Patent Publication Number: US-7711448-B2

Title: Image forming system and inserter device

Description:
This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 208248/2003 filed in Japan on Aug. 21, 2003, the entire contents of which are hereby incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to an image forming system in which a copying machine is combined with an optional device such as an inserter device and a post-processing device; and an inserter device used in the image forming system. 
   BACKGROUND OF THE INVENTION 
   In an image forming system in which a printing apparatus main body is attached with optional devices such as a post-processing device, an inserter device, and a paper feeding device, timing such as timing of transporting sheets to the optional devices is managed and controlled by the printing apparatus main body. 
   An example of the image forming system in which the optional device is attached to the printing apparatus main body is an image forming system shown in Japanese Unexamined Patent Publication No. 2003-21984 (Tokukai 2003-21984, published on Jan. 24, 2003). In this image forming system, an optional device in which a post-processing device and an inserter device are integrated is attached to an image forming apparatus main body. Here, when interleaving sheet insertion and staple processing are performed in the system, the optional devices are controlled in a unified manner by the image forming apparatus. 
   However, the system employing the optional device in which the post-processing device and the inserter device are integrated, as disclosed in Tokukai 2003-21984, offers less flexibility to a user who requires a function provided by the post-processing device (sort function, staple processing function, for example) but does not require a function provided by the inserter device (interleaving sheet insertion function). 
   Further, there is also an image forming system that includes the post-processing device and the inserter device separately as different optional devices and can serve as either a system composed of the image forming apparatus and the post-processing device or a system composed of the image forming apparatus, the post-processing device, and the inserter device. When the image forming system as described above is established as the system to which both the post-processing device and the inserter device are attached, the inserter device is provided between the image forming apparatus main body and the post-processing device. 
   In the system employing the optional device in which the post-processing device and the inserter device are integrated as described in Tokukai 2003-21984 (see  FIG. 10(   a )), and in the system composed of the image forming apparatus and the post-processing device (see  FIG. 10(   b )), only one system of a control line is required to connect the image forming apparatus with the optional device. 
   On the other hand, in the image forming system that includes the post-processing device and the inserter device separately as different optional devices as described above, the image forming apparatus main body manages and controls both the post-processing device and the inserter device. Accordingly, the image forming apparatus is required to use control lines in two systems, as shown in  FIG. 10(   c ). This complicates the arrangement of the control system. 
   Further, in the image forming system provided with the inserter device, a transport path from the main body to the post-processing device is longer by the length of the inserter device, compared with the image forming system that is not provided with the inserter device. Accordingly, the image forming apparatus main body is required to prepare two types of control programs respectively for (i) control (timing control, in particular) of the post-processing device in a case where the inserter device is not attached, and (ii) control of the post-processing device in a case where the inserter device is attached. This increases the workload of control processing on the image forming apparatus. 
   Further, if the specification of the inserter device changes, for example, it is necessary to modify the control program of the image forming apparatus main body accordingly. 
   SUMMARY OF THE INVENTION 
   In order to solve the foregoing problems, the present invention has an objective to provide an image forming system in which the control system is simplified and control processing in the image forming apparatus is reduced. 
   In order to achieve the foregoing objective, an image forming system of. the present invention in which an inserter device and a post-processing device are attached to an image forming apparatus is so arranged that a control command communicated between the image forming apparatus and the post-processing device is relayed by the inserter device. 
   With this arrangement, a control command communicated between the image forming apparatus and the post-processing device is sent via the inserter device. Therefore the image forming apparatus is not required to be provided with control systems respectively for the inserter device and the post-processing device. Accordingly, only one system of the control system is required, so that the arrangement of the control system is simplified. 
   For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an embodiment of the present invention, and is a block diagram schematically showing an arrangement of a control system in an image forming system composed of a copying machine, an inserter, and a finisher. 
       FIG. 2  is a cross-sectional view showing an arrangement of the image forming system. 
       FIG. 3  is a diagram showing an example of a transport plan table created on the occasion when the image forming system performs a print job. 
       FIG. 4  is a flowchart showing an operation in which a sheet that has been subjected to printing processing at the copying machine is output to an eject tray of the finisher (through mode) in a system configuration to which the inserter is not attached. 
       FIG. 5  is a flowchart showing an operation in which a sheet that has been subjected to printing processing at the copying machine is output to an eject tray of the finisher (through mode) in a system configuration to which the inserter is attached. 
       FIG. 6  is a flowchart showing an example of operation in which sheets that have been subjected to printing processing at the copying machine are ejected after an interleaving sheet set on an interleaving sheet feed tray is inserted in the sheets. 
       FIG. 7  is a flowchart showing another example of operation in which sheets that have been subjected to printing processing at the copying machine are ejected after an interleaving sheet set on an interleaving sheet feed tray is inserted in the sheets. 
       FIG. 8  is a flowchart showing a further example of operation in which sheets that have been subjected to printing processing at the copying machine are ejected after an interleaving sheet set on an interleaving sheet feed tray is inserted in the sheets. 
       FIG. 9  is a flowchart showing an example of operation that includes an initial operation at the finisher. 
       FIG. 10(   a ) is a block diagram showing a control system in an image forming system composed of an image forming apparatus and an optional device, in a case where an optional device is arranged so that an inserter device and a post-processing device are integrated. 
       FIG. 10(   b ) is a block diagram showing a control system in an image forming system composed of an image forming apparatus and an optional device, in a case where only a post-processing device is attached as the optional device. 
