Patent Publication Number: US-2011064498-A1

Title: Image forming system and image forming device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-212138 filed Sep. 14, 2009. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image forming system and an image forming device. 
     2. Related Art 
     Heretofore, a printing device has been known that: receives a command that specifies an arbitrary width and length in relation to the size of a page to be printed and a command that specifies a printing direction category; sets an specified origin point and printing direction for physical paper as reference criteria; arranges a logical page with a size of the width and height specified by the command on the physical page; and prints on one face of the paper on this logical page. 
     Further, a two-sided printer device is known that includes: a paper width measurement component that measures a paper width of continuous paper for printing; a print start position control component that calculates a printing start position on the basis of measurement results from the paper width measurement component; and a memory component that memorizes measured values of paper width that have been set up to just before a current measurement of paper width. 
     SUMMARY 
     According to an aspect of the invention, there is provided an image forming system. The image forming system includes: an inversion mechanism that inverts continuous paper between one side and the other side of the continuous paper; an upstream side image forming device; and a downstream side image forming device. The upstream side image forming device includes: a first conveyance component that aligns a first side edge of the continuous paper with a reference surface provided along a conveyance direction and conveys the continuous paper in a conveyance direction, the conveyance direction being in a paper continuation direction; and a first image forming component that forms an image on one side of the continuous paper conveyed by the first conveyance component based on a first reference position, the first reference position being a position that is disposed away from the first side edge of the continuous paper by a first width which is one of a measured width of the continuous paper and a pre-specified width for the continuous paper, and the downstream side image forming device includes: a second conveyance component that aligns a second side edge, which is opposite to the first side edge, of the continuous paper with a reference surface provided along the conveyance direction and conveys the inverted continuous paper by the inversion mechanism in the conveyance direction; and a second image forming component that forms an image on the other side of the continuous paper conveyed by the second conveyance component based on a second reference position, the second reference position being a position that is disposed away from the second side edge by a second width which is the other of the measured width of the continuous paper and the pre-specified width for the continuous paper, and wherein the upstream side image forming device is disposed at a upstream side of the inversion mechanism in the conveyance direction, and the downstream side image forming device is disposed at a downstream side of the inversion mechanism in the conveyance direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic diagram illustrating structure of an image forming system relating to a first exemplary embodiment of the present invention; 
         FIG. 2  is a diagram illustrating a state in which continuous paper is inverted by a turn bar mechanism of an inversion device; 
         FIG. 3  is a diagram illustrating a state in which the continuous paper is cut at a post-processing device; 
         FIG. 4  is a diagram illustrating states in which width direction side edges of the continuous paper abut against conveyance reference surfaces; 
         FIG. 5  is a block diagram illustrating structure of the image forming system relating to the first exemplary embodiment of the present invention; 
         FIG. 6  is a block diagram illustrating functional structure of a system controller of an upstream side system of the image forming system relating to the first exemplary embodiment of the present invention; 
         FIG. 7  is an image diagram illustrating a state in which images represented by first face print data, color adjustment marks, and page adjustment marks are formed on a first face of the continuous paper; 
         FIG. 8A  is a diagram for describing a method of determining an image formation reference position, using measured width information; 
         FIG. 8B  is a diagram for describing a method of determining an image formation reference position, using pre-specified width information; 
         FIG. 9A  is a diagram for describing a method of determining a dot position that serves as an image formation reference position, using measured width information; 
         FIG. 9B  is a diagram for describing a method of determining a dot position that serves as an image formation reference position, using pre-specified width information; 
         FIG. 10  is a block diagram illustrating functional structure of a system controller of a downstream side system of the image forming system relating to the first exemplary embodiment of the present invention; 
         FIG. 11  is a diagram illustrating states in which a width direction side edge of the continuous paper abuts against conveyance reference surfaces; 
         FIG. 12A  is a diagram for describing a method of determining an image formation reference position, using measured width information; 
         FIG. 12B  is a diagram for describing a method of determining an image formation reference position, using pre-specified width information; and 
         FIG. 13  is a schematic diagram illustrating structure of an image forming system relating to a third exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Herebelow, exemplary embodiments of the present invention are described with reference to the drawings. 
     As illustrated in  FIG. 1 , an image forming system  10  relating to a first exemplary embodiment of the present invention is provided with an upstream side system  12  at an upstream side of a conveyance direction, and a downstream side system  14  at the conveyance direction downstream side. 
