Patent Publication Number: US-2020290839-A1

Title: Image Forming System and Image Forming Apparatus

Description:
The entire disclosure of Japanese patent Application No. 2019-044474, filed on Mar. 12, 2019, is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     The present invention relates to an image forming system and an image forming apparatus. 
     Description of the Related art 
     Conventionally, many sheets of paper discharged from an image forming apparatus are accumulated in a high-capacity stacker (hereinafter abbreviated as a “stacker”). The stacker is provided with a discharge tray for storing paper, and accumulates many sheets of paper discharged and stacked onto the discharge tray. In the discharge tray, grooves as well as bumps and dips of metal parts are formed to fit the shape of equipment that carries paper out of the stacker. For this reason, when the sheets of paper discharged from the image forming apparatus to the stacker are left for a long time, the weight of the bundle of paper accumulated in the discharge tray is added to the bottom sheet. This leaves a mark of the grooves or makes wrinkles on the sheet in contact with the discharge tray so that the sheet on which an image is formed (referred to as “printed matter”) is damaged. 
     When bulk printing is performed at a print shop. for example, a print job is kept running during the night hours or the like in which a user is absent. In addition, depending on the work procedure, printed matter may be left in the stacker while waiting for a next process of the printed matter. Thus, in order to buffer the effect of the discharge tray on the printed matter at the bottom of the bundle of paper, a user has manually placed a buffer plate or the like on the discharge tray before the image forming apparatus discharges the printed matter to the stacker. 
     JP 2007-169047 A states that “if a detection mechanism does not detect a sheet of paper when a plurality of sheets is discharged in bundle from a processing tray to a discharge tray. a sheet of paper is discharged onto the discharge tray, and then the sheets are discharged in bundle from the processing tray”. 
     However, if a user is not assigned near the stacker, the user cannot perform the operation of placing the buffer plate or the like on the discharge tray. Moreover, the method that relies on manual work is likely to result in a situation where the user forgets the operation or makes a mistake such as placing a plate or the like of an inappropriate size on the discharge tray. When a plate or the like of an inappropriate size is placed on the discharge tray a mark along the edges of the plate is left on the sheet at the bottom of the bundle of paper. 
     The technique disclosed in JP 2007-169047 A above has been made for the purpose of maintaining the alignment of the sheets on the discharge tray. Thus, when the bundle of paper discharged using the technique disclosed in JP 2007-169047 A is accumulated in the discharge tray for a long time, there is a high possibility that the printed matter at the bottom of the bundle of paper is damaged. 
     SUMMARY 
     The present invention has been made in view of such circumstances, and aims to protect printed matter stored in a stacker. 
     To achieve the abovementioned object, according to an aspect of the present invention, an image forming system reflecting one aspect of the present invention comprises an image forming apparatus and a stacker that includes a discharged paper storage and a transporter, the discharged paper storage storing a sheet discharged from the image forming apparatus, and the transporter transporting the sheet to the discharged paper storage, wherein the image forming apparatus includes: an image former that forms an image on the sheet designated for a job and generates printed matter; and a hardware processor that performs control to cause the transporter to discharge a buffer sheet to the discharged paper storage, in which the printed matter is not discharged, before the job is executed, and that executes the job after the buffer sheet transported through the transporter is stored in the discharged paper storage to cause the transporter to transport the printed matter, which is generated by the image former, and cause the discharged paper storage to store the printed matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The problems, advantages, configurations, effects and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention: 
         FIG. 1  is a diagram of a schematic configuration of an image forming system according to an embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating an example of an internal configuration of an image forming apparatus according to an embodiment of the present invention; 
         FIG. 3  is a block diagram illustrating an example of a hardware configuration of a computer according to an embodiment of the present invention; 
         FIG. 4  is a diagram of a structure of a table for buffer sheet discharge information according to an embodiment of the present invention; 
         FIG. 5  is a diagram of a structure of a table for feed tray designation information according to an embodiment of the present invention; 
         FIG. 6  is a diagram of a structure of a table for buffer sheet setting information according to an embodiment of the present invention; 
         FIG. 7  is an explanatory diagram illustrating a display example of a buffer sheet discharge setting screen according to an embodiment of the present invention; 
         FIG. 8  is an explanatory diagram illustrating a display example of a feed tray selection setting screen according to an embodiment of the present invention; 
         FIG. 9  is a flowchart illustrating an example of buffer sheet discharge determination processing according to an embodiment of the present invention; 
         FIG. 10  is a flowchart illustrating an example of processing in which a feed tray selection unit automatically selects a feed tray in step S 7 ; and 
         FIG. 11  is a diagram of a structure of a table for buffer sheet discharge information according to a variation of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. In the present specification and drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and redundant description is omitted. 
     Embodiment 
     Configuration of Image Forming System 
     First, an example of the configuration of an image forming system according to an embodiment of the present invention will be described with reference to  FIG. 1 . 
       FIG. 1  is a diagram of a schematic configuration of an image forming system  1  according to an embodiment of the present invention. Note that  FIG. 1  illustrates elements considered necessary for the description of the present invention or related elements, and the image forming system of the present invention is not limited to the example illustrated in  FIG. 1 . 
     The image forming system  1  according to the present embodiment includes a paper feeder  2 , an image forming apparatus  3 , and a stacker  4 . 
     The paper feeder  2  includes a plurality of feed trays  2   a  (an example of a feed paper storage) that stores sheets Sh of different paper types to be fed to an image former  20  of the image forming apparatus  3 . The feed trays  2   a  store a large amount of the sheets Sh of different paper types and different sizes. However, the feed trays  2   a  may store the sheets Sh of the same paper type and the same size. In the present embodiment, the sheet Sh to be fed to the image former  20  is stored in the feed tray  2   a  of the paper feeder  2 . The sheet Sh is an example of a recording material, and the image forming apparatus  3  can also form an image on a resin sheet that is an example of the recording material. 
     The sheet Sh set in the feed tray  2   a  is fed to the image forming apparatus  3  at a predetermined timing. In the description of the present embodiment, the sheet Sh on which an image is formed and the sheet Sh discharged as a buffer sheet are both stored in the feed tray  2   a  of the paper feeder  2 , but these sheets Sh may be stored in a feed tray  14  of the image forming apparatus  3 . 