       FIG. 10(   c ) is a block diagram showing a control system in an image forming system composed of an image forming apparatus and an optional device, in a case where an inserter device and a post-processing device are attached as the optional device in accordance with a conventional arrangement. 
       FIG. 10(   d ) is a block diagram showing a control system in an image forming system composed of an image forming apparatus and an optional device, in a case where an inserter device and a post-processing device are attached as the optional device in accordance with an arrangement of the present embodiment. 
   

   DESCRIPTION OF THE EMBODIMENTS 
   The following will explain an embodiment of the present invention with reference to the drawings. 
   As shown in  FIG. 2 , an image forming system  51  in accordance with the present invention includes a copying machine  52 , a sheet supply device  53 , an inserter  54 , and a finisher  55 . 
   The copying machine  52  prints image information on a sheet (print sheet, recording material). The copying machine  52  is schematically provided with an automatic document feeder  56 , an image reading device  57 , an image forming section  58 , and a sheet feeding device  59 . 
   The automatic document feeder  56  and the image reading device  57  are provided above the image forming section  58  so as to read a document to obtain image information of the document. Further, the sheet feeding device  59  is provided below the image forming section  58  so as to supply sheets to the image forming section  58 . 
   On the other hand, the sheet supply device  53  is provided on a side of the copying machine  52  and attached to the copying machine  52 . The sheet supply device  53  is a detachable device for supplying sheets to the image forming section  58  of the copying machine  52 , and is provided separately from the image forming section  58  and copying machine  52 . 
   The inserter  54  is used to insert a desired sheet (cover paper, divider paper, and the like) into a certain position of a group of sheets successively sent from the copying machine  52  or other device. Here, if insertion of the desired sheet as described above is allowed only in the copying machine  52 , for example, a sheet that does not need to pass through the image forming section  58  of the copying machine  52  is also inserted via the image forming section  58 . By using the inserter  54 , it is possible to insert the desired sheet without causing the desired sheet to pass through the image forming section  58  of the copying machine  52 . 
   The inserter  54  includes an interleaving sheet feed tray  67 . On the interleaving sheet feed tray  67 , sheets to be inserted, namely, sheets for cover paper, and sheets prepared by another image forming apparatus such as an ink-jet printer, are placed. In accordance with appropriate timing in preset order, the inserter  54  can insert the sheets placed on the interleaving sheet feed tray  67  into sheets sent from the copying machine  52 . The inserter  54  then transports the resultant sheets to the finisher  55 . 
   The finisher  55  performs post-processing with respect to the sheets transported from the inserter  54 . The finisher  55  has the function to perform the post-processing such as punching holes into the sheets, stapling the sheets, and sorting the sheets, for example. 
     FIG. 1  schematically shows a control system in accordance with the image forming system  51 . 
   The copying machine  52 , the inserter  54 , the finisher  55 , and the paper feeding device (sheet feeding device  59  and large capacity sheet supply device  53 ) that compose the image forming system  51  are provided with a print control section  521 , an inserter control section  541 , a finisher control section  551 , and a paper feed control section  591 , respectively. 
   Further, the copying machine  52  is provided with a paper output sensor  522 . The inserter  54  is provided with a paper input sensor  542  and a paper output sensor  543 . The finisher  55  is provided with a paper input sensor  552  and a paper output sensor  553 . 
   The print control section  521  controls the operation of each part of the copying machine  52  (printing operation at the image forming section  58 , for example), and also functions as a main control section of the image forming system. The print control section  521  sends control commands to the control sections (inserter control section  541 , finisher control section  551 , and paper feed control section  591 ) of the optional devices (inserter  54 , finisher  55 , and paper feeding device) so as to allow the copying machine  2  and the optional devices to operate in an associated manner. 
   In the image forming system  51 , the control system for transmitting the control commands from the print control section.  521  to the inserter control section  541  and the finisher control section  551  is only one system, as shown in  FIG. 10(   d ). Namely, the control commands sent from the print control section  521  to the finisher control section  551  are sent via the inserter control section  541 . Further, in a system configuration that does not adopt the inserter  54 , the control commands are directly sent from the print control section  521  to the finisher control section  551 . 
   In order to perform a print job in the image forming system as described above, the print control section  521  creates a transport plan table in accordance with input instructions for the job.  FIG. 3  shows an example of the transport plan table. 
   The transport plan table shown in  FIG. 3  is composed of paper ID, image ID, image processing information, post-processing information, eject destination information, and paper feeder information. The paper ID is an ID number assigned to each sheet to be ejected in the job. The image ID is an ID number of image data to be printed on each sheet. Two image IDs are given to a sheet to be subject to both-sided (double-sided) printing. The image processing information indicates whether the printing processing to be performed on each sheet is either single-sided printing or both-sided printing. The post-processing information indicates a type of the post-processing to be performed on each sheet. The eject destination information indicates a tray to which each sheet is to be ejected. The paper feeder information indicates a feeder from which each sheet is fed. 
   A job illustrated by the transport plan table shown in  FIG. 3  involves three sheets, and the first sheet (whose paper ID is “ 1 ”) is a sheet supplied from the inserter  54  (cover paper, for example). Therefore the first sheet is not subject to the printing processing by the copying machine  52 . Accordingly, the image ID and the image processing information are not set with respect to the first sheet. Further, Staple S in the post-processing information of the first sheet indicates that the sheet is the first sheet of a group of sheets to be subject to staple processing. Likewise, Staple E in the post-processing information of the third sheet indicates that the sheet is the last sheet of the group of sheets to be subject to the staple processing. 
