Patent Publication Number: US-8985573-B2

Title: Relay apparatus and image forming system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a relay apparatus which relays a signal between an image forming device and a post-processing device which have different interfaces, and an image forming system including the relay apparatus. 
     2. Description of Related Art 
     To a subsequent stage of an image forming device which prints out an image by forming the image on a sheet, one or a plurality of post-processing devices having each function to perform processing such as punching, stitching, and folding, and to bundle a plurality of sheets to create a brochure are connected in series. Thereby, an image forming system is configured. 
     In such an image forming system, various types of information are exchanged between the image forming device and the post-processing device in order to match various sheet conditions (sheet size, paper type, and basis weight) or post-processing conditions. For example, the information is exchanged in the following sequences. 
     At the timing of feeding a sheet from a sheet feeding unit of the image forming device, the image forming device notifies the post-processing device of the sheet feed information including the sheet information relating to the above sheet and the post-processing information indicating the contents of post-processing to be performed for the above sheet. Based on the notified sheet feed information, each post-processing device calculates time necessary for the post-processing in the post-processing device and time corresponding to a sheet interval, and notifies the image forming device of the above calculated time. The image forming device allows the fed sheet to stand by at a predetermined standby position provided on the way to a carrier path, and releases a standby state to discharge the sheet at the timing corresponding to the time notified by the post-processing device. By this control, a sheet interval necessary for the post-processing device is secured. 
       FIG. 23  shows a connection example in the case where an image forming device and a plurality of post-processing devices are connected in series through serial interfaces (I/F) of the same communication system (protocol). In such a connection state, the information is sent in order from upstream to downstream (image forming device→post-processing device  1 →post-processing device  2 →post-processing device  3 ) or from downstream to upstream, and the information is sequentially transmitted. In Japanese Patent Application Publication No. 2007-210775, for example, a technique in which the information relating to jam generated on a downstream side is sequentially sent to an upstream device is disclosed. Further, in Japanese Patent Application Publication No. 2009-83449, a technique in which log data on the downstream side is sequentially sent to an upstream device is disclosed. 
       FIG. 24  shows a specific example in the case where sheet feed information is notified through the above-described sequence in the image forming system shown in  FIG. 23 . In this example, there is shown a communication sequence in which a punch process is performed in the post-processing device  1 , a sheet is carried by a bypass conveyance in the post-processing device  2  (a sheet is carried to a subsequent-stage post-processing device without performing post-processing), and a side stitching process is performed in the post-processing device  3  to create two sets of brochures each of which has two sheets. 
     Every when one sheet is fed, the image forming device outputs sheet feed information (sheet information and post-processing information) relating to a sheet to be fed and carried to the subsequent-stage post-processing devices. The sheet feed information is transmitted in order from the image forming device to the post-processing device  1 →the post-processing device  2 →the post-processing device  3 . In  FIG. 24 , a suffix added to each piece of information indicates that the sheet number of the sheet corresponding to the information and the set number of the set including the above sheet. To be more specific, “1-1”, “1-2”, “2-1”, and “2-2” indicate a first sheet of a first set, a second sheet of the first set, a first sheet of a second set, and a second sheet of the second set, respectively. 
     Based on the received sheet feed information, each post-processing device calculates time of a sheet interval necessary for post-processing (time for allowing a sheet to stand by in the image forming device). Then, each post-processing device notifies wait information indicating the calculated time in the order of the post-processing device  3 →the post-processing device  2 →the post-processing device  1 →the image forming device to notify the image forming device of the wait information. The wait information is sent back for each piece of sheet feed information (for each sheet). For example, the wait information  2 - 1  indicates a sheet interval between the second sheet of the first set and the first sheet of the second set. 
     By stopping a sheet temporarily at a standby position according to the time indicated by the wait information notified from the post-processing device, the image forming device secures the time (sheet interval) necessary for the post-processing device. For example, the standby time at the standby position in the image forming device (timing for releasing the standby state) is controlled so as to set the time until the first sheet of the second set is discharged (output timing of the sheet discharge information  2 - 1 ) after the second sheet of the first set is discharged (output timing of the sheet discharge information  1 - 2 ), to the time indicated by the wait information  2 - 1 . In addition, the sheet discharge information is notified to a subsequent-stage device in accordance with the timing at which a sheet is discharged from each device. 
     In recent years, a post-processing device of the image forming system has been diversified into various kinds. The demand in which not only a post-processing device of a manufacturer which manufactures an image forming device but also a post-processing device of a different manufacturer (hereinafter, referred to as a third vendor) is connected and operated on line, has been increased. 
     On the other hand, with regard to the connection of the post-processing device in the image forming system, each communication specification for exchanging information is not standardized and unified. 
     In this background, it is inefficient that each third vendor is compliant with complicated interface specifications of a manufacturer which manufactures the image forming device. To solve the above problem, a parallel interface is adopted as a simple interface which is common to each third vendor. It is not necessary for a third vendor to be conscious of the interface specification of a manufacturer of the image forming device main body and the interface specification of each manufacturer, and a post-processing device can be developed and provided by using only a simple interface. 
     Further, as shown in  FIG. 25 , the following image forming device is proposed (see Japanese Patent Application Publication No. 2006-350961). In the image forming device, both a serial interface and a parallel interface are provided, and a post-processing device (genuine device) which is compliant with the serial interface and a post-processing device (third vendor device) which is compliant with the parallel interface can be connected. 
     In case that a post-processing device (genuine device) which is compliant with a serial interface a manufacturer of an image forming device and a post-processing device (third vendor device) which is compliant with a parallel interface are mixed to configure an image forming system, because a number of combinations of types of devices to be connected and the number of the devices to be connected are considered, it is difficult for the image forming device to have interfaces for all post-processing devices and to handle all connection patterns. 
     For example, in case of the image forming device which has a serial interface of a communication protocol in which the above-described sheet feed information is transmitted to a post-processing device and a sheet interval (wait information) necessary for the post-processing device is acquired from the post-processing device as a response of the transmitted sheet feed information and which adjusts a standby time at a standby position so as to discharge a sheet at the timing indicated by the acquired wait information, when a third vendor device which is compliant with a simple parallel interface is connected to the above image forming device, the information necessary for the control of carrying the sheet cannot be acquired from the third vendor device. Therefore, it is difficult that the image forming device is operated so as to discharge a sheet in accordance with a sheet interval necessary for the third vendor device. Further, when the number of types of the third vendor device to be connected is increased, it is very troublesome that the necessary functions are added to the image forming device so as to handle all the third vendor devices. 
     Further, because the heights at which the carrier inlet and the carrier outlet for the sheets are disposed from the installation surface are also different from each other depending on the third vendor devices, it is required to adjust the above heights in order to connect the third vendor device to the image forming system and carry the sheet. 
     In addition, in the parallel interface, the amount of information to be exchanged is very small as compared to the serial interface. Therefore, it is difficult to manage the control of carrying the sheets according to the types of the sheets (sheet size, paper type, and basis weight), which is performed in the genuine device having the serial interface. For example, in case of the control of the sheet interval, the control of the sheet interval cannot be performed according to the types of sheets and the above control is performed under worst conditions. As a result, the problem in which the productivity of the system is lowered, has been caused. 
     SUMMARY 
     To achieve at least one of the abovementioned objects, a relay apparatus reflecting one aspect of the present invention, to be communicatively connected to an image forming device which acquires sheet interval information indicating a sheet interval necessary for a downstream post-processing device by performing communication through a first communication system for transmitting sheet information relating to a sheet on which an image is formed, to the downstream post-processing device and for receiving the sheet interval information of the downstream post-processing device from the downstream post-processing device as a response of the transmitted sheet information, and which discharges the sheet at a timing based on the sheet interval information of the downstream post-processing device; and to be communicatively connected to a second post-processing device which is connected to a downstream of the image forming device and which communicates with an upstream device of the second post-processing device through a second communication system which is different from the first communication system, the relay apparatus comprising: 
     a first communication control unit to communicate with the image forming device through the first communication system; 
     a second communication control unit to communicate with the second post-processing device through the second communication system; and 
     a storage unit to previously store information relating to a sheet interval necessary for the second post-processing device, 
     wherein when the relay apparatus receives the sheet information from the image forming device, the first communication control unit determines sheet interval information of the second post-processing device in accordance with the received sheet information and the information relating to the sheet interval, which is previously stored in the storage unit, and transmits the determined sheet interval information of the second post-processing device to the image forming device. 
     Preferably, the sheet interval information is information indicating an interval of the sheets discharged from the image forming device by using a distance. 
     Preferably, the sheet interval information is information indicating an interval of the sheets discharged from the image forming device by using time. 
     Preferably, the communication through the first communication system is performed by a serial communication, and a communication through the second communication system is performed by a parallel communication. 