     The image forming apparatus  3  is an example of an image forming apparatus that forms an image on the sheet Sh by electrophotography in which an image is formed using static electricity. The sheet Sh on which an image is formed is discharged to the stacker  4  as printed matter. The image forming apparatus  3  for example forms a color image on a sheet in a tandem form in which toner images of four colors being yellow (Y), magenta (M), cyan (C), and black (K) are superimposed. The image forming apparatus  3  is connected to a personal computer (PC) operated by a user, a print controller, and the like via a local area network (LAN) not shown. Then, a job is submitted from the PC or print controller to the image forming apparatus  3  via the LAN. The image forming apparatus  3  performs various processings such as image forming processing according to the job submitted. 
     The stacker  4  stores the sheet Sh discharged from the image forming apparatus  3  in a discharge tray  43  or  45  (an example of a discharged paper storage). The sheet Sh discharged to the stacker  4  is either the sheet Sh on which an image is formed by the image forming apparatus  3 , or the sheet Sh fed from the feed tray  2   a  and discharged as the buffer sheet. In the following description, the sheet Sh on which an image is formed by the image forming apparatus  3  is referred to as “printed matter”. Moreover, the sheet Sh that buffers the effect of an affecting part, such as a groove formed in the discharge tray  43 . on the printed matter stored in the discharge tray  43  is referred to as the “buffer sheet”. The buffer sheet is a plurality of the sheets Sh stored at the bottom of the discharge tray  43  before the printed matter is discharged to the discharge tray  43  for the purpose of preventing damage to the printed matter. The buffer sheet may be of the same size and the same type as the sheet Sh being the printed matter, or may be of a different size and a different paper type therefrom. Moreover, as described later, one or a plurality of the sheets Sh may be discharged to the discharge tray  43  as the buffer sheet depending on the paper type. An image may also be formed on the sheet Sb used as the buffer sheet. 
     Here, an example of the internal configuration of the image forming apparatus  3  will be described also with reference to  FIG. 1 . 
     The image forming apparatus  3  includes an image input unit  11  having an auto document feeder (ADF)  12 , and an operation display unit  13 . The image forming apparatus  3  further includes a printer unit  10  having the feed tray  14  and the image former  20 . 
     The image input unit  11  optically reads an image from a document on a document table of the ADF  12 , and performs A/D conversion on the read image to generate image data. Note that the image input unit  11  can also read an image from a document on the platen glass. 
     The operation display unit  13  includes a display part formed of a liquid crystal panel or the like, and an operation part formed of a touch sensor or the like. The display part and the operation part are integrally formed as a touch panel, for example. The operation display unit  13  generates an operation signal indicating details of a user operation input to the operation part, and supplies the operation signal to a controller  30  (see  FIG. 2  described later). Also, the operation display unit  13  displays details of a user operation, setting information, and the like on the display part on the basis of a display signal supplied from the controller  30 . Note that the operation part can be formed of a mouse, a tablet, or the like to be formed separately from the display part. 
     The feed tray  14  (an example of the feed paper storage) is a container that stores the sheet Sh on which an image is formed by the image former  20 . The feed trays  14  store sheets having different paper types, basis weights, and the like. Note that although the present embodiment illustrates an example in which two of the feed trays  14  are provided, the number of the feed trays  14  may be one, or may be three or more. Moreover, the feed tray  14  has a configuration similar to that of the feed tray  2   a  for feeding the sheet Sh. 
     The image forming apparatus  3  is provided with a transport path  15  that transports the sheet Sh fed from any of the feed trays  2   a  and  14  to the stacker  4  via the image former  20 . The transport path  15  is provided with a plurality of transport rollers for transporting the sheet Sh. 
     The transport path  15  is extended and connected to a transport path  40  of the stacker  4  downstream of a fixing unit  26 . The transport path  15  also branches off downstream of the fixing unit  26 . One end of the transport path  15  being branched is connected to a reverse transport path  16  that joins the transport path  15  on the upstream side of the printer unit  10 . The reverse transport path  16  is provided with a reversing unit  17  that reverses the sheet Sh. The sheet Sh reversed by the reversing unit  17  is returned to the upstream side of the transport path  15  through the reverse transport path  16 . In some cases, the sheet Sh reversed by switching of the path is returned to the transport path  15  downstream of the fixing unit  26  and then discharged to the stacker  4 . 
     The image former  20  forms an image on the sheet Sh designated for a job and generates printed matter. The image former  20  includes, for example, four image forming units  21 Y,  21 M,  21 C, and  21 K forming toner images of corresponding colors Y, M, C, and K, and forms an image on the sheet Sh transported through the transport path  15 . No image is usually formed on the sheet Sb when the sheet Sh is used as the buffer sheet. However, the image former  20  may form, on the sheet Sh. an image serving as a mark for indicating to a user that the sheet is the buffer sheet. 
     The image forming units  21 Y,  21 M,  21 C, and  21 K include charging units, exposure units (all not shown), photosensitive drums  22 Y,  22 M,  22 C, and  22 K as image carriers, and developing units  23 Y,  23 M, and  23 C, and  23 K, respectively. 
     The developing units  23 Y,  23 M,  23 C, and  23 K irradiate surfaces (outer peripheral parts) of the corresponding photosensitive drums  22 Y,  22 M,  22 C, and  22 K with light according to images, thereby forming electrostatic latent images on the circumferences of the photosensitive drums  22 Y,  22 M,  22 C, and  22 K. Then, the developing units  23 Y,  23 M,  23 C, and  23 K form toner images on the photosensitive drums  22 Y,  22 M,  22 C, and  22 K by depositing toner to the electrostatic latent images. 
     The image former  20  further includes an intermediate transfer belt  24 . a secondary transfer unit  25 , the fixing unit  26 , and an environment sensor  27 . The intermediate transfer belt  24  is a belt onto which images formed on the photosensitive drums  22 Y,  22 M,  22 C, and  22 K are primarily transferred. The secondary transfer unit  25  is a roller that secondarily transfers the toner images of the respective colors, which have been primarily transferred onto the intermediate transfer belt  24 , onto the sheet Sh transported through the transport path  15 . 
     The fixing unit  26  is disposed downstream of the secondary transfer unit  25  along the sheet transport direction thereof and performs fixing processing on the sheet Sh which is supplied from the image former  20  and on which the color toner image is formed. The fixing unit  26  heats and pressurizes the sheet Sh being transported to fix the image transferred by the image former  20  on the front side of the sheet Sh. The sheet Sh on which the image is fixed by the fixing unit  26  is transported to the stacker  4  through the transport path  15 , or is reversed by the reversing unit  17  through the reverse transport path  16  and then returned to the transport path  15  on the upstream side of the printer unit  10 . When the sheet Sh is reversed, an image is formed on the back side of the sheet by the printer unit  10 . After that, the sheet Sh is subjected to the fixing processing by the fixing unit  26  and transported to the stacker  4 . 