   Next, the operation of the image forming system as described above will be explained. 
     FIGS. 4 and 5  are flowcharts showing operation in which a sheet subjected to the printing processing at the copying machine  52  is output to a paper eject tray of the finisher  55  (through mode). 
   The processing shown in  FIG. 4  is an example of the operation in a case where the inserter  54  is not attached between the copying machine  52  and the finisher  55 . First, the print control section  521  in the copying machine  52  sends to the finisher control section  551 , the paper ID of a sheet on which printing processing is to be performed. Note that,  FIG. 4  shows the processing with respect to the first two sheets of a plurality of sheets successively processed. Thus, the print control section  521  sends to the finisher control section  551 , the paper IDs (paper ID  1  and paper ID  2  in  FIG. 4 ) of the two sheets first. 
   Upon receiving notification of the paper IDs, the finisher control section  551  sends paper intervals to the print control section  521 . The paper interval indicates a period (interval) until a point when the transporting of a certain sheet is allowed after the previous sheet is transported during the operation for successively transporting sheets. The paper interval is calculated by the finisher control section  551  in accordance with the type(s) of the post-processing operation instructed in the finisher  55 , etc. 
   Upon receiving notification of the paper intervals, the print control section  521  causes the copying machine  52  to start transport processing of the first sheet (paper ID  1 ) after waiting for a period of a notified paper interval TID 1  from the time point when the print control section  521  receives notification of the paper interval TID 1 . Note that, as for the transporting of the first sheet, the actual paper interval TID 1  is basically 0 so that the copying machine  52  can start the transport processing of the first sheet almost simultaneously with the receipt of notification of the paper interval. Note that, a position at which the transport processing starts is not limited, but is preferably a position before. reaching the image forming section  58  (position of a PS roller), for example. 
   Further, a paper interval TID 2  for the second sheet (paper ID  2 ) is notified here at the same time, but the paper interval TID 2  is temporarily retained at the print control section  521 . 
   Further, when the transport processing of the sheet in the copying machine  52  starts and the sheet enters the paper output sensor at an exit of the copying machine, the print control section  521  sends a paper output command to the finisher control section  551 . Then, when the sheet passes through the paper output sensor, the print control section  521  sends a paper output completion command to the finisher control section  551 . 
   After receiving the paper output command or the paper output completion command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the copying machine  52  and to eject the sheet. After the finisher  55  ejects the sheet, the finisher control section  551  sends an eject completion command to the print control section  521 . 
   Further, at the same time when the transport processing of the first sheet starts, the print control section  521  enters a waiting period for the second sheet in accordance with the retained paper interval TID 2 , and starts transport processing of the second sheet after the waiting period ends. With this, it is possible to start transporting the second sheet before receiving the eject completion command of the first sheet. This arrangement reduces transport intervals (paper intervals) between sheets to be successively ejected, thereby improving the processing efficiency of the entire system. 
   Note that,  FIG. 4  shows the processing of successive two sheets. However, processing of successive three or more sheets is similarly performed. In this case, it is preferable that the print control section  521  sends notification of the paper ID of an nth (n≧2) sheet before starting transporting an (n−1)th sheet, and enters a waiting state in accordance with a notified paper interval TIDn simultaneously with the start of transporting of the (n−1)th sheet. 
   Next, the processing shown in  FIG. 5  is an example of the operation in a case where the inserter  54  is provided between the copying machine  52  and the finisher  55 . Note that,  FIG. 5  shows the processing with respect to the first two sheets of a plurality of sheets successively processed. 
   First, the print control section  521  in the copying machine  52  sends to the finisher control section  551 , the paper IDs (paper ID  1  and paper ID  2  in  FIG. 5 ) of the sheets on which printing processing is to be performed. 
   In the arrangement where the inserter  54  is provided in the system, a signal sent from the print control section  521  to the inserter and a signal sent from the print control section  521  to the finisher control section  551  are both relayed by the inserter control section  541 . Here, the inserter control section  541  checks the content of the command of the signal, and directly forwards the command if the command does not relate to the operation of the inserter  54 . Accordingly, the paper IDs as described above are directly forwarded by the inserter control section  541  to the finisher control section  551 . 
   Upon receiving notification of the papers IDs, the finisher control section  551  sends paper intervals to the print control section  521 . The paper intervals are sent from the finisher control section  551  to the print control section  521  via the inserter control section  541 . Because the paper interval is a command that does not relate to the operation of the inserter  54 , the inserter control section  541  directly forwards the command to the print control section  521 . 
   Upon receiving notification of the paper intervals, the print control section  521  causes the copying machine  52  to start transport processing of the sheets. First, the print control section  521  causes the copying machine  52  to start transport processing of the first sheet after waiting for a period in accordance with the paper interval TID 1  for the first sheet (the waiting period is actually 0 because the paper interval TID 1  for the first sheet is 0). Further, the print control section  521  sends a paper output command to the inserter control section  541  when a front edge of the transported sheet is detected by the paper output sensor of the copying machine  52  after the transport processing of the sheet starts. The print control section  521  then sends a paper output completion command to the inserter control section  541  when the sheet goes out of the paper output sensor, and, at the same time, the print control section  521  enters a waiting state before transporting the second sheet in accordance with the paper interval TID 2 . 