     Preferably, the relay apparatus further comprises a sheet carrier unit to receive the sheet from a carrier outlet of an upstream device of the relay apparatus, and to carry and discharge the sheet to a carrier inlet of a downstream device of the relay apparatus, the carrier inlet being disposed at a height from an installation surface of the relay apparatus, which is different from a height at which the carrier outlet of the upstream device is disposed from the installation surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
         FIG. 1  shows a system configuration example of the image forming system according to the first embodiment; 
         FIG. 2  shows the connection state of the communication lines in the image forming system according to the first embodiment; 
         FIG. 3  is a block diagram showing an electrical outline configuration of each device of the image forming system according to the first embodiment; 
         FIG. 4  is an explanatory view exemplifying the communication lines and the signals in the serial interface and the communication lines and the signals of the parallel interface; 
         FIG. 5  shows a communication sequence in the case of creating two sets of brochures each of which has two sheets, in the first post-processing device which is a third vendor device in the image forming system according to the first embodiment; 
         FIG. 6  is a timing chart showing the change in each signal of the parallel interface, which is output to the first post-processing device from the relay apparatus in the case of the communication sequence of  FIG. 5 ; 
         FIG. 7  shows a communication sequence in the case where the sheets are carried by the bypass conveyance in the first post-processing device and two sets of brochures each of which has two sheets are created in the second post-processing device which is a genuine device, in the image forming system according to the first embodiment; 
         FIG. 8  is a flowchart showing a main process performed by the relay apparatus of the image forming system according to the first embodiment; 
         FIG. 9  is a flowchart showing details of a process of “control of first post-processing device being discharge destination” ( FIG. 8 : Step S 103 ); 
         FIG. 10  is a flowchart showing details of a process of “control of second post-processing device being discharge destination” ( FIG. 8 : Step S 104 ); 
         FIG. 11  is a flowchart showing the subsequent process of  FIG. 10 ; 
         FIG. 12  shows a system configuration example of the image forming system according to the second embodiment; 
         FIG. 13  shows another configuration example of the image forming system according to the second embodiment; 
         FIG. 14  shows the connection state of the communication lines in the image forming system shown in  FIG. 13 ; 
         FIG. 15  is a block diagram showing an electrical outline configuration of each device of the image forming system shown in  FIGS. 13 and 14 ; 
         FIG. 16  shows a communication sequence in the case of creating two sets of brochures each of which has two sheets in the second post-processing device which is the third vendor device, in the image forming system shown in  FIGS. 13 to 15  according to the second embodiment; 
         FIG. 17  is a flowchart showing details of a process of “control of second post-processing device being discharge destination” ( FIG. 8 : Step S 104 ) performed by the first relay apparatus in the image forming system according to the second embodiment shown in  FIGS. 13 to 15 ; 
         FIG. 18  is a flowchart showing the subsequent process of  FIG. 17 ; 
         FIG. 19  shows the connection state of the communication lines in the image forming system according to the third embodiment; 
         FIG. 20  is a block diagram showing an electrical outline configuration of each device of the image forming system according to the third embodiment; 
         FIG. 21  is a flowchart showing details of a process of “control of second post-processing device being discharge destination” ( FIG. 8 : Step S 104 ) performed by the relay apparatus  30  according to the third embodiment; 
         FIG. 22  is a flowchart showing the subsequent process of  FIG. 21 ; 
         FIG. 23  shows a connection example of a conventional image forming system in which an image forming device and a plurality of post-processing devices are connected in series through serial interfaces of the same communication system (protocol); 
         FIG. 24  shows a communication sequence in the image forming system shown in  FIG. 23 ; and 
         FIG. 25  shows an example of a conventional image forming system in which both of the serial interface and the parallel interface are provided on the image forming device. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be explained with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  shows a system configuration example of an image forming system  5  according to the first embodiment. The image forming system  5  is configured by connecting a relay apparatus  30 , a first post-processing device  50  which is a post-processing device of a third vendor, and a second post-processing device  70  manufactured by the same manufacturer as the image forming device  10  to a subsequent stage (downstream) of an image forming device  10  in this order so as to connect the carrier path  91  (indicated by a broken line in  FIG. 1 ) in series. The image forming device  10 , the relay apparatus  30 , and the second post-processing device  70  are genuine devices manufactured by A manufacturer, and the first post-processing device  50  is a third vendor device manufactured by Z manufacturer. In the image forming system  5 , all carrier outlets and carrier inlets for the sheets are disposed at the same height from the installation surface of each device (hereinafter, referred to as a ground height). 
     The image forming device  10  has a function to feed a sheet stored in a sheet feeding unit  11  to carry it, form (print) an image on it, and then discharge it to a subsequent stage from the carrier outlet. Further, the image forming device  10  can temporarily stop the carry of the sheets fed from the sheet feeding unit  11  at a predetermined standby position (register position)  13  provided on the upstream side of a photoconductive drum  12   a  of an image forming unit  12  which is hereinafter described, in order to allow the sheet to stand by. 
     The relay apparatus  30  has a function to receive the sheet discharged from the carrier outlet of the image forming device  10  and directly carry it to the subsequent-stage first post-processing device  50  to discharge it. In addition, the relay apparatus  30  has a function to relay communication between the image forming device  10  and any one of the first and second post-processing devices  50  and  70 . 
     The first post-processing device  50  has a function to perform the predetermined post-processing to the sheet carried from a previous-stage device (one step upstream side). Here, the first post-processing device  50  has a function to perform the post-processing such as cutting and bookbinding and to store a number of cut and bound sheets. In addition, the first post-processing device  50  has a function of a bypass conveyance to carry sheets to the subsequent stage to discharge them without performing the post-processing. 
     The second post-processing device  70  is a genuine device of the same manufacturer as the image forming device  10 , and has a function to perform the predetermined post-processing to the sheet carried from a previous-stage device. Here, the second post-processing device  70  has a function to perform the side stitching for the sheets. In addition, the second post-processing device  70  has a sheet stacking unit  77  which stacks sheets to be discharged. 
       FIG. 2  shows a connection state of the communication lines in the image forming system  5  shown in  FIG. 1 . The image forming device  10  and the relay apparatus  30  are connected through a serial interface which is compliant with the specifications of A manufacturer. The relay apparatus  30  and the first post-processing device  50  are connected through a parallel interface for the third vendor device. The relay apparatus  30  and the second post-processing device  70  are connected through the serial interface which is compliant with the specifications of A manufacturer and which is the same as the serial interface provided between the relay apparatus  30  and the image forming device  10 . 
     Because the communication connection is performed through the parallel interface between the relay apparatus  30  and the first post-processing device  50 , the amount of information to be exchanged is very small as compared to the serial interface. Further, the first post-processing device  50  and the second post-processing device  70  are not directly connected because of the communication therebetween. 
       FIG. 3  is a block diagram showing an outline configuration of each device of the image forming system  5  shown in  FIGS. 1 and 2  according to the first embodiment. The image forming device  10  comprises a. CPU (Central Processing Unit)  14  which totally controls the operations of the image forming device  10 . The CPU  14  is connected to a ROM (Read Only Memory)  15 , a RAM (Random Access Memory)  16 , the sheet feeding unit  11 , an image processing unit  17 , an image reading unit  18 , the image forming unit  12 , an operation display unit  19 , and a post-processing device serial interface unit  21  via a bus. 
     By the CPU  14 , a middleware, application programs and the like are executed on an OS (Operating System) program as a base. In the ROM  15 , various types of programs are stored. By executing the processes by the CPU  14  in accordance with these programs, various types of functions of the image forming device  10  are realized. 
     The RAM  16  is used as a work memory for temporarily storing various types of data when the CPU  14  executes the programs, an image memory for storing image data, and the like. 
     The image reading unit  18  has a function to optically read an original and acquire image data. For example, the image reading unit  18  comprises a light source for irradiating the original with light, a line image sensor for reading the original line by line in the width direction of the original by receiving the reflected light from the original, a moving unit for sequentially moving the reading position line by line in the longitudinal direction of the original, an optical system having lenses, mirrors and the like for guiding the reflected light from the original to the line image sensor and focusing the reflected light on the line image sensor, a converting unit for converting an analog image signal outputted from the line image sensor into digital image data, and the like. 
     The image forming unit  12  has a function to form an image on a sheet in accordance with print data. In the present embodiment, the image forming unit  12  is configured as the so-called laser printer for forming the image by the electrophotographic process. The laser printer comprises a carrier device of the recording sheets, a photoconductive drum  12   a , a charging device, a laser unit, a developing device, a transfer and separation device, a cleaning device, and a fixing unit. In the image forming unit  12 , other types may be adopted. 
     The sheet feeding unit  11  comprises a sheet feed tray for storing a large number of sheets, and has a function to sequentially send the sheets stored in the sheet feed tray one by one to a carrier path leading into the image forming unit  12 . 
     The image processing unit  17  carries out the rasterization processing for converting print data into image data, the compression/decompression processing of image data and the like, in addition to the processings, such as enlargement/reduction and rotation of the image. 
     The operation display unit  19  has a function to display various operation windows and setting windows, and receive various operations from a user. The operation display unit  19  comprises a display unit such as a liquid crystal display (LCD), various operation switches, and a touch screen which is provided on a display surface of the display unit and detects a pushed position. 
     The post-processing device serial interface unit  21  is a serial communication interface unit which exchanges various types of information with the post-processing device, and performs the communication by using the serial interface which is compliant with the specifications of A manufacturer. Through this serial interface, the image forming device  10  performs the communication sequence shown in  FIG. 24 , and controls the sheet discharge timing, that is, the timing of allowing a sheet to stand by at the standby position  13  (timing for releasing a standby state). 
     That is, the image forming device  10  notifies the subsequent-stage devices of the sheet feed information including the sheet information relating to the sheet and the contents of the post-processing to be performed to the sheet, at the timing of feeding the sheet from the sheet feeding unit  11  thereof. Further, the image forming device  10  receives the wait information as a response of the above notification. The wait information indicates the time necessary for the post-processing of the subsequent-stage device and the time equivalent to the sheet interval. The image forming device  10  allows the fed sheet to stand by at the standby position  13  provided in the carrier path, and releases the standby state and discharges the sheet so as to discharge it at the timing based on the time (sheet interval) indicated in the wait information notified by the subsequent-stage device. 
