Patent Publication Number: US-8982402-B2

Title: Image forming system and image forming system communication control method

Description:
This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-79069 filed on Apr. 5, 2013, the entire disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to improvement of a communication control method in an image forming system in which a sheet processing apparatus of a different type is connected with an image forming apparatus. 
     2. Description of Related Art 
     The image forming apparatus can be used as a printing apparatus because various types of bookbinding processing become possible by being connected with various types of sheet processing apparatuses to form the image forming system. For example, saddle stitching bookbinding can be conducted by applying a stapling process to the crease portion of the sheet bundle made by folding sheets at the center of the sheets. The square back processing which produces a condition similar to the un-sewn binding is possible by applying pressure to the spine portion of a saddle stitched sheet bundle with a roller or the like and by forming a crease at the corner to produce the spine portion. 
     As a pre-processing to make such a crease, a line is made by using a line-making device called by the name of a creaser to apply a line-making process at the place where a crease is to be produced. The performance of the folding process after the line-making process has an advantage to prevent the crease from swelling even if multiple sheets are gathered and folded. Further, by the line-making process before the folding process, there is another advantage to prevent a toner from removing at the crease portion on the sheet convex surface during the folding process. 
     When various bookbinding processes like these are conducted, several sheet processing apparatuses having different functions are connected to the back of the image forming apparatus in series. Then a product subjected to bookbinding of the desired condition is obtained by applying the process to sheets on which images have been formed, by the sheet processing apparatus. 
     In an image forming system constituted by such an image forming apparatus and a sheet processing apparatus, it is necessary to transmit various control signals and sensor detection results between the apparatuses as well as to convey sheets from the top apparatus to the last apparatus. Normally an image forming apparatus and sheet processing apparatus are connected in series and the information is transmitted through a communication function of each apparatus. 
     As the contents of the communication, for using sufficient functions of various complicated sheet processes by the sheet processing apparatus or for operating in cooperation with each other at high productivity as a whole system, various types of and massive information such as a sheet discharge timing, a sheet type, an apparatus condition need to be transmitted without delay. Therefore, a high speed serial communication is used for communication between apparatuses to transmit massive data. 
     On the other hand, recently various sheet processing apparatuses are required. For this reason, it is becoming more difficult that only apparatuses of one manufacturer are used for sheet processing apparatuses arranged in order to cope with various processes. Accordingly, for the image forming system to be used as a printing apparatus, it is desirable that a sheet processing apparatus developed by another manufacturer (hereinafter, referred to as “third-vender sheet processing apparatus”) can be connected with an image forming apparatus and a sheet processing apparatus which are main parts. 
     For methods to cope with these problems, various proposals are provided in Japanese Unexamined Patent Application Publication Nos. 2006-350961 and 2009-271761. In the Japanese Unexamined Patent Application Publication No. 2006-350961, minimum information needed by the sheet processing apparatus is transmitted by the parallel communication which has been used widely in general in the past to cope with the problems. The parallel communication is commonly used in the field of the printer and is a de facto standard, however only the minimum information for the operation can be transmitted because it is simple. 
     In the Japanese Unexamined Patent Application Publication No. 2009-271761, proposed is a technique for using adaptively an in-line finisher and a near-line finisher physically connected with an image forming apparatus in series. The in-line finisher is a sheet processing apparatus connected with the image forming apparatus in series. The near-line finisher is a sheet processing apparatus which is not physically connected with the image forming apparatus and is arranged in the vicinity. Therefore, a technique in which the print job is divided or converted according to which finisher is to be used, is proposed. 
     When a third-vender sheet processing apparatus is connected with an image forming apparatus, it is common that a genuine sheet processing apparatus is connected directly at the rear of the image forming apparatus and the third-vender sheet processing apparatus is connected at the rear of the genuine sheet processing apparatus. The genuine sheet processing apparatus is a sheet processing apparatus of the same manufacturer as the image forming apparatus. Four reasons are explained as follows. 
     Reason 1: The third-vender sheet processing apparatus tends to restrict the contents of possible sheet processes. For example, a certain third-vender sheet processing apparatus only conducts the discharge of saddle stitching booklets and cannot carry out the straight discharge which does not conduct the discharge of saddle stitching booklets. The third-vender sheet processing apparatus is often constructed to be connected as the final stage. Thus it is necessary to provide a genuine sheet processing apparatus having a function of a sub-tray discharge between the image forming apparatus and the third-vender sheet processing apparatus. 
     Reason 2: The speed of input conveyance into the third-vender sheet processing apparatus tends to be fixed. In this case, the speed adjustment is necessary in the previous stage. Thus, a genuine sheet processing apparatus whose speed is adjustable and which has, for example, a function of a relay unit or the like is necessary to be connected between the image forming apparatus and the third-vender sheet processing apparatus. 
     Reason 3: The height of the input position of the third-vender sheet processing apparatus tends to be unmatched with the discharge position of the image forming apparatus. Thus it is necessary to provide a genuine sheet processing apparatus whose heights of input and output positions are adjustable between the image forming apparatus and the third-vender sheet processing apparatus. 
     Reason 4: Only one sheet processing apparatus can be connected directly after the image forming apparatus regardless of whether it is the third-vender sheet processing apparatus or the genuine sheet processing apparatus. Thus even if an interface for the third-vender sheet processing apparatus (for example, the parallel interface having high versatility) is provided on the image forming apparatus, when a genuine sheet processing apparatus is connected with the image forming apparatus with the serial interface, which occupies the majority of the use methods, the parallel interface becomes useless. 
     Because of the above four reasons, it becomes necessary that for example, a genuine sheet processing apparatus for adjusting the conveyance speed and a genuine sheet processing apparatus for securing a discharge on a sub-tray need to be connected between an image forming apparatus and a third-vender sheet processing apparatus. 
     In this case, the connection is made as follows. The image forming apparatus and the genuine sheet processing apparatus are connected so that information is transmitted by the serial communication between them. When multiple genuine sheet processing apparatuses exist, they are connected so that information is transmitted between a genuine sheet processing apparatus and a genuine sheet processing apparatus through the serial communication. The genuine sheet processing apparatus and third-vender sheet processing apparatus are connected so that information is transmitted through the parallel communication. 
     When the connection is arranged for communication as described above, the following problems newly occur. 
     Problem 1: Detailed information regarding the sheet processing, for example, information on a sheet length can be transmitted because assignment of information is possible when the serial communication is used. However, when the parallel communication is used, detailed information regarding sheet processing or the like cannot be assigned and cannot be transmitted. Thus an operation of mode setting is necessary between the apparatuses in advance before the start of operation. 
     Problem 2: Detailed information regarding apparatus operation conditions, for example, information on positions or contents of the jam can be transmitted at the time of occurrence of the jam when the serial communication is used. However, detailed information regarding an apparatus operation condition cannot be transmitted through the parallel communication. Therefore, information on occurrence of some abnormality in the third-vender sheet processing apparatus is transmitted. However, to know the detailed contents of the abnormality which has occurred, the operator needs to see the operation panel of the third-vender sheet processing apparatus. 
     Problem 3: The imposition information or prohibition rule information of the third-vender sheet processing apparatus cannot be transmitted to the image forming apparatus by the parallel communication. For this reason, the mode setting based on the third-vender sheet processing apparatus need to be conducted on the image forming apparatus side before the start of operation. 
     Problem 4: Many third-vender sheet processing apparatuses are structured to be used not only as an in-line finisher but also as a near-line finisher. However, under conditions where the third-vender sheet processing apparatus is connected as an in-line finisher, when the power of the image forming apparatus is turned off, the power of the third-vender sheet processing apparatus is also turned off simultaneously. For this reason, the third-vender sheet processing apparatus cannot be used independently as a near-line finisher. 
     As described above, a problem of worsening the usage occurs when the third-vender sheet processing apparatus is connected to an image forming apparatus. Though the above specific examples shows that the third-vender sheet processing apparatus transmits information through the parallel communication and the image forming apparatus and the genuine sheet processing apparatus transmit information by the serial communication, the situation is not limited to these. For example, when an image forming apparatus and a genuine sheet processing apparatus transmit information through a high-speed serial communication or the third-vender sheet processing apparatus transmits information through a low-speed serial communication, problems similar to the above-described ones can occur. Further, when an image forming apparatus and a genuine sheet processing apparatus transmit information by a serial communication which can deal with various data and a third-vender sheet processing apparatus transmits information by a serial communication which deal with minimum data, problems similar to the above-described ones can occur. 
     In the above description, “information cannot be transmitted” includes not only the case where information cannot be transmitted because of difference of communication protocols, but also the case where amount of assigned commands or data is small because the defined information contents are restricted. Similarly, “information cannot be transmitted” includes the case where precision or the number of digits of numerical value of the handled information is different. Further similarly “information cannot be transmitted” includes the case where the communication of the sheet processing is not at an appropriate timing because the communication speed is low. 
     Further in the above description, though specific examples of third-vender sheet processing apparatus are described, it is not restricted to them. For example, even in the case of products manufactured by the same manufactures, when a high-performance apparatus in which various functions including a communication function is enlarged and a low-performance apparatus in which various functions including a communication function is restricted are connected, there is probability of occurrence of the similar problems. 
     That is to say, to an image forming apparatus as an upstream apparatus, an apparatus of a different type whose information communication is restricted due to the communication (third-vender sheet processing apparatus or sheet processing apparatus of the same manufacturer but of a different type) is connected as the downstream apparatus, it has been made clear that various types of malfunctioning occur. 