   The paper output command and the paper output completion command pass through the inserter control section  541 . Here, the inserter control section  541  recognizes that the commands relate to the operation of the inserter  54 , and performs predetermined processing in accordance with the commands. Specifically, with respect to the paper output command or paper output completion command, the inserter  54  is required to perform relay transport processing for transporting to the finisher  52  the sheet outputted from the copying machine  52 . Therefore, by receiving the paper output command, the inserter control section  541  causes the inserter  54  to start transport processing; and by receiving the paper output completion command, the inserter section  541  knows that the paper output at the copying machine  52  has ended. 
   Further, the inserter control section  541  forwards to the finisher control section  551 , the paper output command or the paper output completion command received from the print control section  551 . Here, if the inserter control section  541  forwards the command immediately after receiving the command from the print control section  521 , a time lag occurs between timing at which the finisher  55  receives the command and timing at which the finisher  55  receives the sheet corresponding to the command. Of course, this is because the inserter  54  attached between the copying machine  52  and the finisher  55  lengthens the transport path of the sheet, and thus lengthens the transport time of the sheet. 
   Therefore the inserter control section  541  temporarily retains the paper output command or the paper output completion command received from the print control section  521 , and forwards the command to the finisher control section  551  in accordance with timing at which the inserter  54  outputs the sheet to the finisher  55 . This timing is controlled in accordance with a signal from the paper output sensor of the inserter  54 . 
   After receiving the paper output command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the inserter  54  and to eject the sheet. After the finisher  55  ejects the sheet, the finisher control section  551  sends an eject completion command to the inserter control section  541 . Because notification of the eject completion is a command that does not relate to the operation of the inserter  54 , the inserter control section  541  directly forwards the command to the print control section  521 . 
   Further, before receiving notification of the eject completion of the first sheet, the print control section  521  starts transport processing of the second sheet after the waiting period in accordance with the paper interval TID 2  ends. The transport processing of the second sheet is performed in a similar manner to the transport processing of the first sheet. Here, the print control section  521  starts the transport processing of the second sheet before receiving notification of the eject completion of the first sheet. However, depending on the waiting period in accordance with the paper interval TID 2 , the print control section  521  may start the transport processing of the second sheet after receiving notification of the eject completion of the first sheet. 
   Further, if the processing shown in  FIG. 5  deals with successive three or more sheets, it is preferable that the print control section  521  sends notification of the paper ID of an nth (n≧2) sheet before starting transporting an (n−1)th sheet, and enters a waiting state in accordance with a notified paper interval TIDn simultaneously with the start of transporting of the (n−1)th sheet. 
   Comparison between the operation of  FIG. 4  and the operation of  FIG. 5  shows that the processing performed by the print control section  521  and finisher control section  551  is the same irrespective of whether or not the inserter  54  is provided. Therefore the print control section  521  of the copying machine  52  does not require two types of control programs respectively for cases where the inserter  54  is provided and where the inserter  54  is not provided. This arrangement reduces the workload of processing on the print control section  521 . In other words, even if the inserter  54  is provided, the print control section  521  is not required to control the transport timing with taking into account a transport time in the inserter  54 . 
   Further, even if the inserter  54  usable in the image forming system may have one of a plurality of different specifications (if the length of the paper transport path in the inserter may differ depending on the size of the inserter, for example), the copying machine  52  and the finisher  55  are not required to prepare different control programs corresponding to the different specifications of the inserter  54 . 
   Further, commands are sent from the print control section  521  to the finisher control section  551  via the inserter control section  541  if the inserter  54  is provided. This arrangement requires only one system of the control system, thereby simplifying the configuration of the control system. 
     FIG. 6  is a flowchart showing an example of operation (insert mode  1 ) in a case where sheets that have been subjected to the printing processing at the copying machine  52  are ejected after an interleaving sheet set on the interleaving sheet feed tray  67  of the inserter  54  is inserted in the sheets. It is assumed in the operation in the insert mode  1  that the first sheet (paper ID:  1 ) is a sheet that has been subjected to the printing processing by the copying machine  52 , and the second sheet (paper ID:  2 ) is an interleaving sheet inserted by the inserter  54 . 
   In the operation in the insert mode  1 , the print control section  521  starts controlling the processing of the second sheet when the print control section  521  finishes controlling the processing of the first sheet. Here, in the processing of the first sheet, the inserter  54  only performs relay transporting of the sheet, and the control sections operate as in the through mode as explained in  FIG. 5 , thus their detailed explanation is omitted here. 
   In the processing of the second sheet, the print control section  521  sends an interleaving sheet feed command to the inserter control section  541 . Upon receipt of the interleaving sheet feed command, the inserter control section  541  causes the inserter  54  to start interleaving sheet feed processing for accepting into the transport path, an interleaving sheet set on the interleaving sheet feed tray  67 , and transport processing for transporting the accepted interleaving sheet to the finisher  55 . Further, the inserter control section  541  sends a paper output command to the finisher control section  551  when the interleaving sheet enters the paper output sensor of the inserter  54 , and sends a paper output completion command to the finisher control section  551  when the interleaving sheet goes out of the paper output sensor. 
   After receiving the paper output command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the inserter  54  and to eject the sheet. When the ejection of the sheet at the finisher  55  ends, the finisher control section  551  sends an eject completion command to the inserter control section  541 . Because notification of the eject completion is a command that does not relate to the operation of the inserter  54 , the inserter control section  541  directly forwards the command to the print control section  521 . 
