     In the interleaf inserting apparatus  40 , when a jam is detected during the primary sheet-feeding conveyance of the back cover sheet of the job  2 , the primary sheet-feeding conveyance of the back cover sheet of the job  2  is stopped and the jam detection information is stored. At this time, in the image forming apparatus  20  and the sheet feeding apparatus  10 , the sheets until the second image forming sheet of the job  1  (Q 1 - 2 ) have been fed. In the image forming apparatus  20  and the sheet feeding apparatus  10 , the image forming sheets before the back cover sheet of the job  2  (Q 1 - 3  and Q 2 - 1  to Q 2 - 2 ) in the order are newly fed, and the image formation is performed to the sheets. In other words, the sheet-feeding of the image forming sheets before the back cover sheet of the job  2  in the order is continued. At the merging point X of the post-processing apparatus  30 , the image forming sheets of the job  2  (Q 2 - 1  to Q 2 - 2 ) are conveyed following the image forming sheets of the job  1  (Q 1 - 1  to  01 - 3 ), and the conveyance is stopped due to the jam at the timing when the back cover sheet of the job  2  is inserted. The recovery is performed from the back cover sheet of the job  2  (P 2 -back). 
     Operation Example 4 
       FIG. 14  illustrates an example of sheet conveying control of the interleaf conveying path in the interleaf inserting apparatus  40 , the image forming sheet conveying path in the image forming apparatus  20  and the sheet feeding apparatus  10 , and the merged conveying path after the merging point X of the post-processing apparatus  30  in an operation example 4. In the operation example 4, it is instructed to discharge three image forming sheets in the job  1 , and to discharge a back cover sheet (interleaf) after two image forming sheets are discharged in the job  2 . Furthermore, in the jobs  1  and  2 , it is instructed to discharge output objects to the sheet discharging tray T 33  of the post-processing unit  30 D. Moreover, in the operation example 4, it is selected that the processing is performed in units of jobs. 
     In the interleaf inserting apparatus  40 , when a jam is detected during the primary sheet-feeding conveyance of the back cover sheet of the job  2 , the primary sheet-feeding conveyance of the back cover sheet of the job  2  is stopped and the jam detection information is stored. At this time, in the image forming apparatus  20  and the sheet feeding apparatus  10 , the sheets until the second image forming sheet of the job  1  (Q 1 - 2 ) have been fed. In the image forming apparatus  20  and the sheet feeding apparatus  10 , the sheet-feeding is continued until the last image forming sheet of the job  1  (Q 1 - 3 ), and the image formation is performed, but the image forming sheets included in the job  2  are not newly fed and the sheet-feeding thereof is stopped. At the merging point X of the post-processing apparatus  30 , the image forming sheets of the job  1  (Q 1 - 1  to Q 1 - 3 ) are conveyed, and the conveyance is stopped due to the jam when the last image forming sheet of the job  1  is discharged. The recovery is performed from the image forming sheets of the job  2  (Q 2 - 1 ). 
     Operation Example 5 
       FIG. 15  illustrates an example of sheet conveying control of the interleaf conveying path in the interleaf inserting apparatus  40 , the image forming sheet conveying path in the image forming apparatus  20  and the sheet feeding apparatus  10 , and the merged conveying path after the merging point X of the post-processing apparatus  30  in an operation example 5. In the operation example 5, it is instructed to discharge an image forming sheet after a front cover sheet (interleaf) is discharged in the job  1 , and to discharge two image forming sheets after a front cover sheet (interleaf) is discharged in the job  2 . Furthermore, in the jobs  1  and  2 , it is instructed to discharge output objects to the sheet discharging tray T 33  of the post-processing unit  30 D. Moreover, in the operation example 5, it is selected that the processing is performed in units of jobs. 
     In the interleaf inserting apparatus  40 , when a jam is detected during the primary sheet-feeding conveyance of the front cover sheet of the job  2 , the primary sheet-feeding conveyance of the front cover sheet of the job  2  is stopped and the jam detection information is stored. At the point when the jam is detected, the sheets until the first image forming sheet of the job  2  (Q 2 - 1 ) have been inserted in the image forming apparatus  20  and the sheet feeding apparatus  10 . The following image forming sheet (Q 2 - 2 ) is not newly fed, and the sheet-feeding thereof is stopped. At the merging point X of the post-processing apparatus  30 , the image forming sheet of the job  1  (Q 1 - 1 ) is conveyed following the front cover sheet of the job  1 , and the discharge in the job  1  is completed. At the timing when the front cover sheet of the job  2  is inserted, the control is changed to the abnormal-sheet conveying control, the fed image forming sheet (Q 2 - 1 ) is discharged to the sheet discharging tray T 32  different from the sheet discharging tray T 33  specified in the jobs  1  and  2 . The recovery is performed from the top sheet of the job  2  (P 2 -front). 
     Note that, in the operation example 5, the conveying control when the processing is performed in units of sheets is the same as that of  FIG. 15 . 
     Operation Example 6 
       FIG. 16  illustrates an example of sheet conveying control of the interleaf conveying path in the interleaf inserting apparatus  40 , the image forming sheet conveying path in the image forming apparatus  20  and the sheet feeding apparatus  10 , and the merged conveying path after the merging point X of the post-processing apparatus  30  in an operation example 6. In the operation example 6, it is instructed to discharge an image forming sheet after a front cover sheet (interleaf) is discharged in the job  1 , and to discharge two image forming sheets after a front cover sheet (interleaf) is discharged in the job  2 . Furthermore, it is instructed to discharge output objects to the sheet discharging tray T 33  of the post-processing unit  30 D in the job  1  and to discharge output objects to the sheet discharging tray T 32  of the post-processing unit  30 C in the job  2 . Moreover, in the operation example 6, it is selected that the processing is performed in units of jobs. 