     The present invention is achieved in view of these problems, and has an objective to provide an image forming system and an image forming system communication control method which can improve the operation conditions without generating restrictions in the image forming system in which an apparatus of a different type is connected as a downstream apparatus. 
     The present invention is achieved in view of these problems, and has an objective to provide an image forming system and an image forming system communication control method which allows the downstream apparatus to operate alone independently of the upstream apparatus without operational restrictions in the image forming system in which an apparatus of a different type is connected as a downstream apparatus. 
     SUMMARY OF THE INVENTION 
     (1) An image forming system reflecting one aspect of the present invention is composed of the following: 
     an upstream apparatus for forming an image on a sheet; 
     a downstream apparatus for applying sheet processing to the sheet on which the image is formed by the upstream apparatus; 
     an exclusive communication path for communicating information which is necessary only for an operation of each apparatus in a state in which a communication partner is fixed between the upstream apparatus and the downstream apparatus; and 
     a general-purpose communication path for communicating information in a state in which a communication partner is selectable between the upstream apparatus and the downstream apparatus; 
     wherein the upstream apparatus and the downstream apparatus communicate the information by using a communication path which is the exclusive communication path or the general-purpose communication path and which can handle the information to be communicated. 
     (2) In the above (1), it is desirable that the general-purpose communication path is configured to be capable of communicating information with an apparatus other than the upstream apparatus and the downstream apparatus when the apparatus is connected with the path, as well as communicating information which is necessary for operations of the upstream apparatus and the downstream apparatus. 
     (3) In the above (1) to (2), it is desirable that the upstream apparatus includes an image forming apparatus which forms an image on a sheet, and a sheet processing apparatus which applies sheet processing to the sheet on which the image is formed by the image forming apparatus and which is connected with the downstream apparatus as a preceding stage of the downstream apparatus. It is desirable that the exclusive communication path includes a first exclusive communication path for communicating between the image forming apparatus and the sheet processing apparatus, and a second exclusive communication path for communicating between the sheet processing apparatus and the downstream apparatus. Further it is desirable that the general-purpose communication path is configured to communicate between the image forming apparatus and the downstream apparatus. 
     (4) In the above (3), information transmitted through the first exclusive communication path includes at least information which is transmitted through the second exclusive communication path. It is desirable that information transmitted through the general-purpose communication path includes information which is transmitted through the first exclusive communication path and further includes another information. 
     (5) In the above (3) to (4), it is desirable that the first exclusive communication path is configured to transmit information by a serial communication. It is desirable that the second exclusive communication path is configured to transmit information by a parallel communication. 
     (6) In the above (3) to (5), it is desirable that the sheet processing apparatus connected with the downstream apparatus through the second exclusive communication path has a function of converting information transmitted from the image forming apparatus through the first exclusive communication path into information to be transmitted through the second exclusive communication path to transmit it to the downstream apparatus and converting information transmitted from the downstream apparatus through the second exclusive communication path into information to be transmitted through the first exclusive communication path to transmit it to the image forming apparatus. 
     (7) In the above (3) to (6), the upstream apparatus includes a plurality of sheet processing apparatuses connected with one another in series, which are configured to include the sheet processing apparatus and which are connected with the image forming apparatus as a subsequent stage of the image forming apparatus. Then, it is desirable that the plurality of sheet processing apparatuses are connected with one another through the first exclusive communication path, and the second exclusive communication path connects a rearmost sheet processing apparatus of the plurality of sheet processing apparatuses and the downstream apparatus. 
     (8) In the above (3), the upstream apparatus is configured to include a plurality of sheet processing apparatuses connected with one another in series, which include the sheet processing apparatus and which are connected with the image forming apparatus as a subsequent stage of the image forming apparatus. Then it is desirable that when information on sheet processing is transmitted from the downstream apparatus to the image forming apparatus through the general-purpose communication path, the image forming apparatus transmits first processing information to the downstream apparatus through the general-purpose communication path, and transmits second processing information including the first processing information to the sheet processing apparatus through the first exclusive communication path, and a rearmost sheet processing apparatus of the plurality of sheet processing apparatuses transmits third processing information which is a part of the second processing information to the downstream apparatus through the second exclusive communication path. 
     (9) In the above (8), it is desirable that the first processing information is information related to a page imposition and a prohibition rule. It is desirable that the second processing information is information related to a sheet length, a conveyance speed, a basis weight, a discharge timing and a sheet processing timing. It is desirable that the third processing information is information related to a discharge and sheet processing. 
     (10) In the above (3), the following transmission of information is desirable when an abnormality occurs in the downstream apparatus. The downstream apparatus creates first abnormality information which indicates the abnormality of the downstream apparatus and transmits the first abnormality information to the sheet processing apparatus through the second exclusive communication path. The sheet processing apparatus creates second abnormality information based on a state of the downstream apparatus and the first abnormality information and transmits the second abnormal information to the image forming apparatus through the first exclusive communication path. The downstream apparatus creates third abnormality information based on a state of the abnormality of the downstream apparatus and transmits the third abnormality information to the image forming apparatus through the general-purpose communication path. 
     (11) In the above (10), it is desirable that the first abnormality information is information which indicates presence and absence of an abnormality occurrence. It is desirable that the second abnormality information is information which is created based on the first abnormality information and the state of the apparatus. It is desirable that the third abnormality information is information which includes information on the abnormality occurrence and a content of the abnormality. 
     (12) In the above (3), it is desirable that the upstream apparatus stops an operation by information on a stop instruction which includes an instruction of an operation stop, which is transmitted from an external apparatus connected with the upstream apparatus through the general-purpose communication path. It is desirable that the downstream apparatus continues an operation by information on sheet processing transmitted from the external apparatus through the general-purpose communication path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       [ FIG. 1 ] is a block diagram showing a structure of an image forming system of an embodiment of the present invention. 
       [ FIG. 2 ] is a structural diagram showing a structure of an image forming system of an embodiment of the present invention. 
       [ FIG. 3 ] is a structural diagram showing a structure of an image forming system of an embodiment of the present invention. 
       [ FIG. 4 ] is an explanatory diagram illustrating a serial communication of an embodiment of the present invention. 
       [ FIG. 5 ] is an explanatory diagram illustrating a parallel communication of an embodiment of the present invention. 
       [ FIG. 6 ] is an explanatory diagram illustrating a serial communication of an embodiment of the present invention. 
       [ FIG. 7 ] is an explanatory diagram illustrating a parallel communication of an embodiment of the present invention. 
       [ FIG. 8 ] is an explanatory diagram illustrating an exclusive communication of an embodiment of the present invention. 
       [ FIG. 9 ] is a flowchart showing an operational condition of an embodiment of the present invention. 
       [ FIG. 10 ] is a sequence diagram showing an operational condition of an embodiment of the present invention. 
       [ FIG. 11 ] is a flowchart showing an operational condition of an embodiment of the present invention. 
       [ FIG. 12 ] is a sequence diagram showing an operational condition of an embodiment of the present invention. 
       [ FIG. 13 ] is a sequence diagram showing an operational condition of an embodiment of the present invention. 
       [ FIG. 14 ] is a structural diagram showing a structure of an image forming system of an embodiment of the present invention. 
       [ FIG. 15 ] is a flowchart showing an operational condition of an embodiment of the present invention. 
       [ FIG. 16 ] is a sequence diagram showing an operational condition of an embodiment of the present invention. 
       [ FIG. 17 ] is a block diagram showing a structure of an image forming system of an embodiment of the present invention. 
       [ FIG. 18 ] is a structural diagram showing a structure of an image forming system of an embodiment of the present invention. 
       [ FIG. 19 ] is a structural diagram showing a structure of an image forming system of an embodiment of the present invention. 
       [ FIG. 20 ] is a flowchart showing an operational condition of an embodiment of the present invention. 
       [ FIG. 21 ] is a sequence diagram showing an operational condition of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following paragraphs, one or more embodiments of the invention will be described by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments. 
     The details of forms for performing the present invention (hereinafter referred to as embodiments) are described referring to drawings 
     [Structure of the Image Forming System ( 1 )] 
     Referring to  FIGS. 1-3 , the structure of an image forming system ( 1 ) of an embodiment of the present invention is described. As shown in  FIGS. 1-3 , this image forming system forms an image forming system in the condition where an image forming apparatus  100  as an upstream apparatus, a sheet processing apparatus  300  as an upstream apparatus and a sheet processing apparatus  400  as a downstream apparatus are connected in series. The words “connected in series” means the condition where a sheet on which an image has been formed is subjected to sheet processing of the sheet processing apparatus  300  and sheet processing apparatus  400  in this order. 
     For a sheet on which an image has been formed by the image forming apparatus  100 , the sheet processing apparatus  300  can conduct a sub-tray discharge, a large capacity stack and a through-conveyance. For the sheet on which an image has been formed by the image forming apparatus  100 , the sheet processing apparatus  400  can conduct a booklet discharge by various sheet processes. 
     The sheet processing apparatus  300  is a genuine sheet processing apparatus manufactured by the same manufacturer as the image forming apparatus  100 . The sheet processing apparatus  400  is a sheet processing apparatus manufactured by the third vender different from that of the image forming apparatus or a sheet processing apparatus of a type different from the image forming apparatus  100  and the sheet processing apparatus  300 . For the following description for the embodiment, the case where the sheet processing apparatus  400  is a sheet processing apparatus manufactured by the third vender different from that of the image forming apparatus is the specific example. 