     The relay apparatus  30  is configured by connecting a CPU  31  which totally controls operations of the relay apparatus  30 , to a ROM  32 , a RAM  33 , a communication conversion unit  34 , a sheet carrier unit  35 , a previous-stage serial interface unit  36 , a subsequent-stage serial interface unit  37 , a subsequent-stage parallel interface unit  38 , an input unit  39  which receives signals from various sensors, and an output unit  41  which outputs control signals to various loads such as a motor via a bus. 
     In the ROM  32 , various types of programs are stored. By executing the processes by the CPU  31  in accordance with these programs, various types of functions of the relay apparatus  30  are realized. The RAM  33  is used as a work memory for temporarily storing various types of data when the CPU  31  executes process in accordance with the programs. 
     The sheet carrier unit  35  has a function to carry the sheet fed from the previous-stage device (image forming device  10 ) and discharge it to the subsequent-stage device (one step downstream device) (in this example, the first post-processing device  50 ). 
     The previous-stage serial interface unit  36  performs the serial communication (serial interface) for exchanging various types of information with the previous-stage device. The subsequent-stage serial interface unit  37  performs the serial communication for exchanging various types of information with the subsequent-stage device. The previous-stage serial interface unit  36  and the subsequent-stage serial interface unit  37  perform the communication by using the serial interfaces which are compliance with the specifications of A manufacturer. The subsequent-stage parallel interface unit  38  has a function to exchange various types of information with the subsequent-stage device by parallel communication (parallel interface). The subsequent-stage parallel interface unit  38  performs the communication via the parallel interface which is commonly used in the third vendor devices. 
     The communication conversion unit  34  performs the process for converting the contents of information and the transmission timing so as to absorb the difference in the communication procedures between the serial interface and the parallel interface. For example, in case that the post-processing device which is the third vendor device is connected to the subsequent stage through the parallel interface, when the sheet feed information is received from the upstream device through the serial interface, the relay apparatus  30  calculates the time corresponding to the sheet interval necessary for the post-processing device which is the third vendor device, and sends back the wait information indicating the calculated time to the upstream device. 
     The first post-processing device  50  which is the third vendor device is configured by connecting a CPU  51  which totally controls operations of the first post-processing device  50 , to a ROM  52 , a RAM  53 , a previous-stage parallel interface unit  54 , a sheet carrier unit  55 , a sheet storing unit  56 , a sheet bookbinding unit  57 , a sheet cutting unit  58 , a relay carrying unit  59 , an input unit  61  which receives signals from various sensors, and an output unit  62  which outputs control signals to various loads such as a motor via a bus. 
     In the ROM  52 , various types of programs are stored. By executing the processes by the CPU  51  in accordance with these programs, various types of functions of the first post-processing device  50  are realized. The RAM  53  is used as a work memory for temporarily storing various types of data when the CPU  51  executes process in accordance with the programs. 
     The previous-stage parallel interface unit  54  has a function to exchange various types of information with the previous-stage device by using the parallel communication. The previous-stage parallel interface unit  54  performs the communication via the parallel interface for the third vendor device. 
     The sheet carrier unit  55  carries the sheet fed from the previous-stage device (herein, the relay apparatus  30 ) to each post-processing unit in the first post-processing device  50 . The sheet storing unit  56  has a function to store the post-processed sheet. The sheet bookbinding unit  57  has a function to bundle the sheets and bind a book. The sheet cutting unit  58  has a function to cut the sheet into a designated size. The relay carrying unit  59  has a function to carry the sheet fed from the previous-stage device and discharge it to the subsequent-stage device (herein, the second post-processing device  70 ). 
     The second post-processing device  70  which is the genuine device is configured by connecting the CPU  71  which totally controls operations of the second post-processing device  70 , to a ROM  72 , a RAM  73 , a previous-stage serial interface unit  74 , a sheet carrier unit  75 , a side stitching unit  76 , the sheet stacking unit  77 , an input unit  78  which receives signals from various sensors, and an output unit  79  which outputs control signals to various loads such as a motor via a bus. 
     In the ROM  72 , various types of programs are stored. By executing the processes by the CPU  71  in accordance with these programs, various types of functions of the second post-processing device  70  are realized. The RAM  73  is used as a work memory for temporarily storing various types of data when the CPU  71  executes process in accordance with the programs. 
     The previous-stage serial interface unit  74  has a function to exchange various types of information with the previous-stage device by using the serial communication. The previous-stage serial interface unit  74  performs the communication via the serial interface which is compliant with the specifications of A manufacturer. 
     The sheet carrier unit  75  carries the sheet fed from the previous-stage device (herein, the first post-processing device  50 ) to each post-processing unit in the second post-processing device  70 . The side stitching unit  76  has a function to perform the side stitching for the sheets. The sheet stacking unit  77  has a function to stack the post-processed sheets (herein, the sheets to which the side stitching process is performed) on a sheet discharge tray or the like. 
       FIG. 4  exemplifies the communication lines and the signals in the serial interface and the communication lines and the signals in the parallel interface. In the serial interface, data to be transmitted and data to be received are transmitted and received through a communication line TxD and a communication line RxD, respectively. In the serial interface, the number of communication lines is small, however, by transmitting and receiving data in series, the information having several bits can be transmitted and received. On the other hand, in the parallel interface of the present embodiment, only ON/OFF information having transmission 4 bits (C0 to C3) and ON/OFF information having reception 4 bits (R0 to R3) can be transmitted and received. For example, the transmission 4 bits include an actuating signal for instructing the post-processing device to perform the ON/OFF operations, a sheet discharge signal switched to ON only during the time from starting discharging a front-end of the sheet until completing discharging a back-end of the sheet, and a set separation signal indicating a final sheet of the set of document to be printed. A number of known techniques relating to the serial interface and the parallel interface are known. Therefore, the detailed explanation thereof is omitted. 
       FIG. 5  shows a communication sequence in the case of creating two sets of brochures each of which has two sheets (two sets of brochures, one set of which has two sheets are created) in the first post-processing device  50  which is the third vendor device, of the image forming system  5  according to the first embodiment shown in  FIGS. 1 to 3  (in the case where the discharge destination is set to the first post-processing device  50 ). In this operation example, all post-processing operations for creating brochures are completed in the first post-processing device  50  and the post-processing operation is not performed in the second post-processing device  70 . Accordingly, sheets are not carried to the second post-processing device  70  and the finished brochures are discharged into the sheet storing unit  56  of the first post-processing device  50  to store them. 
     The image forming device  10  transmits the operation start information to the relay apparatus  30  through the serial interface. The operation start information includes the information indicating the contents of the post-processing and the identification data of the post-processing device to be started. In the present embodiment, as the operation start information, the relay apparatus  30  is notified that two sets of brochures, each of which has two sheets are created in the first post-processing device  50 , and that the post-processing is not performed in the second post-processing device  70 . 
     The relay apparatus  30  analyzes the operation start information received from the image forming device  10  and notifies the first post-processing device  50  to be started of the operation start information (actuating signal ON) through the parallel interface. The relay apparatus  30  does not transmit the operation start information to the second post-processing device  70 . 
     Then, every when the sheet is fed, the image forming device  10  transmits the sheet feed information relating to the fed sheet to the relay apparatus  30 . In each drawing showing the communication sequence, the suffix added to each piece of information indicates that the sheet number of the sheet corresponding to the information and the set number of the set including the above sheet. To be more specific, “1-1”, “1-2”, “2-1”, and “2-2” indicate a first sheet of a first set, a second sheet of the first set, a first sheet of a second set, and a second sheet of the second set, respectively. 
     Even if the relay apparatus  30  receives the sheet feed information from the image forming device  10 , because the communication line to notify the first post-processing device  50  of the sheet feed information is not included in the parallel interface, the relay apparatus  30  does not notify the subsequent-stage first post-processing device  50  of this sheet feed information. Further, the subsequent-stage first post-processing device  50  has no function to notify the upstream devices of the wait information indicating the sheet interval necessary for the post-processing. 
     To solve the above problem, the relay apparatus  30  creates the wait information corresponding to the sheet feed information received from the image forming device  10  in place of the first post-processing device  50 , and sends back the wait information to the image forming device  10 . For example, when the sheet feed information  1 - 1  is received, the relay apparatus  30  creates the wait information  1 - 1  and sends back it to the image forming device  10 . When the sheet feed information  1 - 2  is received, the relay apparatus  30  creates the wait information  1 - 2  and sends back it to the image forming device  10 . 
     The relay apparatus  30  previously stores information relating to the sheet interval necessary for the post-processing device connected to the subsequent stage through the parallel interface (in the present embodiment, the first post-processing device  50 ), and creates the wait information based on the information and sends back it to the image forming device  10 . For example, the relay apparatus  30  sets the sheet information (sheet size, paper type, and basis weight) and the contents of the post-processing, as parameters, and previously stores the sheet interval (wait information) corresponding to each combination of these values of the parameters in the storage unit as a table. When the sheet feed information is received, the relay apparatus  30  searches the sheet interval (wait information) corresponding to the combination of the sheet information indicated by the sheet feed information and the contents of the post-processing from the above table to read it, and sends back it to the upstream devices. As a memory location of the table, for example, the ROM  32  or a nonvolatile memory provided on the communication conversion unit  34  is used. The relay apparatus  30  may previously store the tables corresponding to various types of the post-processing devices which are the third vendor devices, in the storage unit and may select a table in accordance with the post-processing device which is the third vendor device to be actually used. For example, the above selection is performed after specific information relating to the post-processing device to be used is received from the image forming device  10  or is input from the user. Here, the wait information indicating the sheet interval is indicated by using the time. 