   Further, in the processing shown in  FIG. 6 , if the copying machine  52  further continues after the interleaving sheet insertion processing, the processing for outputting sheets that have been subjected to the printing processing, the outputting processing may be performed in a manner similar to that in the through mode as explained in  FIG. 5 . 
     FIGS. 7 and 8  are flowcharts showing other examples of operation in a case where sheets that have been subjected to the printing processing at the copying machine  52  are ejected after an interleaving sheet set on the interleaving sheet feed tray  67  of the inserter  54  is inserted in the sheets. It is assumed in the operation in an insert mode  2  shown in  FIG. 7  that the first sheet (paper ID:  1 ) is a sheet subject to the printing processing by the copying machine  52 , and the second sheet (paper ID:  2 ) is an interleaving sheet inserted by the inserter  54 . 
   The operation in the insert mode  2  differs from the operation in the insert mode  1  in that control of the processing of the second sheet starts before control of the processing of the first sheet ends. 
   First, the print control section  521  sends to the inserter control section  541 , notification of the paper ID of the first sheet and an interleaving sheet feed command for the second sheet. The inserter control section  541  which has received the paper ID and the interleaving sheet feed command directly forwards the paper ID (namely, paper ID  1 ) to the finisher control section  551 . Further, with respect to the paper ID as the interleaving sheet feed command (namely, paper ID  2 ), the inserter control section  541  recognizes that the paper ID  2  indicates the output of an interleaving sheet, and retains the command and then forwards the command to the finisher control section  551 . 
   The finisher control section  551  calculates a paper interval for each of the notified paper ID  1  and paper ID  2 . Then, the finisher control section  551  sends the paper interval for the paper ID  1  to the print control section  521  via the inserter control section  541 , and sends the paper interval for the paper ID  2  to the inserter control section  541 . The inserter control section  541  directly forwards the paper interval for the paper ID  1  to the print control section  521 , and retains the paper interval for the paper ID  2 . 
   Note that, the paper interval for the paper ID  1  is calculated in a similar manner to the calculation of the paper interval shown in  FIG. 4 , etc. On the other hand, the paper interval for the paper ID  2  indicates a time interval until the outputting of the next sheet is allowed after the paper output command for the first sheet is received at the finisher control section  551  (or after a back edge of the sheet is detected by the paper output sensor of the inserter  54  or after a front edge of the sheet is detected by the paper input sensor of the finisher  55 ). Namely, the paper interval for the paper ID  2  is calculated in accordance with the content of the transport processing and post-processing that the finisher  55  performs on the sheet whose paper ID is  1 . 
   Upon receiving notification of the paper interval for the paper ID  1 , the print control section  521  waits if necessary in accordance with the paper interval, and then causes the copying machine  52  to start transport processing of the sheet whose paper ID is  1 . Further, when the sheet enters the paper output sensor at the exit of the copying machine after the transport processing starts, the print control section  521  sends a paper output command to the inserter control section  541 . When the sheet goes out of the paper output sensor, the print control section  521  sends a paper output completion command to the inserter control section  541 . 
   Upon receiving the paper output command from the print control section  521 , the inserter control section  541  causes the inserter  54  to start transport processing for relaying and transporting to the finisher  55 , the sheet transported from the copying machine  52 , and forwards the received paper output command or paper output completion command to the finisher control section  551 . Further, the inserter control section  541  enters a waiting period in accordance with the pre-notified paper interval for the paper ID  2 . Here, the starting point of the waiting period is a time when the inserter control section  541  received the paper output command or the paper output completion command from the print control section  521 . After the waiting period ends, the inserter control section  541  causes the inserter  54  to start interleaving sheet feed processing and transport processing. Here, the waiting period for the interleaving sheet feed processing may be a period obtained by subtracting from the period notified as the paper interval (i) a period for the interleaving sheet feed processing and (ii) a transport time of the sheet from the inserter  54  to the finisher  55 . 
   After receiving the paper output command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the inserter  54  and to eject the sheet. After the finisher  55  ejects the sheet, the finisher control section  551  sends an eject completion command to the inserter control section  541 . The inserter control section  541  directly forwards notification of the eject completion to the print control section  521 . 
   Further, the inserter control section  541  causes the inserter  54  to start interleaving sheet feed processing and transport processing of the thus fed interleaving sheet after the waiting period ends. Note that, the inserter control section  541  may start the interleaving sheet feed processing before receiving notification of the eject completion for the paper ID  1 . When the interleaving sheet enters the paper output sensor of the inserter  54  after the transport processing starts, the inserter control section  541  generates a paper output command and sends the paper output command to the finisher control section  551 . When the interleaving sheet goes out of the paper output sensor, the inserter control section  541  sends a paper output completion command to the finisher control section  551 . 
   After receiving the paper output command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the inserter  54  (namely, the interleaving sheet) and to eject the sheet. After the finisher  55  ejects the sheet, the finisher control section  551  sends an eject completion command to the inserter control section  541 . The inserter control section  541  directly forwards notification of the eject completion to the print control section  521 . 
   Next, in the operation in an insert mode  3  shown in  FIG. 8 , it is assumed that the first sheet (paper ID:  2 ) is an interleaving sheet inserted by the inserter  54 , and the second sheet (paper ID:  3 ) is a sheet that has been subjected to the printing processing at the copying machine  52 . 