     The image forming apparatus  100  and the sheet processing apparatus  300  are connected by using a communication path Line-S of a serial communication as the first exclusive communication path whose communication partner is fixed. The sheet processing apparatus  300  and the sheet processing apparatus  400  are connected by a communication path Line-P of a parallel communication as the second exclusive communication path whose communication partner is fixed. The image forming apparatus  100  and the sheet processing apparatus  400  are connected by a network  1  such as a LAN as a general-purpose communication path through which communication is conducted under the condition where the communication partner is selectable. 
     The network  1  as a general-purpose communication path is connected with an external apparatus such as a computer (PC)  10  as well as the image forming apparatus  100  and the sheet processing apparatus  400 . The exclusive communication path (Line-S or Line-P) transmits only information necessary for operations of the upstream apparatus (the image forming apparatus  100  and the sheet processing apparatus  300 ) and the downstream apparatus (the sheet processing apparatus  400 ). The general-purpose communication path (network  1 ) is configured to be capable of information transmission with the external apparatus when the external apparatus other than the upstream apparatus and downstream apparatus is connected thereto, as well as conducting communication of information necessary for the operations of the upstream apparatus and downstream apparatus. 
     The image forming apparatus  100  is configured to include a control section  101 , a general-purpose communication section  102 L, an exclusive communication section  102 S, an operation display section  103 , a storage section  104 , a sheet supply section  105 , a conveyance section  110 , a document reading section  120 , an image data storage section  130 , an image processing section  140  and an image forming section  150 . 
     The control section  101  controls the entire image forming system as well as controls each section in the image forming apparatus  100 . The general-purpose communication section  102 L communicates with another apparatus connected with the network  1 . The exclusive communication section  102 S communicates with the sheet processing apparatus  300  through the communication path Line-S. The operation display section  103  conducts a condition display for the image forming apparatus  100  as well as transmits operation input signals according to the operation input by the operator to the control section  101 . The storage section  104  is used as a work area for the control program as well as stores the control program and various setting data. The sheet supply section  105  supplies sheets stored in the sheet supply stray. The conveyance section  110  conveys a sheet on which an image is to be formed at a predetermined speed. The document reading section  120  creates image data by scanning a document. The image data storage section  130  stores image data or various data to be used for image forming. The image processing section  140  conducts various types of image processing necessary for image forming. The image forming section  150  conducts image forming (printing) based on a command for image forming and image data. 
     The sheet on which an image has been formed by the image forming apparatus  100  is conveyed toward the sheet processing apparatus  300  on the downstream side in the sheet conveyance direction (hereinafter referred to as the subsequent stage). The sheet processing apparatus  300  is connected at the subsequent stage of the image forming apparatus  100 . The sheet processing apparatus  300  is configured to include a control section  301 , an exclusive communication section  302 S, an exclusive communication section  302 P, a storage section  304 , a discharge path selecting section  305 , a sub-tray discharge section  360 , and a stacker loading section  370 . 
     The control section  301  controls each section in the sheet processing apparatus  300 . The exclusive communication section  302 S communicates with the image forming apparatus  100  through a communication path Line-S. The exclusive communication section  302 P communicates with the sheet processing apparatus  400  through a communication path Line-P. The storage section  304  is used as a work area for the control program as well as stores the control program and various setting data. The discharge path selecting section  305  selects a discharge path for discharging a sheet bundle subjected to the sheet processing. The sub-tray discharge section  360  discharges sheets to the sub-stray. The stacker loading section  370  loads sheets by using a large capacity stack. 
     The sheet processing apparatus  400  is connected at the subsequent stage of the sheet processing apparatus  300  so as to conduct the sheet processing. The sheet processing apparatus  400  is configured to include a control section  401 , an exclusive communication section  402 P, a general-purpose communication section  402 L, an operation display section  403 , a storage section  404 , a discharge path selecting section  405 , a conveyance section  410 , a folding section  420 , aligning section  430 , a stitching section  440 , a cutting section  450  and a booklet loading section  460 . The control section  401  controls each section in the sheet processing apparatus  400 . The exclusive communication section  402 P communicates with the sheet processing apparatus  300  through the communication path Line-P. The general-purpose communication section  402 L communicates with another apparatus connected with the network  1 . The operation display section  403  conducts a condition display for the sheet processing apparatus  400  as well as transmits operation input signals according to the operation input by the operator to the control section  401 . The storage section  404  is used as a work area of the control program as well as stores the control program and various setting data. The discharge path selecting section  405  selects a discharge path for discharging a sheet bundle subjected to the post-processing. The conveyance section  410  conveys sheets at a predetermined speed. The folding section  420  folds a sheet. The aligning section  430  aligns sheets. The stitching section  440  applies stapling to the aligned sheet bundle. The cutting section  450  cuts off an edge portion of the stitched sheet bundle. The booklet loading section  460  loads the sheet bundle at the state of a booklet after stitching and cutting to discharge the sheet bundle. 
     When the sheet processing which the sheet processing apparatus  400  is capable of is limited to only the saddle stitching discharge or the like, the sub-stray discharge of the sheet processing apparatus  300  is substituted for the straight discharge without the discharge of the saddle stitched booklet. When the input conveyance speed to the sheet processing apparatus  400  is fixed and is different from the output conveyance speed of the image forming apparatus, the speed adjustment is performed in the sheet processing apparatus  300 . When the height of input position of the image processing apparatus  400  is different from the height of discharge position of the image forming apparatus  100 , the conveyance height is adjusted in the sheet processing apparatus  300 . 
     When the subsequent stage side communication form of the image forming apparatus is different from the preceding stage side communication form of the sheet processing apparatus  400 , the communication form is converted in the sheet processing apparatus  300 . According to the structure in this case, the image forming apparatus  100  transmits information by a serial communication and the sheet processing apparatus  400  transmits information by a parallel communication. Thus, the sheet processing apparatus  300  conducts conversion between the serial communication and parallel communication. 
     [Description for the Communication] 
     Here, the communication form and communication standard used for the present embodiments are described. In the present embodiments, information is transmitted by the serial communication which transmits and receives data in series through the first exclusive communication path and information is transmitted by the parallel communication which transmits and receives data in parallel through the second exclusive communication path. Through the general-purpose communication path, information is transmitted by transmitting and receiving data in the form of a packet by a TCP/IP protocol through Ethernet (registered trademark) or the like. 
       FIG. 4  shows a communication condition of the serial communication such as a RS232C or RS422 as a communication protocol used in the first exclusive communication path of the present embodiment.  FIG. 4   a  shows an example of a serial communication interface and  FIG. 4   b  shows an example of a transmission and reception timing of serial communication data. The signal T×D means transmission data, signal R×D means reception data, signal RTS means transmission request and signal CTS means transmission possible. Different multiple types of information (refer to  FIG. 6  to be described later) are transmitted or received as data in series. 
     This serial communication can include more detailed information than the parallel communication to be described later. For example, in the case of jam occurrence, information on the jam position or the cause of jam occurrence can be included in the serial communication. As a wait information (information on standby), information on the degree of length of necessary standby time can be included (refer to  FIG. 6 ). 
     On the other hand,  FIG. 5  shows a communication state by the parallel communication such as that of Centronics as a communication protocol used in the second exclusive communication path of the present embodiment.  FIG. 5   a  shows an example of a parallel communication interface.  FIG. 5   b  shows an example of transmission and reception timings of parallel communication data. In this case, the ON/Off of signals whose control contents have been determined independently and in parallel such as signals C 0 , C 1 , C 2 , C 3  and C 4 , and R 0 , R 1 , R 2 , R 3  and R 4  are transmitted or received. 
     In the present embodiment, as signals of the parallel communication, the signals C 0 -C 4  are used for communication from the sheet processing apparatus  300  to the sheet processing apparatus  400 . The signals R 0 -R 4  are used for communication from the sheet processing apparatus  400  to the sheet processing apparatus  300 . 
     Because of the difference of the above-described communication form, generally the serial communication can perform more speedy and larger capacity communication than the parallel communication. Further, the serial communication can perform longer distance transmission than the parallel communication. 
       FIG. 6  shows each name of signals of the serial communication and whether or not they correspond to the parallel communication (“parallel correspondence” in  FIG. 6 ). The item “possible” in the column of the parallel correspondence shows that the parallel communication can also perform information transmission corresponding to the serial communication. The item “partially possible” in the column of the parallel correspondence shows that the parallel communication can also perform transmission of a part of information corresponding to the serial communication. The item “impossible” in the column of the parallel correspondence shows that the parallel communication corresponding to the serial communication is impossible. 
     There are signals which are under severe conditions in regard to the time from transmission or reception of communication till the reflection of it to the operations and there are signals which are not. For example the sheet discharge signal (ON/OFF) C 2  or R 3  is used for control of an acceleration timing of a reception side conveyance roller. Therefore, if the timing is not suitable, this causes reduction of productivity or a control failure. Thus the time condition is very severe. Accordingly, for these signals under severe time conditions, not a LAN communication having possibility of time delay of the signal transmission but the parallel communication without time delay of the signal transmission is used. 
     The wait information in the serial communication is not used in the parallel communication, however, the sheet processing apparatus  300  fills the role instead. Further, in regard to a jam notice, a door-open notice, an alarm notice, when a jam occurs in the sheet processing apparatus  400 , the abnormality notification signal R 1  is turned ON in the parallel communication and the occurrence of abnormality is notified. However, even when the abnormality notification signal R 1  is turned ON in the parallel communication, what kind of abnormality occurs cannot be known. 