     In the interleaf inserting apparatus  40 , when a jam is detected during the primary sheet-feeding conveyance of the front cover sheet of the job  2 , the primary sheet-feeding conveyance of the front cover sheet of the job  2  is stopped and the jam detection information is stored. At the point when the jam is detected, the sheets until the first image forming sheet of the job  2  (Q 2 - 1 ) have been inserted in the image forming apparatus  20  and the sheet feeding apparatus  10 . The following image forming sheet (Q 2 - 2 ) is not newly fed, and the sheet-feeding thereof is stopped. At the merging point X of the post-processing apparatus  30 , the image forming sheet of the job  1  (Q 1 - 1 ) is conveyed following the front cover sheet of the job  1 , and the discharge in the job  1  is completed. At the timing when the front cover sheet of the job  2  is inserted, the control is changed to the abnormal-sheet conveying control, the fed image forming sheet (Q 2 - 1 ) is discharged to the sheet discharging tray T 31  different from the sheet discharging tray T 32  specified in the job  1  and the sheet discharging tray T 33  specified in the job  2 . The recovery is performed from the top sheet of the job  2  (P 2 -front). 
     Note that, in the operation example 6, the conveying control when the processing is performed in units of sheets is the same as that of  FIG. 16 . Furthermore, in the image forming system  100 , when there is no sheet discharging tray different from the sheet discharging trays specified in the jobs  1  and  2 , the conveyance of the fed image forming sheet (Q 2 - 1 ) is stopped while being remained in the apparatus. 
     As described above, according to the image forming system  100  in the present embodiment, when sheets fed from the interleaf inserting apparatus  40  and the sheet feeding trays T 11  to T 15  are to be discharged to a downstream side through the merging point X and a jam occurs in the interleaf inserting apparatus  40 , the image forming sheets which are not fed and are before the order, in which the interleaf causing the jam is supposed to be inserted, are newly fed and conveyed, and it is improve the productivity and work efficiency at the time of the recovery. 
     The interleaf-feeding in the interleaf inserting apparatus  40  is divided into the primary sheet-feeding conveyance and the secondary sheet-feeding conveyance, the primary sheet-feeding conveyance is performed before the timing when the interleaf is inserted. Thus, by continuing the sheet-feeding and conveyance of the image forming sheets before the interleaf causing the jam in the order when a jam is detected in the primary sheet-feeding conveyance unit  43 , it is possible to improve the productivity and work efficiency at the time of the recovery. 
     When a mode for performing the processing in units of sheets is selected, the sheets until the image forming sheet right before the predetermined order, in which the interleaf causing the jam is supposed to be inserted, are newly fed. Thus, the conveyance of the image forming sheets can be continued as much as possible, and it is possible to perform the recovery operation from the interleaf causing the jam. 
     When a mode for performing the processing in units of jobs or sets is selected, the sheets until the sheet right before the top sheet of the job or the set including the sheet causing the jam, and the conveyance of the sheets can be terminated without crossing jobs or sets. Thus, it is possible to perform the recovery operation from the top sheet of the job or set including the sheet causing the jam. By performing the processing in units of jobs or sets, it is possible to meet outputting conditions in a job or a set when image stabilization control, such as density adjustment, or a sample (confirmation chart) output is performed at the time of the recovery after the jam occurrence. 
     Furthermore, when a sheet after the predetermined order, in which the sheet causing a jam is supposed to be inserted, has been fed at the point when the jam is detected, the fed sheets after the predetermined order is stopped or discharged to a discharge destination different from the discharge destination of the sheets before the predetermined order. Thus, it is possible not to mix normal output objects and the abnormal sheet. 
     Note that, the descriptions in the above embodiment are examples of the image forming system according to the present invention, and the present invention is not limited to these. The detail configurations and detail operations of the units composing the system can be changed without departing from the scope of the present invention. 
     For example, in the above embodiment, the example in which the first sheet feeding unit is the interleaf inserting apparatus  40  which feeds interleaves, and the second sheet feeding unit is the sheet feeding trays T 11  to T 15  which feeds sheets to form an image has been described, but both of the first sheet feeding unit and the second sheet feeding unit may feed sheets to form an image. Furthermore, the present invention may be applied to an image forming system which conveys sheets fed from three or more sheet feeding units. 
     In the above embodiment, the example in which the jam detecting unit  47  detects a jam in the primary sheet-feeding conveyance unit  43  has been described, but the jam detecting unit  47  may detect a jam in the secondary sheet-feeding conveyance unit  44 . However, at the stage to perform the secondary sheet-feeding conveyance, the sheets until the sheet right before the interleaf, to which the secondary sheet-feeding conveyance is to be performed, have passed the merging point X, and the present invention is effective especially when a jam occurs in the primary sheet-feeding conveyance unit  43 . 
     In the above embodiment, the image forming system  100  includes the image forming apparatus  20 , the post-processing apparatus  30 , and the interleaf inserting apparatus  40 , but the image forming apparatus  20  may include the interleaf inserting apparatus  40  and the conveying path including the merging point X. Furthermore, the post-processing apparatus  30  may include the interleaf inserting apparatus  40 . Moreover, the processing performed by the image-forming-apparatus control unit  21 , the post-processing-apparatus control unit  31 , and the interleaf-inserting-apparatus control unit  41  may be integrally performed by one control unit or may be dividedly performed by multiple control units. 
     In the above description, a ROM has been exemplified as a computer readable medium storing a program to perform the processing, but the present invention is not limited to this example. A non-volatile memory, such as a flash memory, or a portable recording medium, such as a CD-ROM, may be applied as other computer readable media. Furthermore, a carrier wave may be applied as a medium which provides program data through a communication line. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustrated and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by terms of the appended claims.