     The upstream side system  12  is provided with a pre-processing device  16 , a buffer device  18 , an image forming device  20  and an inversion device  22 . Continuous paper  21  is paper that is loaded at the pre-processing device  16  and is continuous in one direction. The continuous paper  21  is supplied through the buffer device  18  to the image forming device  20 , image forming is performed on one face (a first face) of the continuous paper  21  by the image forming device  20 , and then the continuous paper  21  passes through the inversion device  22  and is inverted, and is conveyed to the downstream side system  14 . The pre-processing device  16  performs various kinds of pre-processing before image formation is carried out on the continuous paper  21  (for example, punching, creation of perforation lines and the like). The inversion device  22  is provided with a turn bar mechanism  22 A and switches between the first face and the second face of the continuous paper  21  (inverts between the same). As illustrated in  FIG. 2 , when the first face and second face of the continuous paper  21  are inverted by the turn bar mechanism  22 A, width direction edges of the continuous paper  21  are also inverted. In the present exemplary embodiment, a case is described in which the upstream side system  12  and the downstream side system  14  use toners as materials for forming images and the images are formed on the continuous paper  21 . 
     The buffer device  18  and the inversion device  22  are structured to accumulate the continuous paper  21  up to pre-specified amounts. The buffer device  18  absorbs a difference between a processing speed of the pre-processing device  16  and a processing speed of the image forming device  20 . The inversion device  22  absorbs a difference between the processing speed of the image forming device  20  and a processing speed of the downstream side system  14 . 
     The pre-processing device  16  is provided with a paper width measurement sensor  19 . A paper width of the continuous paper  21  loaded in the pre-processing device  16  is measured by the paper width measurement sensor  19 . 
     The image forming device  20  is provided with plural conveyance rollers  23  that convey the continuous paper  21  supplied by the pre-processing device  16  in a paper conveyance direction by means of nipping pressure. Thus, the continuous paper  21  is conveyed along a conveyance path. The image forming device  20  is provided with an image forming mechanism  24 , and forms images on the continuous paper  21 . The image forming mechanism  24  is structured to form images on the continuous paper  21  by an electrophotography system. Specifically, a charging device, an exposure device, a developing device, a transfer device, a cleaning device, a neutralizing device and suchlike are arranged in this order around each of photoreceptor drums  26  that correspond to cyan, magenta, yellow and black, and a fixing device  28  is disposed at the downstream side of the conveyance direction of the continuous paper. 
     That is, each photoreceptor drum  26  is rotated, the surface of the photoreceptor drum  26  is uniformly charged by the charging device, and a latent image is formed by the exposure device at the surface of the photoreceptor drum  26 . Then the latent image formed at the surface of the photoreceptor drum  26  is developed by the developing device and a toner image is formed, and this toner image is transferred to the continuous paper  21  by the transfer device. The toner images that have been transferred to the continuous paper  21  are fixed by the fixing device  28 . Toner that remains on the surface of the photoreceptor drum  26  instead of being transferred to the continuous paper  21  by the transfer device is removed by the cleaning device, and the surface of the photoreceptor drum  26  is de-electrified by the neutralizing device. Subsequently, the above-described processing, from charging by the charging device, is repeated, and thus images are formed. Herein, an image forming device that performs color image formation is illustrated in  FIG. 1 , but this is not to be limiting. An image forming device that is provided with one photoreceptor drum  26  and that carries out monochrome image forming may be used. 
     The image forming device  20  is provided with a color adjustment mark reading device  29  on the conveyance path at the downstream side relative to the photoreceptor drums  26 . The color adjustment mark reading device  29  is constituted with, for example, a spot-type optical sensor, and one-dimensionally reads color adjustment marks that are formed as images on a first face of the continuous paper  21  that is being conveyed. 
     The downstream side system  14  at the conveyance direction downstream side is provided with an image forming device  32 , a buffer device  34  and a post-processing device  36 . The continuous paper  21  that is conveyed from the inversion device  22  passes through the buffer device  34  and is supplied to the image forming device  32 . An image is formed on the other face (the second face) of the continuous paper  21  by the image forming device  32 , and then the continuous paper  21  passes through the buffer device  34  and is conveyed to the post-processing device  36 . The post-processing device  36  rolls up the continuous paper  21  and performs various kinds of post-processing on the continuous paper  21  on both of whose faces images have been formed by the image forming device  20  and the image forming device  32 . For example, the post-processing device  36  cuts the continuous paper  21  to the size of regions at which images are formed, as illustrated in  FIG. 3 . 