     As shown above, since the handled information contents are limited in the parallel communication, all of the information transmitted by the serial communication can not be transmitted by the parallel communication. In other words, the parallel communication can be used by many types of apparatuses, however only the minimum information for the operation can be transmitted. In this embodiment, words “information cannot be transmitted” includes not only the case where information transmission is impossible because of different communication protocols but also the case where amount of allocated commands or data is small because defined contents of information are limited. Similarly, the “information cannot be transmitted” includes the case where the precision or the number of digits of numerical value of handled information is different. Further similarly, the “information cannot be transmitted” includes the case where the communication is late for the suitable timing of the sheet processing because of a low communication speed. In this embodiment, “information can be transmitted” or “information can be handled” includes not only the case where communication protocols accord with but also the case where problems do not occur in the information transmission because of defined or allocated contents of information, precision or the number of digits of numerical value of handled information, processing timing caused by the communication speed and the like. 
       FIG. 8  shows an example of information which can be handled by a LAN communication used by the network  1  which is a general-purpose communication path of the present embodiment. The protocol of the LAN communication is a communication made by combining “Ethernet” (registered trademark) which is a general and physical standard and a “TCP/IP” protocol” defining an agreement of communication contents. In this embodiment, the image forming apparatus  100  and the sheet processing apparatus  400  are connected with each other, but the condition is not limited to this. For example, when another apparatus is connected with the network  1 , the apparatus becomes communicable with the image forming apparatus  100  and the sheet processing apparatus  400 . 
     As the network  1 , a multipoint to multipoint communication is possible by using a hub or the like, but when communication is conducted only between the image forming apparatus  100  and the sheet processing apparatus  400 , a one to one communication by using a cross cable is also possible. 
       FIG. 8  shows each signal name of the LAN communication, and whether each signal corresponds to the serial communication (“serial correspondence” in  FIG. 8 ) and whether each signal corresponds to the parallel communication (“parallel correspondence” in  FIG. 8 ). The word “possible” in the columns of the serial correspondence and the parallel correspondence means that information transmission is possible in either the serial communication or parallel communication. The word “partially possible” in the columns of the serial correspondence and the parallel correspondence means that transmission of a part of information is possible in either the serial communication or the parallel communication. The word “impossible” in the columns of the serial correspondence and the parallel correspondence means that information transmission is impossible in the serial communication or the parallel communication. 
     In other words, information transmitted through the first exclusive communication path by a serial communication ( FIG. 6 ) includes at least information transmitted through the second exclusive communication path by the parallel communication ( FIG. 7 ). Further, information transmitted through the general-purpose communication path by a LAN communication ( FIG. 8 ) includes at least information transmitted through the first exclusive communication path by the serial communication ( FIG. 6 ), information transmitted through the second exclusive communication path by the parallel communication ( FIG. 7 ) and other information. The information shown in  FIGS. 6-8  is an example and the situation is not limited to this. 
     [Operation of the Image Forming System ( 1 - 1 )] 
     Here, basic operations of image forming and sheet processing in the image forming system shown in  FIGS. 1-3  (operation ( 1 - 1 )) are described by using a flowchart in  FIG. 9  and a sequence diagram in  FIG. 10 . 
     In the following description of the operations, performance of transmission or reception of information or signals through the general-purpose communication section  102 L or the exclusive communication section  102 S by control of the control section  101  (execution of a communication control program) is described as “the image forming apparatus  100  transmits and receives, or communicates information or signals”. 
     Similarly, operations of transmission and reception of information or signals by control of the control section  301  is described as an operation of the sheet processing apparatus  300 . Operations of transmission and reception of information or signals by control of the control section  401  is described as an operation of the sheet processing apparatus  400 . 
     First, the power of the image forming apparatus  100  is turned ON in the image forming system. In the sheet processing apparatus  300  which has received the instruction of power-on from the image forming apparatus  100  through the communication path Line-S, the power is turned ON, operating together with the image forming apparatus  100 . In the sheet processing apparatus  400  which has received the instruction of power-on from the sheet processing apparatus  300  through the communication path Line-P, the power in turned ON, operating together with the image forming apparatus  100  and the sheet processing apparatus  300  (Step S 101  in  FIG. 9 ). 
     The sheet processing apparatus  400  transmits sheet processing information to the image forming apparatus  100  through the network  1  (Step S 102  in  FIG. 9 , and FIG.  10 ( 1 )). This sheet processing information includes information on possible sheet processing which is practicable in the sheet processing apparatus  400  such as folding or stitching, and further includes information which the sheet processing apparatus  400  requests from the image forming apparatus  100  in order to produce booklets such as information on the imposition regarding a page order or a top and bottom of the image, information on the possible sheet size and information on the possible sheet basis weight (refer to  FIG. 8 ). 
     These pieces of sheet processing information cannot be transmitted by the parallel communication shown in  FIG. 7 . Therefore, by using a LAN communication of the network  1 , the information is transmitted from the sheet processing apparatus  400  to the image forming apparatus  100 . The transmission of sheet processing information is carried out at the time of the start-up of the image forming system or the like. The image forming apparatus  100  receives these pieces of sheet processing information from the sheet processing apparatus  400  and determines the items or values to be set on the operation display section  403  of the sheet processing apparatus  400 . 
     Then, start of the image forming (printing) is instructed from an operator (YES in Step S 103  in  FIG. 9 ). The printing instruction from the operator can be any one of an instruction by the operator on the operation display section  103  of the image forming apparatus  100  and an instruction from a PC  10  to the image forming apparatus  100  through the network  1  and the like. 
     According to the printing instruction, the image forming apparatus  100  transmits information on the sheet supply to the sheet processing apparatus  400  by a LAN communication through the network  1  (step S 104  in  FIG. 9 , and  FIG. 10  ( 2 - 1 )). 
     This sheet supply information includes various types of information such as information on the post-processing mode (folding and stitching), information on the sheet size, information on the adjustment value such as the staple position, information on the sheet type and information on the sheet basis weight. Based on the sheet supply information, the sheet processing apparatus  400  determines a sheet process to be carried out to a sheet conveyed from the preceding stage and control parameters necessary for the sheet processing. 
     The image forming apparatus  100  transmits sheet supply information similar to the above to the sheet processing apparatus  300  through the communication path Line-S (step S 105  in  FIG. 9 , and FIG.  10 ( 2 - 2 )). Regarding the sheet supply information to the sheet processing apparatus  400  by a LAN communication and the sheet supply information to the sheet processing apparatus  300  through the communication path Line-S, an example where the transmission through a LAN (step S 104  in FIG.  9 , and FIG.  10 ( 2 - 1 )) is earlier than the transmission through the communication path Line-S (step S 105  in  FIG. 9 , and FIG.  10 ( 2 - 2 )) is illustrated but approximately simultaneous transmission is desirable. 
     When the sheet processing operation becomes possible after the sheet processing apparatus  400  receives the above-described sheet supply information, the sheet processing apparatus  400  turns the on-line signal R 0  ON, in the communication path Line-P in order to indicate that the sheet processing operation becomes possible and transmits the signal to the sheet processing apparatus  300  (step S 106  in  FIG. 9 , and FIG.  10 ( 3 - 1 )). The online signal from the sheet processing apparatus  400  is converted into ready information in the sheet processing apparatus  300 . The ready information after the conversion is transmitted from the sheet processing apparatus  300  to the image forming apparatus  100  through the communication path Line-S (step S 106  in  FIG. 9 , and FIG.  10 ( 3 - 2 )). When the sheet processing operation of the sheet processing apparatus  300  becomes possible after the sheet processing apparatus  300  receives the above-described sheet supply information, the sheet processing apparatus  300  turns the ready information (Ready) ON, in order to indicate that the sheet processing apparatus  300  itself becomes operable and transmits the information to the image forming apparatus  100  through the communication path Line-S. 
     The image forming apparatus  100  monitors the ready information from the sheet processing apparatus  300  through the communication path Line-S (step S 106  in  FIG. 9 ). When the image forming apparatus  100  can determine that the sheet processing apparatus  300  becomes operable after receiving the ready information (YES in step S 106  in  FIG. 9 ), the image forming apparatus  100  transmits the operation start information indicating an operation start to the sheet processing apparatus  300  through the communication path Line-S (step S 107  in  FIG. 9 , and FIG.  10 ( 4 - 1 )). 
     The image forming apparatus  100  receives the on-line signal which has been converted into the ready signal by the sheet processing apparatus  300 , and when it can be determined that the sheet processing apparatus  400  becomes operable (YES in step S 106  in  FIG. 9 ), the image forming apparatus  100  transmits an operation start signal indicating an operation start to the sheet processing apparatus  400  through the communication path Line-S, the sheet processing apparatus  300  and the communication path Line-P (step S 108  in  FIG. 9 , and FIGS.  10 ( 4 - 1 ) and  10 ( 4 - 2 )). The operation start information transmitted by the serial communication from the image forming apparatus  100  through the communication path Line-S is converted into an operation start signal C 0  of the parallel communication through the communication path Line-P in the sheet processing apparatus  300  and reaches the sheet processing apparatus  400 . 
     In the sheet processing apparatus  300  which has received the above operation start signal, the control section  301  initializes each section. By this initialization, the sheet processing apparatus  300  becomes operable (step S 109  in  FIG. 9 ). Further, in the sheet processing apparatus  400  which has received the above-described operation start signal, the control section  401  initializes each section. By this initialization, the sheet processing apparatus  400  becomes operable. (step S 109  in  FIG. 9 ). 