     The environment sensor  27  detects temperature and/or humidity in the image forming apparatus  3  as information on the environment in the image forming apparatus  3 . The temperature and humidity detected by the environment sensor  27  are output to the controller  30  (see  FIG. 2  described later) of the image forming apparatus  3 . Here, the image forming apparatus  3  need only include, as the environment sensor  27 , at least one of a temperature sensor that detects only temperature and a humidity sensor that detects only humidity. Note that the environment sensor  27  may be provided inside the stacker  4  to detect the temperature and humidity in the stacker  4  and output the detected temperature and humidity to the controller  30 . 
     Next, an example of the configuration of the stacker  4  will be described. 
     The stacker  4  accumulates the sheet Sh discharged from the image forming apparatus  3 . The stacker includes transport paths  40 ,  42 , and  44 , a switching unit  41 , the discharge trays  43  and  45 , and a remaining paper sensor  46 . 
     The transport path  40  is connected to the two transport paths  42  and  44  via the switching unit  41 . The switching unit  41  switches the direction of transport of the sheet Sh such that the sheet Sh is transported to either one of the transport paths  42  and  44 . The transport path  42  is connected to the discharge tray  43 , and the transport path  44  is connected to the discharge tray  45 . The transport path  42  discharges the sheet Sh to the discharge tray  43  when the sheet Sh is transported from the image forming apparatus  3  to the transport path  40 , the sheet Sh being the printed matter on which an image is formed. Thus, in the present embodiment, the transport paths  40  and  42  of the stacker  4  are used as an example of a transporter. On the other hand, the transport path  44  discharges, to the discharge tray  45 , the sheet Sh or the like on which an image is formed by a job different from a job for the sheet Sh that is discharged to the discharge tray  43 . Note that the switching unit  41  is unnecessary if the stacker  4  has only one discharge tray  43 . 
     The discharge tray  43  is lowered according to the number or weight of the sheets Sh accumulated. Thus, as the amount of the sheets Sh discharged increases, the discharge tray  43  gradually moving downward can store more of the sheets Sh. When a predetermined number or more of the sheets Sh are accumulated in the discharge tray  43 , the operation of the image forming apparatus  3  is stopped, and the discharge of the sheets Sh to the discharge tray  43  is also stopped. After that, a user opens a front panel (not shown) provided to the stacker  4 , takes out the sheet Sh from the discharge tray  43 , and carries out the sheet. 
     In the present embodiment, a large amount of the sheets Sh on which images are formed by the image forming apparatus  3  are mainly discharged to the discharge tray  43  and stacked therein. On the discharge tray  43 . affecting parts such as grooves and bumps and dips of metal parts are formed to affect the printed matter stored in the discharge tray  43 . The affecting parts formed in the discharge tray  43  make it easier for a user to take out the printed matter from the stacker  4  even when the discharge tray  43  stores a large amount of printed matter. 
     The remaining paper sensor  46  is provided in the vicinity of the discharge tray  43 . The remaining paper sensor  46  is used to detect the presence or absence of the sheet Sh (printed matter or buffer sheet) discharged to the discharge tray  43 . Information regarding the presence or absence of the sheet Sh detected by the remaining paper sensor  46  is transmitted to the controller  30  (see  FIG. 2  described later) of the image forming apparatus  3 . The remaining paper sensor  46  may be an optical sensor capable of detecting the presence or absence of the sheet Sh by a change in intensity of reflected light of the light emitted toward the discharge tray  43 , or may be a weight sensor capable of detecting the weight of the sheet Sh discharged to the discharge tray  43 . 
       FIG. 2  is a block diagram illustrating an example of the internal configuration of the image forming apparatus  3 . 
     The controller  30  that controls the internal operation of the image forming apparatus  3  includes a job reception unit  31 , a paper presence/absence determination unit  32 , a buffer sheet discharge determination unit  33 , a feed tray selection unit  34 , a buffer sheet discharge control unit  35 , a mark formation instruction unit  36 , and a job execution unit  37 . 
     The job reception unit  31  receives a job from a PC or printer controller (not shown). The job received by the job reception unit  31  is temporarily saved in a storage  38 , for example, and is read by the job execution unit  37  to be executed. 
     The paper presence/absence determination unit  32  determines the presence or absence of printed matter or a buffer sheet stored in the discharge tray  43 . For example, the paper presence/absence determination unit  32  can determine whether or not the sheet Sh, that is, the printed matter or buffer sheet, is loaded in the discharge tray  43  on the basis of information input from the remaining paper sensor  46 . A result of determination as to whether or not the sheet Sh is loaded is output to the buffer sheet discharge determination unit  33 . 
     The buffer sheet discharge determination unit  33  determines whether or not to discharge the buffer sheet at the start of a job on the basis of the result of determination by the paper presence/absence determination unit  32  and buffer sheet discharge information  38   b  in the storage  38 . For example, the buffer sheet discharge determination unit  33  determines to allow for the discharge of the buffer sheet when the paper presence/absence determination unit  32  determines that neither the printed matter nor the buffer sheet is loaded in the discharge tray  43 , and the buffer sheet discharge information  38   b  indicates that a function of discharging the buffer sheet is enabled. In this case, the buffer sheet is discharged to the discharge tray  43  before the job is executed. The buffer sheet is preferably discharged between different jobs or after sheets accumulated in the discharge tray  43  are taken out, for example. The present embodiment uses the sheet Sh stored in the feed tray  2   a  as an example of the buffer sheet, but a thin plate formed of resin or the like may be fed from the feed tray  2   a.    
     On the other hand, if the buffer sheet discharge information  38   b  indicates that the function of discharging the buffer sheet is disabled, the buffer sheet discharge determination unit  33  determines that the buffer sheet cannot be discharged regardless of whether or not the sheet Sh is loaded in the discharge tray  43 . Moreover, the buffer sheet discharge determination unit  33  determines that the buffer sheet need not be discharged when the paper presence/absence determination unit  32  determines that the printed matter or the buffer sheet has already been discharged to the discharge tray  43 . The result of determination by the buffer sheet discharge determination unit  33  as to whether or not to discharge the buffer sheet is output to the feed tray selection unit  34 . 