     The buffer device  34  is structured to accumulate the continuous paper  21  in a pre-specified amount. The buffer device  34  absorbs a difference between a processing speed of the image forming device  32  and a processing speed of the post-processing device  36 . 
     The image forming device  32  is provided with the conveyance rollers  23  and an image forming mechanism  30  similar to the image forming mechanism  24  of the image forming device  20 . The image forming device  32  conveys the continuous paper  21  along the conveyance path and forms images at the other face (the second face) of the continuous paper  21 . Charging devices, exposure devices, developing devices, transfer devices, cleaning devices, neutralizing devices and suchlike are arranged in this order around the photoreceptor drums  26  that correspond to cyan, magenta, yellow and black in the image forming mechanism  30 , and the fixing device  28  is disposed at the continuous paper conveyance direction downstream side thereof. The image forming device  32  is provided with the color adjustment mark reading device  29  on the conveyance path at the downstream side relative to the photoreceptor drums  26 . 
     The image forming device  32  is provided with a page adjustment mark reading device  38  on the conveyance path at the upstream side relative to the image forming mechanism  30 . The page adjustment mark reading device  38  is constituted with, for example, a spot-type optical sensor to one-dimensionally read page adjustment marks that are formed as images on the first face of the continuous paper  21  that is being conveyed. 
     In the image forming device  20 , as illustrated in  FIG. 4 , the edge at one side of the width direction of the continuous paper  21  is abutted against a conveyance reference surface provided along the conveyance direction at the conveyance path, and is conveyed. Because the continuous paper  21  is inverted between front and rear by the inversion device  22  such that the width direction edges of the continuous paper  21  are exchanged, in the image forming device  32 , the edge at the other side of the width direction of the continuous paper  21  is abutted against a conveyance reference surface provided along the conveyance direction at the conveyance path, and is conveyed. In the present exemplary embodiment, a case in which the conveyance reference surfaces in the image forming devices  20  and  32  are disposed at the same side of a direction orthogonal to the conveyance direction of the conveyance path and the width direction side edges of the continuous paper  21  that are abutted against the conveyance reference surfaces are different between the image forming devices  20  and  32  is described as an example. 
     As illustrated in  FIG. 5 , the image forming device  20  of the upstream side system  12  is structured to include a system controller  40 , read-only memory (ROM)  42 , random access memory (RAM)  44 , non-volatile memory (NVM)  46  and a communications interface  48 . The ROM  42 , the RAM  44 , the NVM  46 , the communications interface  48 , the image forming mechanism  24  and the color adjustment mark reading device  29  are connected to the system controller  40 . 
     The ROM  42  functions as a memory component in which an image forming processing program, various parameters, various data required for control, and the like are pre-memorized. The RAM  44  is used as a work area during execution of various programs, and the like. The NVM  46  memorizes various kinds of information that need to be retained if a power switch of the equipment is turned off. 
     The system controller  40  is constituted by a central processing unit (CPU) and peripheral circuits thereof and the like. The system controller  40  functions as a control device that controls the upstream side system  12  at the conveyance direction upstream side as a whole, in accordance with pre-specified programs. The system controller  40  also functions as a computing device that performs various kinds of computing. That is, the system controller  40  controls operations of the image forming mechanism  24 , controls reading and writing of the ROM  42 , the RAM  44  and the NVM  46 , and so forth. 
     The image forming device  32  of the downstream side system  14  is structured to include a system controller  50 , read-only memory (ROM)  52 , random access memory (RAM)  54 , non-volatile memory (NVM)  56  and a communications interface  58 . The ROM  52 , the RAM  54 , the NVM  56 , the communications interface  58 , the color adjustment mark reading device  29 , the page adjustment mark reading device  38  and the image forming mechanism  30  are connected to the system controller  50 . 
     The ROM  52  functions as a memory component in which an image forming processing program, various parameters, various data required for control, and the like are pre-memorized. The RAM  54  is used as a work area during execution of various programs, and the like. The NVM  56  memorizes various kinds of information that need to be retained if the power switch of the equipment is turned off. 