     Then the image forming apparatus  100  starts printing (step S 110  in  FIG. 9 ). The image forming apparatus  100  transmits sheet discharge information to the sheet processing apparatus  300  through the communication path Line-S at the moment the printed sheet is discharged from the image forming apparatus  100  (step S 111  in  FIG. 9 , and FIG.  10 ( 5 - 1 )). Further, the sheet processing apparatus  300  transmits the ON of sheet discharge signal C 2  to the sheet processing apparatus  400  through the communication path Line-P at the moment the sheet which has been conveyed from the image forming apparatus  100  is discharged from the sheet processing apparatus  300  (step S 112  in  FIG. 9 , and FIG.  10 ( 5 - 2 )). 
     When the sheet processing apparatus  400  normally receives a sheet from the image forming apparatus  100  by way of the sheet processing apparatus  300 , the sheet processing apparatus  400  notifies the image forming apparatus  100  of the sheet reception in response to the reception of the above-described sheet discharge signal C 2 . For this notification, the sheet processing apparatus  400  turns the sheet discharge signal R 3  ON, which means the sheet reception, in the communication path Line-P and transmits the signal to the image forming apparatus  100  by way of the sheet processing apparatus  300  (step S 113 , step S 114  and FIGS.  10 ( 6 - 1 ) and  10 ( 6 - 2 )). The sheet discharge signal (FIG.  10 ( 6 - 1 )) of the parallel communication from the sheet processing apparatus  400  through communication path Line-P is converted into page discharge information of the serial communication through the communication path Line-S in the sheet processing apparatus  300  and reaches the image forming apparatus  100  (FIG.  10 ( 6 - 2 )). 
     Because of the above-described page discharge information and sheet discharge signal, the number of sheets processed by the sheet processing apparatus  300  and the sheet processing apparatus  400  can be counted by the control section  101  of the image forming apparatus  100 . 
     The image forming apparatus  100 , the sheet processing apparatus  300  and the sheet processing apparatus  400  repeat the above-described processes from the first page to the last page on which images are to be formed (NO□S 110  in step S 115  in  FIG. 9 ). The sequence diagram in  FIG. 10  indicates the case where printing for two sheets is conducted. To be more specific,  FIG. 10  shows an example in which the sheet discharge information ( 5 - 1 ), sheet discharge signal ( 5 - 1 ), sheet discharge signal ( 6 - 1 ) and page discharge information ( 6 - 2 ) is carried out for the first sheet and the sheet discharge information ( 7 - 1 ), sheet discharge signal ( 7 - 1 ), sheet discharge signal ( 8 - 1 ) and page discharge information ( 8 - 2 ) is carried out for the second sheet 
     When the time for producing a booklet after sheets including the last sheet printed by the image forming apparatus  100  have been sent to the sheet processing apparatus  400  (YES in step S 115  in  FIG. 9 ), finishing information of the serial communication indicating the time for performing the sheet processing is transmitted from the image forming apparatus  100  to the sheet processing apparatus  300  through the communication path Line-S (step S 116  in  FIG. 9 , and FIG.  10 ( 9 - 1 )). The sheet processing apparatus  300  converts the finishing information of the serial communication from the image forming apparatus  100  into the ON of part separation signal C 3  of the parallel communication and transmits it to the sheet processing apparatus  400  through the communication path Line-P (step S 117  in  FIG. 9 , and  FIG. 9-2 )). 
     The sheet processing apparatus  400  which has received the ON of part separation signal C 3  conducts the designated sheet processing (for example, production of a saddle stitching booklet) as the finishing processing (step S 118  in  FIG. 9 ). The sheet processing apparatus  400  loads a produced booklet or the like on the booklet loading section  460  to discharge it (refer to  FIG. 2 ). 
     When the sheet processing apparatus  400  has completed a desired product (for example, a saddle stitched booklet) after performing the designated sheet processing correctly, the sheet processing apparatus  400  turns the bundle discharge signal R 4  ON and transmits the signal to the sheet processing apparatus  300  through the communication path Line-P (step S 119  in  FIG. 9 , and FIG.  10 ( 10 - 1 )). The sheet processing apparatus  300  which has received the ON of the bundle discharge signal R 4  converts the bundle discharge signal R 4  of the parallel communication into the bundle discharge information of the serial communication and transmits the information to the image forming apparatus  100  through the communication path Line-S (step S 120  in  FIG. 9 , and FIG.  10 ( 10 - 2 )). 
     As described above, in the image forming system which includes at least the image forming apparatus  100  as an upstream apparatus forming an image on a sheet and the sheet processing apparatus  400  as a downstream apparatus applying sheet processing to the sheet, the exclusive communication path (Line-S or Line-P) for performing communication at the state of fixing the communication partner between the upstream apparatus and the downstream apparatus and the general-purpose communication path (the network  1  of the LAN communication) for performing communication at the state of the communication partner being selectable between the upstream apparatus and the downstream apparatus are connected. Under this structure, control is carried out to allow the exclusive communication path and the general-purpose communication path to communicate respectively information which can be communicated. Due to this, information whose communication is restricted in the exclusive communication path can be communicated through the general-purpose communication path. Thus even when the sheet processing apparatus  400  as an apparatus of a different type is connected as the downstream apparatus, improvement of the operation state without restrictions becomes possible. 
     For signals whose timing is important such as for the sheet supply or sheet discharge, by not using the network  1  of the LAN communication which has possibility of a time delay but using the exclusive communication path (Line-S or Line-P), information communication having an excellent performance of real-time is secured and certain operations matching various timing for an image forming system. 
     Even when the image forming apparatus  100  has a function of transmitting information by the serial communication through the first exclusive communication path Line-S and the sheet processing apparatus  400  has a function of information communication by the parallel communication through the second exclusive communication path Line-P, the sheet processing apparatus  300  on the upstream side converts the communication form. Thus, when the sheet processing apparatus  400  of the third vender as an apparatus of a different type is connected, the operation as an image forming system is secured. 
     As described above, handling of information which can not be handled by the parallel communication by using the LAN communication and transmission of signals related to timing of the sheet conveyance by the parallel communication eliminate necessity of a mode setting operation respectively on the image forming apparatus  100  and the sheet processing apparatus  400  of the third vender and can constitute an image forming system easy to use for operators. 
     In the operations above, information transmitted through the first exclusive communication path Line-S includes at least information transmitted through the second exclusive communication path Line-P. The information transmitted through the network  1  as a general-purpose communication path includes other information as well as information transmitted through the first exclusive communication path Line-S. Due to this, information restricted in the second exclusive communication path more than the first exclusive communication path Line-S can be transmitted through the general-purpose communication path. Thus even in an image forming system where the sheet processing apparatus  400  as an apparatus of a different type is connected as an downstream apparatus with an upstream apparatus (the image forming apparatus  100  and the sheet processing apparatus  300 ), improvement of the operation state without restrictions is possible. 
     Even in the case where the sheet processing apparatus  400  conducting the parallel communication is connected downstream with the image forming apparatus  100  and the sheet processing apparatus  300  conducting the serial communication, information subjected to restrictions by the parallel communication can be transmitted through the network  1  which is a general-purpose communication path. Thus even in an image forming system where the sheet processing apparatus  400  as an apparatus of a different type is connected as a downstream apparatus with an upstream apparatus (the image forming apparatus  100  and the sheet processing apparatus  300 ), improvement of the operation state without restrictions is possible. 
     The sheet processing apparatus  300  connected with the sheet processing apparatus  400  through the second exclusive communication path Line-P converts information transmitted from the image forming apparatus  100  through the first exclusive communication path Line-S into information to be transmitted through the second exclusive communication path Line-P and transmits it downstream to the sheet processing apparatus  400 . Further, the sheet processing apparatus  300  converts information transmitted from the sheet processing apparatus  400  through the second exclusive communication path Line-P into information to be transmitted through the first exclusive communication path Line-S and transmits it to the image forming apparatus  100 . Due to this, communication of minimum necessary information between the image forming apparatus  100  and the sheet processing apparatus  400  is carried out through the sheet processing apparatus  300  and information other than this is carried out through the network  1  as the general-purpose communication path. Therefore, even in an image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400  with the upstream apparatuses (the image forming apparatus  100  and the sheet processing apparatus  300 ), improvement of the operation state without restrictions is possible. 
     [Operation of the Image Forming System ( 1 - 2 )] 
     Here, by using the flowchart of  FIG. 11  and the sequence diagrams of  FIGS. 12 and 13 , the operation at the time of error handling for the image forming and sheet processing (operation ( 1 - 2 )) on the image forming system shown in  FIGS. 1-3  (the image forming apparatus  100 , the sheet processing apparatus  300  and the sheet processing apparatus  400 ) is described. 
     In the following description for operations, performance of transmission and reception of information or signals through the general-purpose communication section  102 L and the exclusive communication section  102 S by the control of the control section  101  (execution of a communication control program) is described as “the image forming apparatus  100  transmits and receives, or communicates information or signals”. Similarly, operations of transmission and reception of information or signals by control of the control section  301  is described as operations of the sheet processing apparatus  300 . Operations of transmission and reception of information or signals by control of the control section  401  is described as an operation of the sheet processing apparatus  400 . 
     The flowchart in  FIG. 11  illustrates mainly error handling when an error occurs in the sheet processing apparatus  400  on the downstream side. In the sequence diagram in  FIGS. 12 and 13 , the same writing is applied to the same portions as the sequence diagram in  FIG. 10 . 
     First, at any one of timings during operation of the image forming system, some error occurs in the sheet processing apparatus  400  (step S 201  in  FIG. 11 ). As this error, a sheet jam in the sheet processing apparatus  400  (JAM) or opening of some door provided on the sheet processing apparatus  400  (“DOOR OPEN”) are supposed. 