     The feed tray selection unit  34  selects the feed tray  2   a  from which the buffer sheet is discharged on the basis of feed tray designation information  38   c  in the storage  38 , when the buffer sheet discharge determination unit  33  determines that the buffer sheet is to be discharged. When it is determined that the sheet Sh of the same size and type as the sheet Sh used as the printed matter is to be discharged as the buffer sheet as described above, the feed tray selection unit  34  selects the feed tray  2   a  storing the sheet Sh on which an image of printed matter is formed. On the other hand, when the buffer sheet of a different size or different paper type from the sheet Sh being the printed matter is to be discharged, the feed tray selection unit  34  selects the feed tray  2   a  different from the feed tray  2   a  storing the sheet Sh on which an image of printed matter is formed. 
     Note that the sheet Sh that can be discharged as the buffer sheet may not be in the feed tray  2   a  selected by the feed tray selection unit  34 . In this case, the feed tray selection unit  34  acquires information such as free spinning of a pickup roller (not shown) provided in the feed tray  2   a , and determines that the feed tray  2   a  selected has no sheet Sh that can be fed. Then, the feed tray selection unit  34  newly selects another one of the feed trays  2   a  storing the sheet Sh that can be discharged as the buffer sheet. Details of the processing in which the feed tray selection unit  34  selects the feed tray  2   a  will be described with reference to flowcharts illustrated in  FIGS. 9 and 10  later. 
     The buffer sheet discharge control unit  35  performs control to discharge the buffer sheet through the transport path  42  to the discharge tray  43 , in which the printed matter is not discharged, before a job is executed by the job execution unit  37 . Here, the buffer sheet discharge control unit  35  performs control to discharge the buffer sheet when the paper presence/absence determination unit  32  determines that neither the sheet Sh nor the buffer sheet is stored in the discharge tray  43 . Moreover, the buffer sheet discharge control unit  35  performs control to discharge, as the buffer sheet, the sheet Sh fed from the feed tray  2   a  selected by the feed tray selection unit  34 , when the buffer sheet discharge determination unit  33  determines to allow for the discharge of the buffer sheet. When the buffer sheet discharge control unit  35  performs control to discharge the sheet Sh from the feed tray  2   a  as the buffer sheet, the pickup roller (not shown) or the like provided in the feed tray  2   a  is driven to feed the sheet Sh from the feed tray  2   a  selected. After that, the buffer sheet discharge control unit  35  receives information indicating the presence of the sheet Sh from the remaining paper sensor  46  to be able to determine that the buffer sheet has been discharged to the discharge tray  43 . 
     The mark formation instruction unit  36  instructs the image former  20  and the job execution unit  37  to form an image, which serves as a mark for indicating to a user that the sheet Sh is the buffer sheet, on the sheet Sh discharged as the buffer sheet under the control of the buffer sheet discharge control unit  35 . The mark formed on the buffer sheet can be an edge of the buffer sheet filled with a predetermined color. The color may fill, for example, a side of the buffer sheet corresponding to the side from which the buffer sheet discharged in the discharge tray  43  is taken out (the side of a front panel of the stacker  4 ), or another side of the sheet. When the buffer sheet is discharged to the discharge tray  43  with the edge thereof filled with the predetermined color as described above, a user can accurately determine at which position the buffer sheet is located and how may buffer sheets are discharged even if a large number of printed matter is thereafter stacked on the buffer sheet. 
     After the buffer sheet transported through the transport path  42  is stored in the discharge tray  43 , the job execution unit  37  executes a rasterized job read from a job storage area  38   a  of the storage  38  and causes the image former  20  to operate. Then, the job execution unit  37  causes the transport path  42  to transport the printed matter generated by the image former  20  and causes the discharge tray  43  to store the printed matter. Note that when the printer controller is not connected to the image forming apparatus  3 , the job execution unit  37  can perform rasterization processing on a job read from the job storage area  38   a.    
     Moreover, when instructed by the mark formation instruction unit  36  to form a mark on the buffer sheet, the job execution unit  37  changes the order of execution of jobs such that the image former  20  forms the mark on the buffer sheet before the job is executed. As a result, the buffer sheet on which the mark is formed is discharged to the discharge tray  43  of the stacker  4 , and then the sheet Sh on which the image former  20  has formed an image by the job execution unit  37  executing the job is discharged to the discharge tray  43 . Note that when an instruction to form a mark on the buffer sheet is not input, the job execution unit  37  performs control on the image former  20  to discharge the sheet Sh used as the buffer sheet to the discharge tray  43  without forming an image on the sheet Sh. 
     The storage  38  includes the job storage area  38   a . The storage  38  also stores the buffer sheet discharge information  38   b , the feed tray designation information  38   c , and buffer sheet setting information  38   d.    
     A job received by the job reception unit  31  is stored in the job storage area  38   a  to be read and executed as appropriate by the job execution unit  37 . The job storage area  38   a  stores a plurality of different jobs. Therefore, the job execution unit  37  can continuously execute a plurality of jobs read from the job storage area  38   a.    
     The buffer sheet discharge information  38   b  is information that is set in advance by a user via the operation display unit  13 , and is related to whether or not the buffer sheet can be discharged. The buffer sheet discharge information  38   b  indicates that the function of discharging the buffer sheet under the control of the buffer sheet discharge control unit  35  is enabled or disabled according to the paper type of the sheet Sh designated for a job. For example, the sheet Sh having the paper type such as thick paper is less likely to have a mark caused by the affecting part of the discharge tray  43  and does not need the buffer sheet, in which case the function of discharging the buffer sheet is set to be disabled. On the other hand, the sheet Sh having the paper type other than thick paper is more likely to have a mark and needs the buffer sheet, in which case the function of discharging the buffer sheet is set to be enabled. Thus, the buffer sheet discharge determination unit  33  can determine whether or not the buffer sheet can be discharged with reference to the buffer sheet discharge information  38   b.    
     The feed tray designation information  38   c  is information that is set in advance by a user via the operation display unit  13  and is related to the feed tray  2   a . The feed tray selection unit  34  refers to the feed tray designation information  38   c  and selects the feed tray  2   a  storing the sheet Sh to be discharged as the buffer sheet. 