     The system controller  50  is constituted by a central processing unit (CPU) and peripheral circuits thereof and the like. The system controller  50  functions as a control device that controls the downstream side system  14  as a whole, in accordance with pre-specified programs. The system controller  50  also functions as a computing device that performs various kinds of computing. That is, the system controller  50  controls operations of the image forming mechanism  30 , controls reading and writing of the ROM  52 , the RAM  54  and the NVM  56 , and so forth. 
     The image forming system  10  is further provided with a controller  60  and a print server  62  that outputs image formation instructions (print instructions) to the controller  60 . The image forming devices  20  and  32 , the paper width measurement sensor  19  and the controller  60  are connected by a communications component  64  so as to exchange data and commands with one another. A structure is possible in which the print server  62  is included in the image forming system  10 . The print server  62  is constituted by an ordinary server and the controller  60  is constituted by an ordinary personal computer. 
     The print server  62  outputs duplex print data to the controller  60  as image forming instructions. 
     The controller  60  outputs, to the image forming device  20 , image forming instructions that include first face print data for forming images on the first face of the continuous paper  21  and width information of the continuous paper  21  measured by the paper width measurement sensor  19 . The controller  60  also outputs, to the image forming device  32 , image forming instructions that include second face print data for forming images on the second face of the continuous paper  21  and width information of the continuous paper  21  that is set in advance for the first face print data and the second face print data. 
     If the system controller  40  of the image forming device  20  is represented by functional blocks, as illustrated in  FIG. 6 , the system controller  40  is provided with a print buffer  70 , a measured width buffer  72 , a color adjustment mark detection section  73  and a print control section  74 . 
     The print buffer  70  temporarily memorizes print data inputted from the controller  60 . The measured width buffer  72  temporarily memorizes measured width information for the continuous paper  21 , which is inputted from the controller  60 . 
     The color adjustment mark detection section  73  detects color adjustment marks from images that are read by the color adjustment mark reading device  29 . 
     On the basis of the first face print data, color adjustment mark image data and page adjustment mark image data, the print control section  74  controls the image forming mechanism  24  so as to form images  21 A represented by the first face print data, color adjustment marks  21 B and page adjustment marks  21 C on the first face of the continuous paper  21 , as illustrated in  FIG. 7 . On the basis of detection results according to the color adjustment mark detection section  73 , the print control section  74  controls the image forming mechanism  24  so as to reduce mispositioning in the conveyance direction of images of respective colors that are formed by the respective photoreceptor drums  26 . 
     At the print control section  74 , as illustrated in  FIG. 8A , an image formation reference position (a writing start position) is determined on the basis of a position that is separated by a measured width from the one side edge of the continuous paper  21  that is abutted against the conveyance reference surface, and the images  21 A represented by the first face print data, the color adjustment marks  21 B and the page adjustment marks  21 C are formed on the first face of the continuous paper  21 . For example, the image formation reference position is determined as illustrated in  FIG. 9A . Here, a method of determining the image formation reference position for an exposure system based on an LED array is described as an example. In the image forming device  20 , the image formation reference position is calculated using a measured actual paper width. Because mounting errors arise between the LED array and the continuous paper  21 , an adjustment value L xu  for matching the side edge position of the continuous paper  21  with a dot position of the LED array is set in advance. 
     Now, in the image forming device  20 , if a measured width of the continuous paper  21  is denoted by L PwR , an image formation reference position P sU  (a dot position in the LED array) relative to the side edge position of the continuous paper  21  is calculated with the following expression (1). 
         P   sU   =L   PwR   +L   xU   (1)
 
     Herein, as illustrated in the aforementioned  FIG. 7 , the page adjustment marks  21 C are formed at a fixed position of each page. The page adjustment marks  21 C are formed on the first face of the continuous paper  21  with a spacing corresponding to a page continuation direction size of the pages. 
     If the system controller  50  of the image forming device  32  is represented by functional blocks, as illustrated in  FIG. 10 , the system controller  50  is provided with a print buffer  80 , a specified width buffer  82 , a page adjustment mark detection section  84 , a color adjustment mark detection section  86  and a print control section  88 . 
     The print buffer  80  temporarily memorizes print data inputted from the controller  60 . The specified width buffer  82  temporarily memorizes width information of the continuous paper  21  inputted from the controller  60 , which is specified beforehand in relation to the print data. 