     Based on the wait information received from the relay apparatus  30 , the image forming device  10  controls the standby time at the standby position  13 . Thereby, the sheet is discharged at the timing indicated by the wait information. 
     The image forming device  10  outputs the sheet discharge information to the relay apparatus  30  at the timing at which the sheet is actually discharged to the relay apparatus  30 . The relay apparatus  30  comprises a sheet discharge sensor which is provided at the carrier outlet of the relay apparatus  30  and which detects a front-end and a back-end of the sheet to be discharged from the carrier outlet. Based on the detection state of this sheet discharge sensor, the relay apparatus  30  outputs the sheet discharge information to the first post-processing device  50  through the parallel interface every when the sheet is discharged to the subsequent-stage first post-processing device  50  from the relay apparatus  30 . Specifically, when the front-end of the sheet is discharged from the carrier outlet, the relay apparatus  30  switches the sheet discharge signal to ON. On the other hand, when the back-end of the sheet is discharged from the carrier outlet, the relay apparatus  30  switches the sheet discharge signal to OFF. 
     By the sheet discharge signal, the first post-processing device  50  which is the third vendor device, recognizes that the sheet is carried from the upstream device, and performs the post-processing and carrier operations to the sheet. The first post-processing device  50  is not notified of the information indicating the sheet number of the discharged sheet, the set number of the set including the discharged sheet, and the type of the discharged sheet. 
     After the image forming device  10  completes the discharge of the second sheet of the second set, the image forming device  10  transmits the operation stop information to the relay apparatus  30 . After the relay apparatus  30  receiving the operation stop information completes the discharge of the second sheet of the second set to the subsequent-stage device (the first post-processing device  50 ), the relay apparatus  30  transmits the operation stop information to the first post-processing device  50 . Specifically, the relay apparatus  30  switches the actuating signal to OFF. The relay apparatus  30  does not transmit the operation stop information to the second post-processing device  70 . 
       FIG. 6  is a timing chart indicating the change and the like in each signal output from the relay apparatus  30  to the first post-processing device  50  through the parallel interface in the case where the operations are performed in the communication sequence of  FIG. 5 . The upper three signals shown in  FIG. 6  are the main body sheet discharge signal output from the sheet discharge sensor provided on the carrier outlet of the image forming device  10 , the relay apparatus entry signal output from the carrier sensor provided on the carrier inlet of the relay apparatus  30 , the relay apparatus sheet discharge signal output from the sheet discharge sensor provided on the carrier outlet of the relay apparatus  30 . Further, the lower three signals are the actuating signal, the sheet discharge signal, and the set separation signal which are output from the relay apparatus  30  to the first post-processing device  50 . When the signal level is High, the status of each signal is ON. On the other hand, when the signal level is Low, the status of each signal is OFF. 
     The timings indicated by T1, T2 and T3 of  FIG. 6  correspond to the timings indicated by T1, T2 and T3 of  FIG. 5 , respectively. The actuating signal, the sheet discharge signal, and the set separation signal correspond to C0, C1, and C2 of the parallel interface shown in  FIG. 4 , respectively. 
       FIG. 7  shows a communication sequence in the case where the sheet is carried by the bypass conveyance in the first post-processing device  50  and two sets of brochures each of which has two sheets are created in the second post-processing device  70  which is the genuine device (in case that the discharge destination is the second post-processing device  70 ) in the image forming system  5  shown in  FIGS. 1 to 3  according to the first embodiment. In this operation, the first post-processing device  50  allows the sheet carried from the image forming device  10  to directly pass through the inside thereof and discharges the sheet to the subsequent-stage second post-processing device  70 . Then, the post-processing is performed in the second post-processing device  70 . 
     The image forming device  10  transmits the operation start information to the relay apparatus  30  through the serial interface. The relay apparatus  30  analyzes the operation start information received from the image forming device  10  and transmits it to both of the first and second post-processing devices  50  and  70  to be started. Specifically, the relay apparatus  30  notifies the first post-processing device  50  of the operation start information by switching the actuating signal of the parallel interface to ON, and directly transmits the operation start information received from the image forming device  10  to the second post-processing device  70  through the serial interface. 
     Then, every when the sheet is fed, the image forming device  10  transmits the sheet feed information relating to the sheet to the relay apparatus  30 . The first post-processing device  50  which is the third vendor device cannot receive the sheet feed information from the relay apparatus  30 . Further, the first post-processing device  50  cannot receive the wait information. Therefore, the relay apparatus  30  which receives the sheet feed information from the image forming device  10  calculates the wait time necessary for the first post-processing device  50  with reference to the table stored in the storage unit, as described above. 
     The second post-processing device  70  has the serial interface which is compliant with the specifications of A manufacturer, and sends back the wait information in response to the sheet feed information received from the upstream device. The relay apparatus  30  then transmits (transfers) the sheet feed information received from the image forming device  10  to the second post-processing device  70  through the serial interface, and receives the wait information from the second post-processing device  70 . 
     Then, the relay apparatus  30  compares the time indicated by the wait information received from the second post-processing device  70  and the wait time necessary for the first post-processing device  50 , which is calculated by the relay apparatus  30 , and notifies the image forming device  10  of the larger time as the wait information. 
     By controlling the standby time at the standby position  13  based on the received wait information, the image forming device  10  discharges the sheet at the timing indicated by the wait information. 
     The image forming device  10  outputs the sheet discharge information to the relay apparatus  30  at the timing at which the sheet is actually discharged to the relay apparatus  30 . Similarly to the case shown in  FIG. 5 , based on the detection state of the sheet discharge sensor provided on the carrier outlet of the relay apparatus  30 , the relay apparatus  30  outputs the sheet discharge information to the first post-processing device  50  through the parallel interface every when the sheet is discharged from the relay apparatus  30  to the subsequent-stage first post-processing device  50 . Specifically, when a front-end of the sheet is discharged from the carrier outlet, the relay apparatus  30  switches the sheet discharge signal to ON. On the other hand, when a back-end of the sheet is discharged from the carrier outlet, the relay apparatus  30  switches the sheet discharge signal to OFF. 
     By the sheet discharge signal, the first post-processing device  50  which is the third vendor device recognizes that the sheet is carried from the upstream device, and this sheet is carried by the bypass conveyance in the first post-processing device  50 . When the sheet is discharged to the subsequent-stage second post-processing device  70 , the first post-processing device  50  cannot notify the subsequent-stage second post-processing device  70  of the sheet discharge information (sheet discharge signal). To solve the above problem, in consideration of the carrying time through the first post-processing device  50 , the relay apparatus  30  notifies the second post-processing device  70  of the sheet discharge information. Here, the relay apparatus  30  previously stores the carrying time in the case where the sheet is carried by the bypass conveyance in the first post-processing device  50 . When the carrying time elapses since the front-end of the sheet is discharged from the relay apparatus  30 , the relay apparatus  30  transmits the sheet discharge information to the second post-processing device  70  through the serial interface. 
     After the discharge of the second sheet of the second set is completed, the image forming device  10  transmits the operation stop information to the relay apparatus  30 . After the relay apparatus  30  receiving the operation stop information completes the discharge of the second sheet of the second set to the first post-processing device  50 , the relay apparatus  30  transmits the operation stop information to the first post-processing device  50 . Specifically, the relay apparatus  30  switches the actuating signal to OFF. The relay apparatus  30  further transmits (transfers) the operation stop information received from the image forming device  10  to the second post-processing device  70 . 
       FIG. 8  shows a flowchart of the main process performed by the relay apparatus  30  of the image forming system  5  according to the first embodiment. When the operation start information is received from the image forming device  10  (Step S 101 ), the relay apparatus  30  analyzes this operation start information, and determines whether the discharge destination of the sheet after the completion of the post-processing is the first post-processing device  50  or the second post-processing device  70  (Step S 102 ). When the discharge destination is the first post-processing device  50  (Step S 102 ; first post-processing device), the relay apparatus  30  executes “control of first post-processing device being discharge destination” (Step S 103 ). In this case, the operations are performed in the communication sequence shown in  FIG. 5 . When the discharge destination is the second post-processing device  70  (Step S 102 ; second post-processing device), the relay apparatus  30  executes “control of second post-processing device being discharge destination” (Step S 104 ). In this case, the operations are performed in the communication sequence shown in  FIG. 7 . After the process of step S 103  or S 104  is completed, the relay apparatus  30  stops the operations (Step S 105 ). Then, the process is ended. 
       FIG. 9  is a flowchart showing the details of “control of first post-processing device being discharge destination” ( FIG. 8 : Step S 103 ). The relay apparatus  30  switches the actuating signal of the parallel communication (parallel interface) to ON by using the subsequent-stage parallel interface unit  38  (Step S 121 ). Next, when the sheet feed information is received from the image forming device  10  (in the drawings, referred to as a “main body”) (Step S 122 ; Yes), the relay apparatus  30  calculates the wait time necessary for the first post-processing device  50  which is the third vendor device, in accordance with the sheet information included in this sheet feed information (Step S 123 ). Then, the relay apparatus  30  transmits the wait information indicating the wait time to the image forming device  10  (Step S 124 ), and the process proceeds to step S 125 . 