     The buffer sheet setting information  38   d  is information that is set in advance by a user via the operation display unit  13 , and is related to discharge setting of the buffer sheet. The buffer sheet discharge control unit  35  refers to the buffer sheet setting information  38   d  and determines the number of buffer sheets to be discharged according to the paper type and weight of the sheet Sb. The number of buffer sheets to be discharged is set to one or more. 
     Next, the hardware configuration of a computer  5  included in the image forming apparatus  3  will be described. 
       FIG. 3  is a block diagram illustrating an example of the hardware configuration of the computer  5 . 
     The computer  5  is hardware used as a so-called computer. The computer  5  includes a central processing unit (CPU)  51 , a read only memory (ROM)  52 , and a random access memory (RAM)  53  each connected to a bus  54 . The computer  5  further includes a display device  55 , an input device  56 , a non-volatile storage  57 , and a network interface  58 . 
     The CPU  51  reads, from the ROM  52 , a program code of software that implements each function according to the present embodiment, loads the program code into the RAM  53 , and executes the program code. In the RAM  53 , variables, parameters, and the like generated during arithmetic processing of the CPU  51  are temporarily written, and these variables, parameters, and the like are read as appropriate by the CPU  51 . Each functional unit included in the controller  30  in  FIG. 2  is implemented by the CPU  51  executing a program. 
     The display device  55  is, for example, a liquid crystal display monitor and displays a result of processing performed by the computer  5  and the like to a user. The input device  56  includes a keyboard, a mouse, or the like, for example, where a user can perform predetermined operation input and instruction using the input device. In the present embodiment, a touch panel display in which the display device  55  and the input device  56  are combined is used as the operation display unit  13 . 
     The non-volatile storage  57  includes, for example, a hard disk drive (HDD), a solid state drive (SSD), a flexible disk, an optical disc, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a non-volatile memory, or the like. The non-volatile storage  57  records a program that causes the computer  5  to function in addition to an operating system (OS) and various parameters. The ROM  52  and the non-volatile storage  57  permanently record programs, data, and the like necessary for the operation of the CPU  51 , and are each used as an example of a non-transitory recording medium storing a computer-readable program executed by the computer  5 . 
     The network interface  58  includes a network interface card (MC) or the like, for example, and various types of data can be transmitted and received between devices via a local area network (LAN), a dedicated line, or the like connected to a terminal of the NIC. 
     Example of Structure of Table for Buffer Sheet Discharge Information 
       FIG. 4  is a diagram of the structure of a table for the buffer sheet discharge information  38   b . 
     The buffer sheet discharge information  38   b  is a table in which whether the function of discharging the buffer sheet is enabled or disabled is set in advance according to the paper type of the sheet Sh designated for a job executed by the job execution unit  37  (hereinafter referred to as the “present job”). The buffer sheet discharge information  38   b  includes fields corresponding to the paper type of the present job and the discharge of the buffer sheet. 
     The field corresponding to the paper type of the present job stores the paper type of the sheet Sh designated for the present job. In the present embodiment, for example, airy one of thick paper, plain paper, and high-quality paper is designated. 
     The field corresponding to the discharge of the buffer sheet stores the setting of whether the discharge of the buffer sheet is enabled or disabled. For example, the sheet Sh whose paper type is thick paper is less prone to damage, so that the discharge of the buffer sheet is set to be disabled. When set to be disabled, the discharge of the buffer sheet is not performed. On the other hand, the sheet Sb whose paper type is plain paper or high-quality paper is prone to damage, so that the discharge of the buffer sheet is set to be enabled. When set to be enabled, the discharge of the buffer sheet is performed. 
     Example of Structure of Table for Feed Tray Designation Information 
       FIG. 5  is a diagram of the structure of a table for the feed tray designation information  38   c.    
     The feed tray designation information  38   c  is a table in winch information on the feed tray  2   a  storing the sheet Sh that can be discharged as the buffer sheet is set in an identifiable manner according to the paper type of the sheet Sh designated for the present job. The feed tray designation information  38   c  includes fields corresponding to the feed tray, the paper type, the size, and the selection designation. 
     The field corresponding to the feed tray stores an identifier for identifying the feed tray  2   a  that stores the sheet Sh as, for example, “A”, “B”, or “C”. 
     The field corresponding to the paper type stores, for each feed tray  2   a , the paper type of the sheet Sh stored in each feed tray  2   a . Examples of the paper type include plain paper and high-quality paper. 
     The field corresponding to the size stores the size of the sheet Sh stored in each feed tray  2   a . Examples of the size of the sheet Sh include A4 and B4. 
     The field corresponding to the selection designation stores information on the selection designation by a user as to whether or not the sheet Sh stored in the feed tray  2   a  is discharged as the buffer sheet. For example; “yes” is stored under the selection designation field for the feed trays  2   a  corresponding to “A” and “B”. No selection designation is made for the feed tray  2   a  corresponding to “C”. Note that designation for the selection designation field is not essential. In some cases, no selection designation is made for all the feed trays  2   a.    
     Example of Structure of Table for Buffer Sheet Setting Information 
       FIG. 6  is a diagram of the structure of a table for the buffer sheet setting information  38   d . 
     The buffer sheet setting information  38   d  is a table in which the number of the sheets Sh discharged to be used as the buffer sheets is set according to the paper type and the weight of the sheet Sh. The buffer sheet setting information  38   d  includes fields corresponding to the paper type, the weight, and the number of buffer sheets discharged. 
     The field corresponding to the paper type stores the paper type of the sheet Sh that can be used as the buffer sheet. Examples of the paper type include plain paper and high-quality paper. 
     The field corresponding to the weight stores the weight [g/m 2 ] for each paper type. 
     The field corresponding to the number of buffer sheets discharged stores the number of sheets that can be discharged as the buffer sheets for each paper type and weight of the sheet Sh. Typically, high-quality paper is better in quality and harder than plain paper. For this reason, the number of sheets to be discharged as the buffer sheets is set to be the same for high-quality paper and plain paper, or set to be less for high-quality paper than for plain paper. 
     Buffer Sheet Discharge Setting Screen 
       FIG. 7  is an explanatory diagram illustrating a display example of a buffer sheet discharge setting screen W 1 . The buffer sheet discharge setting screen W 1  is a screen in which a user sets in advance the number of sheets of plain paper or high-quality paper to be discharged as the buffer sheets. 