     The page adjustment mark detection section  84  detects page adjustment marks from images read by the page adjustment mark reading device  38 . The color adjustment mark detection section  86  detects color adjustment marks from images read by the color adjustment mark reading device  29 . 
     On the basis of second face print data and the color adjustment mark image data, the print control section  88  controls the image forming mechanism  30  so as to form images represented by the second face print data and color adjustment marks on the second face of the continuous paper  21 , in accordance with page adjustment mark detection timings according to the page adjustment mark detection section  84 . Further, on the basis of detection results from the color adjustment mark detection section  86 , the print control section  88  controls the image forming mechanism  30  so as to reduce mispositioning in the conveyance direction of images of respective colors that are formed by the respective photoreceptor drums  26 . 
     At the print control section  88 , as illustrated in  FIG. 8B , an image formation reference position (a writing start position) is determined on the basis of a position that is separated by a pre-specified width from the other side edge of the continuous paper  21  that is abutted against the conveyance reference surface, and the images  21 A represented by the second face print data and the color adjustment marks  21 B are formed on the second face of the continuous paper  21 . For example, the image formation reference position is determined as illustrated in  FIG. 9B . In the image forming device  32 , the image formation reference position is calculated using a pre-specified paper width. Because mounting errors arise between the LED array and the continuous paper  21 , an adjustment value L xD  for matching the side edge position of the continuous paper  21  with a dot position of an LED array is set in advance. 
     In the image forming device  32 , if a specified width of the continuous paper  21  is denoted by L PwD , an image formation reference position P sD  (a dot position in the LED array) relative to the side edge position of the continuous paper  21  is calculated with the following expression (2). 
         P   sD   =L   PwD   +L   xD   (2)
 
     Next, operations of the image forming system  10  relating to the first exemplary embodiment are described. 
     First, when the controller  60  receives image forming instructions from the print server  62 , width information of the continuous paper  21  is acquired from the paper width measurement sensor  19  and image formation control processing is executed at the CPU of the controller  60 . Here, the image forming instructions include an image forming instruction that includes instructions to form images at both faces (the first face and the second face) of the continuous paper  21 , and include first face print data and second face print data representing images to be formed on the continuous paper  21  and pre-specified width information of the continuous paper  21  for the first face print data and the second face print data. 
     The controller  60  compares the width information acquired from the paper width measurement sensor  19  included in the image forming instruction with the pre-specified width information of the continuous paper  21  included in the image forming instruction, and determines whether or not a difference between the sets of width information is at or above a pre-specified value. If the difference between the sets of width information is at or above the pre-specified value, the controller  60  judges that there is a problem with specifications or a problem with the continuous paper  21 , and the image formation control processing stops. 
     The controller  60  inputs the first face print data representing images to be formed at the first face and the paper width information acquired from the paper width measurement sensor  19 , which are included in the image forming instruction, to the image forming device  20 . The controller  60  also inputs the second face print data representing images to be formed at the second face and the pre-specified paper width information of the continuous paper  21 , which are included in the image forming instruction, to the image forming device  32 . 
     The system controller  40  of the image forming device  20  determines the image formation reference position on the basis of the inputted width information measured for the continuous paper  21  and controls the image forming mechanism  24  so as to form the images  21 A represented by the first face print data, the color adjustment marks  21 B and the page adjustment marks  21 C at the first face of the continuous paper  21 . Thus, the images  21 A represented by the first face print data, the color adjustment marks  21 B and the page adjustment marks  21 C are formed on respective pages of the first face of the continuous paper  21 . Moreover, the system controller  40  detects the color adjustment marks from images read by the color adjustment mark reading device  29 , and controls the image forming mechanism  24  on the basis of the detection results so as to reduce conveyance direction mispositioning of the images of the respective colors that are formed by the respective photoreceptor drums  26 . 
     The system controller  50  of the image forming device  32  determines the image formation reference position on the basis of the inputted width information specified in advance for the continuous paper  21 . Then the system controller  50  detects the page adjustment marks from images read by the page adjustment mark reading device  38 , and controls the image forming mechanism  30  so as to form the images  21 A represented by the first face print data and the color adjustment marks  21 B at the second face of the continuous paper  21  in accordance with detection timings of the page adjustment marks. Thus, the images  21 A represented by the first face print data and the color adjustment marks  21 B are formed on respective pages of the second face of the continuous paper  21 . Moreover, the system controller  50  detects the color adjustment marks from images read by the color adjustment mark reading device  29 , and controls the image forming mechanism  30  on the basis of the detection results so as to reduce conveyance direction mispositioning of the images of the respective colors that are formed by the respective photoreceptor drums  26 . 