     In case that the sheet feed information is not received from the image forming device  10  (Step S 122 ; No), the process proceeds to step S 125 . 
     At step S 125 , the relay apparatus  30  determines whether the sheet discharge sensor of the relay apparatus  30  changes. If the sheet discharge sensor does not change (Step S 125 : No change), the process proceeds to step S 128 . When the sheet discharge sensor changes from OFF to ON (Step S 125 ; OFF→ON), because the front-end of the sheet is detected, the relay apparatus  30  switches the sheet discharge signal of the parallel communication to ON (Step S 126 ) and the process proceeds to step S 128 . When the sheet discharge sensor changes from ON to OFF (Step S 125 ; ON→OFF), because the back-end of the sheet is detected, the relay apparatus  30  switches the sheet discharge signal of the parallel communication to OFF (Step S 127 ) and the process proceeds to step S 128 . 
     At step S 128 , the relay apparatus  30  determines whether to receive the operation stop information from the image forming device  10 . In case that the relay apparatus  30  does not receive the operation stop information (Step S 128 ; No), the process returns to step S 122  and is continued. When the relay apparatus  30  receives the operation stop information (Step S 128 ; Yes), the relay apparatus  30  switches the actuating signal of the parallel communication to OFF (Step S 129 ), and the process returns to the process shown in  FIG. 8  (return). The references T1, T2, and T3 of  FIG. 9  indicate the timings corresponding to T1, T2, and T3 of  FIG. 6 . 
       FIGS. 10 and 11  are a flowchart showing the details of “control of the second post-processing device being the discharge destination” ( FIG. 8 : Step S 104 ). The relay apparatus  30  switches the actuating signal of the parallel communication (parallel interface) to ON by using the subsequent-stage parallel interface unit  38  (Step S 141 ). At the same time, the relay apparatus  30  transfers the operation start information from the subsequent-stage serial interface unit  37  to the subsequent-stage second post-processing device  70  by the serial communication (serial interface) (Step S 142 ). 
     Next, when the sheet feed information is received from the image forming device  10  (main body) (Step S 143 ; Yes), the relay apparatus  30  transmits this sheet feed information to the second post-processing device  70  through the serial communication using the subsequent-stage serial interface unit  37  (Step S 144 ), and the process proceeds to step S 145 . In case that the sheet feed information is not received from the image forming device  10  (Step S 143 ; No), the process proceeds to step S 145 . 
     At step S 145 , the relay apparatus  30  determines whether to receive the wait information from the second post-processing device  70 . In case that the relay apparatus  30  does not receive the wait information (Step S 145 ; No), the process proceeds to step S 150 . When the relay apparatus  30  receives the wait information (Step S 145 ; Yes), the relay apparatus  30  calculates the wait time necessary for the first post-processing device  50  which is the third vendor device, in accordance with the sheet information received from the image forming device  10  at step S 143  (Step S 146 ). The relay apparatus  30  compares the calculated wait time and the wait time indicated by the wait information received from the second post-processing device  70  (Step S 147 ). 
     In case that the wait time in the first post-processing device  50  as the third vendor device, which is calculated at step S 146 , is longer (larger) than the wait time in the second post-processing device  70  (Step S 147 ; wait of third vendor&gt;wait of second post-processing device), the relay apparatus  30  transmits the wait information indicating the wait time in the first post-processing device  50  to the image forming device  10  (Step S 148 ), and the process proceeds to step S 150 . 
     In case that the wait time indicated by the wait information received from the second post-processing device  70  is longer (larger) than or equal to the other wait time (Step S 147 ; wait of the third vendor≦wait of second post-processing device), the relay apparatus  30  transmits the wait information received from the second post-processing device  70  to the image forming device  10  (Step S 149 ), and the process proceeds to step S 150 . 
     At step S 150 , the relay apparatus  30  determines whether the sheet discharge sensor of the relay apparatus  30  changes. When the sheet discharge sensor does not change (Step S 150 : No change), the process proceeds to step S 154 . When the sheet discharge sensor changes from OFF to ON (Step S 150 ; OFF→ON), the relay apparatus  30  switches the sheet discharge signal of the parallel communication to ON (Step S 151 ). Further, the relay apparatus  30  starts to count the time until the sheet is discharged from the first post-processing device  50  which is the third vendor device (Step S 152 ), and the process proceeds to step  154 . 
     When the sheet discharge sensor changes from ON to OFF (Step S 150 ; ON→OFF), the relay apparatus  30  switches the sheet discharge signal of the parallel communication to OFF (Step S 153 ), and the process proceeds to step S 154 . 
     At step S 154 , the relay apparatus  30  determines whether the count of the time until the sheet is discharged from the first post-processing device  50  is completed (the count reaches a specified count value). In case that the count is not completed (Step S 154 ; No), the process proceeds to step S 156 . When the count is completed (Step S 154 ; Yes), the relay apparatus  30  transmits the sheet discharge information to the second post-processing device  70  (Step S 155 ), and the process proceeds to step S 156 . 
     At step S 156 , the relay apparatus  30  determines whether to receive the operation stop information from the image forming device  10 . In case that the relay apparatus  30  does not receive the operation stop information (Step S 156 ; No), the process returns to step S 143  and is continued. When the relay apparatus  30  receives the operation stop information (Step S 156 ; Yes), the relay apparatus  30  switches the actuating signal of the parallel communication to OFF (Step S 157 ) and transmits the operation stop information to the second post-processing device  70  (Step S 158 ). Then, the process returns to the process shown in  FIG. 8  (return). 
     Second Embodiment 
     In the second embodiment, the ground heights of the carrier outlet and the carrier inlet of the genuine device are different from those of the third vendor device. The difference between the ground heights is absorbed by the relay apparatus interposed between the devices. 
       FIG. 12  shows a system configuration example of the image forming system  5 B according to the second embodiment. The image forming system  5 B is configured by connecting a first relay apparatus  30 B which is the genuine device of A manufacturer, a first post-processing device  50 B which is a post-processing device of the third vendor (Y manufacturer), a second relay apparatus  30 C which is the genuine device of A manufacturer, and a second post-processing device  70  which is the genuine device of A manufacturer to a subsequent stage (downstream) of the image forming device  10  which is the genuine device of A manufacturer in this order so as to connect the carrier path  91  in series. 
     The image forming device  10  and the second post-processing device  70  which are the genuine devices of A manufacturer are different from the first post-processing device  50 B which is the third vendor device manufactured by Y manufacturer in the ground heights of the carrier outlet and the carrier inlet. Therefore, the first relay apparatus  303  which is the genuine device of A manufacturer is interposed between the image forming device  10  and the first post-processing device  50 B. Further, the second relay apparatus  30 C which is the genuine device of A manufacturer is interposed between the first post-processing device  50 B and the second post-processing device  70  so as to absorb the difference of the ground heights and connect the carrier path  91 . 
     In the present example, the ground heights of the carrier outlet and the carrier inlet of the first post-processing device  50 B are higher than those of the carrier outlets and the carrier inlets of the genuine devices of A manufacturer. The ground height of the carrier inlet of the first relay apparatus  30 B is the same as the ground height of the genuine device of A manufacturer (the ground height of the carrier outlet of the image forming device  10 ). The ground height of the carrier outlet of the first relay apparatus  30 B is higher than the ground height of the genuine device of A manufacturer, and is the same as that of the carrier inlet of the first post-processing device  50 B. The ground height of the carrier inlet of the second relay apparatus  30 C is the same as that of the carrier outlet of the first post-processing device  50 B. The ground height of the carrier outlet of the second relay apparatus  30 C is lower than that of the carrier outlet of the first post-processing device  50 B, and is the same as the ground height of the genuine device of A manufacturer (the ground height of the carrier inlet of the second post-processing device  70 ). 
       FIG. 13  shows an image forming system  5 C as another system configuration example according to the second embodiment. The image forming system  5 C is configured by connecting the first relay apparatus  30 B which is the genuine device of A manufacturer, the first post-processing device  50 B which is the post-processing device of the third vendor (Y manufacturer), a second relay apparatus  30 D which is the genuine device of A manufacturer, and a second post-processing device  70 C which is a post-processing device of a third vendor (X manufacturer) to a subsequent stage (downstream) of the image forming device  10  which is the genuine device of A manufacturer in this order so as to connect the carrier path  91  in series. 
     The image forming device  10  which is the genuine device of A manufacturer, the first post-processing device  50 B which is the third vendor device of Y manufacturer, and the second post-processing device  70 C which is the third vendor device of X manufacturer are different in the ground heights of the carrier outlets and the carrier inlets, respectively. Therefore, the first relay apparatus  30 B which is the genuine device of A manufacturer is interposed between the image forming device  10  and the first post-processing device  50 B. Further, the second relay apparatus  30 D which is the genuine device of A manufacturer is interposed between the first post-processing device  50 B and the second post-processing device  70 C so as to absorb the difference in the ground height and connect the carrier path  91 . 