     A user can operate the operation display unit  13  (an example of a discharge count setter) and set, in the storage  38 , the number of the sheets Sh to be discharged as the buffer sheets through the buffer sheet discharge setting screen W 1 . Here, the user can operate the operation display unit  13  to set, in the storage  38 , the number of sheets to be discharged according to the paper type and the weight of the sheet Sh. The buffer sheet discharge control unit  35  then performs control to discharge the set number of the sheets Sh as the buffer sheets. 
     Here, the buffer sheet discharge setting screen W 1  includes a setting switch button W 1   a  and a discharge count setting area W 1   b.    
     The setting switch button W 1   a  includes radio buttons that allow the setting to be switched between “batch setting” and “individual setting”. The “batch setting” is a button for the user to set that a preset number of the sheets Sh are discharged as the buffer sheets regardless of the paper type and the weight of the sheet. The “individual setting” is a button for the user to set the number of sheets according to the paper type and the weight of the sheet Sh. For example, when the radio button for the “individual setting” is selected, the user can set the number of sheets to be discharged in the discharge count setting area W 1   b.    
     The discharge count setting area W 1   b  is an area for the user to individually set the number of sheets to be discharged according to the paper type and the weight of the sheet Sh used as the buffer sheet. For example, the sheet Sh whose paper type is plain paper or high-quality paper is used as the buffer sheet. The user can manually set the number of the sheets Sh discharged to be used as the buffer sheets while varying the number according to the paper type and the weight as illustrated in  FIG. 6 . The number of sheets to be discharged set for each paper type and weight in the discharge count setting area W 1   b  is stored in the buffer sheet setting information  38   d  illustrated in  FIG. 6 . 
     Note that the buffer sheet discharge setting screen W 1  may include a setting item for setting the total thickness of the buffer sheets discharged to the discharge tray  43  to a specified value or thicker. For example, when the total thickness is set to 5 mm or thicker, the buffer sheet discharge control unit  35  may automatically determine the total number of buffer sheets corresponding to the paper type of the sheet Sh such that the total thickness of the buffer sheets loaded equals 5 mm or thicker. Accordingly, a plurality of the sheets Sh can be used as the buffer sheets regardless of the paper type of the sheet Sh. 
     Moreover, the buffer sheet is more likely to have a wrinkle when the humidity in the image forming apparatus  3  and the stacker  4  rises, and the wrinkle may serve as a new affecting part to affect the printed matter. The buffer sheet discharge control unit  35  can thus perform control to discharge the buffer sheet by automatically increasing the number of buffer sheets discharged in accordance with the increase in the humidity in the image forming apparatus  3  detected by the environment sensor  27 . 
     Feed Tray Selection Setting Screen 
       FIG. 8  is an explanatory diagram illustrating a display example of a feed tray selection setting screen W 2 . The feed tray selection setting screen W 2  is a screen for setting the feed tray  2   a  that stores the sheet Sh selected as the buffer sheet. 
     The feed tray selection setting screen W 2  includes a setting switch button W 2   a.    
     The setting switch button W 2   a  includes radio buttons that allow a user to switchably select the setting among “same tray”, “arbitrary”, and “automatic selection”. 
     When “same tray” is selected, the sheet Sh fed from the feed tray  2   a  storing the sheet Sh on which a document image is formed is discharged as the buffer sheet. That is, the sheet Sh of the same paper type and weight as those of the sheet Sh on which a document image is formed is discharged as the buffer sheet. 
     When “arbitrary” is selected, the feed tray selection unit  34  selects the feed tray  2   a  that is arbitrarily selected in advance from a plurality of the feed trays  2   a  by the user. The buffer sheet discharge control unit  35  then performs control to discharge, as the buffer sheet, the sheet Sh fed from the feed tray  2   a  selected by the feed tray selection unit  34 . In this case, the sheet Sh of a different paper type or weight from that of the sheet Sh on which a document image is formed may be discharged as the buffer sheet. 
     The feed tray selection unit  34  selects another one of the feed trays  2   a  when the sheet Sh is not stored in the feed tray  2   a  selected. The buffer sheet discharge control unit  35  then performs control to discharge the sheet Sh fed from the other feed tray  2   a  as the buffer sheet. 
     When “automatic selection” is selected, the sheet Sh fed from the feed tray  2   a  that is automatically selected by the feed tray selection unit  34  is discharged as the buffer sheet. The feed tray selection unit  34  selects the feed tray  2   a  storing the sheet Sh that call be used as the buffer sheet according to the paper type and weight of the sheet Sh on which an image is formed. 
     Note that one needs to prevent collapsing of a large number of printed matter stacked in the discharge tray  43 . Thus, the feed tray selection unit  34  can select, from among the plurality of the feed trays  2   a , the feed tray  2   a  storing the sheet Sh of the size (that is, the lengths along a main scanning direction and a sub scanning direction) larger than or equal to the size of the sheet Sh designated for a job. The buffer sheet discharge control unit  35  then performs control to discharge, as the buffer sheet, the sheet Sh fed from the feed tray  2   a  selected. 
       FIG. 9  is a flowchart illustrating an example of buffer sheet discharge determination processing. The present processing assumes that a job received by the job reception unit  31  is stored in the job storage area  38   a  of the storage  38 . Then, the following processing is performed before the job execution unit  37  starts executing the job. 
     First, the paper presence/absence determination unit  32  acquires information on the presence/absence of the sheet Sh input from the remaining paper sensor  46 , and determines whether the sheet Sh has been discharged to the discharge tray  43  (S 1 ). In step S 1 , the paper presence/absence determination unit  32  may determine whether a predetermined number of the sheets Sh has been discharged to the discharge tray  43 . 
     If the sheet Sh has already been discharged to the discharge tray  43  (YES in S 1 ), the subsequent processing for discharging the buffer sheet is unnecessary so that the processing proceeds to step S 9 . On the other hand, if the sheet Sh has not been discharged to the discharge tray  43  (NO in S 1 ), the buffer sheet discharge determination unit  33  refers to the buffer sheet discharge information  38   b  illustrated in  FIG. 2  and determines whether or not the buffer sheet discharge setting is enabled (S 2 ). If the buffer sheet discharge setting is not enabled (NO in S 2 ), that is, if the setting is disabled, the subsequent processing for discharging the buffer sheet is unnecessary so that the processing proceeds to step S 9 . 
     On the other hand, if the buffer sheet discharge setting is enabled (YES in S 2 ). the feed tray selection unit  34  determines whether the feed tray  2   a  storing the sheet Sh used as the buffer sheet is the same as the feed tray  2   a  storing the sheet Sh designated for the present job to be executed (S 3 ). 