   First, the print control section  521  sends to the inserter control section  541 , a paper ID command for the first sheet (interleaving sheet), and a paper ID command for the second sheet. The inserter control section  541  which has received the paper IDs recognizes that the paper ID command for the first sheet, namely, the paper ID  2  indicates the output of an interleaving sheet, and retains the command and then forwards the command to the finisher control section  551 . The inserter control section  541  directly forwards the next paper ID (namely, paper ID  3 ) to the finisher control section  551 . 
   The finisher control section  551  calculates a paper interval for each of the notified paper ID  2  and paper ID  3 . Then, the finisher control section  551  sends the paper interval for the paper ID  2  to the inserter control section  541  and the paper interval for the paper ID  3  to the print control section  521  via the inserter control section  541 . The paper intervals for the paper ID  2  and paper ID  3  are calculated in a manner similar to the calculation of the paper intervals for the paper ID  2  and paper ID  1  shown in  FIG. 7 . 
   The inserter control section  541  retains the paper interval for the paper ID  2 , and forwards the paper interval for the paper ID  3  to the print control section  521 . On the other hand, the inserter control section  541  forwards to the print control section  52 , the paper interval for the paper ID  3  after adding a processing time at the inserter  54  to the paper interval. 
   Namely, the copying machine  52  starts transport processing after a predetermined waiting period in accordance with the notified paper interval ends. Since the interleaving sheet insertion processing is performed at the inserter  54  before the transport processing starts, the waiting period of the copying machine  52  is to include a time for the interleaving sheet insertion processing at the inserter  54 . The paper interval (paper interval A) for the paper ID  3  calculated by the finisher control section  551  does not include the processing time at the inserter  54 . Accordingly, the inserter control section  541  adds the processing time at the inserter  54  to the paper interval A that is notified from the finisher control section  551 , and forwards to the print control section  521 , the resultant paper interval as the paper interval A′. The print control section  521  enters a waiting state immediately after receiving notification of the paper interval A′. 
   Further, upon receiving notification of the paper interval for the. paper ID  2 , the inserter control section  541  waits if necessary in accordance with the paper interval, and then causes the inserter  54  to start interleaving sheet feed processing and interleaving sheet transport processing of the sheet for the paper ID  2 . Further, when the sheet enters the paper output sensor of the inserter  54  after the interleaving sheet transport processing starts, the inserter control section  541  sends a paper output command to the finisher control section  551 . When the sheet goes out of the paper output sensor, the inserter control section  541  sends a paper output completion command to the finisher control section  551 . 
   After receiving the paper output command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the inserter  54  (namely, interleaving sheet) and to eject the sheet. After the finisher  55  ejects the sheet, the finisher control section  551  sends an eject completion command to the inserter control section  541 . The inserter control section  541  directly forwards notification of the eject completion to the print control section  521 . 
   After the waiting period in accordance with the paper interval A′ ends, the print control section  521  causes the copying machine  52  to start transport processing of the sheet whose paper ID is  1 . Note that, the print control section  521  may start the transport processing before receiving notification of the eject completion for the paper ID  2 . Further, the print control section  521  outputs either a paper output command or paper output completion command simultaneously with the start of the transport processing. 
   Upon receiving the paper output command from the print control section  521 , the inserter control section  541  causes the inserter  54  to start transport processing for relaying and transporting to the finisher  55 , the sheet transported from the copying machine  52 , and forwards the received paper output command or paper output completion command to the finisher control section  551 . 
   After receiving the paper output command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the inserter  54  and to eject the sheet. After the finisher  55  ejects the sheet, the finisher control section  551  sends an eject completion command to the inserter control section  541 . The inserter control section  541  directly forwards notification of the eject completion to the print control section  521 . 
   In a case where interleaving sheet insertion processing is performed for inserting an interleaving sheet fed by the inserter  54  into the sheets successively output from the copying machine  52 , the processing shown in  FIGS. 7 and 8  may be performed at a portion where the interleaving sheet is to be inserted. 
   Note that,  FIGS. 7 and 8  both show the processing with respect to the first two sheets of a plurality of sheets successively processed. Thus, the print control section  521  almost simultaneously sends the notification of the first paper ID and the interleaving sheet feed command. However, processing of successive three or more sheets may be similarly performed. In this case, the operations shown in  FIG. 7 and 8  can be applied to the processing of three or more sheets if the print control section  521  sends notification of the paper ID of an nth (n≧2) sheet (or sends an interleaving paper feed command) before starting transporting an (n−1)th sheet. Note that, at a portion where sheets output from the copying machine  52  are successively ejected, the operation shown in  FIG. 5  may be performed. 
   In the operations shown in  FIGS. 6 through 8 , the processing for sending commands and calculating paper intervals at the print control section  521  and finisher control section  551  do not need to take into account processing performed by the inserter  54  even if the inserter  54  is provided. In other words, control and adjustment concerning the processing performed by the inserter  54  are all performed by the inserter control section  541 . Therefore the print control section  521  of the copying machine  52  does not require two types of control programs respectively for cases where the inserter  54  is provided and where the inserter  54  is not provided, thereby reducing the workload of processing on the print control section  521 . 
   Further, even if the inserter  54  usable in the image forming system may have one of a plurality of different specifications, the copying machine  52  and the finisher  55  are not required to prepare different control programs corresponding to the different specifications of the inserter  54 . 
   Further, the commands are transmitted between the print control section  521  and the finisher control section  551  via the inserter control section  541 . This arrangement requires only one system of the control system, thereby simplifying the configuration of the control system. 