     In the present example, the ground heights of the carrier outlet and the carrier inlet of the first post-processing device  50 B are higher than those of the carrier outlets and the carrier inlets of the genuine devices of A manufacturer, and the ground height of the carrier inlet of the second post-processing device  70 C is lower than the ground height of the genuine devices of A manufacturer. The ground height of the carrier inlet of the first relay apparatus  30 B is the same as the ground height of the genuine device of A manufacturer (the ground height of the carrier outlet of the image forming device  10 ). The ground height of the carrier outlet of the first relay apparatus  30 B is higher than the ground height of the genuine device of A manufacturer, and is the same as that of the carrier inlet of the first post-processing device  50 B. The ground height of the carrier inlet of the second relay apparatus  30 D is the same as that of the carrier outlet of the first post-processing device  50 B. The ground height of the carrier outlet of the second relay apparatus  30 D is the same as that of the carrier inlet of the second post-processing device  70 C which has the ground height lower than the ground height of the genuine device of A manufacturer (the ground height of the carrier inlet of the second post-processing device  70 ). 
       FIG. 14  shows a connection state of the communication lines in the image forming system  5 C shown in  FIG. 13 . The first post-processing device  50 B manufactured by the third vendor (Y manufacturer) has no interface with the subsequent-stage device. The image forming device  10  and the first relay apparatus  30 B are connected through the serial interface which is compliant with the specifications of A manufacturer. The first relay apparatus  30 B and the first post-processing device  50 B are connected through the parallel interface for the third vendor device. The first relay apparatus  30 B and the second relay apparatus  30 D are connected through the serial interface which is compliant with the specifications of A manufacturer. The second relay apparatus  30 D and the second post-processing device  70 C which is manufactured by the third vendor (X manufacturer) are connected through the parallel interface for the third vendor device. 
       FIG. 15  is a block diagram showing an outline configuration of each device of the image forming system  5 C shown in  FIGS. 13 and 14 . Each electrical configuration of the image forming device  10 , the first relay apparatus  30 B, the second relay apparatus  30 D, and the first post-processing device  50 B is the same as that of the image forming device  10 , the relay apparatus  30 , and the first post-processing device  50  shown in  FIG. 3 . Therefore, the explanation thereof is omitted. 
     The second post-processing device  70 C is different from the second post-processing device  70  shown in  FIG. 3  in that the second post-processing device  70  has the previous-stage serial interface unit  74 , and on the other hand, the second post-processing device  70 C has a previous-stage parallel interface unit  81 . With respect to the other electrical configurations, the second post-processing device  70 C and the second post-processing device  70  are the same. The previous-stage parallel interface unit  81  performs the communication with the previous-stage device by using the parallel interface for the third vendor device. 
       FIG. 16  shows a communication sequence in the case of creating two sets of brochures each of which has two sheets (two sets of brochures, one set of which has two sheets are created) in the second post-processing device  70 C which is the third vendor device, of the image forming system  5 C according to the second embodiment shown in  FIGS. 13 to 15 . In this operation, the sheet is carried by the bypass conveyance in the first post-processing device  50 B. 
     The image forming device  10  transmits the operation start information to the first relay apparatus  30 B through the serial interface. The first relay apparatus  30 B receiving the operation start information notifies the first post-processing device  50 B of the operation start information (actuating signal ON) through the parallel interface. In addition, the first relay apparatus  30 B transfers the operation start information to the second relay apparatus  30 D through the serial interface. 
     The operations of the second relay apparatus  30 D are the same as those of the relay apparatus  30  in the communication sequence of  FIG. 5  explained in the first embodiment, except that the upstream device is the first relay apparatus  30 B. The second relay apparatus  30 D analyzes the received operation start information and notifies the second post-processing device  70 C of the operation start information (actuating signal ON) through the parallel interface. 
     Then, every when the sheet is fed, the image forming device  10  transmits the sheet feed information relating to the fed sheet to the first relay apparatus  30 B. The first relay apparatus  30 B receiving the sheet feed information transmits the received sheet feed information to the second relay apparatus  30 D. Further, the first relay apparatus  30 B calculates the wait time in the first post-processing device  50 B, which corresponds to the sheet feed information received from the image forming device  10 . 
     In place of the second post-processing device  70 C, the second relay apparatus  30 D creates the wait information indicating the wait time in the second post-processing device  70 C, which corresponds to the received sheet feed information, and sends back the wait information to the first relay apparatus  30 B. A method for calculating the wait time in the first relay apparatus  30 B and in the second relay apparatus  30 D is the same as that in the relay apparatus  30  shown in the first embodiment. Therefore, the explanation thereof is omitted. 
     The first relay apparatus  30 B compares the wait time in the first post-processing device  50 B, which is calculated by the first relay apparatus  30 B and the wait time in the second post-processing device  70 C, which is indicated by the wait information received from the second relay apparatus  30 D, and transmits the wait information indicating the longer wait time to the image forming device  10 . 
     By controlling the standby time at the standby position  13  based on the received wait information, the image forming device  10  discharges the sheet at the timing indicated by the wait information. 
     The image forming device  10  outputs the sheet discharge information to the first relay apparatus  30 B at the timing at which the sheet is actually discharged to the first relay apparatus  30 B. Based on the detection state of the sheet discharge sensor of the first relay apparatus  30 B, the first relay apparatus  30 B outputs the sheet discharge information to the first post-processing device  50 B through the parallel interface every when the sheet is discharged to the subsequent-stage first post-processing device  50 B from the first relay apparatus  30 B. Specifically, when the front-end of the sheet is discharged from the carrier outlet, the first relay apparatus  30 B switches the sheet discharge signal to ON. On the other hand, when the back-end of the sheet is discharged from the carrier outlet, the first relay apparatus  30 B switches the sheet discharge signal to OFF. 
     By this sheet discharge signal, the first post-processing device  50 B which is the third vendor device, recognizes that the sheet is carried from the upstream device, and carries the sheet by the bypass conveyance in the first post-processing device  50 B. 
     Further, the first relay apparatus  30 B notifies the second relay apparatus  30 D of the sheet discharge information by delaying the above notification for the time necessary for the bypass conveyance in the first post-processing device  50 B. Here, the first relay apparatus  30 B previously stores the carrying time in the case of carrying the sheet by the bypass conveyance in the first post-processing device  50 B. When the carrying time elapses since the front-end of the sheet is discharged from the first relay apparatus  30 B, the first relay apparatus  30 B transmits the sheet discharge information to the second relay apparatus  30 D through the serial interface. 
     Based on the detection state of the sheet discharge sensor of the second relay apparatus  30 D, the second relay apparatus  30 D outputs the sheet discharge information to the second post-processing device  70 C through the parallel interface every when the sheet is discharged to the subsequent-stage second post-processing device  70 C from the second relay apparatus  30 D. Specifically, when the front-end of the sheet is discharged from the carrier outlet, the second relay apparatus  30 D switches the sheet discharge signal to ON. On the other hand, when the back-end of the sheet is discharged from the carrier outlet, the second relay apparatus  30 D switches the sheet discharge signal to OFF. 
     By the sheet discharge signal from the second relay apparatus  30 D, the second post-processing device  70 C which is the third vendor device, recognizes that the sheet is carried from the upstream device. Further, the second post-processing device  70 C performs the post-processing and discharge operations to this sheet. 
     After the image forming device  10  completes the discharge of the second sheet of the second set, the image forming device  10  transmits the operation stop information to the first relay apparatus  30 B. After the first relay apparatus  30 B receiving the operation stop information completes the discharge of the second sheet of the second set to the first post-processing device  50 B, the second relay apparatus  30 B transmits the operation stop information to the first post-processing device  50 B. At the same time, the first relay apparatus  30 B transmits the operation stop information to the second relay apparatus  30 D. After the second relay apparatus  30 D receiving the operation stop information completes the discharge of the second sheet of the second set to the second post-processing device  70 C, the second relay apparatus  30 D transmits the operation stop information to the second post-processing device  70 C. 
     Next, the operations of the first relay apparatus  30 B and the second relay apparatus  30 D will be explained. The operations of the second relay apparatus  30 D are the same as those shown in  FIGS. 8 and 9 . In case of the operations of the second relay apparatus  30 D, the first post-processing device and the main body are replaced with the second post-processing device  70 C and the first relay apparatus  30 B, respectively. 
     The operations shown in  FIGS. 8 and 9  are almost the same as those of the first relay apparatus  30 B. In case of the operations of the first relay apparatus  30 B, the first post-processing device and the second post-processing device are replaced with the first post-processing device SOB and the second post-processing device  70 C, respectively. Further, in the case of the first relay apparatus  30 B, the process contents of step S 104  in  FIG. 8  are shown in  FIGS. 17 and 18 . The above process contents are almost the same as those shown in  FIGS. 10 and 11 . The difference between the process contents shown in  FIGS. 10 and 11  and those shown in  FIGS. 17 and 18 , is that the second relay apparatus  30 D (relay apparatus  2 ) is used as the subsequent-stage device of the first relay apparatus  30 B in place of the second post-processing device  70 . 
     In the process of “control of second post-processing device being discharge destination” shown in  FIGS. 17 and 18 , the first relay apparatus  30 B switches the actuating signal of the parallel communication (parallel interface) to ON by using the subsequent-stage parallel interface unit  38  (Step S 171 ). At the same time, the first relay apparatus  30 B transmits the post-processing start information from the subsequent-stage serial interface unit  37  to the second relay apparatus  30 D by using the serial communication (serial interface) (Step S 172 ). 