     If it is determined that the feed trays  2   a  are the same (YES in S 3 ), the buffer sheet discharge control unit  35  performs control to discharge, as the buffer sheet, the sheet Sh fed from the feed tray  2   a  that stores the sheet Sh designated for the present job, the feed tray being selected by the feed tray selection unit  34  (S 4 ). Thereafter, the processing proceeds to step S 8 . 
     On the other hand, if it is determined that the feed trays  2   a  are not the same (NO in S 3 ), the feed tray selection unit  34  determines whether the selection designation for selecting the feed tray  2   a  that stores the sheet Sh used as the buffer sheet has been made on the feed tray selection setting screen W 2  (S 5 ). If the selection designation for the feed tray  2   a  has been made (YES in S 5 ), the buffer sheet discharge control unit  35  performs control to discharge, as the buffer sheet, the sheet Sh fed from the feed tray  2   a  designated to be selected (S 6 ). 
     On the other hand, if the selection designation for the feed tray  2   a  has not been made (NO in S 5 ), the feed tray selection unit  34  refers to the feed tray designation information  38   c  and automatically selects the feed tray  2   a  storing the sheet Sh in accordance with the size of the sheet Sh designated for the job. The buffer sheet discharge control unit  35  then performs control to discharge, as the buffer sheet, the sheet Sh fed from the feed tray  2   a  automatically selected (S 7 ). 
     Here, the processing of step S 7  will be described with reference to  FIG. 10 . 
       FIG. 10  is a flowchart illustrating an example of the processing in which the feed tray selection unit  34  automatically selects the feed tray  2   a  in step S 7 . 
     First, the feed tray selection unit  34  selects an arbitrary one of the feed trays  2   a  (S 11 ). Next, the feed tray selection unit  34  determines whether the sheet Sh fed from the feed tray  2   a  selected can be discharged as the buffer sheet (S 12 ). If the sheet Sh can be discharged as the buffer sheet (YES in S 12 ), the feed tray selection unit  34  determines whether the sheet Sh stored in the feed tray  2   a  selected is of the same size as or larger than the sheet Sh designated for the present job (S 13 ). 
     If the sheet Sh stored in the feed tray  2   a  selected is of the same size as or larger than the sheet Sh designated for the present job (YES in S 13 ), the buffer sheet discharge control unit  35  settles on the feed tray  2   a  selected by the feed tray selection unit  34  and performs control to discharge the sheet Sh fed from the feed tray  2   a  as the buffer sheet (S 14 ). This completes the present processing, and the processing proceeds to step S 8  in  FIG. 9 . 
     On the other hand, if it is determined in step S 12  that the sheet Sh cannot be discharged as the buffer sheet (NO in S 12 ), or if it is determined in step S 13  that the sheet is smaller than the sheet Sh designated for the present job (NO in S 13 ), the feed tray selection unit  34  determines whether there is a next feed tray  2   a  (S 15 ). For example, when the sheet Sh designated for the present job has size B4. the sheet Sh that can be discharged as the buffer sheet desirably has size B4 or larger. However, the sheet Sh stored in the feed tray  2   a  with the identifier “A” in the feed tray designation information  38   c  illustrated in  FIG. 5  has size A4, whereby the sheet Sh cannot be discharged as the buffer sheet. In this case, the feed tray selection unit  34  continues the determination for the sheet Sh stored in the feed tray  2   a  with the identifier “B” following the feed tray  2   a  with the identifier “A”. If there is a next feed tray  2   a  (YES in S 15 ), the feed tray selection unit  34  returns to step S 12  and continues the subsequent processing. 
     If determining in step S 15  that there is no next feed tray  2   a  (NO in S 15 ), the feed tray selection unit  34  selects the feed tray  2   a  that stores the sheet Sh designated for the present job. For example, in the feed tray designation information  38   c  illustrated in  FIG. 5 , the feed tray  2   a  storing the sheet Sh of size B4 has the identifier “B”. Therefore, the buffer sheet discharge control unit  35  performs control to discharge, as the buffer sheet, the sheet Sh fed from the feed tray  2   a  (with the identifier “B”) that stores the sheet Sh designated for the present job (S 16 ). This completes the present processing, and the processing proceeds to step S 8  in  FIG. 9 . 
     Returning to step S 8  of  FIG. 9 , the description of the processing will be continued. 
     After any of steps S 4 , S 6 , and S 7 , the buffer sheet discharge control unit  35  determines whether a set number of the buffer sheets has been discharged (S 8 ). The number of buffer sheets discharged is stored in the storage  38  as a value obtained by the buffer sheet discharge control unit  35  counting the number of the sheets Sh discharged to be fed as the buffer sheets from the feed tray  2   a . Then, the buffer sheet discharge control unit  35  compares the number of the sheets Sh discharged to be fed as the buffer sheets, which is stored in the storage  38 , with the number of sheets discharged in the buffer sheet setting information  38   d  illustrated in  FIG. 6 . If the buffer sheet discharge control unit  35  determines that the set number of the buffer sheets has not been discharged (NO in S 8 ), the processing returns to step S 3  and the controller  30  repeats the processing. 
     If it is determined YES in step S 1  or NO in step S 2 , or after the buffer sheet discharge control unit  35  determines in step S 8  that the set number of buffer sheets has been discharged (YES in S 8 ), the job execution unit  37  executes the present job and starts a printing operation (S 9 ). After the present job is finished, the present processing is ended. 
     The image forming system  1  according to the embodiment described above discharges a plurality of the buffer sheets before discharging printed matter, when no printed matter is loaded in the discharge tray  43  of the stacker  4 . Here, an, appropriate number of the buffer sheets is discharged according to the paper type and weight of the sheet Sh stored in the feed tray  2   a . As a result, the printed matter is stacked on the buffer sheets. Thus, even if a large number of the printed matter accumulated is left for a long time, the buffer sheets are deformed to prevent the affecting part formed in the discharge tray  43  from affecting the printed matter. The printed matter stored in the discharge tray  43  can be protected as a result. 
     The information  38   b  to  38   d  stored in the storage  38  can be changed by a user. Therefore, a value according to the paper type and the weight of the sheet Sh can be set appropriately. The user can also change the setting for the discharge of the buffer sheet. Thus, the sheet Sh fed from only a specific one of the feed trays  2   a  may be discharged as the buffer sheet, or the sheet Sh fed from the feed tray  2   a  that is automatically selected may be discharged as the buffer sheet. 