   Note that, in the processing shown in  FIG. 6 , if the interleaving sheet insertion processing is performed between sheets that have been subjected to the printing processing at the copying machine  52 , the interleaving sheet insertion processing is performed after the outputting operation of the immediately preceding sheet ends. This arrangement simplifies the control of the interleaving sheet insertion, but, to a certain degree, lowers the performance on the outputting of the sheets at a portion where the interleaving sheet insertion is performed. 
   On the other hand, in the processing shown in  FIGS. 7 and 8 , if the interleaving sheet insertion processing is performed between the sheets that have been subjected to printing processing at the copying machine  52  as described above, the paper intervals are appropriately controlled with taking account of the interleaving sheet insertion processing. Therefore, though the control becomes complicated to a certain degree, the performance on the outputting of the sheets is not lowered at the portion where the interleaving sheet insertion is performed. 
     FIG. 9  is a flowchart showing an example of the operation that includes an initial operation at the finisher  55 . Note that, the initial operation is running for setup, checking operation, etc., of parts of the finisher  55  when the finisher  55  starts operating first. 
   First, the print control section  521  notifies the finisher control section  551  of the paper ID of the sheet. The inserter control section  541  which has received the paper ID directly forwards the paper ID to the finisher control section  551 . 
   The finisher control section  551  which has received notification of the paper ID causes the finisher  55  to start the initial operation in response to the notification. Further, the finisher control section  551  calculates a paper interval (paper interval B) and sends the calculated paper interval to the print control section  521 . The paper interval B calculated here is a time required for the initial operation at the finisher  55 . The inserter control section  541  sends to the print control section  521  paper interval B′ obtained by subtracting a transport time at the inserter  54  from the paper interval B. Here, the inserter control section  541  performs the above subtraction processing for the following reason. 
   When receiving notification of the paper interval B′, the print control section  521  waits if necessary in accordance with the notified paper interval, and then causes the copying machine  52  to start transport processing of the sheet whose paper ID is  1 . Here, a predetermined time for the waiting may be a period obtained by subtracting from the period notified as the paper interval (i) a period for the image forming processing at the copying machine  52  and (ii) a transport time of the sheet from the copying machine  52  to the finisher  55 . Note that, the transport time of the sheet from the copying machine  52  to the finisher  55  does not include a transport time of the sheet at the inserter  54 . 
   Therefore if the paper interval B calculated by the finisher control section  551  is directly used as the paper interval notified to the print control section  521 , transporting of the sheet to the finisher  55  is delayed for a period of the transport time at the inserter  54 . 
   Therefore, in the system configuration where the inserter  54  is provided between the copying machine  52  and the finisher  55 , the inserter control section  541  subtracts the transport time at the inserter  54  from the paper interval B notified from the finisher  55 , so that the print control section  521  can obtain a paper interval that takes into account the transport time at the inserter  54 . With this, it is possible to cause the sheet to reach the finisher in accordance with timing at which the finisher  55  finishes the initial operation, thereby improving printing performance. 
   Further, the print control section  521  causes the copying machine  52  to start transport processing of the sheet, and outputs a paper output command or a paper output completion command. 
   Upon receiving the paper output command from the print control section  521 , the inserter control section  541  causes the inserter  54  to start transport processing for relaying and transporting to the finisher  55 , the sheet transported from the copying machine  52 . When the sheet enters the paper output sensor of the inserter  54 , the inserter control section  541  sends a paper output completion command to the finisher control section  551 . When the sheet goes out of the paper output sensor, the inserter control section  541  sends a paper output completion command to the finisher control section  551 . 
   After receiving the paper output command, the finisher control section  551  controls the finisher  55  to perform transport processing and post-processing on the sheet sent from the inserter  54  and to eject the sheet. After the finisher  55  ejects the sheet, the finisher control section  551  sends an eject completion command to the inserter control section  541 . The inserter control section  541  directly forwards notification of the eject completion to the print control section  521 . 
   In the operation shown in  FIG. 9 , the processing for sending commands and calculating paper intervals at the print control section  521  and finisher control section  551  do not need to take into account processing performed by the inserter  54  even if the inserter  54  is provided. In other words, control and adjustment concerning the processing performed by the inserter  54  are all performed by the inserter control section  541 . Therefore the print control section  521  of the copying machine  52  does not require two types of control programs respectively for cases where the inserter  54  is provided and where the inserter  54  is not provided, thereby reducing the workload of processing on the print control section  521 . 
   Further, even if the inserter  54  usable in the image forming system may have one of a plurality of different specifications, the copying machine  52  and the finisher  55  are not required to prepare different control programs corresponding to the different specifications of the inserter  54 . 
   Further, the commands are transmitted between the print control section  521  and the finisher control section  551  via the inserter control section  541 . This arrangement requires only one system of the control system, thereby simplifying the configuration of the control system. 
   As described above, the image forming system in accordance with the present embodiment in which the inserter device and the post-processing device are attached to the image forming apparatus is so arranged that timing of transporting sheets that are relayed by the inserter is adjusted and controlled by the inserter. With this, the image forming apparatus main body and the post-processing device are not required to prepare a paper transport control program that takes into account the inserter. 
   Note that, the foregoing explanation showed the examples in which the paper IDs for the two sheets are notified first in a case where a plurality of sheets are successively output. However, if the form that can output input images to ten sheets, for example, has been prepared before the printing starts, the paper IDs for all the ten sheets may be notified to the finisher before the printing starts. 