     Next, the first relay apparatus  30 B waits for the reception of the sheet feed information from the image forming device  10  (main body). When the first relay apparatus  30 B receives the sheet feed information (Step S 173 ; Yes), the first relay apparatus  30 B transmits this sheet feed information from the subsequent-stage serial interface unit  37  to the second relay apparatus  30 D through the serial communication (Step S 174 ), and the process proceeds to step S 175 . On the other hand, in case that the first relay apparatus  30 B does not receive the sheet feed information (Step S 173 ; No), the process proceeds to step S 175 . 
     At step S 175 , the first relay apparatus  30 B determines whether to receive the wait information from the second relay apparatus  30 D. In case that the first relay apparatus  30 B does not receive the wait information (Step S 175 ; No), the process proceeds to step S 180 . When the first relay apparatus  30 B receives the wait information (Step S 175 ; Yes), the first relay apparatus  30 B calculates the wait time necessary for the first post-processing device  50 B which is the third vendor device, in accordance with the sheet information included in the sheet feed information received from the image forming device  10  at step S 173  (Step S 176 ). The first relay apparatus  30 B compares the calculated wait time and the wait time indicated by the wait information received from the second relay apparatus  30 D (wait time necessary for the second post-processing device  70 C which is the third vendor device) (Step S 177 ). 
     In case that the wait time in the first post-processing device  50 B, which is calculated at step S 176 , is longer (larger) than the wait time in the second post-processing device  70 C (Step S 177 ; wait of third vendor  1 &gt;wait of third vendor  2 ), the first relay apparatus  30 B transmits the wait information indicating the wait time in the first post-processing device  50 B to the image forming device  10  (Step S 178 ), and the process proceeds to step S 180 . 
     In case that the wait time indicated by the wait information received from the second relay apparatus  30 D (wait time necessary for the second post-processing device  70 C) is longer (larger) than or equal to the other wait time (Step S 177 ; wait of third vendor device  1 ≦wait of the third vendor device  2 ), the first relay apparatus  30 B transmits the wait information received from the second relay apparatus  30 D to the image forming device  10  (Step S 179 ), and the process proceeds to step S 180 . 
     At step S 180 , the first relay apparatus  30 B determines whether the sheet discharge sensor of the first relay apparatus  30 B changes. When the sheet discharge sensor does not change (Step S 180 : No change), the process proceeds to step S 184 . When the sheet discharge sensor changes from OFF to ON (Step S 180 ; OFF→ON), the first relay apparatus  30 B switches the sheet discharge signal of the parallel communication to ON (Step S 181 ). Further, the first relay apparatus  30 B starts to count the time until the sheet is discharged from the first post-processing device  50 B which is the third vendor device (Step S 182 ), and the process proceeds to step S 184 . 
     When the sheet discharge sensor changes from ON to OFF (Step S 180 ; ON→OFF), the first relay apparatus  30 B switches the sheet discharge signal of the parallel communication to OFF (Step S 183 ), and the process proceeds to step S 184 . 
     At step S 184 , the first relay apparatus  30 B determines whether the count of the time until the sheet is discharged from the first post-processing device  50 B is completed (the count reaches a specified count value). In case that the count is not completed (Step S 184 ; No), the process proceeds to step S 186 . When the count is completed (Step S 184 ; Yes), the first relay apparatus  30 B transmits the sheet discharge information to the second relay apparatus  30 D through the serial interface (Step S 185 ), and the process proceeds to step S 186 . 
     At step S 186 , the first relay apparatus  30 B determines whether to receive the operation stop information from the image forming device  10 . In case that the first relay apparatus  30 B does not receive the operation stop information (Step S 186 ; No), the process returns to step S 173  and is continued. When the first relay apparatus  30 B receives the operation stop information (Step S 186 ; Yes), the first relay apparatus  30 B switches the actuating signal of the parallel communication to OFF (Step S 187 ) and transmits the operation stop information to the second relay apparatus  30 D (Step S 188 ). Then, the process returns to the process shown in  FIG. 8  (return). 
     The system configuration of the image forming system is not limited to those exemplified in the first and second embodiments. Also in a system in which a post-processing device which is the genuine device and a post-processing device which is the third vendor device are mixed, by the combination of the first and second embodiments, it is possible to perform the control, the sheet carrier, and the post-processing operations like the above embodiments, regardless of the configuration, the connection order and the like. 
     Third Embodiment 
     An image forming system  5 E according to the third embodiment has a system configuration in which a first post-processing device which is a third vendor device has no interface with a subsequent-stage device and in which a second post-processing device which is a third vendor device is connected. In the present embodiment, the second relay apparatus is not required, that is, the first post-processing device which is the third vendor device and the second post-processing device which is the third vendor device are manufactured by the same manufacturer, and the ground heights of the carrier inlet and the carrier outlet are the same. 
       FIG. 19  shows a connection state of the communication lines in the image forming system  5 E. The image forming device  10  and a relay apparatus  30 E are genuine devices, and are connected through the serial interface which is compliant with the specifications of the genuine device manufacturer. The relay apparatus  30 E and the first post-processing device  50  are connected through the parallel interface (referred to as parallel communication  1 ) for the third vendor device. Further, the relay apparatus  30 E and the second post-processing device  70 E are connected through the parallel interface (referred to as parallel communication  2 ) for the third vendor device. 
       FIG. 20  is a block diagram showing an outline configuration of each device of the image forming system  5 E shown in  FIG. 19 . The image forming device  10  and the first post-processing device  50  are the same as those of the first embodiment ( FIG. 3 ). The relay apparatus  30 E has the substantially same configuration as the relay apparatus  30  of  FIG. 3 , and is different from the relay apparatus  30  in that the replay apparatus  30 E comprises a second subsequent-stage parallel interface unit  42  in place of the subsequent-stage serial interface unit  37 . The second post-processing device  70 E has the substantially same configuration as the second post-processing device  70  of  FIG. 3 , and is different from the second post-processing device  70  in that the second post-processing device  70 E comprises a previous-stage parallel interface unit  81  in place of the previous-stage serial interface unit  74 . 
     The main process performed by the relay apparatus  30 E according to the third embodiment is the same as that of  FIG. 8 . In the third embodiment, the second post-processing device  70 E is used as the second post-processing device. Further, the process contents of step S 104  are replaced with those of  FIGS. 21 and 22 . 
     The relay apparatus  30 E switches the actuating signal of the parallel communication  1  to ON by using the subsequent-stage parallel interface unit  38  which communicates with the first post-processing device  50  (Step S 201 ). At the same time, the relay apparatus  30 E switches the actuating signal of the parallel communication  2  to ON by using the second subsequent-stage parallel interface unit  42  which communicates with the second post-processing device  70 E (Step S 202 ). 
     Next, the relay apparatus  30 E waits for the reception of the sheet feed information from the image forming device  10  (main body). When the relay apparatus  30 E receives the sheet feed information (Step S 203 ; Yes), the relay apparatus  30 E calculates the wait time necessary for the first post-processing device  50  which is the third vendor device, in accordance with the sheet information included in the sheet feed information (Step S 204 ). Further, the relay apparatus  30 E calculates the wait time necessary for the second post-processing device  70 E which is the third vendor device, in accordance with the sheet information included in the sheet feed information (Step S 205 ). A method for calculating the wait time is the same as that of the first embodiment. 
     The relay apparatus  30 E compares the wait time in the first post-processing device  50  which is the third vendor device and the wait time in the second post-processing device  70 E which is the third vendor device (Step S 206 ). In case that the wait time in the first post-processing device  50  which is the third vendor device is longer (larger) than the wait time in the second post-processing device  70 E (Step S 206 ; wait of third vendor  1 &gt;wait of third vendor  2 ), the relay apparatus  30 E transmits the wait information indicating the wait time in the first post-processing device  50  which is the third vendor device, to the image forming device  10  (Step S 207 ), and the process proceeds to step S 209 . 
     In case that the wait time in the second post-processing device  70 E which is the third vendor device is longer (larger) than or equal to the other wait time (Step S 206 ; wait of third vendor device  1 ≦wait of third vendor device  2 ), the relay apparatus  30 E transmits the wait information indicating the wait time in the second post-processing device  70 E which is the third vendor device, to the image forming device  10  (Step S 208 ), and the process proceeds to step S 209 . 
     At step S 209 , the relay apparatus  30 E determines whether the sheet discharge sensor of the relay apparatus  30 E changes. When the sheet discharge sensor does not change (Step S 209 : No change), the process proceeds to step S 214 . When the sheet discharge sensor changes from OFF to ON (Step S 209 ; OFF→ON), the relay apparatus  30 E switches the sheet discharge signal of the parallel communication  1  to ON (Step S 210 ). Further, the relay apparatus  30 E starts to count the time until the front-end of the sheet is discharged from the first post-processing device  50  which is the third vendor device (Step S 211 ), and the process proceeds to step S 214 . 
     When the sheet discharge sensor changes from ON to OFF (Step S 209 ; ON→OFF), the relay apparatus  30 E switches the sheet discharge signal of the parallel communication  1  to OFF (Step S 212 ). Further, the relay apparatus  30 E starts to count the time until the back-end of the sheet is discharged from the first post-processing device  50  which is the third vendor device (Step S 213 ), and the process proceeds to step S 214 . 