     The sheet processing apparatus  400  turns the abnormality notification R 1  ON indicating an occurrence of abnormality and transmits it to the sheet processing apparatus  300  through the communication path Line-P (step S 202  in  FIG. 11 ). The abnormality notification R 1  of the parallel communication through the communication path Line-P can notify of only the occurrence of abnormality by turning itself ON. However, the abnormality notification R 1  cannot include information on the position or contents of the abnormality. 
     The sheet processing apparatus  300  determines the apparatus state whether at the time of abnormality occurrence, the sheet processing apparatus  400  are executing sheet processing or not, based on the operation start command from the image forming apparatus  100  or the sheet discharge signal from the sheet processing apparatus  400  (step S 203  in  FIG. 11 ). If it is after the operation start command from the image forming apparatus  100  is transmitted and before the sheet discharge signal or bundle discharge signal from the sheet processing apparatus  400  is transmitted, it can be determined that the sheet processing apparatus  400  is executing sheet processing. 
     Here, details are described by supposing that a jam occurs in the sheet processing apparatus  400  after the sheet processing apparatus  300  turns the sheet discharge signal C 2  ON ( FIG. 12  ( 5 - 2 ) (“JAM” in  FIG. 12 ). 
     When a jam occurs during the sheet processing operation in the sheet processing apparatus  400 , the sheet processing apparatus  400  turns the abnormality notification R 1  ON by the parallel communication through the communication path Line-P toward the sheet processing apparatus  300  as described above (step S 202  in  FIG. 11 , and  FIG. 12  (JAM 1 - 1 )). 
     The sheet processing apparatus  300  cannot understand what kind of abnormality has occurred from the ON of the abnormality notification R 1 . However, in view of the fact that the abnormality notification comes while the sheet discharge signal has not come from the sheet processing apparatus  400  during the operation (refer to  FIG. 12 ), the sheet processing apparatus  300  can understand that the jam occurred during the sheet processing as the apparatus state (YES in step S 203  in  FIG. 11 ). 
     The sheet processing apparatus  300  converts the abnormality notification R 1  from the communication path Line-P (step S 202  in  FIG. 11 ) into a jam notification and transmits it to the image forming apparatus  100  through the communication path Line-S (step S 204  in  FIG. 11 , and  FIG. 12  (JAM 1 - 2 )). Further, the sheet processing apparatus  300 , in order not to send a sheet which is left unconveyable (a succeeding sheet to the jammed sheet) in the sheet processing apparatus  300  to the sheet processing apparatus  400 , discharges it onto the sub-stray in the sub-tray discharge section  360  (step S 205  in  FIG. 11 ). The sheet processing apparatus  300  stops the operation (step S 208  in  FIG. 11 ) at the time of completion of discharge of the succeeding sheet whose sub-tray discharge is possible (YES in step S 206  in  FIG. 11 ). 
     The jam notification transmitted from the sheet processing apparatus  300  to the image forming apparatus  100  is information made by estimation from the abnormality notification R 1 . Therefore, the image forming apparatus  100  which controls the whole of the image forming system cannot grasp what type of jam occurred, where the jam occurred or where is the remaining sheet 
     However, the operator needs detailed information on the jam to remove the remaining sheet as a jam recovery process. Therefore, the sheet processing apparatus  400  transmits detailed jam information such as on the type of jam, jam position, and position of the remaining sheet to the image forming apparatus  100  by a LAN communication through the network  1  (step S 209  in  FIG. 11 , and  FIG. 12  (JAM 2 - 1 )). 
     The image forming apparatus  100  which has received this detailed jam information through the network  1  displays how to remove the jammed sheet or remaining sheet on the operation display section  103  as a jam recovery process (step S 210  in  FIG. 11 ). 
     Next, when discharging a saddle stitched booklet, the sheet processing apparatus  400  turns the bundle discharge signal R 4  ON (FIG.  13 ( 10 - 1 )) and transmits it to the sheet processing apparatus  300 . Then, the detailed operation of the present embodiment will be described referring to the sequence diagram in  FIG. 13  on the supposition that a door-open occurs in the sheet processing apparatus  400  after the sheet processing apparatus  300  which has received this bundle discharge signal R 4  transmits the bundle discharge information to the image forming apparatus  100  (“DOOR OPEN” in  FIG. 13 ). 
     The bundle discharge signal R 4  from the sheet processing apparatus  400  is converted into the bundle discharge information in the sheet processing apparatus  300  and transmitted to the image forming apparatus  100 . After this, if the door-open of any door occurs in the sheet processing apparatus  400  (“DOOR OPEN” in  FIG. 13 ), the sheet processing apparatus  400  turns abnormality notification R 1  ON by the parallel communication through the communication path Line-P toward the sheet processing apparatus  300  as described above (step S 202  in  FIG. 11 , and (DrErr 1 - 1 )). 
     The sheet processing apparatus  300  cannot understand what kind of abnormality has occurred from the ON of the abnormality notification R 1 . However, since the abnormality notification R 1  comes after the bundle discharge signal R 4  comes from the sheet processing apparatus  400  during the operation (refer to  FIG. 13 ), it can be determined that a door-open has occurred because a sheet does not exist in the sheet processing apparatus  400  as the apparatus state (No in step S 203  in  FIG. 11 ). 
     The sheet processing apparatus  300  converts the abnormality notification R 1  from the communication path Line-P (step S 202  in  FIG. 11 ) into a door-open notification and transmits to the image forming apparatus  100  through the communication path Line-S (step S 207  in  FIG. 11 ,  FIG. 13  (DrErr 1 - 2 )). The sheet processing apparatus  300  stops its operation (S 208  in  FIG. 11 ). 
     Since the door-open notification transmitted from the sheet processing apparatus  300  to the image forming apparatus  100  is information made based on assumption from the abnormality notification R 1 , the image forming apparatus  100  which controls the whole of the image forming system cannot grasp which door occurs the door-open. 
     However, for the operator to close the door as a door-close process, detailed information on the door-open is necessary. The sheet processing apparatus  400  transmits detailed jam information such as on the door-open position and the position of the remaining sheet to the image forming apparatus  100  by a LAN communication through the network  1  (step S 209  in  FIG. 11 , and  FIG. 13  (DrErr 2 - 1 )). 
     The image forming apparatus  100  which has received this detailed door-open information through the network  1 , displays how to close the open door on the operation display section  103  as the recovery process for door-open (door-close process) (step S 210  in  FIG. 11 ). 
     As described above, when an abnormality occurs in the sheet processing apparatus  400 , the sheet processing apparatus  400  creates the first abnormality information (abnormality notification R 1 ) indicating an abnormality occurrence of the sheet processing apparatus  400  and transmits it to the sheet processing apparatus  300  through the communication path Line-P. The sheet processing apparatus  300  based on the state information of the sheet processing apparatus  400  (conditions of each type of signals) and the first abnormality information, creates the second abnormality information (jam notification or door-open notification) and transmits it to the image forming apparatus  100  through the communication path Line-S. The sheet processing apparatus  400  creates the third abnormality information (detailed jam information or detailed door-open information) based on the abnormal condition of the sheet processing apparatus  400  and transmits it to the image forming apparatus  100  through the network  1 . Therefore, information which the first abnormality information transmitted upstream from the sheet processing apparatus  400  through the communication path Line-P fails to include, can be transmitted to the image forming apparatus  100  through the network  1  as the third abnormality information. Thus, even for the image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400 , the operation state can be improved without restrictions. 
     The first abnormality information is information indicating presence or absence of the abnormality occurrence and the second abnormality information is information created from first abnormality information and the apparatus state, and then the third abnormality information is information including the abnormality occurrence and abnormality contents. Due to this, information which the first abnormality information transmitted upstream from the sheet processing apparatus  400  through the second exclusive communication path Line-P fails to include, can be transmitted to the image forming apparatus  100  through the network  1  as the third abnormality information. Thus, even for the image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400 , the operation state can be improved by transmitting information on the abnormality occurrence and abnormality contents to the image forming apparatus  100  without restrictions to the operations. 
     To be specific, even in an image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400 , the operation state can be improved by transmitting information on the abnormality occurrence and abnormality contents and by conducting a recovery process for the jam or door-open without restrictions to the operations. 
     [Structure of the Image Forming System ( 2 )] 
     Referring to  FIGS. 14-16 , the structure of image forming system ( 2 ) of an embodiment of the present invention will be described. 
     As shown in  FIG. 14 , in this image forming system, the first image forming apparatus  100 A as an upstream apparatus, the sheet processing apparatus  300  as an upstream apparatus and the sheet processing apparatus  400  of the third vendor as a downstream apparatus are connected in serial. That is to say, this image forming system forms an in-line image forming system where sheets are conveyed between the first image forming apparatus  100 A, the sheet processing apparatus  300  and the sheet processing apparatus  400  (“SHEET CONVEYANCE” in  FIG. 14 ). 
     The in-line image forming system applies sheet processing to a sheet on which an image is formed by the first image forming apparatus  100 A, by using the sheet processing apparatus  300  and the sheet processing apparatus  400  in this order, and because it is the same as the system already described as the structure ( 1 ), repeated description will be omitted. 
     An external apparatus such as a computer (PC) and the second image forming apparatus  100 B are connected with the network  1  as a general-purpose communication path as well as the first image forming apparatus  100 A and the sheet processing apparatus  400 . 
     The second image forming apparatus  100 B is not mechanically connected with the in-line image forming system as the sheet conveyance path. The second image forming apparatus  100 B is connected communicable with the first image forming apparatus  100 A or the sheet processing apparatus  400  through the network  1  and is positioned near the in-line image forming system. Accordingly, sheets printed by the second image forming apparatus  100 B can be manually conveyed to a sheet supply opening of the sheet processing apparatus  400  (“MANUAL SHEET CONVEYANCE” in  FIG. 14 ). In other words, sheets printed by the second image forming apparatus  100 B can be subjected to sheet processing called as a near-line processing by the sheet processing apparatus  400 . 