     The mark is formed on the edge of the buffer sheet discharged. A user can thus distinguish the printed matter from the buffer sheet correctly even if the printed matter and the buffer sheet discharged to the discharge tray  43  are of the same size. 
     Note that when the humidity in the stacker  4  increases, the sheet Sh discharged to the discharge tray  43  is likely to be wrinkled. Thus, the number of the sheets Sh discharged as the buffer sheets can be increased or decreased according to the humidity in the stacker  4 . For example, the number of the buffer sheets can be increased if the humidity in the stacker  4  is higher than or equal to specified humidity, or the number of the sheets Sh can be maintained or decreased if the humidity is lower than the specified humidity 
     When the buffer sheet is stored in the discharge tray  43  while not overlapping the affecting part, the affecting part does not affect the printed matter stored in the discharge tray  43 . Also, when the size of the sheet Sh discharged as the buffer sheet is smaller than the size of the printed matter, or depending on the orientation in which the buffer sheet is discharged, the affecting part is not located directly under the buffer sheet discharged in the discharge tray  43  and thus does not affect the buffer sheet and the printed matter. If the effect of the affecting part is small as described above, the first printed matter that is designated in a job executed by the job execution unit  37  and is stored first in the discharge tray  43  is less likely to be damaged. Thus, the buffer sheet discharge control unit  35  stops control for discharging the buffer sheet when the affecting part does not affect the printed matter stored in the discharge tray  43 . That is, the printed matter is discharged to the discharge tray  43  without the buffer sheet being discharged. Note that when stopping the control for discharging the buffer sheet, the buffer sheet discharge control unit  35  may perform control to display, on the operation display unit  13 , a message for prompting a user to perform resetting of the buffer sheet. 
     Moreover, when a user takes out the sheet Sh on which an image is formed from the discharge tray  43 , checks the sheet Sh, and determines that the sheet Sh has a quality defect even though the buffer sheet is discharged, the user may input that the quality defect has occurred through the operation display unit  13 . In this case, the setting is changed such that the number of the buffer sheets discharged in the buffer sheet setting information  38   d  automatically increases. When a subsequent job is executed, a larger number of the buffer sheets is discharged to the discharge tray  43  so that no quality defect occurs on the sheet Sh on which an image is formed. 
     Moreover, depending on the paper type and the weight, the printed matter discharged in the discharge tray  43  may be less likely to have a wrinkle or mark without the buffer sheet. For this reason, when the job execution unit  37  executes a job, whether the discharge of the buffer sheet is enabled or disabled may be set depending on the paper type of the printed matter that is fed first from the feed tray  2   a.    
     Variation of Buffer Sheet Setting Information 
     Note that the buffer sheet discharge information  38   b  may include settings for the influence of paper feed and the number of the buffer sheets discharged in addition to whether the function of discharging the buffer sheet is enabled or disabled as illustrated in  FIG. 4 . 
       FIG. 11  is a diagram of the structure of a table for buffer sheet discharge information  38   b   1 . 
     The buffer sheet discharge information  38   b   1  is obtained by adding fields for the influence of paper feed and the number of the buffer sheets discharged to the fields of the buffer sheet discharge information  38   b  illustrated in  FIG. 4 . 
     The field corresponding to the influence of paper feed stores the influence of paper feed according to the paper type of the sheet Sh designated for the present job. The influence of paper feed is an index that indicates a degree of the influence, such as a mark left on the sheet Sh at the bottom of a bundle of paper when the sheet Sh discharged as the printed matter is stacked in the discharge tray  43 , and is expressed as relative values including “small”, “moderate”, and “large”. For example, when the paper type of the sheet Sb is thick paper, the discharge of the buffer sheet is set to be disabled so that there is no influence of paper feed. On the other hand, when the paper type of the sheet Sh of the present job is plain paper or high-quality paper, the influence of paper feed is any one of “small”, “moderate”, and “large”. 
     The field corresponding to the number of the buffer sheets discharged stores the number of the buffer sheets discharged according to the influence of paper feed. When the discharge of the buffer sheet is enabled, the number of the buffer sheets discharged increases as the influence of paper feed increases in the order of “small”, “moderate”, and “large”. When the influence of paper feed is “small”, the influence on the printed matter stacked on the buffer sheet is small even if the number of the buffer sheets is small. Thus, when the influence of paper feed is “small”, the number of the buffer sheets discharged is set to be small. Meanwhile, when the influence of paper feed is “large”, the printed matter stacked on the buffer sheet is more likely to have a mark if the number of the buffer sheets is small, whereby the influence on the sheet Sh is large. Thus, when the influence of paper feed is “large”, the number of the buffer sheets discharged is set to be large. When the influence of paper feed is “moderate”, the number of the buffer sheets discharged is set to roughly an intermediate value between the number of sheets discharged that is set when the influence of paper feed is “small” and the number of sheets discharged that is set when the influence of paper feed is “large”. 
     Note that when the discharge of the buffer sheet is disabled, the number of sheets discharged is set to zero. 
     By referring to the buffer sheet discharge information  38   b   1 , the buffer sheet discharge control unit  35  can perform control to discharge the buffer sheets in number corresponding to the influence of paper feed. Various values under the field corresponding to the influence of paper feed and the field corresponding to the number of the buffer sheets discharged in the buffer sheet discharge information  38   b   1  can be set and changed by a user as appropriate. 
     Also, when the image forming apparatus  3  is used alone, the apparatus need only perform control to feed the sheet Sh from the feed tray  14  and discharge the printed matter, on which an image is formed by the image former  20 , to the discharge tray that is attached to the image forming apparatus  3 . In this case, only the transport path  15  of the image forming apparatus  3  is used as an example of the transporter, and one or a plurality of the buffer sheets being one or a plurality of the sheets Sh is discharged to the discharge tray. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation, and can of course adopt various other application examples and variations without departing from the scope of the present invention described in the claims. The scope of the present invention should be interpreted by terms of the appended claims. 
     For example, the above embodiment describes the configurations of the apparatus and the system specifically and in details in order to provide a clear description of the present invention, and is not necessarily limited to one including all the configurations described. It is also possible to perform addition of another configuration, deletion, and/or replacement on a part of the configuration of each embodiment. 
     Furthermore, the control lines and information lines are those that are considered necessary for the description, and not all the control lines and information lines on the product are necessarily illustrated. In practice, one may consider that almost all the configurations are connected to one another.