   In other words, it is possible to achieve high-speed printing in the specification of the present system if the image forming apparatus receives a paper interval for an nth sheet before starting transporting an (n−1)th sheet. 
   As described above, an image forming system of the present invention in which an inserter device and a post-processing device are attached to an image forming apparatus is so arranged that a control command communicated between the image forming apparatus and the post-processing device is relayed by the inserter device. 
   With this arrangement, a control command communicated between the image forming apparatus and the post-processing device is sent via the inserter device. Therefore the image forming apparatus is not required to be provided with control systems respectively for the inserter device and the post-processing device. Accordingly, only one system of the control system is required, so that the arrangement of the control system is simplified. 
   Further, the image forming system is preferably arranged so that the image forming apparatus and the post-processing device generate the control command without taking into account processing at the inserter device; and the inserter device judges content of the control command upon receiving the control command issued by the image forming apparatus, and forwards the control command after converting the control command or adjusting output timing of the control command if the control command needs to take into account the processing at the inserter device. 
   With this arrangement, the image forming apparatus and the post-processing device generate the control command without taking into account processing at the inserter device. Therefore, even if the image forming system is usable in a system configuration that is not provided with the inserter device, it is not necessary to vary the processing in accordance with whether or not the inserter device is provided. In other words, the image forming apparatus does not require two types of control programs respectively for cases where the inserter device is provided and where the inserter device is not provided, thereby reducing the workload of processing on the image forming apparatus. 
   Note that, if a control command communicated between the image forming apparatus and the post-processing device needs to take into account processing at the inserter device in the system configuration provided with the inserter device, the inserter device itself converts the control command or adjusts output timing of the control command before forwarding the control command. Therefore even if the inserter device usable in the image forming system may have one of a plurality of different specifications, the image forming apparatus and the post-processing device are not required to prepare different control programs corresponding to the different specifications of the inserter device. 
   Further, the image forming system is preferably arranged so that if the inserter device receives a paper output command issued by the image forming apparatus, the inserter device starts in response to the receipt of the paper output command, relay transport processing of a sheet outputted from the image forming apparatus, and sends the paper output command to the post-processing device in accordance with timing at which the inserter device outputs the sheet to the post-processing device (timing at which a paper output sensor provided to the inserter device detects a front edge of the sheet, for example). 
   With this arrangement, the image forming apparatus can send a paper output command without regard to whether or not the inserter device is provided, when issuing and sending the paper output command. Specifically, the transport time of the sheet transported from the image forming apparatus to the post-processing device becomes longer if the inserter device is provided because the sheet passes through the inserter device. However, timing of the paper output command corresponding to the sheet is adjusted at the inserter device so as to coincide with the timing at which the sheet is transported. With this, it is possible to reduce the workload of processing on the image forming apparatus. 
   The image forming system is preferably arranged so that if the inserter device receives a paper output completion command issued by the image forming apparatus, the inserter device sends the paper output completion command to the post-processing device in accordance with timing at which the inserter device finishes outputting the sheet to the post-processing device (timing at which a paper output sensor provided to the inserter device detects a back edge of the sheet, for example). 
   With this arrangement, the image forming apparatus can send a paper output completion command without regard to whether or not the inserter device is provided, when issuing and sending the paper output completion command as in the case of the paper output command. 
   Further, the image forming system is preferably arranged so that if the inserter device receives an interleaving sheet feed command from the image forming apparatus, the inserter device starts interleaving sheet feed processing in response to the receipt of the interleaving sheet feed command, and sends either a paper output command or paper output completion command to the post-processing device in accordance with predetermined timing. 
   With this arrangement, the image forming apparatus is only required to send an interleaving sheet feed command to the inserter device in order to cause the inserter device to perform the interleaving sheet feed processing. Namely, a paper output command or paper output completion command to be sent to the post-processing device with respect to the interleaving sheet transported from the inserter device to the post-processing device is generated by the inserter device. Further, transmission timing of the paper output command or paper output completion command is adjusted at the inserter device so as to coincide with the timing at which the interleaving sheet is transported. With this, it is possible to reduce the workload of processing on the image forming apparatus. 
   Note that, the predetermined timing at which the paper output command is sent to the post-processing device is timing at which the inserter device outputs the interleaving sheet to the post-processing device. Further, the predetermined timing at which the paper output completion command is sent to the post-processing device is timing at which the inserter device finishes outputting the interleaving sheet. 
   The image forming system is preferably arranged so that if the inserter device receives a command with which the post-processing device notifies the image forming apparatus of transport timing of a sheet, the inserter device adjusts the transport timing in the command if necessary so that the transport timing takes into account a transport time of the sheet in the inserter device, and then forwards to the image forming apparatus the command containing the adjusted transport timing. 
   In this image forming system, a command with which the post-processing device notifies the image forming apparatus of transport timing of a sheet may be sent from the post-processing device to the image forming apparatus. This is intended to shorten the transport intervals between sheets consecutively ejected (paper interval) so as to improve the processing efficiency of the entire system. 
   With the foregoing arrangement, the post-processing device can send the command for notifying the transport timing without taking into account whether or not the inserter device is provided. Specifically, the transport time of the sheet transported from the image forming apparatus to the post-processing device becomes longer if the inserter device is provided because the sheet passes through the inserter device. However, in the foregoing arrangement, transport timing of the sheet is adjusted if necessary so as to take into account the transport time of the sheet in the inserter device. With this, the image forming apparatus can obtain appropriate transport timing. 
   The invention being thus described, it will be obvious that the same way may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.