     As described above, the image formation reference position at the conveyance direction upstream side image forming device  20  is determined on the basis of the measured width information of the continuous paper  21 , and the image formation reference position at the conveyance direction downstream side image forming device  32  is determined on the basis of the preset width information of the continuous paper  21 . Therefore, the amount of an error in the width information of the continuous paper  21  is assigned to the same width direction side edge of the continuous paper  21  for both the first face and the second face of the continuous paper  21 . 
     Hence, at the post-processing device  36 , the continuous paper  21  is cut to match the size of the images formed at both faces—the first face and the second face—of the continuous paper  21 . 
     Next, a second exemplary embodiment is described. Here, because structure of an image forming system relating to the second exemplary embodiment is the same structure as in the first exemplary embodiment, the same reference numerals are assigned and descriptions concerning structures are not given. 
     The second exemplary embodiment principally differs from the first exemplary embodiment in that even though the first face and second face of the continuous paper  21  are exchanged by an inversion device, width direction edges of the continuous paper  21  are not exchanged. 
     In the inversion device  22  of the image forming system relating to the second exemplary embodiment, the first face and second face of the continuous paper  21  are swapped over (exchanged) without the width direction edges of the continuous paper  21  being exchanged. 
     As illustrated in  FIG. 11 , a conveyance reference surface of the image forming device  20  is disposed on the conveyance path at the one edge side of the direction orthogonal to the conveyance direction, and a conveyance reference surface of the image forming device  32  is disposed on the conveyance path at the other edge side of the direction orthogonal to the conveyance direction. Thus, the width direction side edges of the continuous paper  21  that are abutted against the conveyance reference surfaces are different between the image forming devices  20  and  32 . 
     At the image forming device  20 , as illustrated in  FIG. 12A , the image formation reference position (the writing start position) is determined on the basis of a position that is separated by a measured width from the one side edge of the continuous paper  21  that is abutted against the conveyance reference surface, and the images  21 A represented by the first face print data, the color adjustment marks  21 B and the page adjustment marks  21 C are formed on the first face of the continuous paper  21 . 
     At the image forming device  32 , as illustrated in  FIG. 12B , an image formation reference position (a writing end position) is determined on the basis of a position that is separated by a pre-specified width from the other side edge of the continuous paper  21  that is abutted against the conveyance reference surface, and the images  21 A represented by the second face print data and the color adjustment marks  21 B are formed on the second face of the continuous paper  21 . 
     As described above, the image formation reference position at the conveyance direction upstream side image forming device  20  is determined on the basis of the measured width information of the continuous paper  21 , and the image formation reference position at the conveyance direction downstream side  32  is determined on the basis of the pre-specified width information of the continuous paper  21 . Therefore, the amount of an error in the width information of the continuous paper  21  is assigned to the same width direction side edge of the continuous paper  21  for both the first and second faces of the continuous paper  21 . 
     Other structures and operations of the image forming system relating to the second exemplary embodiment are the same as in the first exemplary embodiment, so will not be described. 
     Hereabove, in the first exemplary embodiment and the second exemplary embodiment, cases in which the image formation reference position at the conveyance direction upstream side image forming device is determined using measured width information and the image formation reference position at the conveyance direction downstream side image forming device is determined using pre-specified width information have been described as examples, but these are not to be limiting. An image formation reference position at a conveyance direction upstream side image forming device may be determined using pre-specified width information and an image formation reference position at a conveyance direction downstream side image forming device may be determined using measured width information. 
     Furthermore, cases in which images are formed at both sides of the continuous paper by the conveyance direction upstream side image forming device and the conveyance direction downstream side image forming device have been described as examples, but these are not to be limiting. Images may be formed at only one face of the continuous paper in accordance with image forming instructions. In such a case, at the conveyance direction upstream side image forming device, the image formation reference position is determined using measured width information and an image is formed at the one face of the continuous paper, and at the conveyance direction downstream side image forming device, it is sufficient to perform processing to convey the continuous paper without forming an image. 