     [Operation for the Image Forming System ( 2 )] 
     By using the flowchart in  FIG. 15  and the sequence diagram in  FIG. 16 , the operation at the time of the near-line processing (operation ( 2 )) in a power saving mode on the image forming system shown in  FIGS. 14-16  (the first image forming apparatus  100 A, the second image forming apparatus  100 B, the sheet processing apparatus  300  and the sheet processing apparatus  400  of the third vendor) will be described. 
     The near-line processing in a power saving mode means that the first image forming apparatus  100 A and the sheet processing apparatus  300  are kept in the power saving mode and the sheet processing apparatus  400  is kept in an operation mode in the in-line image forming system. 
     In the following description of the operations, performance of transmission and reception of information or signals through a communication section by the control of the control section in each apparatus (execution of a communication control program) is described as “each apparatus transmits and receives, or communicates information or signals”. 
     Here, it is assumed that regarding a booklet produced by sheet processing in the sheet processing apparatus  400 , the second image forming apparatus  100 B can print a sheet or can use a print mode, which the first image forming apparatus  100 A cannot print or use. In this case, the operator by operating a PC  10  gives a print instruction to the second image forming apparatus  100 B (step S 301  in  FIG. 15 , and FIG.  16 ( 11 )). The second image forming apparatus  100 B executes the instructed printing and when a sheet bundle is outputted on the discharge section (not illustrated) of the second image forming apparatus  100 B, transmits a print completion notification to the PC  10  through the network  1  (YES in step S 302  in  FIG. 15 , and FIG.  16 ( 12 )). 
     Next, the PC  10  gives an instruction of the operation stop to the first image forming apparatus  100 A, which does not need to operate, for the sheet processing by the near-line processing by the sheet processing apparatus  400  (step S 303  in  FIG. 15 , and FIG.  16 ( 13 - 1 )). For example, as this instruction of operation stop, a sleep switchover instruction for switching the operation mode to a sleep mode is corresponded. This sleep switchover instruction in preparation for the near-line processing is an instruction for switching the first image forming apparatus  100 A and the sheet processing apparatus  300  to the sleep mode. 
     The first image forming apparatus  100 A which has received this sleep switchover instruction through the network  1  gives the sleep switchover instruction to the sheet processing apparatus  300  through the communication path Line-S (FIG.  16 ( 13 - 2 )). 
     At this time, the sheet processing apparatus  300  transmits the OFF of the main body status signal C 4  indicating the sleep mode of the first image forming apparatus  100 A to the sheet processing apparatus  400  through the communication path Line-P (YES in step S 304  in  FIG. 15 , and FIG.  16 ( 13 - 3 )). 
     After the sleep switchover is completed (YES in step S 304  in  FIG. 15 ), the sheet processing apparatus  300  transmits the notification of the sleep switchover completion to the first image forming apparatus  100 A through the communication path Line-S (FIG.  16 ( 14 - 1 )). Further, after the sleep switchover is completed (YES in step S 304  in  FIG. 15 ), the first image forming apparatus  100 A transmits the notification of the sleep switchover completion to the PC  10  through the network  1  (FIG.  16 ( 14 - 2 )). 
     After this, the PC  10  transmits information on the near-line sheet processing to the sheet processing apparatus  400  through the network  1  (step S 305  in  FIG. 15 , and FIG.  16 ( 15 )). This near-line sheet processing information includes information on the sheet size or sheet processing mode. 
     Due to this, when executing the near-line sheet processing by using the second image forming apparatus  100 B and the sheet processing apparatus  400 , the operator does not need to set the sheet processing mode on the operation display section of the sheet processing apparatus  400 . To be specific, the operator only need to carry a sheet bundle subjected to the printing output by the second image forming apparatus  100 B to the sheet supply opening of the sheet processing apparatus  400  and to instruct a sheet processing start. As the start instruction to the sheet processing apparatus  400 , the operator can operate on the operation display section at the time of carrying the sheet or the operator can give the instruction of sheet processing start of the sheet processing apparatus  400  from the PC  10 . 
     By doing as described above, while the first image forming apparatus  100 A and the sheet processing apparatus  300  which do not need to be used in the image forming system, are kept in the sleep mode for contribution to power saving, the near-line processing using the second image forming apparatus  100 B which is not connected with the image forming system and the sheet processing apparatus  400  in the image forming system can be conducted efficiently. 
     Because information on such as the near-line sheet processing mode can be transmitted to the sheet processing apparatus  400  through a LAN communication of the network  1  for the operation, the usability is enhanced. Further, by using the near-line sheet processing, the operation efficiency of the sheet processing apparatus  400  of the third vendor which is connected as the image forming system can be enhanced. 
     To be specific, the upstream apparatuses (the image forming apparatus  100  and the sheet processing apparatus  300 ) stop their operations after the stop instruction information including an instruction for stopping the operation is transmitted from the PC  10  connected trough the network  1  as a general-purpose communication path is transmitted thereto. Then, the sheet processing apparatus  400  continues its operation by transmission of the sheet processing information from the PC  10  through the network  1  as a general-purpose path. Due to this, in the image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400 , operations of only the sheet processing apparatus  400  independent of the upstream apparatuses (the image forming apparatus  100  and the sheet processing apparatus  300 ) without restrictions of the operations is possible. Due to this, the sheet processing apparatus  400  can be operated as a finisher for the near-line from another image forming apparatus  100 . 
     In the above-described image forming system, the exclusive communication path (Line-S or Line-P) conducts transmission of only necessary information for the operations of the upstream apparatus (the image forming apparatus  100  and the sheet processing apparatus  300 ) and the downstream apparatus (the sheet processing apparatus  400 ). The general-purpose communication path (network  1 ) is configured to be capable of information transmission with an external apparatus other than the upstream apparatus and downstream apparatus such as a PC  10  when the external apparatus is connected, as well as conducts transmission of information necessary for operations of the upstream apparatus and downstream apparatus. Due to this, communication between the downstream apparatus and the external apparatus becomes possible and in an image forming system where an apparatus of a different type is connected as a downstream apparatus, various operations become possible. 
     [Structure of the Image Forming System ( 3 )] 
     Referring to  FIGS. 17-19 , the structure of image forming system ( 3 ) of an embodiment of the present invention will be described. 
     As shown in  FIGS. 17-19 , this image forming system is in the state where the image forming apparatus  100  as an upstream apparatus and the sheet processing apparatus  400  as the downstream apparatus are connected in series. The image forming system is capable of a booklet discharge by various types of sheet processing in the sheet processing apparatus  400  for the sheet on which an image is formed by the image forming apparatus  100 . 
     In  FIGS. 17-19 , by giving the same number to the same thing as the image forming system shown in  FIGS. 1-3 , repeated description is omitted. As a different part, the image forming system is in the state where the sheet processing apparatus  300  is removed from the image forming system. The sheet processing apparatus  400  is a third-vender sheet processing apparatus manufactured by another company different from the image forming apparatus  100 . In this case, when the output conveyance speed of the image forming apparatus  100  and the input conveyance speed of the sheet processing apparatus  400  is the same, and the height of discharge position of the image forming apparatus  100  and the height of input position of the sheet processing apparatus  400  is the same, the image forming apparatus  100  and the sheet processing apparatus  400  can be connected without using the sheet processing apparatus  300 . 
     The image forming apparatus  100  and the sheet processing apparatus  400  are connected with each other by a communication path Line-P of the parallel communication in the state where the communication partner is fixed. The image forming apparatus  100  and the sheet processing apparatus  400  are connected with the network  1  of a LAN or the like as a general-purpose communication path which conducts communication in the state where the communication partner is selectable. 
     The network  1  as a general-purpose communication path is connected with an external apparatus such as a computer (PC)  10  other than the image forming apparatus  100  and the sheet processing apparatus  400 . 
     [Operation for the Image Forming System ( 3 )] 
     Here, using the flowchart in  FIG. 20  and the sequence diagram in  FIG. 21 , basic operations for the image forming and sheet processing in the image forming system shown in  FIGS. 17-19  (operation ( 3 )) are described. 
     In the following description for operations, performance of transmission and reception of information or signals through the general-purpose communication section  102 L or the exclusive communication section  102 S by the control of the control section  101  (execution of a communication control program) is described as “the image forming apparatus  100  transmits and receives, or communicates information or signals”. Similarly, operations of transmission and reception of information or signals by control of the control section  401  is described as operations of the sheet processing apparatus  400 . 
     First, in the image forming system, the power of the image forming apparatus  100  is turned ON. Due to this, the sheet processing apparatus  400  receives the power ON instruction from the image forming apparatus  100  through the communication path Line-P. Then the power of the sheet processing apparatus  400  which has received the power ON instruction turns ON by operating together with the image forming apparatus  100  (step S 401  in  FIG. 20 ). 
     At this time, the sheet processing apparatus  400  transmits the sheet processing information to the image forming apparatus  100  through the network  1  (step S 402  in  FIG. 20 , and FIG.  21 ( 1 )). This sheet processing information includes information on possible sheet processing which the sheet processing apparatus  400  can practice such as folding or stitching, imposition information which the sheet processing apparatus  400  requests from the image forming apparatus  100  to produce a booklet such as information on the page order or top and bottom of the image, information on the possible sheet size, or information on the possible sheet basis weight (refer to  FIG. 8 ). 