     At step S 214 , the relay apparatus  30 E determines whether the count of the time until the front-end of the sheet is discharged from the first post-processing device  50  which is the third vendor device, is completed (the count reaches a specified count value). In case that the count is not completed (Step S 214 ; No), the process proceeds to step S 216 . When the count is completed (Step S 214 ; Yes), the relay apparatus  30 E switches the sheet discharge signal of the parallel communication  2  to ON (Step S 215 ). Then, the process proceeds to step S 216 . 
     At step S 216 , the relay apparatus  30  determines whether the count of the time until the back-end of the sheet is discharged from the first post-processing device  50  which is the third vendor device, is completed (the count reaches a specified count value). In case that the count is not completed (Step S 216 ; No), the process proceeds to step S 218 . When the count is completed (Step S 216 ; Yes), the relay apparatus  30 E switches the sheet discharge signal of the parallel communication  2  to OFF (Step S 217 ), and the process proceeds to Step S 218 . 
     At Step S 218 , the relay apparatus  30 E determines whether to receive the operation stop information from the image forming device  10 . In case that the relay apparatus  30 E does not receive the operation stop information (Step S 218 ; No), the process returns to step S 203  and is continued. When the relay apparatus  30 E receives the operation stop information (Step S 218 ; Yes), the relay apparatus  30 E switches the actuating signal of the parallel communication  1  to OFF (Step S 219 ) and an actuating signal of the parallel communication  2  to OFF (Step S 220 ), and the process returns to the process shown in  FIG. 8  (return). 
     As described above, in the relay apparatus and the image forming system including the relay apparatus according to at least one of the embodiments, by communicatively connecting a plurality of post-processing devices having different communication system to the image forming device  10 , the sheet carrier and the post-processing operations can be performed. In particular, in the image forming device  10  and the post-processing device which is the third vendor device, it is not required to consider the connection between the image forming device  10  and the post-processing device having the different communication systems from each other. Therefore, the burden, such as the development, the design, the manufacture of the image forming system, is reduced. 
     Further, the relay apparatus switches the operation for the subsequent-stage post-processing device or the operation for the subsequent-stage relay apparatus according to the contents of the post-processing or the discharge destination (in at least one of the embodiments, the relay apparatus switches between the control of the first post-processing device to be the discharge destination and the control of the second post-processing device to be the discharge destination). Therefore, the relay apparatus can automatically control various types of post-processings without changing the configuration (connection order or the like) of the image forming system. 
     Further, in the second embodiment, the difference in the ground heights between the carrier outlet and the carrier inlet of the third vendor device and the carrier outlet and the carrier inlet of the genuine device is absorbed by the relay apparatus. Therefore, by connecting a plurality of different devices through the above relay apparatus, the intended image forming system can be configured so as to solve not only the problem relating to the communication system but also the problem relating to the ground heights of the carrier outlet and the carrier inlet for sheets. 
     As described above, the embodiments are explained by using the drawings. However, in the present invention, the concrete configuration is not limited to the above embodiments. In the present invention, various modifications of the above embodiments or the addition of various functions or the like to the embodiments can be carried out without departing from the gist of the invention. 
     In at least one of the embodiments, the case in which the sheet interval and the wait information as the sheet interval information are indicated by using the time, is explained. Further, the sheet interval and the wait information may be indicated by using the distance between sheets. For example, the distance and the carrier speed are converted into the time. 
     In at least one of the embodiments, in the relay apparatus the carrier path is included. In case that the ground heights of the carrier outlet and the carrier inlet are the same in each device like the first and third embodiments, the relay apparatus does not have the carrier path of sheets and may be simply configured as a device for performing the relay of the communication. In this case, in order to form the carrier path, one or a plurality of post-processing devices may be connected in series to a subsequent stage of the image forming device  10 . In case that only the relay of the communication is performed without having the carrier path as described above, the relay apparatus may be integrated with the image forming device  10 . 
     In at least one of the embodiments, the relay apparatus selects the longer (larger) wait time of the wait time in the first post-processing device and the wait time in the second post-processing device, and transmits the wait information indicating the longer wait time to the image forming device  10 . The wait time is not limited to longer one. One wait time determined from the wait time in the first post-processing devices and the wait time in the second post-processing devices in accordance with a certain standard, may be transmitted as the sheet interval information to the image forming device  10 . In addition, the relay apparatus may transmit both of the wait information indicating the wait time in the first post-processing device and the wait information indicating the wait time in the second post-processing devices, to the image forming device  10 . In accordance with the above transmitted information, the image forming device  10  may calculate the standby time at the standby position  13 . 
     In at least one of the embodiments, the longer wait time is selected as described above. In the case where the post-processing is performed in the first post-processing device and the post-processing is not performed in the second post-processing device, or in the case where the sheet is carried by the bypass conveyance in the first post-processing device and the post-processing is performed only in the second post-processing device, the relay apparatus may select the wait time in the post-processing device in which the post-processing is performed. That is, when the post-processing is performed in only one of the first and second post-processing devices, the relay apparatus selects the sheet interval information relating to the post-processing device in which the post-processing is performed, and transmits the selected sheet interval information to the image forming device  10 . 
     In at least one of the embodiments, the example in which when the post-processing is performed in the second post-processing device, the sheet is carried by the bypass conveyance in the first post-processing device, is explained. However, the post-processings may be performed in both of the first and second post-processing devices. 
     In at least one of the embodiments, the communication between the genuine devices is performed through the serial interface and the communication between the genuine device and the third vendor device is performed through the parallel interface. However, the present invention is not limited to the above communications. The present invention can be applied to the case in which different communication systems are used. 
     One of the objects of the above embodiments is to provide a relay apparatus which connects a post-processing device having a different communication system to an image forming device and an image forming system comprising the above relay apparatus, so as to secure the sheet interval necessary for the post-processing device. 
     In at least one of the above embodiments, the second post-processing device which is not compliant with the first communication system can be connected to the image forming device which performs the communication through the first communication system, via the relay apparatus. That is, the relay apparatus comprises the storage unit which previously stores the information relating to the sheet interval necessary for the second post-processing device connected to a downstream of the image forming device. When the sheet information relating to the fed sheet is received from the image forming device, the relay apparatus determines the sheet interval information of the second post-processing device in accordance with the received sheet information and the information relating to the sheet interval necessary for the second post-processing device, which is previously stored in the storage unit, and transmits the determined sheet interval information to the image forming device. 
     In at least one of the above embodiments, both of the second post-processing device which is not compliant with the first communication system and the third post-processing device which is compliant with the first communication system can be connected to the image forming device which performs the communication through the first communication system, via the relay apparatus. That is, the relay apparatus comprises the storage unit which previously stores the information relating to the sheet interval necessary for the second post-processing device connected to a downstream of the image forming device. When the sheet information relating to the fed sheet is received from the image forming device, the relay apparatus determines the sheet interval information of the second post-processing device in accordance with the received sheet information and the information relating to the sheet interval necessary for the second post-processing device, which is previously stored in the storage unit. Further, the relay apparatus transmits the sheet information received from the image forming device to the third post-processing device and acquires the sheet interval information from the third post-processing device. Then, the relay apparatus transmits both of the determined sheet interval information of the second post-processing device and the sheet interval information received from the third post-processing device to the image forming device or transmits the sheet interval information determined in accordance with the sheet interval information of the second post-processing device and the sheet interval information of the third post-processing device, to the image forming device. 
     In at least one of the above embodiments, both of the second post-processing device which performs the communication through the second communication system and the third post-processing device which performs the communication through the second communication system can be connected to the image forming device which performs the communication through the first communication system, via the relay apparatus. That is, the relay apparatus comprises the storage unit which previously stores the information relating to the sheet interval necessary for the second post-processing device and the information relating to the sheet interval necessary for the third post-processing devices. The second and the third post-processing devices are connected to a downstream of the image forming device. When the sheet information relating to the fed sheet is received from the image forming device, the relay apparatus determines the sheet interval information of the second post-processing device and the sheet interval information of the third post-processing device in accordance with the received sheet information and the information stored in the storage unit. Further, the relay apparatus transmits both of the sheet interval information of the second post-processing device and the sheet interval information of the third post-processing device, to the image forming device or transmits the sheet interval information determined in accordance with the sheet interval information of the second post-processing device and the sheet interval information of the third post-processing device, to the image forming device. 
     In at least one of the above embodiments, the relay apparatus selects the sheet interval information of one of the second and third post-processing devices, in which longer time is required for the post-processing, and transmits the selected sheet interval information to the image forming device. 
     In at least one of the above embodiments, in case that only one of the second and third post-processing devices performs the post-processing, the relay apparatus selects the sheet interval information of the device which performs the post-processing, and transmits the selected sheet interval information to the image forming device. 
     In at least one of the embodiments, the relay apparatus comprises the sheet carrier unit which carries and discharges the sheet received from an upstream device to a downstream device. In case that the height at which the carrier outlet of the upstream device is disposed from the installation surface of the relay apparatus is different from the height at which the carrier inlet of the downstream device is disposed from the installation surface of the relay apparatus, the relay apparatus is connected between the above devices as the carrier path for absorbing the difference in the height. 
     According to the relay apparatus and the image forming system, the post-processing device having a different communication system can be connected to the image forming device so as to secure the sheet interval necessary for the post-processing device. 
     The present U.S. patent application claims the priority of Japanese Patent Application No. 2012-175362, filed on Aug. 7, 2012, according to the Paris Convention, and the entirety of which is incorporated herein by reference for correction of incorrect translation.