     A case in which the width of the continuous paper is measured by the paper width measurement sensor at the pre-processing device has been described as an example, but this is not to be limiting. The paper width measurement sensor may be provided and measure the width of the continuous paper in the conveyance direction upstream side image forming device. Further, paper width measurement sensors may be provided in both the conveyance direction upstream side image forming device and the conveyance direction downstream side image forming device, and each measure the width of the continuous paper. In such a case, it may be determined whether or not error amounts between the measured width information and the pre-specified width information are at or above a preset value in both the conveyance direction upstream side image forming device and the conveyance direction downstream side image forming device, and the image forming processing may be stopped if the error amount is determined to be at or above the preset amount at either or both of the image forming devices. 
     Next, a third exemplary embodiment is described. Here, portions with similar structures to the first exemplary embodiment are assigned the same reference numerals and are not described. 
     The third exemplary embodiment differs from the first exemplary embodiment in that images are formed at both faces of the continuous paper by a single image forming device. 
     As illustrated in  FIG. 13 , an image forming system  310  relating to the third exemplary embodiment is provided with the pre-processing device  16 , an image forming device  314  and the post-processing device  36 . 
     The image forming device  314  is provided with a buffer section  318 , an upstream side image forming section  320 , the inversion device  22 , a downstream side image forming section  332  and a buffer section  334 . The buffer section  318 , the upstream side image forming section  320 , the downstream side image forming section  332  and the buffer section  334  have similar structures to the buffer device  18 , the image forming device  20 , the image forming device  32  and the buffer device  34  described in the first exemplary embodiment. Therefore, descriptions concerning the structures thereof will not be given. 
     At the upstream side image forming section  320 , the image formation reference position is determined on the basis of the measured width information of the continuous paper  21 , and at the downstream side image forming section  332 , the image formation reference position is determined on the basis of the pre-specified width information of the continuous paper  21 . Thus, the amount of an error in the width information of the continuous paper  21  is assigned to the same width direction side edge of the continuous paper  21  at both the first face and the second face of the continuous paper  21  by the upstream side image forming section  320  and the downstream side image forming section  332 . 
     Other structures and operations of the image forming system relating to the third exemplary embodiment are the same as in the first exemplary embodiment, so will not be described. 
     In the exemplary embodiment described hereabove, a case in which the image formation reference position at the conveyance direction upstream side image forming section is determined using measured width information and the image formation reference position at the conveyance direction downstream side image forming section is determined using pre-specified width information has been described as an example, but this is not to be limiting. The image formation reference position at the conveyance direction upstream side image forming section may be determined using pre-specified width information and the image formation reference position at the conveyance direction downstream side image forming section may be determined using measured width information. 
     Furthermore, a case in which images are formed at both sides of the continuous paper by the conveyance direction upstream side image forming section and the conveyance direction downstream side image forming section has been described as an example, but this is not to be limiting. Images may be formed at only one face of the continuous paper in accordance with image forming instructions. In such a case, at the conveyance direction upstream side image forming section, the image formation reference position is determined using measured width information and an image is formed at the one face of the continuous paper, and at the conveyance direction downstream side image forming section, it is sufficient to perform processing to convey the continuous paper without forming an image. 
     A case in which the width of the continuous paper is measured by the paper width measurement sensor at the pre-processing device has been described as an example, but this is not to be limiting. The paper width measurement sensor may be provided and measure the width of the continuous paper in the conveyance direction upstream side image forming section. Further, paper width measurement sensors may be provided in both the conveyance direction upstream side image forming section and the conveyance direction downstream side image forming section, and each measure the width of the continuous paper. In such a case, it is determined whether or not error amounts between the measured width information and the pre-specified width information are at or above a preset value in both the conveyance direction upstream side image forming section and the conveyance direction downstream side image forming section, and the image forming processing may be stopped if the error amount is determined to be at or above the preset amount at either or both of the image forming sections. 
     Further still, in the first exemplary embodiment to third exemplary embodiment described above, cases in which the image forming devices form images on the continuous paper using toners as materials for forming images have been described, but this is not to be limiting. An image forming device may form images on continuous paper using inks as materials for forming images. Furthermore, materials for forming these images are not to be limited to toners and inks, and may be other materials. 
     Cases in which the measured width information is acquired when the controller has received an image forming instruction from the print server have been described, but this is not to be limiting. For example, measured width information may be acquired from the paper width measurement sensor when the continuous paper is loaded at the pre-processing device.