     These pieces of the sheet processing information cannot be transmitted by the parallel communication through the communication path Line-P. Therefore, these pieces of the sheet processing information are transmitted from the sheet processing apparatus  400  to the image forming apparatus  100  by using a LAN communication of the network  1 . The transmission of the sheet processing information is conducted at time such as the time of start-up of the image forming system. The image forming apparatus  100  determines items or values to be set on the operation display section  403  of the sheet processing apparatus  400  by receiving these pieces of sheet processing information from the sheet processing apparatus  400 . 
     The start of image forming (printing) is instructed from the operator by an instruction from an operation on the operation display section  103  of the image forming apparatus  100  or by an instruction from a PC  10  through the network  1  (YES in step S 403  in  FIG. 20 ). In response to the printing instruction, the image forming apparatus  100  transmits the sheet supply information to the sheet processing apparatus  400  by a LAN communication through the network  1  (step S 404  in  FIG. 20 , and FIG.  21 ( 2 ). 
     The sheet supply information includes various types of information such as information on the post-processing mode (folding, stitching and the like), sheet size information, information on an adjustment value such as a stapling position, sheet type information, and information on the sheet basis weight. Based on the sheet supply information, the sheet processing apparatus  400  can determine sheet processing to be applied to a sheet conveyed from the image forming apparatus  100  and the control parameter necessary to conduct the sheet processing. 
     When the sheet processing operation becomes possible after the sheet processing apparatus  400  receives the above-described sheet supply information, the sheet processing apparatus  400  turns the on-line signal R 0  ON in the communication path Line-P and transmits it to the image forming apparatus  100  in order to indicate that sheet processing operation becomes possible (step S 405  in  FIG. 20 , and FIG.  21 ( 3 )). 
     The image forming apparatus  100  monitors the on-line signal from the sheet processing apparatus  400  through the communication path Line-P (step S 406  in  FIG. 20 ). When the image forming apparatus  100  receives the on-line signal and determines that the sheet processing apparatus  400  becomes capable of the operation (YES in step S 405  in  FIG. 20 ), the image forming apparatus  100  transmits an operation start signal indicating the operation start to the sheet processing apparatus  400  through the communication path Line-P (step S 406  in  FIG. 20 , and FIG.  21 ( 4 )). 
     In the sheet processing apparatus  400  which has received the above-described operation start signal, the control section  401  initializes each section. Due to this initialization, the sheet processing apparatus  400  becomes capable of the operation (step S 407  in  FIG. 20 )). The image forming apparatus  100  starts printing (step S 408  in  FIG. 20 ) and at the moment of discharge of the printed sheet from the image forming apparatus  100 , the ON of the sheet discharge signal C 2  is transmitted from the image forming apparatus  100  to the sheet processing apparatus  400  through the communication path Line-P (step S 409  in  FIG. 20 , and FIG.  21 ( 5 )). 
     When the sheet processing apparatus  400  receives a sheet from the image forming apparatus  100  normally, notifies the image forming apparatus  100  of the sheet reception in response to the above-described reception of the sheet discharge signal C 2 . For this reason, the sheet processing apparatus  400  turns the sheet discharge signal R 3  ON indicating the sheet reception in the communication path Line-P and transmits it to the image forming apparatus  100  (step S 410  in  FIG. 20 , and FIG.  21 ( 6 )). Because of the sheet discharge signal, the number of the sheets subjected to the processing by the sheet processing apparatus  400  can be counted by the control section  101  in the image forming apparatus  100 . 
     The image forming apparatus  100  and the sheet processing apparatus  400  repeat the above-described processing from the first page to the last page (NO□S 408  in step S 411  in  FIG. 20 ). The sequence diagram in  FIG. 21  shows the case of execution of printing for two sheets. To be specific, an example in which the sheet discharge signal ( 5 ) and sheet discharge signal ( 6 ) are transmitted for the first sheet, and the sheet discharge signal ( 7 ) and sheet discharge signal ( 8 ) are transmitted for the second sheet is illustrated. 
     Then the sheets including the last sheet printed by the image forming apparatus  100  has been sent to the sheet processing apparatus  400  and when the time for production of the booklet comes (YES in step S 411  in  FIG. 20 ), the ON of the part separation signal C 3 , which indicates the timing of performance of the sheet processing, is transmitted to the sheet processing apparatus  400  through the communication path Line-P (step S 412  in  FIG. 20 , and FIG.  21 ( 9 )). 
     The sheet processing apparatus  400  which has received the ON of part separation signal C 3 , carries out the designated sheet processing (for example, production of a saddle stitched booklet) as a finishing processing (step S 413  in  FIG. 20 ). The sheet processing apparatus  400  loads the produced booklet or the like on the booklet loading section  460  to discharge it (refer to  FIG. 2 ). 
     When a desired product (for example, a saddle stitched booklet) is made after correctly executing the designated sheet processing, the sheet processing apparatus  400  turns the bundle discharge signal R 4  ON and transmits it to the image forming apparatus  100  through the communication path Line-P (step S 414  in  FIG. 20 , and FIG.  21 ( 10 )). 
     As described above, in an image forming system which includes at least an image forming apparatus  100  which forms an image on a sheet as an upstream apparatus and a sheet processing apparatus  400  which applies sheet processing to the sheet as a downstream apparatus, an exclusive communication path (line-P) which communicates in a state where the communication partner is fixed between the upstream apparatus and downstream apparatus and a general-purpose communication path (a network  1  of a LAN communication) which communicates in a state where the communication partner is selectable between the upstream apparatus and downstream apparatus are connected. By controlling to provide the exclusive communication and the general-purpose communication with information which is manageable by the communication path respectively for transmission by sharing the information, information whose transmission is restricted in the exclusive communication path can be transmitted through the general-purpose communication path. Therefore, even when the sheet processing apparatus  400  as an apparatus of a different type is connected as a downstream apparatus, the operation state can be improved without restrictions. 
     For signals whose timings are important for such as for the sheet supply and sheet discharge, performance by the exclusive communication path (Line-P) instead of the network  1  of a LAN communication secures information communication with excellent real-time performance and secures a certain operation matching various timings as an image forming system. 
     As described above, information which cannot be handled in the parallel communication is handled by the LAN communication and signals related to timings for the sheet conveyance is handled by the parallel communication. Due to this, operations for the mode setting respectively on the image forming apparatus  100  and the sheet processing apparatus  400  are not necessary and a user-friendly image forming system can be constituted for the operators. 
     [Structure of the Image Forming System ( 4 )] 
     For the positioning and structure of the image forming apparatus and sheet processing apparatus of the image forming system in the above description, an example is described and various modifications can be possible. 
     According to the structures of image forming systems ( 1 ) and ( 2 ), the image forming apparatus  100 , the sheet processing apparatus  300  and the sheet processing apparatus  400  are connected in series but the structure is not limited to this. 
     For example, an image forming system where the image forming apparatus  100  and multiple sheet processing apparatuses  300  and the sheet processing apparatus  400  are connected in series can be included in the structure. In this case, the image forming apparatus  100 , the sheet processing apparatus  300  other than the rearmost sheet processing apparatus  300  and the preceding stage side of the rearmost sheet processing apparatus  300  are connected with the communication path Line-S of the serial communication, and the subsequent stage side of the rearmost sheet processing apparatus  300  and the sheet processing apparatus  400  are connected with the communication path Line-P of the parallel communication. Further, the image forming apparatus  100  and the sheet processing apparatus  400  are connected with the network  1  of a LAN communication. Even in such an image forming system, operations similar to ones in the above operational description are possible. 
     To be specific, the image forming apparatus  100  and multiple sheet processing apparatuses  300  communicate necessary information through the first exclusive communication path Line-S. The image forming apparatus  100  communicates minimum necessary information with the sheet processing apparatus  400  through the sheet processing apparatus  300  and the second exclusive communication path Line-P. Another information is communicated through the network  1  as a general-purpose communication path between the image forming apparatus  100  and the sheet processing apparatus  400 . Thus, even in an image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400  with the upstream apparatuses (the image forming apparatus  100  and the sheet processing apparatus  300 ), the operation state can be improved without restrictions. 
     Here, the case where information on the sheet processing is transmitted from the sheet processing apparatus  400  to the image forming apparatus  100  of an upstream apparatus through the network  1  as a general-purpose communication path is considered. In this case, the image forming apparatus  100  transmits the first processing information to the sheet processing apparatus  400  through the network  1  as a general-purpose communication path. The image forming apparatus  100  transmits the second processing information including the first processing information to the sheet processing apparatus  300  through the first exclusive communication path Line-S. The rearmost sheet processing apparatus  300  of the multiple sheet processing apparatuses  300  transmits the third processing information which is a part of the second processing information to the sheet processing apparatus  400  through the second exclusive communication path Line-P. Due to this information which the third processing information transmitted through the second exclusive communication path Line-P fails to include can be transmitted as the first processing information through the network  1  as a general-purpose communication path, and thereby even in an image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400 , the operation state can be improved without restrictions. 
     Here, the first processing information is information related to a page imposition and prohibition rule. The second processing information is information related to a sheet length, conveyance speed, basis weight, discharge timing, and sheet processing timing. The third processing information is information related to the discharge and sheet processing. Due to this, information which the third processing information transmitted through the second exclusive communication path Line-P fails to include (information related to the page imposition or prohibition rule or the like) can be transmitted as the first processing information through the network  1  as a general-purpose communication path. Therefore, even in an image forming system where an apparatus of a different type is connected as the sheet processing apparatus  400 , the operation state can be improved without restrictions.